Studies of charmonium production in e + e - annihilation and B decays at BaBar

Transcription

1 Studies of charmonium production in e + e - annihilation and B decays at BaBar I. Garzia, INFN Sezione di Ferrara On behalf of the BaBar Collaboration XVI International Conference on Hadron Spectroscopy September 13-18, 2015 Newport News, VA

2 OUTLINE The BaBar detector Measurement of inclusive production of charm and charmonium states in the two body decays B X c K ± BaBar Preliminary Dalitz plot analysis of B 0 D - D 0 K + and B + D 0 D 0 K + Phys. Rev. D 91, (2015) I. Garzia, HADRON

3 The BaBar detector PEP-II: asymmetric e + e - collider at the ϒ(4S) resonance ( s=10.58 GeV): 9 GeV (e-) x 3.1 GeV (e+) Data taking: Primary goal: B physics Instrumented Flux Return RPCs/LSTs 1.5 T superconducting solenoid BaBar collected about 531 fb -1 around the ϒ(4S) resonance 467 million BB pairs 690 million charm events NIM A479,1 (2002), update: NIM A729, 615 (2013) EMC 6580 CsI(Tl) crystals Drift Chamber 40 layers DIRC (PID) 144 quartz bars, PMs Silicon Vertex Tracker 5 layers, double sided strips I. Garzia, HADRON

4 Charmonium the B factories B meson decays Two-photon production States of any quantum number can be produced Initial State Radiation (ISR) C-even charmonium states with J 1 can be produced Double-charmonium production Only states with J PC =1 can be produced I. Garzia, HADRON 2015 Only charmonium states with C = + are allowed to be produced in association with the J/ψ or the ψ(2s) 4

5 Measurement of inclusive production of charm and charmonium states in two body decays B X c K ± BaBar Preliminary I. Garzia, HADRON

6 Introduction The inclusive B decays to 2-body final state B ± K ± X c is a powerful laboratory to study charmonium state production Allow the measurements of absolute branching fractions (BFs) for ordinary charmonium spectrum, and search for exotic charm mesons previous BaBar results based on L=210 fb -1 [PRL96,052002(2006)] ü Measurement of absolute BF(B ± K ± X c ) ü Upper limit for B ± K ± X(3872) New BaBar preliminary results: ü update of the 2006 publication ü L=424 fb -1 ü Improvement on the B hadronic reconstruction ü Charged kaon recoil against a neutral B meson ü The search of narrow resonances is extended to a larger mass region ü Sensitivity: BF ~ 10-4 I. Garzia, HADRON

7 Analysis strategy: inclusive B + sample A typical approach of this analysis is based on the fully reconstruction of the B meson decay (exclusive reconstruction). In this analysis, we use a complementary approach: Recoil (missing mass) spectra measure inclusive decay B ± K ± X c BF This approach is based on the measurement of the kaon momentum spectrum measured in the B center-of-mass (c.m.) frame The B c.m. frame is determined by fully reconstructing the other B meson Peaks in the kaon momentum spectrum will be observed Fit to m ES to determine B event yield: q m ES = E 2 CM /4 p2 B Neutral network (NN) is used to increase the signal to noise ratio Most K produced in B-decays are daughters of D-meson Another NN is used to discriminate between daughter and grand-daughter K The two NNs are combined into a SuperNN to further optimize the S 2 /(S+B) ratio BaBar Preliminary Generic B Generic B 0 ccbar uds data I. Garzia, HADRON m ES

8 Charmonium mass regions Low mass charmonium region BaBar Preliminary High mass charmonium region BaBar Preliminary Excited D ** mesons χ 1 signal: unknown admixture of χ c1 and h c states NO X(3872), ψ(3770) and χ c2 ü Signal parameters: fixed to MC values ü Bkg shape: fourth-degree polynomial ü 5 free parameters: J/ψ and η c yields, and 3 parameters used for bkg description ü Region blinded during the analysis ü Signal: 8 gaussians of fixed position (PDG) and width from MC ü Bkg. shape: fourth-degree polynomial ü 11 free parameters: 3 for bkg description, and the yield of the 8 gaussians I. Garzia, HADRON

9 Full charmonium mass region and neutral D (*) resonances Background subtracted spectrum ü Uniform cut of the SuperNN value > 0.92 ü Only 6 peaks are clearly evident: ψ, η c, χ c1, χ c0, J/ψ and η c ü No narrow resonances observed in the very high mass region (0.2<p K <1.2 GeV/c 2 ) D **0 (2680) BaBar Preliminary BaBar Preliminary Low mass region : excited D resonances ü Two-body peaks corresponding to the B ± K ± D system ü The statistical significance of the D **0 (2680) is ~ 3.3σ D **0 (2420) D *0 D 0 I. Garzia, HADRON

10 Inclusive B 0 sample: charged D (*), and search for charmonium-like states ü Charged kaon selected with a fully reconstructed B 0 meson ü High purity sample ü In the D region: D ±, D *±, and their excited states ü In the charmonium region: charmonium-like charged states (Z c (3900), Z c (4050), ) BaBar Preliminary BaBar Preliminary D **± (2420) D *± D ± Charged D (*) region: ü Clear signals seen for D ±, D *±, and D **± (2420) ü No higher mass states are observed High mass region: ü no evidence for any resonance is found ü BF upper limits for the Z c (3900), Z c (4050), and Z c (4430) are , , and , respectively (at 90% c.l.) I. Garzia, HADRON

11 Charmonium and D-meson: fit results (MeV) (MeV) Low mass region B ± K ± X c High mass region 3632±7 (MeV) B ± K ± X c low mass region: excited D resonances B 0 K ± X c low mass region: excited D resonances D ** (2420) 0 D ** (2680) 0 D ** (2420) ± 2680±3 I. Garzia, HADRON

12 Dalitz plot analysis of B 0 D - D 0 K + and B + D 0 D 0 K + Phys. Rev. D 91, (2015) I. Garzia, HADRON

13 Introduction The study of B D (*) D (*) K decays allows to search for Charmonium or charmonium-like resonances: D (*) D (*) cs resonances: D (*) K Determine properties of the D s1 (2536), ψ(3770) meson, and X(3872) state PRL100, (2008) PRL97, (2006) Determine the properties of the D * s1 (2700)+ meson ü Observed first by BaBar in PRL 97,222001(2006) and PRD 80, (2009) ü Confirmed by Belle in B D 0 D 0 K + decays (PRL 100, (2008)) ü Studied also by LHCb: JHEP 10,151 (2012) D sj (2700) + ψ(3770) ψ(4160) threshold Phace-space component I. Garzia, HADRON

14 Data sample L=429 fb -1 collected at the ϒ(4S) 22 decay modes: D 0 K - π +, D 0 K - π + π 0, D 0 K - π + π - π + D + K - π + π + For D 0 D 0 K +, at least one D 0 is required to decay to K - π + Two kinematic variables used to isolate B signal Events with ΔE <10-14 MeV Beam-energy-substituted mass 5.275<m ES <5.284 GeV/c 2 ü B 0 D - D 0 K + : 1470 events with purity of (36.8 ± 2.8 ± 2.1)% ü B + D 0 D 0 K + : 1894 events with purity of (41.6 ± 2.5 ± 3.1)% I. Garzia, HADRON

15 Dalitz plot analysis: method We use an isobar model formalism: The decays are described by a sum of amplitudes: M= i c i A i A i = complex amplitude complex coefficients c i ρ i e iφ_i Unbinned maximum likelihood fit to extract the complex amplitudes, and the mass and the width of the D * s1 (2700)+ - m 1 and m 2 are the invariant mass of DD 0 and D 0 K + for the event n - p = signal purity - ε(m 1,m 2 ) is the efficiency across the Dalitz plot - B(m 12,m 22 ) is the background in the Dalitz plot We minimize the total negative log likelihood, and we choose the fit with the smallest value I. Garzia, HADRON

16 Dalitz plot analysis: preliminary fits Known amplitudes that give a contribution: Non resonant events D * s1 (2700)+ meson D * s2 (2573)+ D 0 K +, never observed in D (*) D (*) K Additional contribution for the B + D 0 D 0 K + ψ(3770) meson ψ(4160) meson χ c2 (2P), ψ(4040), ψ(4415) mesons can also decay to D 0 D 0 : they are treated separately and not included in the fit ü Mass and width of D * s1 (2700)+ are free parameters ü All the other masses and widths are fixed to their world average values I. Garzia, HADRON

17 D 0 K + low-mass excess Fit projections on the D 0 K + invariant mass: The D 0 K + region between 2350 and 2500 MeV/c 2 is not well described Belle experiment also reported this enhancement [PRL100,092001(2008)] We checked that this enhancement is due to signal and not to background The excess could be explained by an additional resonance speculative assumption Since it is not possible to conclude that a real resonance contributes in the low-mass region, an exponential function (arbitrary function) is used to describe the enhancement. I. Garzia, HADRON

18 Results ü Large contribution of the D * s1 (2700)+ resonance, observed for the first time in the decay B 0 D - D 0 K + ü Small contribution of the D * s2 (2573)+ meson to B 0 D - D 0 K +, negligible compared to the other mode ü Low-mass effect has an important contribution ü B + D 0 D 0 K + : Observation of ψ(3770) D 0 D 0 ψ(4160) D 0 D 0 is needed to improve the description of the data ü No need for D * sj (2860), D sj (3040), χ c2 (2P), ψ(4040), ψ(4415) I. Garzia, HADRON

19 Conclusion 1. BaBar has obtained preliminary results of the inclusive production of charm and charmonium states in two-body decays B KX c ü Improvement of absolute BF measurements, which is needed for the deep understanding of charmonium physics ü Evidence of a new D **0 resonance is observed at a mass of (2680±3) MeV, with a significance of 3.3σ. We do not observe the charged partner 2. Dalitz plot analysis of the modes B 0 D - D 0 K + and B + D 0 D 0 K + was performed at BaBar and published in PRD 91,052002(2015) ü D s1* (2700) meson is observed in both final states (J P =1 ). This resonance could be interpreted as the n 2S+1 L J =1 3 D 1 cs state (PRD 89,074023), or as the first radial excitation of the D * s (2112) meson (23 S 1 ) (PRD 80,071502; PRD 86,054024), or as a mixture between the 2 3 S 1 and the 1 3 D 1 states (E.P.J.C 71,1582), ü Enhancement observed between 2350 MeV and 2500 MeV in the D 0 K + invariant mass: ü Not able to understand this effect ü described by an ad hoc function in the Daliz plot fit ü D * sj (2860)+ and D sj (3040) + resonances not observed in these final states I. Garzia, HADRON

20 BK slides

21 Very high charmonium mass region B ± K ± +X cc BaBar Preliminary Sensitive to narrow peaks (Γ < 20 MeV). The only structure observed (p K = GeV, m recoil = GeV) has a statistical significance < 3σ when considering the look elsewhere effect. Not sensitive to Y(4260) due to its width (Γ ~ 100 MeV) I. Garzia, HADRON 2015 bk1

22 Very high charmonium mass region B 0 K ± +X cc BaBar Preliminary Sensitive to narrow peaks (Γ < 20 MeV). No structures evident. Sensitivity to BF s ~ (3 5) x I. Garzia, HADRON 2015 bk2

23 Data sample I. Garzia, HADRON 2015 bk3

24 Partial Branching Fractions Phys. Rev. D 91, (2015) I. Garzia, HADRON 2015 bk4

25 Feynmann Diagrams for the Amplitudes B s b s W + c c s s J/, c, c, 0, 0 c,x(3872), J/ K + K, W + s u K + s K + B + b u c D ( )0 W + u B 0 d b c D ( ) d I. Garzia, HADRON 2015 bk5