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ATLAS, CMS B-Physics Reach

ATLAS, CMS B-Physics Reach. UK HEP FORUM The Cosener's House, Abingdon, 24th-25th April 2004 'From the Tevatron to the LHC'. M.Smizanska, Lancaster University, UK. 100 m b. 230 m b. ATLAS,CMS: b-events from central pp LHC collisions.

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ATLAS, CMS B-Physics Reach

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  1. ATLAS, CMS B-Physics Reach UK HEP FORUM The Cosener's House, Abingdon, 24th-25th April 2004 'From the Tevatron to the LHC' M.Smizanska, Lancaster University, UK

  2. 100mb 230mb ATLAS,CMS: b-events from central pp LHC collisions ATLAS.CMS, LHCb three different strategies to measure B production within partially overlapping phase space

  3. bb - b-events: LHC vs Tevatron LHCb ATLAS/CMS Bjorken x1 vs x2 for events that passed trigger&offline for at least one of B hadrons CDF

  4. ATLAS/CMS ATLAS CDF b-events: LHC vs Tevatron, cont In hadron-hadron collisions b and anti b quarks are produced with angular distances(0-p). At LHC a contribution of topologies with b anti b different from ‘back-to back’ is expected to be even higher than in Tevatron. Implications: B-Trigger strategies Tagging uncertaintes

  5. ATLAS,CMS B – physics Trigger strategies

  6. Decision times 2 x 108 109 Hz Implementation < 2.5 s Hardware (FPGA) ~ 10 ms General Purpose Processors optimised algorithms Higher Level Trigger High Level Trigger ~ few sec General Purpose Processors : offline type algorithms FPGA = Field Programmable Gate Array ATLAS Trigger Architecture

  7. single-muon all h b c all b h di-muon J/y c @1033cm-2s-1 ATLAS,CMS B – physics Trigger strategies Different scenarios for diff. luminosity conditions & rates 1. Di-muon trigger: L1 2m + L2 full precision m tracking Bd(Bs,Bc ) J/y (mm) + Ks0 (K0*,f,h), Lb (Sb, Xb) J/y (mm) L, B  mm,b  smm 2. Muon-electron(g) trigger: L1 m + L1 E/g cluster (ET>2GeV)+ L2 tracking in region Bd(Bs,Bc ) J/y (ee) + Ks0 (K0*,f,h) + Bm Lb (Sb, Xb) J/y (ee)L + Bm b  sg + B  m 3. Muon-hadron triggers: L1 m + L1 Jet (ET>5GeV) + L2 tracking in region L1 m + L2 full-scan tracking in Inner Detector B pure hadronic decays + Bm

  8. LVL1 Jet RoI ET > 6 GeV Bs pT GeV LVL1 Jet RoI ET > 6 GeV ATLAS LVL1 Jet RoI For hadronic final states use LVL1 Jet RoI (events with LVL1 muon) • LVL1 Jet Clusters in EM & Hadron Calorimeters. • Threshold of ET > 6 GeV (efficient for Bs with pT > ~ 16GeV) • Final threshold chosen will depend on RoI multiplicity • Preliminary simulation studies gives a mean multiplicity of 2 for a 6 GeV threshold (final value may be higher). ET GeV

  9. Reduce • # of track seeds • # of operations per seed HLT Tracking does not need to be as accurate as in the offline CMS High-Level Trigger Tracking Limited amount of CPU time available for trigger decision: 500 ms on a 1GHz machine possibly 50 ms in 2007 Regional seed generation Limited to some region identified by Lvl1 objects (e.g. cone around  direction) Partial/Conditional Tracking • Stopped when: • N hits are reconstructed • PTresolution  given threshold • PT value  given threshold • ……………………………………..

  10. CMS BS -+ • @ L1: • 2 trigger, PT 3 GeV, ||  2.1 • @ High Level Trigger: • Regional tracking look for pixel seeds only in a cone around • the 2, with PT 4 GeV and d0  1mm, and compatible with PV • Conditional tracking reconstruct tracks from good seeds • Stop reconstruction if PT  4 GeV @ 5 • Keep only tracks withσ(PT)/PT 2%, Nhit =6 • IF 2 Opposite Signs tracks found • Calculate the invariant mass • Retain pairs witha)|M-MBS| 150 MeV • b)Vertex 2  20 & d0 150 m

  11. ATLAS,CMS Inner detector and B-phys performance

  12. Radius~ 110cm, Length/2 ~ 270cm 6 layers TOB 4 layers TIB 3 disks TID 9 disks TEC CMS Tracker Design and Performances Pixel around interaction point 4.2, 7, 10 cm and +- 60 cm in z Silicon strip : R = 10-60 m Pixel: R, z = 10-20 m, cell size ~ 100x150mm

  13. The ATLAS Inner Detector Three sub-detectors using different technologies to match the requirements of granularity and radiation tolerance Sub- Detector r(cm) element size resolution hits/track Pixel 5.0; 8.8 50mm x400mm 12mm x 60mm 3 (Silicon) 12.2 (3D) SCT 30-52 80mm x 12cm 16mm x 580mm 4 (Silicon Strip) (stereo) Barrel: 4 cylinders;End-cap: 9 Wheels TRT 56-107 4mm x 74cm 170mm 36 (Straw Tubes) (projective) Initial LHC may be without: 1 pixel layer at 8.8cm, one of 3 endcap pixel disks and forward TRT wheels: so called ‘Initial layout’

  14. ATLAS: Inner detector performance

  15. Comparison of ATLAS and CMS impact parameter resolutions

  16. ATLAS particle identification in B-physics events Low pT electron identification Combined EM calorimeter-TRT electron identification TRT electron identification Rejection of bb m6X events without electron vs efficiency of events bb m6e5X. Eff=70%,R=570, level-2 rate of signal is 40Hz, fake rate 10Hz due to hadrons misidentified as electrons. Invariant mass for all track pairs in bb J/y (ee)K0 events before and after TRT selection cuts. Electrons have pT>1GeV.

  17. ATLAS particle identification in B-physics events, cont. Low and medium-pT muon performance Lowest pT muon identification & reconstruction efficiency J/y(mm) reconstruction in the environment of b-jet with pT~(50-80) GeV (for QCD b-production studies) Inner detector + Muon spectrometer the same in log scale Inner detector + Muon spectrometer + Hadron calorimeter Even in high pT jet a mass reconstruction is negligibly affected by fake pairs when a muon identified in Muon spectrometer match to a wrong track in Inner Detector.

  18. Precise measurementsofBd J/yKs0decay • Method: maximum likelihood fit using experimental inputs: • proper time resolution • tag probability • wrong tag fraction • background contribution and composition • Neglected at present stage: • Direct CP violation term • Any new physics contributions • Production asymmetry – possibly fcn of (pT h) • Wrong tag fraction – as fcn of (pT h) • The statistics used in the table includes: • ‘dimuon triggers mu6mu3’, using LVL1 efficiency 80%/per muon. • ‘di-electron LVL2 trigger e1e1’. • With more realistic e4e4 the precision of ATLAS, CMS degrade by factor 1.2.

  19. sensitivity in 1. Divergencies appeare as sin or cos->1 2. Linear |P/T| approximation is not justified for value 0.36 suggested by current evaluations. 3. The current theoretical uncertainty |P/T|~30% dominates other systematical and statistical errors of full LHC potential. Exact: |P/T|2 Approx: |P/T|

  20. f q1 q2 Bs Physics of Bs meson Program for precise measurements of Bs-anti-Bs system parameters : DGs, Dms and probing Bs mixing phase fs= -2lhallowing to investigate new physics Dms from Bs  Ds p and Bs  Ds a1already after 1 year sensitivity up to Dms - 36 ps-1 fully explore SM allowed range Dms (14.3 - 26) ps-1 DGs and fs= - 2l2h from Bs  J/yf or Bs J/yh both sensitive, but precision sufficient only in Bs  J/yf Angular analyses of cascade decay Bs J/y (mm)f(KK) determine DGs, Gs and fs simultaneously with 4 parameters of 3 helicity amplitudes A||, AT, A0 :A||(t=0), AT(t=0), d1, d2. Parameter Dms will be measured by flavor specific decays.

  21. Standard Model region-updated 2003 New physics Left-right symmetric model (NP-LR) - needs update (2000 version used here). ATLAS (3y): 1st level trigger 1m only. 2m 1st trigger under investigation, not included. TDR Detector, 240Evts. ATLAS - same – as above with Initial Detector CMS updated for realistic trigger in 2004 3y@1033 : 252k Evts. The estimated precision between the two ATLAS curves. LHCb(5Y): full 1st Level trigger, performance parameters as given in 2000 Experimental potential of both experiments not yet fully exploited: more studies on additional triggers, tagging. CP - violation weak phase in Bs J/y f

  22. Potential for Rare decays B  mm Will measure branching ration of Bs mm which is in SM of order Br < (10-9 Perform high sensitivity search on Bd mm A study proved good performance at nominal LHC luminosity. After 1 year 1034cm-2 s-1 Before LHC Bmm can be seen before LHC only if drastically enhanced. BK*mm will be measured but mass and angular distributions detailed enough to show New Physics only at LHC. 3 years at 1033cm-2 s-1 Different conclusions about BG: 1.CMS - already exploit isolation cuts in calorimetry 2. Different assumptions about tails in VTX resolution.

  23. Exclusive Rare decays of B mesons ATLAS statistics will allow angular analyses that can carry evidence for new physics. E.g. forward-backward asymmetry: Three points: mean values of AFB in three q2/MB2 experimental regions with error bars Lowest mass region: sufficient accuracy to separate SM and MSSM if Wilson coefficient C7g <0 SM MSSM C7g >0 MSSM C7g <0

  24. other studies of ATLAS, CMS b-physics group • Undergoing physics studies not mentioned here: • Double heavy flavor mesons (b,c) • QCD tests of beauty production at LHC central region. Correlations bb. • Physics of Beauty baryons, production polarizations, decays. • Rare decays of b s gamma. • Rare decays of L b  L mm

  25. ATLAS, CMS b-physics-related software • ATLAS, CMS – B-related online software under development: reconstruction Algorithms, trigger simulations. • ATLAS: offline MC simulation, reconstruction software, physics analyses software. • Within a successful Data Chalenges-1 period 2002-2003 B-physics group studied B-performance for the Final version of detector layout. • Data Chalenges-2 started 2004: grid production, Geant 4, databases, new Event Model • ATLAS, CMS: B-event Generators software • For bb production we use Pythia tuned to Tevatron data. Herwig – we never tried. NLOQCD ( MNR code) does not give whole events. • Installation of B-decays dedicated package ‘EvtGen’ in common use and development with BaBar (main developer) , LHCb, CDF, D0.

  26. B-physics prospects with ATLAS, CMS - conclusions • General purpose central LHC detectors are preparing a multi thematic B-physics program - including B-decays and B-production. • ATLAS, CMS B-physics trigger strategy rely on dimuon trigger for luminosity 2*1033 cm-2s-1 - extend selection menue at lower luminosities when there is spare processing capacity. • In CP violation the main emphasis will be on underlying mechanisms and evidence of New physics. ATLAS, CMS is especially precise in measurement of b. LHC ‘gold-platted’ mode is also Bs  J/y f • Rare decays B mm have the most favorable experimental signature allowing to measure also at nominal LHC luminosity 1034cm-2 s-1. Will measure branching ration of Bs mm and sensitivity test for Bd mm . Precision measurements will be done for B  K*mm. • Beauty production at central LHC collisions will be measured for QCD tests.

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