J/ψ production related analysis at Belle

Transcription

1 J/ψ production related analysis at Belle X. H. He, J. Wang, Y. Ban Peking University October 13, 2011 J/ψ production related analysis at Belle 1

2 Outline e + e - J/ψ ρ (φ) Introduction Monte Carlo simulation Data reconstruction Data fitting & results Systematics Summary e + e - J/ψ X(1835) Introduction Event selection Background analysis Data fitting and results Systematics Summary J/ψ production related analysis at Belle 2

3 KEKB/Belle =10.58GeV J/ψ production related analysis at Belle 3

4 e + e - J/ψ + ( ) Measurements of e + e - J/ψ + ( ) decays (J/ψ μ + μ -, π + π -, K + K - ) J/ψ production related analysis at Belle 4

5 Introduction: e + e - J/ψ + ( ) 1. e + e - -> ρ 0 ρ 0 and e + e - -> ρ 0 φ were studied by BABAR(PRL 97, (2006)). The charge-conjugation parity C = +1 judged from the final states, is contradict to e + e - annihilation via one single virtual photon with C= Two-virtual-photon exchange model for production of neutral vector meson pairs in e + e - annihilation was studied in arxiv:hep-ph/ The theory calculation is consist with the result measured by BABAR. J/ψ production related analysis at Belle 5

6 Decay mechanism Theory model Two-virtual-photo exchange or Two-Virtual-Photon Annihilation(TVPA) for the production of neutral vector meson pairs in e + e - annihilation, for masses which are small compared to s to leading order in m 2 /s, gives [1] where θ is the angle between the electron and the V 1 momenta in c.m. frame. According to this model, there would be a sin²θ H distribution in the ρ -> π + π -,φ -> K + K - decays. θ H is the angle between π + (K + ) momenta in ρ (φ) frame and ρ (φ) momenta in c.m frame. [1] M. Peskin arxiv:hep-ph/ , 2006 J/ψ production related analysis at Belle 6

7 Monte Carlo simulation The production angle cosθ and helicity cosθ H distributions are reweighted to reproduce the expectation from TVPA as shown in the following figures for e + e - -> J/ψ as a demonstration. Figure: Production angle distributions of ρ, helicity distributions of ρ. J/ψ production related analysis at Belle 7

8 Data set and selection criteria Data set: all Belle data, 960/fb Selection criteria: Good K, pi and μ identification Recoil mass of J/φ > 0 Angle between J/φ and ρ(φ)> 175 o The difference between the energy of J/ψ ρ(φ) in center of mass frame and s -0.3 to 0.2 J/ψ mass window is 30Mev J/ψ production related analysis at Belle 8

9 Event reconstruction from data Mass distributions during the selection (J/psi reconstructed from μ + μ - ) e + e - -> J/ψ + ρ μμ mass in ρ window ππ mass in J/ψ window mass recoil to J/ψ μμ mass in ρ window KK mass in J/ψ window e + e - -> J/ψ + φ mass recoil to J/ψ J/ψ production related analysis at Belle 9

10 Backgrounds (J/ψ sideband data) The red line is global fit The blue line is background of e + e - ->μμρ The green line is e + e - ->μμππ J/ψ production related analysis at Belle 10

11 Data fitting J/ψ signal region a ±0.012 a ±0.011 nsig 161±19 nbkg 25±13 N bkg1 J/ψsideband 98 scaled N bkg2 J/ψsideband 41 The red line is signal(breit-wigner) The yellow line is background of ee- > μ μ π π and ee-> μ μ ρ The green line is background of ee->j/ ψ π π J/ψ production related analysis at Belle 11

12 Data fitting J/ψ signal region nsig 7.7±2.8 nbkg 5.0±3.8 N bkg1 J/ψsideband 4.9 scaled N bkg2 J/ψsideband 0.45 ee -> J/ψφ ee -> μμφ ee ->J/ψKK ee -> KKμμ J/ψ production related analysis at Belle 12

13 Production angle and helicity study MC MC Consistent with theoretic prediction using Two-Virtual Photon Annihilation very well. J/ψ production related analysis at Belle 13

14 Systematics The error from tracking efficiency is ~1% per track; The uncertainty on lepton identification is ~1.5% per track; The uncertainty on kaon/pion identification is ~0.5% per track; The systematics from fitting procedure is estimated from the variation in the number of events in different fitting methods: * mass and width fixed to MC shape; * mass and width fixed to J/ψ sideband ρfitting shape; * mass and width vary ±σ; The systematics from combinatorial background subtraction is estimated from the fitting results variation by varying the input bg position and contribution; J/ψ production related analysis at Belle 14

15 Systematics The systematic uncertainties is summed in the follow table. J/ψ production related analysis at Belle 15

16 e + e - J/ψ ( ): Summary After considering the systematics, the final results (960/fb) as as below: σ fid (e + e - ->J/ψ+ρ) = 10.1 ±1.2(stat)±1.2(syst) fb σ fid (e + e - ->J/ψ+ φ) = 1.38 ±0.5(stat)±0.2 (syst) fb ( upper limit: 2.1 fb at 90% CL) The results are consistent with the theoretic prediction with TVPA mechanism: (hep-ph/ ) J/ψ production related analysis at Belle 16

17 X(1835) search at Belle Search for X(1835) in the J/ψ recoil mass in decay e + e - J/ψ + X J/ψ production related analysis at Belle 17

18 Introduction: X(1835) found by BES M = ±6.1(stat) ±2.7(syst) Γ = 67.7±20.3(stat)±7.7(syst) Resonance state of pp or glueball state or others? J/ψ production related analysis at Belle 18

19 Introduction In theory, X(1835) can also produced in e + e - J/ψ X(1835)[1]. Figure: Feynman diagram of e + e - H + G J [1] A. S. Goldhaber and T. Goldman, Phys. Lett. B 344 (1995) J/ψ production related analysis at Belle 19

20 Search method and selection criteria We selected events of ee J/ψ+anything, then search X(1835) in the recoil mass spectrum of J/ψ. Selection criteria: Number of charged tracks N >4; Good muon, electron identification; Recoil mass of J/ψ is constrained to improve the J/ψ resolution J/ψ vertex fit is performed to the reconstructed J/ψ J/ψ production related analysis at Belle 20

21 Searching for X(1835) in recoil mass against J/ψ (672 fb -1 data) Signal window: η c χ c0 η c (2S) J/ψ sideband: J/ψ production related analysis at Belle 21

22 Background study Green : background of combination μμ Red: continuum background (u,d,s,c) MC generated using EvtGen; Blue: just u,d,s continuum MC data. Combinatorial events fallen in J/psi mass window(green histogram); Peaking background: 1. Prompt J/ψ a. b. 2. Non-prompt J/psi J/ψ production related analysis at Belle 22

23 Fitting/Result f cut off : the fraction of non-isr(e radiativeγ <10Mev) events; ξ Born = [2] [2] T.Uglov. Belle note636 J/ψ production related analysis at Belle 23

24 Systematics The uncertainties caused by the background estimation are significant; The X(1835) found by BES exhibits (1+cos 2 θ) distribution, we generate flat and sin 2 θ distribution to estimate the systematic error caused by polarization of J/ψ; The selection of mass window of J/ψ, we different mass region as mass window ; Other contributions of systematics come from the uncertainty of luminosity; track reconstruction efficiency and lepton identification in J/ψreconstruction etc. J/ψ production related analysis at Belle 24

25 e + e - J/ψ X(1835) search: summary With 672 fb -1 data samples collected on and off Υ(4S) resonance with the Belle detector at KEKB, the process e + e - J/ψX(1835) was studied by using recoil mass method. No significant evidence is found for e + e - J/ψX(1835). An upper limit is set to be: ς Born (e + e - J/ψ X(1835)) B(X(1835) > 2tracks ) < C.L J/ψ production related analysis at Belle 25

26 e + e - J/ψ X(1835) search: more statistics 672/fb 960/fb With more statistic, no significant X(1835) signal found in J/ψ recoil mass spectrum. J/ψ production related analysis at Belle 25

27 Conclusion We measured the cross section of e + e - J/ψ+ ρ (φ) ( cosθ*<0.8) to be: σ fid (e + e - J/ψ+ρ) = 10.1 ±1.2(stat)±1.2(syst) fb, σ fid (e + e - J/ψ+ φ) = 1.38 ±0.5(stat)±0.2 (syst) fb (2.1 The angular distribution indicates that, the decays are consistent with Two Virtual-Photons Annihilation mechanism, instead of e + e - annihilation via single virtual photon (C= -1). If X(1835) is a glue-ball candidate, it can be produced with J/ψ. from J/ψ recoil mass spectrum we give an upper limit of X(1835) at 672/fb data: ς Born (e + e - J/ψ X(1835)) B(X(1835) > 2tracks ) < C.L more statistics is needed to confirm the glue-ball hypothesis in the search via e + e - J/ψ+ G J. J/ψ production related analysis at Belle 26

28 Thanks!

29 Back up 1. Cross section of e + e - -> ρ 0 ρ 0 and e + e - -> ρ 0 φ measured in BABAR(PRL 97, (2006)) σ fid (e + e - ->ρ 0 ρ 0 ) = 20.7 ±0.7(stat)±2.7(syst) fb, σ fid (e + e - ->ρ 0 φ) = 5.7 ±0.5(stat)±0.8 (syst) fb 2. The TVPA model gives the angular distribution dσ V1V2 dcosθ ~ a+cos 2 θ b cos 2 θ a = 1+8Mv2 s b = 1+ 4Mv4 s 2 for m v = m ρ s =(10.58) 2 Gev 2, a = 1.043, b =