Charmonium decays at the BESIII experiment Hu Jifeng for BESIII - PowerPoint PPT Presentation

Charmonium decays at the BESIII experiment Hu Jifeng for BESIII Collaboration Graduate University of Chinese Academy of Science Beijing, China Jun. 13-17, 2011, Hadron2011, Muchen, Germany 6/13/2011 HU Jifeng 1

Outline • BEPCII/BESIII status • Recent Results of Charmonium Decays χ → = φ ω [ , ] VV V cJ χ → γ = ρ φ ω [ , , ] V V cJ + − χ → ppK K cJ ψ → γ = π η η 0 ' [ , , ' ] P P • Summary 6/13/2011 HU Jifeng 2

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

BEPCII storage rings Beam energy: 1.0-2.3 GeV Design Luminosity: 1 × 10 33 cm -2 s -1 Optimum energy: 1.89 GeV Energy spread: 5.16 × 10 -4 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 HU Jifeng μ m 6/13/2011

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

χ Hadronic decays of cJ • Motivation χ → → ( )( ) gg q q q q C. Amsler and F. E. Close, PRD 53:295(1996) – Study gluonium cJ G. T. Bodwin eta al., PRL 51:1125(1995) – Study Color Octet Mechanism 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. BESIII Experiment: + K − 1. χ cJ cannot directly originate from ee collisions. p p K = ω φ ( , ) VV 2. Ψ ’ radiative decay ( ψ’ � γχ cJ ) provides a clean environment to study these questions . 6/13/2011 HU Jifeng 7

χ cJ � arXiv: 1104. 5068, submitted to PRL χ c → VV is suppressed due to helicity selection rule Nucl. Phys. B201,492 1 χ → ωφ is doubly OZI suppressed. cJ SOZI BESII measurements BR(10 -3 ) χ c0 χ c2 Exp. Th. Exp. Th. DOZI � φφ 0.94 ± 0.21 ± 0.13 1.70 ± 0.30 ± 0.25 0.086 0.154 � ωω 2.29 ± 0.58 ± 0.41 1.77 ± 0.47 ± 0.36 - - 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

+ − χ → φφ φ → , @ K K BESIII cJ arXiv: 1104. 5068, submitted to PRL 1. Using kinematic fit to select γ 2(K + K - ) candidates Signal region Sideband regions 2. KK pairs reconstructed by minimizing : φ ∑ − 2 ( ) M M φ + − K K 3. Fitting M(VV) spectrum to extract Br. Signal: χ cJ shape from MC Backgrounds: Normalized sidebands Phase-space for non- χ cJ . 2-nd order polynomial or combinatorial bg. Clear signal χ → φφ 1 c First observation 6/13/2011 HU Jifeng 9

+ − χ → ωω ω → π π π 0 , cJ arXiv: 1104. 5068, submitted to PRL 1. Using kinematic fit to select ω 5 γ 2( π + π − ) candidates. 2. Two π 0 pair reconstruction: ∑ minimizing − 2 ( ) M M γγ π 0 by looping over 5 γ . 3. ω reconstruction: minimizing χ → ωω ∑ − 2 ( ) 1 M M c ω + − π π π 0 Fitting strategy follows the previous First observation 6/13/2011 HU Jifeng 10

+ − + − χ → ωφ φφ ω φ → π π π φ → 0 ( ), ( ) , K K cJ arXiv: 1104. 5068, submitted to PRL 1. Using kinematic fit to select 3 γ2K2π candidates. 2. K+K- are identified by minimizing ∑ − 2 ( ) M KK M φ 3. π 0 ω are reconstructed by − 2 + − 2 ( ) ( ) minimizing M M M M γγ + − ω 0 π γγπ π χ → φφ cJ χ → ωφ cJ Doubly OZI suppressed χ cJ � ω φ • are observed for the first time. 6/13/2011 HU Jifeng 11

12 arXiv: 1104. 5068, submitted to PRL Summary for χ cJ � VV HU Jifeng 6/13/2011

Motivation and Status Phys. Rev. D 83, 112005 (2011) pQCD Relation: • two gluon coupling • possible glueball or hybrid states • hadronization 6/13/2011 HU Jifeng 13

ρ ω φ , , Reconstruction Phys. Rev. D 83, 112005 (2011) + − Applying 4C φ → + − ρ → π π K K kinematic fit to γγπ + π - or γγ K + K - . Using 5C(4-momentum+ π 0 mass) kinematic fit + − ω → π π π 0 for 4 γπ + π - candidates. π 0 reconstruction: − − M M M M ω + − π π γ γ γ γ 0 + π 2 2 2 ( ) ( ) 1 1 2 σ σ ω 0 π Fitting: Signal shape: BW Background: Polynomial 6/13/2011 HU Jifeng 14

Analysis Results Phys. Rev. D 83, 112005 (2011) ( γρ ) M ( γω ( γφ ) ) M M Fitting: Br. are in unit of 10 -6 . Signal shape: MC Background: sideband + polynomial pQCD predictions too lower than consistent experimental measurements. See an non-pQCD explanation “hadronic loop correction”, D.Y Chen et al. arXiv:1005.0066v2[hep-ph] new CLEOc: PRL 101, 151801 (2008) pQCD: Y.J. Gao et al., hep-ph/0701009 6/13/2011 HU Jifeng 15

Helicity Angle Phys. Rev. D 83, 112005 (2011) L: Longitudinal polarization, T: Transverse polarization, θ : Helicity angle Γ 1 d ∝ − 2 θ + 2 θ ( 1 ) cos sin f f Γ θ T T cos 2 d χ → γ V • Longitudinal polarization dominates in the 1 c As expected in axial-vector particle radiative decaying to a vector. χ → γρ χ → γω χ → γφ 1 1 1 c c c + + + 0 . 044 0 . 10 = ± 0 . 015 0 . 158 0 . 034 = + = + 0 . 090 0 . 13 0 . 247 0 . 29 f f f − 0 . 014 − − T 0 . 087 − 0 . 12 − 0 . 026 0 . 09 T T 6/13/2011 HU Jifeng 16

χ cJ � ppK + K - final state arXiv:11032661 Accepted by PRD First observation ψ → γχ → γ ' p p KK 1. Using 4C kinematic fit to select cJ χ γ ppKK candidates. 1 c Λ ( 1520 ) − − > | ( ) 1 . 52 | 0 . 07 χ χ M pK GeV 0 2 c c + − > | ( ) 1 . 52 | 0 . 07 M p K GeV − + − > | ( ) 1 . 02 | 0 . 03 M K K GeV χ cJ � ppK+K- Non-resonance φ Λ ( 1520 ) − − < | ( ) 1 . 52 | 0 . 05 M pK GeV + − < | ( ) 1 . 52 | 0 . 05 M p K GeV χ → Λ Λ ( 1520 ) ( 1520 ) cJ baryon pairs 6/13/2011 HU Jifeng 17

χ → Λ Λ ( 1520 ) ( 1520 ) χ cJ � ppK+K- cJ Non-resonance double resonances Λ Λ ( 1520 ) ( 1520 ) selections − + − < − < | ( ) 1 . 52 | 0 . 05 | ( ) 1 . 52 | 0 . 05 M pK GeV M p K GeV χ χ χ 0 1 2 c c c 6/13/2011 HU Jifeng 18

+ χ → Λ + ( 1520 ) . . p K c c cJ + K − < < 3 . 365 ( ) 3 . 455 χ M p p K 2 c + K − < < 3 . 490 ( ) 3 . 530 M p p K + K − < < 3 . 530 ( ) 3 . 580 M p p K Fitting: BW ⊗ ( σ 0 , ) Gaussian χ 0 χ c Branching fractions in unit of 10 -4 1 c χ 0 c χ 1 c χ 2 c 6/13/2011 HU Jifeng 19

+ − χ → φ φ → , p p K K cJ + K − < < 3 . 365 ( ) 3 . 455 χ M p p K 2 c + K − < < 3 . 490 ( ) 3 . 530 M p p K + K − < < 3 . 530 ( ) 3 . 580 M p p K Fitting: BW ⊗ ( σ 0 , ) Gaussian χ χ 0 1 c c Branching fractions in unit of 10 -5 χ 0 c χ 1 c χ 2 c 6/13/2011 HU Jifeng 20

Evidence for ψ ’ � γπ 0 /γη PRL 105:261801(2010) [arxiv:hep-ex/101.0885v1] ψ → γπ 0 ψ → γη ψ → γη ' ' ' ' Mass (GeV/c 2 ) Mass (GeV/c 2 ) Branching fractions in units of 10 -6 6/13/2011 HU Jifeng 21

Discussion PRL 105:261801(2010) [arxiv:hep-ex/101.0885v1] • Related to rho-pi puzzle? 6/13/2011 HU Jifeng 22

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 → = φ ω [ , ] – VV V arXiv:1104. 5068, submit to PRL cJ χ → γ = ρ φ ω [ , , ] – V V Phys. Rev. D 83, 112005 (2011) cJ + − χ → – ppK K arXiv:1103.2661 Accepted by PRD cJ ψ → γ = π η η 0 ' [ , , ' ] – P P PRL 105:261801(2010) 6/13/2011 HU Jifeng 23

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

25 backup HU Jifeng 6/13/2011

Radiative decays of ψ ’ PRL 105:261801(2010) [arxiv:hep-ex/101.0885v1] • 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