Recent results from LHCb. A.Hicheur (UFRJ, Brazil) On behalf of the LHCb collaboration SILAFAE 2016, Guatemala November 14-18, 2016

Transcription

1 Recent results from LHCb A.Hicheur (UFRJ, Brazil) On behalf of the LHCb collaboration SILAFAE 2016, Guatemala November 14-18, 2016

2 Outline Physics program LHCb experiment Highlights of recent results Mostly from Run I data, some analyses include ongoing Run II data 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 Forward EW and QCD physics Search for exotics Heavy ion physics... 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 ( ) Run I 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 LHCb data ( ) ongoing Run II Bunch colliding at 13 TeV (bb) ~ TeV* in LHCb acceptance About 2.3 times the 7-8 TeV * LHCb-PAPER

9 angle from B DK (h,hh) decays (*) V ud V *ub * V td V tb * V cd V cb Use interfering amplitudes in tree-level B DK(*)(h,hh) decays + ri: amplitude ratios i: relative strong phases AB K-D0 AD B- ABrBei( B- ) 0 In general: rd and fd used fd as external inputs (e.g. from CLEO-c data) ADrDei D KD Fits use ratios of allowed/suppressed BF + asymmetries - For multibody D decays, dilution factor due to D variation across phase space Compare to from loop diagrams: mismatch? BSM particles in the loop? Combine LHCb analyses to make averages 9

10 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) 10

11 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) 11

12 from B DK in LHCb Many channels under study in LHCb Using either CP, flavour, or multibody final states of D arxiv:

13 combination of results LHCb-PAPER , arxiv: submitted to JHEP NEW Combination of analyses : B+ DK+ B0 DK*0 PRD93 (2016) B DK PRD90 (2014) , JHEP 08 (2016) 137 B0 DK PLB760 (2016) 117, PRD91 (2015) , JHEP 10 (2014) 097, PLB733 (2014) 36 PRD92 (2015) , Time dependent Bs DsK+ JHEP 11 (2014) 060 LHCb result dominates the world average 13

14 Rare (loop) decays Weak/Electromagnetic box diagrams b s(d)ℓ+ℓ- Observation of B0 K+K- 14

15 b s(d)ℓ ℓ + - ℓ+ Bq b b q W u,c,t W s(d) q ℓ+ ℓ-, Z b W ℓW s(d) u,c,t q q K, New physics can intervene in the loops/boxes Can be probed through the analysis of the dynamics of the decays Or testing, e.g., lepton universality b s e +e-/b s

16 Dynamics for B0 K*0 + -, Bs + - q2 = + - invariant mass squared Formula slightly different between K* (self-tagging) and FL: fraction of longitudinal polarization of K*/ A6 ~ AFB = forward-backward asymmetry of the dimuon system A5 = S5 in the case of K* They depend on B K*/ form factors and Wilson Coefficients of the OPE 16

17 B X results + - Bs + - B K* JHEP 1509 (2015) 179 JHEP 02 (2016) 104 ' P 5= Differential branching fraction is 3.1 below SM prediction in the lower q half, no discrepancy for the angular variables with this statistics Form-factor S5 independent F L ( 1 F L ) 3.7 combined difference with SM 17

18 Observation of B K K arxiv: submitted to PRL Bs0 K+K- can proceed through a penguin B0 K+K- : annihilation or W exchange only Significance : 5.8 including systematics 18

19 CP violation in baryon decays arxiv: Submitted to Nature CPV seen in B and K decays, never in baryons Search for direct CPV in b p hh decays Look at triple scalar products Observable measuring CPV : 19

20 b p hh signals and CP arxiv: Submitted to Nature First observation Overall 3.3 CP violation found for b p First evidence of CP violation in baryon decays No CP violation for b p 20

21 Semileptonics ℓ b W,X c,u Theoretically well-understood in the SM Decays to light leptons well-measured by B factories a) Not as good for lepton b) Good way to extract Vqb CKM element a) Any new (charged) intermediate boson/mediator would couples preferentially to : LHCb studied B0 D*+ / B0 D*+ (LHCb-PAPER , arxiv: ) b) Use of b u to improve Vub (relative uncertainty still ~ 12-13%) + solve the tension between measurements from exclusive B and inclusive B Xu Use of b p (LHCb-PAPER , arxiv: ) 21

22 B D 0 *+ Using decay: Measure: = in SM (PRD (2012)), with very good precision - K D0 D *+ PV B0 D - K D0 *+ Very specific topologies + use of missing mass, muon energy and momentum transfer q O ha n g d r oi n on g ic ef f f in or al t f o s t r at e PV B 0 LHCb-PAPER , arxiv:

23 R(D*) result R(D*) = Follows historical trend, above SM prediction by ~ 2.1 Combined R(D) and R(D*) gives 4 discrepancy from SM Future results to test lepton universality : R(J/ ) from Bc, R c) from b, R(Ds(*)) from Bs 23

24 Direct CPV measurement in D K K arxiv: LHCb-PAPER Submitted to PLB The flavour (D0 or D0) is kinematically determined in the chain D*+ D0 + / D*- D0 - In practice : Production asymmetry is measured using the raw asymmetries of the decays and Slow pion detection asymmetry which is known to be small and under control Fit to 24

25 Direct CPV measurement in D K K Combined LHCb value : Most precise single-experiment measurement No CP violation in the charm sector! 25

26 Bc physics Unique hadron with two heavy quarks Bc+ = bc Decays through either charm or beauty quark Decays could include lighter B mesons! Spectroscopy not very well known About 10 measurements (8 upper limits!) Limitation due to the lack of knowledge of the production pp( b) Bc cross-section : measure products of branching fractions and cross-section ratios 26

27 LHCb pioneering work in Bc physics 0.68±0.02 % 0.079±0.007± fb-1 3 fb-1 JHEP 09 (2016) 153 And many ongoing results and studies... 27

28 Search for Bc annihilation in the KK final state Run I data only LHCb-PAPER arxiv: To be published in PRD-RC Other processes in the phase space : Spectrum analysed in bins of Decision Tree classifier Normalizing channel : Measured observable : 28

29 Fit Regions definition 5.2 < mk, mkk < 5.5 GeV: B inclusive 1.834<mK <1.894 GeV: D0 band Excluding these two: non-b and non-d region Annihilation mk < GeV Bs KK region defined as 5.3 < mkk < 5.4 GeV c KK region n.b: For annihilation and D0, veto B (and c0) band(s), efficiency accounts for this. 29

30 Signal in annihilation region Simultaneous fit to bins of Decision Tree Classifier ~ 21±10 signal events With a global significance of 2.4 Increasing purity Hint of annihilation signal? Adding Run II data will help to confirm Compare to SM-based conservative range : 30

31 Observation of Bc c0( KK) Increasing purity m(kk ) m(kk) ~ 21±6 signal events With a global significance of 4 Strong evidence Similar to (7.0±0.3) 10-6 for J/ 31

32 Forward physics 32

33 Forward physics, resolving W+bb, W+cc, tt LHCb-PAPER arxiv: , submitted to PLB W+ ( + ) + j1 j2 template fit Analysis done for 4 samples W±( /e ) + j1 j2 Main background : Z( /ee) + j1 j2 33

34 Results on W+bb, W+cc, tt Still compatible with NLO SM-based predictions 34

35 Upgrade Planned during LS2 ( ) Prepare for acquisition of 50 fb-1 Detectors: full upgrade of the tracking system new RICH (Particle ID) detectors Calorimeters and muon system: new electronics, more shielding, etc... Triggering: full software trigger This removes the limitation of the L0 Hardware trigger (1 MHz) 35

36 Summary A big variety of results A lot of recent results not shown : e.g., Bs polarisation (arxiv: ), p (LHCb-CONF ), etc... Pushing the SM further in the corners and hunt for intervention of NP: e.g., persisting discrepancies in some observables of rare decays Forward physics and Heavy Ion physics programs progressing as well Run II data taking is going on efficiently, 2 fb-1 of data already recorded with (bb)(13 TeV) > 2 x (bb)(7-8 TeV) A lot of news should come with the analysis of the full Run I sample Preparation for upgrade is well advanced and most of the R&D phases are now achieved 36