1 Ю. Щеглов, А.Дзюба, А.Воробьёв, Н.Сагидова ПИЯФ Статус поиска распада Bs 2µ в LHCb. Новогодняя научная сессия ОФВЭ 27 Декабря 2011 µ µ 12/27/2011Юрий. - презентация

1 1 Ю. Щеглов, А.Дзюба, А.Воробьёв, Н.Сагидова ПИЯФ Статус поиска распада Bs 2µ в LHCb. Новогодняя научная сессия ОФВЭ 27 Декабря 2011 µ µ 12/27/2011Юрий Щеглов, Научная сессия ОФВЭ, ПИЯФ, Декабрь, 2011 Mμμ = GeV, BDT = 0.90, B meson decay length = 11.5 mm

2 OUTLOOK Introduction. Recent Bs,d 2 µ results Physics motivation LHCB detector. Fast facts Main backgrounds Strategy of the analysis. List of BDT input parameters Bs 2 µ analysis jungle. Normalization channels. BDT response and invariant mass resolution calibrations Background estimates Extraction of the limit. Results and future plans Progress in Bs µ + µ- search during last 10 years Conclusions 12/27/2011Юрий Щеглов, Научная сессия ОФВЭ, ПИЯФ, Декабрь,

3 Introduction. B mesons penguin diagram decays SM forbids flavor-changing neutral currents (FCNC) diagrams FCNC can be introduced by penguin one loop diagrams If some B-meson decays can be realized only via penquin diagram decay, these decays can be sensitive to the new physics 12/27/2011Юрий Щеглов, Научная сессия ОФВЭ, ПИЯФ, Декабрь, Decay examples: Bs2µ, BdK*μ+μ-, BdK*γ, Bsφγ, etc...and many of them now can be studied at LHCB detector

4 Introduction. Bs 2 µ decay. Existing upper limits Observed upper limits at the Tevatron and LHC before summer 2011 : CDF observed limit at L = 3.7 fb-1 : Br (Bs 2µ ) < 4.3 x10-8 (95% CL) Br (Bd 2µ ) < 7.6 x10-8 (95% CL ), [ CDF public note 9892 ] D0 observed limit at L = 6.1 fb-1 : Br (Bs 2µ ) < 5.1 x10-8 (95% CL), Phys. Lett. B 693, 539 (2010), [arXiv: ] LHCB published observed limit at L = 37 pb-1 : Br (Bs 2µ ) < 5.6 x10-8, Br (Bd 2µ ) < 1.5 x10-8 at 95% CL, Phys. Lett. B (2011), [hep-ex/ ] LHCB provided approximately the same result as CDF with 100 times less integrated luminosity! (more higher cross –section, better geometric and muon pT acceptance) …but last summer news from CDF arXiv: [hep-ex] : 0.46 x 10-8 < BR < 90% CL, (BR= ) x 10-8 Not confirmed. Huge signal fluctuation ?? Юрий Щеглов, Научная сессия ОФВЭ, ПИЯФ, Декабрь, /27/20114

5 Physics motivation: Bs 2 µ Standard Model diagrams Bs 2 µ is double suppressed decay: FCNC process and helicity suppressed 12/27/2011Юрий Щеглов, Научная сессия ОФВЭ, ПИЯФ, Декабрь, As a result SM diagrams give branching ratios: Br(Bs 2 µ) =(3.2±0.2) x10-9, Br(Bd 2 µ) = (1.1±0.1) x10-10, (A.J.Buras: arXiv: , E. Gamiz et al: Phys.Rev.D 80 (2009) )

6 Physics motivation: MSSM models Click to edit Master text styles – Second level – Third level Fourth level – Fifth level 12/27/2011Юрий Щеглов, Научная сессия ОФВЭ, ПИЯФ, Декабрь, 2011 Bs 2 µ branching ratio can be very sensitive to the SUSY diagrams contributions. Two Higgs-Dublet (2HDM) model provides a big contribution in the region of the large tan β NUHM1 model. The indirect Bs 2 µ search power (blue regions) can be comparable with the results of direct SUSY searches (gray region): 6

7 Physics motivation: mSUGRA model Юрий Щеглов, Научная сессия ОФВЭ, ПИЯФ, Декабрь, 2011 If we believe to the G-2 experiment restriction (light blue color) we have very exiting time on LHCB now, because LHCB has a plan to reach the sensitivity Br(Bs 2 µ ) ~ 7-8 x 10-9 (90% CL) with the 2011 year experimental data G-2 restrictions Evaluation of the Br(Bs 2 µ ) behavior for the different mSUGRA model parameters 12/27/20117 G-2 collab. David Hertzog: We are central to the US Intensity Frontier..

8 LHCb detector Click to edit Master text styles – Second level – Third level Fourth level – Fifth level Юрий Щеглов, Научная сессия ОФВЭ, ПИЯФ, Декабрь, 2011 Detectors are critical for the analysis : M1, M2, M3, M4, M5 – muon stations VELO (Vertex Locator) – vertex detector TT, T1,T2,T3 – tracking stations RICH1, RICH2 – Cherenkov detectors 12/27/20118 Data taking efficiency close to 91 % including data quality!

9 12/27/2011Юрий Щеглов, Научная сессия ОФВЭ, ПИЯФ, Декабрь, Fast facts σ inelastic(pp, s=7 TeV ) = 60 mb, σ(bb) = ±28.9 µb Number of bunches Lmax = 4 x 1032, ~ 2.65 x 1032 cm-2s-1 Average number of interactions v = 1.6 The total recorded luminosity (today), Ldt = 1100 pb b decays in our acceptance Ldt = 370 pb-1 used for the last BS μμ analysis muon identification efficiency : ε(μμ) ~ 98% misidentification rate ε(hμ) 10 GeV/c invariant mass resolution : σ (M Bs,dµµ) = 26 MeV/c2 impact parameter resolution: σ(IP) =25 μm at pT=2 GeV/c Luminosity and interactions Parameters are relevant to the BS μμ analysis

10 Main backgrounds 12/27/2011Юрий Щеглов, Научная сессия ОФВЭ, ПИЯФ, Декабрь, 2011 bb X events can be suppressed using different geometric and kinematic criteria photoproduction dimuon background Isolated muons with a possible contribution to the Bs mass region (removed at pT(B)> 500 MeV/c) misidentified muons from Bd/s h+h- decays ( contribution from Bd/s h+h- can be calculated from Bd/s h+h- MC with a known misidentification probablity measured in data Resulting misID expectations for the 300 pb-1: 0.5±0.4 misID events in Bs mass region 2.5±0.5 misID events in Bd mass region 10 After reconstruction the SM prediction for 300 pb-1 is 3.4 (0.32) BS (Bd) μμ events

11 Strategy. Key points of the analysis Selection conditions Muon trigger used Preliminary selections to reduce datasets size Blind signal region 5306 < MBs

12 List of input parameters for Boosted Decision Tree method 12/27/2011Юрий Щеглов, Научная сессия ОФВЭ, ПИЯФ, Декабрь, Transverse momentum of the Bs - meson Minimum muon pT Cosine of the Bs polarization angle, cos P Bs meson impact parameter, IP_Bs Minimum distance between muon tracks, DOCA Muon track impact parameter significance, IPS_µ Bs time life, t(Bs ) Muon isolation Bs isolation A decision tree is able to split the phase space into a large number of hypercubes, where each can be identified as signal-like or background-like The phase space in the analysis is defined by 9 input parameters:

13 Normalization channels 12/27/2011Юрий Щеглов, Научная сессия ОФВЭ, ПИЯФ, Декабрь, 2011 Click to edit Master text styles – Second level – Third level Fourth level – Fifth level B+J/ K+BSJ/ B0 -K+ Calculated from MCMeasured from dataNumber of events in normalization channel To calculate the Bs + - branching ratio we need to know the total number of Bs mesons and next to use this number for the normalization We have used 3 normalization channels : Fragmentation ratioNormalization channel branching *combined LHCB measurements 13 Final numbers for 370 pb-1

14 BDT response calibration 12/27/2011Юрий Щеглов, Научная сессия ОФВЭ, ПИЯФ, Декабрь, 2011 For the calibration of signal BDT response we have used the data from B mesons hadronic decays - Bd/s h+h- (Bd/s KK, K, ) The main advantage is same topology as Bs + -. The problem is a difference between muon and hadronic trigger. As a result for the signal calibration only events triggered independently from the - Bd/s h+h- signal were used The calibration results: the probability density function for the signal is almost flat (dark squares on the plot) the probability density function (blue circles on the plot) for the combinatorial background is obtained from the dimuons in the Bs + - mass sidebands LHCb preliminary 300 pb-1 LHCb preliminary 300 pb-1 14

15 Invariant mass calibration 12/27/2011Юрий Щеглов, Научная сессия ОФВЭ, ПИЯФ, Декабрь, 2011 Invariant mass shape modeled by a Crystal Ball function (Gaussian core portion + low end tail) To calculate the resolution we interpolate dimuon resonances (J/ψ, ψ(2s), Upsilons) masses σ(Bs) = (24.6±0.2±1.0) MeV/c2 σ(Bd) = (24.3±0.2±1.0) MeV/c2 The calculated resolutions were checked up with the invariant mass shape of Bs K+K- and B0 K+π- decays LHCb 300 pb-1 LHCb 300 pb-1 σ(J/Ψ) = 16 MeV/c2 σ(Y) = 40 MeV/c2 As a result we have : 15

16 Юрий Щеглов, Научная сессия ОФВЭ, ПИЯФ, Декабрь, 2011 Background estimates The combinatorial background estimate was derived from a fit of the mass sidebands for BDT bins with the blind signal region The systematics of the backround prediction was studied using the exponential, double exponential and linear fitting functions 12/27/201116

17 Bs Signal mass region for BDT response bins Юрий Щеглов, Научная сессия ОФВЭ, ПИЯФ, Декабрь, 2011 As we can see we have good enough agreement between expected background, Standard Model predictions and number of events observed in the signal region 12/27/ black dots are data; the light grey shows the contribution of the combinatorial background; the dark grey the contribution of SM Bs2µ events

18 Expected combinatorial background events, expected peaking and signal events (SM branching) search window. 12/27/2011Юрий Щеглов, Научная сессия ОФВЭ, ПИЯФ, Декабрь,

19 Extraction of the limit 12/27/2011Юрий Щеглов, Научная сессия ОФВЭ, ПИЯФ, Декабрь, 2011 mass window MBs,d± 60 MeV BDT distribution for signal and background µµ mass – BDT response plane The CLs analysis was performed in 2D space (dimuon mass – BDT response) For the each observed event we calculated a probability to be compatible with the Signal + Background hypothesis or only Background hypothesis as a function of the branching ratio. Next we exclude the assumed branching ratio value at a given confidence level 19

20 LHCB upper limit with the 370 pb data Юрий Щеглов, Научная сессия ОФВЭ, ПИЯФ, Декабрь, 2011 Combination with 2010 data (37pb-1), Br < 1.4 x 10-8 at 95 % CL Improvement with the factor ~4 by comparison with the 2010 data result! 12/27/ Br(Bs2µ) upper limit with 370 pb-1Br(Bd2µ) upper limit with 370 pb-1 Results of CLs analysis for Bs2µ and Bd2µ decays

21 Future plans year 12/27/2011Юрий Щеглов, Научная сессия ОФВЭ, ПИЯФ, Декабрь, 2011 Exclusion curves for the Bs µ + µ - branching 3 sigma evidence curves We have a chance to exclude Bs µ + µ - decay on the level Br =5.5÷11 x 10-9 at the 95% CL with the recorded integrated luminosity 1.1 fb-1.. or to provide 3 sigma evidence for the Br = 3.3÷8 x 10-9 (3.3 x 10-9 SM level!) 21

22 Tevatron and LHC progress in Bs µ + µ- search 12/27/2011Юрий Щеглов, Научная сессия ОФВЭ, ПИЯФ, Декабрь, ~ 200 times for 10 years LHCB + CMS CDF+D0

23 Conclusions LHCb with the integrated luminosity 370 pb-1 provided the upper limits - Br (Bs µ + µ - )< 1.4 x 10-8 at 95 % CL and Br(Bd µ + µ - )< 3.2 x 10-9 at 95 % CL LHCB-CMS combined result Br(Bs µ + µ -) < 1.1 x 10-8 at 95 % CL (CMS result Br(Bs 2µ) < 1.8 x 10-8 (95 % CL) Excess of the Bs µ + µ - events reported by CDF (hep-ex/ ) not confirmed LHCb plans: to reach the sensitivity Br(Bs 2µ) = 8 x 10-9 (95 % CL) with the existing integral luminosity L = 1.1 fb-1 We hope to get a 3 σ evidence or better for the Bs 2µ SM signal with the additional integrated luminosity L = 1.5 fb-1 in the next 2012 year Юрий Щеглов, Научная сессия ОФВЭ, ПИЯФ, Декабрь, /27/ С наступающим Новым Годом! PNPI participation: we are in primary authors in two last LHCb Bs 2µ papers: hep-ex/ , arXiv: v2

24 12/27/2011Юрий Щеглов, Научная сессия ОФВЭ, ПИЯФ, Декабрь, Backup slides

25 Search for NP in BdK*μ+μ- 12/27/2011Юрий Щеглов, Научная сессия ОФВЭ, ПИЯФ, Декабрь, Forward-backward asymmetry AFB of lepton system as a function of lepton invariant mass (q2) is sensitive to the helicity structure of New Physics The rare decay B0 K0μ+μ is a b s, flavour changing neutral current decay, mediated by electroweak box and penguin diagrams in the SM New particles (beyond the SM )can enter in competing loop-order diagrams resulting in large deviations from SM predictions

26 12/27/2011Юрий Щеглов, Научная сессия ОФВЭ, ПИЯФ, Декабрь, Results from CDF and B-factories show possible disagreement with SM at low q2 Search for NP in BdK*μ+μ- Despite Standard model predictions experiments demonstrate positive magnitudes for the AFB in the region 0< q2 < 4 GeV2/c4

27 12/27/2011Юрий Щеглов, Научная сессия ОФВЭ, ПИЯФ, Декабрь, Events selection using Boosted Decision Tree from sample of 309 pb-1 Veto decays in J/Ψ and Ψ(2S) resonance regions Search for NP in BdK*μ+μ-

28 12/27/2011Юрий Щеглов, Научная сессия ОФВЭ, ПИЯФ, Декабрь, Data are consistent with the SM predictions at present sensitivity and indicate for the first time that the asymmetry is changing sign as predicted by the SM LHCb result based on 309 pb-1 and 300 candidates C. Bobeth et al. [arXiv: v2] LHCb-CONF Search for NP in BdK*μ+μ-

29 12/27/2011Юрий Щеглов, Научная сессия ОФВЭ, ПИЯФ, Декабрь, Search for NP in BdK*μ+μ-

30 30 CP violation in Charm CERN seminar yesterday, paper submitted to PRL CP-violating asymmetries in charm provide a unique probe of physics beyond the Standard Model (SM) SM charm physics is (almost) CP conserving New Physics can enhance CP-violating observables CP violation in charm not observed 12/27/2011Юрий Щеглов, Научная сессия ОФВЭ, ПИЯФ, Декабрь, 2011

31 31 CP violation in Charm D flavour tagged with slow pion from D* Productio n PhysicsDetector 1 kHz of trigger bandwidth allocated to charm 1.4 million candidates 12/27/2011Юрий Щеглов, Научная сессия ОФВЭ, ПИЯФ, Декабрь, 2011

32 32 CP violation in Charm Result stable over time different magnet polarities and changing cuts First 3.5σ evidence for CP violation in charm sector! Analysis based on 60 % of collected data. Update on full dataset for Winter Conferences. In addition parallel measurement possible using semi-leptonic B decays to tag D flavour 12/27/2011Юрий Щеглов, Научная сессия ОФВЭ, ПИЯФ, Декабрь, 2011

33 33 CP violation in Charm Measure essentially direct CP Result attracting theoretical interest Before LHCb result consensus measurement at this level signified NP (Phys Rev D75 (2007) ] ) Conclusion now being revisited (e.g arXiv: ) 2010 LHCb study of indirect CP violation [LHCb-CONF ] 12/27/2011Юрий Щеглов, Научная сессия ОФВЭ, ПИЯФ, Декабрь, 2011