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J/  Physics at BESIII/BEPCII

J/  Physics at BESIII/BEPCII. Xiaoyan SHEN Institute of High Energy Physics, CAS BESIII/CLEO-c Workshop, Jan. 13-15, 2004, Beijing. Outline. Introduction BESIII/BEPCII project Physics at BESIII/BEPCII -- non-qq states -- meson spectroscopy -- baryon spectroscopy

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J/  Physics at BESIII/BEPCII

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  1. J/ Physics at BESIII/BEPCII Xiaoyan SHEN Institute of High Energy Physics, CAS BESIII/CLEO-c Workshop, Jan. 13-15, 2004, Beijing

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

  3. 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.

  4. 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.)

  5. BESIII/BEPCII project BEPCII design goal: luminosity: 11033 @ 1.89 GeV BESIII design goal: MDC:Momentum resolution: dE/dX resolution: 6-7% EMC : CsI(Tl) crystals Energy resolution: 2.5%@1GeV Position resolution: 6mm@1GeV

  6. 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

  7. Search for glueballs • Some QCD-based theories make • predictions to the glueball mass. • LQCD predicts the lowest glueball • state is 0++. The mass is around • 1.5 GeV – 1.7 GeV. • LQCD predicts the next lightest • glueball is 2++. The mass is • around 2.4 GeV. • The mix of glueball with ordinary • qq meson makes the situation • more difficult. • Glueball candidates: f0(1500), f0(1700), (2230), ... Morningstar 1997

  8. 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.

  9. BESII and f0(1710) (1525) K+K- BESII 58M J/ BKG K K

  10. Search for exotic 1－＋state at BESII (58M J/) • The JPC 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 f1(1285), b1(1235). • Theoretical model predicts: M 1-+  1.9 GeV • BES is analyzing J/  0 to search for 1-+ state.

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

  12. Fit reults Fitted peak J/ygpp +3 +5 -10 -25 Mass: M=1859 MeV/c2 Width: G < 30 MeV/c2 (90% CL) Fitted curve c2/dof=56/56 0 0.1 0.2 0.3 M(pp)-2mp (GeV) Eff. curve BG curve

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

  14.  in J/   BESII 58M J/ BES II Preliminary

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

  16. Meson spectroscopy • The low mass 0++ states have been confusing for many years. There are so many 0++s’, such as f0(1370), f0(1500), f0(1710) ….PWA ofJ/  … • Two ground-state isoscalar 1++ states at 1240 and 1480 MeV in the quark model. But there are 3 1++ states in this region -- f1(1285) , f1(1420), f1(1530). • whether 0++ f0(980) and a0(980) are molecular states or not. PWA of J/  , KK,  … • extra 2++ states PWA of J/   and KK, …

  17. 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.

  18. 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.

  19. N*(1520) N*(1535) N*(1650) N*(1675) N*(1680) N*(1650) N*(1440) ? BES II Preliminary BES II Preliminary excited baryon states at BESII

  20. 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/)  10-5 – 10-8 Br(J/e)  10-5 – 10-7 --- search for J/ and J/e with 1010 or more J/ data.

  21. 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.

  22. 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 <10-8. • Since the penguin c  u transition is small in SM, the theoretical estimation gives: Br(J/  D0Xu)  10-10 Br(J/  D+Xu)  10-9 • Considering new physics effects, Br(J/  D/D Xu)  10-5 Br(J/  Ds+K-)  10-5

  23. 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%

  24. 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.

  25. Simulation of possible 2++ glueball in J/’ (Take (2230) as an example) • (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)

  26. J/’, , ’0, 0+- final state: 42 -- a detector with good photon detection -- a high statistics. • assuming Br(J/(2230))Br(’)  3  10-6. • assuming 6109 J/ events • f0(1500), X(1910) and X(2150) are included • according to the results from other experiments. • the backgrounds are included in the simulation.

  27. (2230)

  28. Breit-Wigner fit results

  29. 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 MKK > 2.0 GeV • are: (2230) and f4(2050) (f0(2100)). • main backgound: J/  K* K • assuming 1109 J/ events • for (2230), assuming 2++, x=0.5, y=0.5 • for f4(2050), assuming 4++, x=0.5, y=0.5

  30. PWA Results • the JPCs’ of (2230) and f4(2050) • being 2++ and 4++ gives the best • Log Likelihood value. • excluding either (2230) or f4(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. Crosses are generated Monte-Carlo data, histogram is the PWA fit projection.

  31. Simulation ofJ/00 • assuming 6 109 J/ events • J/a0(980), a2(1320), • (1390), (2300) are • included. • background included • PWA can well separate these • states

  32. 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 108 J/): Background:

  33. 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

  34. Simulation of J/Ds+K- • assuming 1010 J/ events • main background is J/KK • signal channel J/DsK , Ds, KK

  35. Br(J/DsK) = 1.010-6 Br(J/DsK) = 1.010-7 Br(J/DsK+) < 2.48  10-7 at 90% C.L.

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

  37. Thank you!

  38. Is Mpeak really less than 2mp? weight events by q0/q: (i.e. remove threshold factor) No turnover at threshold peak mass must be <2mp M(pp)-2mp (GeV)

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