ATLAS B-Physics Reach M.Smizanska, Lancaster University, UK

M.Smizanska: ATLAS B-physics reach 2 ATLAS: b-events from central pp LHC collisions 230  b 100  b

M.Smizanska: ATLAS B-physics reach 3 B-physics strategy with tight funding constraints Recent work has addressed the issue of maximizing B-physics capabilities in context of reduced initial Trigger/DAQ system (funding limitations) –Extend Region-of-Interest mechanism of level-2 trigger to reconstruction of B decays: Level-1 muon was always used to provide region of interest Now, level-1 jet to guide reconstruction of hadronic modes, e.g. B s  D s , and electrons, e.g. J   e + e - –Use result of level-2 trigger to seed reconstruction in the Event Filter Only reconstruct limited region of Inner Detector containing B candidate –Strong reduction in processing requirements compared to previous strategy that involved full scan of Inner Detector at level-2 Nevertheless, with presently assured funding, the initial Trigger/DAQ system will be almost saturated by the priority “discovery physics” programme when the luminosity is at the target of L = 2  cm -2 s -1 –At this luminosity, B-physics would be based on dimuon trigger only which has very low rate but nevertheless covers many interesting channels –At lower luminosities, e.g. towards end of LHC coast, spare Trigger/DAQ capacity can be used to extend the B physics potential

M.Smizanska: ATLAS B-physics reach 4 B – physics trigger strategies, cont. Level-1: single-muon or di-muon Efficient down to p T 5GeV ( lower still in endcap). Different scenarios according to luminosity conditions & rates single-muon di-muon all h h b b c c J/ 33 cm -2 s Di-muon trigger: L1 2  + L2 precision  tracking in muon spectrometer and Inner detector. B d  J/  K s 0, B s  J/ ,  etc  b  J/  , rare decays B   B d  K 0 *  B d    etc 2. Muon-electron(  ) trigger: L1  + L1 e/  cluster (E T >2GeV)+ L2 tracking in region B d  J/  (ee) + K s 0 + B    b  J/  (ee)  + B   B d  K 0 *  + B  etc 3. Muon-hadron trigger: L1  + L1 Jet (E T >5GeV) + L2 tracking in region B   + B  B s  D s  B  etc

M.Smizanska: ATLAS B-physics reach 5 ATLAS performance parameters principal for B-physics Low p T electron identification Combined EM calorimeter-TRT electron identification Rejection of bb   6X events without electron vs efficiency of events bb   6e5X. Eff=70%,R=570, level-2 rate of signal is 40Hz, fake rate 10Hz due to hadrons misidentified as electrons. TRT electron identification Invariant mass for all track pairs in bb  J/  (ee)K 0 events before and after TRT selection cuts. Electrons have p T >1GeV.

M.Smizanska: ATLAS B-physics reach 6 ATLAS performance parameters principal for B-physics, cont. Low and medium-p T muon performance Lowest p T muon identification & reconstruction efficiency Inner detector + Muon spectrometer Inner detector + Muon spectrometer + Hadron calorimeter J/  ) reconstruction in the environment of b-jet with p T ~(50-80) GeV (for QCD b-production studies) the same in log scale Even in high p T jet, a mass reconstruction is negligibly affected by fake pairs when a muon identified in Muon spectrometer match to the wrong track in the Inner Detector. muons pions

M.Smizanska: ATLAS B-physics reach 7 Precise measurements of B d  J/  K s 0 decay Method: maximum likelihood fit, using experimental inputs: proper time resolution, tag probability, wrong tag fraction, background composition. Direct CP violation term neglected here.

M.Smizanska: ATLAS B-physics reach 8 sensitivity in The current theoretical uncertainty |P/T|~30% dominates other systematical and statistical errors of full LHC potential.  -sensitivity as a function of  and theoretical uncertainty of |P/T| using full LHC potential

M.Smizanska: ATLAS B-physics reach 9 Physics of B s meson  m s from B s  D s  and B s  D s a 1 already after 1 year sensitivity up  m s - 36 ps -1 fully explore SM allowed range  m s ( ) ps -1 Program for precise measurements of B s -anti-B s system parameters :  s,  m s and probing B s mixing phase  s    allowing to investigate new physics.  s and  s = -    from B s  J/  or B s  J/  both sensitive, but precision sufficient only in B s  J/  Angular analyses of cascade decay B s  J/  determine  s,  s and  s simultaneously with parameters of helicity amplitudes A||(t=0), A T (t=0), A 0 (t=0),  1,  2. Parameter  m s will be measured by decays to flavor specific final states B s  D s  and B s  D s a 1. Bs   

M.Smizanska: ATLAS B-physics reach 10 CP - violation weak phase in B s  J/  Standard Model region-updated 2003 New physics Left-right symmetric model (NP-LR) - version used here last updated in ATLAS (3years): 1st level trigger 1  only. Extension by 2  trigger under investiga- tion, not included. TDR Detector. ATLAS - same – as above with Final Detector Layout– Preliminary LHCb(5years): 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.

M.Smizanska: ATLAS B-physics reach 11 Potential for Rare decays Before LHC B  K*  will be measured however mass and angular distributions detailed enough to show New Physics only at LHC. B  can be seen before LHC only if drastically enhanced. A study proved good performance at nominal LHC luminosity. After 1 year cm -2 s -1 3 years at luminosity cm -2 s -1 B  Will measure branching ration of B s   which is in SM of order Br<(10 -9 ) Perform high sensitivity search on B d  

M.Smizanska: ATLAS B-physics reach 12 Exclusive Rare decays of B mesons ATLAS statistics will allow angular analyses that can carry evidence for new physics. E.g. forward-backward asymmetry: SM MSSM C7  >0 MSSM C7  <0 Lowest mass region: sufficient accuracy to separate SM and MSSM if Wilson coefficient C7  <0 Three points: mean values of A FB in three q 2 /M B 2 experimental regions with error bars

M.Smizanska: ATLAS B-physics reach 13 Studies not mentioned here: 1.Double heavy flavor mesons. 2.QCD tests of beauty production at LHC central region. Correlations bb. 3.Physics of Beauty baryons, production polarizations, decays. other studies of ATLAS b-physics group

M.Smizanska: ATLAS B-physics reach 14 B-physics prospects with ATLAS - conclusions 1.ATLAS is preparing a multi thematic B-physics program - including B-decays and B-production. 2.ATLAS B-physics trigger strategy revised to maximize physics potential within tight funding constraints - rely on dimuon trigger for initial luminosity 2  cm -2 s -1 - extend selection at lower luminosities when there is spare processing capacity. 3.In CP violation the main emphasis will be on underlying mechanisms and evidence of New physics. ATLAS is especially precise in measurement of  In B s  J/  large CP violation would indicate new physics. 4. Bs mixing studies make clear that there is sensitivity to  m s beyond SM expectations. The width difference  s can be measured best in B s  J/  with relative precision  5. Rare decays B   have favorable experimental signature allowing to measure also at nominal LHC luminosity cm -2 s -1. Will measure branching ration of Bs   which is in SM of order Br<(10 -9 ) Precision measurements will be done for B  K* . 6.Beauty production and bb correlations in central LHC collisions will be measured for QCD tests.