BESⅢ实验上ψ→pΦ分支比的测量和对Λ-()振荡的寻找

1、BESE实验上书(2S) f p 分支比的测量和对A -(?)振荡的寻找At present, Standard Model (SM) is the most successful theory toexplain the com-position and interaction of the matter, and QuantumChromo Dynamics (QCD) is the elementary theory of strong interaction in the framework of SM. The predictions of the QCDin the high en

2、ergy regime have been extensively approved. However, QCDbe-comes invalid in the low energy regime due to the perturbative theory does not work in the case of the large effective coupling. Therefore, it is more important to study the hadron physics experimentally in the low energy regime, which is on

3、e of the main rea-sons that the Beijing Electron-Positron Collider (BEPCn )operates at the center of-mass energy within 2.0 -4.6 GeV. According to the current knowledge, a mesonconsists of quark and anti-quark pair, and a baryon consists of three quarks. In addition, QCD also predicts the existence

4、of the exotic states, such as the glueball, hybrid, multi-quark and molecule states and so on. The Beijing Spectrometer (BESE) is notonly a gen-eral purpose magnetic spectrometer operating at BEPCII, but also a worldwide unique detector running at the energy region of 2.0 -4.6 GeV. Since successfull

5、y constructed in 2008, BES E has accumulated the largest samples of J/ 书 and 书(2S) in the world.The decays of J/ 书 and 书(2S) can provide not only the unprecedented opportunity for studying the hadron spectroscopy, but also the excellent laboratory for searching the exotic states and new physics beyo

6、nd the SM. In 2003, a strong enhancement near the pp mass threshold, known as the X(pp), was first observed by the BES n experiment in the radiative decay J/书丫pp. It was later confirmed by the CLEO and BESEexperiments. In theory,X(pp) is assumed to be a baryonium, a multi-quark state or an effect du

7、e to pure final-state interaction (FSI), its nature has not been clarified yet. I n additi on, long time ago it was proposed that p product ion iswell suited to search the exotic pentaquark candidate with hidden strangeness. Just in 2015, LHCbreported the observation of two charmonium pentaquark str

8、uctures with the quark content ccuud in the pJ/书 massspectrum. Therefore, it is very important to search the pentaquark can didate with the quark content ssuud in the p or p massspectrum.Using the data sample of 4.48x 108 书(2S) events accumulatedwith the BESH detector, the decay 书(2S) pp is studied

9、in detail via two decay modes K+K- and KSOKLOThe average branching fraction of 书(2S) pp is measured to be B(书(2S) pp)=(6.33 0.36(stat) 0.43(syst) x 10-6 for the first time and the result has verified 12% rule very well. No significant enhancement near pp invariant mass threshold is observed and the

10、upper limit on the branching fraction ofB(书(2S) X(pp).B(X(pp) pp) is measured to be 1.92 x 10-7at90%confidence level (C.L.). The mass spectrum of p and p arealso studied but the evidence of the resonance B is not prominent.Inaddition, at the present level of sensitivity, N - N oscillations probe int

11、ermedi-ate energy scales, between the Electro weak and Grand unification theory scale. N - N oscillations have been performed in the past, both with free neutron beamsand within nuclear environment in large underground detectors. The best limit on the characteristic time of oscillation derived from

12、free neutron beam ist N-N > 0.86 x 108sfrom Insti-tute Max von Lau-Paul Langevin (ILL) experiment at Grenoble,France. If N - N oscil-lationexits, then ( A - A )oscillationmayalso takeplace, as firstly proposed by K.B.Luk,and the possibility of searching for theA-AA oscillations for coherent AA pr

13、oduc-tion, using quantum correlation to extract the oscillation parameters, in the J/ 书AA decay process was firstly proposed by Xian-Wei Kang and Hai-Bo Li. Assuming no signal events for J/书) AA the estimated upper limit on R < 3.5x 10-7 with one year s luminosity at BES- H . In this thesis, a se

14、archfor J/ 书 AA + charge conju-gation(c.c.) is carried out with huge datasample accumulated at the center-of-mass energy (?)=3.097 GeV with the BESIII detector at BEPCII collider, corresponding to 1310.6 million J/书 events. J/ 书 AA channel is also studied to check the consistency of results and also for normalization to avoid somesources of systematic uncertainities.The branching fraction value achieved for J/书AA iscon siste nt with BES川 al-ready published value within statisticalsystem