1. Workhop on Recent Developments in High Energy Physics and Cosmology, Athens, 17-20 April 2003 Th. Lagouri, A.U.Th. B-physics with the Atlas detector Theodota Lagouri (for the Atlas Collaboration) Aristotle University of Thessaloniki

2. Workhop on Recent Developments in High Energy Physics and Cosmology, Athens, 17-20 April 2003 Th. Lagouri, A.U.Th. Outline The initial experiment conditions The ATLAS Physics Programme The ATLAS detector & trigger B-physics potential with the nominal detector @ L=10 33 cm -2 s -1 ; Preliminary estimate of the B-physics potential with the initial detector and luminosity; Conclusions

3. Workhop on Recent Developments in High Energy Physics and Cosmology, Athens, 17-20 April 2003 Th. Lagouri, A.U.Th. The initial experiment conditions Results presented here refer to the nominal detector configuration and L= 1x10 33 cm -2 s -1 [CERN 2000-004] ; The analysis with the initial detector layout (including the change of the B-layer radial position, re-evaluation of the material distribution in the ID) as a function of luminosity and the trigger conditions is on-going (within the Data Challenge project); preliminary results about the physics performance at Initial conditions will be presented.

4. Workhop on Recent Developments in High Energy Physics and Cosmology, Athens, 17-20 April 2003 Th. Lagouri, A.U.Th. The ATLAS Physics Programme 1.The most prominent issues for the LHC are the quest for the origin of the spontaneous symmetry-breaking mechanism (SM and MSSM) and the search for new physics: SuSy, Heavy Bosons, etc… 2.ATLAS (and CMS) is a general-purpose experiment optimized to maximize the potential discovery new physics: Higgs boson(s), SuSy particles, W’ and Z’, etc… 3.However we have to consider that: –The LHC is a beauty factory  dedicated B- experiment (LHCb); –The ATLAS detector allows also a wide programme of B-physics studies, competitive with LHCb in some channels;

5. Workhop on Recent Developments in High Energy Physics and Cosmology, Athens, 17-20 April 2003 Th. Lagouri, A.U.Th. The ATLAS experiment Tile Calorimeter Module(s) Barrel toroid coil LAr Calorimeter Cryostat LAr e.m. barrel module Solenoid magnet MDT chamber assembly

6. Workhop on Recent Developments in High Energy Physics and Cosmology, Athens, 17-20 April 2003 Th. Lagouri, A.U.Th. Detectors Front-end Pipelines Readout Buffers Event Builder Buffers & Processing Farms Data Storage Readout Drivers 1 GHz interaction rate / <75 (100) kHz O (1) kHz output rate O (100) Hz output rate ~100 GB/s output data flow O (100) MB/s output data flow O (1) GB/s output data flow 2  s latency O (10) ms latency ~ seconds latency 40 MHz bunch-crossing rate LVL2 RoI –Region-of- Interest (RoI) –Specialized algorithms –Fast selection with early rejection EF –Full event available –Offline derived algorithms –Seeding by LVL2 –Best calibration / alignment –Latency less demanding LVL1 –Hardware based (FPGA and ASIC) –Coarse calorimeter granularity –Trigger muon detectors: RPCs and TGCs The ATLAS Trigger/DAQ System RoI Pointers HLT

7. Workhop on Recent Developments in High Energy Physics and Cosmology, Athens, 17-20 April 2003 Th. Lagouri, A.U.Th. The Atlas B-Physics Programme The main physics processes that can be studied: –CP violation: Asymmetry in B 0 d  J/  K 0 s  measurement of sin2  ; Asymmetry in B 0 s  J/   test of the SM; Asymmetry in B 0 d,s  h  h   measurement of  ; –B 0 s - B 0 s oscillations; –Rare B-decays with dimuons; Also: –B-production cross-section measurement; –  b polarisation measurement; –Related to B-physics: direct J/ ,  production

8. Workhop on Recent Developments in High Energy Physics and Cosmology, Athens, 17-20 April 2003 Th. Lagouri, A.U.Th. The B-trigger L=1 x 10 33 cm -2 s -1 ; Level-1: single muon trigger p T > 6 GeV/c, |  |<2.5; –Rate is expected to be about 23 kHz; –dominated by in-flight decays of ,K and heavy flavour muon production; –Dimuon trigger possibly with lower thresholds; –Raise thresholds for higher luminosities; Level-2, step 1: confirm level-1 muon trigger in RoI; –Use precision muon system together with ID for momentum measurement  important rejection of in- flight decays; –Rate: about 5 kHz;

9. Workhop on Recent Developments in High Energy Physics and Cosmology, Athens, 17-20 April 2003 Th. Lagouri, A.U.Th. The B-trigger Level-2, step 2: –Specific selections are applied for different channels; in all cases we perform a track reconstruction in the Inner Detector with: 1.Either an ID full-scan; 2.Or RoI-based ID track reconstruction. J/       : two opposite muons p T (1) >6 GeV and p T (2) >3 GeV (  in TileCal); mass cuts; J/   e  e  : two opposite-charge electrons with both p T (1) >1GeV; mass cuts; rate @ lvl2: 40 Hz (lvl1 mu8, L=1 x 10 33 cm -2 s -1 ); B  hadrons: example: B  h  h  : two opposite tracks with p T >4 GeV; mass cuts;

10. Workhop on Recent Developments in High Energy Physics and Cosmology, Athens, 17-20 April 2003 Th. Lagouri, A.U.Th. The B-trigger Event Filter: track refit, including a vertex fit; decay length and fit quality cuts are applied; about a factor of 10 wrt LVL2 can be achieved by exclusive selections.

11. Workhop on Recent Developments in High Energy Physics and Cosmology, Athens, 17-20 April 2003 Th. Lagouri, A.U.Th. B 0 d  J/  K 0 s J/   l  l  reconstruction; mass resolution: 40 MeV (muons) and 60 MeV (electrons); K 0 s      : 4.5 – 7.0 MeV mass resolution; B 0 d : 3D kinematic fit applying vertex and mass constraint; B 0 d mass resolution: 19 (26) MeV; Background mainly from B decays with a J/  in the final state; small contribution from false J/  ; B 0 d reconstruction; CDF has shown a similar signal;  b /  tot and prod. rate improved at LHC

12. Workhop on Recent Developments in High Energy Physics and Cosmology, Athens, 17-20 April 2003 Th. Lagouri, A.U.Th. B 0 d  J/  K 0 s Flavour tagging: –Opposite-side tagging: muon (trigger) or electron (pt>5 GeV) –Same-side tagging: B-  algorithm (charged meson associated with the B-hadron) Event yield for 30 fb  @ L=1x10 33 cm  s  J/  (ee)K 0 s signal back. J/  (     )K 0 s signal back. e tags - 5800 500  tags 14400 90011900 1100 B-  tags - 376100 13700

13. Workhop on Recent Developments in High Energy Physics and Cosmology, Athens, 17-20 April 2003 Th. Lagouri, A.U.Th. B 0 d  J/  K 0 s J/  (ee)K 0 s J/  (     )K 0 s lepton tags 0.0180.023 B-  tags -0.015 Estimate of the statistical error of sin2  using a time-dependent analysis with an integrated luminosity of 30 fb . Overall statistical error: 10 fb -1 : 0.018 30 fb -1 : 0.010 Competitive with LHCb and B-factories

14. Workhop on Recent Developments in High Energy Physics and Cosmology, Athens, 17-20 April 2003 Th. Lagouri, A.U.Th. B 0 d  J/  K 0 s Systematic error: analysis of control samples: –B +  J/  (  )K + –B 0 d  J/  (  )K *0 Invariant mass distribution for B +  J/  K + with superimposed the estimated background. Global systematic error: 0.01 Final error: 0.01 (stat) + 0.01(sys)

15. Workhop on Recent Developments in High Energy Physics and Cosmology, Athens, 17-20 April 2003 Th. Lagouri, A.U.Th. Rare decays with dimuons The decays B 0 s   +   and B 0 d   +   have very small BR but they can be selected by the atlas trigger even at the nominal LHC luminosity. With 130 fb  of data the reaction B 0 s   +   can be seen with 4.7  assuming the S.M. BR of 4.9 10  9. Another interesting class of reactions are inclusive decays such as B 0 s   0  +  , B 0 d   0  +  , B 0 d   *0  +  , … Detailed measurements of the decays can test the SM  search for new physics (eg A FB in decay)

16. Workhop on Recent Developments in High Energy Physics and Cosmology, Athens, 17-20 April 2003 Th. Lagouri, A.U.Th. Initial detector configuration Limited resources and technical/schedule constraints –effect: detector staging and TDAQ staging: Stage the following components (defer for 1-2 years) –One of the three pixel layers (not the B-layer) –Outermost TRT wheels, half of the CSC layers –MDT chambers in transition region (EES, EEL) –Cryostat gap scintillators, part of high luminosity shielding –Reduction of Read-Out Drivers for LAr calorimeter

17. Workhop on Recent Developments in High Energy Physics and Cosmology, Athens, 17-20 April 2003 Th. Lagouri, A.U.Th. Initial detector configuration However the main effect to the B-physics performance wrt to the Yellow Book results comes from the change of the B-layer radial position (from 4.30 cm to 5.05 cm) and from the material in and before that layer (increased thickness of the beam pipe and pixel services); preliminary estimations with DC1 data analysis: –Impact parameter resolution and proper time resolution degraded by about 30%; –Mass resolutions degraded by about 15%; –Reconstruction efficiencies: no important degradation found;

18. Workhop on Recent Developments in High Energy Physics and Cosmology, Athens, 17-20 April 2003 Th. Lagouri, A.U.Th. Summary of B-physics DC1 validations Physics channels and software used in validation Results on software validations B-performance with new geometry Athena reconstruction

19. Workhop on Recent Developments in High Energy Physics and Cosmology, Athens, 17-20 April 2003 Th. Lagouri, A.U.Th. Physics channels Input: TDR Generator events Masses and proper-times from different topologies: Bs  D s  D s       d  J/  J/  ee from B d  J/  s and B s  J/  s study yet. Charged particles from B-events combined with single particles

20. Workhop on Recent Developments in High Energy Physics and Cosmology, Athens, 17-20 April 2003 Th. Lagouri, A.U.Th. Software Simulation: atlsim3.2.1, realistic ID field Reconstruction: Atrecon (xKalman) 4.0.0 and 4.5.0 or Atlsim (xKalman) 4.0.0 and 4.5.0. Output to CBNT Vertexing code - still homogenous field ATL-COM-PHYS-2003-003 B. Epp, V.M. Ghete, A. Nairz, R. Jones, V. Kartvelishvili, M. Smizanska, N. Nikitine, S. Sivoklokov, K. Toms, J.F. Laporte, T. Lagouri, H. Bikolon, M. Testa

21. Workhop on Recent Developments in High Energy Physics and Cosmology, Athens, 17-20 April 2003 Th. Lagouri, A.U.Th. Validation of reconstruction software (1) All reconstructed masses displaced from generated: B s  D s  (-7 MeV) J/   (-4 MeV) in both B d  J/  K s, B s  J/  B d   (-3 MeV)… non trivial:  -dependent effect B d   (-5 MeV) - barrel, B d   (+4 MeV) - endcap D s  ,  (K + K - ) (obviously not shifted) No shifts in TDR

22. Workhop on Recent Developments in High Energy Physics and Cosmology, Athens, 17-20 April 2003 Th. Lagouri, A.U.Th. Validation of reconstruction software (2) Is the displacement due to Vertex code? If yes- not due to 2 T instead of 2.085T near the IP If yes - not only: we did not use vertexing for masses J/  , B d   If yes - not only: there are shifts in single - particle parameters just after Atrecon: e.q. shift in ‘pull’ distribution of muons p T = 1 GeV (1/p Trec -1/p Ttrue )/  (1/p T ) (-0.05) (no shift for high p T muons p T = 200 GeV)

23. Workhop on Recent Developments in High Energy Physics and Cosmology, Athens, 17-20 April 2003 Th. Lagouri, A.U.Th. B-performance with new geometry Despite problems in reconstruction software-first conclusions about B-performance in new geometry and realistic field versus TDR geometry and homogeneous field. Mass resolutions degraded by (10-20 %) Variables more sensitive to B-layer radius and material in and before: secondary vertices, proper- times degraded by (25-35 %) This matches with degradation (~30%) of impact parameter resolution of charged tracks at P T ~ 5 GeV in  < 0.25

24. Workhop on Recent Developments in High Energy Physics and Cosmology, Athens, 17-20 April 2003 Th. Lagouri, A.U.Th. Athena ID Reconstruction iPatRec 5.3.0 DC1 data, detector simulation with atlsim 3.2.1 J/  s  J/      events Reconstruction with iPatRec 5.3.0 in Athena Athena ID reconstruction validation No mass shift observed!

25. Workhop on Recent Developments in High Energy Physics and Cosmology, Athens, 17-20 April 2003 Th. Lagouri, A.U.Th. Athena ID reconstruction validation Peak position  (3096 ± 0.6) MeV  Shift (-0.9  1.5) MeV No shift  Nominal value: 3069. 9 MeV  DC1 Atrecon 4.5.0 (xKalman++): Shift (-4.9 ± 0.3) MeV Mass resolution   ±  eV (16 %)  TDR  39.3 ± 0.4 MeV  DC1 (Atrecon 4.5.0 )  (44.6 ± 0.5) MeV (13 %)

26. Workhop on Recent Developments in High Energy Physics and Cosmology, Athens, 17-20 April 2003 Th. Lagouri, A.U.Th. Athena ID reconstruction validation Barrel (  <1 both muons)  Mass resolution:  (38.9 ± 0.6) MeV  Peak shift: (+0.1 ± 0.5) MeV (No Shift) Endcap (  >1.2 both muons)  Mass resolution:  (61.7 ± 0.2) MeV  Peak shift: (-1.9 ± 1.9) ? MeV (limited statistics)  Material implementation corrected for 6.0.2 to include the insertable pixel layout support structure (significant effect in endcap region)

27. Workhop on Recent Developments in High Energy Physics and Cosmology, Athens, 17-20 April 2003 Th. Lagouri, A.U.Th. DC1 Atrecon-xKalman vs TDR Mean:(3092 ± 0.3 ) MeV  44.6± 0.5 ) MeV Mean:(3095 ± 0.3 ) MeV  39.3± 0.4 ) MeV DC1 Atrecon(4.5.0) - xKalman++ TDR - iPatRec Shift: (-1.9 ± 0.3) MeVShift: (-4.9 ± 0.3) MeV

28. Workhop on Recent Developments in High Energy Physics and Cosmology, Athens, 17-20 April 2003 Th. Lagouri, A.U.Th. DC1 Athena-iPatRec vs TDR DC1 Athena (5.3.0) - iPatRec TDR - iPatRec Mean:(3095 ± 0.3 ) MeV  39.3± 0.4 ) MeV Mean:(3096 ± 0.6 ) MeV  45.5± 0.6 ) MeV Shift: (-0.9 ± 0.6) MeVShift: (-1.9 ± 0.3) MeV

29. Workhop on Recent Developments in High Energy Physics and Cosmology, Athens, 17-20 April 2003 Th. Lagouri, A.U.Th. Athena-ipatRec Barrel-Endcap Barrel |  <1Endcap |  Mean:(3097 ± 0.5 ) MeV  38.9± 0.6 ) MeV Mean:(3095 ± 1.9 ) MeV  61.7± 0.2 ) MeV Shift: (+0.1 ± 0.5) MeV Shift: (-1.9 ± 1.9 ) MeV

30. Workhop on Recent Developments in High Energy Physics and Cosmology, Athens, 17-20 April 2003 Th. Lagouri, A.U.Th. T/DAQ Deferrals & LHC lum. The target initial luminosity was doubled to L= 2 x 10 33 cm -2 s -1 ; –  the low pt inclusive muon trigger will be replaced by a low-pT dimuon trigger; Consequences: –CP violation:  sin2  : 0.010  0.015 (dimuon trigger only); –Mixing cannot be studied with dimuon trigger only; –Rare B decays: unaffected; Restore the low lumi trigger menu as soon as L approaches values close to 1x10 33 cm -2 s -1 ;

31. Workhop on Recent Developments in High Energy Physics and Cosmology, Athens, 17-20 April 2003 Th. Lagouri, A.U.Th. Summary Although ATLAS is designed to probe the O(1TeV) energy scale, this experiment can make several useful measurements in the B-physics sector: –Sensitivity to sin2  comparable to that of LHCb; –Measurement of the B 0 s - B 0 s oscillations; –Unique opportunity to search for rare B 0 s decays (not possible by BaBar, Belle): potential indirect evidence of new physics.