The document summarizes the status of the B-physics trigger working group. It discusses various B-physics trigger selections being studied at Level 2 and the event filter, including tighter cuts being applied to improve rate reduction. Future work is outlined, such as robustness studies, algorithm development, and investigations using new detector layout simulations and data sets.

1. B-Physics Trigger Working Group Status Report http://hepunx.rl.ac.uk/atlasuk/simulation/level2/meetings/AweekFeb01/ Bphys210201.ppt Bphys210201.pdf Bphys210201.ps John Baines Contents: B-trigger selections at LVL2 and EF EF rates, status at end 2000 Progress: Tighter cuts for D s selection J/  rate v. p T threshold Example of rates with tighter cuts Robustness studies Future Work Summary

2. Example B-Physics Trigger Menu Level 2 : Confirm muon ID full-scan require additionally: Second  p T > 3-5 GeV or electron p T > 5 GeV or Reconstruct characteristic decay products e.g.: e  e  pair, J/   ee  invariant mass window 3 hadrons,  0 (KK) and D s (KK  ) mass 2 hadrons, B d (  ) mass window Level 1 : muon p T > 6 GeV EF: Re-do ID recon. using offline-type algorithms: Apply tighter cuts to J/   ee  D s (KK  ), B d (  ) Apply cuts to select J/     LVL2  and  -e triggers)  Use offline-type cuts for rare decay channels (accepted by LVL2  trigger).  bb eX B d (J/  (  )K 0 )  bb  X B d (J/  (ee)K o )  bb  X B d (J/  (ee)K o ) B d     B d J/  (  )(K/K*) B s J/  (  )  B  B K 0 *  , etc.  b  0 J/  (  ) B c J/  (  )  Better track resolution Tighter Mass cuts Vertex fit cuts on  2 , decay length, angular cuts based on event topology B  B K 0 *  , etc. B s D s  B s D s a 1 D s  o  ,  o K  K  To be studied further.

3. B-physics Trigger Rates Status at TDAQ Week Nov 2000 Note: Events with direct J/  (  ) and J/  (ee) are also needed, however these can be pre-scaled. Rates subject to uncertainties in cross-sections & muon rates. Physics programme and trigger menu will evolve with time up to and after LHC switch-on. EF rate estimates are based on offline code. In particular K/  rejection at EF (and LVL2) has to be demonstrated with algorithms suitable for EF (LVL2). Work is continuing on EF selections for B d,s - >  X  channels. Level-2  6 +  5  6 + e5  6 + B(  )  6 + D s (  (KK)    6 + J/  (ee) Total (B-physics triggers) 100 Hz 50 Hz 50 Hz 150 Hz 200 Hz 550 Hz muon p T >6 Level-1 23 kHz muon p T >6 (ID+muon) Level-2 5 kHz EF B d,s - >  (X) (  p T >6) J/  - >   6 + B(  )  6 + D s (  (KK)    6 + J/  (ee) Total (B-physics triggers) small 10 Hz 5 Hz 25 Hz 20 Hz 60 Hz muon p T >6 (ID+muon) EF 5 kHz

4. B d     Trigger Efficiency for B  events with pile-up (L = 10 33 cm -2 s -1 ): 78% : B  events, p T (  ,  ) > 4 GeV 93% : B  events selected offline 0.93% : Background B  X events Level-2 rate ~50 Hz for 5 kHz  6 EF selection reduces rate to ~5 Hz Event Filter Selection: Tighter mass cut Vertex fit cuts :  2 / N d.o.f. < 8, L xy > 100  m,  xy < 5 Level-2 selection: Tracks separated from trigger  by  R  > 0.2 p T > 3.9 GeV o Two opposite sign tracks with: p T + p T > 10 GeV  z 0 < 2 cm 4.3 < M(  ) < 6.3 GeV + -  xy L xy Decay Vertex 10 15 20 25 30 35 40 45 50 p T of B d (GeV) B d p T spectrum both  p T >4 GeV 100 80 60 40 20 0 Level-2 Efficiency (%) x y LVL2 0 2 4 6 8 M(      (GeV) Signal Events + min. bias

5. D s  Trigger o Level-2 Selection: Tracks: p T > 1.4 GeV  R  > 0.2 w.r.t. trigger  EF Event Selection: Tracks: p T > 1.5 GeV Mass cuts : M(KK) - M(  ) < 14 MeV M(KK  ) - M(D s ) < 56 MeV  vertex fit cuts:  2 prob. >0.5%, L xy > 200  m D s vertex fit :  2 prob. >0.5%, L xy > 200  m Two opp. sign tracks satisfying: M(KK) - M(  ) < 17 MeV (~3  trigger ) Third track with: M(KK  ) - M(D s ) < 74 MeV (~3  trigger ) New selection cuts by Innsbruck Level-2 Efficiencies for B s D s (  (KK))  events with pile-up (L = 10 33 cm -2 s -1 ): 58% : Signal events with p T (  ,  and K) > 1.5 GeV 63% : Signal events selected offline 3% : Background B  X events Level-2 Trigger rate ~150 Hz for 5 kHz  6 EF selection reduces rate to 21 Hz 4  offline mass cuts 17 Hz 3.5  offline mass cuts 13 Hz 3  offline mass cuts for 5 kHz  6  offline (  ) = 3.4 MeV  offline ( D s ) = 14 MeV

6. Effect of higher muon p T threshold: D s (KK)  trigger Study by Innsbruck of impact of raising muon p T threshold on D s (KK)  trigger Signal efficiency falls of fairly rapidly, more rapidly than background.

7. J/  e  e  Trigger Event Filter Selection: Tighter mass cuts Vertex fit cuts :  2 / N d.o.f. < 8, L xy > 220  m,  xy < 40 Two opposite-sign e tracks with: p T + p T > 4 GeV |  | < 1.4, |  z 0 | < 2 cm cos(  ee ) > 0.2 2 < M(ee) < 3.5 GeV + - Level-2 Selection: Tracks: p T > 0.5 GeV Identified as electrons by TRT Level-2 Efficiencies for B d J/  (ee)K s events with pile-up (L = 10 33 cm -2 s -1 ): 44% : Signal events with p T (e,e) > 1.5 GeV 57% : Events selected offline 4% : Background B  X events Level-2 Trigger rate ~200 Hz for 5 kHz  6 EF selection reduces rate to ~20 Hz o Signal Events + Min. Bias 0 1 2 3 4 5 M(ee) (GeV) LVL2

8. Effect of electron p T Threshold 25 20 15 10 5 0 Rate (Hz) Signal Efficiency (%) Efficiency for B d - > J/  (ee) K 0 (  ) Rate for B - >  X + pile-up for 5 kHz  6 rate p T cut (GeV) p T cut (GeV) 0.5 1.0 1.5 2.0 2.5 3.0 Study by Moscow of effect of raising p T threshold for e in J/  (ee) trigger Further rate reduction, with some loss of physics, e.g. : Raising p T cut from 0.5 GeV to 0.8 GeV gives Rate reduced from 17 Hz to 8 Hz 4% efficiency loss for B d - > J/  (ee) K 0 100 80 60 40 20 0 0.5 1.0 1.5 2.0 2.5 3.0

9. B-physics Trigger Rates - Example of tighter cuts muon p T >6 (ID+muon) EF 5 kHz Note: Tightening D s and  mass cut gives negligible signal loss provided the same mass resolution can be achieved at the EF as offline => need to assess impact of calibration, availability of survey info and impact of any speed-up of algorithms c.f. offline. Similarly for other “offline-type” selections. small 10 Hz 5 Hz 13 Hz 10 Hz 38 Hz 5 kHz Notes: Assuming offline-type selection Estimate (conservative?) (Signal ~2 Hz, Bg about same) Rounded up from 3 Hz from Flora Mass cuts tightened to 3  offline add  transverse decay length cut.. p T threshold raised to 0.8 GeV => 4% signal loss. EF B d,s - >  (X) (  p T >6) J/  - >   6 + B(  )  6 + D s (  (KK)    6 + J/  (ee) Total (B-physics triggers) small 10 Hz 5 Hz 25 Hz 20 Hz 60 Hz

10. LVL2 Robustness Studies Misalignment (  m) Misalignment (  m) 1 10 100 1000 1 10 100 1000 90 80 70 60 50 40 Efficiency (%)  D s (MeV) 60 40 20 Effect of Pixel Barrel Misalignment on B(  ) trigger Effect of SCT barrel Misalignment on D s (  (KK)  ) trigger Fraction of Hits/Spacepoints deleted 60 50 40 30 Efficiency (%) 0.001 0.01 0.1 Effect of inefficiency on D s (  (KK)  ) trigger Pixel Barrel 15 30 Endcap 50 100 Limits on R  precision (  m) for signal loss <2% <5% SCT Barrel 60 100 Endcap 80 100

11. Future Work - Robustness Robustness Studies: Extend LVL2 robustness studies to J/  channel including TRT Compare robustness of TRT-guided c.f. pixel-guided reconstruction for J/  Look at EF selection, expected to be more sensitive than LVL2 due to: vertex fit quality cuts transverse decay length cuts tighter mass cuts . Easter 2001 Moscow End 2001?? Who?? Easter 2001 Moscow

12. Future Work - LVL2 LVL2 Studies: Repeat B-trigger measurements including muon simulation (previously used Kine). Effect of New layouts: - evaluate effect of latest ID layout (Insertable pixel layout). LVL2 Algorithm Development : Scan of pixels+SCT (more robust than pixel-scan) two techniques: - based on pixel-scan : Genova - based on hit filtering algorithm + kalman fitter : Nikos Vertex reconstruction at LVL2 - Nikos? Reproduce cTrig functionality in new framework Add new functionality in new framework:  and e reconstruction in ID RoI Need new data-sets => Spring 2002?? Time-scales set by PESA s/w group - September 2001 Autumn 2001?? All Need muon code and new data-sets. Probably use new framework => Mid 2002 Autumn 2002? End 2001?

13. Future Work - EF Selection EF Selections : Investigate EF selections for B - >  X channels Check compatibility of cuts with offline selections, particularly background estimations, systematic bias etc. Check effects of layout changes Timing measurements for B-selections, development of algorithms suitable for EF (ID, Muon, Calorimeter reconstruction). Pythia studies : Easter 2001 September 2001?? Need new data-sets => Spring 2002?? Need all algorithms in new framework Mid 2002?? Moscow, Innsbruck? Full simulation - needs data-sets => End 2001?? Moscow (Nikolai) B Physics WG Who??

14. Datasets Datasets with ID ‘insertable’ layout, modular TRT, true solenoid B-field: Single particle datasets for tests Whole detector (incl. muons): Signal datasets :  6 + B  ,  6 + B D s  B D s a 1 ,  6 + B J/  (ee), B J/  (  6,  ), B  (X) Background : B  X Datasets for studies with  and e in LVL2 RoI from ID:  6 + B J/  (e5e) e5 + B J/  (  6,  ) B J/  (  6,  ) Easter 2001? Autumn 2001?? End 2001??

15. B-trigger Workplan 2002 2001 Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Pythia studies EF: B  (X) full sim. studies EF Timing Timing for B selection J/  , TRT Robustness EF Robustness studies Algorithm develop. Pixel scan incl. SCT LVL2 vertexing Studies in New f-w cTrig Functionality New s/w Reconstruct e in RoI from ID Reconstruct  in RoI from ID repr. TP results verify TP - new layout add LVL1 + LVL2 mu TP results + mu Full B-menu ID sngl prt Dataset Prd. New layout Sig. & bg all det.

16. Summary D s (  (KK)  ) trigger: tighter EF cuts studied => ~halving of rate. Effect of raising muon p T thresholds studied, but signal efficiency falls rapidly J/  (ee) trigger: raising e p T threshold studied, can ~halve rate for 4% signal loss. Robustness studies: LVL2 Trigger robust w.r.t. SCT misalignment. Pixel R  misalignment limit: 15  m (barrel). Trigger robust w.r.t. SCT inefficiency. Main concern is impact of dead pixels on pixel-scan efficiency, but a new more robust algorithm is being developed. Studies will be extended to the J/y(ee) trigger and TRT Studies will be extended to EF if someone can be found for this work. Algorithm development is continuing. Vertex finding at LVL2 will be investigated. Studies started for EF selection for B  (X), initially at the particle level. Future work will be focussed on: new data-sets with the whole detector and updated ID layout. additional functionality in the new s/w framework leading to a simulation of the complete B-physics trigger menu ~end 2002.