at BESIII (Representing BES Collaboration) Institute of High Energy Physics, Beijing OCPA6, Aug. 3-7, 2009, Lanzhou, China

Transcription

1 Results from BESII and Prospects at BESIII Xiaoyan SHEN (Representing BES Collaboration) Institute of High Energy Physics, Beijing OCPA6, Aug. 3-7, 2009, Lanzhou, China

2 Outline Introduction Results from BESII (selected topics) Results on light hadron spectroscopy R measurement Non-DD decays and the line shape of the hadron cross section Physics at BESIII Summary

3 In 1963, from the existing exp. data, Gell- Mann etc. guessed the internal structure of the observed particles and calculated (predicted) the masses of the particles. Gell-Mann Quark Model:3 kinds of quarks u, d and s Meson: q q q Baryon: qqq π + (u d) proton (uud) M. Gell-Mann 1969 Nobel 3

4 s s K 0 (d s) K + (u s) K* 0 K* + π - ( u d) η π 0 π + (u d) I 3 ρ 0 ρ + - ω ρ φ I 3 K - (s u) K 0 (s d) K* - K* K 0 Spin 0 u u-d d Spin 1 π 0 = s (ddd) + (udd) (uud) (uuu) n(udd) p(uud) Σ *- Σ 0 Σ *+ (dds) (uds) (uus) Σ 0 (uds) Σ + (uus) Σ - (dds) I 0 3 Ξ* - Ξ *0 Λ (dss) (uss) Ω - (sss) Ξ - (dss) Quark model predicted: m Ω MeV exp. m Ω ±0.29 MeV Ξ 0 (uss) 4

5 Not the end of the story Sam Ting,B. Richter discovered J/ψ charm (c) mc ~ 1.5GeV J/ψ :(c c c ) Many c c states (charmonium states) observed since then L.Lederman discovered ϒ ( 9.5GeV ) Beauty (Bottom) (b) mb ~5GeV ϒ(9.5): (b b b ) Fermilab. CDF discovered Top quark (t) mt ~176GeV 5

6 Fundamental Matter Particles Charge +2/3-1/3 heavier u c t d s b quarks (q) 0-1 ν e ν μ ν τ e μ τ leptons 6

7 Standard Model (SM) Matter are made of leptons and quarks: e ν e μ τ ν ν μ τ Interactions are mediated by: u d c s t b photons electromagnetic Electroweak W ± and Z weak theory gluons strong QCD Origin of masses Higgs (not yet found) 7

8 Test of Standard Model (EW+QCD) Many precision tests on SM, especially EW theory. 4 exps. at LEP Great successful of EW theory The asymptotic freedom in the theory of the strong interaction is verified at high energies (> 10 GeV) experimentally. 8

9 9

10 However, At low energy, it is difficult to be tested due to non-perturbative nature. Many questions need to be answered. whether the new forms of hadrons predicted by QCD exist or not? PQCD s 12% rule obeyed or not? Is ψ(3770) non-ddbar decays really so big? 10

11 Beijing Electron Positron Collider (BEPC) at IHEP BES Storage ring Linac BSRF 11

12 (BEPC/BES) beam energy: (2.5) GeV BES Physics goal 1-2.3GeV e+ e- collisions produce charmonium states (J/ψ,ψ(2S), χ cj and ψ(3770) etc.), charm mesons and τ lepton

13 We are unique now in τ-charm region Physics at BEPC/BES From PDG The Y s are here! In transition region between pqcd and non-pqcd. 13

14 Physics Topics at BES Study of Light hadron spectroscopy search for non-qqbar or non-qqq states meson spectroscopy baryon spectroscopy Study of the production and decay mechanisms of charmonium states: J/ψ, ψ(2s), η C (1S), χ C{0,1,2}, η C (2S), h C ( 1 P 1 ), ψ(3770), etc. New Charmonium states above open charm threshold. Precise measurement of R values Precise measurement of CKM matrix Search for DDbar mixing, CP violation, etc. 14

15 Study of the spectroscopy a way of understanding the internal structure Atomic spectrum atomic structure foundation of atomic physics Quantum Mechanics Lattice QCD: glueball llspectrum Hadron spectroscopy hadronic structure Quark Model QCD 15 Y. Chen et al., PRD 73 (2006)

16 qq, qqq

17 New forms of hadrons Hadrons consist of 2 or 3 quarks: Naive Quark Model: Meson( ( q q ) Baryon(q qq) q) QCD predicts the new forms of hadrons: Multi-quark states :Number of quarks >= 4 Hybrids : qqg,qqqg Glueballs : gg, ggg

18 Multi-quark states, glueballs and hybrids have been searched for experimentally for a very long time, but none is established. The observation of the new forms of hadrons will be a direct test of QCD. This has been one of the important physics goals for many experiments.

19 R measurement R : one of the most important and fundamental quantities in particle physics. R σ σ e - e + e - q - q hadrons μ - e + μ + lowest order Why precise R important? t? Essential for precise tests of SM. the global fit of Higgs mass order anomalous μ magnetic 2 = ΣQ f moment from g-2 flavor color 19

20 Precise measurement of CKM elements -- Test EW theory CKM matrix elements are fundamental SM parameters that describe the mixing of quark fields due to week interaction. d s b ' ' ' 5% precision 10% precision = V V V ud cd V V V Three generations of quark? td us cs ts V V V tb ub cb d s b Unitary matrix? CKM matrix Expect precision < 2% at BESIII Improve the precision at BESIII Precision of measurement CKM matrix elements -- a precise test to SM! New physics beyond SM? 20

21 CP violation and 0 0 D D mixing CP violation is regarded as the origin of asymmetry of the matter and anti-matter. CP violation predicted by theoretical models is not big enough to describe the asymmetry. CP violation is observed in K and B decays, but has never been in charm sector. e + e - ψ(3770) D 0 D CP D D 0 In SM, the mixing is very small. At BESIII, the sensitivity of the mixing rate: D D 21 mixing : a good place to search for CP violation

22 BEPC VC: σ xy = 100 μm TOF: σ T = 180 ps μ counter: σ rφ = 3 cm MDC: σ xy = 220 μm BSC: ΔE/ E= 22 % σ z = 5.5 cm σ de/dx = 8.5 % σ φ = mr B field: 0.4 T Δp/p =1.7% (1+p 2 ) σ z = 3.1 cm 22

23 BESI: run from BESII: run from L ~ /cm 2 s s at J/ψ E beam ~ GeV BESII data samples Data BESII CLEOc J/ψ 58 M -- ψ(2s) 14 M 27 M ψ(3770) 33 pb pb -1 23

24 Observation of an anomalous enhancement near the threshold of ppmass spectrum acceptance weighted BW X(1860) BES II J/ψ γpp M=1859 MeV/c 2 Γ < 30 MeV/c 2 (90% CL) 3-body bd phase space Phys. Rev. Lett. 91, (2003) χ 2 /dof=56/ M(pp)-2m p (GeV) acceptance 24

25 X(1860) has large BR to pp BES measured: BR( J / ψ γx (1860)) BR( X (1860) pp ) ~ For a 0 -+ meson: BR ( J / ψ γ X (1860)) ~ So we would have: BR( X (1860) pp) ~ 4 14% (This BR to pp might be the largest among all PDG particles) Considering that decaying into pp is only from the tail of X(1860) and the phase space is very small, such a BR indicates X(1860) has large coupling to pp! 3 25

26 This narrow threshold enhancement is NOT observed in J/ψ ωpp at BESII J/ψ ωpp Preliminary No narrow strong enhancement 2 near threshold M pp 2M p GeV/c Br ( J / ψ ω X ) / Br ( J / ψ γ X ) < C.L. 26

27 Not in B + pp K + at BaBar and Belle BaBar 210 fb -1 B + pp K + _ dbf / dm pp 10 6 ((GeV/c 2 ) -1 ) Belle _ M pp (GeV/c ) The pp threshold enhancement observed in J/ψ decay is different from the enhancements observed by Belle and BaBarB in B decay. X(1860) BES II J /ψ γpp The one in B decay can be explained by fragmentation. 27

28 This narrow threshold enhancement is NOT observed in Υ(1S) γpp at CLEO Br( Υ(1S ) γ X) / Br( J < 90% CL PRD73, (2006) / ψ γ X) This result cannot be explained ed by pure FSI effect, ect, since FSI is a universal effect. FSI interpretation of the narrow and strong pp threshold enhancement is disfavored. No enhancement near threshold 28

29 pp bound state (baryonium)? There is lots & lots of literature about this possibility deuteron: attractive nuclear force baryonium: attractive force? + n + loosely bound 3-q 3-q color singlets with M d = 2m p - ε loosely bound 3-q 3-q color singlets with M b = 2m p -δ? Observations of this structure t in other decay modes are desirable. 29

30 + Observation of X(1835) in J /ψ γη ' π + J /ψ γη' π π η' ηπ + π η' π X(1835) 51σ 5.1 σ J / ψ γη' π + π η' X(1835) 6.0 σ η' γρ 30

31 Combine two channels + ψ γ π π η J 7.7σ Statistical Significance σ X(1835) N obs = 264 ± 54 M = ± 6.1± Γ = 67.7 ± 2.7 MeV/c 20.3 ± 7.7 MeV/c 2 2 B ( J c. f. : + ψ γ X ) B ( X π π η ) = (2.22 ± 0.4 ± 0.4) B( J ψ γx ) B( X pp) = (7.0 ± )

32 The observation of new N* peaks in J / ψ p n π π J / ψ pn + c. c. N*(1520) N*(1650) N*(1440)? N*(1535) N*(1675) N*(1680)? Missing mass spectrum (GeV/c 2 ) 32

33 J / ψ pn π + c. c. N*(2065) Phys. Rev. Lett. 97 (2006) BW fit yields: M = 2065 ± 3 Γ = 175 ± 12 ± MeV/c MeV/c PWA is performed. well-established N* s are fixed to PDG values. for N*(2065), L=1 is much worse than L=0 in the fit. 1/2 + or 3/2 + (improve log likelihood by 400) 1/ /2 + (improve log likelihood further by 60) 33

34 Nx(2065) is also observed in J J / ψ ppπ 0 stat. sig. >>5σ, the spin-parity favors 3/2+ M = ± 25 MeV, Γ = 230 ± 8 ± 52 MeV N* M(MeV/c 2 ) Γ(MeV/c 2 ) J P fraction(%) Br ( 10-4 ) + N(1440) ± ± 67 1/ ~ ~3.54 N(1520) ± ±37 8 3/2-2.38~ ~ N(1535) ± ± /2-6.83~ ~ N(1650) ± ± /2-6.89~ ~ N(1710) ± ± / ~ ~ N(2065) ± 25 ± / ~ ~3.11

35 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) Kuang obtained a partial width for ψ(3770) π + π - J/ψ in the range of kev. (Y.P. Kuang, PRD 65 (2002) ) 35

36 BES first reported ψ(3770) non-dd decay ψ(3770) π + π - J/ψ Open histogram is for e + e -, histogram in yellow is for μ+μ- The histogram is ψ error bars are ψ +ψ ' ψ production due to ISR data MC 27.7 pb -1 ψ '' + J /ψπ π mainly 20 times large than the data N( ψ(3770) J / ψπ + π ) = 11.8 ± 4.8 hep-ex/ PLB 605 (2005) 63 + ψ' J /ψπ π Brψ ( ψ (3770 ) π + π J / ψ ) = (0.34 ± 0.14 ± 0.09)% 09)% + Γ( ψ(3770) π π J / ψ) = (80± 33± 23) kev 36

37 ψ(3770) ππ J/ψ is confirmed by CLEO J / e + + ψ e or μ μ 281pb pb σ 38σ 3.8 σ + Br( ψ(3770) π π J 0 0 Br( ψ(3770) π π J / ψ) = (0.189± / ψ) = (0.087± Br( ψ(3770) ηj / ψ) < 0.14% at 90%C.L. 0 Br( ψ(3770) π J / ψ) < 0.026% at 90%C.L. )% )% 37

38 Anomalous LineShape of σ[e + e - Hadrons] in energy region from to GeV 1. Significances of the two amplitudes are more than 7σ 2. Significance ifi of the interference between the two amplitudes is 3.6 σ 3. The hypothesis of ψ(3770) amplitude +G(3900) and interference does not significantly improve the fit from the one ψ(3770) amplitude hypothesis Two data sets taken in March and December 2003 A fine scan in this area is needed! Phys.Rev.Lett101,102004,2008

39 R Measurement Previous exps: ΔR/R 15 % below 5 GeV , BESII measured 6+85 points R values in 2-5 GeV region. ΔR/R 6 % Phys. Rev. Lett., 88 (2002)

40 In 2003, from a dedicated ψ(3770) scan data, the R values at 68 energy points from GeV were measured. stat. error: 3-4% syst. error: 4% Phys Rev Lett 97 Phys. Rev. Lett., 97 (2006)

41 R values at 2.6, 3.07 and 3.65 GeV measured with the precision of about 3.5% at BESII in The running coupling constant α s (s) was determined

42 BEPCII/BESIII In the 1990s, there was discussion of the future. The conclusion was to continue tau-charm physics with a major upgrade of the accelerator and detector (BEPCII/BESIII). Officially approved in The physics window is precision charm physics and the search for new physics. High statistics: high luminosity machine + high quality detector. Small systematic error: high quality detector.

43 BEPC II Storage ring: Large angle, double-ring nsrf SR mrad822 2 RF.1Beam energy: 1023GeV GeV Luminosity: cm -2 s -1 O energy: 1.89 GeV 0.Optimum Energy spread: cn2.5m81.5cno. of bunches: 93 m mbunch length: 1.5 cm Total current: 0.91 A SR mode: 2.5 GeV IP

44 Main parameters achieved in collision mode parameters design Achieved BER BPR Energy (GeV) Beam curr. (ma) Bunch curr. (ma) 9.8 >10 >10 Bunch number RF voltage ν β x* /β y* (m) 1.0/0.015 ~1.0/0.016 ~1.0/0.016 Inj. Rate (ma/min) 200 e / 50 e + >200 >50 Lum. (10 33 cm -2 s -1 )

45 BEPCII BEPC 0.4 T 45

46 Totally 42 institutions USA (6) University of Hawaii University of Washington Carnegie Mellon University Univ. of Minnesota University of Rochester Indiana University 46 Europe (8) GSI, Germany University of Bochum, Germany University of Giessen, Germany KVI/University of Groningen, Netherland INFN, Laboratri Nazionali di Frascati University of Torino, Italy JINR, Dubna, Russia Budker institute of Nuclear Physics Russia China (25) IHEP, CCAST, GUCAS, Others in Asia(3) Tokyo University Univ. of Sci. and Tech. of China Seoul National Univ. Shandong Univ., Zhejiang Univ. Univ. of Punjab, Lahore Huazhong Normal Univ., Wuhan Univ. Zhengzhou Univ., Henan Normal Univ. Peking Univ., Tsinghua Univ., Zhongshan Univ.,Nankai Univ. Shanxi Univ., Sichuan Univ Hunan Univ., Liaoning Univ., Huangshan College. Nanjing Univ., Nanjing Normal Univ. Guangxi Normal Univ., Guangxi Univ. Hong Kong University Chinese Univ. of Hong Kong

47 First collision event on July 19, 2008

48 Data accumulated at BESIII Mar. 6 April 14 May 24 June M ψ(2s) data 45 pb -1 dt data 30 at 3.65 GeV June 12 Jul M J/ψ data

49 Statistics at BESIII at peak Luminosity (assuming 10 7 s data taking time each year) Energy Peak Luminosity Events/year Existing data Physics (GeV) (10 33 cm 2 s 1 ) J/ψ (BESII) τ 3.67(?) ψ (CLEOc) (BESII) D (CLEOc) Ds (BESI) Ds (CLEOc) Rscan (?)10 0.6(?) A review (Yellow Book): τ-charm physics at BES3 arxiv:

50 Some physics signals π signal Λ signal η 250 signal 200 BESIII preliminary Red: K* Blue: K*

51 E1 transitions: inclusive photon spectrum χ c2 χ c1 χ co χ c1,2 γ J/ψ η c BESIII preliminary

52 ψ(2s) π 0 h c, h c γη c Part of BESIII data CLEOc: 25M BESIII preliminary BES confirms the CLEOc observation & will improve the precision of the h c properties.

53 ψ γγ l + l -: signals of χ π 0 cj, and η η m γγ π 0 χ χ c1 c 2 m γψ

54 BESIII preliminary ψ(2s) ) γχ cj

55 Study of ψ(2s) γπ 0 π 0, γηη (η γγ, π 0 γγ ) ψ(2s) γπ 0 π 0 BESIII preliminary ψ(2s) γηη BESIII preliminary Branching fractions (10-3 ) * CLEO-c arxiv: χ c0 χ c2 π 0 π 0 PDG 2. 43± ±0.08 CLEO-c * 2.94±0.07± ±0.03±0.08 ηη PDG 2.4±0.4 <0.5 CLEO-c * 3.18±0.13± ±0.05±0.06

56 Confirmation of the BESII observation: pp threshold h enhancement BES II J / ψ γ pp BES III preliminary ψ(2s) ππj/ψ J / ψ γ pp PRL 91 (2003)

57 Confirmation of BESII observation: pp threshold enhancement BES II ψ γ pp BES III preliminary ψ γ pp M pp (GeV) No significant narrow strong enhancement near threshold (~2σ if fitted with X(1860)) PRL 99 (2007)

58 Structures in χ c0 π + π - K + K - at BESIII BESIII preliminary BESII: PRD72,

59 Summary Selected results from BESII are presented. 100M ψ(2s) data, 200M J/ ψ are already accumulated at BESIII. Expecting new and exciting results from new data.

60