The LHCb Experiment: First Results and Prospects. Mitesh Patel (Imperial College London) RHUL Particle Physics Seminar, 26 th Oct 2011

Size: px

Start display at page:

Download "The LHCb Experiment: First Results and Prospects. Mitesh Patel (Imperial College London) RHUL Particle Physics Seminar, 26 th Oct 2011"

Elfreda Summers
5 years ago
Views:

1 The LHCb Experiment: First Results and Prospects Mitesh Patel (Imperial College London) RHUL Particle Physics Seminar, 6 th Oct 011

2 Outline An extended Higgs sector? (B d µ + µ and B s µ + µ - ) New CP violating phases in B s mixing? (φ s from B s J/ψφ) New particles, couplings? (angular observables in B d K*µµ) A whistlestop tour Will try and give you a feel for the prospects in each of these areas Results from partial 011 dataset ~300 pb-1 Now have ~3 times this on tape

3 The decays B d µ + µ and B s µ + µ - 3

4 Introduction The branching ratios of the decays B d µ + µ and B s µ + µ - allow the parameters of an extended Higgs sector to be probed The decays are doubly suppressed in the SM FCNC Helicity suppression However, rates well calculable in the SM, B(B s µ + µ ) = (3.±0.) 10-9 B(B d µ + µ ) = (1.0±0.1) [Buras et al., arxiv: ] Sensitive to NP contributions in the scalar/pseudo-scalar sector: ( ) ( ) MSSM, large tanβ approximation 4

Motivation fully complementary to direct searches at ATLAS/CMS tanβ vs M A plane Best fit contours in tanβ vs M A plane in the NUHM1 model [O. Buchmuller et al., arxiv:0907.

5 Motivation fully complementary to direct searches at ATLAS/CMS tanβ vs M A plane Best fit contours in tanβ vs M A plane in the NUHM1 model [O. Buchmuller et al., arxiv: ] 5σ discovery contours for observing the heavy MSSM Higgs bosons H, A in the three decay channels H,A τ + τ - jets (solid line), jet+µ (dashed line), jet+e (dotted line) assuming 30 fb -1 collected by CMS 5

Motivation fully complementary to direct searches at ATLAS/CMS tanβ vs M A plane [F. Mahmoudi, arxiv: 08083144]!"#$ %& #"#$ %& '"#$ %(!

6 Motivation fully complementary to direct searches at ATLAS/CMS tanβ vs M A plane [F. Mahmoudi, arxiv: ]!"#$ %& #"#$ %& '"#$ %(!"#$%&' Measuring BR(B s µ + µ ) at the level would be like probing similar region to that of H,A τ + τ - search with 30 fb -1 6

Experimental Results (before the summer) Published B s µµ limits @ 95% CL Experiment

7 Experimental Results (before the summer) Published B s µµ 95% CL Experiment Data set Limit CDF 3.7 fb x 10-8 D0 6.1 fb x 10-8 LHCb fb x

8 New CDF Result (July 011) New CDF result based on: double sample size (3.7 fb -1 7 fb -1 ) +0% acceptance for muons improved Neural Network M µµ distribution in Bs search window for different NN bins Barrel-barrel background Barrel-endcap Signal (SMx5.6) 8

9 New CDF Result (July 011) 0.46 x 10-8 < BR < 90% CL (BR= ) x LHCb should 10-8 observe ~0.8 σ assuming bkg-only hypothesis events! 1.9% compatibility with bkg+sm hypothesis M µµ distribution in Bs search window for different NN bins Barrel-barrel background Barrel-endcap Signal (SMx5.6) 9

10 The Experimental Environment σ(pp, s=7 TeV ~60 mb, only 1/00 events contains a b quark, looking for BR ~10-9 In nominal conditions LHCb would operate at an instantaneous luminosity of 10 3 cm - s -1, 50 lower than ATLAS/CMS, with a mean number of pp interactions per crossing ~0.5 However, during 011 data-taking, reduced number bunches; to get high luminosity smaller β* Mean number of pp interactions of 1.5 (3 design) Instantaneous luminosity cm - s -1 (1.5 design) Using luminosity leveling to keep this constant during fill 10

11 The LHCb Detector 11

identification: ε(µ µ) ~97% for ε(h µ)<1% for p>10 GeV/c Very good mass resolution: δp/p~ 0.35% 0.

12 Key ingredients for B s,d µ + µ Efficient trigger: p T cuts on muons kept low ε(trigger B s,d µ + µ ) ~ 90% Background reduction: Excellent vertex & IP resolution: σ(ip) ~5 p T = GeV/c Particle identification: ε(µ µ) ~97% for ε(h µ)<1% for p>10 GeV/c Very good mass resolution: δp/p~ 0.35% 0.55% for p=(5-100) GeV/c σ(mb s,d ) ~ 6 MeV [CDF: 5 MeV, CMS: 40 >80 MeV] Signal = 87 ± 73 σ = (15.0 ± 0.4) MeV 1

13 Analysis Strategy Soft selection: Reduces the dataset to a manageable level Discrimination between S and B via MultiVariate Discriminant variable (Boosted Decision Tree) and Invariant Mass (IM) Events in the sensitive region are classified in bins of the D plane Invariant Mass-BDT Normalisation: Convert the signal PDFs into a number of expected signal events by normalising to channels of known BR (get rid of L and σ(bb)) use B + J/ψK +, B s J/ψφ, B d Kπ; use measured f d /f s = [arxiv: ] Extraction of the limit: Assign to each observed event a probability to be S+B or B-only as a function of the BR(B s,d µ + µ ) value; exclude (observe) the assumed BR value at a given confidence level using the CLs binned method 13

14 LHCb B s,d µ + µ analysis M(µµ) vs BDT plane 4 BDT bins 6 mass bins Search windows (M(B s,d ) ± 60 MeV BDT distributions for signal and background 14

15 Calibration The analysis has been design to extract all the relevant quantities from data mass lineshape & BDT shape from B hh events Background in search window Bd mass window Bs mass window Bà hh sample for calibra0on expected background in search windows from fit of data sidebands 15

Result: B d µ + µ (300pb -1 ) Bà hh misid background BDT<0.5 0.5<BDT<0.5 0.5<BDT<0.75 0.75<BDT Exp.

16 Result: B d µ + µ (300pb -1 ) Bà hh misid background BDT< <BDT< <BDT< <BDT Exp.combinatorial 3175 ± ± ± ± 0.4 Exp. MisID 0.6± ± ± ± 0.1 Observed

17 Result: B d µ + µ (300pb -1 ) CDF: 6.0 x 95% CL 17

18 Result: B s µ + µ (300pb -1 ) BDT< <BDT< <BDT< <BDT Exp.combinatorial 968 ± 69 5 ±.5.99 ± ± 0.40 Exp. SM signal 1.6 ± ± ± ± 0.07 Observed

Result: B s µ + µ (300pb -1 ) BDT<0.5 0.5<BDT<0.5 0.5<BDT<0.75 0.75<BDT Exp.combinatorial 968 ± 69 5 ±.

19 Result: B s µ + µ (300pb -1 ) BDT< <BDT< <BDT< <BDT Exp.combinatorial 968 ± 69 5 ±.5.99 ± ± 0.40 Exp. SM signal 1.6 ± ± ± ± 0.07 Observed

20 A B s µ + µ candidate? 0

21 Result: B s µ + µ (300pb -1 ) background only hypothesis Background + signal with BR=BR(SM) 011 only LHCb combined 1. x x10-8 CMS 1.14J x x

22 CMS/LHCb Combination Combination has been performed by LHCb just adding CMS bins (1 for barrel, 1 for endcap): CMS+LHCb combined 95% exclusion limit BR(B s à µµ) < 1.1 x 95% CL (3.4xSM)

23 Impact on Global SUSY Fits F. Ronga for MasterCode Collaboration at Workshop LHC results for TeV scale physics, CERN, August 011 tanβ vs M A plane pre-lhc data Now in interesting situation where direct searches push M A, tan β up, and B s µ + µ (~tan 6 β) tries to push down Fit probabilities for constrained models ~10% 3

Projections for early 01 011 exclusion curve @ 95% CL (bkg+sm hyp.

24 Projections for early exclusion 95% CL (bkg+sm hyp.) For the winter conferences (assuming no changes in the analysis / data quality) LHCb might put a limit down to 95%CL or could claim a 3 sigma evidence if the BR is ~8 x10-9 LHCb-CMS combined could claim a 3σ evidence if BR=(5-6)x10-9 4

25 The CPV Phase φ s 5

B s J/ψφ Introduction B s J/ψφ decay dominated by b ccs transition small penguin contribution, δp Interference between decay or mixing and then decay results in CP violating

26 B s J/ψφ Introduction B s J/ψφ decay dominated by b ccs transition small penguin contribution, δp Interference between decay or mixing and then decay results in CP violating phase: φ S = φ M -φ D SM prediction: φ S = -β s + δp ~ -β s = 0.04 J/ψφ is not a CP eigenstate required angular analysis (in transversity base) to statistically separate CP-even/odd 6

27 Experimental Status Rick van Kooten, Lepton- Photon 7

28 Principle of the measurement Three angles Ω=(θ, φ, ψ) describe directions of the J/ψ and φ 8

29 Road towards φ S at LHCb Select signal and control channels Determine lifetimes for: B s J/ψφ, B d J/ψK*, B d J/ψK S, Λ b J/ψΛ Angular analysis and determination of ΔΓ s Angular analysis of B d J/ψK* Untagged angular analysis of B s J/ψφ Determination of B production flavour Determination of B s mixing frequency Δm s Determination of φ S Tagged analysis of B s J/ψφ decays 9

30 Proper time resolution Measure using prompt J/ψ background Isolate using s-weights [LHCb-CONF ] Use simulation to verify that this background is representative for the signal % systematic error Effective resolution σ τ ~50 fs Measure B s oscillation frequency Δm s =17.75 ± ± 0.06 ps -1 [LHCb-CONF ] 30

31 Angular Analysis & Acceptance Corrections [LHCb-CONF ] Angular analysis in transversity basis: Acceptance correction for reconstruction and selection 3-dim. correction obtained from full simulation Acceptance Correction Maximum deviation from uniform 5% Deviations owe to Acceptance of detector 10< θ <400 mrad Implicit momentum cuts in reconstruction Verify using momentum distributions of final state particles Cross-check of complete procedure using another P VV decay B 0 J/ψK*(Kπ) 31

32 Flavour Tagging Use neural nets, trained on MC, to extract tagging decision and mis-tag probability, η Calibrate on data using selftagging decay modes such at B + J/ψK + Using only OS taggers, tagging power εd =.08±0.41% 3

33 B s J/ψφ Fit Projections Projections very well described Goodness of fit using point-to-point dissimilarity test statistic [arxiv: 1006:3019] p-value

34 φ s from B s J/ψφ Two ambiguous solutions φ s π-φ s ; ΔΓ s -ΔΓ s World s most precise measurement of φ s φ s = 0.13 ± 0.18 (stat) ± 0.07 (sys) rad consistent with SM prediction φ s SM = ± 0.00 rad [arxiv: ] 4σ evidence for ΔΓ s 0 ΔΓ s = 0.13 ± 0.09 (stat) ± (sys) ps -1 34

35 B s J/ψf 0 (980). f 0 (980) is a scalar with a ss cpt, decays predominantly in ππ Find f 0 (980) looks pure scalar CP odd final state no angular analysis required 35

36 B s J/ψφ and B s J/ψf 0 combination Simultaneous fit of B s J/ψφ and B s J/ψf 0 data φ s = 0.03 ± 0.16 (stat) ± 0.07 (sys) rad (+ ambiguous solution) With present statistics no evidence for deviation from SM Next steps: Add same-sign kaon tagging Break ambiguity by looking at s-wave phase vs m(kk) in B s J/ψφ Control penguin contamination : measure ACP(B s J/ψK*), exploit the U-spin relation between B s J/ψK* and B s J/ψφ [S. Faller et al., PRD 79:014005, 009] 36

37 B d K*µµ 37

B d K*µµ Introduction Flavour changing neutral current loop Sensitive to interference between O 7γ O 9,10 and their primed counterparts Exclusive decay theory uncertainty

38 B d K*µµ Introduction Flavour changing neutral current loop Sensitive to interference between O 7γ O 9,10 and their primed counterparts Exclusive decay theory uncertainty from form factors Altmannshofer et al, JHEP 0901:019,009 Multitude of observables in which uncert. cancel to some extent e.g. A FB, A T (i) zero-crossing point of A FB 38

errors too large to give real discrimination between SM and NP models

39 Experimental Status Babar, Belle and CDF have all measured angular asymmetry A FB : Measurements look consistent with each other but errors too large to give real discrimination between SM and NP models BABAR: PRL 10, (009); CDF: Note (010); Belle: PRL 103, (009) 39

40 Selection Selection: Remove cc resonances 946 <m µµ < 3176 MeV/c 3586 <m µµ < 3776 MeV/c Treat peaking backgrounds with a specific set of criteria ( residual backgrounds ~3% of signal) Combinatorial backgrounds reduced with a Boosted Decision Tree (BDT) selection Use Belle q binning and an (overlapping) 1<q <6 GeV /c 4 bin favoured by theorists ) (MeV / c M µµ M Kπµµ (MeV / c )

41 Boosted Decision Tree Train BDT on 010 data i.e. totally independent of 011 data sample Signal sample B d K*J/ψ data Bkgrd sample B d K*µµ mass sideband events Resulting selection Background-to-signal ratio ~0.3 Comparable to B-factories Does not induce further biases in cos θ L, cos θ K and q cf reconstruction biases introduced are primarily from detector geometry easy to model ) ) Events / ( 10 MeV/c Events / ( 0 MeV/c ( MeV/c ) Full q range B d K*µµ m Kπµµ 1<q <6 GeV / c 4 B d K*µµ ( MeV/c ) 41 m Kπµµ

42 Acceptance Correction Correct angular and q distributions for the effect of the detector and selection weight 6 5 LHCb simulation To be model independent, use an eventby-event weight which is determined on the basis of the θ L, θ K, q of the signal candidates that are found Simulation quality verified with range of control channels (B d K*J/ψ, J/ψ µµ, D* D 0 (Kπ)π) Tracking efficiency Hadron (mis-)identification probabilities Muon (mis-)identification Overall momentum and η distributions cthetak Weight depends on cos θ K Vast majority of events have weights ~1 cos θ K 4

43 Fit Procedure and Validation Simultaneous fit to the 1d projections of cos θ L, cos θ K and m Kπµµ in bins of q Events weighted according to acceptance correction Use Bayesian approach to construct stat. errors with flat prior over physical region Systematics effects are very small and can be reduced with further data Cross-check with a simple counting approach (don t use angular distributions) Validate fitting on B d K*J/ψ A FB consistent with zero, as expected s-wave contribution induces an asymmetry in cos θ K distribution, A FB K Acceptance correction makes cos θ K asymmetric symmetric Variation of A FB K with m Kπ matches BaBar data(**) across m Kπ range (**) BABAR: PRD 76, (007) 43

44 B d K*µµ yields ) Events / ( 0 MeV/c < q <.00 GeV /c ) Events / ( 0 MeV/c < q < 4.30 GeV /c ) Events / ( 0 MeV/c < q < 8.68 GeV /c ) Events / ( 0 MeV/c m Kπµµ ( MeV/c ) < q < 1.86 GeV /c m Kπµµ ( MeV/c ) ) Events / ( 0 MeV/c m Kπµµ ( MeV/c ) < q < GeV /c m Kπµµ ( MeV/c ) ) Events / ( 0 MeV/c m Kπµµ ( MeV/c ) < q 4 < GeV /c m Kπµµ ( MeV/c ) 44

45 B d K*µµ yields ) Events / ( 0 MeV/c < q <.00 GeV /c ) Events / ( 0 MeV/c < q < 4.30 GeV /c ) Events / ( 0 MeV/c < q < 8.68 GeV /c ) Events / ( 0 MeV/c m Kπµµ ( MeV/c ) < q < 1.86 GeV /c m Kπµµ ( MeV/c ) ) Events / ( 0 MeV/c m Kπµµ ( MeV/c ) < q < GeV /c m Kπµµ ( MeV/c ) ) Events / ( 0 MeV/c m Kπµµ ( MeV/c ) < q 4 < GeV /c m Kπµµ ( MeV/c ) 45

46 A FB Measurement Theory predictions from C.Bobeth et al., arxiv: v 46

47 A FB Measurement In 1<q <6 GeV / c 4 bin, A FB = -0.10±0.14±0.05 c.f. Belle ±0.07 Theory predictions from C.Bobeth et al., arxiv: v LHCb preliminary 47

48 F L Measurement Theory predictions from C.Bobeth et al., arxiv: v 48

49 F L Measurement In 1<q <6 GeV / c 4 bin, F L = ±0.03 c.f. Belle 0.67±0.3 ±0.07 Theory predictions from C.Bobeth et al., arxiv: v LHCb preliminary 49

50 d(br)/dq Theory predictions from C.Bobeth et al., arxiv: v 50

51 d(br)/dq LHCb preliminary Theory predictions from C.Bobeth et al., arxiv: v 51

52 Constraints on C 7 5

53 Constraints on C 7 53

B d K*µµ Outlook More data will enable a full angular fit to extract complete information from B d K*µµ decays host of theoretically well calculable observables S ~A T CP-

54 B d K*µµ Outlook More data will enable a full angular fit to extract complete information from B d K*µµ decays host of theoretically well calculable observables S ~A T CP- averaged angular coeff. Two more observables with a zero: S 4, S 5 S 6 ~A FB Correlation between measurements also of interest ~A T 3 ~A T 4 Ball et al. arxiv: v 54

55 B d K*µµ Outlook More data will enable a full angular fit to extract complete information from B d K*µµ decays host of theoretically well calculable observables S 6C ~ Re(C S - C S ), if phase of C S modified C P /C S =0 i.e. NP only from S terms Correlation between measurements also of interest C P /C S =- 1 (MSSM) µ>0,cmssm with large tan β µ<0,cmssm with large tan β 55

56 A whistlestop tour 56

57 CKM Measurements B s J/ψφ measurement about looking for NP in B s mixing Still scope for NP in B d mixing? CKM angle γ determined indirectly (68 ± 4) o Loop processes sin (β + φ NP bd ) cf. direct measurement of γ from tree processes ( currently ( ) o ) 57

58 CKM Measurements Time independent strategies: B + D(hh)K + B - à D 0 π - With D 0 à Kπ B 0 D(hh)Kπ + B + D(K S ππ)k + B + D(Kπππ)K + B s D s φ σ γ ~10 o with 1fb -1 Time dependent strategies: B s D s- K + B hh [loops] With D 0 à K s ππ With D 0 à KK With D 0 à ππ 58

59 B hh decays Work also in progress to extract γ from B hh decays In meantime direct CP asymmetries have been studied The measured asymmetries must be corrected for: Detector induced K + π - /π - K + charge asymmetries (D* D 0 (Kπ,KK)π) B production asymmetry (B 0 J/ψ(µµ)K*(Kπ)) 59

60 B hh decays Selecjon opjmised for A CP (B 0 Kπ) Selecjon opjmised for A CP (B s Kπ) 60

B hh decays Correcting raw asymmetries A CP (B 0 K + π - ) = -0.088 ± 0.011 ± 0.

61 B hh decays Correcting raw asymmetries A CP (B 0 K + π - ) = ± ± (5σ CPV in B system at HC) A CP (B s π + K - ) = 0.7 ± 0.08 ± 0.0 (1 st evidence CPV in B s πk) Also make first observation of B s π + π - (5.3σ) 61

Charm Enormous sample of charm decays also available at LHCb Already looked at CP asymmetry in 010 data (38pb -1 ) If take ΔA CP =A RAW (D 0 K + K - )-A RAW (D 0 π + π - ) production and soft pion

62 Charm Enormous sample of charm decays also available at LHCb Already looked at CP asymmetry in 010 data (38pb -1 ) If take ΔA CP =A RAW (D 0 K + K - )-A RAW (D 0 π + π - ) production and soft pion detection asymmetries will cancel No detector asymmetry i.e. all the D*-related production and detection asymmetries cancel Find ΔA CP =(-0.75 ± ± 0.5)% - comparable errors to B- factories, still a little off CDF 30 times more data on the way... 6

63 Searching for Majorana Neutrinos Lepton Number Violating decays B + h - µ + µ + (ΔL=) strictly forbidden in SM Sterile Majorana ν of mass O(1GeV/c ) could enhance BR significantly X + Q l + l + W + Q 1 ν M W q q 1 Y Analysis Strategy Tight selection, use opposite sign B + K - µ + µ decays as a proxy for signal Normalise to B + J/ψK + Detector performance measured from control channels used to estimate peaking bkgrd Observed signal / background <0.3 (0.1) bkgrd evts expected in πµµ (Kµµ) Zero events observed in both signal and mass sideband regions Candidates / ( 10 MeV / c Candidates / ( 10 MeV / c ) ) LHCb B + K - µ + µ (MeV / c ) M K µ LHCb B + J/ψK + µ (MeV / c ) M K J/ψ 63

Searching for Majorana Neutrinos Lepton Number Violating decays B + h - µ + µ + (ΔL=) strictly forbidden in SM Sterile Majorana ν of mass O(1GeV/c ) could enhance BR significantly X + Q l + l + W + Q

64 Searching for Majorana Neutrinos Lepton Number Violating decays B + h - µ + µ + (ΔL=) strictly forbidden in SM Sterile Majorana ν of mass O(1GeV/c ) could enhance BR significantly X + Q l + l + W + Q 1 ν M W q q 1 Y Analysis Strategy Tight selection, use opposite sign B + K - µ + µ decays as a proxy for signal Normalise to B + J/ψK + Detector performance measured from control channels used to estimate peaking bkgrd Observed signal / background <0.3 (0.1) bkgrd evts expected in πµµ (Kµµ) Zero events observed in both signal and mass sideband regions Candidates / ( 10 MeV / c Candidates / ( 10 MeV / c ) ) BR(B + K - µ + µ + ) LHCb < LHCb B + K - µ + µ (MeV / c ) M K µ µ - Observed 90% CL 500 BR(B + π - µ + B µ + J/ψK ) < Factor 00 40(30) improvement 100 cf previous best limit (CLEO) (MeV / c ) M K J/ψ 64

65 Conclusions B d µ + µ and B s µ + µ - World s best limits With the data collected in 011 should be able to explore BR~(6-7)x10-9 φ s from B s J/ψφ World s best measurement Add SS tagger, control penguin contamination to push errors down B d K*µµ World s best measurements New observables Large number of other analyses in progress CKM angle γ, charm physics, exotics should be a range of new results for winter conferences 65

66 f d /f s B 0 D - K + B 0 D - π + Combined: ( LHCb preliminary ) N(B 0 D - π + )=4109±75 N(B 0 D - K + )=53±1 N(B s0 D s- π + )=670±34 66

67 Signal Invariant Mass calibration Mass resolutions σ(m(b d,s )) from : 1) Bà hh inclusive sample: ) Interpolation from dimuon resonances The ϒ family: ϒ(1S), ϒ(S), ϒ(3S) Entries/(0 MeV) Mass histogram for!'s m!(1s) m!(s) µ = ± µ = ± 1 4 µ = ± 5 " 3 = 44.9 ± 0.4 " 4 = 47.3 ± 0.9 " 5 = 51 ± 5000 m!(3s) Events / ( 50 MeV/c ) LHCb 0 B "! +! B " [K! ]cc 0 + Bs " [K! - ]cc Bs " K K - # b " [pk ]cc - # b " [p! ]cc comb phys m µµ (MeV/c )! [MeV] mass (µ + µ ) [MeV] Interpolation of mass resolution at m_b s 55 " /N dof = / Const = 3.04 ± 0.4 Linear = ± # = M(B s,d ) 0 - similar kinematics/topology 15 - Selection identical to the signal one: à Avoid to using PID and use only events triggered by the other b to avoid bias in the phase space [eg resolution] 5 J/ψ, ψ(s) Mass resolution at m Bs :! = 6.83 ± mass (µ + µ ) [MeV]

68 Trigger for B s,d µ + µ Muon Lines L0 HLT1 HLT Single-µ: p T > 1.5 GeV/c µµ: p T1 p T >1.3 GeV/c single-µ: p T >1.8 GeV/c IP>0.11 mm Several di-muon lines with M µµ cuts and/or displaced vertex + Global Event Cuts for events with high multiplicity 1/3 of the available 3 khz bandwidth is given to the muon lines p T cuts on muons kept low ε(trigger B s,d µ + µ ) ~ 90% 17 68

69 µ ID performance & bkgrd composition µ ID performance measured with samples of J/ψ µµ, K s ππ, φ KK, Λ pπ Efficiency ε(µ µ) ~ Data (97.1 J/" detached ± 1.3)% MC J/" detached ! Momentum (MeV/c) Efficiency In the B q µµ p range: Data K s ε(π µ)~(7.1±0.5) 10 MC K -3 s ε(hh µµ)~(3.5±0.9) Momentum (MeV/c) Background is dominated by bb µµx component i.e. double semileptonic decays and cascade processes Mis-id µ + genuine µ ~10% and double mis-id µ ~0.3% Peaking bkgrd from B hh expect <0.1 evts in signal region 69

70 Measuring the BR Use the CL s binned method For each bin in the GL vs mass plane, the compatibility of the observed number of events with, S+B [CL S+B ] B only [CL B ] hypotheses is computed Get expected background from mass sidebands (in bins GL) For expected signal need mass and GL PDFs and an absolute normalisation GL Geometrical Likelihood vs Mass B d mass region LHCb B s mass region M(µ +,µ ) (MeV/c ) 70

71 Normalisation The signal PDFs can be translated into a number of expected signal events by normalising to a channel with known BR Three different channels used: 1) BR(B + J/ψ(µ + µ - ) K + ) = (5.98±0.) % uncertainty Similar trigger and PID. Tracking efficiency (+1 track) dominates the systematic in the ratio of efficiencies. Needs fd/fs as input use LHCb measurement fs/fd = [arxiv: ] 7% uncertainty ) BR(Bs J/ψ(µ + µ - )φ(k + K - )) = (3.35±0.9) % uncertainty Similar trigger and PID. Tracking efficiency (+ tracks) dominates the syst. 3) BR(B 0 K + π - ) = (1.94±0.06) % uncertainty Same topology as the signal. Different trigger dominates the syst. Needs fd/fs All three normalisation channels give compatible results: Weighted avge accounting for correlated systematic uncertainties 71

72 En passant, B s mixing frequency ΔM s (world best) " LHCb, preliminary result, 341/pb (LHCb-CONF ) Paper in preparation Compare older results: CDF (006) (PRL97,4003 (006)) LHCb, 37/pb (LHCb- CONF ) New WA fully dominated by LHCb result and in agreement with SM predictions: B s à D s π Combined with ΔM d from B factories: (R. van Kooten, LP011) 36

The LHCb Experiment: First Results and Prospects. Mitesh Patel (Imperial College London) The University of Birmingham, 4 th May 2011

The LHCb Experiment: First Results and Prospects Mitesh Patel (Imperial College London) The University of Birmingham, 4 th May 2011 Outline An extended Higgs sector? (B d µ + µ and B s µ + µ - ) New CP