Measurements of R K and R K* at LHCb

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1 Measurements of R K and R K* at LHCb Marie-Hélène Schune Laboratoire de l Accélérateur Linéaire, Orsay On behalf of the LHCb Collaboration B K* (K π) e + e - candidate Instant Workshop on B meson anomalies,may 18th 17 1

2 The R ratios family In the SM : l=e, μ or τ R K, R K*, R φ q = M(ll ) R H =1 (at 1-3 ) in the SM (neglecting lepton masses) QED effects ~ % arxiv: Instant Workshop on B meson anomalies,may 18th 17

3 Experimentally challenging at the LHC B à K * µµ Signal Signal arxiv: B à K * ee ψ(s) J/ψ PartReco Background PartReco Background Electrons emit a large amount of bremsstrahlung degraded momentum and mass resolutions recovery procedure is in place but incomplete (calorimeter acceptance, E T of the photon > 75 MeV.) the reconstructed B mass shifts towards lower values and events migrate in and out of the q bins Instant Workshop on B meson anomalies,may 18th 17 3

4 LHC : 15 MHz of visible crossing LHCb : readout of the detector : 1 MHz hardware trigger : L Muon p T > GeV L Electron E T >.5 3. GeV L Hadron E T > 3.5 GeV K* ll Generator level, 1.1<q <6 GeV /c 4 LHCb Internal For illustration only Max of lepton p T (GeV) Electron channels : three exclusive trigger categories Muon channels : one single muon trigger category Other (LI) 3 4

5 Selection as similar as possible between µµ and ee for physics-related variables Mitigating electron/muon differences The ee channels are treated separately for the various trigger categories (different mass shapes, different background levels, different efficiencies ) The efficiencies are determined using simulation, but tuned using data Blind analyses Instant Workshop on B meson anomalies,may 18th 17 5

6 in 14 : R(K) PRL 113 (14) Run1 : 3 fb -1 1<q < 6 GeV /c 4 J/ψ µµ 16 ± k ee 54 ± 8 6k Electron trigger Hadron trigger TIS trigger Instant Workshop on B meson anomalies,may 18th 17 6

7 1<q < 6 GeV /c 4 PRL 113 (14) LE LH LI.6 standard deviations from the SM prediction Instant Workshop on B meson anomalies,may 18th 17 7

8 Replace the K by a K * Run1 : 3 fb -1 arxiv: K* : M(K + π ) = M(K(89) ) ± 1 MeV Two hadrons instead of one : lower p T, higher combinatorial background Low-q : [ ] GeV /c 4 M(ll ) : [1 149] MeV/c Central-q : [1.1-6.] GeV /c 4 M(ll ) : [ ] MeV/c The φ resonance is fully included in the low-q region The J/ψ leakage is limited in the central-q region 8

9 Analysis roadmap : Selection using MVA & kinematics properties of the event (ee) Data/simulation differences in Kπ ee mass reconstruction obtained from J/ψ(ee) Kπ Partially reconstructed background : simulation checked against data Details in the backup slides To compute the absolute scale of the efficiency in the ee and µµ channels : large set of corrections to the simulation, based on tag and probe technique Particle Identification Generator (event multiplicity, B kinematics) Trigger Residual discrepancies in variables entering the MVA tool used to separate the signal from background. Instant Workshop on B meson anomalies,may 18th 17 9

10 Low-q Central-q J/ψ B K* µµ Candidates per 1 MeV/c Pulls LHCb Signal Combinatorial.45<q <1.1 [GeV /c 4 ] m(k + π µ + µ ) [MeV/c ] Candidates per 1 MeV/c Pulls LHCb Signal Combinatorial 1.1<q <6. [GeV /c 4 ] m(k + π µ + µ ) [MeV/c ] Candidates per 1 MeV/c Pulls LHCb Signal Combinatorial + Λ K pj/ψ ( µ + µ b ) * B K J/ψ ( µ + µ s ) m(k + π µ + µ ) [MeV/c ] m(k 56 π µ + µ ) [MeV/c 58 ] m(k 56 π µ + µ ) [MeV/c 58 ] m(k 56 π µ + µ ) [MeV/c 58 ] B K* ee Candidates per 34 MeV/c Candidates per 34 MeV/c Pulls 5 LHCb 1 LHCbSignal Combinatorial Signal 15 B X ( YK * )e + e Combinatorial 1 1 B X( YK *.45<q <1.1 [GeV)e/c + e 4 ] m(k m(k π + e π + e + e) ) [MeV/c ] Candidates per 34 MeV/c Candidates Pulls per 34 MeV/c LHCb LHCb Signal Combinatorial Signal B X Combinatorial ( YK * )e + e * B J/ψ ( e* K X( YK + e )ee ) B K J/ ψ( ee) 1.1<q <6. [GeV /c 4 ] m(k π e + e ) [MeV/c ] m(k m(k π + e π + e + e) ) [MeV/c ] * Candidates per 34 MeV/c Candidates per 34 MeV/c Pulls m(k π e + e ) [MeV/c ] LHCb LHCb Signal Combinatorial Signal Combinatorial Λ pj/ψ ( e + e b K ) * B + J/ψ ( e K pj/ψ ( e + e + s K ) e ) m(k m(k π + e π + e + e) ) [MeV/c ] Λ b + * B K J/ψ ( e + e s ) Yields : Low-q Central-q J/ψ µµ 85 ± ± 1 74k ee 89 ± ± 14 58k arxiv: Instant Workshop on B meson anomalies,may 18th 17 1

11 Crosschecks : = ~ independent of the decay kinematics and event multiplicity (non flatness in the systematics of R K* ) Extremely stringent test, systematics due to corrections larger than those for R K* BR(B à K * µµ) in good agreement with arxiv: compatible with expectations If corrections to simulation are not accounted for, the ratio of the efficiencies (and thus R K* ) changes by less than 5% Instant Workshop on B meson anomalies,may 18th 17 11

12 Other checks : distributions obtained from background-subtracted data (splot NIM A555, (5)) and compared to simulation Low-q Central-q Good agreement between electrons and muons and data and simulation Distributions normalized to the same area arxiv: Instant Workshop on B meson anomalies,may 18th 17 1

13 Low-q Central-q arxiv: ee/µµ difference expected (threshold) Distributions normalized to the same area Instant Workshop on B meson anomalies,may 18th 17 13

14 Systematics uncertainties on R K* : arxiv: Use of a double ratio : many experimental systematic effects cancel Statistically dominated (~ 15%) (table in %) Brem tail description Residual background contamination due to B K * J/ψ(ee) events with a K e or π e swap Instant Workshop on B meson anomalies,may 18th 17 14

15 ln L best ) (ln L LHCb LE LH LI Combined Combined (stat) ln L best ) (ln L LHCb LE LH LI Combined Combined (stat) 1.45<q <1.1 [GeV /c 4 ] R K * 1 1.1<q <6. [GeV /c 4 ] R K * arxiv: Good agreement between trigger categories Instant Workshop on B meson anomalies,may 18th 17 15

16 arxiv: arxiv: arxiv: , , arxiv: , arxiv: , , flav-io/flavio arxiv: Compatibility with the SM expectation(s) : Low-q :.1.3 standard deviations Central-q :.4.5 standard deviations Instant Workshop on B meson anomalies,may 18th 17 16

17 Summary PRL 113 (14) arxiv: K φ Mitesh talk! Instant Workshop on B meson anomalies,may 18th LHCb the R factory

18 Backup slides Instant Workshop on B meson anomalies,may 18th 17 18

19 Fit MC to extract initial parameters Fit the data allowing (some) parameters to vary Signal Ipatia Free parameters Backgrounds Combinatorial Λ b mass shift and width scale exponential simulation & data µµ B s same as signal but shifted by m Bs -m B Instant Workshop on B meson anomalies,may 18th 17 19

20 Fit MC in different trigger and bremsstrahlung categories to extract initial parameters (separately for all modes) Combine bremsstrahlung PDFs into one signal model per each trigger category (bremsstrahlung fractions fixed from MC) Fit the data in trigger categories allowing (some) parameters to vary Signal γ (1γ and γ) Crystal-Ball (Crystal-Ball and Gaussian) Free parameters mass shift and width scale Backgrounds Combinatorial exponential Λ b simulation & data, yield constrained using muons B s same as signal but shifted by m Bs -m B, yield constrained using muons Leakage simulation, yield constrained using data Part-Reco simulation & data ee * Create a K 1 +K cocktail from simulation but using data to determine the relative fraction * Use splotted data from LHCb-PAPER-14-3 to re-weight B Kππee simulated events Candidates per 35 MeV/c 6 LHCb (a) + B K + π + π - µ + µ - Instant Workshop on B meson anomalies,may 1 18th JHEP 1 (14) 64 m(k + π + π - ) [MeV/c ]

21 Fraction of events [%] LHCb B K * J/ ψ ( e + e ) Data Simulation Fraction of events [%] LHCb B K * γ ( e + e ) Data Simulation LE LH LI LE LH LI LE LH LI γ 1γ γ LE LH LI LE LH LI LE LH LI γ 1γ γ Instant Workshop on B meson anomalies,may 18th 17 1

22 Selection steps Pre-selection requirements on trigger and quality of the candidates Cuts to remove the peaking backgrounds Particle identification to further reduce the background Multivariate classifier to reject the combinatorial background Kinematic requirements to reduce the partially-reconstructed backgrounds Multiple candidates randomly rejected Instant Workshop on B meson anomalies,may 18th 17

23 On the low q region and the hadronic resonances : In the SM R K* ~.9, we are in a regime where electrons and muons are very similar V BR(Vàee) BR(V൵) BR(B àk*v) BR(B àk*v(ee)) BR(B àk*v(µµ)) φ (.95 ±.3) 1-4 (.87 ±.19) 1-4 (1. ±.5) 1-5 (9.5 ± 1.5)1-1 (8.7 ±.4 ) 1-1 ρ (4.7 ±.5) 1-5 (4.55 ±.8) 1-5 (3.9 ± 1.3) 1-6 (1.84 ±.61 )1-1 (1.77 ±.6 ) 1-1 ω (7.8 ±.14) 1-5 (9. ± 3.1) 1-5 (. ±.5) 1-6 (1.46 ±.37 )1-1 (1.8 ±.77 ) 1-1 φ : larger product of BR, no lepton mass effect ρ : product of BR significantly smaller than the φ. wide resonance : interference? But should be the same for electrons and muons ω : significantly smaller than the φ We are not subtracting these backgrounds ; if anything they should increase the measured value of R K* Instant Workshop on B meson anomalies,may 18th 17 3

24 V BR(Vàee) BR(V൵) BR(B àk*v) BR(B àk*v(ee)) BR(B àk*v(µµ)) η < (5.8 ±.8) 1-6 (1.59 ±.1) 1-5 < (9. ± )1-1 BR(ηàeeγ) = (6.9 ±.4 ) 1-3 BR(η൵γ) = (.31 ±.4 ) 1-3 One missing photon à in the partially reconstructed background arxiv:11.63 Instant Workshop on B meson anomalies,may 18th 17 4