[L'angolo del PhD] Sara Borroni - XXIII Ciclo - 2010

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This thesis is focused on the study of the Z -> µ+ µ- process. This process is quite interesting. From the detector performance point of view, it can be used to measure from data muon trigger and reconstruction efficiencies. To extract these efficiencies, in the past three years I developed and optimized a method, called Tag&Probe, using Monte Carlo simulation. In the past few months, with the first ATLAS data, it allowed to measure the muon efficiencies from data for the first time. A data sample of 1.3 pb^-1 of integrated luminosity has been used and the results have been compared with the MC expectations.

The efficiencies estimation is also relevant for the cross-section measurement of all processes involving muons. In fact, when comparing the measured cross-section from data with the theoretical expectations, one has to correct for the detector inefficiencies, which at the start-ip are not perfectly reproduced in the simulation. In this thesis, these muon efficiencies have been used for a first data/MC comparison of the Z -> µ+ µ- cross-section, both inclusive and differential as a function of the jet multiplicity.

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[L'angolo del PhD] Sara Borroni - XXIII Ciclo - 2010

  1. 1. Study of the pp → Z → µ+ µ− Process at ATLAS: Detector Performance and First Cross-Section Measurement at 7 TeV Candidate: Sara Borroni Supervisor: Cesare Bini Co-supervisor: Stefano Rosati Sapienza, Università di Roma XXIII Ciclo di Dottorato November 3, 2010
  2. 2. Introduction and Motivations Tag&Probe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Theoretical Introduction The Standard Model of Particle Physics The past century has seen a really big step forward for the elementary particle physics. The Standard Model (SM) has been developed which describes the behavior of matter and its interactions. This theoretical framework managed to give a unified description of strong, electromagnetic and weak interactions but the gravity The SM has been extensively tested in the last decades at LEP and Tevatron and it successfully explains most of the known phenomena in elementary particle physics. Nevertheless a number of open problems are still left which need for further studies to be done. Experimental facts not explained by SM evidence that neutrinos have non-zero masses dark matter must exist observed matter-antimatter asymmetry ... Theoretical issues not solved in the SM the Higgs or some new physics must exist to make the SM consistent unification of the gauge couplings unification of gravity is still missing ...Sara Borroni November 3, 2010 2/36
  3. 3. Introduction and Motivations Tag&Probe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Theoretical Introduction The Standard Model of Particle Physics The past century has seen a really big step forward for the elementary particle physics. The Standard Model (SM) has been developed which describes the behavior of matter and its interactions. This theoretical framework managed to give a unified description of strong, electromagnetic and weak interactions but the gravity The SM has been extensively tested in the last decades at LEP and Tevatron and it successfully explains most of the known phenomena in elementary particle physics. Nevertheless a number of open problems are still left which need for further studies to be done. Experimental facts not explained by SM evidence that neutrinos have non-zero masses dark matter must exist observed matter-antimatter asymmetry ... Theoretical issues not solved in the SM the Higgs or some new physics must exist to make the SM consistent unification of the gauge couplings unification of gravity is still missing ...Sara Borroni November 3, 2010 2/36
  4. 4. Introduction and Motivations Tag&Probe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Theoretical Introduction The Standard Model of Particle Physics The past century has seen a really big step forward for the elementary particle physics. The Standard Model (SM) has been developed which describes the behavior of matter and its interactions. This theoretical framework managed to give a unified description of strong, electromagnetic and weak interactions but the gravity The SM has been extensively tested in the last decades at LEP and Tevatron and it successfully explains most of the known phenomena in elementary particle physics. Nevertheless a number of open problems are still left which need for further studies to be done. Experimental facts not explained by SM evidence that neutrinos have non-zero masses dark matter must exist observed matter-antimatter asymmetry ... Theoretical issues not solved in the SM the Higgs or some new physics must exist to make the SM consistent unification of the gauge couplings unification of gravity is still missing ...Sara Borroni November 3, 2010 2/36
  5. 5. Introduction and Motivations Tag&Probe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Theoretical Introduction The Standard Model of Particle Physics The past century has seen a really big step forward for the elementary particle physics. The Standard Model (SM) has been developed which describes the behavior of matter and its interactions. This theoretical framework managed to give a unified description of strong, electromagnetic and weak interactions but the gravity The SM has been extensively tested in the last decades at LEP and Tevatron and it successfully explains most of the known phenomena in elementary particle physics. Nevertheless a number of open problems are still left which need for further studies to be done. Experimental facts not explained by SM evidence that neutrinos have non-zero masses dark matter must exist observed matter-antimatter asymmetry ... Theoretical issues not solved in the SM the Higgs or some new physics must exist to make the SM consistent unification of the gauge couplings unification of gravity is still missing ...Sara Borroni November 3, 2010 2/36
  6. 6. Introduction and Motivations Tag&Probe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup The Large Hadron Collider Motivations and Experiments Answer these kind of questions is the reason why the Large Hadron Collider (LHC) has been built, with its four experiments: ATLAS, CMS, LHCb and ALICE. LHC today proton - proton collider 7 TeV center of mass energy (proj. 14 TeV ) instantaneous peak luminosity 2 · 1032 cm−2 s−1 (proj. 1034 cm−2 s−1 ) integrated luminosity delivered ∼ 40 pb−1 2011 full year data taking - 2012 technical stop (?)Sara Borroni November 3, 2010 3/36
  7. 7. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup The ATLAS Experiment ATLAS in (Very-)Short Usual collider multi-purpose experiment: many concentrical layers to detect different particles Inner Tracker in a solenoidal magnetic field (2 T ) for charged particles detection → resolution order 10 ÷ 100 µm Electromagnetic and Hadronic calorimeters for electrons, photons and hadrons ∆E 11.0% (EM) = p ⊕ 0.4% E E[GeV ] ∆E 50% (HAD) = p ⊕ 3% E E[GeV ] External Muon Spectrometer in an air-core toroidal magnetic field (0.6 T ) for muons → resolution ∼ 50 µm on the sagittaSara Borroni November 3, 2010 4/36
  8. 8. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup The ATLAS Experiment Variables used to describe the event kinematics in an hadron collider experiment only the transverse components of energies and momenta (pT , missing transverse energy..) azimutal angle φ pseudo-rapidity η = ln tan θ/2 Distance between two reconstructed objects p ∆R = ∆η 2 + ∆φ2Sara Borroni November 3, 2010 5/36
  9. 9. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup W /Z Bosons Physics A sketch The hadronic nature of the proton-proton collisions opens a wide range of exploration possibilities, from the precise measurements of Standard Model parameters to the search for new physics phenomena up to the TeV scale H1 p1 x1 p 1 , ν k1 γ, Z, W ± k2 p2 x1 p 2 ¯¯ , ν H2 Uncertainty sources: During each bunch crossing are NOT the proton to collide but the partons inside the protons, each carrying a momentum fraction x Uncertainty on the Parton Distribution Functions (PDF) → describe the x distribution for each parton typeSara Borroni November 3, 2010 6/36
  10. 10. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup W /Z Bosons Physics A sketch The hadronic nature of the proton-proton collisions opens a wide range of exploration possibilities, from the precise measurements of Standard Model parameters to the search for new physics phenomena up to the TeV scale H1 p1 x1 p 1 , ν k1 γ, Z, W ± k2 p2 x1 p 2 ¯¯ , ν H2 Uncertainty sources: During each bunch crossing are NOT the proton to collide but the partons inside the protons, each carrying a momentum fraction x Uncertainty on the Parton Distribution Functions (PDF) → describe the x distribution for each parton typeSara Borroni November 3, 2010 6/36
  11. 11. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup W /Z Bosons Physics A sketch The measurement of the well known Standard Model processes is the first step towards all new physics searches theoretical predictions tuning at a new unexplored energy: which theoretical model correctly describes the data? standard candles both for the detectors understanding and performance assessmentSara Borroni November 3, 2010 7/36
  12. 12. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup W /Z Bosons Physics A sketch The W ± and Z 0 bosons are suitable theoretical predictions (NNLO) have a small uncertainty (about 5%) mainly due to the uncertainty on the PDF measured with high experimental precision at LEP and Tevatron copiously produced at LHC leptonic decays are clear and “simple to disentangle from the background Expected W/Z events @ 7 TeV σ × BR(Z → ll) ∼ 1 nb : →∼ 33000 evts in 100 pb−1 after selection σ × BR(W → lν) ∼ 10 nb : → 370000 evts in 100 pb−1 after selectionSara Borroni November 3, 2010 8/36
  13. 13. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup A cross-section measurement The Standard Model Re-discovery Let’s re-discover the Standard Model and assess the detector performance starting from the Z boson cross-section measurement! The cross-section measurement is a counting experiment where one has to deduce how many events NS of a certain type have been produced when Nsel of them are observed. Nsel − Nb NS = L · σ −→ σ = L·A· Example: efficiency for Z → µ+ µ− process: efficiency is correlated to the probability of the event with two muons in ζ1 and ζ2 kinematic bins to be selected which is a combination of the single muon efficiencies P(R, ζi ) and P(T |R, ζi ) 2 3 2 3 Y Y P(event, ζ) = 4 P(R, ζi )5 · 41 − (1 − P(T |R, ζi ))5 i=1,n i=1,n I want to measure the reconstruction efficiency P(R, ζi ) and the trigger efficiency for a reconstructed muon P(T |R, ζi )Sara Borroni November 3, 2010 9/36
  14. 14. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup A cross-section measurement The Standard Model Re-discovery Let’s re-discover the Standard Model and assess the detector performance starting from the Z boson cross-section measurement! The cross-section measurement is a counting experiment where one has to deduce how many events NS of a certain type have been produced when Nsel of them are observed. Nsel − Nb NS = L · σ −→ σ = L·A· Example: efficiency for Z → µ+ µ− process: efficiency is correlated to the probability of the event with two muons in ζ1 and ζ2 kinematic bins to be selected which is a combination of the single muon efficiencies P(R, ζi ) and P(T |R, ζi ) 2 3 2 3 Y Y P(event, ζ) = 4 P(R, ζi )5 · 41 − (1 − P(T |R, ζi ))5 i=1,n i=1,n I want to measure the reconstruction efficiency P(R, ζi ) and the trigger efficiency for a reconstructed muon P(T |R, ζi )Sara Borroni November 3, 2010 9/36
  15. 15. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup A cross-section measurement The Standard Model Re-discovery Let’s re-discover the Standard Model and assess the detector performance starting from the Z boson cross-section measurement! The cross-section measurement is a counting experiment where one has to deduce how many events NS of a certain type have been produced when Nsel of them are observed. Nsel − Nb NS = L · σ −→ σ = L·A· Example: efficiency for Z → µ+ µ− process: efficiency is correlated to the probability of the event with two muons in ζ1 and ζ2 kinematic bins to be selected which is a combination of the single muon efficiencies P(R, ζi ) and P(T |R, ζi ) 2 3 2 3 Y Y P(event, ζ) = 4 P(R, ζi )5 · 41 − (1 − P(T |R, ζi ))5 i=1,n i=1,n I want to measure the reconstruction efficiency P(R, ζi ) and the trigger efficiency for a reconstructed muon P(T |R, ζi )Sara Borroni November 3, 2010 9/36
  16. 16. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup A cross-section measurement The Standard Model Re-discovery Let’s re-discover the Standard Model and assess the detector performance starting from the Z boson cross-section measurement! The cross-section measurement is a counting experiment where one has to deduce how many events NS of a certain type have been produced when Nsel of them are observed. Nsel − Nb NS = L · σ −→ σ = L·A· Example: efficiency for Z → µ+ µ− process: efficiency is correlated to the probability of the event with two muons in ζ1 and ζ2 kinematic bins to be selected which is a combination of the single muon efficiencies P(R, ζi ) and P(T |R, ζi ) 2 3 2 3 Y Y P(event, ζ) = 4 P(R, ζi )5 · 41 − (1 − P(T |R, ζi ))5 i=1,n i=1,n I want to measure the reconstruction efficiency P(R, ζi ) and the trigger efficiency for a reconstructed muon P(T |R, ζi )Sara Borroni November 3, 2010 9/36
  17. 17. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup A cross-section measurement The Standard Model Re-discovery Let’s re-discover the Standard Model and assess the detector performance starting from the Z boson cross-section measurement! The cross-section measurement is a counting experiment where one has to deduce how many events NS of a certain type have been produced when Nsel of them are observed. Nsel − Nb NS = L · σ −→ σ = L·A· Example: efficiency for Z → µ+ µ− process: efficiency is correlated to the probability of the event with two muons in ζ1 and ζ2 kinematic bins to be selected which is a combination of the single muon efficiencies P(R, ζi ) and P(T |R, ζi ) 2 3 2 3 Y Y P(event, ζ) = 4 P(R, ζi )5 · 41 − (1 − P(T |R, ζi ))5 i=1,n i=1,n I want to measure the reconstruction efficiency P(R, ζi ) and the trigger efficiency for a reconstructed muon P(T |R, ζi )Sara Borroni November 3, 2010 9/36
  18. 18. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup A cross-section measurement The Standard Model Re-discovery Let’s re-discover the Standard Model and assess the detector performance starting from the Z boson cross-section measurement! The cross-section measurement is a counting experiment where one has to deduce how many events NS of a certain type have been produced when Nsel of them are observed. Nsel − Nb NS = L · σ −→ σ = L·A· Example: efficiency for Z → µ+ µ− process: efficiency is correlated to the probability of the event with two muons in ζ1 and ζ2 kinematic bins to be selected which is a combination of the single muon efficiencies P(R, ζi ) and P(T |R, ζi ) 2 3 2 3 Y Y P(event, ζ) = 4 P(R, ζi )5 · 41 − (1 − P(T |R, ζi ))5 i=1,n i=1,n I want to measure the reconstruction efficiency P(R, ζi ) and the trigger efficiency for a reconstructed muon P(T |R, ζi )Sara Borroni November 3, 2010 9/36
  19. 19. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Muon Reconstruction Muons in the Muon Spectrometer (MS) are curved by the toroidal magnetic field The momentum of the muon is measured reconstructing the track sagitta (stand-alone reconstruction) The stand-alone track can be combined with an track reconstructed in the inner detector to have a more precise measurement (combined reconstruction) the reconstruction efficiency is flat in pT starting from ∼ 10 GeV (muons with pT 3 don’t arrive to the MS, due to the energy loss in the calorimeters) η and φ structure is defined by the geometry and the acceptance of the precision chambers plateau value is around 94% due to the detector acceptance (central crack, lefts and feet)Sara Borroni November 3, 2010 10/36
  20. 20. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Muon Reconstruction Muons in the Muon Spectrometer (MS) are curved by the toroidal magnetic field The momentum of the muon is measured reconstructing the track sagitta (stand-alone reconstruction) The stand-alone track can be combined with an track reconstructed in the inner detector to have a more precise measurement (combined reconstruction) the reconstruction efficiency is flat in pT starting from ∼ 10 GeV (muons with pT 3 don’t arrive to the MS, due to the energy loss in the calorimeters) η and φ structure is defined by the geometry and the acceptance of the precision chambers plateau value is around 94% due to the detector acceptance (central crack, lefts and feet)Sara Borroni November 3, 2010 10/36
  21. 21. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Muon Reconstruction Muons in the Muon Spectrometer (MS) are curved by the toroidal magnetic field The momentum of the muon is measured reconstructing the track sagitta (stand-alone reconstruction) The stand-alone track can be combined with an track reconstructed in the inner detector to have a more precise measurement (combined reconstruction) the reconstruction efficiency is flat in pT starting from ∼ 10 GeV (muons with pT 3 don’t arrive to the MS, due to the energy loss in the calorimeters) η and φ structure is defined by the geometry and the acceptance of the precision chambers plateau value is around 94% due to the detector acceptance (central crack, lefts and feet)Sara Borroni November 3, 2010 10/36
  22. 22. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Muon Reconstruction Muons in the Muon Spectrometer (MS) are curved by the toroidal magnetic field The momentum of the muon is measured reconstructing the track sagitta (stand-alone reconstruction) The stand-alone track can be combined with an track reconstructed in the inner detector to have a more precise measurement (combined reconstruction) the reconstruction efficiency is flat in pT starting from ∼ 10 GeV (muons with pT 3 don’t arrive to the MS, due to the energy loss in the calorimeters) η and φ structure is defined by the geometry and the acceptance of the precision chambers plateau value is around 94% due to the detector acceptance (central crack, lefts and feet)Sara Borroni November 3, 2010 10/36
  23. 23. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Muon Reconstruction Muons in the Muon Spectrometer (MS) are curved by the toroidal magnetic field The momentum of the muon is measured reconstructing the track sagitta (stand-alone reconstruction) The stand-alone track can be combined with an track reconstructed in the inner detector to have a more precise measurement (combined reconstruction) the reconstruction efficiency is flat in pT starting from ∼ 10 GeV (muons with pT 3 don’t arrive to the MS, due to the energy loss in the calorimeters) η and φ structure is defined by the geometry and the acceptance of the precision chambers plateau value is around 94% due to the detector acceptance (central crack, lefts and feet)Sara Borroni November 3, 2010 10/36
  24. 24. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Muon Reconstruction Muons in the Muon Spectrometer (MS) are curved by the toroidal magnetic field The momentum of the muon is measured reconstructing the track sagitta (stand-alone reconstruction) The stand-alone track can be combined with an track reconstructed in the inner detector to have a more precise measurement (combined reconstruction) the reconstruction efficiency is flat in pT starting from ∼ 10 GeV (muons with pT 3 don’t arrive to the MS, due to the energy loss in the calorimeters) η and φ structure is defined by the geometry and the acceptance of the precision chambers plateau value is around 94% due to the detector acceptance (central crack, lefts and feet)Sara Borroni November 3, 2010 10/36
  25. 25. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Muon Trigger Three trigger levels L1 hardware based on geometrical coincidences, with 6 programmable pT thresholds (selects muons with pT threshold). It defines the Regions of Interest (ROIs) L2 refinement of the raw pT measurement done at L1, accessing ony data of the tracking detectors in the RoI EF (Event Filter) refinement of trigger decision using the whole event and sub-detectors info pT structure of the trigger turn-on curves is defined by the threshold logic η and φ structure is defined by the geometry and the acceptance of the trigger chambers plateau value is around 85% due to the detector acceptance (mainly in the barrel)Sara Borroni November 3, 2010 11/36
  26. 26. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Muon Trigger Three trigger levels L1 hardware based on geometrical coincidences, with 6 programmable pT thresholds (selects muons with pT threshold). It defines the Regions of Interest (ROIs) L2 refinement of the raw pT measurement done at L1, accessing ony data of the tracking detectors in the RoI EF (Event Filter) refinement of trigger decision using the whole event and sub-detectors info pT structure of the trigger turn-on curves is defined by the threshold logic η and φ structure is defined by the geometry and the acceptance of the trigger chambers plateau value is around 85% due to the detector acceptance (mainly in the barrel)Sara Borroni November 3, 2010 11/36
  27. 27. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Muon Trigger Three trigger levels L1 hardware based on geometrical coincidences, with 6 programmable pT thresholds (selects muons with pT threshold). It defines the Regions of Interest (ROIs) L2 refinement of the raw pT measurement done at L1, accessing ony data of the tracking detectors in the RoI EF (Event Filter) refinement of trigger decision using the whole event and sub-detectors info pT structure of the trigger turn-on curves is defined by the threshold logic η and φ structure is defined by the geometry and the acceptance of the trigger chambers plateau value is around 85% due to the detector acceptance (mainly in the barrel)Sara Borroni November 3, 2010 11/36
  28. 28. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Muon Trigger Three trigger levels L1 hardware based on geometrical coincidences, with 6 programmable pT thresholds (selects muons with pT threshold). It defines the Regions of Interest (ROIs) L2 refinement of the raw pT measurement done at L1, accessing ony data of the tracking detectors in the RoI EF (Event Filter) refinement of trigger decision using the whole event and sub-detectors info pT structure of the trigger turn-on curves is defined by the threshold logic η and φ structure is defined by the geometry and the acceptance of the trigger chambers plateau value is around 85% due to the detector acceptance (mainly in the barrel)Sara Borroni November 3, 2010 11/36
  29. 29. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Muon Trigger Three trigger levels L1 hardware based on geometrical coincidences, with 6 programmable pT thresholds (selects muons with pT threshold). It defines the Regions of Interest (ROIs) L2 refinement of the raw pT measurement done at L1, accessing ony data of the tracking detectors in the RoI EF (Event Filter) refinement of trigger decision using the whole event and sub-detectors info pT structure of the trigger turn-on curves is defined by the threshold logic η and φ structure is defined by the geometry and the acceptance of the trigger chambers plateau value is around 85% due to the detector acceptance (mainly in the barrel)Sara Borroni November 3, 2010 11/36
  30. 30. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Muon Trigger Three trigger levels L1 hardware based on geometrical coincidences, with 6 programmable pT thresholds (selects muons with pT threshold). It defines the Regions of Interest (ROIs) L2 refinement of the raw pT measurement done at L1, accessing ony data of the tracking detectors in the RoI EF (Event Filter) refinement of trigger decision using the whole event and sub-detectors info pT structure of the trigger turn-on curves is defined by the threshold logic η and φ structure is defined by the geometry and the acceptance of the trigger chambers plateau value is around 85% due to the detector acceptance (mainly in the barrel)Sara Borroni November 3, 2010 11/36
  31. 31. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Muon Efficiencies Measurement The Concept to measure the efficiency of the Muon Spectrometer (MS) we need to select a muon without using the MS and test if the MS reconstructed/triggered it how to recognize a muon without using the MS?!? take advantage of a known process: Z → µ + µ− the TagProbe method has been developed to provide an in-situ determination of muon trigger and reconstruction efficiency taking advantage of the kinematic correlation between muons coming from Z boson decaySara Borroni November 3, 2010 12/36
  32. 32. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Muon Efficiencies Measurement The Concept to measure the efficiency of the Muon Spectrometer (MS) we need to select a muon without using the MS and test if the MS reconstructed/triggered it how to recognize a muon without using the MS?!? take advantage of a known process: Z → µ + µ− the TagProbe method has been developed to provide an in-situ determination of muon trigger and reconstruction efficiency taking advantage of the kinematic correlation between muons coming from Z boson decaySara Borroni November 3, 2010 12/36
  33. 33. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Muon Efficiencies Measurement The Concept to measure the efficiency of the Muon Spectrometer (MS) we need to select a muon without using the MS and test if the MS reconstructed/triggered it how to recognize a muon without using the MS?!? take advantage of a known process: Z → µ + µ− the TagProbe method has been developed to provide an in-situ determination of muon trigger and reconstruction efficiency taking advantage of the kinematic correlation between muons coming from Z boson decaySara Borroni November 3, 2010 12/36
  34. 34. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Muon Efficiencies Measurement The Concept to measure the efficiency of the Muon Spectrometer (MS) we need to select a muon without using the MS and test if the MS reconstructed/triggered it how to recognize a muon without using the MS?!? take advantage of a known process: Z → µ + µ− the TagProbe method has been developed to provide an in-situ determination of muon trigger and reconstruction efficiency taking advantage of the kinematic correlation between muons coming from Z boson decaySara Borroni November 3, 2010 12/36
  35. 35. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Muon Efficiencies Measurement The Concept to measure the efficiency of the Muon Spectrometer (MS) we need to select a muon without using the MS and test if the MS reconstructed/triggered it how to recognize a muon without using the MS?!? take advantage of a known process: Z → µ + µ− the TagProbe method has been developed to provide an in-situ determination of muon trigger and reconstruction efficiency taking advantage of the kinematic correlation between muons coming from Z boson decaySara Borroni November 3, 2010 12/36
  36. 36. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Muon Efficiencies Measurement: the TagProbe Method The Concept Tag A TAG muon is selected requiring tight criteria to ensure a pure selection A fundamental requirement to not to bias the analysis is to ask the tag to have fired the trigger Probe Then for each tag, taking advantage from the kinematical correlation: select the second muon to be used as a PROBE from the tracks in the inner tracker and never using the MS info −→ has this track been reconstructed by MS? select the second muon to be used as a PROBE from reconstructed muons and never using the Muon Trigger info −→ has this track been triggered? Muons The efficiencies are measured wrt a certain muon reconstruction definition i.e. the same used in the physics analysis the efficiencies are meant to be used forSara Borroni November 3, 2010 13/36
  37. 37. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Muon Efficiencies Measurement: the TagProbe Method The Concept Tag A TAG muon is selected requiring tight criteria to ensure a pure selection A fundamental requirement to not to bias the analysis is to ask the tag to have fired the trigger Probe Then for each tag, taking advantage from the kinematical correlation: select the second muon to be used as a PROBE from the tracks in the inner tracker and never using the MS info −→ has this track been reconstructed by MS? select the second muon to be used as a PROBE from reconstructed muons and never using the Muon Trigger info −→ has this track been triggered? Muons The efficiencies are measured wrt a certain muon reconstruction definition i.e. the same used in the physics analysis the efficiencies are meant to be used forSara Borroni November 3, 2010 13/36
  38. 38. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Muon Efficiencies Measurement: the TagProbe Method The Concept Tag A TAG muon is selected requiring tight criteria to ensure a pure selection A fundamental requirement to not to bias the analysis is to ask the tag to have fired the trigger Probe Then for each tag, taking advantage from the kinematical correlation: select the second muon to be used as a PROBE from the tracks in the inner tracker and never using the MS info −→ has this track been reconstructed by MS? select the second muon to be used as a PROBE from reconstructed muons and never using the Muon Trigger info −→ has this track been triggered? Muons The efficiencies are measured wrt a certain muon reconstruction definition i.e. the same used in the physics analysis the efficiencies are meant to be used forSara Borroni November 3, 2010 13/36
  39. 39. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Muon Efficiencies Measurement: the TagProbe Method The Concept Tag A TAG muon is selected requiring tight criteria to ensure a pure selection A fundamental requirement to not to bias the analysis is to ask the tag to have fired the trigger Probe Then for each tag, taking advantage from the kinematical correlation: select the second muon to be used as a PROBE from the tracks in the inner tracker and never using the MS info −→ has this track been reconstructed by MS? select the second muon to be used as a PROBE from reconstructed muons and never using the Muon Trigger info −→ has this track been triggered? Muons The efficiencies are measured wrt a certain muon reconstruction definition i.e. the same used in the physics analysis the efficiencies are meant to be used forSara Borroni November 3, 2010 13/36
  40. 40. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Muon Efficiencies Measurement: the TagProbe Method The Concept Tag A TAG muon is selected requiring tight criteria to ensure a pure selection A fundamental requirement to not to bias the analysis is to ask the tag to have fired the trigger Probe Then for each tag, taking advantage from the kinematical correlation: select the second muon to be used as a PROBE from the tracks in the inner tracker and never using the MS info −→ has this track been reconstructed by MS? select the second muon to be used as a PROBE from reconstructed muons and never using the Muon Trigger info −→ has this track been triggered? Muons The efficiencies are measured wrt a certain muon reconstruction definition i.e. the same used in the physics analysis the efficiencies are meant to be used forSara Borroni November 3, 2010 13/36
  41. 41. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Muon Efficiencies Measurement: the TagProbe Method The Concept Tag A TAG muon is selected requiring tight criteria to ensure a pure selection A fundamental requirement to not to bias the analysis is to ask the tag to have fired the trigger Probe Then for each tag, taking advantage from the kinematical correlation: select the second muon to be used as a PROBE from the tracks in the inner tracker and never using the MS info −→ has this track been reconstructed by MS? select the second muon to be used as a PROBE from reconstructed muons and never using the Muon Trigger info −→ has this track been triggered? Muons The efficiencies are measured wrt a certain muon reconstruction definition i.e. the same used in the physics analysis the efficiencies are meant to be used forSara Borroni November 3, 2010 13/36
  42. 42. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Muon Efficiencies Measurement: the TagProbe Method The Concept Tag A TAG muon is selected requiring tight criteria to ensure a pure selection A fundamental requirement to not to bias the analysis is to ask the tag to have fired the trigger Probe Then for each tag, taking advantage from the kinematical correlation: select the second muon to be used as a PROBE from the tracks in the inner tracker and never using the MS info −→ has this track been reconstructed by MS? select the second muon to be used as a PROBE from reconstructed muons and never using the Muon Trigger info −→ has this track been triggered? Muons The efficiencies are measured wrt a certain muon reconstruction definition i.e. the same used in the physics analysis the efficiencies are meant to be used forSara Borroni November 3, 2010 13/36
  43. 43. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup TagProbe on the first 1.3 pb−1 The method has been applied to a data integrated luminosity of 1.3 pb−1 (April-August 2010 data-taking periods) Indet probes −→ for reconstruction efficiency Muon probes −→ for trigger efficiency (L1_MU10 is taken as example) The disagreement between data and MC is manly due to the difference in the efficiencies (see next slide). No correction factors are applied in the plot Probes Selected with 1.3 pb−1 Indet probes Muon probes # selected probes 655 567 Expected from MC 714.0 ± 1.4 686.98 ± 0.59 Background estimation (MC) 1.8 ± 0.4% 1.0 ± 0.1%Sara Borroni November 3, 2010 14/36
  44. 44. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Muon Reconstruction Efficiency from Data Muon reconstruction efficiency vs pT (left) and η (right) Reconstruction Efficiencies Region η value Efficiency Scale Factor Barrel 0.1 |η| 1.05 0.90 ± 0.02 0.94 ± 0.02 End-Caps 1.05 |η| 2.4 0.85 ± 0.03 0.91 ± 0.01 Crack |η| 0.1 0.69 ± 0.09 1.36 ± 0.17 Average −2.4 η 2.4 0.89 ± 0.01 0.95 ± 0.01Sara Borroni November 3, 2010 15/36
  45. 45. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Trigger Efficiency from Data Muon trigger efficiency vs pT (left) and η (right) Relative Trigger Efficiencies L1_MU10 Region η value Efficiency Scale Factor Barrel |η| 1.05 0.81 ± 0.02 1.02 ± 0.02 End-Caps 1.05 |η| 2.4 0.85 ± 0.02 0.89 ± 0.02 Average |η| 2.4 0.83 ± 0.01 0.94 ± 0.02Sara Borroni November 3, 2010 16/36
  46. 46. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Z → µ+ µ− + jets cross-section measurement With the same 1.3 pb−1 data sample a first cross-section measurement of the Z → µ+ µ− process has been performed 430 Z → µ+ µ− candidates have been found in a mass window of 71 mµµ 111 GeV correcting for the measured efficiencies and all the other factors the resulting inclusive cross-section is: σ = 427.3 ± 10.0(stat)+53.5 (syst) ± 47.0(lumi) pb −11.4Sara Borroni November 3, 2010 17/36
  47. 47. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Z → µ+ µ− + jets cross-section measurement It’s interesting to perform a differential cross-section measurement The shape of the differential distributions strongly depend on the MC models These measurements are important to be compared to the theoretical predictions and to tune the MC It necessary to know the efficiencies in # of jets bins!Sara Borroni November 3, 2010 18/36
  48. 48. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Dependence on the # of Jets Muon reconstruction (left) and trigger (right) efficiencies vs # of jets in the event The dependence studied in MC is not jet significative in data (due to the statistics)Sara Borroni November 3, 2010 19/36
  49. 49. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Inclusive Z → µ+ µ− cross-section: a comparison Published inclusive cross-section measurement with ∼ 300 nb−1Sara Borroni November 3, 2010 20/36
  50. 50. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Summary and Conclusions Development and optimization of a TagProbe method to measure the muon trigger and reconstruction efficiencies from data Optimization using MC samples Application to the first 1.3 pb−1 of data @ 7 TeV → efficiencies measurement and comparison with MC expectations Application of the efficiencies to measure the inclusive pp → Z → µ+ µ− cross-section ATLAS Collaboration, “Measurement of the W → lν and Z /γ ∗ → ll production cross sections in proton-proton collisions √ at s = 7 TeV with the ATLAS detector , arXiv:1010.2130v1 , submitted to JHEP Study of the efficiencies dependence from the jets variables to estimate the production of a Z boson in association with jets √ A. Ahmada et al., “Measurement of the cross-section for jets produced in association with a Z -boson in pp collisions at s = 7 TeV, in preparation √ A. Ahmada et al., “Measurement of the cross-section for jets produced in association with a W -boson in pp collisions at s = 7 TeV, ATL-COM-PHYS-2010 THANKS!Sara Borroni November 3, 2010 21/36
  51. 51. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Summary and Conclusions Development and optimization of a TagProbe method to measure the muon trigger and reconstruction efficiencies from data Optimization using MC samples Application to the first 1.3 pb−1 of data @ 7 TeV → efficiencies measurement and comparison with MC expectations Application of the efficiencies to measure the inclusive pp → Z → µ+ µ− cross-section ATLAS Collaboration, “Measurement of the W → lν and Z /γ ∗ → ll production cross sections in proton-proton collisions √ at s = 7 TeV with the ATLAS detector , arXiv:1010.2130v1 , submitted to JHEP Study of the efficiencies dependence from the jets variables to estimate the production of a Z boson in association with jets √ A. Ahmada et al., “Measurement of the cross-section for jets produced in association with a Z -boson in pp collisions at s = 7 TeV, in preparation √ A. Ahmada et al., “Measurement of the cross-section for jets produced in association with a W -boson in pp collisions at s = 7 TeV, ATL-COM-PHYS-2010 THANKS!Sara Borroni November 3, 2010 21/36
  52. 52. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Publications Contributions to Conferences: XVIII International Workshop on Deep-Inelastic Scattering and Related Subjects, Convitto della Calza, Firenze, 19 - 23 April 2010; talk given W/Z Production at ATLAS, ATL-COM-PHYS-2010-179 Incontri di Fisica delle Alte Energie, Sapienza Univeristá di Roma, Italy April 7 - 9 2010; poster presented Inclusive Muon Production in 900 GeV p-p Collisions with ATLAS Detector ”The 2009 Europhysics Conference on High Energy Physics, Krakow, Poland July 16 - 22 2009; poster presented ”ATLAS Electroweak Measurements With Early Data, ATL-PHYS-SLIDE-2009-196 ”Signaling the Arrival of the LHC Era, ICTP Trieste, Italy December 8 - 13 2008; talk given ”Studies on ATLAS muon efficiency measurement with Z → µµ, ATL-MUON-SLIDE-2009-151, ATL-COM-MUON-2008-017 Publications with major contribution: A. Ahmada et al., “Measurement of the cross-section for jets produced in association with a Z -boson in pp √ collisions at s = 7 TeV, in preparation A. Ahmada et al., “Measurement of the cross-section for jets produced in association with a W -boson in pp √ collisions at s = 7 TeV, ATL-COM-PHYS-2010 J. Barreiro Guimaraes da Costa et al., “W → µν and Z → µµ cross-sections measurements in √ proton-proton collisions at s = 7 TeV with the ATLAS Detector, ATL-COM-PHYS-2010-685 ATLAS Collaboration, “Measurement of the W → lν and Z /γ ∗ → ll production cross sections in √ proton-proton collisions at s = 7 TeV with the ATLAS detector , arXiv:1010.2130v1 , submitted to JHEP P.Bagnaia et al.,“Calibration model for the MDT chambers of the ATLAS Muon Spectrometer, ATLAS group note, ATL-MUON-PUB-2008-004, ATL-COM-MUON-2008-006Sara Borroni November 3, 2010 22/36
  53. 53. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Publications Other publications: ATLAS Collaboration, Measurement of inclusive jet and di-jet cross sections in proton-proton collisions at 7 TeV centre-of-mass energy with the ATLAS detector, arXiv:1009.5908v2, submitted to EPJC ATLAS Collaboration, Search for Quark Contact Interactions in Di-jet Angular Distributions in pp Collisions at sqrt(s) = 7 TeV Measured with the ATLAS Detector, arXiv:1009.5069v1, submitted to PLB ATLAS Collaboration, Search for New Particles in Two-Jet Final States in 7 TeV Proton-Proton Collisions with the ATLAS Detector at the LHC, Phys. Rev. Lett. 105, 161801 (2010), arXiv:1008.2461v2 √ ATLAS Collaboration, Charged-particle multiplicities in pp interactions at s = 900 GeV measured with the ATLAS detector at the LHC, CERN-PH-EP-2010-004, arXiv:1003.3124, Phys Lett B 688, 2010, Issue 1, 21-42 ATLAS Collaboration, Readiness of the ATLAS Liquid Argon Calorimeter for LHC Collisions, arXiv:0912.2642, submitted to EPJC ATLAS Collaboration, Drift Time Measurement in the ATLAS Liquid Argon Electromagnetic Calorimeter using Cosmic Muons, arXiv:1002.4189, submitted to EPJC ATLAS Collaboration, ATLAS Inner Detector commissioning and calibration, arXiv:1004.5293, submitted to EPJCSara Borroni November 3, 2010 23/36
  54. 54. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup BackupSara Borroni November 3, 2010 24/36
  55. 55. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup W /Z Bosons Physics A sketch The hadronic nature of the proton-proton collisions opens a wide range of exploration possibilities, from the precise measurements of Standard Model parameters to the search for new physics phenomena up to the TeV scale H1 p1 x1 p 1 , ν k1 γ, Z, W ± k2 p2 x1 p 2 ¯¯ , ν H2 Uncertainty sources: extrapolation to a new kinematical x region → x = momentum fraction carried by the colliding parton uncertainty on the Parton Distribution Functions (PDF) → describe the x distribution for each parton typeSara Borroni November 3, 2010 25/36
  56. 56. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup TagProbe Selection Details Muon Pre-selection Cuts Muon Pre-Selection Cuts Type Combined Muon pT 15.0 GeV |η| 2.5 Track Isolation (0.2) 1.8 GeV # PIX hits 1 # SCT hits 5 # TRT hits 0 (only for |η| 2.0) |pID − pMS |/pID T T T 0.5 pMS T 10 GeV d0 0.1 mm z0 10 mm Table: Muon pre-selection cuts. This is chosen to be the same used for the inclusive Z and Z+jets 7 TeV analysis. The variables used in the selection are defined in the text.Sara Borroni November 3, 2010 26/36
  57. 57. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup TagProbe Selection Details Probes Selection Cuts TagProbe Selection @ 7 TeV Cut Tag Indet Probes Muon Probes Type Combined Muon InDet Track Pre-selected Muon Charge - OS OS Trigger L1_MU10 - - pT 10.0 GeV 5.0 GeV - |η| 2.5 2.5 - d0 - 0.1 mm - ∆z0 - 0.5 mm 0.5 mm Track Isolation - 0.1 - ∆Φ - 2.14 rad 2.14 rad CaloMuon matching - True False ∆M - MZ ± 20 GeV MZ ± 20 GeV Table: TagProbe selection for 7 TeV analysis. Jet selection: pT 20 GeV in |y| 2.8Sara Borroni November 3, 2010 27/36
  58. 58. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup TagProbe Selection Details Selection Variables DistributionsSara Borroni November 3, 2010 28/36
  59. 59. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup TagProbe Cut-Flow Event Selection Cut Data MC Initial Events 24105444 – GRL 21793697 – Indet Probes Selection Cut Data MC pT 1727031 15972.56 |η| 1718121 15856.2 Charge 862812 8655.86 d0 152147 3055.87 ∆z0 118744 2911.73 Track Isolation 21933 1499.05 ∆Φ 12567 1178.82 CaloMuon 1675 953.79 ∆M 655 713.99 ± 1.40 Muon Probes Selection Cut Data MC Type 5883 7059.27 Charge 880 890.23 ∆z0 825 878.68 ∆Φ 715 796.73 ∆M 567 686.98 ± 0.59 Table: Probes selection cut-flow, data and MC expectations. MC is normalized to the data integrated luminosity (1.3 pb−1 )Sara Borroni November 3, 2010 29/36
  60. 60. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup TagProbe Systematic Uncertainties Systematic Uncertainties Cut Reconstruction Absolute Trigger Relative Trigger Efficiency Efficiency Efficiency d0 0.3% 0.2% – Isolation 1.2% 0.4% – ∆z0 0.6% 0.6% 0.3% ∆Φ 0.5% 0.8% 0.6% ∆M 0.6% 0.1% 0.6% 1.6% 1.1% 0.9% Table: Systematics uncertainties on efficiencies measurement. The unceratinties are evaluated varying the selection cuts in the range explained in the text and estimating the corresponding maximal average efficiency variation.Sara Borroni November 3, 2010 30/36
  61. 61. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Dependence on # of Jets Efficiencies vs Number of Jets Cut Reconstruction Relative Trigger Absolute Trigger Efficiency Efficiency Efficiency Data No cut 0.889 ± 0.013% 0.782 ± 0.016% 0.825 ± 0.016 0 0.902 ± 0.023% 0.762 ± 0.030% 0.823 ± 0.030 1 0.942 ± 0.035% 0.811 ± 0.046% 0.808 ± 0.054 2 0.909 ± 0.097% 0.800 ± 0.090% 0.818 ± 0.113 Monte Carlo No cut 0.924 ± 0.001% 0.903 ± 0.001% 0.859 ± 0.001 0 0.920 ± 0.003% 0.898 ± 0.003% 0.857 ± 0.001 1 0.915 ± 0.007% 0.895 ± 0.007% 0.857 ± 0.004 2 0.913 ± 0.017% 0.875 ± 0.008% 0.883 ± 0.020 Systematicsl Uncertainty 0 0.4% 0.5% 0.2% 1 0.9% 0.8% 0.2% 2 1.1% 2.7% 2.4% Table: Dependence on the muon efficiencies from the number of jets in the event from data and Monte Carlo. Within the statistical errors data don’t show a clear dependence from the jets so the average value can be considered instead of the binned one. The systematic error introduced integrating over this variable can be estimated from the Monte Carlo samples.Sara Borroni November 3, 2010 31/36
  62. 62. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Details of Z +Jets AnalysisSara Borroni November 3, 2010 32/36
  63. 63. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Details of Z +Jets AnalysisSara Borroni November 3, 2010 33/36
  64. 64. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Muon ResolutionSara Borroni November 3, 2010 34/36
  65. 65. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Muon ResolutionSara Borroni November 3, 2010 35/36
  66. 66. Introduction and Motivations TagProbe Method for Efficiencies Z+jets measurement Summary and Conclusions Backup Example: Efficiency for 2 Muons Process Single object and event efficiencies Suppose to measure the cross-section of a 2 muon process (e.g Z → µ+ µ− ): Efficiency is correlated to the probability of the event with two muons in ζ1 and ζ2 kinematic bins to be selected Z df = dζ1 dζ2 P(event, ζ1 , ζ2 ) dζ1 dζ2 which is a combination of the single muon efficiencies P(R, ζi ) and P(T |R, ζi ) 2 3 2 3 Y Y P(event, ζ) = 4 P(R, ζi )5 · 41 − (1 − P(T |R, ζi ))5 i=1,n i=1,n I want to measure the reconstruction efficiency P(R, ζi ) and the trigger efficiency for a reconstructed muon P(T |R, ζi )Sara Borroni November 3, 2010 36/36

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