Search for the rare decays B 0 s à μ+ μ and B 0 à μ + μ. 1- Nov Hiroshi Nakano

Transcription

1 Search for the rare decays B 0 s à μ+ μ and B 0 à μ + μ 1- Nov Hiroshi Nakano

2 Contents The LHCb detector 3. Analysis strategy 4. Event 5. of the factor 6. Signal and background likelihoods 7. Results & 8. Conclusions

3 1. P1

4 SM and New Physics Branching of B 0 s,d à μ+ μ in SM Bà μμ is one of the Golden mode for NP in LHCb

5 2. The LHCb detector P1 P2

6 LHCb Point CMS bb pairs are predominantly produced in the same forward or backward. LHCb 4π detector (CMS) and LHCb detector mrad in the bending plane (horizontal) mrad in the non- bending plane

7 Luminosity LHCb s luminosity is tuned to 2 x [cm - 2 s - 1 ] (defocusing the beams) 0 [events/cross] (~60%) 1 [events/cross] (~30%) 2 [events/cross] (~10%) ATLAS & CMS LHCb 2 x [cm - 2 s - 1 ] = 200 [μb - 1 s - 1 ] 200[ub - 1 s - 1 ] x 10 7 [s/year] = 2[c - 1 ] bb cross sec@on@14 TeV TeV ~300[μb] à ~10 12 [bb/year]

8 side- view (non- bending plane) Detector (1/4) Vertex locator (silicon micro strip) reconstruct primary vertex (b & secondary vertex (b, c decay) Impact parameter resolu@on (Belle)

9 side- view (non- bending plane) Detector (2/4) A warm dipole magnet Bdl = 4Tm Tracker sta@ons (3 layers) (silicon micro strip for small angle region) (straw- tubes for large angle region) Trigger Tracker (4 layers of silicon micro strip) δp/p = 0.35 % (@5GeV/c) = 0.5 % (@100GeV/c) Belle δpt/pt = 0.2pt 0.3/β %

10 side- view (non- bending plane) Detector (3/4) Calorimeter system ECAL + HCAL ID high E T hadron, e, gamma à L0 trigger RICH system Charged hadron ID (p range: GeV) w/o RICH with RICH ECAL σ E E = 10% 1.5% E[GeV] HCAL σ E E = 80% 10% E[GeV] LHCb ECAL HCAL 25X λ I 5.6λ I Belle ECL KLM 16X λI 3.9λI

11 Detector (4/4) side- view (non- bending plane) Muon systems (1+ 4 layers) Gold- plated CP sensi@ve decays B 0 d J/ψ(µ + µ )K 0 s Bs 0 J/ψ(µ + µ )φ Golden modes for New Physics: B µ + µ B K µ + µ

12 Trigger (bunch crossing rate) L0 trigger Pileup system à discriminate single pp calorimeter trigger for gamma, e, hadron muon trigger (Single mu: pt>1.4gev or di mu: pt > 0.48 GeV, 0.56GeV ) High Level Trigger 1+2 using L0 informa@on, tracking, vertexing ex. for muon pt > 1.8GV or IP > 0.11mm, Pt> 0.8GeV for di muon invariant mass is calculated

13 3. Analysis strategy P2 4. Event 5. of the factor 6. Signal and background likelihoods

14 4. Event P2 P3

15 Purpose : Sop selec@on to reduce size of dataset. (signal efficiency à as high as possible sample efficiency à as similar as possible to signal efficiency) μ ID using muon sta@ons. Good quality events (tracks, vertex) are selected. Condi@on for signal candidate: ΔM < 60MeV/c2

16 Aper all 343 (342) Bs (Bd)à mu+mu- candidates are remain. In those candidates, 0.3 (0.04) events are expected. Dominant background : ~90% bb à mu mu X ~10% fake + mu

17 5. of the factor P3 P4

18 Concept of BR signal = N signal N / ε signal signal = N total N total N signal = ε signal * N signal N : detected # N : occurred # N total = L * σ or N total = N sample / ε sample sample: normaliza@on with well known events. BR sample N signal / ε signal = L * σ N signal / ε signal = BR sample * N sample / ε sample 1) Rely on MC 2) Many systema@cs 1) Rely on data > MC 2) Many systema@cs cancel

19 exact formula of Br HFAG average of LEP/Tevatron value f d /f s = 3.71 ± 0.47

20 Results à used for of # of signal events

21 6. Signal and background likelihoods P4 P5

22 Events are classified in two dimensional plane. invariant mass geometrical likelihood (GL) GL à 4 bins Δm à 6 bins expected signals & BGs are calculated

23 GL: Obtained from data using inclusive B 0 à h + h Agree with distribu@on obtained from B 0 à μ + μ variables used for GL: Life@me & pt of the B Impact parameter of μ, B distance of μμ... etc background probability in the B 0 s mass window Signal ~25% for each BG cluster around 0 à used for expecta@on of # of signal events

24 Mass are calculated in two ways 1) J/ψ, ψ(2s), Υ(1S), Υ(2S), Υ(3S) à μ + μ CB func@on fit à σ = ± 0.14 MeV Gaussian fit 2) inclusive B 0 q à h+ h reconstruc@on à σ = 25.8 ± 1.0 MeV σ = 26.7 ± 0.9 MeV à used for expecta@on of # of signal events

25 Sideband region ±1200MeV for upper GL bins ±600MeV for lower GL bins (fi ed with A*exp[- k*x]) à used for of # of BG events

26 B 0 s predic@on for the number of events in the signal region

27 B 0 d predic@on for the number of events in the signal region

28 Green shaded area CL b : BG only hypothesis compa@ble within 1σ Solid (Dashed) line CL s : Signal + BG hypothesis Observed (Expected) Results CLs is higher than 0.1 at BR < 4.3 x 10-8 à The area BR > 4.3 x 10-8 is excluded at CL 90%. BR Bs0à mumu < 4.3(5.6) x 90(95)%CL BR Bd0à mumu < 1.2(1.5) x 90(95)%CL

29 7. Results & 8. Conclusions P6 P7 P8

30

31 latest result (at EPS July 2011) CDF 7L- s=1.96tev 0.46 x 10-8 < Br( Bsà μμ ) < 3.9 x 90% C.L. Br( Bdà μμ ) < 0.6 x 95%C.L. CMS 1.14L- s=7tev Br( Bsà μμ ) < 1.6(1.9) x 90(95)%C.L. Br( Bdà μμ ) < 0.37(0.46) x 90(95)%C.L. LHCb 0.3L- s=7tev Br( Bsà μμ ) < 1.3(1.6) x 90(95)%C.L. Br( Bdà μμ ) < 0.42(0.52) x 90(95)%C.L. Events observed!?

32 Future prospects 2012? 2012?

33 Back up

34 VELO 21

35 TT

36 The LHCb Detector at the LHC The LHCb bibliography Search for the very rare decays Bs/d µ+µ- at LHCb Serrano Search for B 0 s(d) µ+ µ with CMS Urs Langenegger Updated Search for Bs/Bd µ+µ at CDF Thomas Kuhr h p://lpc.web.cern.ch/lpc/lumiplots.htm (Many materials from this slide) Search for the rare decays Bs µ+µ- and B0 µ+µ with the LHCb Experiment Johannes Albrecht Panning for the Golden Decay B 0 s Jan Amoraal J/ψφ at LHCb