Recent BES Results and Future Prospects

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1 Recent BES Results and Future Prospects Xiaoyan SHEN Representing BES Collaboration Institute of High Energy Physics, Beijing Moriond 2007, EW Session March 10 17, 2007, La Thuile, Italy 1

2 Outline Light hadron spectroscopy First measurements of ψ(2s) radiative decays ψ(3770) non-dd decays Search for η/η Invisible from J/ψ φη/η BESIII/BEPCII project 2

3 Beijing Electron Positron Collider (BEPC) L ~ /cm 2 s at J/ψ E beam ~ GeV BESI started running in 1989 BESII started in 1997 BESIII will start in

4 BESII Detector World J/ψ and ψ(2s) Samples ( 10 6 ) J/ψ BESII 58M J/ψ 0 30 CBAL MKII MKIII DM2 BESI BESII BESII 14M ψ(2s) VC: σ xy = 100 μm TOF: σ T = 180 ps MDC: σ xy = 220 μm BSC: ΔE/ E= 21 % σ de/dx = 8.5 % σ φ = 7.9 mr Δp/p=1.78 (1+p 2 ) σ z = 2.3 cm μ counter: σ rφ = 3 cm B field: 0.4 T σ z = 5.5 cm ψ(2s) MKI MKII MKIII CBAL BESI BESII CLEOc 33 pb -1 ψ(3770) data 4

5 Light Hadron Spectroscopy 5

6 6 Observation of ωφ threshold enhancement in J/ψ γωφ ), ( K K φ π π π ω OZI DOZI + K K J φ γφφ ψ, / γωφ /ψ J φ φ φ φ φ ω

7 Clear φ and ω signals M(K + K - ) ωφ φφ φ ω M(π + π - π 0 ) φ M KK M < 15MeV φ 20 MeV M M < 35MeV KK < φ M 2 (γφ) M(K + K - ) Dalitz plot M(π + π - π 0 ) M 2 (γω) 7

8 A clear threshold enhancement is observed φω Eff. curve Phase Space Side-bands Side-bands do not have mass threshold enhancement! 8

9 PWA shows: the enhancement favors 0 ++ over 0 -+ and M = Γ = 105 ± 20 ± ± 18 MeV/c 28 MeV/c 2 2 Br( J / ψ γx ) Br( X ωφ) = (2.61± 0.27 ± 0.65) 10 4 Is it the same 0 ++ observed in γkk or φππ (f 0 (1710), or f 0 (1790)), or is it a glueball, or a hybrid..? Further look in ωω, K*K*, φφ. is desirable! Phys. Rev. Lett., 96 (2006)

10 Observation of a broad 1 -- resonance in J/ψ K + K - π 0 Phys. Rev. Lett. 97 (2006)

11 J/ψ K + K - π 0 π 0 K * (1410) X(1580) K*(892) background? π 0 sideband PID and kinematic fit can significantly reduce the dominant background from J/ψ π + π - π 0. 11

12 What is this broad structure? J PC should be 1 --, 3 --, (Parity conservation) PWA results Following components are needed K * (892), K * (1410), ρ(1700), X 1 is much better than 3 Pole position of X is (1576 Br(J/ψ ) i( ) MeV/c Xπ 0, X K + K - ) = (8.5 ± ) component Big destructive interference among X, ρ(1700) and PS Broad width multiquark state? 12

13 First observation of N(2050) quark model predicts: N(2050) N*(1440)? N*(1520) N*(1535) N*(1650) N*(1675) N*(1680) Not observed.? N(2050): 1/2 + or 3/2 + J / ψ pnπ + c. c. M = 2065 ± 3 MeV/c Γ =175 ± 12 ± 40MeV/c N(1440): N(1440) peak never been seen directly before). M = ± 6 ± 16 MeV/c,179 ± 26 ± 50 MeV/c 2 Phys. Rev. Lett

14 The study of σ evidence for a low mass pole in the early DM2 and BESI data on J/ψ ωππ. huge event concentration in the I=0 S-wave ππ channel seen in M ππ ~ MeV in the pp central production exp. to explain ππ scattering phase shift dataσ should be introduced in chiral perturbative theory. FNAL E761 exp. D + π + π - π + data M = ± 17 MeV, Γ = ± 21MeV 14

15 The σ pole in J /ψ ωπ + π at BESII σ M(π + π - ) σ Different parameterizations of BW are used in PWA. Averaged pole: ( 541± 39) i(252 ± 42) MeV BES, PLB 598 (2004)

16 observation of σ in ψ π + π - J/ψ Measure the universal pole position (552 - i232 MeV) World largest σ signal (with ~ 40,000 tagged events) Phys. Lett. B 645 (2007) 19 16

17 The study of κ A possible κ pole is controversial. Some analyses of LASS Kπ scattering data needs κ(800), some don t. Scadron et al. favors a nonet made up of σ, κ(800), f 0 (980) and a 0 (980). Julich group used t-channel exchanges to explain Kπ scattering data. evidence of κ in FNAL E791 data on D + K - π + π + M = 797 ± 19 ± 43 MeV, Γ = 410 ± 43 ± 87 MeV slightly lower statistics of CLEO D 0 K - π + π 0 data find no evidence of κ FOCUS data on K + K - π + μ + ν require K* 0 interfere with either a constant amplitude or a broad 0 + resonance in Kπ 17

18 BES observed κ in J/ψ K*Kπ KπKπ A possible κ pole is controversial. BES II 58 M J/ψ PWA result: κ is needed in the fit. Pole position of κ: (841± 30 i ) (309 ± 45 72) MeV/c Phys. Lett. B 633 (2006)

19 First measurements of ψ radiative decays Expected 1% BR, but only 0.05% observed. Potential channels for hadron spectroscopy study, including non-qqbar states search, if statistics is enough. ~ 0.1% more observed modes in this analysis. hep-ex/

20 Search for the strong pp mass threshold enhancement X(1860) in ψ (2S ) γpp A strong pp mass threshold enhancement was observed in J /ψ γpp No obvious strong pp mass threshold enhancement was observed in ψ (2S ) γpp M= MeV/c Γ < 30 MeV/c 2 (90% CL) EVENTS/(20 MeV/c 2 ) Fit acceptance acceptance M(pp)-2m p (GeV) B ( J / ψ γx (1860 ) γpp ) ~ m pp - 2m p (GeV/c 2 ) X(1860) B ( ψ (2S ) < γx ( % ) γpp ) CL 20

21 ψ(3770) non-dd decays ψ(3770) decays most copiously into DD. ψ(3770) is a mixture of the 1 3 D 1 and 2 3 S 1, other ψ(2s)-like decays for ψ(3770) are expected. (mixing angle 12±2 o ). Many theoretical calculations estimate the partial width for ψ(3770) π + π - J/ψ. (Lipkin, Yan, Lane, Kuang, Rosner) BES observed ψ(3770) π + π - J/ψ decays. Further confirmed by CLEO-c. 21

22 Determination of BF[ψ(3770) D 0 D 0,D + D -,DD and non-dd] with the measured R values at 3.650, and GeV obs σ DD Single tag method σ obs = D D Radiative correction factor g BES II = ± BF ND tag 2 L Br ε = 6.14 ± 0.12± PLB 603(2004) nb Born σ ψ (3770) = ± ± nb BF( ψ(3770) DD) = g σ = σ obs B N N prd DD prd ψ(3770) σ = σ Born DD Born ψ(3770) = g σ obs DD Born BES II σψ (3770) Some systematic uncertainties can be canceled out Radiative correction factor obtained based on new ψ(3770) resonance parameters measured by BES-II, hep/ ( ψ (3770) D D ) = (49.9 ± 1.3 ± 3.8)% + BF( ψ (3770) D D ) = (35.7 ± 1.1± 3.4)% BF ( ψ (3770) DD) = (85.5 ± 1.7 ± 5.8)% BF( ψ (3770) non DD) = (14.5 ± 1.7 ± 5.8)% PLB641(2006)145 22

23 Line shape of the cross sections for hadron and DD-bar production Inclusive hadrons Inclusive hadrons D 0 D 0 Inclusive hadrons D + D Mar data set PRL(2006) Simultaneously.fitting to the inclusive hadron and the DD-bar production cross sections BF Branching fractions 0 0 ( ψ (3770) D D ) = (46.7 ± 4.7 ± 2.3)% + BF ( ψ (3770) D D ) = (36.9 ± 3.7 ± 3.1)% BF ( ψ (3770) DD) = (83.6 ± 7.3 ± 4.7)% BF( ψ (3770) non DD) = (16.4 ± 7.3 ± 4.7)% 23

24 Search for η/η Invisible from J/ψ φη/η First attempt to search for the evidence of dark matter from J/ψ decays. Phys. Rev. Lett., 97 (2006)

25 Theoretical estimation: B.McElrath PRD 72, (2005) Br(Y(1S) χχ ) ~ 0.61% Br(J/ψ χχ ) ~ 0.037% Br(χ C0 χχ ) ~ Br(η C χχ ) ~ Br(η χχ ) ~ Br(η χχ ) ~ Br(η(1405) χχ ) ~ Br(η(1475) χχ ) ~ Br(ω χχ ) ~ Br(φ χχ ) ~

26 Event Selection Tag direction Missing direction o Two good charged K; o No any detector hits outside of 30 0 decay core; o cos(θ missing ) < 0.7 ; o < m(k + K - ) < GeV; φ signal M KK η η Missing momentum 26

27 Search for η/η Invisible decays in J/ψ φη/η An unbinned extended Maximum Likelihood Fit: Br(η invisible ) < % C.L. Reconstructed φ mass 58 M J/ψ Missing momentum Br(η invisible ) < % C.L. Phys. Rev. Lett., 97 (2006) The sensitivity can be improved at BESIII 27

28 Future Prospects BESIII/BEPCII project. Government approved. Started construction from the end of

29 BEPCII: a high luminosity double ring collider SC RF Two rings tunnel 29

30 BEPCII Design goal Energy range GeV Optimum energy 1.89 GeV Luminosity 1 x cm -2 s 1.89 GeV Injection Synchrotron mode Full energy injection: GeV Positron injection speed > 50 ma/min GeV Dual purpose machine May achieve to Ebeam = 2.3 GeV 30

31 BESIII Detector Muon Counter SC magnet TOF Be beam pipe Drift Chamber CsI(Tl) calorimeter 31

32 Magnet: 1 T Super conducting BESIII Detector Two rings, 93 bunches: Luminosity cm 2 s cm 2 s cm 2 s 2.1GeV MDC: small cell & He gas σ xy =130 μm σ p /p = de/dx=6% TOF: σt = 100 ps Barrel 110 ps Endcap Muon ID: 9 layer RPC EMCAL: CsI crystal ΔE/E = GeV σz = 0.6 cm/ E Data Acquisition: Event rate = 3 khz Thruput ~ 50 MB/s Trigger: Tracks & Showers Pipelined; Latency = 6.4 μs 32

33 BEPCII Status and Plan Dec. 2006, ring commissioning, beam accumulation, Synchrotron run. Aug. 07, BESIII moved to the beam line. Sep. 07, Commissioning ring and detector together. Dec. 07, test run. Dec. 08, to achieve a lum. of cm -2 s

34 BESIII Collaboration Institute of High Energy Physics University of Science and Technology Peking University Tsinghua University Shangdong University Nankai University Central China Normal University University of Anhui University of Zhejiang University of Zhengzhou Nanjing Normal University Nanjing University Shanxi University Sichuan University Henan Normal University University of Hawaii University of Washington University of Tokyo Joint Institute of Nuclear Research, Dubna GSI University of Bochum University of Giessen 34

35 Yearly Event Production Average Lum: L = 0.5 Peak Lum.; data taking time: T = 10 7 s/year N event /year = σ exp L T Resonance Energy(GeV) Peak Lum. (10 33 cm -2 s -1 ) Physics Cross Section (nb) Nevents/yr J/ψ τ ψ(2s) D 0 D 0 bar D + D DsDs DsDs Huge J/ψ and ψ(2s) samples at BESIII 35

36 An ωφ mass threshold enhancement was observed in J/ψ γωφ. J PC =0 ++ is favored. A very broad 1 -- resonance X(1580) is observed in J/ψ K + K - π 0. σ and κ Summary Measurements of psi radiative decays Psi(3770) non-ddbar decays Search for η/η Invisible from J/ψ φη/η BESIII/BEPCII will start taking data in

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