0 ATLAS preparations for precise measurements in B-physics channels potentially sensitive to NP SUSY 2005, M.Smizanska, Lancaster University, UK

1 The ATLAS Detector Inner Detector (ID)  Semiconductor pixel and strip detector  Transition radiation tracker: straw-tubes interspersed with a radiator (e/  separation)  Inside solenoid of 2T magnetic field Calorimeter  Highly granular LAr EM calorimeter:  < 3.2  Hadron calorimeter:  < 4.9 (scintilator-tile in barrel and LAr in end-caps and forward) Muon spectrometer  Air-core toroid system on average ~ 0.5 T  MDTs & CSCs; RPCs & TGCs

2 ATLAS is Getting Ready

3 ATLAS Detector in 2007 According to the present schedule the ATLAS detector will have full geometrical coverage for muons, electrons and hadrons for first collisions in 2007 However, it will have some differences compared to the design that was presented in the early layout - TDR, some of which affect the B-physics programme In the Inner Detector  The innermost pixel layer will be at a radius of 5 cm (4.3 cm in TDR) from the beam line As a consequence, the secondary vertex resolution degrades by ~40% with respect to the originally foreseen  Some parts of the TRT wheels will not be installed Reduced number of hits per track in forward region High Level Trigger System  Computing resources at startup will be reduced Nominal early luminosity is now foreseen to be cm -2 s -1 All values in this presentation are for Final (2007) Detector layout and for 33 cm -2 s -1

4 ATLAS B-physics trigger strategies Flexible B trigger strategies, according to luminosity conditions. All ATLAS LVL1-trigger objects: , e/  jet to be combined At luminosity few times cm -2 s -1   (p T >6GeV) +  (5GeV) B s → J/  B d →    B →    (p T >6GeV) + e/  (E T >6GeV) B d → K   B s →  B →    (p T >6GeV) + Jet (E T >10GeV) B s → D s  At nominal luminosity cm -2 s -1 2  ( p T > 6 GeV) B →  At low luminosity (end of spill) 6-8 GeV) leaving further selections for High Level triggers. Objects identified at LVL1 are futher analysed at High-level triggers using full detector granularity. Inner detector is involved. B-events written to permanent storage → 10 8 /year all passed criteria for specific exclusive B-decays modes.

5 Number of events after trigger + offline reconstruction 33 cm -2 s -1 Models used in MC or to confront experimental sensitivities. Signal Backgr B s → J/  B s → J/   s  s, 300k % <100% SM: Fleisher CERN-TH NP: Ball,Khalil, Phys.Rev.D69:115011,2004 Bs→Ds Bs→Dsa1Bs→Ds Bs→Dsa1 MsMs <100% NP: Ball,Khalil, Phys.Rev.D69:115011,2004 ATLAS sensitivity in B s tree-level dominated decay channels with possible signatures of NP

6 LHC sensitivity to CPV B s mixing phase in B s  J/  Expected LHC sensitivity after 3 years SUSY model Ball,Khalil,2004 ATLAS(2005) final detector LHCb (2003) performance still to be updated SUSY example for R = M 12 SUSY / M 12 SM = 0.5 Not full experimental potential exploited since far – work continues SM – is already OUT of experimental sensitivity (would need 30 years …)

7 Sensitivity to CPV B s mixing phase comparison Expected LHC sensitivity after 3 years Update 2005 Situation in 2000  ATLAS final detector (Roma-2005), early detector (before 2000)  LHCb final detector (TDR-2003), early detector (before 2000)  SM combined fit tighter in 2004 than in 2000  SUSY model Ball, Khalil,2004 replacing old NP- LR model Ball,Fleischer, excluded by data at 2003

8 Another parameters of B s  J/  B s  J/  : Extraction of weak phase  s from B s  J/  requires simultaneous determination of other weak Γ s, ΔΓ s, x s and parameters of strong amplitudes : A ┴,A ║, δ 1,δ 2. Despite enormous LHC statistics (ATLAS /3years) and well controlled background (ATLAS 15%) – several parameters get highly correlated in maximum likelihood fit.  To avoid failing a fit due to high x s –  s correlation x s - was fixed – will be determined independently in B s  D s  ΔΓs13% Γs1% A║A║ 0.9% A┴A┴ 3%  s (X s = 20)  s (X s = 40) ГsГs ΔΓ s δ1δ1 δ2δ2 ГsГs 70% ΔΓ s δ1δ1 98% δ2δ2 σ(  Bs )=96fs ΔГ s  =0.1 Errors:Correlations:

9 BR used in the MC Signature after trigger +offline reconstruction 33 cm -2 s -1 Models used in MC or to confront experimental sensitivities. SignalBackgr       B d →    B d →  B s →  Br.fraction  -mass A FB < <3000 Melikhov, Nikitin, Simula, PRD57,98; Melikhov, Stech, PRD62, 2000 WC: SM Buras, Munz, PRD52, 95; MSSM Cho, Misiak,Wyller, PRD54,96.  b →  1500NP: Chen, Geng, PRD64,2001 Aliev NPB649,2003 Semi-muonic exclusive rare B-decays in ATLAS

10 Variables to be measured in semi-muonic exclusive rare decays Most th authors - suggest to measure variables describing di-muon system, namely: shapes of s = mass(  ) 2 and Forward-backward asymmetry A FB as a function of s. The calculations show differences between SM and SUSY in some parts of phase space. Shapes of this distributions are sensitive to trigger and offline selections cuts – especially for small opening di-muons angles and for p T near threshold. The acceptance control is one of the main subjects in these studies.

11 Semi-muonic rare decays, sensitivity to trigger All events produced in pp collisions LVL1 trigger selections (x 100) All trigger cuts (x 100) Example of a preliminary study for  b →  to investigate sensitivity to trigger. Comparison of q 2 /M B 2 (left) and of ‘A FB versus q 2 /M B 2’ (right) before and after trigger A FB - q 2 /M B 2 shape is less sensitive to trigger cuts than q 2 /M B 2 distribution. Results are preliminary. Study continues to include a control of fake and real di-muon background sources, which may have impact especially on small opening angles.

12 Examples of offline reconstruction performance for semi-muonic decays Inv. Mass Res. 47 MeV Reconstruction of B s   (K + K - )  +  Inv. Mass Res. 51 MeV Reconstruction of  0 b  +  -  0 (p  - ) Proper Time Resolution 102 fs Reconstruction of B d  K *0 (K +  - )  +  - Resolution for cos θ angle between  + and  0 b

13 Sensitivity to New Physics in B d →  K 0* In low values of di-muon masses ATLAS can after 3 33 cm -2 s -1 = 30 fb -1 distinguish MSSM C 7geff >0 from SM ATLAS statistical errors2% in this area  →    3000 events with 30 fb -1 SM MSSM C 7geff >0 MSSM C 7geff <0 A FB (muon asymmetry) plotted versus  mass 2 /M B 2

14 Sensitivity to New Physics in  b →  ATLAS can already after 3 33 cm -2 s -1 = 30 fb -1 distinguish MSSM C 7geff >0 from SM in low values of di-muon mass  b →   events with  30fb -1 ATLAS MC events generated with SM after trigger and reconstruction analysis ATLAS MC events generated with MSSM C 7geff >0 after trigger and reconstruction analysis ATLAS statistics errors corresponding to 1500 events – expected after 3 years ATLAS statistical errors 5% in this area

15 Signature after trigger + offline reconstruction 33 cm -2 s -1 Models used in MC or to confront experimental sensitivities. Signal Backgr B d → K   B s →  S/√B >5 S/√B >7 Ali, Braun, Simma, Z.Phys.C63,1994; Melikhov, Stech, PRD62,2000 WC SM : Buras, Munz, PRD52, Radiative rare B-decays in ATLAS A complete trigger strategy to select these channels has been studied showing that at a luminosity of cm -2 s -1 the output rate is controllable  LVL1:  p T > 6GeV + secondary EM RoI E T > 5GeV  trigger not required by signal, however reduce rate while enrich B yield 25 times. in CP violation studies all events will be tagged  LVL2:  identification and reconstruction of K *0 and   EF: Inv. Mass cuts and vertex reconstruction An important ingredient is the rejection of B  K 0 *  0  Good  0 /  separation Data were collected at the test-beam in 2004 for a dedicated study of this

16 BR used in the MC Signature after trigger +offline reconstruction 33 cm -2 s -1 Models used in MC or to confront experimental sensitivities. SignalBackgr B s →  21 <60 Ali, Greub, Mannel, DESY B d →  at 34 cm -2 s -1 95%CL B d →  B s →  B d →   particle level since far Melikhov, Nikitin, PRD70, 2004 WC: SM Buras, Munz, PRD52, ATLAS performance for B   decays Full trigger and detector TDR study was made also for luminosity cm -2 s -1 It proved that the B →  program can be continued at nominal LHC luminosity. already after 1 year a signal of 92 B s →  events can be extracted over background of 900 events and a limit can be posed on B d →  The study continues for Final detector layout. Values in table given for cm -2 s -1 are already for Final detector.

17 B 0 d,s →µ + µ - γ as BG to B 0 d →µ + µ - B 0 d,s →µ + µ - γ as BG to B 0 d →µ + µ - Interesting study (since far limited to “particle-level” = fiducial and trigger cuts) checks B 0 d,s →µ + µ - γ as a possible background to B 0 d →µ + µ -. Study concluded the background is small in comparison with signal and negligible comparing to combinatorial background. Plan is to study a feasibility of extraction of B 0 d,s →µ + µ - γ as a signal. Preliminary results show potential background from channel B 0 d,s →µ + µ -  0 Number of events p T (γ) < 2 GeV ← φ – resonant contribution B 0 s →µ + µ - γ B 0 d →µ + µ - γ M µµ GeV B 0 d →µ + µ - p T (γ) < 4 GeV B 0 d →µ + µ - ← φ – resonant contribution B 0 s →µ + µ - γ B 0 d →µ + µ - γ Number of events

18 Conclusions -1 Conclusions -1 ATLAS preparations for B channels potentially sensitive to New Physics are in progress both at trigger and off line. In B s  J/  there is clearly a potential to achieve NP values of weak phase  s, precision will depend on value of x s. Rate  s will be measured in the same analysis with precision of 13%. Strong phases cannot be decoupled. Semi-muonic rare decays of all B-mesons species B d, B s  b are under preparation and will allow to distinguish between SM and certain classes of MSSM. ATLAS can collect B  K 0 *  and 3400 B s  events in 3 years. In 3 years of cm -2 s -1 ATLAS can observe B s  with st significance of 3. After 1 year of nominal LHC luminosity cm -2 s -1 ATLAS can pose a limit of on branching fraction of B d →  with 95%CL.

19 Conclusions-2 Conclusions-2 ATLAS B-group physicists are excited about the work on New physics signatures and would welcome  more theory works predicting B exclusive channels we can measure in LHC  more types of measurable variables sensitive to NP contributions  models allowing to study synergy of Beauty and high-pT SUSY measurements: You are warmly invited to FLAVOUR IN THE ERA OF THE LHC a Workshop on the interplay of flavour and collider physics First meeting: CERN, November

20 … and in 2006 we warmly invite you to … and in 2006 we warmly invite you to The 7th International Conference on Hyperons, Charm And Beauty Hadrons- BEACH 2006 will be held from 2nd to 8th July, 2006 at the University of Lancaster, England. University of Lancaster

21 Backups

22 ATLAS Final detector layout with 1 st pixel layer radius 5cm ( 4.3 cm in Early layout ‘98) Proper-time resolution for representative B-decays Detector layout Final ‘2005 Early ‘1998 B s  D s  99 fs66 fs B   101 fs69 fs B s  J/  96 fs63 fs Final Layout p T - range B  Early Layout p T - range B s  D s  Impact parameter resolution  (d0) and p T -range of secondary tracks for two example B-decays channels Impact Parameter and Proper Time Reconstruction Proper Time Resolution 102 fs

23 ATLAS measurement of  m s with B s  D s  BsDsBsDsBsDsBsDs Already after 1 year ATLAS reach %CL