Measurement Of The Process X_cJ→p（?）and Search For η_c（2S）→p（?）at BESⅢ

Charmonium is a bound state composed of a pair of positive and negative charm quarks,because the non-perturbation theory of strong interactions described by quantum chromodynamics（QCD）has great uncertainty in the charmonium energy region So the study of charmonium state is important for the improvement of the standard model.Among them,（ψ）（3686）can be produced by0)⁺0)^-collision and annihilation,and then radiation transition occurs,resulting in a large number ofX_cJX_cJisX_cJ,1.2-X_cJ a P-wave triplet quinone that can be used to verify the Helicity selection rule.In the theory,when theX_cJdecay to→p（?）,unless the helicity of the positive and negative proton pairs is 0,the branch fraction will be severely depressed,and the processX_cJ→p（?）is the process of the forbidden rule of the helicity selection rule.The theoretical prediction branch fraction is 0.However,BESⅢmeasured a large branch fraction,the process ofχ_cj1,2→p（?）is also different for theoretical predictions and experimental measurements.These contradictions point the way for us to study the QCD of the charmonium state.In order to study the decay mechanism of charmonium state batter,and understand the helicity selection rules,it is necessary to give accurate measurements ofX_cJ→p（?）.So we accurately measured the branching fraction ofX_cJ→p（?）three processes,which can help understand the decay mechanism ofX_cJ→p（?）.And we also measured the angular distribution ofX_cJ→p（?）,which can help to get information about the dynamics of these processes.The Beijing Electron-Positron Collider can produce high-quality data samples of（ψ）（3686）that had collected 448.1M in 2009 and 2012 years.This is the largest（ψ）（3686）data sample in the world.Such large data statistics provide us with accurate measurements condition.After measuring the decay channelsX_cJ→p（?）in the decay chain（ψ）（3686）→yX_cJX_cJ→p（?）,the measured branch fraction ofX_cJ→p（?）are（24.75±0.39±0.99）×10^-5、（7.87±0.19±0.37）×10^-5、（8.04±0.20±0.33）×10^-5.These results are the most accurate results in the world and matches the previous results of BESIII,but the statistical error and systematic error are both reduced.These results help us to understand the decay mechanism of the charmonium family particles better,understand the deviation between theory and experiment,and then modify the theoretical model.We also measured the angular distribution ofX_cJ→p（?）,the measurement result areX_cJ→p（?）=0.04±0.06±0.03、-0.40±0.08±0.04、-0.34±0.10±0.04,The accuracy of BESⅢresults has been significantly improved,which is the most accurate result in the world.For all the results shown,the first is the central value,the second is the statistical error,and the third is the systematic error.We have also searched this processη_c（2s）→p（?）,because the process ofη_c（2s）→p（?）is also a possible decay channel,and an article points out that,if there is a quantum ball with a quantum number 0^-+in theη_c（2s）wave function,then there is a possibility that the process ofη_c（2s）→p（?）have a large branch fraction,but the process was not found after searching.