1Eckhard von Toerne, Bonn ATLAS Higgs MeasurementsTalk at BW 2013 – Beyond the Standard Models25 – 29 April, 2013, Vrnjačk...
2Eckhard von Toerne, Bonn ATLAS Higgs Measurements• “Observation of a new particle”in July 2012• Overview of properties: m...
3Eckhard von Toerne, Bonn ATLAS Higgs Measurements• xProduction of SM Higgs @ LHCCross sections at 8 TeV [pb]ggH 19.4VB Fu...
4Eckhard von Toerne, Bonn ATLAS Higgs MeasurementsDecay of SM Higgs56.9 % bb22.3 % WW6.2 %2.8 % ZZ0.23 % γγ@ mH=125.5 GeV
5Eckhard von Toerne, Bonn ATLAS Higgs Measurements• xLHC runs in 2011 + 2012Z→μμ event with25 reconstructed vertices
6Eckhard von Toerne, Bonn ATLAS Higgs MeasurementsATLAS detector
7Eckhard von Toerne, Bonn ATLAS Higgs Measurements• Two isolated high-ptphotons (ET>40, 30 GeV)• Mass peak withresolution ...
8Eckhard von Toerne, Bonn ATLAS Higgs Measurements• Two isolated high-ptphotons (ET>40, 30 GeV)• Mass peak withresolution ...
9Eckhard von Toerne, Bonn ATLAS Higgs Measurementslocal significance:- observed: 7.4σ-expected-(SM Higgs): 4.1σBest fit ma...
10Eckhard von Toerne, Bonn ATLAS Higgs MeasurementsH• 2.0 excess for VBFproduction over bgd.• 14 categories to optimizese...
11Eckhard von Toerne, Bonn ATLAS Higgs MeasurementsHZZ(*)ATLAS-CONF-2013-013mH = 124.3 ± 0.6 (stat) ± 0.4 (syst) GeVμ (12...
12Eckhard von Toerne, Bonn ATLAS Higgs MeasurementsHZZ(*)ATLAS-CONF-2013-013mH = 124.3 ± 0.6 (stat) ± 0.4 (syst) GeVμ (12...
13Eckhard von Toerne, Bonn ATLAS Higgs Measurements• xH  ZZ(*)  4 µm12=86.3 GeV, m34=31.6 GeV, m4μ = 125.1 GeV, ATLAS-CO...
14Eckhard von Toerne, Bonn ATLAS Higgs MeasurementsHiggs mass combinationCombined ATLAS resultDifference reduced by700 MeV...
15Eckhard von Toerne, Bonn ATLAS Higgs Measurements• limited mass sensitivity due to neutrino contribution• Transverse mas...
16Eckhard von Toerne, Bonn ATLAS Higgs Measurements• Observed significance (125 GeV) 3.8σ (3.7σ expected)• Signal strength...
17Eckhard von Toerne, Bonn ATLAS Higgs Measurements• xHbb• Limits derived from Mbb distribution (~16% mass resolution)• 9...
18Eckhard von Toerne, Bonn ATLAS Higgs Measurements• xHbb candidate
19Eckhard von Toerne, Bonn ATLAS Higgs Measurements• xH candidate
20Eckhard von Toerne, Bonn ATLAS Higgs Measurements• Global compatibilitybetween presentedchannels and the SMexpectation i...
21Eckhard von Toerne, Bonn ATLAS Higgs MeasurementsATLAS combined Higgs signal significanceMoriond 2013 status, ATLAS-CONF...
22Eckhard von Toerne, Bonn ATLAS Higgs MeasurementsSpin and Parity• SM predicts JP=0+• Spin studies in three different mod...
23Eckhard von Toerne, Bonn ATLAS Higgs Measurements• Spin information from cosθ* shape, not sensitive to parity• Minimize ...
24Eckhard von Toerne, Bonn ATLAS Higgs MeasurementsSpin and Parity: HZZ(*)Combine all kinematic variables in a Boosted De...
25Eckhard von Toerne, Bonn ATLAS Higgs MeasurementsSpin and Parity: HWWATLAS-CONF-2013-0310+ Hyp. 2+ Hyp.BDT to combine a...
26Eckhard von Toerne, Bonn ATLAS Higgs Measurements• the 3 channels combined exclude 2+m scenario at 99.9% CL• ZZ analysis...
27Eckhard von Toerne, Bonn ATLAS Higgs Measurements• Overwhelming evidence for a new boson at• M = 125.5 ± 0.2 (stat) ± 0....
28Eckhard von Toerne, Bonn ATLAS Higgs Measurements• xhttps://twiki.cern.ch/twiki/bin/view/AtlasPublic/HiggsPublicResults
29Eckhard von Toerne, Bonn ATLAS Higgs MeasurementsAdditional Slides
30Eckhard von Toerne, Bonn ATLAS Higgs Measurements• xHiggs Mass
31Eckhard von Toerne, Bonn ATLAS Higgs Measurements
32Eckhard von Toerne, Bonn ATLAS Higgs Measurements• ATLAS-CONF-2012-101ATLAS ET-mis Performance
33Eckhard von Toerne, Bonn ATLAS Higgs MeasurementsHiggs couplings OverviewGood agreement with SM predictionIf µVBF tested...
34Eckhard von Toerne, Bonn ATLAS Higgs MeasurementsFermion vs. vector couplings2-parameter model, group fermion and vector...
35Eckhard von Toerne, Bonn ATLAS Higgs Measurements• Custodial symmetry protects ratio of W, Z couplings (λWZ).W vs Z coup...
36Eckhard von Toerne, Bonn ATLAS Higgs MeasurementsHZZ(*) spin variables,example: decay plane phi
37Eckhard von Toerne, Bonn ATLAS Higgs MeasurementsHWW spin variables, example: deltaPhi
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E. von Törne, Overview of the ATLAS Higgs Measurements

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Balkan Workshop BW2013
Beyond the Standard Models
25 – 29 April, 2013, Vrnjačka Banja, Serbia

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E. von Törne, Overview of the ATLAS Higgs Measurements

  1. 1. 1Eckhard von Toerne, Bonn ATLAS Higgs MeasurementsTalk at BW 2013 – Beyond the Standard Models25 – 29 April, 2013, Vrnjačka Banja, SerbiaOverview of theATLAS HiggsMeasurementsEckhard von ToerneUniversity of Bonnon behalf of theATLAS Collaboration
  2. 2. 2Eckhard von Toerne, Bonn ATLAS Higgs Measurements• “Observation of a new particle”in July 2012• Overview of properties: mass,spin/parity, (couplings)• A Note:While existence of new boson at mass of~125 GeV is undisputed, its nature isunder active study.Boson exhibits Higgs-like properties.For brevity the term “Higgs-like boson” isshortened to Higgs boson or Higgs(working hypothesis).PLB 716(2012) 1-29,http://arxiv.org/abs/1207.7214IntroductionSee also: ATLAS Coll., Science 338, 1576 (2012)
  3. 3. 3Eckhard von Toerne, Bonn ATLAS Higgs Measurements• xProduction of SM Higgs @ LHCCross sections at 8 TeV [pb]ggH 19.4VB Fusion 1.6WH+ZH 1.1ttH 0.1mH = 125.5 GeV
  4. 4. 4Eckhard von Toerne, Bonn ATLAS Higgs MeasurementsDecay of SM Higgs56.9 % bb22.3 % WW6.2 %2.8 % ZZ0.23 % γγ@ mH=125.5 GeV
  5. 5. 5Eckhard von Toerne, Bonn ATLAS Higgs Measurements• xLHC runs in 2011 + 2012Z→μμ event with25 reconstructed vertices
  6. 6. 6Eckhard von Toerne, Bonn ATLAS Higgs MeasurementsATLAS detector
  7. 7. 7Eckhard von Toerne, Bonn ATLAS Higgs Measurements• Two isolated high-ptphotons (ET>40, 30 GeV)• Mass peak withresolution 1.77 GeVabove large backgr.(S/B=3%).• Reducible backgr. j, jj(~25%)• Irreducible bgd fromQED reaction qq(~75%)• Example event withm =126.6 GeVH
  8. 8. 8Eckhard von Toerne, Bonn ATLAS Higgs Measurements• Two isolated high-ptphotons (ET>40, 30 GeV)• Mass peak withresolution 1.77 GeVabove large backgr.(S/B=3%).• Reducible backgr. j, jj(~25%)• Irreducible bgd fromQED reaction qq(~75%)• Example event withm =126.6 GeVHZoom intoCalorimeter cluster• LayeredCalorimeter • Photon direction• Selection of vertex
  9. 9. 9Eckhard von Toerne, Bonn ATLAS Higgs Measurementslocal significance:- observed: 7.4σ-expected-(SM Higgs): 4.1σBest fit mass: 126.8 ± 0.2 (stat) ± 0.7 (syst) GeVSignal Strength µ = obs/ SM = 1.65 ± 0.24(stat) ± 0.22(syst)HProb. of a backgroundfluctuation to be more signal-like than observed signal.
  10. 10. 10Eckhard von Toerne, Bonn ATLAS Higgs MeasurementsH• 2.0 excess for VBFproduction over bgd.• 14 categories to optimizesensitivity (different S/B ratios)• and to categorize ggF, VBF, VH
  11. 11. 11Eckhard von Toerne, Bonn ATLAS Higgs MeasurementsHZZ(*)ATLAS-CONF-2013-013mH = 124.3 ± 0.6 (stat) ± 0.4 (syst) GeVμ (124.3 GeV) = 1.7 ± 0.4Need to reconstruct low pt leptons
  12. 12. 12Eckhard von Toerne, Bonn ATLAS Higgs MeasurementsHZZ(*)ATLAS-CONF-2013-013mH = 124.3 ± 0.6 (stat) ± 0.4 (syst) GeVμ (124.3 GeV) = 1.7 ± 0.4
  13. 13. 13Eckhard von Toerne, Bonn ATLAS Higgs Measurements• xH  ZZ(*)  4 µm12=86.3 GeV, m34=31.6 GeV, m4μ = 125.1 GeV, ATLAS-CONF-2012-169
  14. 14. 14Eckhard von Toerne, Bonn ATLAS Higgs MeasurementsHiggs mass combinationCombined ATLAS resultDifference reduced by700 MeV compared toDecember resultConsidering allsystematics and theircorrelations, compatibilityof both results is at 1.5%(2.4σ level)With alternativetreatment of systematics,compatibility rises to 8%Main systematics:energy scalemH = 125.5 ± 0.2 (stat) ± 0.6 (syst) GeV
  15. 15. 15Eckhard von Toerne, Bonn ATLAS Higgs Measurements• limited mass sensitivity due to neutrino contribution• Transverse mass• S/B ~ 15%HWW
  16. 16. 16Eckhard von Toerne, Bonn ATLAS Higgs Measurements• Observed significance (125 GeV) 3.8σ (3.7σ expected)• Signal strength at 125 GeV μ = 1.01 ± 0.21(stat) ± 0.23(syst)[ 0.21(stat) ± 0.19(theo) ± 0.12(exp) ± 0.04(lumi) ]HWW
  17. 17. 17Eckhard von Toerne, Bonn ATLAS Higgs Measurements• xHbb• Limits derived from Mbb distribution (~16% mass resolution)• 95%CL limit at 125 GeV: 1.8 x SM (expected limit 1.9)• μ(125) = -0.4 ± 0.7(stat) ± 0.8(syst),• Analysis still in flux and not all of 2012 data used• Main benchmark analysis yields 4.0σ observation of bosonpairs WZ(bb)/ZZ(bb)Combination of search channel WH, Wl / ZH, Zll / ZH, Z
  18. 18. 18Eckhard von Toerne, Bonn ATLAS Higgs Measurements• xHbb candidate
  19. 19. 19Eckhard von Toerne, Bonn ATLAS Higgs Measurements• xH candidate
  20. 20. 20Eckhard von Toerne, Bonn ATLAS Higgs Measurements• Global compatibilitybetween presentedchannels and the SMexpectation is 8%• Dependence of signalstrength on mass isweakATLAS combined signal strengthATLAS-CONF-2013-034
  21. 21. 21Eckhard von Toerne, Bonn ATLAS Higgs MeasurementsATLAS combined Higgs signal significanceMoriond 2013 status, ATLAS-CONF-2013-034• Combination of allchannels• Local p0 = 10-23•  ~10 excessaround 125 GeV
  22. 22. 22Eckhard von Toerne, Bonn ATLAS Higgs MeasurementsSpin and Parity• SM predicts JP=0+• Spin studies in three different modes• H : sensitivity decay angle in Higgs rest frame *• HWW decy angles no directly reconstructable due toneutrinos, however other kinematic vars. quite sensitivedue to V-A nature of W decays.• HZZ fully reconstructed, decay plane is sensitive• Spin 1 disfavored by Landau-Yangtheorem and H decay• Spin 2 case may be quite evolved• Here: tensor with minimalcouplings to SM particles (2+m model)• Dependency on 2+m production mode. free parameter fqq, fqq+fgg=1
  23. 23. 23Eckhard von Toerne, Bonn ATLAS Higgs Measurements• Spin information from cosθ* shape, not sensitive to parity• Minimize correlation between cosθ* and mass for bgd byapplying absolute pt cuts• control the background cosθ* shape via mass sidebands• Largest sensitivity if 2+m is created by 100% gg fusionSpin and Parity: H
  24. 24. 24Eckhard von Toerne, Bonn ATLAS Higgs MeasurementsSpin and Parity: HZZ(*)Combine all kinematic variables in a Boosted DecisionTree to optimize sensitivitysensitive to parity
  25. 25. 25Eckhard von Toerne, Bonn ATLAS Higgs MeasurementsSpin and Parity: HWWATLAS-CONF-2013-0310+ Hyp. 2+ Hyp.BDT to combine all sensitive variables, most sensitive: fqq=100%
  26. 26. 26Eckhard von Toerne, Bonn ATLAS Higgs Measurements• the 3 channels combined exclude 2+m scenario at 99.9% CL• ZZ analysis excludes the 0-, 1+ and (1-) hypotheses at the>95% (94%) CLSpin and Parity: combinedATLAS-CONF-2013-040
  27. 27. 27Eckhard von Toerne, Bonn ATLAS Higgs Measurements• Overwhelming evidence for a new boson at• M = 125.5 ± 0.2 (stat) ± 0.6 (syst) GeV• Measurements of signal strength and spin/parity inagreement with SM hypothesis.• Not covered in this talk: Meas. of couplings also in goodagreement.• Improved measurements of pre-shutdown data and aftershutdown will further investigate this particle.• Search for rare decays• Search for additional states• Moving towards precision Higgs Physics• …if something walks like a duck and quacks like a duck,it is probably a duck. This particle is looking more andmore like a Higgs boson.Conclusion and Outlook
  28. 28. 28Eckhard von Toerne, Bonn ATLAS Higgs Measurements• xhttps://twiki.cern.ch/twiki/bin/view/AtlasPublic/HiggsPublicResults
  29. 29. 29Eckhard von Toerne, Bonn ATLAS Higgs MeasurementsAdditional Slides
  30. 30. 30Eckhard von Toerne, Bonn ATLAS Higgs Measurements• xHiggs Mass
  31. 31. 31Eckhard von Toerne, Bonn ATLAS Higgs Measurements
  32. 32. 32Eckhard von Toerne, Bonn ATLAS Higgs Measurements• ATLAS-CONF-2012-101ATLAS ET-mis Performance
  33. 33. 33Eckhard von Toerne, Bonn ATLAS Higgs MeasurementsHiggs couplings OverviewGood agreement with SM predictionIf µVBF tested alone  3.1 evidence for VBF production
  34. 34. 34Eckhard von Toerne, Bonn ATLAS Higgs MeasurementsFermion vs. vector couplings2-parameter model, group fermion and vector couplings togetherκV = κZ = κW ; κF = κt = κb = κ = κg = κWe assume only SM-loop contributions to kg and kOne overall un-observable sign, chose kV>0Sign sensitivity mostly from interference in Hgg (t vs W in loop)Only slight preference for kF>0  no conclusions yet2D compatibility with SM 8%
  35. 35. 35Eckhard von Toerne, Bonn ATLAS Higgs Measurements• Custodial symmetry protects ratio of W, Z couplings (λWZ).W vs Z couplingsλWZ = 0.80 ± 0.15 in agreement with SM prediction
  36. 36. 36Eckhard von Toerne, Bonn ATLAS Higgs MeasurementsHZZ(*) spin variables,example: decay plane phi
  37. 37. 37Eckhard von Toerne, Bonn ATLAS Higgs MeasurementsHWW spin variables, example: deltaPhi

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