0 25. Sept 2006 M.Smizanska, Lancaster University, UK LHC preparations for precise measurements of muonic very rare B-decays 25. Sept 2006 M.Smizanska, Lancaster University, UK

1 Outline 1. Current experimental limits 2. Different strategies of LHC experiments 1.Detector layouts and luminositites 2.Detector performance 3.Triggers 3. Challenge of measurements of very rare B-decays to muons 1.Signal selections and statistics 2.Background environments – combinatorial and non combinatorial detector dependent backgrounds. 4. Conclusions

2  Current Experimental Limits on B   B s   B d   SM Ali, Greub, Mannel, DESY CDF (780 pb-1)1.0* %CL3.0* %CLNote 8176Note D0 (700 pb-1)2.0 * %CL11.1* %CLpreliminary Belle 78 fb * % CLPRD68, BaBar 111 fb * % CLPRL94, Today experimental limits still factor of 20 above SM – leave space for NP Expect improvement by factor of 5-8x by the end of Tevatron run

3 LHC strategies for measurements of B →  LHC pp  total = 100 mb  inelastic = 80 mb  bb = 500  b ATLAS/CMS Central detectors: Muons seen in transverse direction after 11  this limits  p T >3-6GeV LHCb Forward detector Muon detector in forward direction can be reach by  of any p T  p T one B ‘in’ |  | 9-10 GeV  ~ 100  b GeV  ~ 230  b Luminosity for B physics L = 2 × cm -2 s -1 rare B cm -2 s -1 L = 2 × cm -2 s -1 1 y Statistics B   cm -2 s -1 ~350 in fiducial volume ~7 after trig + signal selections (<20 backgr.) 1 2 × cm -2 s -1 ~161 in fiducial volume ~ 17 after trig + signal selections (<5.7 bckgr.) Different layouts of LHC detectors - lead to different luminosity, trigger and offline strategies - different strategies in measurements of B → 

4 Understanding detector performance differences relevant for B- 

Impact parameter resolution LHC b 1/p t distribution for B tracks Understanding of performance differences for B-  - impact parameter resolution LHCb is precise in R-z so IP precision is determined by large p z lead to  m resolution for B-  tracks even at very low p T >1.3 GeV ATLAS/CMS are precise in x-y ATLAS B-  p T >6GeV  m CMS B-  p T >3-6 GeV  m p T - range for muons form B  IP resolution for ATLAS Final detector CMSATLAS  < 0.25

Understanding of performance differences for B-  p T and mass resolution CMS  =36 MeV, 4 Tesla ATLAS  = 84 MeV 2 Tesla LHCb  =18 MeV

Understanding trigger strategies for B- 

8 ATLAS di-muon triggers for rare decays LVL1: 2  RoI p T (  ) > 6GeV (~500 L=10 33 cm -2 s -1 ) LVL2:  Confirm each  RoI from LVL1  In precision muon chambers  Combine  with Inner Detector track  Mass cut 4 GeV < M(  )< 6 GeV EF: Refit ID tracks in Level-2 RoI Decay vertex reconstruction Transverse Decay length cut: L xy > 200  m Efficiency estimation L2/EF: bb   +  - for both  p T >6 GeV –70% of B   +  - –(60% of B  K *  +  - ) Online reconstruction of di-  mass, (MeV) B  K *  +  - B   +  - Not normalized Selected from J.Kirk – this conference

9 CMS Triggers for B-  First level trigger: two muons each with threshold p T >3GeV.

10 LHCb L0 and HLT Trigger - selected features for di-muon case L0 Pile-up system -reject events with multiple interactions per bunch crossing Muon Trigger (high P T muons) -select 2 muons with the highest P T in each quadrant pT>1.3 GeV for rare decays HLT (High Level Trigger) reduce rate from 1MHz to ~2kHz – for di- muon 600Hz full detector info available software trigger Efficiency of (L0+HLT) for B →  signal that passed signal selection cuts (see later) = 79% Selected from LHCb and Metlica BEACH2006

Offline Selection strategies for B-  and combinatorial background rejection

12 LHCb offline signal selections Later: B s impact parameter cut was changed to : IP/  < 3 and pointing angle (momentum/decay length) < 5 mrad 17 signal events 2fb-1 <5.7 combinatorial background More recent (preliminary) study gives 30 signal evts with no background left of 30M bb sample.

13 CMS offline selections 6.1 Evts/10fb-1 Background

ATLAS Offline Selections M  = M Bs MeV (asymmetry to distinguish B 0 s and B 0 d ) isolation: no charged tracks with p T > 0.8 GeV in cone q < 15 degrees vertex fit with pointing to primary vertex constraint transverse decay length L xy /s(L xy ) > 11 Isolation Decay Length

15 LHC overview rare B-decays: for early data and later luminosity conditions Integral LHC Luminosity ExperimentExpected Signal Combinatorial background Upper limit at 90% CL 100 pb -1 ATLAS or CMS ~ 0~ 0.26 ×10 -8 (each) 10 fb ATLAS~ 7~ 201.2×10 -8 CMS~ 6.1~13.8 ( – 13.8) 1.4× fb LHCb~17<5.7Not given yet 10 fb ~54<27 30 fb ATLAS~ 21~ 607 ×10 -9 (each) CMS~18.3~ But can run as long as LHC ATLAS (2000)~92 Bs~660 CMS (2000)~26 Bs~6.4 6

16 BR used in the MC Models used in MC or to confront experimental sensitivities B s →  Ali, Greub, Mannel, DESY B d →  B d →  B s →  B d →   Melikhov, Nikitin, PRD70, 2004 WC: SM Buras, Munz, PRD52, Other rare decays close to B  

17 ATLAS: 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 Review of non combinatorial BG sources for B-  at LHC BG processBr Effective Br in B-  signal region (ATLAS ) B 0 → π - µ + ν µ ~10 -4 ~ 5 ∙ B + → µ + µ - ℓ + ν ℓ < 5 ∙10 -6 < 5 ∙10 -8 B + → J/  (µ + µ - )    ~ 6 ∙ ~ B c → µ + µ - ℓ + ν ℓ < < B 0 d → π 0 µ + µ - ~ 2 ∙ ~ B 0 s →µ + µ - γ~ 2 ∙10 -8 ~ B d → K  B s →KK 2 ∙ < ( LHCb) 13

B 0 s →hh background at LHCb, Kirill Voronchev Misidentification and Fake Rates in LHCb Misindetification and fake rates are detector dependent. Two-body hadronic decays in LHCb B 0 d,s →  +  -, B 0 d,s → K -  +, B 0 d,s → K + K - are estimated to have effective branching~ 0.5 · in signal region. Mass resolution is important ( s LHCb = 18 MeV) estimate of B 0 s → hh background at LHCb: convoluted fake probability with K,  spectrum BR(B 0 s → KK) ~ 2 · BR(B 0 s → K  ) ~ 5 · => this background under control - results in ~ 2 events / 2 fb -1 (in ± 2· s mass window) log 10 (events) Fake RatesSpectrum

20 Particle level study (ATLAS) of backgrounds from B 0 d →π - μ + ν μ and B + →  Br(B + → µ + µ - ℓ + ν ℓ ) ≈ 5*10 -6 Number of events B + → µ + µ - ℓ + ν ℓ p T (ℓ + ) < 0.5 GeV B + → µ + µ - ℓ + ν ℓ p T (ℓ + ) < 0.5 GeV Fake events from B 0 d →π - μ + ν μ Fake events from B 0 d →π - μ + ν μ B 0 s →µ + µ - B 0 d →µ + µ - B 0 s →µ + µ - B 0 d →µ + µ - Number of events Mµµ 12 Br( B 0 → π - µ + ν ) ~ 10 -4

21 Conclusions All LHC experiments confirm to be able to search for B →  signature starting from the early LHC run:  Their Lo/L1 triggers are capable to take di-muon signatures with high efficiency  HLT software is written and tested to reconstruct data online All three experiments are capable to measure signal of B s →  at luminosity of All experiments are able to continue at luminosity of and improve measurements of B s →  signal and make sensitivity search for B d →  Combinatorial background cannot be well estimated within available CPU capacities before LHC start, but factorization of cuts give prediction roughly at the level of signal ( higher in ATLAS/CMS, and lower in LHCb). Specific backgrounds need estimation! LHC will be sensitive to Br where this background is relevant. ( Tevatron did not reach this sensitivity so they may not seen them).

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