J/  Physics at BESIII/BEPCII Xiaoyan SHEN Institute of High Energy Physics, CAS BESIII/CLEO-c Workshop, Jan , 2004, Beijing

Outline Introduction BESIII/BEPCII project Physics at BESIII/BEPCII -- non-qq states -- meson spectroscopy -- baryon spectroscopy -- probing new physics --  c physics Summary

Introduction Strong interaction is described by non-Abelian gauge field theory – QCD  interaction of quarks and gluons. QCD predicts the existence of a new type of hadrons with explicit gluonic degrees of freedom. Study of the hadron spectroscopy helps to understand the strong interaction. Confirmation of the glueball or hybrid state is a directly test of QCD.

Experiments Hadronic peripherial production K-p experiment (LASS,…)  -p experiments (BNL E852, VES, GAMS …) Central production (WA76, WA91, WA102, …) annihilation (E760 and E835 at FNAL, Crystal Barrel at CERN) annihilation (OBLIX at CERN) Electro- and photo-production experiments e + e - storage ring facilities (Crystal Ball, MarkIII, DM2, BES) (two photon collisions in CLEO and LEP) (recently Babar and Belle exps.)

BESIII/BEPCII project BEPCII design goal: MDC: Momentum resolution: dE/dX resolution: 6-7% EMC : CsI(Tl) crystals Energy resolution: Position resolution: luminosity: 1  GeV BESIII design goal:

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

Some QCD-based theories make predictions to the glueball mass. LQCD predicts the lowest glueball state is The mass is around 1.5 GeV – 1.7 GeV. LQCD predicts the next lightest glueball is The mass is around 2.4 GeV. The mix of glueball with ordinary qq meson makes the situation more difficult. Glueball candidates: f 0 (1500), f 0 (1700),  (2230),... Search for glueballs Morningstar 1997

Glueball search and study at BESII (58M J/  ) PWA of J/  KK shows a dominant 0 ++ in 1.7 GeV mass region. PWA of J/    and  to study 0 ++ glueball candidates. PWA of J/    and  KK  to study 0 -+ structures around 1.44 GeV.  (2230) was observed by MARKIII, BESI etc.. Not seen in the mass spectra of KK,  and pp by BESII. Careful PWA is being performed by BESII.

K+K-K+K- K BKG (1525) f 0 (1710) BESII 58M J/  BESII and

Search for exotic 1 －＋ state at BESII (58M J/  ) The J PC of the ordinary qq meson cannot be the exotic numbers 0 +-, 0 --, 1 -+, 2 +-, 3 -+, … The hybrid states with the exotic quantum numbers would be evidence for non-qq degrees of freedom. Theoretical model predicts : exotic hybrid state preferentially to pairs of S wave and P wave mesons, such as f 1 (1285) , b 1 (1235) . Theoretical model predicts: M 1-+  1.9 GeV BES is analyzing J/    0 to search for 1 -+ state.

Search for other non-qq states at BESII Near pp threshold enhancement in enhancement cc

Fit reults Mass: M=1859 MeV/c 2 Width:  < 30 MeV/c 2 (90% CL) J/    pp M(pp)-2m p (GeV) BG curve Eff. curve  2 /dof=56/56 Fitted peak Fitted curve  10  25

This enhancement is important:  excluded from the known particles  cannot be explained by theories, such as FSI.  mass≤2m p ， width is narrow  Hard to be explained as a conventional qq meson Important in testing and developing QCD !

BESII 58M J/   in J/      

Before K*(892) 0 cut After K*(892) 0 cut  in J/  K + K -     and K*K 

Meson spectroscopy The low mass 0 ++ states have been confusing for many years. There are so many 0 ++ s’, such as f 0 (1370), f 0 (1500), f 0 (1710) …. PWA of J/    … Two ground-state isoscalar 1 ++ states at 1240 and 1480 MeV in the quark model. But there are states in this region -- f 1 (1285), f 1 (1420), f 1 (1530). whether 0 ++ f 0 (980) and a 0 (980) are molecular states or not. PWA of J/   ,  KK,  … extra 2 ++ states PWA of J/    and  KK , …

Baryon spectroscopy The understanding of the internal quark-gluon structure of baryons is one of the most important tasks in both particle and nuclear physics. The systematic study of various baryon spectroscopy will provide us with critical insights into the nature of QCD in the confinement domain. Jefferson Lab, ELSA, GRAAL, SPRING8 and BES have started to study the baryon and excited baryon states. The available experimental information is still poor, especially for the excited baryon states with two strange quarks, e.g.,  *. Some phenomenological QCD-inspired models predict more than 30 such kinds of baryons, however only two are experimentally well settled. Totally only about 10% excited baryons are observed.

Advantages of studying excited baryons from J/  decays excited baryons can be produced through J/  decays. for J/    NN and  NN decays, the N  and N  systems are limited to be pure isospin ½ due to isospin conservation. search for “missing” baryon states and hybrid baryon with BESIII/BEPCII.

excited baryon states at BESII N*(1440) N*(1520) N*(1535) N*(1650) N*(1675) N*(1680) ? N*(1650)

Probing for new physics in J/  decays 1. Lepton flavor violation (LVF) --- In SM, lepton flavor symmetries are conserved. --- neutrinos having mass and flavor oscillation indicate the existence of LVF --- J/   e ,  and e  are LVF processes --- some theoretical models predict: Br(J/  )  – Br(J/  e  )  – search for J/  and J/  e  with or more J/  data.

2. CP test in J/  decays --- CP violation was first discovered in K system --- CP violation was also found in B system --- no experimental indication of CP violation in other processes --- search for CP violation in other places where SM predicts no or tiny CP violation With BESIII J/  data, CP test can be done in: --- J/   particle + antiparticle (  ), where the polarization can be measured through subsequential decays of . --- J/   , clean sample, but low efficiency because of K decay  large sample is needed.

3. Flavor changing processes --- J/  can decay to single D meson + X --- In SM, these Cabbibo suppressed and/or favored weak decays can proceed through tree and penguim processes and have the branching ratios < Since the penguin c  u transition is small in SM, the theoretical estimation gives: Br(J/   D 0 X u )  Br(J/   D + X u )  Considering new physics effects, Br(J/   D/D X u )  Br(J/   Ds + K - )  10 -5

 c physics  c produced from J/    c (  1.3%) E   116 MeV good photon detection capability  c  multi – charged tracks good PID and good momentum resolution  c decays to hadrons through annihilating to two gluons. The sum of  c decay branching ratios < 30%

 c decays  c  Vector + Vector PQCD forbidden. Observed  c  and  c , search for  c   with BESIII data.  c  baryon pairs (only have  c  pp)  c  two photons More  c decay channels CP violation test in  c decays.

Simulation of possible 2 ++ glueball in J/  ’  (2230) is a 2 ++ glueball candidate --- LQCD calculation --- some glueball favored exps. observed it (narrow, flavor blind, …); some didn’t find it --- small coupling to 2-photon process Theoretical calculations predict:  (2230) can be largely coupled to  ’ and  ’  ’, if it exists and is a gleuball. J/  ’, ,  ’  0,  0  +  - might be one of the main decay channels of  (2230) (Take  (2230) as an example)

assuming Br(J/  (2230))Br(  ’)  3  assuming 6  10 9 J/  events f 0 (1500), X(1910) and X(2150) are included according to the results from other experiments. the backgrounds are included in the simulation. final state: 4  2  -- a detector with good photon detection -- a high statistics. J/  ’, ,  ’  0,  0  +  -

 (2230)

InputOutput (B=1.0T) X(1910) M(MeV)  (MeV) Br(  )    0.30 X(2150) M(MeV)  (MeV) Br(  )    0.33  (2230) M(MeV)  (MeV) Br(  )    0.33 Breit-Wigner fit results

Separation of 0 ++, 2 ++ and 4 ++ in J/  K + K - The structures in the K+K- mass region over 2.0 GeV are quite complicated. Distinguishing 0 ++, 2 ++ and 4 ++ in this mass region is important. possible resonances included in the simulation for M KK > 2.0 GeV are:  (2230) and f 4 (2050) (f 0 (2100)). main backgound: J/   K* K assuming 1  10 9 J/  events for  (2230), assuming 2 ++, x=0.5, y=0.5 for f 4 (2050), assuming 4 ++, x=0.5, y=0.5

the J PC s ’ of  (2230) and f 4 (2050) being 2 ++ and 4 ++ gives the best Log Likelihood value. excluding either  (2230) or f 4 (2050) makes the log likelihood value be worse apparently. 0 ++, 2 ++ and 4 ++ can be separated clearly in the mass region over 2.0 GeV with BESIII detector. PWA Results Crosses are generated Monte-Carlo data, histogram is the PWA fit projection.

assuming 6  10 9 J/  events J/  a 0 (980),  a 2 (1320),  (1390),  (2300) are included. background included PWA can well separate these states Simulation of J/  0  0

Precise measurement of K* mass splitting There is mass splitting between the different isospin states (K*(892)  and K(892)* 0 ). Different theoretical models give different  m. Precise measurement of  m requires a large statistics and a detector with good PID and momentum resolution. Signal (6  10 8 J/  ): Background:

The signals are fitted using: Background is fitted with the 3rd. order polynomial. When the input  m = 6.0 MeV, we obtain the mass splitting as:  m = 5.79  0.16  0.13 MeV

Simulation of J/  Ds + K - assuming J/  events main background is J/  KK  signal channel J/  DsK, Ds ,  KK

Br(J/  DsK) = 1.0  Br(J/  DsK) = 1.0  Br(J/  Ds  K + ) < 2.48  at 90% C.L.

Summary With BESIII/BEPCII: -- search for non-qq states -- systematic study of meson spectroscopy -- systematic study of baryon spectroscopy -- probing new physics --  c physics

Is M peak really less than 2m p ? No turnover at threshold  peak mass must be <2m p weight events by q 0 /q: (i.e. remove threshold factor) M(pp)-2m p (GeV)