Heavy flavour spectroscopy at LHCb

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1 Heavy flavour spectroscopy at LHCb Paolo Gandini University of Oxford on behalf of the LHCb collaboration Moriond QCD, La Thuile

2 Outline Several new results produced for winter conferences I will concentrate only on newest results available Heavy flavour spectroscopy is a rich and active field New! Observation of a resonance in the Ξb-π+ mass spectrum Measurement of the mass and lifetime of the Ωb baryon Model independent analysis of Λb J/Ψ p KNew searches for interesting final states Tetraquark searches at LHCb in Bsπ 2

3 LHCb Detector Fully instrumented: 2 < η < 5 Forward spectrometer Good Vertex measurements Precise Tracking Excellent PID up to 100 GeV Versatile Trigger 3

4 New! - + Ξ b Ξb π Observation of a resonance in the Ξb-π+ mass spectrum LHCb-PAPER

5 LHCb-PAPER Introduction LHCb has successfully observed two Ξb charged states Now look for the neutral CMS published in 2012 the observation of Ξb 0 PRL 108, (2012) Aim is to confirm CMS observation and measure width PRL 114, (2015) Full Run1 dataset Use a fully hadronic decay of the Ξb Look near threshold Fit with RBW convolved with resolution function from MC (BKG is a threshold function) Preliminary No other significant structure at higher mass 5

6 LHCb-PAPER Results We observe one resonant state with the following properties: Systematics CMS PRL 108, (2012) We also perform a relative production measurement Relative efficiency is taken from MC Several cross checks correct for MC/Data differences Need to take into account only the efficiency of the slow pion Most systematics cancel out Most Ξb mesons produced come from higher resonances 6

7 LHCb-PAPER Conclusions We see a consistent picture with CMS (10x precision) The state is consistent with the JP = 3/2+ resonance expected in the quark model Most precise determination of the mass and the first measurement of the width We see only ONE state above Ξb-π+ threshold But TWO are expected in this region (Ξb' Ξb* ) Therefore lower state is below the Ξb-π+ threshold Has to decay via neutral particle Ξb0π0 Ξb0γ Depending on how below threshold 7

8 New! Ωb Ωc π Measurement of the mass and lifetime of the Ωb baryon LHCb-PAPER

9 LHCb-PAPER Introduction Recent measurement of Λb Ξb- Ξb0 lifetimes by LHCb have reached < 1 2% precision Naive Heavy Quark Effective Theory predicts lifetime hierarchy: Current experimental results dominated by LHCb: Ωb events are still rare all measurement statistically limited Low production in hadronic collisions Presence of flying hyperons So far only studied by LHCb in Ωb J/Ψ Ω Phys.Lett. B736 (2014) Look for fully hadronic decays All daughters in the VELO Perform a relative lifetime measurement with respect to similar decay 9

10 LHCb-PAPER Lifetime Idea: measure signal yield in lifetime bins Used before in many analyses performed by LHCb PRL 109, (2012) PLB, 734, (2014) 122 PRL 112, (2014) PRL 113, (2014) Signal decay distribution: Exponentials Acceptance function Shape parameters fixed to full fit The efficiency corrected yield ratio is then: Fit data with a simple exponential Use known lifetime of the control mode to get an absolute value 10

11 LHCb-PAPER Lifetime Same selection for signal and control mode MVA selection Reconstruct 60 signal event Binning scheme optimized with pseudo exper Check any possible bias Ratio of efficiencies taken from MC Preliminary Ratio of yields Preliminary Phys.Lett. B736 (2014)

12 New! Model independent analysis of Λb J/Ψ p K LHCb-PAPER

13 LHCb-PAPER Introduction LHCb recently observed pentaquarks candidates in Λb J/Ψ p K Rich spectrum of Λ* resonances Pentaquark amplitudes required to describe the spectra PRL (arxiv: ) Can structures in J/ψp be due to Λ* resonances not accounted for in the model? Same dataset as previous model dependent analysis model independent analysis signal events with 5.4% background Essentially a 2 D Dalitz plot analysis working under the assumption that only contributions from resonances decaying to Kp are present Referred to as the H0 (i.e. null ) hypothesis. One can then demonstrate compatibility/incompatibility with the data. 13

14 LHCb-PAPER Methodology We work with the rectangular Dalitz variables mkp and cosθλ Describe resonance structure in (m and cosθλ) with Legendre polynomials Kp Detailed description of the analysis in the paper Summarise here only the key points Data is efficiency corrected Same efficiency parametrization as in the amplitude analysis We generate a high statistics toy data sets to illustrate possible contributions to the moments from: Λ states Pc states No interpretations are imposed on the m distribution: interpolation Kp Use PDG to get lmax Preliminary 14

15 LHCb-PAPER Null hypothesis Null hypothesis pseudo experiments Preliminary We can project the null hypothesis on mj/ψp distribution Projection on m also shows clear discrepancies J/ΨK Preliminary Preliminary H0 null hyp H0 null hyp 15

16 LHCb-PAPER Summary We have demonstrated that conventional Kp contributions fail to reproduce the data with minimal assumptions on their spins, and without any assumptions on their number, shapes or how they interfere. Non Kp contributions must be present in the data, and can be either of the exotic hadron type or due to rescattering effects among ordinary hadrons. Quantitatively, we can reject this H0 hypothesis at over 9 sigma This analysis adds to the previous model dependent evidence for exotic pentaquark states from the amplitude analysis of the same data set 16

17 New! Observation of Λb Ψ(2S) p K- and Λb J/Ψ π π p Kand precise measurement of the Λb baryon mass LHCb-PAPER

18 Λb Ψ(2S) p K- and Λb J/Ψ π π p KLHCb-PAPER

19 New! Search for Bc decays to ppπ final state LHCb-PAPER

20 Search for Bc decays to ppπ final state Charmless should decay via annihilation diagram Look below the charmonium threshold m < 2.85GeV pp Use B+ as control mode, same final state BDT selection fit in bins of BDT response B signal: LHCb-PAPER Preliminary Preliminary No significant Bc signal is found Set an upper limit 20

21 New! Tetraquark searches at LHCb in Bsπ LHCb-CONF

22 Tetraquark searches at LHCb in Bsπ D0 announced a new state on 24 Feb: X(5568) Bsπ arxiv: CERN seminar 21 March (Monday) High production rate and significance of 5.1sigma Generated several citations investigation by other collaborations Nev = 5582 ±

23 Tetraquark searches at LHCb in Bsπ Very large, clean Bs samples, different final states 66k LHCb-CONF k Slightly different selection compared to what shown at Moriond QCD Add a pion no peak observed at 5568 MeV Several cross check with B plus pion modes We can put an UL on production Resolution on mass < 1MeV BW + poly bkg 23

24 Conclusions New! Presented only newest analyses performed by LHCb Confirmed the observation of Ξb 0, measured its width and production Performed lifetime analysis of Ωb baryon in hadronic final state Performed model independent analysis of Λb J/Ψ p Kconventional Kp contributions fail to reproduce the data No evidence of a tetraquark state in Bsπ at LHCb with 10x D0 statistics 24

25 Backup Slides 25

26 - + Ξ b Ξb π Preliminary 26

27 Model dependent analysis of Λb J/Ψ p K - Λb J/Ψ p K used for precise lifetime measurement Full dataset 26k events with 5% background Unexpected peak in J/Ψ p 27 -

28 Model dependent analysis of Λb J/Ψ p K 6D amplitude fit Amplitude model includes all known Λ* states Tried to fiit without J/ψp states Adding further higher resonances and other cross checks Fit without Pq: 28 -

29 Model dependent analysis of Λb J/Ψ p K Adding two pentaquarks LHCb analysis added 2 Pc states Good fit even with reduced Λ* set Resonant behaviour Preference for JP =(3/2-,5/2+) Phase rotation visible Need to confirm quantum numbers 29 -

30 Cross checks on Tetraquark 30