Physics at BES Shan JIN (for the BESIII Collaboration) Institute of High Energy Physics (IHEP) USTRON09, Poland September 12-16, 2009

Outline  Introduction of BES experiments and Physics at BES  Highlights at BESII  Status of BESIII and preliminary results  Future prospects at BESIII  Conclusion

3 Linac Storage Ring BES BSRF Beijing Electron Positron Collider (BEPC) at IHEP BESI: BESII: L ~ 5  /cm 2  s at J/  E beam ~ 1 – 2.5 GeV BESIII: Physics run started in March, M  (2S) and 200M J/  events collected BEPCII: L reached 3  /cm 2  s at  (3770) designed L: /cm 2  s

注入器长 202 米 储存环的周长为 米 对撞能量 2-5GeV 物理目标 北京正负电子对撞机（ BEPC ）示意图

Why tau-charm physics is interesting  Abundant resonances(J/  family, huge Xsections)  Tau-charm threshold production(in pairs  tagging  background free, no fragmentation, kinematic constrains, quantum coherence,…)  Charm quark: A bridge between pQCD and non-pQCD  A ruler for LQCD  J/  decay    Gluon rich environment  Flavor physics  Complementary to LHC: virtual vs real  A broad spectrum & efficient machine: in the past in the era of LHC in the future

What (highlight) physics interested us  Light hadron spectroscopy Full spectra: normal & exotic hadrons QCD How quarks form a hadron ? non-pQCD  Charm physics CKM matrix elements  SM and beyond mixing and CPV  SM and beyond  Charmonium physics Spectroscopy and transition  pQCD & non-pQCD New states above open charm thresholds  exotic hadrons ? pQCD:  puzzle  a probe to non-pQCD or ?  Tau physics and QCD Precision measurement of the tau mass and R value  Search for rare and forbidden decays Precision test of SM and search for new physics hep-ex/

Light hadron spectroscopy  Motivation: Establish spectrum of light hadrons Search for non-conventional hadrons Understand how hadrons are formed Study chiral symmetry in QCD  Why at a tau-charm collider ? Gluon rich Larger phase space than at higher energies Clean environment, J PC filter Glueball spectrum from LQCD Y. Chen et al., PRD 73 (2006) Many results in BESII: ~ 50 publications Much more from BESIII:  100 statistics,  10  resolution

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, the effort has never been stopped, especially, during the past three years, a lot of surprising experimental evidences showed the existence of hadrons that cannot (easily) be explained in the conventional quark model. Searches for new forms of hadrons are of special importance at BES since J/psi decays are believed as an ideal factory to search and to study exotic hadrons.

Charmonium physics  What to study ? Production, decays, transition, spectrum  For what ? A lab for pQCD and non-pQCD Calibrate LQCD How quarks form a hadron ?  Why at a tau-charm collider ? A clean environment Tagging possible Abundantly produced Examples of interesting/long standing issues:   puzzle Missing states ? Mixing states ? New states above open charm thre.(X,Y,Z,…)

Highlights at BESII

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+p 2 )  z = 2.3 cm

World J/  and  (2S) Samples (10 6 ) J/   (2S)

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)

At BESII: Observation of X(1835) in The  +  -  mass spectrum for  decaying into  +  -  and   Statistical Significance 7.7  Phys. Rev. Lett. 95, (2005) The same origin as ppbar mass threshold?  a ppbar bound state? BES II

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)

M 2 (  ) M2()M2() Background X(1810) Observation of  mass threshold structure X(1810) in J/    at BESII M(  ) Phys. Rev. Lett., 96 (2006) J pc favors 0 ++ Possible theoretical interpretations: glueball, hybrid, multiquark? BES II

Background Very broad resonance X(1580) observed in K + K - mass spectrum in J/  K + K -  0 at BESII Phys. Rev. Lett. 97 (2006) So far the only reasonable interpretation is a multiquark state due to its very broad width BES II

σ at BES  BES II observed σ in J/    +  -.  Pole position from PWA: BES II

κ at BESII  BESII firmly established neutral  in J/   K* 0 K   K  K  in 2006:  PWA result Pole position: BES II

Observation of charged  at BESII  New result: Charged  observed at BESII in  Different parameterizations are tried in PWA. The pole position: M(K   0 ) GeV/c 2 BESII Preliminary  K*(1410), K*(1430) consistent with neutral 

QCD studies at low energies  Understand where exactly pQCD becomes invalid  Precision measurement of  s  running  Precision measurement of R  input to  Related to  QED (s), prediction of higgs mass and g-2  A new measurement at BESII on R Precision at ~ 3.5% A new determination o f  s (s):  s (M 2 Z ) =  ? Phys.Lett.B677,(2009)239 E cm (Ge V) L(pb -1 )R  s (S)  0.02   0.02   0.01  0.07 In good agreement with previous results BESIII: < 2%

Resonance parameter fit  Heavy charmonia parameters were fitted with the data between 3.7–5.0GeV, taking into accounts the phase angles, interference, energy-dependent width, etc. Phys. Lett. B660, (2008)315 Probability =31.8%

PRL101 (2008) Black dots: data Red dots: data subtracting J/  and continuum contribution Green line: fit with one  (3770) hypothesis; Red line: fit with two cross section Blue line: fit with two amplitude Anomalous  (3770) lineshape Check all lines !!! quantityTwo AM One AMY(3770)+G(3900) 22 125/103112/102182/106170/104   (3686) (MeV)  0.0  0.5 M 1 (MeV)  2.4   11.8   0.5   0.5  0.5 M 2 (MeV)  0.6   1.3  (Fixed)

Status of BESIII and preliminary results

BEPC II Storage ring: BEPC II Storage ring: Large angle, double- ring RF SR IP Beam energy: GeV 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 BESIII detector

BESIII Commissioning and data taking milestones Mar. 2008: first full cosmic-ray event April 30, 2008: Move the BESIII to IP July 18, 2008: First e + e - collision event in BESIII Nov. 2008: ~ 14M  (2S) events collected April 14, 2009 ~100M  (2S) events collected May 30, pb -1 at continuum collected July 28, 2009 ~200M J/  events collected Peak Nov. 2008: 1.2  cm -2 s -1 Peak May 2009: 3.2  cm -2 s -1

Detector performance and calibration ● Layer 7 ● Layer 22 Wire reso. Design: 130  m dE/dx reso.: 5.80% Design：6-8% CsI(Tl) energy reso. Design: 1 GeV Barrel TOF reso.: 78 ps Design：80-90 ps Bhabha

E1 transitions: inclusive photon spectrum  c2  c1  co  c1,2   J/  cc BESIII preliminary

Observation of h c : E1-tagged  (2S)   0 h c,h c   c  Select E1-photon to tag h c  A fit of D-Gaussian signal+ sideband bkg. yield: M(h c ) Inc = ±0.16±0.10 MeV  (h c ) Inc = 0.89±0.57±0.23 MeV (First measurement) Br(  ’    h c )×Br(h c   c ) Inc =(4.69±0.48(stat)) ×10 -4 (  (h c ) floated) =(4.69±0.29(stat)) ×10 -4 (  (h c ) fixed at  (  c1 )) background subtracted Systematic errors under study CLEO’s results (arXiv v1) : M(h c ) Inc = ±0.23±0.15 MeV Br(  ’    h c )×Br(h c   h c ) Inc =(4.22±0.44±0.52) ×10 -4 (  (h c ) fixed at  (  c1 ) ~0.9MeV CLEOc: Combined E1-photon-tagged spectrum and exclusive analysis M(h c ) avg = ±0.19±0.12 MeV Br(  ’    h c )×Br(h c   h c ) avg =(4.19±0.32±0.45) ×10 -4 BESIII preliminary N(h c )= 2540±261  2 /d.o.f = 39.5/41.0 (arXiv v1)

Observation of h c : Inclusive  (2S)   0 h c  Select inclusive  0  A fit of D-Gaussian signal + 4 th Poly. bkg yield N(h c ) = 9233±935,  2 /d.o.f = 38.8/38.0  Combined inclusive and E1-photon-tagged spectrum Br(  ’    h c ) =(8.42±1.29(stat)) ×10 -4 (First measurement) Br(h c   c ) =(55.7±6.3(stat))% (First measurement) 31 background subtracted Inclusive   recoil mass spectrum Systematic errors under study BESIII preliminary

BR (10 -3 )  c0  c2 0000 BESIII 3.25±0.03(stat)0.86±0.02(stat) PDG 2. 43± ±0.08 CLEO-c 2.94±0.07± ±0.03±0.08  BESIII 3.1±0.1(stat)0.59±0.05(stat) PDG 2.4±0.4<0.5 CLEO-c 3.18±0.13± ±0.05±0.06 CLEO-c arxiv: Study of  (2S)→  0  0,   → ,  0 →   Interesting channels for glueball searches  Based on 110M  (2S)  BK study from 100M inclusive MC sample and 42pb -1 continuum sample  Unbinned Maximum Likelihood fit: Signal: PDF from MC signal Background: 2 nd order Poly.  2S)   0  0 N  c ±175 N  c2 4149±82  2S)   N  c0 1541±56 N  c2 291±23

Confirmation of the BESII observation: pp threshold enhancement in J/  decays  PRL 91 (2003) BES III preliminary  (2S) →  J /  M= ± 5.3MeV/c 2  < 33 MeV/c 2 (90% CL) M=1859 MeV/c 2  < 30 MeV/c 2 (90% CL)  10  BES II M(pp)-2m p (GeV)

Confirmation of BESII observation: No pp threshold enhancement in  ’ decays  No significant narrow enhancement near threshold (~2  if fitted with X(1860)) M pp (GeV) BES III preliminary PRL 99 (2007) BES II No enhancement in  ’ decays In fact, no enhancement in ψ’, ϒ (1S) decays and in the process of J/    ppbar show that FSI unlikely.

Study of  cJ  VV, V=   Test QCD-based theory at  cJ decays  Puzzles for  c0  VV: no helicity suppress   c1   highly suppressed owing to symmetry of identical particles   c1   OZI doubly suppressed BESIII preliminary BESII results: BR(10 -3 )  c0  c2  0.93   0.3  2.3   0.7 Backgrounds from sideband & 100M MC events Clear  c1   signal to be understood

First observation of  c1    Background from sideband & 100M MC events  Clear signal from  c1           (K + K - ) BESIII preliminary

Future prospects at BESIII

Event statistics at BESIII Physics Channel Energy (GeV) Luminosity (10 33 cm –2 s –1 ) Events/year J/  ×10 10  ×10 7  ’ ×10 9 D ×10 7 Ds ×10 6 Ds ×10 6 *CLEO took 10 nb D production cross section while we took 5 nb

Precision measurement of CKM: Branching rations of charm mesons  V cd /V cs: Leptonic and semi-leptonic decays  V cb: Hadronic decays  V td /V ts: f D and f Ds from Leptonic decays  V ub: Form factors of semi-leptonic decays  Unitarity Test of CKM matrix

CKM matrix elements measurement CurrentBESIII V ub 25%5% V cd 7%1% V cs 16%1% V cb 5%3% V td 36%5% V ts 39%5%

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

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

R-value measurement Error on R  (5) had (M Z 2 ) 5.9% ± % ± % ± Errors on R will be reduced to 2% from current 6%

Prospects of glueball searches at BESIII

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., “J P, I” filter.

One Important Physics Goal of BESIII With J/psi events, we hope to answer:  Whether glueballs exist or not? Naively, we estimate in each exclusive decay mode: If the eff. is about 20%, we would have events for each decay mode  we should observe a relative narrow (width: 50~200MeV) glueball if it exists.

Difficulties (I)  Theoretically: Predictions on glueball masses from LQCD may be unreliable due to quench approximation. No predictions on the widths so far (even the order). No prediction on the production rate  (J/    G). Mix with qqbar mesons or even with 4q, qqg mesons? (dirty?) What is the mixing mechanism from the first principle?

Difficulties (II)  Experimentally: Data sample is not big enough (it is not a problem for BESIII) No good way modeling background at low energy, in many cases we have to study bck via data. Interferences among mesons make the mass/Dalitz plots very complicated   PWA is crucial for hadron spectroscopy at BESIII  But PWA may face many uncertainties.

About scalar glueball  Many scalar mesons in the mass range 1.4~1.8 GeV, where a scalar glueball is predicted to be. More studies will be performed at BESIII.  More theoretical studies are also needed: Not only glueball mass, but also width Decay patterns Production rate in J/psi radiative decays Mixing mechanism

2 ++ glueball candidates  Lattice QCD predicts the 2 ++ glueball mass in the range of 2.2~2.4 GeV   (2230) was a candidate of 2 ++ glueball: It was first observed at MARKIII in J/  KK It was observed at BES I in J/  KK, ,  ppbar It was not observed at DM2.

BES-I  (2230) Result  (2230)

The situation at BESII  The mass plots shows no evident  (2230) peaks in J/  KK, ,  ppbar, which is clearly different from BESI.  Careful PWA is needed to draw firm conclusion on its existence since it may be still needed in the PWA although no clear mass peak observed.  Difficult to draw firm conclusion at present. We hope to give a final answer at BESIII on  (2230).

Other 2 ++ glueball candidates  No other obvious good candidates have been observed in J/psi radiative decays in the mass range predicted by LQCD.  What does it mean: LQCD prediction might not be very reliable, or BR(J/    G)xBR(G  hh) is small ( <10 -4 ) so that we don’t have the sensitivity to observe it ( quite possible ), or, The width of a glueball is very large ( ~1GeV, E.Klepmt ).

Where to search for the 0 -+ glueball?  Lattice QCD predicts the 0 -+ glueball mass in the range of 2.3~2.6 GeV.   (1440) and X(1835) were suggested being possible candidates, but their masses are much lower than LQCD predictions.

No 0 -+ glueball candidate observed in the mass range 2.3~2.6 GeV  No evidence for a relatively narrow state ( 100 ~ 200 MeV width ) above 2GeV in  Again: LQCD reliable? Production rate could be very low. Glueball width could be very large.

Summary  Physics at BES (tau-charm threshold) are very rich.  There are many exciting discoveries at BESII.  BESIII is operational since 2008: Detector performance excellent, ready for physics High quality data samples in hand Analysis in progress, papers in a few months  With much more statistics of data sample and much improved detectors at BESIII, more exciting discoveries can be expected.  Some fundamental questions, such as the existence of glueballs, might be answered at BESIII with close collaboration with theorists.

Thanks! 谢谢！

Prospects: a bright future  BESIII will resume data taking after summer shutdown, ~5 months until next summer  Possible plans: M J/  events (2-4 months) M  (2s) (2-4 months) 2fb -1  (3770) (4 months) Lineshape scan of  (3770) (2 weeks)  Future charm programs LHCb at CERN （ soon ） BELLE II at SuperB factory （ ~ 2014 ） PANDA at GSI （ ~ 2015 ）  New programs under discussion: Frascati(super flavor factory) Novosibirsk(super tau-charm factory) Fermilab  TeV fixed target exp. ?  Ppbar exp. ? To be decided in Nov. L ~ cm -2 s -1 Expand the life time of tau-charm colliders to > 50 years !