Rare decays of beauty mesons

Transcription

1 Rare decays of beauty mesons on behalf of the LHCb collaboration -

2 The LHCb experiment ECAL, HCAL Particle Id RICH system Muon chambers Interaction point Velo Tracking Tracking stations 2 / 25

3 B 0 (s) µ+ µ Branching fraction measurement [arxiv: ] 2 B 0 (s) e± µ Branching fraction measurement [arxiv: ] 3 B ± K ± µ + µ Observation of a resonance at low recoil: [arxiv: ] CP asymmetry measurement: [arxiv: ] 4 B 0 K µ + µ New observables: [arxiv: ] 5 B + K + π + π γ CP and Up-Down asymmetries [LHCb-CONF ] 3 / 25

4 B0s µ+ µ Branching fractions well predicted in the SM: [Eur. Phys. J. C72 (202) 272] B(Bs0 µ+ µ ) = (3.35 ± 0.28) 0 9 B(B 0 µ+ µ ) = (.07 ± 0.0) 0 0 A doubly suppressed decay : FCNC process and helicity suppressed Very interesting to test models with an extended Higgs sector For the combined LHCb and CMS results, see Mitesh s talk 4 / 25

5 Analysis strategy Strategy similar to the previous 202 analysis. [Phys. Rev. Lett ] Blind analysis using the full 3fb of data recorded in 20 and 202. [arxiv: ] MultiVariate Analysis (MVA): Kinematic and geometrical variables Train with MC calibrated in data Tracking and PID efficiencies and mµµ resolution calibrated from data. Normalization using B+ J/ψK+ and Bd K± π Signal and background classification in BDT vs mµµ plane 5 / 25

6 Branching fractions Branching fraction measurement using a simultaneous unbinned likelihood fit to the invariant mass in 8 BDT bins. The Bs, B0 and the combinatorial yields are free. Results: [arxiv: ] : Significance = 4.0σ B(Bs0 µ+ µ ) = (stat) 0. (syst) : Significance = 2.0σ B(B 0 µ+ µ ) = (stat) 0.4 (syst) 0 6 / 25

7 B0(s) e ± µ [arxiv: ] Charged LFV forbidden in SM 0 54 But allowed in some other models (SUSY, Leptoquarks...) Previous limits from CDF experiment: [Phys. Rev. Lett. 02 (2009) 2090] B(Bs0 e ± µ ) < 2.0(2.6) 0 7 at 90(95)% CL B(B 0 e ± µ ) < 6.4(7.9) 0 8 at 90(95)% CL Using similar analysis strategy as B(s) µ+ µ : Analysis using fb of data recorded in 20 Sign and bkg classification in BDT vs meµ plane Normalized to Bd K π yield in data 7 / 25

8 B(B0(s) e± µ ) results Expected (LHCb fb ) Observed (LHCb fb ) Current (CDF 2fb ) [arxiv: ] B(Bs0 e ± µ ) at 90(95)% CL.5 (.8) 0 8. (.4) (20.6) 0 8 B(B 0 e ± µ ) at 90(95)% CL 3.8 (4.8) (3.7) (79.0) 0 9 Lower bounds on the Pati-Salam Leptoquark [Phys. Rev. D 0 (974) 275]: mlq (Bs0 e ± µ ) > 07 (0) TeV/c2 at 90(95)% CL mlq (B 0 e ± µ ) > 35 (26) TeV/c2 at 90(95)% CL 8 / 25

9 b sµµ decays NP can modify the SM amplitudes in the FCNC processes like the rare decays b sl+ l Theoretically well predicted Experimentally clean Three or four particle in the final states provide many angular observables, rates and asymmetries sensitive to NP The B± K± µ+ µ and B0 K µ+ µ have a similar analysis strategy: Pre-Selection of the events (a loose cut-based selection) BDT against combinatorial backgrounds Special vetoes to remove peaking backgrounds (ex: B0s φµµ) 9 / 25

10 Resonance in B± K± µ+ µ at low recoil full dataset, 3fb collected in 20 and 202 LHCb is able to see the structure coming from the charmonium states above the DD threshold. Results: [arxiv: ] The structure is identified as the ψ(460) see by the BES experiment. Unconstrained B[ 0 9 ] Mass [ MeV/c ] Width [ MeV/c 2 ] Phase [rad].7 ± 0.3 ψ(460) ± 5 66 ± 2.8 ± 0.3 > 6σ significance, good agreement with BES experiment 0 / 25

11 CP asymmetry in B± K± µ+ µ ACP (B ± K ± µ+ µ ) = ARAW (B ± K ± µ+ µ ) ARAW (B ± J/ψK ± ) Analysis using only the fb recorded in 20 Using the B± J/ψ K± decay to correct the production and detection asymmetry Averaging measurement with different magnet polarities to remove the left-right detector asymmetry Results: [arxiv: ] ACP (B± K± µ+ µ ) = ± 0.033(stat.) ± 0.005(syst.) ± 0.007(J/ψ K+ ) In agreement with the SM and the B0 K 0 µµ decay mode / 25

12 B0 K ( K + π )µ+ µ The decay rate of the four body final state after combining B and B decays is described by the equation below The observables FL and Si are function of Wilson coefficients and form factors. d3 (Γ + Γ ) 9 = Γ d cos θ` d cos θk dφ 32π 3 ( FL ) sin2 θk + FL cos2 θk + ( FL ) sin2 θk cos 2θ` 4 4 FL cos2 θk cos 2θ` + S3 sin2 θk sin2 θ` cos 2φ + S4 sin 2θK sin 2θ` cos φ + S5 sin 2θK sin θ` cos φ + S6 sin2 θk cos θ` + S7 sin 2θK sin θ` sin φ + S8 sin 2θK sin 2θ` sin φ + S9 sin2 θk sin2 θ` sin 2φ i 2 / 25

13 Folding technique [arxiv: ] Some authors have proposed observables with limited dependence in form-factor uncertainty: Kruger-Matias (2005), Matias et al. (202), Egede-Matias-Hurth-Ramon-Reece (2008), Bobeth-Hiller-Van Dyk (200-20), Beciveric-Schneider (202) (2) AT = P40 = p P60 = p 2S3 ( FL ) S4 ( FL )FL S7 ( FL )FL ARe T = P50 = p P80 = p S6 ( FL ) S5 ( FL )FL S8 ( FL )FL Use the following folding :φ φ (if φ < 0) and θl π θl (if θl < π/2), to measure of the P05 observables. d3 (Γ + Γ ) 9 = Γ d cos θ` d cos θk dφ 8π 3 ( FL ) sin2 θk + FL cos2 θk + ( FL ) sin2 θk cos 2θ` 4 4 (2) FL cos2 θk cos 2θ` + ( FL )AT sin2 θk sin2 θ` cos 2φ 2 p + FL ( FL )P50 sin 2θK sin θ` cos φ ] the other transformations for P04,6,8 are similar. 3 / 25

14 [arxiv: ] 0.8 SM Predictions 0.6 P 6' P 4' Results P04, P06, P08 LHCb Data q 2 [GeV2/c 4] P 8' SM Predictions LHCb 0.6 Data q 2 [GeV2/c 4] 0.8 LHCb SM Predictions Analysis using the fb recorded in 20, [arxiv: ] Results in good agreement with the SM predictions 0.6 Data q 2 [GeV2/c 4] 4 / 25

15 P 5' Results P05 [arxiv: ] 0.8 LHCb 3.7 σ local discrepancy in the region 4.3 <q2 < 8.68 GeV2 /c4 SM Predictions Data 0.5% (2.8 σ)probability to observe such a deviation considering the 24 independent measurements q 2 [GeV2/c 4] Some theoretician (Descotes-Genon et al. [arxiv: ], Altmannshofer, Straub [arxiv:308.50]) have suggested that the observed discrepancy in the observable P05 could be caused by a smaller value of the Wilson coefficient C9 w.r.t SM. See saturday Mitesh s talk 5 / 25

16 Resuslts on B+ K+ π + π γ decay Analysis using the 2fb data recorded in 202: [LHCb-CONF ] Signal Combinatorial background CP asymmetry results: Missing π Partially reconstructed ACP = 0.007±0.05(stat.)±0.008(syst.) First CP asymmetry measurement in B+ K+ π + π γ Full fit Up-Down asymmetry results: R Aud = 0 h R i R0 dγ dγ ds ds ds Im n ( J J ) 3 23 dcosθ dcos dcos θ 3 dcosθ R = λγ R θ 2 dγ 4 ds ds3 ds23 J dcosθ dcosθ Aud = ± 0.09(stat.) ± 0.003(syst.) First evidence of photon polarization in b sγ decay Significance of 4.6σ 6 / 25

17 Conclusion Rare decay are powerful probe to look for NP LHCb it s a powerful tool in the search of rare electroweak decay Confirmed evidence of Bs µ+ µ with a 4 σ significance New world s best limit on B0(s) e± µ branching fraction Observation of the ψ(460) production at high q2 in B+ K+ µ+ µ decay CP asymmetry of B+ K+ µ+ µ in agreement with SM Observation of a local discrepancy in the low q2 region in the observable P05 in the decay B0 K 0 µ+ µ CP and Up-Down asymmetries in the B+ K+ π + π γ c We are now looking at the full dataset sample, stay tuned for the 3fb analyses 7 / 25

18 BACKUP 8 / 25

19 B0 µ+ µ upper limit Limit at Exp. bkg+sm Exp. bkg Observed 90% CL %CL No significant evidence of signal over background 9 / 25

20 Pati-Salam Model The Pati-Salam Model is a unified model describing a quark-lepton unification. In this model, the lepton number is identified as a fourth color. The Pati-Salam bosons are called Leptoquarks since they mediate transition between leptons and quarks. Search for leptoquarks are also done at ATLAS and CMS: Limit at 95%CL st generation scalar leptoquarks 2nd generation scalar leptoquarks 3rd generation scalar leptoquarks ATLAS mlq > 660 GeV mlq > 685 GeV mlq > 534 GeV mlq mlq mlq CMS > 830 GeV > 840 GeV > 525 GeV ATLAS results: [arxiv: ], [arxiv: ], [arxiv: ] CMS results: [arxiv: ], [arxiv: ], [arxiv: ] 20 / 25

21 Resonance in B± K± µ+ µ at low recoil The different hypothesis tested for the resonance in B± K± µ+ µ 2 / 25

22 Folding for P04 The folding for P04 (S4 ) is defined as : φ φ (for φ < 0), φ π φ (for θl > π/2), θl π θl (for θl > π/2) and gives: d3 (Γ + Γ ) 9 = Γ d cos θ` d cos θk dφ 8π 3 ( FL ) sin2 θk + FL cos2 θk + ( FL ) sin2 θk cos 2θ` 4 4 (2) 2 FL cos θk cos 2θ` + ( FL )AT sin2 θk sin2 θ` cos 2φ 2 p + FL ( FL )P40 sin 2θK sin 2θ` cos φ ] 22 / 25

23 Folding for P06 The folding for P06 (S7 ) is defined as : φ π φ (for φ > π/2), φ π φ (for φ < π/2), θl π θl (for θl > π/2) and gives: d3 (Γ + Γ ) 9 = Γ d cos θ` d cos θk dφ 8π 3 ( FL ) sin2 θk + FL cos2 θk + ( FL ) sin2 θk cos 2θ` 4 4 (2) 2 FL cos θk cos 2θ` + ( FL )AT sin2 θk sin2 θ` cos 2φ 2 p + FL ( FL )P60 sin 2θK sin θ` sin φ ] 23 / 25

24 Folding for P08 The folding for P08 (S8 ) is defined as : φ π φ (for φ > π/2), φ π φ (for φ < π/2), θl π θl (for θl > π/2), θk π θk (for θl > π/2) and gives: d3 (Γ + Γ ) 9 = Γ d cos θ` d cos θk dφ 8π 3 ( FL ) sin2 θk + FL cos2 θk + ( FL ) sin2 θk cos 2θ` 4 4 (2) FL cos2 θk cos 2θ` + ( FL )AT sin2 θk sin2 θ` cos 2φ 2 p + FL ( FL )P80 sin 2θK sin 2θ` sin φ ] 24 / 25

25 Up-Down asymmetry in B± K± π + π γ [LHCb-CONF ] Invariant K ππγ mass for B+ (left) and B (right) candidates and Up (top) and Down (bottom) subsamples 25 / 25