1. What we learned from DC1 B-physics validations M.Smizanska, Lancaster University for B-physics validation team. pp  B(J/  (  ) K 0 ) X

2. 15.12.2003 M.Smizanska, et al, DC1 B-validation, UK-physics meeting 2 DC1 B-physics validation teams: University of Lancaster, Lancaster, UKE.Bouhova-Thacker, R.Jones, V.Kartvelishvili, M.Smizanska Institute for Experimental Physics, University of Innsbruck, Austria B.Epp, V.M.Ghete Moscow State University, RussiaN.Nikitine, S.Sivoklokov, K.Toms Physics Department, ThessalonikiT.Lagouri Charles University, PragueP.Reznicek CEA, Saclay J.F.Laporte CERNN. Benekos, A.Nairz INFN, Frascati, ItalyH.Bilokon INFN, Roma-1, Italy M.Testa

3. 15.12.2003 M.Smizanska, et al, DC1 B-validation, UK-physics meeting 3 List of Physics processes ProcessDetector layouts pp  Bs X Bs  D s  D s   K+K- TDR, Complete layout, 400  m Initial layout, 400  m Complete layout, 300  m (DC1) pp  Bs X Bs   pp  Bs X Bs  J/  K+K- ) pp  Bd X Bd  J/  K  (  +  -)  pp   b X  b  J/  0 (p  ) pp  bb X, b  6X’ Bs  D s  D s   K+K-  b  J/  0 (p  ) + min bias for L =2 x 10 33 cm -2 s -1 Initial layout, 400  m Complete layout, 400  m

4. 15.12.2003 M.Smizanska, et al, DC1 B-validation, UK-physics meeting 4 Software tools, status at the start of DC0: 1.Detector simulation a)‘TDR’ detector layout was obsolent for several years, but the changes were not implemented in ATLAS software. atlsim 98_2 was identical to 97_6 for the ID description, which corresponded to a description in ID TDR. b)… so an impact of important changes in the ID: increasing the radius of b-layer, eliminating second pixel layer and some other parts in the endcap - had to be estimated by ATLFAST – using simple approximations of the resolutions derived from TDR ones. c)Physics performance for conferences was for a long time presented for TDR layout. d)DC1 validation was important step forward: first publicly presentable B-physics results with new ID layout.

5. 15.12.2003 M.Smizanska, et al, DC1 B-validation, UK-physics meeting 5 Software tools, status at the start of DC0, cont 2.ATHENA, Generators a)TDR B-physics generator Atgenb – a branch of Atgen an ATLAS interface package that stop to be supported in 97. b) In DC0 – Atgenb – rewritten to PythiaB – ATHENA algorithm, was in use for DC1 production. 3.Reconstruction: a) atsim, atrecon – longest survivors over TDR-DC0-DC1 … finally were useful for ATHENA validations – most of our DC1 done in parallel using atrecon (or atlsim!) and ATHENA b) ATHENA-reconstruction much progress during DC1 … c)… but we did not reach the same performance for the 3 packages in DC1. The sources of differences are more-less understood, but all these packages stop at DC1. All manpower - to DC2.

6. 15.12.2003 M.Smizanska, et al, DC1 B-validation, UK-physics meeting 6 Detector Layouts in DC1 validations Detector layoutsCompleteInitialComplete- 300  m TDR Radius of b-layer5 cm 4.3 cm Longitudinal pixel size of b-layer 400  300  Middle pixel layeryesmissingyes Pixel disk #2 and forward TRT wheels yesmissingyes

7. 15.12.2003 M.Smizanska, et al, DC1 B-validation, UK-physics meeting 7 Software in DC1 validations Layout Software CompleteInitialComplete- 300  m TDR Event GenerationPythiaB(Athena) and old data from TDR – for consistency checks atgenb Detector simulationatsim 6.0.2atlsim 6.0.2atsim 3.2.1atlsim98_3 TDR Reconstruction mostly xKalman in Inner Detector *) atrecon6.5.0 (6.0.3, 4.5.0) atlsim4.5.0 (only 1chan) Athena 6.5.0, 7.0.0 atrecon6.5.0 (6.0.3, 4.5.0) Athena 6.5.0, 7.0.0 atrecon4.5.0atreconTDR 1. optimal strategy for Initial layout (4) 2. default strategy(7) Physics Analyses Vertexing CBNT analyses (from atrecon or from athena) CTVMFT vertexing from TDR *) part of Complete and Initial also with iPatrec, 6.0.3

8. 15.12.2003 M.Smizanska, et al, DC1 B-validation, UK-physics meeting 8 Performance results

9. 15.12.2003 M.Smizanska, et al, DC1 B-validation, UK-physics meeting 9 Mass reconstruction Mass resolution single Gauss fit  [MeV/c 2 ] CompleteInitial Complete- 300  m (dc1) TDR Bs  Ds(  46 4542 B  79 80 69 Bs  J/  17 1615 Bd  J/  K  21 -19  b  J/  p  2526-22 J/  4243 39 Core of mass distributions similar with Complete and Initial layouts and Complete-300  m. Degradation vrt TDR: 10-15%

10. 15.12.2003 M.Smizanska, et al, DC1 B-validation, UK-physics meeting 10 Complete vs Initial layout: reconstruction of B-signal mass xKalman6.5.0 optimized track finding strategy Complete Layout Initial Layout Initial Layout: 1. Efficiency to reconstruct B only 4.5% smaller then in Complete. 2. Only 0.3 % fails the vertex fit in both Complete and Initial layouts. Example for channel B s  J/  (  )      … and B-vertex reconstructed  = 82.3% (5% B in tails)  = 77.7% (6% B in tails) All four tracks of B reconstructed  = 82.5% (5% B in tails)  =77.9% (6% B in tails)

11. 15.12.2003 M.Smizanska, et al, DC1 B-validation, UK-physics meeting 11 …the same events with default xKalman track search strategy – failed for Initial layout, ok for Complete layout. Complete Layout Initial Layout All four tracks of B reconstructed  = 83% (4% B in tails)  =77% (11% B in tails) … and B-vertex reconstructed  = 82% (4% B in tails)  = 67% (8% B in tails) Initial Layout: 1. More B’s in tails. 2. Efficiency to reconstruct B tracks only 6% smaller, 3. however next 10% fails the vertex fit Example for channel B s  J/  (  )     

12. 15.12.2003 M.Smizanska, et al, DC1 B-validation, UK-physics meeting 12 B-hadrons - proper time resolution Single-Gauss fitCompleteInitialComplete -300  m (dc1) TDR Bs  Ds  100 fs98 fs86 fs67 fs B  99 fs98 fs92 fs69 fs Bs  J/  85 fs82 fs85 fs63 fs Bd  J/  K  89 fs86 fs- 69 fs  b  J/  p  101 fs95 fs-73 fs Core of proper-time distribution similar in Complete and Initial layouts. Degradation vrt TDR: 20-35%. Degradation Complete 400  m vrt 300  m : 14%

13. 15.12.2003 M.Smizanska, et al, DC1 B-validation, UK-physics meeting 13 B-hadrons proper-time resolution, optimized xKalman Both Complete and Initial layout similar: Bs proper-time reconstruction: 8% in tails only 0.3% fails vertex fit in both layouts Example for channel B s  J/  (  )      Complete Layout Initial Layout

14. 15.12.2003 M.Smizanska, et al, DC1 B-validation, UK-physics meeting 14 B-hadrons proper-time resolution, default xKalman Bs proper-time resolution: 1. Complete layout 7% in tails 2. Initial layout 16% in tails … and lower efficiency of track reconstruction and less sucessful vertex fits -> all these factors lead to decrease of efficiency. After final selection cuts in this channel Initial : Complete 3:5 Complete Layout Initial Layout Example for channel B s  J/  (  )      All four tracks of B reconstructed and B-vertex reconstructed  = 82% (7% B in tails)  = 67% (16% B in tails)

15. 15.12.2003 M.Smizanska, et al, DC1 B-validation, UK-physics meeting 15 Efficiency of reconstruction of B-signal including vertex fit Initial vs Complete, optimal xKalman Initial/Complete Bs  D s  D s   K+0.5K- 0.5) 0.94 Bs  J/  (K+0.5K-0.5) 0.93 Bd  J /  K  0.5  0.5  0.937  b  J/  p0.5  0.5  0.94

16. 15.12.2003 M.Smizanska, et al, DC1 B-validation, UK-physics meeting 16 Complete layout vrt Initial layout similar performance. … so are we going to miss second pixel layer? 1.The simulation was optimistic 2. inefficiencies underestimated 3. no misalignement 4.degradation appears at higher multiplicities - already at L =2 x 10 33 cm -2 s -1

17. 15.12.2003 M.Smizanska, et al, DC1 B-validation, UK-physics meeting 17 Single-track performance: Detector layoutComplete layout 400  m Initial layout 400  m Process pp  Bs X Bs  J/  pp  BsX Bs  J/  pp  bb X, b  6X’ + min bias for L =2 x 10 33 cm -2 s -1 p T ( 0.5-1.0 ) GeV0.0210.0290.075 p T ( 1. - 3. ) GeV0.0200.0220.039 p T ( 3. - 6. ) GeV0.0160.0240.038 p T > 6. GeV0.0130.0180.039 Complete layout vrt Initial similar - if only a signal event simulated. Degradation at higher multiplicities (already at L =2 x 10 33 cm -2 s -1 ). wrong hit on track in b-layer; dependence on: layout, multiplicity and pT.

18. 15.12.2003 M.Smizanska, et al, DC1 B-validation, UK-physics meeting 18 Athena7.0.0 versus atrecon… different performance Can ATHENA7.0.x be corrected ?? B-proper-time resolution[fs] Bs->Ds  Bs->J/  b->J/  atrecon6.5.089.682.292.9 ATHENA7.0.097.392.1107.7 atrecon6.5.0 'private' with pixel cluster errors as 95.387.3103.9 ATHENA worse by ~10% than atrecon6.5.0 atrecon 'private' ~8% worse than atrecon6.5.0. Degradation due to pixel clusters errors. Other -smaller factor: ATHENA more inefficiencies

19. 15.12.2003 M.Smizanska, et al, DC1 B-validation, UK-physics meeting 19 Athena7.0.0 versus atrecon… different performance 1.We finish DC1 with ATHENA reconstruction in which we are aware of errors 2. Degraded performance in proper-time vrt atrecon. 3. Can ATHENA 7.0.x be improved?? NO a)cannot invest time for old code – need people for 7.3.0… b)DC1 Simulation not realistic anyway, for instance misalignment…

20. 15.12.2003 M.Smizanska, et al, DC1 B-validation, UK-physics meeting 20 Conclusions 1.Initial vrt Complete layout - similar performance – if no pileup, with optimized track search strategy in atrecon6.5.0. a)Track-finding efficiency -7% for pt (0.5-1.0) GeV, only -2%. for pT>1GeV b)Tracks with wrong hit in B-layer: Initial 3%, in Complete 2% for pT<1GeV c)Efficiency of B-signal reconstruction Initial vrt Complete: lower by ~6% - due to track search inefficiency. Only 0.3% fails vertex fit in both Initial and Complete layouts. 2.Comparisons with other layouts a)Mass resolution: degraded 10-15% vrt TDR, b)Time resolution: degraded 20-30% vrt TDR, and 14% 400  m vrt 300  m. 3.Still to be done in DC1: Signal events with minimum bias.

21. 15.12.2003 M.Smizanska, et al, DC1 B-validation, UK-physics meeting 21 Conclusions,cont 4.We are aware of insufficiencies of DC1 and we understand their impact on performance. 5.This will alllow us to use reasonably the DC1 software validation results as a starting point to validate DC2 software.