New Results and Prospects of Light Hadron Spectroscopy Shan JIN Institute of High Energy Physics (IHEP) [email protected] Presented by Yi-Fang Wang Charm 2007 Ithaca, August 7, 2007
Download ReportTranscript New Results and Prospects of Light Hadron Spectroscopy Shan JIN Institute of High Energy Physics (IHEP) [email protected] Presented by Yi-Fang Wang Charm 2007 Ithaca, August 7, 2007
New Results and Prospects of Light Hadron Spectroscopy Shan JIN Institute of High Energy Physics (IHEP) [email protected] Presented by Yi-Fang Wang Charm 2007 Ithaca, August 7, 2007 Outline New results on 0-+ mesons New results on 0++ mesons New results on 1-- mesons New results on baryons at BESII Prospects of glueball searches at BESIII New results on -+ 0 mesons (1760) in J / at BESII J / , 0 M(+-0)(GeV/c2) signal with multiple entries M(+-0)(GeV/c2) Phys. Rev. D 73 (2006) 112007 M(+-0)(GeV/c2) M(+-0)(GeV/c2) sideband signal after best candidate selection (best w masses) M() Phase Space Eff. curve M() Side-band PWA analysis Total f2(1910) f2(1910) (1760) (1760) > 10 f2(1640) f2(160) M() M() (GeV/c2) f 0 f0(1710) BG BG f0(1710) f0(1790) f0(1810) Using observed mass and width for f0(1810) in J/ The existence of (1760) is confirmed Its mass and width were first correctly measured with PWA. M 1744 10 15 MeV/c2 24 244 21 25 MeV/c2 Br( J / (1760))Br( (1760) ) (1.98 0.08 0.32)10-3 Phys. Rev. D 73 (2006) 112007 Candidate of 0-+ baryonium Observation of X(1835) in J at BESII Statistical Significance 7.7 J N obs 264 54 m 1833.7 6.1 2.7MeV 67.7 20.3 7.7MeV Phys. Rev. Lett. 95, 262001 (2005) The +- mass spectrum for decaying into +- and Observation of an anomalous enhancement near the threshold of pp mass spectrum at BES II BES II J/pp acceptance weighted BW M=1859 +3 +5 MeV/c2 10 25 < 30 MeV/c2 (90% CL) c2/dof=56/56 0 Phys. Rev. Lett. 91, 022001 (2003) 3-body phase space 0.1 0.2 M(pp)-2mp (GeV) acceptance 0.3 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) M pp 2mp Candidate of 0-+ ppbar Bound State X(1835) could be the same structure as ppbar mass threshold enhancement X(1860)/X(1830). 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. There is already an (1760) nearby , so that X(1835) is very likely to be an unconventional 0-+ meson. This strong threshold enhancement is NOT observed in pp ) S1( at CLEO Br ( (1S ) X) / Br ( J / X) 0.7% @ 90% CL Phys.Rev.D73, 032001(2006) This result cannot be explained by pure FSI effect, since FSI is a universal effect. FSI interpretation of the narrow and strong ppbar threshold enhancement is disfavored. This indicates that X(1860) has a production property similar to ’ meson. c.f.: Br ( (1S ) ' ) / Br ( J / ' ) No enhancement near threshold 0.4% @ 90% CL ( PDG ) No strong threshold enhancement is observed in pp ' at BESII Br ( ' X) / Br ( J / X) 8% @ 90% C.L. Phys.Rev.Lett.99, 011802 (2007) FSI interpretation of the narrow and strong ppbar threshold enhancement is disfavored. This again indicates that X(1860) has a production property similar to ’ meson. c.f.: Br ( ' ' ) / Br ( J / ' ) No significant narrow strong enhancement near threshold (2.0 if fitted with X(1860)) 3 ~ 4% This strong threshold enhancement is NOT observed in pp / J at BESII Br ( J / X) / Br ( J / X) 0.5 @ 95% CL BESII Preliminary No narrow strong enhancement near threshold This again disfavors FSI and indicates that X(1860) has a production property similar to ’ meson. c.f.: Br ( J / ' ) / Br ( J / ' ) 0.04 This also indicates X(1860) may have strong coupling to gluons as ’ meson. Summary of new studies on ppbar mass threshold structure X(1860) Pure FSI effect cannot explain X(1860) structure. X(1860) has production properties similar to ’ meson • Why a baryonium (candidate) has a production properties similar to ’ meson? • ’ excitation? Why an ’ excitation dominantly decays into ppbar above ppbar mass threshold? New results on ++ 0 mesons Observation of mass threshold enhancement at BESII Phys. Rev. Lett. 96,162002 (2006) We studied DOZI process: J/ + + +-0 K+ K recoiling against A clear mass threshold enhancement is observed Acceptance Side-bands 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 181219 , width 1052028 MeV, 26 18MeV and the corresponding branch ration is (2.610.270.65)x10-4. It could be a multiquark/hybrid/glueball state. Its relation with f0(1710),f0(1790)? PWA of J/ +- and 00 at BESII Phys. Lett. B 642 (2006) 441 PWA of J/ +- and 00 J / f 0 (1500) ? f 0 (1710) ? The channels fitted in PWA: M(+- ) M(00 ) J / 0 0 PWA components: f 0 (1500) f 2 (1270) f 4 (2050) f 0 (1710) ? f 0 (2020) f 2 (1810) f 2 (2150) all 0++ all 2++ PWA results Lower 0++ : 0++ is strongly preferred over 2++ M (1466 6 16) MeV 14 11 (108 21) MeV f0(1370) cannot be excluded. Higher 0++: f0(1710) or f0(1790) M (176543 11) MeV (145 8 23 ) MeV J / J / 0 0 Phys. Lett. B 642 (2006) 441 About f0(1500) It is first clearly observed in J/psi radiative decays. Its production rate in J/psi radiative decays: BR( J / f 0 (1500)) BR( f 0 (1500) ) ~ 1104 ( BESII) BR( f0 (1500) ) ~ 35%( PDG) BR( J / f0 (1500)) ~ 3104 The production rate of f0(1500) in J/psi radiative decays is lower than f0(1710): BR( J / f0 (1710)) 9 104 ( PDG) It indicates f0(1710) has stronger coupling to gluons than f0(1500) which one contains more glueball content? New results on -1 mesons New observation of a broad 1-resonance in J/ K+K- 0 at BESII Phys. Rev. Lett. 97 (2006) 142002 J/ K+K-0 K*(1410) 0 X(1580) K*(892) background 0 sideband ? PID and kinematic fit can significantly reduce the dominant background from J/ + - 0. Partial Wave Analysis of J/ K+K- 0 events Four decay modes are included : 1 component : J / ( X , (1700)) 0 , ( X , ) K K K * (890) K 0 J / ( K * ) K , ( K * ) K 0 where K * K * (890), K * (1410) Amplitudes are defined by Covariant tensor formalism K * (1410) K 0 points : data hist : PWA fit B.S. Zhou and D.V. Bugg, Eur. Phys. J. A16, 537(2003) BW with energy-dependent width 1 BW ( s ) ; 2 s M R i s R ( s ) M R2 p( s ) 2l 1 R ( s ) R ( M ) ( ) 2 s p( M R ) 2 R J.H. Kuhn, A. Satamaria, Z. Phys. C48, 445 (1990). 1 component : X K K (1700) K K PS Partial Wave Analysis of J/ K+K- 0 events Parity conservations in J/ K+K- 0 requires that spin-parity of K+K- should be 1--,3--,… X , (1700), K * (890), K * (1410) PWA fit with and phase space (PS) gives: J PC 1 ( 3 can be ruled out by much worse likelihood ) 98 11 32 2 (157649 ) i (409 ) MeV / c 5591 1267 X pole position Br ( J / X ) Br ( X K K ) (8.5 0.6 3.6 ) 10 0 2.7 4 big destructive interference among X , (1700) and PS Broad X cannot be fit with known mesons or their interference It is unlikely to be (1450), because: • The parameters of the X is incompatible with (1450). • (1450) has very small fraction to KK. From PDG: Br ( (1450) K K ) 1.6 103 (95%C.L.) It cannot be fit with the interference of (770) , (1900) and (2150): • The log-likelihood value worsens by 85 (c2=170). How to understand broad X(1580)? Search of a similar structure in J/ KSK will help to determine its isospin. X(1580) could have different nature from conventional mesons: • There are already many 1- - mesons nearby. • Width is much broader than other mesons. • Broad width is expected for a multiquark state. Evidence of a new 1-- resonance Y(2175) at BaBar A structure at 2175MeV was observed in e+e-f0(980), via initialstate radiation at BABAR. m 2175 10 15 MeV 58 16 20 MeV Phys. Rev. D 74 (2006) 091103(R) What is Y(2175)? A conventional ss state? An ss analog of Y(4260) ( ss g )? An ss ss 4-quark state? More experimental information needed, especially we can search for it in J/psi decays at BESII and BESIII. New results on baryons at BESII N* in J/ pp at BESII 0 . 0 M2(p0) M M2 (p 0 ) N* in J/ pp 0 . Resonances used in the PWA The best results to now N* in J/ pp 0 . data Fit results Fit results between agree with data reasonably, The comparison data and PWA fit results. especially in the low mass region. N* in J/ pp 0 . K mass threshold enhancement Observation of a strong enhancement near the threshold of K mass spectrum at BES II NX* BES II J / pK M K Λ (GeV/c 2 ) PS, eff. corrected (Arbitrary normalization) MKΛ MK M 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. Nx* is N(1535)? From: BR( J / pN(1535)) BR( N1535 p ) ~ 1 ~ 2 104 BR( J / pNX* ) BR( N X* K) ~ 2 104 If Nx* is N(1535), we would have g K2 ~ 10 2 g p Then N(1535) would have very large ssbar component (a 5-quark system). Such a big coupling to K of N(1535) is NOT observed in p K process at SAPHIR BES J / pK Phase Space shape A ΛK resonance predicted by chiral SU(3) quark model Based on a coupledchannel 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. Phys. Rev. C71: 064001, 2005 ) Ecm – ( MΛ+MK ) (MeV) The KΛ mass threshold enhancement NX(1610) could be a KΛ bound/resonant state. Whether NX(1610) is N(1535) needs further study. Study of J/ pp at BESII No obvious N* in Dalitz plot. We measured: BR(J/ pp ) 3 (1.00 0.03 0.18) 10 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., “JP, I” filter. One Important Physics Goal of BESIII With 1010 J/psi events, we hope to answer: Whether glueballs exist or not? • Naively, we estimate in each exclusive decay mode: BR( J / G) BR(G hh) ~ 105 103 102 • If the eff. is about 20%, we would have 20000 events for each decay mode we should observe a relative narrow (width: 50~200MeV) glueball if it exists. 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 J / K K J / K s0 K s0 The mass plots shows no evident (2230) peaks in J/KK, , ppbar, which is different from BESI. However, it is difficult to exclude its existence since we may still need a small signal at the 4.5 level in the PWA based on our preliminary study. Its mass, width and BR are consistent with BESI and MARKIII results 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(Ghh) 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 X (1835) No evidence for a relatively narrow state ( 100 ~ 200 MeV width ) above 2GeV in J / KK , , K * K *, , ' ... Again: M ' • LQCD reliable? • Production rate could be very low. • Glueball width could be very large. Summary New results on light 0-+,0++ and 1-- mesons as well as excited baryons were briefly reviewed. We would expect more new observations on light hadron spectroscopy at BESIII and we hope to answer whether glueballs exist or not at that time. 谢 Thank 谢！ You! Discussion on KΛ mass threshold enhancement NX(1610) NX(1610) has strong coupling to KΛ: • From BR( J / pp) 2 103 (S&D-wave decay) and J / pNX (1600) is a P-wave decay, we can estimate BR( J / pNX ) 1.0 103 • From BESII, BR( J / pNX ) BR( N X K) ~ 2 104 BR( N X K) 20% • 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 p K suggests an evidence of new baryon : It is unlikely to be N*(1535). If NX were N*(1535), it should be observed in p K process, since: • (p N * K) BR( N * p) BR( N * K) • From PDG, for the N* in the mass range 1535~1750 MeV, N*(1535) has the largest BR( N * p) , 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.