New Observations at BESII and Prospects at BESIII/BEPCII Shan JIN (for BES Collaboration) Institute of High Energy Physics (IHEP) jins@mail.ihep.ac.cn DIF 06 Frascati, March 1, 2006

Outline New Observatins at BESII Prospects at BESIII/BEPCII A possible bound state: mass threshold enhancement in and new observation of X(1835). mass threshold enhancement in  mass threshold enhancement in J/   Prospects at BESIII/BEPCII

Multi-quark State, Glueball and Hybrid Hadrons consist of 2 or 3 quarks： Naive Quark Model： New forms of hadrons: Multi-quark states ：Number of quarks >＝ 4 Hybrids ： qqg，qqqg … Glueballs ： gg， ggg … Meson（ q q ） Baryon（q q q） How quarks/gluons form a hadron is far from being well understood.

Multi-quark states, glueballs and hybrids have been searched for experimentally for a very long time, but none is established. However, during the past two years, a lot of surprising experimental evidences showed the existence of hadrons that cannot (easily) be explained in the conventional quark model. Most of them are multi-quark candidates. Searching for multi-quark states becomes the hottest topic in the hadron spectroscopy.

J/ decays are an ideal factory to search for and study light exotic hadrons: The production cross section of J/ is high. The production BR of hadrons in J/ decays are one order higher than ’ decays (“12% rule”). The phase space to 1-3 GeV hadrons in J/ decays are larger than  decays. Exotic hadrons are naively expected to have larger or similar production BR to conventional hadrons in J/ decays. Clean background environment compared with hadron collision experiments, e.g., “JP, I” filter.

BESII VC: xy = 100 m TOF: T = 180 ps  counter: r= 3 cm MDC: xy = 220 m BSC: E/E= 22 % z = 5.5 cm dE/dx= 8.5 %  = 7.9 mr B field: 0.4 T p/p=1.7%(1+p2) z = 2.3 cm

World J/ and (2S) Samples (106) Largest from BES J/ (2S) 2001 2002

A possible ppbar bound state

Observation of an anomalous enhancement near the threshold of mass spectrum at BES II J/ygpp acceptance weighted BW +3 +5 -10 -25 M=1859 MeV/c2 G < 30 MeV/c2 (90% CL) c2/dof=56/56 0.1 0.2 0.3 Phys. Rev. Lett. 91, 022001 (2003)    M(pp)-2mp (GeV) 3-body phase space acceptance

NO strong dynamical threshold enhancement in cross sections (at LEAR) With threshold kinematic contributions removed, there are very smooth threshold enhancements in elastic “matrix element” and very small enhancement in annihilation “matrix element”:  much weaker than what BES observed ! |M|2 |M|2 BES BES Both arbitrary normalization Both arbitrary normalization

Any inconsistency? NO! For example: with Mres = 1859 MeV, Γ = 30 MeV, J=0, BR(ppbar) ~ 10%, an estimation based on: At Ecm = 2mp + 6 MeV ( i.e., pLab = 150 MeV ), in elastic process, the resonant cross section is ~ 0.6 mb : much smaller than the continuum cross section ~ 94  20 mb .  Difficult to observe it in cross sections experimentally.

In ppbar collision, the background is much lager (I) J/ decays do not suffer large t-channel “background” as ppbar collision. >>

In ppbar collision, the background is much lager (II) In ppbar elastic scattering, I=1 S-wave dominant, while in J/ radiative decays I=0 S-wave dominant. ppbar elastic cross section near threshold I=1 S-wave P-wave I=0 S-wave A.Sibirtsev, J. Haidenbauer, S. Krewald, Ulf-G. Meißner, A.W. Thomas, Phys.Rev.D71:054010, 2005

So, the mechanism in ppbar collision is quite different from J/ decays and the background is much smaller in J/ decays It would be very difficult to observe an I=0 S-wave ppbar bound state in ppbar collisions if it exists. J/ decays (in e+e- collider) have much cleaner environment: “JP, I” filter

This narrow threshold enhancement is NOT observed in B decays The structure in B decays is obviously different from the BES observation: Belle The structure in B decays is much wider and is not really at threshold. It can be explained by fragmentation mechanism. BES II Threshold enhancement in J/ decays is obviously much more narrow and just at threshold, and it cannot be explained by fragmentation mechanism.

Re-fit to J/p pbar including FSI Include FSI curve from A.Sirbirtsev et al. ( Phys.Rev.D71:054010, 2005 ) in the fit (I=0) M = 1830.6  6.7 MeV  = 0  93 MeV

Crystal Ball results on inclusive photon spectrum of J/psi decays

X(1830) has large BR to ppbar We (BES) measured: From Crystal Ball result, we etimate: So we would have: (This would be the largest BR to ppbar among all known mesons) Considering that decaying into ppbar is only from the tail of X(1830) and the phase space is very small, such a BR indicates X(1830) has large coupling to ppbar !

pp bound state (baryonium)? There is lots & lots of literature about this possibility E. Fermi, C.N. Yang, Phys. Rev. 76, 1739 (1949) … I.S. Sharpiro, Phys. Rept. 35, 129 (1978) C.B. Dover, M. Goldhaber, PRD 15, 1997 (1977) Datta, P.J. O’Donnell, PLB 567, 273 (2003)] M.L. Yan et al., hep-ph/0405087 B. Loiseau et al., hep-ph/0411218 deuteron: baryonium: attractive nuclear force attractive force? + n + - loosely bound 3-q 3-q color singlets with Md = 2mp- e loosely bound 3-q 3-q color singlets with Mb = 2mp-d ? Observations of this structure in other decay modes are desirable.

What do we expect from J/psigamma ppbar results? The baryonium interpretation of the ppbar mass threshold enhancement predicts a new particle around 1.85 GeV which should be observed in other decay mode with full BW resonant structure.

New Observation of X(1835) in PRL 95, 262001 (2005)

Analysis of X(1835) 5.1 

Analysis of X(1835) 6.0 

Observation of X(1835) in Statistical Significance 7.7  The +- mass spectrum for  decaying into +- and  

Mass spectrum fitting 7.7 The +- mass spectrum for  decaying into +- and   7.7 BESII Preliminary

Comparison of two decay modes Mass and width from m=1827.48.1MeV/c2 , =54.234.5MeV/c2 m=1836.37.9MeV/c2 , =70.323.1MeV/c2 The mass, width and branching fractions obtained from two different decay modes are consistent with each other.

Re-fit to J/p pbar including FSI Include FSI curve from A.Sirbirtsev et al. ( Phys.Rev.D71:054010, 2005 ) in the fit (I=0) M = 1830.6  6.7 MeV  = < 153 MeV @90%C.L. In good agreement with X(1835)

A Possible ppbar Bound State X(1835) could be the same structure as ppbar mass threshold enhancement. It could be a ppbar bound state since it dominantly decays to ppbar when its mass is above ppbar mass threshold. Its spin-parity should be 0-+: this would be an important test.

Observation of mass threshold enhancement in

Observation of an anomalous enhancement near the threshold of mass spectrum at BES II 3-body phase space Phys. Rev. Lett. 93, 112002 (2004)    For a S-wave BW fit: M = 2075 12  5 MeV Γ = 90  35  9 MeV

Possible Interpretations FSI？ Theoretical calculations are needed. Conventional K* or a multiquark resonance？ Search for its Kπ 、Kππ decay modes would help to understand its nature. We are now studying J/  KKπ 、KKππ

K mass threshold enhancement

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

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

A ΛK resonance predicted by chiral SU(3) quark model Based on a coupled-channel study of ΛK and ΣK states in the chiral SU(3) quark model, the phase shift shows the existence of a ΛK resonance between ΛK and ΣK mass threshold. ( F. Huang, Z.Y. Zhang et al. hep-ph/0501102 ) Ecm – ( MΛ+MK ) (MeV)

The KΛ mass threshold enhancement NX(1610) could be a KΛ bound/resonant state.

Observation of  mass threshold enhancement

We studied DOZI process: J/    +  +    +-0 K+ K-

Clear  and  signals    recoiling against 

Daliz Plot

A clear mass threshold enhancement is observed Acceptance

Side-bands do not have mass threshold enhancement

The radiative decay of J/ has been observed in the 58M J/ data. A significant structure of  has been found near the mass threshold. PWA shows the structure favors 0++, with a mass , width 1052028 MeV, and the corresponding branch ration is (2.610.270.65)x10-4. It should be observed in KK mode. Its relation with f0(1710),f0(1790)?

Is the STRONG threshold enhancement universal/naïve in J/ decays Is the STRONG threshold enhancement universal/naïve in J/ decays ? —— NO ! Actually in many other cases we do NOT see STRONG threshold enhancements ! For example: In J/ decays at BES II

Summary of BESII New Observations (I) BES II has observed several strong mass threshold enhancements in J/ decays. Why strong mass threshold structures are important? Multiquark states may be only observable near mass thresholds with limited decay phase space.  Otherwise, it might be too wide to be observed as a resonance since it can easily fall apart into two or more mesons. I can see f0(980) I can see broad  under other peaks broad resonance or phase space? any broad resonance under other peaks?

Summary of BESII New Observations (II) Summary (II) A unique very narrow and strong mass threshold enhancement is observed in decays at BES II: It is not observed in cross sections. It is not observed in B decays. Its large BR to suggests it be a bound state. X(1835) is observed in It could be same structure as the ppbar mass threshold enhancement, i.e., it could be a ppbar bound state.

Summary of BESII New Observations (III) Summary (III) Summary of BESII New Observations (III) mass threshold enhancement was observed in Evidence of NX(1610) was observed near KΛ mass threshold, suggesting a KΛ bound or resonant state. An  mass threshold enhancement was observed in J/   J/ψ decay is an ideal place to study exotic structures.

Prospects at BESIII/BEPCII

The need for upgrade Interesting physics limited by statistics: glueball/hybrid/multi-quark searches, CKM matrix elements, DDbar mixing, rp puzzle, non-pQCD… Large systematic errors due to limited resolutions of the detector Detector is aging Multi-bunch mode & High event rate

We are unique In a regime of transition between pQCD and non-pQCD Can provide calibrations and tests of LQCD Rich spectra of light hadrons for Quark model test and for searches of new hadrons Rich gluonic matter production for QCD test Near the production threshold of tau-charm

Physics at BEPCII/BESIII Light hadron spectroscopy QCD and hadron production Charmonium physics Precision measurement of CKM matrix elements Precision test of Standard Model Search for new physics/new particles

BEPCII Design goal Collision Mode SR Mode Beam energy range 1-2.1 GeV Optimized beam energy 1.89 GeV Luminosity 1  1033 cm-2s-1 @1.89 GeV Full energy injection 1-1.89 GeV SR Mode Beam energy 2.5 GeV Beam current 250 mA

Event statistics at BESIII Physics Channel Energy (GeV) Luminosity (1033 cm–2s –1) Events/year J/y 3.097 0.6 1.0×1010 t 3.67 1.0 1.2×107 y’ 3.686 3.0 ×109 D 3.77 2.5×107 Ds 4.03 1.0×106 4.14 2.0×106 *CLEO took 10 nb D production cross section while we took 5 nb

Precision measurement of CKM: Branching rations of charm mesons Vcd /Vcs: Leptonic and semi-leptonic decays Vcb: Hadronic decays Vtd /Vts: fD and fDs from Leptonic decays Vub: Form factors of semi-leptonic decays Unitarity Test of CKM matrix

CKM matrix elements measurement Current BESIII Vub 25% 5% Vcd 7% 1% Vcs 16% Vcb 3% Vtd 36% Vts 39%

Precision test of SM and Search for new Physics DDbar mixing DDbar mixing in SM ~ 10 –3 - 10 –10 DDbar mixing sensitive to “new physics” Our sensitivity : ~ 10-4 Lepton universality CP violation Rare decays FCNC, Lepton no. violation, ...

QCD and hadron production R-value measurement pQCD and non-pQCD boundary Measurement of as at low energies Hadron production at J/y, y’, and continium Multiplicity and other topology of hadron event BEC, correlations, form factors, resonance, etc.

R-value measurement Errors on R will be reduced to 2% from current 6% Error on R Da(5)had (MZ2) 5.9% 0.02761 ±0.00036 3% 0.02761 ±0.00030 2% 0.02761 ±0.00029 Errors on R will be reduced to 2% from current 6%

BEPC II Storage ring: Large angle, double-ring RF SR RF e + e - IP

Double ring installation – Wood model No spacing problems

Mass production of the most ring components is completed。 Storage rings Mass production of the most ring components is completed。

Installation of linac is complete

Production of IR equipment

CsI(Tl) calorimeter, 2.5 %@1 GeV The BESIII Detector SC magnet, 1T Magnet yoke RPC TOF, 90ps Be beam pipe MDC, 120 mm CsI(Tl) calorimeter, 2.5 %@1 GeV

Main drift chamber Rin: 63mm; Rout: 810mm; length: 2400 mm Inner cylinder: 1 mm Carbon fiber, outer cylinder: 10 mm Carbon fiber with 8 windows End flange: 18 mm thick Al 7075 ( 6 steps) 7000 Signal wires: 25(3% Rhenium) mm gold-plated tungsten 22000 Field wires: 110 mm gold-plated Aluminum Small cell: inner---6*6 mm2, outer--- 8.2 *8.2 mm2, Gas: He + C3H8 (60/40) Momentum resolution@1GeV: dE/dX resolution: ~ 6%.

Beam test at KEK Weighted average s ~ 93 mm

CsI(Tl) crystal calorimeter Barrel: 5280 crystals，Endcap: 960 crystals each crystals (5.2x 5.2 – 6.4 x 6.4) x 28cm3 Readout: 13000 Photodiodes, 1cm2cm, Energy range：20MeV – 2 GeV Energy resolution: 2.5%@1GeV position resolution: 6 mm@1GeV Tiled angle: theta ~ 1-3o, phi ~ 1.5o

Crystal production will be completed soon. Assembly should start soon, but the mechanics for the barrel is delayed by ~ two months. Mechanics for the endcap should go out for bid soon By the end of the year, the assembly should be completed

Structure of TOF Aim: particle identification (PID) Barrel TOF Endcap TOF Scintillator: 2.4 m long, 5cm thick

TOF 70±2ps 104±11ps 94±3ps 质子 电子 Time resolution from a beam test of the Prototype（including scintillator,PMT, preamp., electronics, cable) PMT and scintillator ordered

m system : RPC 9 layer, 2000 m2 Bakelites and glass, no lineseed oil 4cm strips, 10000 channels Tens of prototypes (up to 1*0.6 m2 ) Noise less than 0.2 Hz/cm2

The super-conducting magnet in place

Trigger and DAQ The trigger design is almost finalized. No. of types of trigger boards are reduced from 23 to 17 All the boards are tested, some for several prototyping. By the end of the year, all the boards should be tested and installed. The whole DAQ system tested to 8K Hz for the event size of 12Kb, a factor of two safety margin during beam test with MDC and EMC

Offline software Beta release on 2005-11-17

Physics preparation Write a yellow book on BESIII physics: a summary of theoretical and experimental tau-charm physics and the BESIII physics reach http://bes.ihep.ac.cn/bes3/phy_book/book/book.html Workshops： Charm 2006: International tau-Charm workshop Beijing June 5-7 2006, US-China workshop on HEP cooperation Charm2006: Workshop on Tau-Charm Physics June 5 – 7, 2006, Beijing, China

Welcome to join in BESIII 谢 谢！ Thank You!

Pure FSI disfavored (I) Theoretical calculation (Zou and Chiang, PRD69 034004 (2003)) shows: The enhancement caused by one-pion-exchange (OPE) FSI is too small to explain the BES structure. The enhancement caused by Coulomb interaction is even smaller than one-pion-exchange FSI. |M|2 |M|2 BES BES Both arbitrary normalization Both arbitrary normalization one-pion-exchange FSI Coulomb interaction

FSI Factors Most reliable full FSI factors are from A.Sirbirtsev et al. ( Phys.Rev.D71:054010, 2005 )，which fit ppbar elastic cross section near threshold quite well. ppbar elastic cross section near threshold I=1 S-wave P-wave I=0 S-wave

Pure FSI disfavored I=0 S-wave FSI CANNOT fit the BES data.

So, pure FSI is disfavored So, pure FSI is disfavored. However, we do not exclude the contribution from FSI.

From B.S. Zou, Exotics 05: From A. Sirbirtsev : `pp near threshold enhancement is very likely due to some broad sub-threshold 0-+ resonance(s) plus FSI. From A. Sirbirtsev : FSI factors should be included in BW fit.

Discussion on I=1 S-wave FSI

Pure FSI disfavored (III) — I = 1 Pure I=1 S-wave FSI is disfavored by more than 3 . FSI + BW Pure FSI M = 1773  21 MeV  = 0  191 MeV

I=0 dominant in J/  radiative decays Most I = 0 states have been observed in J/  radiative decays with big production rate ( especially for 0-+ mesons ) such as , ’, (1440), (1760), f2(1270), f2(1525), f0(1500), f0(1710). The only observed I=1 meson in J/  radiative decays is 0 with low production rate 4*10– 5, e.g., no evidence for (1800) in J/   3  process. It is unlikely to be from (1800) . I=1 S-wave FSI seems unlikely.

The large BR to ppbar suggest it could be an unconventional meson For a conventional qqbar meson, the BRs decaying into baryons are usually at least one order lower than decaying into mesons. There are many examples in PDG. E.g. So the large BR to ppbar (with limited phase space from the tail of X(1860)) seems very hard to be explained by a conventional qqbar meson.

ppbar bound state in NNbar potential Paris NNbar potential: ( Paris 93, B. Loiseau et al., hep-ph/0411218, 0501112 ) For 11S0 , there is a bound state: E = - 4.8 - i 26.3 MeV quite close to the BES observation. However, Julich NNbar model: ( A. Sibirtsev et al., hep-ph/0411386 ) For 11S0 : E = - 104 - i 413 MeV seems quite far away from BES observation. They both predict an 11S0 ppbar bound state, although they are quantitatively different.

BES II Preliminary No (1800)

NO strong dynamical threshold enhancement in cross sections (at LEAR) With threshold kinematic contributions removed, there are very smooth threshold enhancements in elastic “matrix element” and very small enhancement in annihilation “matrix element”:  much weaker than what BES observed ! |M|2 |M|2 BES BES Both arbitrary normalization Both arbitrary normalization

This enhancement is NOT observed in process at SAPHIR

Discussion on KΛ mass threshold enhancement NX(1610) NX(1610) has strong coupling to KΛ: From (S&D-wave decay) and is a P-wave decay, we can estimate From BESII, The phase space of NX to KΛ is very small, so such a big BR shows NX has very strong coupling to KΛ, indicating it has a big hidden ssbar component. (5-quark system)

Non-observation of NX in suggests an evidence of new baryon : It is unlikely to be N*(1535). If NX were N*(1535), it should be observed in process, since: From PDG, for the N* in the mass range 1535~1750 MeV, N*(1535) has the largest , and from previous estimation, NX would also have almost the largest BR to KΛ. Also, the EM transition rate of NXto proton is very low.

Similar enhancement also observed in 4 away from phase space.