Charmonium decays at the BESIII experiment

Transcription

1 Charmonium decays at the BESIII experiment Hu Jifeng for BESIII Collaboration Graduate University of Chinese Academy of Science Beijing, China Jun , 2011, Hadron2011, Muchen, Germany 6/13/2011 HU Jifeng 1

2 BEPCII/BESIII status Outline Recent Results of Charmonium Decays χ cj VV[ V = φ, ω] χ γv[ V = ρ, φ, ω] cj χ cj ppk Summary K 0 ψ ' γp[ P = π, η, η'] 6/13/2011 HU Jifeng 2

3 Air view of BEPCII /BESIII LINAC South BESIII detector 2004: start BEPCII construction 2008: test run of BEPCII 2009-now: BECPII/BESIII data taking 6/13/2011 HU Jifeng 3

4 BEPCII storage rings Beam energy: GeV Design Luminosity: cm -2 s -1 Optimum energy: 1.89 GeV Energy spread: No. of bunches: 93 Bunch length: 1.5 cm Total current: 0.91 A Circumference: 237m 6/13/2011 HU Jifeng 4

5 BESIII detector μm 6/13/2011 HU Jifeng 5

6 status So far world largest data samples: ~225 Million J/Ψ ~106 Million Ψ ~2.9 fb -1 Ψ(3770) ~0.5 fb -1 at 4.01GeV Very soon also data at higher energies to search for XYZ states and Ds physics, etc First collisions: March 2008 First collisions in BESIII: July 2008 Massive physics run in BESIII: March 2009 Record luminosity : 6.5x10 32 cm -2 s -1 6/13/2011 HU Jifeng 6

7 Hadronic decays of Motivation Study gluonium χcj gg Study Color Octet Mechanism ( qq)( qq) χ cj C. Amsler and F. E. Close, PRD 53:295(1996) G. T. Bodwin eta al., PRL 51:1125(1995) H.-W. Huang and K.T. Chao, PRD 54:6850(1996) J. Bolza et al., Eur. Phys. J. C 2:705(1998) Theory: 1. Color Octet Mechanism (COM) agrees reasonably well with experimental measurements for pseudoscalar or baryon pairs, but leaves some exceptions, for example, χ cj ΛΛ etc. 2. χ cj VV, to test COM. p pk K VV ( = ω, φ) BESIII Experiment: 1.χ cj cannot directly originate from ee collisions. 2. Ψ radiative decay (ψ γχ cj ) provides a clean environment to study these questions. 6/13/2011 HU Jifeng 7

8 χ cj arxiv: , submitted to PRL χc 1 VV χ cj ωφ BR(10-3 ) φφ ωω is suppressed due to helicity selection rule is doubly OZI suppressed. Exp. BESII measurements χ c0 0.94±0.21± ±0.58±0.41 Th χ c2 Exp. 1.70±0.30± ±0.47±0.36 Th Nucl. Phys. B201,492 SOZI DOZI BESII, PLB 642, 197 (2006) BESII, PLB 630, 7 (2005) Q. Zhao, PLB659, 221(2008) Experimental values are much larger than that from pqcd predictions. Does Color octet mechanism have a better interpretation in theory? 6/13/2011 HU Jifeng 8

9 χ cj φφ, φ Clear signal χ φφ c1 arxiv: , submitted to PRL Signal region Sideband regions φ K BESIII 1. Using kinematic fit to select γ2(k K - ) candidates 2. KK pairs reconstructed by minimizing : ( M Mφ Signal: χ cj shape from MC K K 2 ) 3. Fitting M(VV) spectrum to extract Br. Backgrounds: Normalized sidebands Phase-space for non- χ cj. 2-nd order polynomial or combinatorial bg. First observation 6/13/2011 HU Jifeng 9

10 χ cj arxiv: , submitted to PRL ωω, ω π π π ω 0 1. Using kinematic fit to select 5γ2(π π ) candidates. 2. Twoπ 0 pair reconstruction: minimizing 2 ( M γγ M π 0 ) by looping over 5γ. χ ωω c1 3. ω reconstruction: minimizing ( M π 0 M ω ) π π 2 Fitting strategy follows the previous First observation 6/13/2011 HU Jifeng 10

11 χ ωφ φφ ω φ cj π π π 0 ( ), ( ), φ K arxiv: , submitted to PRL 1. Using kinematic fit to select 3γ2K2π candidates. K 2. KK- are identified by minimizing ( M KK M φ ) 3. π 0 ω are reconstructed by minimizing 2 ( M γγ M 0 ) ( M M ω ) π 2 γγπ π 2 χ φφ cj χ ωφ cj Doubly OZI suppressed χ cj ωφ are observed for the first time. 6/13/2011 HU Jifeng 11

12 Summary for χ cj VV arxiv: , submitted to PRL 6/13/2011 HU Jifeng 12

13 Motivation and Status Phys. Rev. D 83, (2011) Relation: two gluon coupling possible glueball or hybrid states hadronization pqcd 6/13/2011 HU Jifeng 13

14 ρ, ω, ρ π π φ Phys. Rev. D 83, (2011) Reconstruction φ K K Applying 4C kinematic fit to γγπ π - or γγk K -. ω π π 0 π Using 5C(4-momentumπ 0 mass) kinematic fit for 4γπ π - candidates. π 0 reconstruction: M ( 6/13/2011 HU Jifeng 14 γ γ 1 2 σ M π 0 π 0 ) 2 M ( π π γ1γ 2 σ ω Fitting: Signal shape: BW Background: Polynomial M ω ) 2

15 Phys. Rev. D 83, (2011) Analysis Results M (γρ) M (γω) M (γφ) Br. are in unit of Fitting: Signal shape: MC Background: sideband polynomial consistent new pqcd predictions too lower than experimental measurements. See an non-pqcd explanation hadronic loop correction, D.Y Chen et al. arxiv: v2[hep-ph] CLEOc: PRL 101, (2008) pqcd: Y.J. Gao et al., 6/13/2011 HU Jifeng hep-ph/

16 Helicity Angle Phys. Rev. D 83, (2011) L: Longitudinal polarization, T: Transverse polarization, θ: Helicity angle dγ 2 1 (1 f T )cos θ f T sin Γd cosθ 2 Longitudinal polarization dominates in the 2 θ χc 1 γv As expected in axial-vector particle radiative decaying to a vector. χ c1 γρ χ c1 γω χ c1 γφ f T = ± f T = f T = /13/2011 HU Jifeng 16

17 χ cj ppk K - final state arxiv: Accepted by PRD ψ ' γχ cj γp pkk χ c0 Λ(1520) χ c1 χ c2 Λ(1520) φ First observation 1. Using 4C kinematic fit to select γppkk candidates. M ( pk ) 1.52 > 0. 07GeV M ( pk ) 1.52 > 0. 07GeV M ( K K ) 1.02 > 0. 03GeV χ cj ppkk- Non-resonance M ( pk ) 1.52 < 0. 05GeV M ( pk ) 1.52 < 0. 05GeV χ cj Λ( 1520) Λ(1520) baryon pairs 6/13/2011 HU Jifeng 17

18 χ cj Λ( 1520) Λ(1520) Non-resonance Λ( 1520) Λ(1520) double resonances selections M ( pk ) 1.52 < 0. 05GeV M ( pk ) 1.52 < 0. 05GeV χ cj ppkk- χc0 χc 1 χ c 2 6/13/2011 HU Jifeng 18

19 χ pk Λ( 1520) c. c. cj χ c < M ( p pk K ) < < M ( p pk K ) < < M ( p pk K ) < Fitting: BW Gaussian( 0, σ ) χ c0 χ c1 Branching fractions in unit of 10-4 χ c0 χ c1 χ c2 6/13/2011 HU Jifeng 19

20 χ p pφ, cj φ K K χ c < M ( p pk K ) < < M ( p pk K ) < < M ( p pk K ) < Fitting: BW Gaussian( 0, σ ) χc0 χ c 1 Branching fractions in unit of 10-5 χ c0 χ c1 χ c2 6/13/2011 HU Jifeng 20

21 Evidence for ψ γπ 0 /γη PRL 105:261801(2010) [arxiv:hep-ex/ v1] ψ ' γη ψ ' γη' 0 ψ ' γπ Mass (GeV/c 2 ) Mass (GeV/c 2 ) Branching fractions in units of /13/2011 HU Jifeng 21

22 Discussion PRL 105:261801(2010) [arxiv:hep-ex/ v1] Related to rho-pi puzzle? 6/13/2011 HU Jifeng 22

23 Summary BEPCII/BESIII: Peak luminosity > 6.3X10-32 pb -1 s -1 achieved. 106M ψ, the largest data sample in the world. Rich studies χ cj VV[ V = φ, ω] χ cj γv[ V = ρ, φ, ω] χ cj ppk K 0 ψ ' γp[ P = π, η, η'] arxiv: , submit to PRL Phys. Rev. D 83, (2011) arxiv: Accepted by PRD PRL 105:261801(2010) 6/13/2011 HU Jifeng 23

24 Thanks for your attention 6/13/2011 HU Jifeng 24

25 backup 6/13/2011 HU Jifeng 25

26 Radiative decays of ψ PRL 105:261801(2010) [arxiv:hep-ex/ v1] What can I learn? two-gluon coupling to cc states mixing of η c -η final-state radiation of light quarks π 0 form factor in time-like region Experimental challenges: ψ γη anomalously suppressed Tiny branching fraction ~10-6 6/13/2011 HU Jifeng 26

27 Branching fraction measurements of χ c0 andχ c2 to π0 π 0 and ηη PRD 81:052005(2010) [arxiv:hep-ex/ v2] 0 0 ψ ' γπ π ψ ' γηη π 0 γγ χ c2 χ c0 χ c0 χ c2 η γγ Theory: J. Bolz et al., Eur. Phys. J. C 2:705(1998) 6/13/2011 HU Jifeng 27

28 First Observation of the decaysχ cj π 0 π 0 π 0 π 0 PRD 83:012006(2011) [arxiv:hep-ex/ v2] Events with 9 photon candidates < 15 χ c0 0 π ψ γχ cj projection Branching fractions excluding χ cj K s K s,k s π 0 π 0 Sub-structure needs more study B( χ B( χ B( χ c0 c1 c π π π π ) = (3.34 ± 0.06 ± 0.44) π π π π ) = (0.57 ± 0.03 ± 0.08) π π π π ) = (1.21± 0.05 ± 0.16) /13/2011 HU Jifeng 28

29 Hadronic decays of χ cj PRD 83:012006(2011) [arxiv:hep-ex/ v2] Motivation Study gluonium χcj gg Study Color Octet Mechanism BESIII experiment: ψ' γχ cj ( qq)( qq) C. Amsler and F. E. Close, PRD 53:295(1996) G. T. Bodwin eta al., PRL 51:1125(1995) H.-W. Huang and K.T. Chao, PRD 54:6850(1996) J. Bolz et al., Eur. Phys. J. C 2:705(1998) Color Octet Mechanism have large contribution to the decays of P-wave charmonium states? Color singlet graphs(qq) Color octet graphs(qqg) Reasonably well for pseudoscalar or baryon pairs 6/13/2011 HU Jifeng 29

30 Introduction to the BESIII Experiment R σ e = σ e e hadrons e μ μ se e GeV Their properties and their decays QCD 6/13/2011 HU Jifeng 30

31 χ cj ωφ φφ ω φ π π π 0 ( ), ( ), ω φ φ φ K K 1. Using kinematic fit to select 3γ2K2π candidates. 2. KK- are identified by minimizing M ( M KK φ 2 ) 3. π 0 ω are reconstructed by minimizing 2 M M ) ( M M ) ( γγ 0 π γγπ π ω 2 Doubly OZI suppressed χ cj ωφ are observed for the first time. 6/13/2011 HU Jifeng 31

32 η / η' / η π π, π π c Search the CP or P violation through pseudoscalar decays to ππ A branching fraction of order10-27 exists only in weak interaction in SM. Higher branching fractions are possible New source existed? 0 0 6/13/2011 HU Jifeng 32

33 6/13/2011 HU Jifeng 33