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New Observations on Light Hadron Spectroscopy at BESIII

New Observations on Light Hadron Spectroscopy at BESIII. Yanping HUANG For BESIII Collaboration Institute of High Energy Physics (IHEP) ICHEP2010, Paris, Jul 21-28, 2010. Outline. Introduction mass threshold study in J/ y and y ’ radiative decays

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New Observations on Light Hadron Spectroscopy at BESIII

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  1. New Observations on Light Hadron Spectroscopy at BESIII Yanping HUANG For BESIII Collaboration Institute of High Energy Physics (IHEP) ICHEP2010, Paris, Jul 21-28, 2010

  2. Outline • Introduction • mass threshold study in J/y and y’ radiative decays • Confirmation of X(1835) and observation of two new resonances in • Observation of X(1870) in • Summary ICHEP2010

  3. Introduction • Multi-quark states, glueballs and hybrids have been searched for experimentally for a very long time, but none have been established. • However, during the past three years, a lot of unexpected experimental evidence for hadrons cannot (easily) be explained by the conventional quark model. For example, at BESII: • threshold enhancement was observed in • X(1835) was observed in ICHEP2010

  4. The BEPCII/BESIII Project Double-ring collider Designed Luminosity: 1×1033 cm-2s-1 Record Luminosity : 3.2  1032cm-2s-1 J/ ’ Beginning of 2004, construction starts Apr. 14, 2009: ~106 M ψ’ events (42.3pb-1 at 3.65GeV) July 28, 2009: ~226 M J/ events We have opportunities to confirm the existence of threshold enhancement and X(1835) at BESIII… and for new observations! ICHEP2010

  5. mass threshold study in J/y and y’ radiative decays

  6. Observation of mass threshold enhancement @ BESII 3-body phase space BESII X(1860) • theoretical speculation: • bound state (baryonium) • FSI effect • …… 0.3 0.2 0 0.1 acceptance Mpp-2mp (GeV) ICHEP2010

  7. Several non-observations EPJ C53 (2008) 15 PRD 73 (2006) 032001 No significant narrow strong enhancement near threshold (~2 if fitted with X(1860)) PRL 99 (2007) 011802 Mpp(GeV) ICHEP2010

  8. Mass Spectrum and Dalitz Plot 3-body phase space • Narrow threshold enhancement is evident in mass spectrum. ICHEP2010

  9. Mass spectrum fitting BESII 0.3 0.2 0 0.1 Mpp-2mp (GeV) +3 +5 -10 -25 M=1859 MeV/c2 G < 30 MeV/c2 (90% CL) M=1861 +6 -13+7-26 MeV/c2 G < 38 MeV/c2 (90% CL) PRL 91 (2003) 022001 Chinese Physics C 34, 421 (2010) ICHEP2010

  10. invariant mass spectrum and Dalitz plot BES III Preliminary Significant narrow threshold enhancement exists ICHEP2010

  11. Mass spectrum fitting BES III Preliminary Study on more sophisticated fits, such as including FSI, is ongoing +3 +5 -10 -25 BESII M=1859 MeV/c2 G < 30 MeV/c2 (90% CL) 0 0.1 0.2 0.3 Mpp-2mp (GeV) ICHEP2010

  12. threshold mass spectrum in y’ radiative decay BES III Preliminary BESII Mpp(GeV) PRL 99 (2007) 011802 No significant narrow strong enhancement near threshold (~2 if fitted with X(1860)) Noobvious narrow threshold enhancement Pure FSI interpretation of the narrow and strong threshold enhancement is disfavored. ICHEP2010

  13. Confirmation of X(1835) and observation of two new structures in

  14. Observation of X(1835) in at BESII PRL 95,262001(2005) • Confirmation of X(1835) is necessary with high statistic data sample. • LQCD predicts the 0-+ glueball mass is ~2.3GeV. • A 0-+ glueball may have similar property as hc (the main hc decay mode is pph’). • It is important and interesting to study ICHEP2010

  15. Mass spectrum of BES III Preliminary BES III Preliminary Combination for  to +- and  BES III Preliminary • X(1835) and hcis observed. • Two additional structures at M~2.1GeVand 2.3GeV • There maybe some f1(1510). ICHEP2010

  16. Fitting for the combined mass spectrum • Fitting with four resonances (acceptance weighted BW gauss) • Three background components: • Contribution from non-h’ events estimated by h’ mass sideband • Contribution from with re-weighting method • Contribution from “PS background” Red line: estimated contribution of ①+ ② Black line: total background BES III Preliminary • Stat. sig. is conservatively estimated: • fit range, background shape, contribution of extra resonances ICHEP2010

  17. X(1835) resonance is confirmed at BESIII, but the width is significantly larger than that measured at BESII with one resonance in the fit. • Two new resonances, X(2120) and X(2370), are observed with significances larger than 7.2s and 6.7s respectively. • PWA is needed not only to determine the spin-parities of above three resonances, but also to make more precise measurements on masses, widths and BRs by considering possible interferences among them. ICHEP2010

  18. Observation of in

  19. Analysis of @BESIII • With a0(980): • Veto a0(980): X(1870) f1(1285) a0(980) h’ h(1405) BES III Preliminary BES III Preliminary BES III Preliminary The f1(1285), h(1410) and X(1870) primarily decay via a0(980)p± ICHEP2010

  20. Mass spectrum fitting • Fitting with three resonances (acceptance weighted BW Gauss) • Background component described by Polynomial function BES III Preliminary Whether the X(1870) is the X(1835) or h2(1870), or a new resonance, needs further study. ICHEP2010

  21. Summary • is confirmed in J/y radiative decay, and no obvious similar structure was observed in y’ radiative decay. • is confirmed in , and two new resonances, X(2120) and X(2370) are observed with significance larger than 7.2s and 6.7s respectively. • A new process J/ywX(1870)wa0p is observed. • Whether or not the X(1860), X(1835) and X(1870) are the same resonance, still needs further study. ICHEP2010

  22. Thank You ICHEP2010

  23. Summary on the previous experimental results The strong and narrow mass threshold enhancement has only been observed in J/y radiative decay, not in any other place so far. Any model trying to interpret the mass threshold enhancement should also answer why it is not observed in other places, especially in y(2S) and ϒ(1S) radiative decays as well as in process. ICHEP2010

  24. Mass spectrum fitting method Fit function: signal: acceptance weighted S-wave BW function: q : the proton momentum in cms of ppb k : the photon momentum k: the ppb orbital angular momentum background shape: a1 and a2 are obtain from a fit to an uniform phase space MC sample ICHEP2010

  25. pp threshold enhancement @ CLEOc • CLEO-c does fit the same as BES and obtains: CLEO-c preliminary QWG2010 Z. Metreveli agrees with BESII results [PRL91(2003)022011]. • CLEO-c fits with three contributions: BES considered these (2) and (3) as systematic errors. ICHEP2010

  26. Event selection for • Initial selection criteria： • Ncharged=4，Ng>=2 • Nπ>2 • Kinematic fit(4C): • Final selection criteria： ICHEP2010

  27. Event selection for • Initial selection criteria： • Ncharged=4，Ng>=2 • Nπ>2 • Kinematic fit(4C,5C): • Final selection criteria： ICHEP2010

  28. Fitting for the combined mass spectrum Fitting with one resonance as BESII BES III Preliminary BESII X(1835) confirmed by BESIII ICHEP2010

  29. Mass spectrum of Fit with one resonances + polynomial background: BES III Preliminary BES III Preliminary Stat. sig. ~9 Stat. sig. ~18 ICHEP2010

  30. Mass spectrum fitting • Fitting with three resonances (acceptance weighted BW Gauss) • Background component described by Polynomial function BES III Preliminary Study of Background component is ongoing ICHEP2010

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