Selection of latest LHCb results

Transcription

1 Selection of latest LHCb results A.Hicheur (UFRJ, Brazil) On behalf of the LHCb collaboration Xth SILAFAE conference, Medellin, Colombia November 2014

2 Outline Physics program LHCb experiment Highlights of recent results Prospects Conclusion 2

3 LHCb physics scope Main scope Use heavy flavours (b,c) decays to probe New Physics indirectly Deviations from Standard Model on cleanly-predicted observables Constraints on New Physics parameters even if no detected sign Precise measurements on weak couplings of quarks, CKM physics Understand better EW CP violation, as an input to the cosmological puzzle Other topics are considered Heavy Quarks production at pp collisions Properties of heavy hadrons (e.g., b baryons) EW and QCD physics in the forward region Search for exotics in the forward region 3

4 CKM picture: where we start... Weak interaction couples quarks through elements of the CabibboKobayashi-Maskawa (CKM) matrix Weak eigenstates are different from mass eigenstates = CKM matrix is not diagonal and may relate quarks of different generation u c t d s b V ud V us V ub V CKM = V cd V cs V cb V td V ts V tb ( ) ~1 ~0.2 ~ 0.04 ~ Clear hierarchy in the couplings: the further from diagonal, the weaker Unitarity imposes relations, among which V ik V *jk =0 k Elements forming sides (and angles) of 3 independent unitarity triangles, of which only a couple are of interest for heavy-flavour decays 4

5 ...and where we stand Most interesting relation: * ub * cb * tb V ud V + V cd V + V td V =0 Sides usually measured in semileptonic decays and oscillation frequency, angles in CP asymmetries * ub * cb * tb V us V + V cs V + V ts V =0 V ud V *ub B0d π + π * V td V tb B D K V us V * ub V cd V * cb * V ts V tb * V cs V cb s Bd triangle B0d J / ψ K S Bs triangle (very squeezed) B0s J / ψ h+ h- CKM picture verified but with higher precision, discrepancies could still arise, e.g. need for precise measurement of angle 5

6 LHCb detector Forward single-arm spectrometer with warm magnet (possibility to inverse polarity) Inside LHCb acceptance 10 m Optimize for b and c hadron studies Vertexing Tracking stations Particle ID Ring Imaging Cherenkov Calorimeters and Muon Chambers Acceptance 2 < < 5 Momentum resolution ~ 0.5% IP resolution ~ 20 m Time resolution ~ 45 fs 20 m 6

7 LHCb data ( ) 1011 protons per bunch colliding at 7 (2011) and 8 (2012) TeV Luminosity at IP8 (LHCb): 2-4 x 1032 cm-2 s-1 About 1500 charged particles produced at each pp collision (bb) ~ 75 7 TeV* in LHCb acceptance ~ 40% B+, 40% B0, ~ 10% Bs Remaining b baryons, Bc, etc... Output rate 3 khz in khz in 2012 * J. High Energy Phys.08 (2013) 117 7

8 Physics selected topics Unitarity triangle with trees or loops Charm physics CP Violation, mixing/decay Semileptonics Bs mixing Charmless 3 body decays EW and QCD in Forward region Z+b-jet production Rare Decays Bs,d ℓℓ Heavy hadrons studies Bc decays b excitations NP Exotics Massive long-lived particles 8

9 Determination of the angle From tree decays B D K * V ud V ub From loop decays γ = arg( * ) V cd V cb Current constraints from tree only Current constraints from loop only Only loop diagrams could involve new heavy particles: could there be a mismatch in the apex values? 9

10 from B DK, the idea Interference between tree decays leading to the same final state + D0 and D0 must decay to the same final state Theoretically very clean, ~ 10-7 (JHEP 1401 (2014) 051) ri: amplitude ratios AB i: relative strong phases 0 KD - AD In general: rd and fd used as external inputs B- ABrBei( B- ) 0 KD - ADrDei D fd 10

11 from B DK in LHCb Many channels under study in LHCb Using either CP, flavour, or multibody final states of D Published with 1 fb-1 (2011 data) B+ DK+ (D hh') PLB 712 (2012) 203, update on-going Bs DsK+ (neutral B) LHCb exclusive arxiv: , sub to JHEP B+ DK+ (D K3π ) PLB 723 (2013) 44 With 3 fb-1 (full Run I) B+ DK+ (D KShh) hep-ex/ , JHEP 10 (2014) 097 B0 D0K*0 (D hh') (neutral B) hep-ex/ , sub to PRD B+ DK+ (D KSKπ ) arxiv: , PLB 733C (2014) 36 11

12 Model-independent B D0(KSh+h-)K GGSZ method, PRD68 (2003) hep-ex/ JHEP 10 (2014) 097 Use full Run I statistics CPV: look at the B- - B+ difference in the K sh+h- Dalitz plot Use binned D decay phase space: model uncertainty removed by using CLEO-c data PRD 82 (2010) Binning optimized for statistical sensitivity KS + Ks - KS + x±=r B cos( δ B ± γ) Extraction of KSK+KKSK- y ±=r B sin(δ B± γ) KSK+ 12

13 B D(KSh+h-)K results KS + - hep-ex/ JHEP 10 (2014) 097 KSK+K- (Ks + -) K+ (Ks + -) K- 13

14 B D (KSK )K : ± 0 ± ± GLS method, PRD67 (2003) (R) B- arxiv: PLB 733C (2014) 36 B+ First measurement of this channel Contribution to measurement is still limited statistically Strong phase variation of D0 KSK± over Dalitz plane taken from CLEO PRD85 (2012)

15 Combination of results in tree decays LHCb-CONF Combining results from ± ± 0 0 B DK, B D K *0, and 0 s B Ds K LHCb Preliminary Frequentist = 72.9 Bayesian = Most precise single-experiment result 15

16 from loop decays arxiv: Submitted to PLB Use decays B0 and Bs to extract the angle, involve mainly tree + penguin loop diagrams W u W d,s s,d u,c,t b b u u g* u q q q q Two methods are considered and combined Fleischer, as in PLB 459 (1999) 306 Use of B0 and Bs and U-spin assumption Ciuchini et al., as in JHEP 10 (2012) 029, based on Gronau-London approach Use of and assuming isospin 16

17 from loop: summary of results arxiv: Submitted to PLB With up to 50% U-spin symmetry breaking ( = 0.5), one obtains: No improvement expected with statistics (impact of U-spin breaking) In the same fit, using constrained from tree measurements, one obtains: Expected improvement with statistics (less influence of U-spin and non-factorization) U-spin (k = 0.5) U-spin + isospin (k = 0.5) 68% interval 95% interval U-spin (k = 0.5) U-spin + isospin (k = 0.5) 17

18 Charmless 3 body decays B+ h+h-k+, h+h- B+ pph+ h = or K 18

19 B hhh pph dynamics and CP asymmetries b W- s,d hg* - B b + h,p u B- h -,p Loop dominates for: KKK K p p K W- u hu h +,p h -,p Tree dominates for KK pp Same short range dynamics for each category Different long-range (hadronization) behaviour : baryons vs. Mesons. Role of FSI in generating strong phases? Measure production and charge asymmetries: N ( B f ) N ( B f ) Araw = + + N ( B f )+ N ( B f ) Use control samples to correct for production and detection asymmetries ± + - B J / ψ( μ μ / p p) K ± 19

20 B h hk + - K arxiv: Accepted in PRD KKK Important charge asymmetries localized at low masses with possible exchanges due to KK scattering out of the, f resonances sector Local asymmetries reach up to 60% Integrated asymmetries: Similar patterns are observed for B h+h- 20

21 B pph arxiv: PRL 113, (2014) pp ppk ~ 19k ~ 2k Near pp threshold enhancement with opposite occupation in the hp dimension c, J/, (2S) Region of interest: charmless or below-charmonium region, m(p p)<2.85 GeV/c2 21

22 B pph arxiv: PRL 113, (2014) Different occupation of nearthreshold region translates into opposite h meson angular asymmetry Study of ppk charge asymmetry in the DP reveals a sign-inversion pattern near-threshold for After corrections, 4 CP asymmetry is found (cos( )<0 near 22 threshold)

23 Mixing parameters Semileptonics b ccs decays 23

24 Semileptonic asymmetries A q sl Reveals asymmetry in neutral B meson mixing To measure it, use flavour tagged eigenstates and compare wrong-sign decays B0 f and B0 f occurring because of the mixing Γ ( B q Bq f ) Γ ( B q B q f ) Δ Γq q A= tan(φ 12 ) Γ ( B q Bq f )+Γ ( Bq B q f ) Δ mq q sl Mixing phase ~ 0 in SM Semileptonic decays are used to tag the final state f, B D X Results for 0 PLB 728C (2014) Assl with 1 fb-1, using Bs D s μ ν X d and Asl with 3 fb-1, using *+ - Bd D μ ν X and Bd D μ ν X arxiv: Submitted to PRL X includes additional particles due to X feed down or particles from high D* excitations 24

25 Semileptonic asymmetries extraction in LHCb Practically, we measure (without tagging original flavour): N ( B0q f, t) N ( B 0q f, t) Aqsl A qsl cos( Δ M q t) = AD + ( A P + ) Δ Γqt N ( Bq f, t)+ N ( B q f, t) cosh( ) 2 Detection asymmetry B0 production asymmetry (~ 1%) (inferred from control samples) For q production asymmetry (~ 1%) B0s time-integration is trivial since oscillations are very fast: 0 s 0 s 0 s 0 s N ( B f ) N ( B f ) s sl A = AD + 2 N ( B f )+ N ( B f ) For B0d time-dependent fit needed to disentangle AP and Asl Reconstructed time is corrected for non-visible mass: nom B L. M t= pvis K ( M vis ) However, precise knowledge of K factor has limited impact on Asl pvis/ptrue, from simulation 25

26 Semileptonic asymmetries results B(0d, s) - K 0 D ) (K) D(( *s )+ ) Topology of separated B and D vertices, restricting K (K) mass window Fitting simultaneously mass and time distributions of K (K) candidates PV s sl A =( 0.06±0.50 ( stat )± 0.36( syst )) % d Asl =( 0.02±0.19( stat )±0.30 ( syst)) % AP ( 7 TeV )=( 0.66 ±0.26± 0.22) % AP ( 8 TeV )=( 0.48±0.15± 0.17) % 26

27 Semileptonic results: consequences Beside the tension coming from D0 result, the LHCb measurements are pulling back toward SM 27

28 Mixing and decay: Bs J/ h h + - PLB, 736, (2014) 186 arxiv: , sub to PRL Mixing-induced CP violation with the decays ( D~0): CP violating phase s small in SM: B 0 s D~0 φ SM s = 2β s= 2 arg( J / ψ h + h- V ts V *tb V cs V * cb )= 0.036±0.001 Tag the flavour at production and study the production rate vs decay time, using s D 0 Bs decay angles to unfold the contributions Bs J/ K+K- (J/ dominated) precisely studied in complete fit NEW Dependence of s on KK polarization published for the first time (no effect) Bs J/ + - final state occurs mainly from interfering f0 and f2 states 28

29 Bs J/ h h results + - J/ + - PLB, 736, (2014) 186 arxiv: , sub to PRL Bs sin s) Using s, s, ms as external inputs: s = 0.075±0.067±0.008, assuming no CPV in decay, or s = 0.070±0.068±0.008 otherwise J/ + s = ±0.049±0.006 s = ±0.0027± ps-1 s = ±0.0091± ps-1 ms = ±0.056±0.011 ps-1 Combined: s = ±0.039, most precise measurement to date; in agreement with SM NEW 29

30 Rare Decays Bs,Bd ℓ+ℓ

31 Lepton universality with B K ℓ ℓ decays PRL 113, (2014) Decay through electroweak loop diagrams ℓ+ b u,c,t - B W u W s u ℓ- ℓ+ ℓ-, Z b W W s u,c,t u Beyond SM particles can intervene in loops u K- Theoretical uncertainties mostly cancel in ratios of branching fractions and in asymmetries Lepton universality: same electroweak couplings for electron and muon: RK = K- + -/K-e+e- should be one (within 10-3). Intervention of extra-sm particles may cause deviations 31

32 B K ℓ ℓ decays: extraction of RK PRL 113, (2014) B- K-J ℓ+ℓ-) used as a control and normalization mode K- + K-e+e- 2S) 2S) Integrate over relevant ℓ+ℓ- invariant mass (q2) range: [1,6] GeV2 RK = ± from unity Γ ( B K e e )=( ( stat ) ( syst )) 10 Most precise measurements to date -7 32

33 B K* (1 fb, update on-going) PRL 111 (2013) arxiv: Same motivation as B- K-ℓ+ℓ-: use of theoretically clean observables to chase deviations from SM. Complicated angular analysis with many DoFs. Mainly consistent with SM except one angular variable ' 5 P= S5 Coeff of sin (2 θ K ) sin(θ l )cos( φ) F (1 F ) L L Local discrepancy in P5 at the 3.7 level Fraction of longitudinal Needs more data and study to understand amplitude 33

34 Bs,Bd Has been hunted for a long time Very rare, correctly understood in the Standard Model W b b t s,d Z W W t s,d t Branching fraction predicted in SM: (3.65±0.23) 10-9 (Bs), (1.06±0.09) (Bd) PRL 109, (2012); PRL 112, (2014) b H t s,d W 0 h,a Prediction in MSSM: Γ ( B μ μ ) m2b mμ2 tan 6 (β) m 4A After evidences for signals (2013), LHCb and CMS decided to combine 34

35 Bs,Bd combined results (joint paper) arxiv: NEW First observation R= B μ μ / Bs μ μ - Within 2.3 of the SM/MFV prediction 35

36 Heavy hadrons studies Bc decays New b states 36

37 Bc decays Bc meson: doubly heavy flavoured (charged) meson Mass is ~ 1 GeV above the other B mesons Decays occur either from the c (~70%) or the b quarks b and c can also annihilate into a W (suppressed) Fragmentation b c not well known, <~ 1% Lifetime with Bc- J/ X: τ = 509 ± 8 ± 12 fs EPJC 74 (2014) 2839 Baryonic decays: observation of Bc- J/ pp But LHCb statistics permit to explore properties Phys. Rev. Lett. 113, (2014) Other studies on-going 37

38 Bc- J/ pp Measured using the control channel Bc- J/ First observation of a baryonic Bc decay with a significance of 7.3 Bc- J/ Bc- J/ pp 38

39 Observation of two b excitations Filling b-hadron spectroscopy part of LHCb program b baryons are formed of bsd and bsu quarks Already known: ground states b-, b0 and b(5945) Analogically to c, expect JP = 1/2+, 3/2+ states Combine b0 c+(pk- +) - candidates with charge pions Exploit particle ID, b0 and c vertices arxiv: Submitted to PRL NEW b'- b* m b0 -m b -m( MeV) 120 b'- events 240 b* events 39

40 Forward physics Massive long-lived particles Z + b-jet 40

41 Search for massive long-lived particles Several extensions of SM predict the existence of long-lived particles decaying into SM particles (LSP with L/B violation*, NLSP in SUGRA**, etc...) Neutral v (v-pion) in Hidden Valley Models: PLB651 (2007) 374, PLB661 (2008) 263, JHEP 0807 (2008) 008 Produced through H0 v v, decay v qq In LHCb: seek for a signal v bb in the ranges = [1,200] ps and m = [25,50] GeV/c2 Limitations in due to prompt background (low) and VELO acceptance (high); in m due to identification of two hadronic jets (low) and rapidity coverage (high) Unique coverage at small lifetimes and masses compared to similar searches in CMS [CMS-PAS-EXO ] and ATLAS [Phys.Rev.Lett. 108 (2012) ] Example study, but can be generalized to any massive long-lived particle * PRL 99 (2007) , PRL 103 (2009) , JHEP 0710 (2007) 056, PRD79 (2009) ** arxiv:

42 Results for v bb LHCb-PAPER In preparation for EPJC (H)xBR(H v v) (pb) NEW preliminary mass (GeV) Lifetime (ps) Comparison of coverages for results of different experiments c (cm) 42

43 What about the Higgs itself? Some (preliminary) analyses published/presented last year Forward H + - with 1 fb-1 (7 TeV) Updates not available yet JHEP05(2013)132, arxiv: H bb: suffers from huge background Prefer associated production W/Z + H bb Needs good knowledge of standard bb production, e.g. LHCbCONF & LHCb-CONF Preparative studies on-going Acceptance 7 TeV, 5% of bb from Higgs in LHCb acceptance, similar reduction for leptons from Z. Proportion is 14 TeV. But given the H bb branching fraction, still worth the effort 43

44 Z + b-jet 7 TeV arxiv: Submitted to JHEP Measured by ATLAS and CMS for <2.1 LHCb complements for 2< <4.5 Sensitivity to proton PDF for low and high x Reconstruction Z with PT( )>20 GeV/c Tag b-jet with secondary vertex (arxiv: ) p PV NEW + - Fit distribution of SV corrected mass Mcorr using template distributions M corr = M 2 + p 2 sin2 (θ ) + p sin(θ ) 44

45 Z + b-jet production - results pt(jet)>10 GeV/c, 72 Z+b arxiv: Submitted to JHEP pt(jet)>20 GeV/c, 40 Z+b NEW pt>10 GeV/c pt>20 GeV/c Agrees with LO and NLO calculations 45

46 Prospects - Run 2 Run 2 will start in spring 13 TeV bb cross-section will increase by ~ 1.6 Expected integrated LHCb: 6 fb times Run 1 sample Expected improvements Systematics due to finite size of control samples, detector induced asymmetries, Particle ID calibration Many objectives Improve precision on Bs mixing parameters and angle Better knowledge of rare b qℓ+ℓ- and B + - processes Finer Dalitz analyses More heavy hadron spectroscopy, etc... For several studies, the full exploitation of Run 1 data is still on its way 46

47 Conclusion Diversified research program with many active analysis > 200 papers for Run I data, more to come (yet) A lot of important results and interesting studies Constraining CKM elements: tree vs loop decays Some ratios of observables in rare decays hint for discrepancies Peculiar CPV patterns in three-body decays Results on heavy hadrons and Forward Physics Statistical uncertainties are still dominating Run II is coming in 2015: several break-through results expected Further in the pipeline: upgrade ~ , THE big jump! 47

48 Back up 48

49 a Performance and techniques involved in analyses Flavour tagging (leptons, kaons) b hadron Primary vertex Separation of secondary vertices Bs - few mms + good mass resolution (typically ~ 10 MeV) 0 - Bd D s D - J + good particle ID + B0s D -s D+ 49

50 2015 Trigger lines Calibrations performed between High Level Triggers 1 and 2 50

51 from B DK, different techniques fd = CP eigenstates, D0 K+K-, + -, Ks 0 fd = flavour states: D0 K+ -, K- + Gronau, London, Wyler (GLW) 1991 Atwood, Dunietz, Soni (ADS) 1997 fd = multibody final states (variation of D over phase space) Ksh+h- Giri, Grossman, Soffer, Zupan 2003; Poluektov 2004 (GGSZ-P) K± + -, multibody ADS KsK±, GLS Some variants involving neutrals, B0 and Bs Observables: charge asymmetries and BF ratios of suppressed/favoured D decays (applies for self-tagging decays) 51

52 from trees Case of D0 K- + (Cabibbo Allowed), D0 K+ - (double Cabibbo Suppressed) ± h R= Γ( B± DDCS h±) ± ± Γ ( B DCA h ) = r 2B +r 2D + 2r B r D cos(δ B+ δ D ± γ ) 2 1+(r B r D ) +2 r B r D cos(δ B δ D ± γ) For multibody decays, must take into account the interference term between the two amplitudes in the D meson phase space, using a coherence factor D PRD68 (2003) , arxiv:hep-ph/ r B r D cos(δ B +δ D± γ) 2r B r D κ D cos(δ B +δ D ± γ) 52

53 from loop: observables arxiv: Submitted to PLB Use of CP averaged branching fractions: m ( m + m ) F( B d d )= 2 B m 2 B 2 2 τb And CP asymmetries 53

54 from loop: fit parameters arxiv: Submitted to PLB Observables are function of CKM angles,, s; and hadronic parameters (amplitude ratios d, D, strong angle differences ): And similarly for the four branching fractions Bhh U-spin symmetry implies d = d, ', etc... U-spin breaking studied and parameterized as distortions in magnitude ( ) and angles of the amplitude ratios. Deviations from factorization hypothesis also considered 54

55 from loop: effect of non-factorizable U-spin 95% interval 68% interval 55

56 Common features of B hhh pph Extraction of signals All analyses use common multivariate techniques to reduce combinatorial background Particle ID requirements to suppress cross-feed due to K + + misid N ( B f ) N ( B f ) Correction to raw charge asymmetries Araw = N ( B f )+ N ( B f ) Decay chains B J/ ( + -)K, J/ (pp)k used to estimate B production and K detection asymmetries. Outcome of analyses on D meson decays enable to extract detection asymmetry Trigger and kinematic effects accounted for ACP (hh π / K )= Araw ( hh π / K ) ( A P + Adet (π / K )) AP + A det ( π / K )= Araw (J / ψ(μ μ / p p) K ) ACP (J / ψ(μ μ/ p p) K )( A det (K )+ Adet ( π)) 56

57 arxiv: Accepted in PRD B h h + - KK f0(980) Important charge asymmetries localized at low masses Local asymmetries reach up to 60% Integrated asymmetries: 57

58 Further information on J/ + - Tagging power tag(1-2wtag)2: 3.9% tag= Ntag/ Ntot, wtag= Nwrong/ Ntag Full angular and CP components analysis as input PRD 90, (2014) Definition of the angles (helicity basis) 58

59 More on J/ + Main results Amplitudes CPV parameters Polarization dependent fit q Ak λ k =η k p Ak φ k = arg( λ k ) 59

60 Bs,Bd analyses (LHCb and CMS) Similar analysis strategies: exploit B displaced vertex, use kinematical and topological variables in MVA along with mass as a discriminant against hadronic two body or semileptonic B decays. J/ ( )K used as a normalization mode LHCb, PRL 111 (2013) CMS, PRL 111 (2013) Evidences published last year: 60

61 Bs,Bd MVA categories LHCb CMS 61

62 Bs,Bd comparisons 62

63 Flavour tagging b Bq signal Same-Side tagging q q -, K- with kaons and pions u u proton K+ proton c hadron b hadron Opposite Side tagging with lepton or secondary kaon ℓ+ Effective efficiency tag(1-2wtag) % for opposite-side 1.25% for same-side (kaon-only) 63

64 Systematics (%) for A d sl 64

65 Mixing formalism Mass and width differences between eigenstates: 65

66 Impact of New Physics on mixing - example 2i Model-independent search for distortion M12 M12. h.e2i 2003 PRD 89, (2014) 2013 Bd Bs 66

67 LHCb-PAPER In preparation for EPJC Search for v bb Performed with limited statistics ( TeV) due to specific trigger tunings. Update will be done with bigger statistics NEW Two displaced b-jet vertices preliminary Backgrounds: Beam-gas and beam-halo removed by requiring minimum transverse vertex position Beam-splashes removed by requirement of azimuthal isotropy Try to fit a bump at higher invariant mass on top of big standard b b production Shape for candidates with = 10 ps, m = 35 GeV/c2 With fitted yields, set a limit on (H)xBR(H v v) Interpretations as v qq signals also considered 67

68 Fits for v bb, m = 35 GeV, = 10 ps 68