Recent results from LHCb on searches for new physics

Transcription

1 Recent results from LHCb on searches for new physics M. Witek (IFJ PAN Cracow, Poland) On behalf of the LHCb Collaboration Theory Meeting Experiment 2013 Warsaw, Poland 850 physicists 17 countries 63 institutes CERN LHC Large Hadron Collider LHCb CMS Atlas Alice

2 Outline Introduction LHCb experiment Selected results. As of today 122 papers in the list at Searches for New Physics Rare decays CPV for beauty CPV for charm Standard measurement Precision measurement of X(3872) quantum numbers Summary 2

3 CPV and Baryogenesis Planck satellite n n baryon baryon baryon 10 n n n ~ O 10 The source of current matter domination over antimatter is unknown. CPV is one of the three necessary conditions (Sacharow 1967) d' V The unique source of CPV in Standard Model is a s' V single phase in the CKM matrix b' V ud cd td V V V us cs ts V V V ub cb tb d s Vˆ b CKM d s b CPV predicted in SM gives Δn baryon /n γ ~O(10-20 ). It is too small. There must be other CPV beyond SM 3

4 Two ways of search for New Physics Direct observations Probe up to ~4 TeV Direct production of new objects at s =14 TeV LHC operates now at s =8 TeV only Indirect searches Probe up to ~100 TeV Precision measurements of well predicted observables in SM, in particular these with small values, search for suppressed processes. Examples of indirect discoveries: Prediction of third generation of quarks (b,t) to introduce CPV in SM c and t quarks first seen in FCNC processes in K and B mesons (ν+n ν+n) seen in 1973; direct Z observation 10 years later 4

5 LHCb experiment LHCb physics programme Search for New Physics (NP) which may appear in CP violation or in rare decays mediated by new particles at high mass scale Atlas/CMS and LHCb are complementary CMS/ATLAS: direct search for New Physics LHCb: indirect search for New Physics 5

6 LHCb detector Forward spectrometer with 15 < θ < 300 mrad and Bdl = 4Tm VELO: silicon strip detector for precise secondary vertex reconstruction TT,T1,T2,T2: tracking stations, silicon strip and straws for charged particles RICH1, RICH2: ring imaging Cherenkov detectors (π/k/p separation) ECAL, HCAL: electromagnetic & hadronic calorimeters (trigger and neutrals) M1-M5: tracking stations for muon identification 6

7 Trigger system Challenge is to efficiently select most interesting beauty and charm decays. while maintaining manageable data rates Main backgrounds minimum bias inelastic pp scattering other beauty and charm decays On-line charm and strange signals Signal/background ratio used to inspect data quality 7

8 LHCb performance summary plot Monte Carlo Fast oscillations of B s neutal mesons Data Δm s = ± (stat) ± (syst) ps 1 Demanding measurement which includes all: momentum resolution tracking resolution & efficiency particle identification, flavour tagging, trigger New J. Phys.15 (2013)

9 Rare decays B s,d μ + μ - D 0 μ + μ - K 0 s μ + μ - B d K*μ + μ - 9

10 B 0 (s) μμ GIM and helicity suppressed in SM Very high sensitivity to New Physics, eg. CMSSM and NUHM1: [O. Buchmuller et al, arxiv: v2, May 2012] 10

11 Analysis strategy B 0 (s) μμ Phys. Rev. Lett.110 (2013)

12 BDT discriminant - B 0 (s) μμ BDT discrimination is performed using 9 input variables. The topological variables are chosen to avoid correlation with invariant mass i.e. kinematical variables of B and μ related to impact parameter, vertex isolation, transverse momenta, 12

13 B 0 (s) μμ Phys. Rev. Lett. 110 (2013)

14 B 0 (s) μμ Phys. Rev. Lett. 110 (2013) First evidence 14

15 B 0 (s) μμ Unoffficial compilation based on arxiv: (D. M. Straub) 15

16 D 0 μμ FCNC has been extensively studied in the strange and beauty sectors In the charm sector most effectively suppressed by the GIM mechanism Absence of a high mass down type quark Small D mixing and small BR of rare D decays D 0 μμ dominated by the long distance contribution to the two-photon intermediate state SM Long distance SM limit > 6 x Best exp limit from Belle Phys. Rev. D81 (2010) orders of magnitude to gain before reaching the SM long distance contributions 16

17 D 0 μμ arxiv:

18 D 0 μμ [arxiv: ] arxiv: ] 18

19 K 0 s μμ SM Exp BR(K 0 L μμ) ~ ρ ( 6.85 ± 0.32 ) 10 9 ( 6.84 ± 0.11 ) 10 9 BR(K 0 S μμ) ~ η ( 5.0 ± 1.5 ) < Long (a) and short (b) contributions comparable NP contribution to BR(K 0 S μμ) at the level of is still allowed. 19

20 K 0 s μμ J. High Energy Phys.01 (2013) 090 L=1.0 fb -1 20

21 B 0 K * m + m Sensitive to NP in loops which modify angular distributions (SUSY, graviton exchange, extra dimension). Forward-backward asymmetry A FB sensitive to modification of the helicity structure. A FB (q 2 ) asymmetry in the m + m rest frame, q 2 = m 2 m+m Phys. Rev. Lett.110 (2013) q 2 at zero of A FB is a good probe of NP 21

22 CPV for beauty decays 22

23 ϕ s - the phase of CPV for B s How to measure the phase ϕ s? Interference of two amplitudes B s J/y f - golden mode B s J/y f 0 - independent measurement 23

24 ϕ s - the phase of CPV for B s Mixture of CP-odd and CP-even Need angular analysis >97.7% CP-odd No angular analysis arxiv: Phys. Lett. B713 (2012)

25 BR(B 0 s μμ) ϕ s - the phase of CPV for B s Unoffficial compilation based on arxiv: (D. M. Straub) The world most precise measurements arxiv: Comparison with other experiments Impact of ϕ s measurement (together with BR(B 0 s μμ) S ψφ = -sin ϕ s 25

26 CPV for charm decays 26

27 Direct CP violation in D 0 decays D 0 mixing now established but CPV not yet seen experimentally In SM, indirect CP violation in charm is expected to be very small asymmetries A CP ~ O(10-5 ) Direct CP violation can be a bit larger in SM: A CP ~ O(10-3 ) - O(10-4 ) Both direct and indirect CPV can be affected by New Physics: A CP up to O(10-2 ) Measure difference between two asymmetries ΔA CP between D *+ D 0 (K + K - )π + and D *+ D 0 (π + π - )π + A D and A P cancel. Nearly all systematic effects cancel in the double difference ΔA CP measures direct CPV for charm 27

28 Direct CP violation in D 0 decays At the end of 2011 LHCb presented 3.5σ evidence for direct CPV in 0.6/fb sample ΔA CP = [ ± 0.21(stat) ± 0.11(syst) ]% Phys. Rev. Lett. 108 (2012) Two new analyses were presented in Moriond QCD2013. Independent samples, totally different systematics: D* prompt sample, updated with full 2011 reprocessed data (1/fb) D 0 from a sample of B D μ ± X (1/fb), with D 0 flavor tagged by the sign of the μ 28

29 Direct CP violation in D 0 decay ΔA CP with prompt D* The result is closer to zero that the result in 2011, but the shift is consistent with originating from the larger statistics (LHCb-CONF ) ΔA CP with semileptonic tag (Phys. Lett. B 723 (2013) 33-43) The results are statistically compatible (2.2 σ) LHCb results combined ΔA CP = (-0.15 ± 0.16)% New preliminary world average ΔA CP = (-0.33 ± 0.12)% Previous evidence for CPV in charm not confirmed 29

30 X(3872) 30

31 arxiv: X(3872) quantum numbers X(3872) found 10 years ago by Belle. J PC narrowed to 1 ++ or 2 -+ by CDF The angular correlations in the B+ decay carry information about X(3872) quantum numbers. Details in arxiv: and refs therein. 5D fit to angular variables to test against J PC hypotheses 31

32 X(3872) quantum numbers Projection of 5D fit 2*10 6 toy experiments arxiv: J PC = 2 -+ rejected at 8σ y J PC =1 ++ favours unconventional explanations (such as D*D molecule, tetra-quarks) 32

33 Summary Indirect measurements probes New Physics at mass scales orders of magnitude above 100 GeV The LHCb performed many precise measurements searching for the phenomena beyond the Standard Model World s most sensitive measurements of mixing and CPV in b- and c-hadron decays. World s most sensitive measurements of very rare b- and c-hadron decays No sign of New Physics seen yet 200% of additional data is being analysed currently 33

34 Backup slides 34

35 Mixing of B (s) 0 mesons Flavour eigenstates are not mass eigenstates, both are not CP eigenstates. Eigenstates differ by Δm i ΔΓ Large mixing, large CPV test SM CPV Fast mixing, small CPV test non SM CPV LHCb specialty 35

36 B 0 K * m + m angular observables 36

37 B 0 (s) μμ 37