KnE Energy | The 3rd International Conference on Particle Physics and Astrophysics (ICPPA) | pages: 435–440

and

1. Introduction

The charmonium spectroscopy is of great importance to understand the quantum chromo-dynamic (QCD) theory in perturbative and non-perturbative calculation. The charmonium states below the DD¯ threshold are well measured, and all these measured states are in good agreement with the theoretical predications of relativistic potential model [1]. However, it is still desirable to investigate the decay properties of these charmonium states. With the high statistics collected for J/ψ and ψ(3686) decays, the first observations or more precise results could be achieved. In this proceeding, the study of J/ψ and ψ(3686) decay to ΛΛ¯ and Σ0Σ¯0 , improved measurements of ψ(3686)γχcJ , observation of hcγη' and evidence of hcγη , and ψ(3686) Dalitz decay to χcJ and χcJ Dalitz decay to J/ψ are presented.

The BESIII experiment is operated at the Beijing electron positron collider II (BEPCII) with a peak luminosity of 1.0×1033cm-2s-1 at a center-of-mass energy of 3773 MeV. The BESIII experiment aims to study the multiple-purpose physics in the τ-c region based the world's largest charmonium data sample at on-threshold production. A detailed description of the detector can be found in Ref. [2].

2. The study of J/ψ and ψ(3686) decay to ΛΛ¯ and Σ0Σ¯0 [3]

The study of J/ψ and ψ(3686) (denoted as ψ ) decays plays an important role in the test of perturbative QCD (pQCD) calculation. Since the discovery of ρπ puzzle which violates the 12% rule, more decay channels are required to further investigate the rule and give information for the development of the future theories.

In this analysis, the branching fractions (BFs) of ψ decay to ΛΛ¯ and Σ0Σ¯0 are measured with the improved precision based on 1.3 billion J/ψ and 448 million ψ(3686) decays. Both baryon and anti-baryon are tagged by their subsequent decay products. The left panel of Fig. figlamesults shows the distributions of invariant masses of pπ- ( Mpπ- ) and pπ-γ ( Mpπ-γ ) for the ψ decay to ΛΛ¯ and Σ0Σ¯0 , respectively. The production yields are extracted from the fits to these distributions. The polar angle distributions of baryons in the ψ reference frame can be interpreted as 1+αcos2θ , and they are measured in the right panel of Fig. figlamesults. The fitted α values and the measured BFs are listed in Table. tablamres. Note that the α value for J/ψΣ0Σ¯0 decay is negative, which is contradictory with the existing theories. The possible explanation for this negative value could be the re-scattering effect [4] of baryon and anti-baryon in the final states. The 12% rule is observed to be violated since the ratios (ψ(3686)ΛΛ¯)(J/ψΛΛ¯) and (ψ(3686)Σ0Σ¯0)(J/ψΣ0Σ¯0) are calculated to be ( 20.43±0.11±0.58 )% and ( 20.96±0.27±0.92 )%, respectively.

Figure 1

Left panel: Fit results to the Mpπ- distributions for the decays (a) J/ψΛΛ¯ and (b) ψ(3686)ΛΛ¯ , and the Mpπ-γ distributions for the decays (c) J/ψΣ0Σ¯0 and (d) ψ(3686)Σ0Σ¯0 . Right panel: Fit results to the efficiency corrected distributions of polar angle of the baryons for the corresponding decays.

Table 1

The fitted α values and the measured BFs for ψ decay to ΛΛ¯ and Σ0Σ¯0 , respectively.


Decay channel α BF ( 10-4 )
J/ψΛΛ¯ 0.469±0.026±0.008 19.43±0.03±0.33
J/ψΣ0Σ¯0 -0.449±0.020±0.008 11.64±0.04±0.23
ψ(3686)ΛΛ¯ 0.82±0.08±0.02 3.97±0.02±0.12
ψ(3686)Σ0Σ¯0 0.71±0.11±0.04 2.44±0.03±0.11

;

3. Improved measurements of ψ(3686)γχcJ [5]

The electro-magnetic (EM) decay ψ(3686)γχcJ is an important decay mode since the decay is very sensitive to the inner structure of the ψ(3686) charmonium state. Based on the data set of 106 M ψ(3686) decays collected in the year 2009, the precision on the BF of decay ψ(3686)γχcJ is improved. This improvement is quite necessary in the determination of BFs of χcJ decays.

In this analysis, the inclusive decays of ψ(3686)γX where X represents all the possible final states are used to determine the BF of the decay ψ(3686)γχcJ . To constrain the signal shape, a clear γ spectrum from ψ(3686)γχcJ , χcJ decays to two or four charged particles is used. Figure figchicjesults shows the reconstructed γ spectrum for the inclusive and exclusive ψ(3686) decays, respectively. Simultaneous fit is used to extract the BF of the decay ψ(3686)γχcJ . The five peaks from left to right in the left panel of Fig. figchicjesults correspond to the decay ψ(3686)γχc2 , γχc1 , γχc0 , and χc1 and χc2 to γJ/ψ . The BFs of ψ(3686)γχc0,1,2 are determined to be ( 9.389±0.014±0.332 )%, ( 9.905±0.011±0.353 )% and ( 9.621±0.013±0.272 )%, respectively.

Figure 2

The reconstructed γ spectrum for the inclusive (left) and exclusive (right) ψ(3686) decays, respectively.

Figure 3

The distributions of M(γη') and M(γη) , respectively.

fig-5.jpg
Figure 4

The distributions of M(γJ/ψ) and M(e+e-J/ψ) , respectively.

fig-6.jpg
Figure 5

The comparison of q2 between the data and Monte Carlo (MC) simulation.

fig-7.jpg

4. Observation of hcγη' and evidence of hcγη [6]

The knowledge on the hc decay is quite limited since only two decay modes are observed before this study, the radiative decay hcγηc with a BF of about 50% and the hadronic decay hc2(π+π-)π0 with a BF of about 2%. Search for more decay modes are desirable to understand the properties of the hc particle.

Based on the data sample of 448 M ψ(3868) decays, we present the first observation and the evidence for the radiative decay of hcγη' and hcγη , respectively. The particle η' in the decay channel hcγη' is reconstructed from the decay η'π+π-η , ηγγ and η'γπ+π- , while the particle η in the decay channel hcγη is reconstructed from the decay ηγγ and ηπ+π-π0 . Figure figgetapresults shows the distributions of invariant masses of γη' ( M(γη') ) and γη ( M(γη) ), respectively. Production yields of the decay hcγη' and hcγη are extracted from the fits to these mass distributions. The BFs of the decay hcγη' and hcγη are calculated to be (1.52±0.27±0.29)×10-3 and (4.7±1.5±1.4)×10-4 with a statistical significance of 8.4σ and 4.0σ , respectively. With these two values, the ratio between the BF of hcγη and hcγη' is calculated to be (30.7±11.3±8.7) %, from where the η-η' mixing angle can be extracted to test the SU(3) flavor symmetry.

5. ψ(3686) Dalitz decay to χcJ and χcJ Dalitz decay to J/ψ [7]

The investigation of EM Dalitz transition plays an essential role in the understanding of the internal structure of hadrons and the interaction between the photons and hadrons. Such transition has not been observed in the charmonium decays before this analysis. The Dalitz decay of ψ(3686)e+e-χcJ and χcJe+e-J/ψ can have access to the EM transition form factor (TFF) of these charmonium states by studying the square of invariance mass of e+e- pair ( q2 ) dependence.

Based on the data sample of 448 M ψ(3868) decays, we present the first observation of the Dalitz decay of ψ(3686)e+e-χcJ and χcJe+e-J/ψ , where the χcJ in the former and latter decay channel is reconstructed by χcJγJ/ψ and χcJe+e-J/ψ , J/ψl+l- , respectively. Figure figepemresults shows the distributions of invariant masses of γJ/ψ ( M(γJ/ψ) ) and e+e-J/ψ ( M(e+e-J/ψ) ), respectively. The BFs are measured to be (ψ(3686)e+e-χc0,1,2=(11.7±2.5±1.0)×10-4 , (8.6±0.3±0.6)×10-4 , (6.9±0.5±0.6)×10-4 and (χc0,1,2e+e-J/ψ=(1.51±0.30±0.13)×10-4 , (3.73±0.09±0.25)×10-3 , (2.48±0.08±0.16)×10-3 , respectively. Figure figcmp_polar shows the consistency of q2 distribution between the data and Monte Carlo (MC) simulation, where MC simulated sample is generated according to the model based on the assumption of a point-like meson described in Ref. [8].

References

1 

S. Godfrey N. Isgur Mesons in a relativized quark model with chromodynamicsPhysical Review D: Particles, Fields, Gravitation and Cosmology198532118923110.1103/physrevd.32.189

2 

M. Ablikim et al. (BESIII Collaboration), Nucl. Instrum. Meth. A 614, 345 (2010).

3 

M. Ablikim et al. (BESIII Collaboration), Phys. Rev. D 95, 052003 (2017).

4 

H. Chen, R. G. Ping, Phys. Lett. B 644, 54 (2007).

5 

M. Ablikim et al. (BESIII Collaboration), Phys. Rev. D 96, 032001 (2017).

6 

M. Ablikim et al. (BESIII Collaboration), Phys. Rev. Lett. 116, 251802 (2016)).

7 

M. Ablikim et al. (BESIII Collaboration), Phys. Rev. Lett. 118, 221802 (2017).

8 

A. Faessler, C. Fuchs, and M. I. Krivoruchenko, Phys. Rev. C 61, 035206 (2000).

FULL TEXT

Statistics

  • Downloads 24
  • Views 98

Navigation

Refbacks



ISSN: 2413-5453