Recent Highlights from the LHCb experiment looking for the Mass in the Flavour Shop

Transcription

1 Recent Highlights from the LHCb experiment looking for the Mass in the Flavour Shop Giacomo Graziani (INFN Firenze) on behalf of the LHCb Collaboration Origin of Mass 216 CP³-Origins, SDU Odense, Denmark May 3, 216

2 The Flavour problem The flavour sector is probably the most demanding test-bench for any model beyond the Standard Model Indirect bounds on the scale for generic New Physics couplings from flavour measurements (and in particular from F = 2 transitions) go well beyond the scale accessible for production of new particles at the LHC b _ s s _ b New Physics at TeV scale is not natural for flavour, models need ad hoc requirements to comply with current measurements (MFV, alignment,... ) plot from Neubert, EPS-HEP 211 G. Graziani slide 2 MASS 216

3 ] Example: B s µ + µ B (s) µ+ µ is helicity suppressed FCNC decay, predicted with high accuracy in the SM: THEORY B(B s µ + µ ) = (3.56 ±.18) 1 9 B(B µ + µ ) = (1.7 ±.1) 1 1 Weighted candidates per 4 MeV/c Observation by LHCb and CMS in good agreement with SM: CMS and LHCb (LHC run I) 6 Data Signal and background + 5 Bs µ µ + B µ µ Combinatorial background 4 Semi-leptonic background Peaking background [MeV/c 2 ] Nature 522 (215) 68 B(B s µ + µ ) = ( B(B µ + µ ) = ( ) ) 1 1 m µ + µ 6.2 σ 3.2 σ High sensitivity to new neutral mediators in loops! 9 [1 µ ) µ + B(B a CMS and LHCb (LHC run I) % B(B µ + µ ) [1 ] 95.45% 99.73% s 7 2ΔlnL 2ΔlnL B(B µ + µ ) [ SM SM B(B µ + µ ) [1 G. Graziani slide 3 MASS 216 SM b c s 9 ] 9 ]

4 The killer of MSSM parameter space! G. Graziani slide 4 MASS 216

5 Outline Principles of LHCb Results and plans beyond b Physics Charm and strange Production 13 TeV Spectroscopy: new exotic states Fixed target Physics A selection from recent bounds and hints from b LHCb Results from semileptonic b decays: mixing frequency m d CP Violation in B mixing V ub from b baryon decays Lepton universality in b decays G. Graziani slide 5 MASS 216

6 LHC is the biggest b quark factory on earth b is the richest flavour physics laboratory: Many decay channels Relatively large CPV effects from 3 generation mixing High mass reduce theory uncertainty Lifetime ( 1.5 ps) large enough to study CPV effects as a function of time LHCb Principles Detector requirements: Forward geometry optimize acceptance for bb pairs ( 25 %) Tracking : best possible proper time and momentum resolution Particle ID excellent capabilities Trigger with high efficiency down to p T 1 GeV/c Low pileup : running with 1 collision per crossing (lower luminosity wrt ATLAS/CMS) G. Graziani slide 6 MASS 216

7 LHCb Detector JINST 3, (28) S85 Int.J.Mod.Phys.A3 (215) Capable to resolve fast Bs oscillations G. Graziani slide 7 MASS 216

8 LHCb Dataset Luminosity leveled to cm 2 s 1 since 212 (stable DAQ conditions with fixed rate) 3 fb 7-8 TeV from Run 1 corresponding to bb pairs in LHCb 13 TeV 5% increase in b prod..4 fb 1 collected so far aiming at 5 fb 1 G. Graziani slide 8 MASS 216

9 Golden modes for CPV in Neutral B mesons _ b b d(s) mixing Tagging b Tree level decays to common final states for B (s) and B (s) allow clean determination of weak phases from CPV in interference between decays with/without mixing Golden modes: B J/ψK S sin(2β), large CPV effect (B factories, confirmed by LHCb) B s J/ψφ and similar φ s, suppressed in SM. best measurement from LHCb [PRL 736 (214) 186] B DK and similar γ angle (more difficult), LHCb combined result lowering uncertainty below 8 degrees [LHCB-CONF-216-1] All results consistent with CKM picture _ b d(s) _ c _ c s J/ ψ K S (φ) G. Graziani slide 9 MASS 216

10 Measurements from B semileptonic decays _ b d(s) b mixing Tagging b _ b d(s) c, u V ub/vcb ν l + Lepton Universality m CP violation CKM matrix Tensions in previous measurements G. Graziani slide 1 MASS 216

11 Precision measurement of m d arxiv: Using abundant and relatively clean sample of B D ( ) µ + ν µ X decays Invariant mass of D Kππ candidates (212 data) 3 1 ) Events / ( 1.4 MeV/c LHCb Data Total fit Signal Comb. δm = M(D ) M(D) for D D ( Kπ)π ) Events / (.125 MeV/c LHCb Data Total fit * D D Comb [MeV/c 2 ] m K ππ δm [MeV/c 2 ] Dµ background from B ± and other b hadrons suppressed to < 1% through Multi Variate Analysis using kinematic and isolation criteria Average correction applied to decay time to account for the missing momentum (k-factor method) G. Graziani slide 11 MASS 216

12 Result for m d arxiv: ideally A(t) = N unmix (t) N mix (t) N unmix (t) + N mix (t) = cos( m dt), diluted by mistagging and backgrounds m d = (55. ± 2.1(stat) ± 1.(syst)) ns 1 Most precise single measurement! Agrees with previous World Average m d = 51 ± 3 ns 1 Recent improvements in lattice calculations allow tighter constraints on the CKM triangle (A. Bazarov et al., arxiv: ) A(t).5 LHCb (a) (c) 5 1 (b) (d) 5 1 B DµνX sample, 212 data 4 plots for different tagging categories t [ps] G. Graziani slide 12 MASS 216

13 The Semileptonic charge asymmetry a sl CP violation in the B B mixing probability a q sl = P (B q B q ) P (B q B q ) P (B q B q ) + P (B q B q ) Γ q m q tan(φ q 12 ) is predicted to be small in SM due to the smallness of Γ and of the CPV phase φ q 12 : a d sl = ( 4.7 ±.6) 1 4 a s sl = ( 2.22 ±.27) 1 5 Artuso, Borissov, Lenz, arxiv: G. Graziani slide 13 MASS 216

14 New Physics in B mixing? Intriguing like-sign dimuon event asymmetry observed by D (without distinguishing B and B s): 3.9σ from SM. Not confirmed so far by B factories and LHCb LHCb can measure a sl from charge asymmetry of inclusive semileptonic decays B D ( ) µ + ν µ X B D s µ + ν µ X PRD 84, 527 (211) G. Graziani slide 14 MASS 216

15 a d sl in LHCb PRL 114 (215) 4161 Measured from time-dependent asymmetry in B D ( K + π π )µ + ν µ X and B D ( D π K + π π )µ + ν µ X A raw (t) = where N are bkg-subtracted rates N(f, t) N(f, t) N(f, t) + N(f, t) A D + ad sl 2 + A D = ε(d µ + ) ε(d + µ ) ε(d µ + ) + ε(d + µ ) is the detection asymmetry, measured from control channels, and A P = N(B) N(B) N(B) + N(B) is the production asymmetry, obtained from the fit Using full Run1 sample a d sl Events / ps Asymmetry [%] ( ) A P ad sl cos( m d t) 2 LHCb D µ + Data Total Signal + B bkg. Comb. bkg = (.2 ±.19(stat.) ±.3(syst.))% 3 t [ps] G. Graziani slide 15 MASS 216

16 assl in LHCb Preliminary new result! LHCB-PAPER ( K K π )µ νµ X decays Time integrated analysis of B D s (fast oscillations suppress the integral of time-dependent component) Backgrounds are main source of systematic è split measurement in 3 regions of Dalitz plot with different background contamination: D+ s φπ, Ds K K, Non Resonant Ds K K π G. Graziani slide 16 MASS 216

17 Result for a s sl LHCB-PAPER a s sl = (.45 ±.26(stat.) ±.2(syst.))% Most precise measurement of CPV in B s mixing Compatible with no CPV and SM prediction Does not confirm D anomaly G. Graziani slide 17 MASS 216

18 Measurement of V ub The smallest and least know CKM element: σ( V ub )/ V ub = 12% Long standing puzzle: inclusive and exclusive measurements do not agree Exclusive use B π + l ν l decay experimentally clean needs theory for hadronization PDG 214: V ub = (3.28 ±.29) 1 3 Inclusive use B X u lν decays experimentally less clean theory still needed to account for phase space region not accessible PDG 214: V ub = (4.14 ± ) σ all most precise measurements so far from B factories G. Graziani slide 18 MASS 216

19 V ub in LHCb using Λ b baryons Measurement using exclusive decay Λ b pµ ν µ Profiting of large Λ b production at hadron colliders (2% fragm. fraction) Reduced background from other b hadrons Using only high q 2 region where theoretical errors are smaller (q 2 has 2-fold ambiguity, cut applied to both solutions) Normalization to Λ b Λ c µ ν µ, using only V ub 2 V cb 2 = B(Λ b pµ ν µ ) q2 >15 B(Λ b Λ c µ ν µ ) q2 >7 R F F Nature Physics 1 (215) 138 Ratio of form factors from recent lattice calculations W Detmold et al., Phys.Rev.D92, 3453 (215) R F F =.68 ±.7 5% uncertainty on V ub / V cb Relative efficiency for signal and normalization controlled within few % Largest single systematic source if BR of normalization mode, known to 5% accuracy (from Belle) Analysis based on fit to corrected mass M corr = p 2 + M(hµ) + p h = p, Λ c G. Graziani slide 19 MASS 216

20 Candidates / (5 MeV/c 2 ) Result for V ub from Λ b pµ ν µ Nature Physics 1 (215) Combinatorial Mis-identified D pµ ν * Λ + c µ ν + Λcµ ν * N µ ν pµ ν Corrected pµ LHCb mass [MeV/c 2 ] V ub V cb = (83 ± 4 ± 4) 1 3 Signal Result agrees with previous exclusive measurements 3.5 σ from inclusive measurements puzzle confirmed Candidates / (4 MeV/c 2 ) LHCb + Λcµ *+ Λ c ν Corrected pk µ ν Combinatorial π + µ mass [MeV/c 2 ] 3 V cb 1 G. Graziani slide 2 MASS V ub inclusive V ub exclusive V ub Indirect (HFAG) V ub /V cb Λb exclusive * D V cb exclusive inclusive V cb D V cb

21 Right-handed weak current? Nature Physics 1 (215) 138 Possible solution to the puzzle suggested by previous results: significant right handed component in the SM current [ PRD 9, 943 (214)] This measurement has different sensitivity to the right handed fraction ε R due to the spin of the proton The result does not support this explanation 3 1 L V ub inclusive B πlν Λ b pµν (LHCb) combined G. Graziani slide 21 MASS 216 ε R

22 B D + τ ν τ Another intriguing anomaly from B factories: possible breaking of lepton universality in R(D ( ) ) = B(B D ( )+ τ ν τ ) B(B D ( )+ µ ν µ ) Very clean theoretically (2% uncertainty) Sensitive to charged Higgs, Leptoquark... PRD 88 (213) 7212 Both Babar and Belle find excess of τ mode wrt SM 3 neutrinos in final state, challenging measurement! Missing mass can t be well measured at hadron colliders (B factories can use opposite side reconstruction) G. Graziani slide 22 MASS 216

23 Never say Never PRL 115 (215) First measurement of R(D ) at hadron colliders from LHCb Totally different technique wrt B factories: estimate B momentum assuming (β z γ) visible = (β z γ) B (B energy Q-value) 18% resolution then compute q 2, E µ, m 2 missing in B rest frame candidates dominated by background from partially reconstructed b decays and combinatorial: carefully model all components using control sample or simulation validated on data Data B D*τν B D*H c ( lνx')x B D**lν B D*µν Combinatorial Misidentified µ G. Graziani slide 23 MASS 216

24 Result for R(D ) PRL 115 (215) In agreement with B factories, 2.1σ larger than SM R(D ) =.336 ±.27(stat.) ±.3(syst.)% Combination of results (including latest one from Belle) disagrees with SM at 4σ level G. Graziani slide 24 MASS 216

25 Other hints from rare decays in LHCb Another test for lepton universality: R K = B(B+ K + µ + µ ) B(B + K + e + e ) expected =1 in SM with negligible error measured value in LHCb is 2.6 σ: R K (1 < q 2 < 6 GeV 2 ) = ±.36 R K LHCb BaBar Belle LHCb Angular analysis of B K µ + µ dynamics of 4-body decay can be described with 8 observables that can receive many possible NP contributions theorists proposed combination of observables with reduced hadronic uncertainty P 5 variable, sensible to Z, exhibits 3σ deviation from SM JHEP 2 (216) 14 Result recently confirmed by Belle 1 SM q 2 [GeV 2 /c 4 ] PRL Performing the same test on other modes... arxiv: G. Graziani slide 25 MASS 216

26 Conclusions on b Physics LHCb and B factories confirm the triumph of CKM paradigm at tree level Entering era of precision ( 1%) measurement of flavour observables Semileptonic decays are well manageable also at hadron colliders! Models beyond SM severely constrained by results on CPV and rare b decays But a pattern of possible NP signals is starting to emerge: V ub, R(D ), B K µ + µ... soon to exclude fluctuations or systematics (in theory or data interpretation) Nice interplay between experimental and theoretical development What about the underlying event? Progress in understanding hadronic interactions, including soft regime, is also essential for flavour physics LHCb is also committed to hadronic physics, exploiting its unique coverage of forward region... 5 of our 1 most cited topics are production/spectroscopy studies! G. Graziani slide 26 MASS 216

27 Interlude: LHCb Trigger CERN-LHCC LHCb-PROC Single Hardware level (L) up to 1 MHz to software trigger (HLT) Evolution following expansion of physics program: original output bandwidth for core program (TDR 23) : 2 Hz now 125 Hz Pioneering new concepts: asynchronous software trigger, running after up to date calibrations are available: same reconstruction quality in trigger and offline well consolidated analysis can run directly in HLT (TURBO lines) More space for charm and strange, hadronic (production and spectroscopy), EW physics, heavy ions, exotic searches and more G. Graziani slide 27 MASS 216

28 LFV in charm decays Charm sample: D and D mesons within LHCb acceptance in Run1 sample (2-3 CDF sample in 1 fb 1 ) Example: search for lepton flavour violating D eµ decay PLB 754 (216) 167 Forbidden in SM, suggested in several extensions (including some leptoquark scenarios) with BR up to 1 6 () Previous best limit from Belle: < at 9 % CL Normalizing to D K π CL S LHCb result: B(D eµ) < % CL Observed CLs Expected CLs - Median Expected CLs ± 1 σ Expected CLs ± 2 σ B(D e ± µ ± ) G. Graziani slide 28 MASS 216

29 Kaon Physics LHC is also the largest kaon factory: K S produced within LHCb acceptance, 4% decaying within vertex detector Main limitation is the trigger (K S products have too low p T ) Only result so far: search for K S µ + µ very suppressed in SM: (5. ± 1.5) 1 12 LHCb result: B(K S µ + µ ) < improves previous limit by factor 3 trigger efficiency was 1%, improvement in place in 212 (updated analysis in 9% CL JHEP 131 (213) 9 in 211 data Effort ongoing in dedicated trigger lines also for other K S decays (π µ + µ, π + π e + e,... ) G. Graziani slide 29 MASS 216

30 J/ψ 13 TeV JHEP 151 (215) 172 First prompt analysis obtained in the trigger (TURBO lines) from 3 pb 1 of 13 TeV data LHCb can measure production in forward region, distinguishing prompt (direct + feed-down from strong decays of higher states) and detached (b decays) components Candidates per 5 MeV/c LHCb s = 13 TeV, L =3.5 pb -1 int 3 < y < < p < 3 GeV/c T Candidates per.2 ps LHCb s = 13 TeV, L int =3.5 pb 3 < y < < p < 3 GeV/c 5 Data 1 Total fit -1 J/ψ-from-b 4 Prompt J/ψ 1 Wrong PV T Background m µ + - µ [MeV/c 2 ] t z [ps] G. Graziani slide 3 MASS 216

31 Results for 13 TeV JHEP 151 (215) 172 NRQCD: Shao et al., JHEP 5 (215) 13 FONLL: Cacciari et al., arxiv: [nb/(gev/c)] [nb/(gev/c)] T T dσ/dp LHCb prompt J/ ψ, 2.< y <4.5 NRQCD, 2.< y <4.5 dσ/dp 1 LHCb J/ ψ -from-b, 2.< y <4.5 FONLL, 2.< y < p (J/ ψ ) [GeV/c] T 5 1 p (J/ ψ ) [GeV/c] T ) T R 13/8 (dσ/dp 3 2 LHCb s = 13 TeV/ s = 8 TeV cross-section ratio ) T R 13/8 (dσ/dp 3 2 LHCb s = 13 TeV/ s = 8 TeV cross-section ratio 1 LHCb NRQCD 5 1 p (J/ ψ ) [GeV/c] 5 1 (J/ ψ ) [GeV/c] T T G. Graziani slide 31 MASS LHCb FONLL p

32 Spectroscopy of exotic Heavy States Heavy hadron decays provide clean samples for study of exotic heavy resonances LHCb confirmed the tetraquark candidate Z(443) in B Z( ψ π )K + decays [PRL 112 (214) 2222] Sample of 26 Λ b J/ψpK candidates used to study J/ψ p resonances, with minimum quark content ccuud 6D amplitude analysis performed on Dalitz plot PRL 115 (215) 721 ] 2 [GeV ψp J/ m LHCb G. Graziani slide 32 2 m 2 [GeV ] MASS

33 Pentaquarks! PRL 115 (215) 721 M(J/ψ p) distribution not explained by known resonances At least 2 new resonances needed to fit the data: P c (438) P c (445) Mass (MeV/c 2 ) 438 ± 8± ± 1.7 ± 2.5 Width (MeV/c 2 ) 25± 18 ± 86 39± 5 ± 19 fraction (%) 8.4 ±.7 ± ±.5 ± 1.1 Spin (best fit) 3/2 5/2+ Events/(15 MeV) 8 7 (b) LHCb m J/ψp [GeV] Events/(15 MeV) (a) LHCb data total fit background P c (445) P c (438) Λ(145) Λ(152) Λ(16) Λ(167) Λ(169) Λ(18) Λ(181) Λ(182) Λ(183) Λ(189) Λ(21) Λ(211) Λ(235) Λ(2385) Events/(15 MeV) (b) LHCb m Kp [GeV] m J/ψp [GeV] G. Graziani slide 33 MASS 216

34 LHCb as Fixed target experiment New ideas: exploit fixed-target-like geometry for doing... fixed target physics! Gas target available since 212 and used for luminosity determination: System for Measuring the Overlap with Gas (SMOG) Can introduce small amount of noble gas (He, Ne, Ar) in the beam pipe around the vertex detector Increasing by two orders of magnitudes local vacuum pressure (1 9 to 1 7 mbar) Combined with Van Der Meer scan, allowed to determine the luminosity in LHCb with 1.2% accuracy [214 JINST 9 P125] But gas target can also be exploited for physics... G. Graziani slide 34 MASS 216

35 SMOG in the Heavy Ion Physics program An obvious advantage of the gas target is the possibility to change the target nucleus Nuclear effects in heavy hadron production can be studied for different atomic number and at energy scale in between those explored at SPS and RHIC Together with p-p, p-pb and Pb-Pb collision data, quark-gluon plasma effects on heavy probes can be disentangled from cold nuclear matter effects G. Graziani slide 35 MASS 216

36 Heavy flavour production in fixed target data Measurements with He, Ne and Ar were taken during the 215 run to study nuclear effect in heavy hadron production. J/ψ and D signals with 8 hours of proton-neon data 2 2 entries / 16 MeV/c LHCb preliminary 215 pne data entries / 8 MeV/c LHCb preliminary 215 pne data µ + µ invariant mass (MeV/c ) π K invariant mass (MeV/c ) G. Graziani slide 36 MASS 216

37 SMOG for Astroparticle Physics The other advantage of fixed target is the possibility for production studies in wider x F regions, notably in the target fragmentation region x F, where perturbative QCD and Bjorken scaling break such measurements are particularly useful to tune simulation of cosmic ray interactions in cosmos and atmosphere LHCb is carrying out the measurement of antiproton production in p-he collision, whose poor knowledge is currently limiting the interpretation of recent AMS results on antiproton flux in cosmic rays AMS Days at CERN, 15-17/4/215 Giesen et al., arxiv: G. Graziani slide 37 MASS 216

38 LHCb is pushing the precision of flavour physics Acting as a SM gatekeeper... Conclusions... but also suggesting possible new signatures... Physics program continuously expanding, also toward unexpected directions Actively preparing for near and long term future... upgrade of most detectors being prepared for Run 3 (221) increase of instantaneous luminosity by factor 5, aiming at collecting 5 fb 1 within Run4 for pushing sensitivity to rarest processes G. Graziani slide 38 MASS 216

39 Additional Material G. Graziani slide 39 MASS 216

40 B K µ + µ rare FCNC decay in the SM (BR 1 6 ). Analysis of decay kinematics provides a rich test-bench of effective operators describing the decay dynamics. NP can contribute in many ways Most studied variables are traditionally: A FB : forward-backward asymmetry F L : fraction of the K longitudinal polarization Differential branching fraction as a function of q 2 G. Graziani slide 4 MASS 216

41 The P 5 anomaly New basis of observables, less dependent on hadronic form factors (i.e. on long-distance effects), introduced by theorists in recent years [JHEP 5 (213) 137] Measurements in new basis exhibit significant discrepancy in the P 5 variable. Could be explained by the contribution of a new vector current (Z ). A global fit of the observables results in a value of the vector coupling strength Re(C 9 ) which is 3.4 σ away from the SM prediction. 5 P' 2 1 LHCb SM from DHMV 2 χ 15 SM q 2 5 LHCb Re (C 9 ) 2 [GeV /c 4 ] JHEP 2 (216) 14 G. Graziani slide 41 MASS 216

42 γ angle 1-CL γ = arg ( V udvub V cd V cb ) is the least known CKM angle Preliminary result LHCB-CONF Measured from tree level B DK decays, expected to be nearly insensitive to New Physics loop processes like B hh comparison can reveal NP % LHCb Preliminary 95.5% γ [ ] B s B + B decays decays decays Combination LHCb combination : γ = ( )o B factories: BaBar: γ = (7 ± 18) o Belle: γ = ( )o G. Graziani slide 42 MASS 216

43 Status of φ s from B s J/ψKK and B s J/ψπ + π G. Graziani slide 43 MASS 216

44 Implications of φ s and B s µ + µ G. Graziani slide 44 MASS 216

45 Argand plots for tetra/pentaquark candidates The resonant character of the new exotic states can be tested by fitting the Re and Im part of their amplitude in bins of the invariant mass. For a physical resonance, the resulting Argand plot is expected to show the typical circular trajectory; The technique was used in LHCb to assess the resonant character of the Z(443) state For the pentaquark candidates, statistics is more limited, though the circular behavior can be seen for the 445 MeV state Z Im A.2 LHCb Z(443) Im A P c (a) (b) PRL 112 (214) 2222 Z Re A P c (445) P c (438) LHCb PRL 115 (215) P c Re A Re A P c G. Graziani slide 45 MASS 216

46 LHCb Outreach Selected list of NP-sensitive tests on flavour G. Graziani slide 46 MASS 216