Observation of threshold enhancement from Phys Rev Lett
Observation of threshold enhancement from Phys. Rev. Lett. 91, 022001(2003) Ji Xiaobin IHEP Oct. 28 – Nov. 1, 2006
Content z Introduction z Events Selection z Results and Discussion z Summary 晨光杯(桂林)
The Beijing Electron Positron Collider L ~ ~5 1030 /cm 2 s at J/ peak Ecm~2 -5 Ge. V 晨光杯(桂林)
BESII Detector VC: xy = 100 m TOF: MDC: xy = 220 m BSC: d. E/dx= 8. 5 % p/p=1. 78% (1+p 2) T = 180 ps E/ E= 22 % = 7. 9 mr z = 3. 1 cm 晨光杯(桂林) counter: r = 3 cm z = 5. 5 cm B field: 0. 4 T
World J/ Samples (106) 晨光杯(桂林)
The Analysis of Events Selection z 2 good charged tracks z 1 (isolated from charged tracks) z Particle ID for both charged tracks z 4 C-fit 晨光杯(桂林)
mass from selected events Besides C peak, there is a clear enhancement near threshold. 晨光杯(桂林)
Backgrounds Main backgrounds remained after selection for mass peak near threshold No clear enhancement near threshold 晨光杯(桂林)
Fit Signal with an S(P)-wave BW q = daughter momentum q 0 = daughter momentum @ peak 晨光杯(桂林)
fitted peak location Fit results +3 +5 M=1859 -10 -25 Me. V/c 2 < 30 Me. V/c 2 (90% CL) 0 2/dof=56/56 0. 2 0. 1 M(pp)-2 mp (Ge. V) 晨光杯(桂林) 0. 3
Mass Determination BW “peak” High Statistics is crucial to the determination of BW “peak” below Threshold. observed peak threshold 晨光杯(桂林)
Is Mpeak real less than 2 mp ? weight events by q 0/q: (i. e. remove threshold phase space factor) No turnover at threshold peak mass must be <2 mp M(pp)-2 mp (Ge. V) 晨光杯(桂林)
P-wave fit? ? M=1876. 4 ± 0. 9 Me. V = 4. 6 ± 1. 8 Me. V M=2 mp 2/dof=59/56 晨光杯(桂林) OK!
cosq distribution 1+cos 2 q (expected for J/ 0 -+ ) M(pp)<1. 9 Ge. V sin 2 q 晨光杯(桂林)
Further Checks z Only selected events with Pp z PID: d. E/dx TOF + d. E/dx 晨光杯(桂林) > 0. 4 Ge. V/c 2
rec d. Edx Other tests(p>0. 4) M = 1859 2 Me. V efficiency = 0 19 Me. V 晨光杯(桂林)
Other tests(PID) PHMP TOF d. E/dx TOF+d. E/dx P(Ge. V/c) 晨光杯(桂林)
Other tests(PID d. E/dx TOF+d. E/dx) M = 1856 2 Me. V = 0 22 Me. V 晨光杯(桂林)
Further Checks The results are compatible with publish ones 晨光杯(桂林)
Possible understandings of the new observation z Exclude interpretations of known resonances — Could it be a tail of a known resonance? — FSI (Final States Interaction)? z Baryonium interpretation 晨光杯(桂林)
Could it be a tail of a known resonance? 0 -+ resonances in PDG tables: (1760) M=1760 = 60 Me. V (1800) M=1801 = 210 Me. V Definitely excluded! ( >>5 ) 2/dof=323/58 晨光杯(桂林) 2/dof=412/58
Pure FSI disfavored I=0 S-wave FSI CANNOT fit the BES data. FSI curve from A. Sirbirtsev et al. ( Phys. Rev. D 71: 054010, 2005 ) in the fit (I=0) FSI * PS * eff + bck 晨光杯(桂林)
pp bound state (baryonium)? There is lots & lots of literature about this possibility E. Fermi, C. N. Yang, Phys. Rev. 76, 1739 (1949) … I. S. Sharpiro, Phys. Rept. 35, 129 (1978) C. B. Dover, M. Goldhaber, attractive PRD 15, 1997 (1977) nuclear force? … A. Datta, P. J. O’Donnell, PLB 567, 273 (2003)] B. M. L. Yan et al. , hep-ph/0405087 B. Loiseau et al. , hep-ph/0411218 … deuteron: attractive + baryonium: n + - loosely bound 3 loosely bound -q Observations 3 -q color of this 3 -q structure in singlets with other decay modes are desirable. Md = 2 mp- e Mb = 2 mp-d ? 晨光杯(桂林)
Summary z z A narrow peak seen near 2 mp in the Mpp distribution for decays using BES-II 58 M J/ events No narrow peak in decays Any PDG particles can be excluded, including possible effect of interference. Its mass and unexpected narrow width suggest a possible interpretation as “deutron like” protonantiproton bound state (baryonium) 晨光杯(桂林)
Interference effect of several resonances? z z Three 0 -+ resonances : (1760) : M=1760 ; = 60 Me. V (2150) : M=2150 ; = 200 Me. V (2190) : M=2190 ; = 500 Me. V Fitted CL: 6 × 10 -6 — Excluded by more than 4. 5 — The inconsistency is mainly from the threshold peak 晨光杯(桂林)
Interference effect of several resonances? § Three 0 -+ resonances : X : to be determined by fit (2150) : M=2150 ; = 200 Me. V (2190) : M=2190 ; = 500 Me. V § Fitted mass and width: M = 1864 ± 3 Me. V = 0 ± 17 Me. V § Basically remain the same as the results without any interference. 晨光杯(桂林)
FSI Explanation z A. Sibitsev, PRD 71, 054010(2005) 晨光杯(桂林)
Re-fit to J/ p pbar including FSI Include FSI curve from A. Sirbirtsev et al. ( Phys. Rev. D 71: 054010, 2005 ) in the fit (I=0) M = 1830. 6 6. 7 Me. V = < 153 Me. V @90%C. L. In good agreement with X(1835) 晨光杯(桂林)
The + - mass spectrum for decaying into + - and 7. 7 PRL 95, 262001 (2005) 晨光杯(桂林)
NO strong dynamical threshold enhancement in cross sections (at LEAR) With threshold kinematic contributions removed, there are very smooth threshold enhancements in elastic “matrix element” and very small enhancement in annihilation “matrix element”: much weaker than what BES observed ! z |M|2 BES Both arbitrary normalization 晨光杯(桂林) BES Both arbitrary normalization
Observation of X(1835) in Statistical Significance 7. 7 The + - mass spectrum for decaying into + - and 晨光杯(桂林)
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