| As the lightest charm baryon,most charm baryons will decay to ∧c+ baryon eventually.Thus,detail study on the decays of ∧c+ baryon can help us understand the charm baryon spectrum.Due to the lack of clean ∧c+ baryon data sample with high statistics,the study on the semileptonic decays of ∧c+ baryon is relatively slow.Currently,only∧c+→ ∧l+vl(l = e,v)is measured.In 2014,BESIII collected a data sample at a center-of-mass energy √s= 4.6 GeV corresponding to an integrated luminosity of 567 pb-1 which is the largest ∧c+ sample taken just above the ∧c+∧c-threshold ever collected.With this data sample,we can systematically study the decays of ∧c+ baryon.Both lifetimes of the ∧c+ baryon and D0/D+ mesons are dominated by the weak decays of the charm quark.Especially,the inclusive semileptonic decay Ac+ → e+X is strongly correlated to the inclusive decay D0/D+ → e+X.One could hope for the baryonic case to be similar with the replacement of a light antiquark spectator in D case by a ud-diquark with I = J = 0 in ∧c+case.However,the ud-diquark can undergo internal excitations,making the situation more complicated than that in the mesonic case.Thus,the measurement of the branching fraction of the inclusive semileptonic ∧c+ decay is important to understand the internal structure and decay dynamics of the charmed baryon.In this thesis,we present the first absolute mea-surement of the branching fraction of the inclusive semileptonic ∧c+ decay using a double-tag method.This analysis is based on a data sample corresponding to an in-tegrated luminosity of 567 pb-1 accumulated at a center-of-mass energy √s=4.6 GeV and recorded with the BESIII detector.To reduce the dependence on the mod-el and the systematic uncertainty,the particle identification(PID)efficiency and the mis-PID possibility is determined by studying the control samples selected from da-ta.The branching fraction of the inclusive semileptonic ∧c+ decay is measured to be(∧c+→Xe+ve)=(3·95 ± 0.34 士 0.09)%,where the first and second uncer-tainties are statistical and systematic,respectively.Compared to the MARKII result,B(∧c+→Xe+ve)=(4.5 ±1.7)%,the precision is improved by a factor of three.Based on the BESIII measurements,we obtain the ratio of the branching fraction to be B(∧c+→∧e+ve)/B(∧c+→Xe+ve)=(91.9±12.5±5.4)%,where the systematic uncertainty related to the tracking efficiency of the positron cancels.Using the known ∧c+ lifetime,we obtain the semileptonic decay width Γ(∧c+→Xe+ve)=(1.98 ± 0.18)x 1011 s-1.Comparing this with the charge-averaged semileptonic decay width of nonstrange charmed mea-sons Γ(D→ Xe+ve),the ratio Γ(∧c+→Xe+ve)/Γ(D→Xe+ve)can be obtained.This ratio is predicted to be 1.67 using an effective-quark theory calculation and about 1.2 based on a calculation using the heavy-quark expansion.Our result shows that Γ(∧c+→Xe+ve)/Γ(C→Xe+ve)=1.26±0.12,which favors the latter calculation.It should be noted that the systematic uncertainties are not given in both theoretical calculations.In 2012,the Daya Bay experiment measured the neutrino oscillation parameter sin2 2θ13 = 0.0841± 0.0027±0.0019.013 is much larger than expected,which makes it possible to determine the neutrino mass hierarchy.By measuring the antineutrino spectrum with excellent energy resolution,the Jiangmen Underground Neutrino Ob-servatory(JUNO)will determine the neutrino mass hierarchy at a(3-4)σ significance with six years of running.To reach the expected physical goal,the energy resolution of the detector should be better than 3%/√Evis,where Evis is the visible energy of the inverse beta decay events.For a real experiment,the parametrization of the energy resolution is σ/Evis ＝√A2/Evis+B2+C2/Evis2,where the stochastic term A comes from the photon-electron s-tatistics,the constant term B and quadratic term C come from detector effects such as PMT dark noise,variation of the PMT QE.Detail study finds that √A2/Evis+B2 + C2/Evis2≈√A2/Evis+(1.6B)2/Evis+c2/1.62Evis.Therefore,the requirement for the energy resolution changes to √(A)2 +(1.6B)2 +(C/1.6)2 ≤ 3%.However,the energy resolution has a large B ter-m even if we do not consider the detector effects,such as variation of the PMT QE.In this thesis,we study the possible origins of the constant term,including cherenkov process and quenching.We find that the constant term in current detector simulation comes from the cherenkov process,which is unexpected.Further study finds that the distribution of scintillation light from cerenkov photons is much wider than statistical fluctuation,which worses the energy resolution and increase the constant term. |
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