Recent BESII Results and Future Prospects Zhipeng ZHENG Representing BES Collaboration Institute of High Energy Physics, CAS

Outline Introduction New observations at BESII Study of the scalars BESIII/BEPCII project

Beijing Electron Positron Collider (BEPC) L ~ 5  /cm 2  s at J/  E beam ~ 1 – 2.5 GeV BESI started running in 1989 BESII started running in 1997 BESIII will start running in 2008

BESII Detector VC:  xy = 100  m TOF:  T = 180 ps MDC:  xy = 220  m BSC:  E/  E= 21 %  dE/dx = 8.5 %   = 7.9 mr  p/p=1.78  (1+p 2 )  z = 2.3 cm  counter:  r  = 3 cm B field: 0.4 T  z = 5.5 cm J/   (2S) World J/  and  (2S) Samples (×10 6 ) BESII 58M J/  BESII 14M  (2S)

BEPC / BES ￣ ￣

Tau mass measurement, （ 1991 － 1992 ） World average (1991) BES result: Universality for lepton is stand up

tau mass fit

 －  universality comparation from 1992 to 1996

BEPC/BES R measurement

New observations at BESII

Observation of an anomalous enhancement near the threshold of mass spectrum at BES II M=1859 MeV/c 2  < 30 MeV/c 2 (90% CL) J/    pp M(pp)-2m p (GeV) body phase space acceptance  2 /dof=56/56 acceptance weighted BW  10  25 BES II Phys. Rev. Lett. 91, (2003) X(1860)

X(1860) has large BR to pp BES measured: From Crystal Ball result, we estimate: So we would have: 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 !

B +  pp K + at BaBar and Belle BaBar 210 fb -1 Belle BES II  The pp threshold enhancement observed in J/  decay is different from the enhancements observed by Belle and BaBar in B decay.  The one in B decay can be explained by fragmentation. X(1860)

This result cannot be explained by pure FSI effect, since FSI is a universal effect. FSI interpretation of the narrow and strong pp threshold enhancement is disfavored. This narrow threshold enhancement is NOT observed in  (1S)  pp at CLEO No enhancement near threshold PRD73, (2006)

This again disfavors FSI’ This narrow threshold enhancement is NOT observed in at BESII No narrow strong enhancement near threshold BESII Preliminary Observations of this structure in other decay modes are desirable.

Search for the strong mass threshold enhancement X(1860) in A strong mass threshold enhancement was observed in No obvious strong mass threshold enhancement was observed in acceptance X(1860) Fit M(pp)-2m p (GeV) M=1859 MeV/c 2  < 30 MeV/c 2 (90% CL)  10  25 acceptance BESII preliminary

Statistical Significance 7.7  X(1835) 7.7  PRL 95 (2005) BES: X(1835) in

M =  6.7 MeV  = 0  93 MeV In good agreement with X(1835) Include FSI curve from A.Sirbirtsev et al.(hep-ph/ ) in the fit (I=0) Fit to J/    pp including FSI BES II Preliminary I=0 I=1

X(1835) could be the same structure as pp mass threshold enhancement. It is likely to be a pp bound state since it dominantly decays to pp when its mass is above pp mass threshold.  ’  mode is expected to be the favorable decay mode for a pp bound state below pp mass threshold G.J. Ding and M.L. Yan, hep-ph/

Observation of p  mass threshold enhancement in J/  pK - 

Observation of an anomalous enhancement near the threshold of mass spectrum at BES II BES II 3-body phase space For a S-wave BW fit: M = 2075  12  5 MeV Γ = 90  35  9 MeV Phys. Rev. Lett. 93, (2004)

K -  mass threshold enhancement

PS, eff. corrected Observation of a strong enhancement near the threshold of mass spectrum at BES II (Arbitrary normalization) BES II NX*NX*

A strong enhancement is observed near the mass threshold of M K  at BES II. Preliminary PWA with various combinations of possible N* in the fits —— The structure N x * has: Mass 1500~1650MeV Width 70~110MeV J P favors 1/2 - The most important is: It has large BR(J/ψ  pN X *) BR(N X *  KΛ)  2 X 10 -4, suggesting N X * has strong coupling to KΛ.

Observation of  threshold enhancement in J/    OZI DOZI      

M(  +  -  0 ) M(K + K - )   M(K + K - )    M(  +  -  0 ) Dalitz plot Clear  and  signals M 2 (  ) M2()M2()

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

PWA shows: the enhancement favors 0 ++ over 0 -+ and Is it the same 0 ++ observed in  KK or  (f 0 (1710), or f 0 (1790)), or is it a glueball, or a hybrid …..? Further look in , K*K*,  …. is desirable ! Phys. Rev. Lett., 96 (2006)

New observation of a broad 1 -- resonance in J/   K + K -  0 Phys. Rev. Lett. 97 (2006)

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

What is the broad resonance? J PC should be 1 --, 3 --, …(Parity conservation) PWA results  Following components are needed K * (892), K * (1410),  (1700), X  1 – is much better than 3 —  Pole position of X is  Br  Big destructive interference among X,  (1700) and PS 1 -- component

Study of the scalars  There have been hot debates on the existence of  and .  Lattice QCD predicts the 0 ++ scalar glueball mass in the range GeV. f 0 (1500) and f 0 (1710) are good candidates.

 study  in study  in  study f 0 (980), f 0 (1370), f 0 (1500), f 0 (1710) and f 0 (1790) in 0 ++

The study of  evidence for a low mass pole in the early DM2 and BESI data on J/   . huge event concentration in the I=0 S-wave  channel seen in M  ~ 500 – 600 MeV in the pp central production exp. to explain  scattering phase shift data ，  should be introduced in chiral perturbative theory. FNAL E761 exp. D +  +  -  + data

The  pole in at BESII M(  +  - ) BES, PLB 598 (2004) 149   Different parameterizations of BW are used in PWA. Averaged pole:

observation of  in  ’  +  - J/  Measure the universal pole position (552 - i232 MeV) World largest  signal (with ~ 40,000 tagged events) Phys. Lett. B 645 (2007) 19

The study of  A possible  pole is controversial.  Some analyses of LASS K  scattering data need  (800), some don’t.  Scadron et al. favors a nonet made up of ,  (800), f 0 (980) and a 0 (980).  Julich group used t-channel exchanges to explain K  scattering data.  evidence of  in FNAL E791 data on D +  K -  +  +  slightly lower statistics of CLEO D 0  K -  +  0 data find no evidence of   FOCUS data on K +  K -  +  + require K* 0 interfere with either a constant amplitude or a broad 0 + resonance in K 

PWA result:  is needed in the fit. Pole position of  : BES observed  in J/  K*K  K  K  BES II 58 M J/  Phys. Lett. B 633 (2006) 681 A possible  pole is controversial.

Lattice QCD: the lightest scalar glueball in the region of GeV Glueball searches should be performed in simultaneously. Study of other scalars

0 ++ states: f 0 (980), f 0 (1370), f 0 (1500), f 0 (1710), f 0 (1790) PDG 2006 values: f 0 (980): M = 980  10 MeV,  = 40 – 100 MeV  , KK f 0 (1370): M = 1200 – 1500 MeV,  = 200 – 500 MeV  2 , 4 , KK … f 0 (1500): M = 1507  5 MeV,  = 109  7 MeV  2 , 4 , ,  ’, KK … f 0 (1710): M = 1714  5 MeV,  = 140  10 MeV  2 , 2K, 4 , ,  ’ …

Important parameters from PWA fit: Large coupling with KK indicates big component in f 0 (980) f 0 (980) Phys. Lett. B 607 (2005) 243

There has been debate whether f 0 (1370) exists or not. f 0 (1370) clearly seen in J/   , but not seen in J/   . PWA 0 ++ components f 0 (1370) NO f 0 (1370) f 0 (1370) Phys. Lett. B 607 (2005) 243

Clear f 0 (1710) peak in J/    KK. No f 0 (1710) observed in J/    ! f 0 (1710) NO f 0 (1710) Phys. Lett. B 603 (2004) 138

PWA analysis shows one scalar in 1.7 GeV region Phys. Rev. D 68 (2003)

A clear peak around 1790 MeV is observed in J/   . No evident peak in J/    KK. If f 0 (1790) were the same as f 0 (1710), we would have: Inconsistent with what we observed in J/   ,  KK New f 0 (1790)?? f 0 (1790) ?  f 0 (1790) is a new scalar ??

Scalars in J/    Two scalars in J/    :  One is around 1470 MeV, may be f 0 (1500).  The other is around 1765 MeV, is it f 0 (1790) or f 0 (1710) or a mixture of f 0 (1710) and f 0 (1790)? Phys. Lett. B 642 (2006) 441

OZI rule and flavor tagging in J/  hadronic decays In J/  hadronic decays, an  or  signal determines the or component, respectively.  OZI rule

Unusual properties of f 0 (1370), f 0 (1710) and f 0 (1790) f 0 (1710):  It dominantly decays to KK (not to  )   It is mainly produced together with  (not  )   What is it ? f 0 (1370) and f 0 (1790)  They dominantly decays to  (not to KK)   It is mainly produced together with  (not  )   What are they ?  Scalar Puzzle

Future Prospects BESIII/BEPCII project. Government approved. Started construction from the end of 2003.

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

BEPCII Design goal Dual purpose machine May achieve to Ebeam = 2.3 GeV

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

Magnet: 1 T Super conducting MDC: small cell & He gas  xy =130  m  p /p = dE/dx=6% TOF:  T = 100 ps Barrel 110 ps Endcap Muon ID: 9 layer RPC EMCAL: CsI crystal  E/E = GeV  z = 0.6 cm/  E Trigger: Tracks & Showers Pipelined; Latency = 6.4  s Data Acquisition: Event rate = 3 kHz Thruput ~ 50 MB/s BESIII Detector Two rings, 93 bunches: Luminosity cm  s 6  cm  s 6  cm  s 2.1GeV

MDC Parameters R inner: 63mm ; R outer: 810mm Length (out.): 2582 mm Inner cylinder: 1.2 mm Carbon fiber Outer cylinder: 11.5 mm CF with 8 windows Sense wire : 25 micron gold-plated tungsten (plus 3%Rhenium ) Layers (Sense wire ): 43 Expected performance Field wire: 110 micron gold-plated Aluminum Gas: He + C3H8 (60/40) Cell: inner chamber mm outer chamber mm

Wire Stringing Completed, bad wires are replaced, glue used to make gas tight

CsI(Tl) crystal calorimeter Design goals:  Energy: 1GeV  Spatial: 1GeV Crystals:  Barrel: 5280 w: kg  Endcaps: 960 w: 4051 kg  Total: 6240 w: 25.6 T France Sanit - Gobain Shanghai Institute of Ceramics Beijing Hamamats u Total Ordered2040(960) (960) Arrived2023(824) (824) Rejecte d

Mechanical structure A 1/60 prototype Status: Assembly will start soon. Should be completed early next year. By the end of the year, all FED boards should be tested and installed.

晶体支撑架和工装架

All RPC production, assembly, testing, and installation completed.

BEPCII Status and Plan Dec. 2006, ring commissioning, beam accumulation, Synchrotron run. Dec. 07, BESIII moved to the beam line. 2008, Commissioning ring and detector together, test run. Dec. 08, to achieve a lum. of 3  cm -2 s -1.

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

ResonanceEnergy(GeV)Peak Lum. (10 33 cm -2 s -1 ) Physics Cross Section (nb) Nevents/yr J/   10 9   10 6  (2S)  10 9 D 0 D 0 bar  10 6 D+D-D+D  10 6 DsDs  10 6 DsDs  10 6 Average Lum: L = 0.5×Peak Lum.; data taking time: T = 10 7 s/year N event /year =  exp  L  T Yearly Event Production Huge J/  and  (2S) samples at BESIII

J/  Physics at BESIII/BEPCII Search for glueballs, hybrids and multi- quark states Systematic study of light hadron spectroscopy Study of the excited baryon states Search for more J/  decay channels Probing for new physics in J/  decays  c physics

New states : X(1860), X(1835), X(2075), X(1812), X(1580) were observed  and  studies Other scalars BESIII/BEPCII will start taking data in Summary