Remarks on the lifetime of charmed baryonΛ c +

The interference andW-exchange contributions toΛ _c ⁺ inclusive nonleptonic decay rate are expressed in terms of matrix elements of effective fourquark operators and evaluated in the MIT bag model. It is found that although theW-exchange is not necessarily subject to helicity and color suppression, it does not suffice to explain the measured lifetime ofΛ _c ⁺. The observed semileptonic branching ratio ofΛ _c ⁺, however, requires that its inclusive decay rate be dominated by the nonspectator contribution and thus theW-exchange be substantially enhanced by some nonperturbative effects. The implication for exclusive two-body decays ofΛ _c ⁺ is briefly discussed.     

Diffractive production of the charmed baryon Λ+c at the CERN ISR

In a sample of diffractive events of high multiplicity a sharp five standard deviation signal is observed at M = 2255 MeV/c² in the K^?pπ⁺ mass distribution and, although with less statistical strength, at the same mass in the Λ⁰π⁺π⁺π^? channel. These signals are identified as being due to the decay of the charmed baryon Λ⁺_c which is produced with a cross section times branching ratio σ_cB in the range 0.7?1.8 μb for the K^?π⁺p decay and 0.3?0.7 μb for the Λ^-π⁺π⁺ π^? system.     

First observation of the doubly charmed baryon Xi(+)(cc)

We observe a signal for the doubly charmed baryon Xi(+)(cc) in the charged decay mode Xi(+)(cc)-->Lambda(+)(c)K-pi(+) in data from SELEX, the charm hadroproduction experiment at Fermilab. We observe an excess of 15.9 events over an expected background of 6.1+/-0.5 events, a statistical significance of 6.3sigma. The observed mass of this state is 3519+/-1 MeV/c(2). The Gaussian mass width of this state is 3 MeV/c(2), consistent with resolution; its lifetime is less than 33 fs at 90% confidence.     

Exploring the doubly charmed baryon

The doubly charmed baryon,like the proton and neutron,is formed by three quarks.However,they are different,as such a baryon consists of two heavy quarks(charm-quark)and one light quark,while the proton and neutron respectively contain three light quarks.Therefore the doubly charmed baryon is expected to have different internal structures and properties.For example,its mass is 3-4 times higher than those of the proton and neutron.Studying the doubly charmed baryons can provide important information to understand the three-body bound system,the hadronic interaction and the quark model.     

Weak production of charmed baryon resonances

We evaluate weak neutrino production cross sections for 7 conjectured charmed baryon resonances in the four flavour quark model. Effects resulting from the mass difference of uncharmed and charmed quarks are explicitly taken into account. The quark model results are only taken at q²=0 to determine the q² = 0 values of the invariant transition form factors. These are then continued to q ≠ 0 by suitably chosen form factors. Our numerical results are compared with the results of other calculations of weak charm production.     

Higher power QCD mechanisms for largep T strange or charmed baryon production in polarized proton-proton collisions

We investigate potential higher power mechanisms for strange or charmed baryon production of large transverse momentum and calculate the corresponding helicity asymmetries, which turn out to be large and significantly different to those obtained from the leading power mechanism.     

Hunting the doubly charmed baryon with strangeness

正In the standard model of particle physics, the baryon is formed by three quarks. Unlike the well-known proton and neutron that are composed of three light quarks, the doubly charmed baryon consists of two heavy charm quarks and a light quark.Therefore, it is expected to have different internal structures and properties, and to serve as a unique system for understanding the three-body bound system and testing the mechanism of quantum chromodynamics (QCD).     

On the lifetime of charged charmed particles first direct observation of a charmed baryon decay

Two new examples of production by neutrinos and subsequent decay of charged charmed hadrons are reported. Together with two similar events reported previously they show that the lifetime of charged charmed particles is in the neighbourhood of 5 × 10^?13 s, as expected from current theoretical models. One of the new events is identified as a baryon λ_c⁺ of mass 2.295 ± 0.015 GeV/c² which undergoes the decay process λ_c⁺ → pπ⁺K^? with a proper decay time (7.3 ± 0.1) × 10^?13 s.     

Diffractive production of charmed strange mesons by neutrinos and antineutrinos

The diffractive production of charmed strangeD _s ^* and possiblyD _s mesons by neutrinos and antineutrinos on nucleons in hydrogen, deuterium and neon targets is observed. The slope parameter of thet distribution is 3.3±0.8 (GeV)^?2. The production rate per charged current neutrino interaction with an isoscalar target times the D _s ⁺ →φτ⁺ branching fraction is (1.03±0.27)×10^?4.     

Belle实验发现新超子和新粲重子

过去一年里,运行在日本高能加速器研究机构的Belle实验在重子研究,尤其是在超子和粲重子研究上取得了一系列重要实验进展,包括发现了两个超子Ξ(1620)和Ω(2012)、一个粲重子Ξ_c(2930)等新的重子,并首次测量了粲重子Ξ_c衰变的绝对分支比等,为完善重子谱和深入理解强相互作用性质提供了关键的实验数据。     

Direct observation of the strange b baryon Xib-

We report the first direct observation of the strange b baryon Xi(b)- (Xi(b)+). We reconstruct the decay Xi(b)- -->J/psiXi-, with J/psi-->mu+mu-, and Xi--->Lambdapi--->ppi-pi- in pp collisions at square root of s =1.96 TeV. Using 1.3 fb(-1) of data collected by the D0 detector, we observe 15.2 +/- 4.4(stat)(-0.4)(+1.9)(syst) Xi(b)- candidates at a mass of 5.774 +/- 0.011(stat) +/- 0.015(syst) GeV. The significance of the observed signal is 5.5 sigma, equivalent to a probability of 3.3 x 10(-8) of it arising from a background fluctuation. Normalizing to the decay Lambda(b)-->J/psiLambda, we measure the relative rate sigma(Xi(b-) x B(Xi)b})- -->J/psiXi-)/sigma(Lambda(b)) x B(Lambda(b)-->J/psiLambda) = 0.28+/-0.09(stat)(-0.08)(+0.09)(syst).