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Register a new userStudy of Sigma(1385) and Xi(1321) hyperon and antihyperon production in deep inelastic muon scattering
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Large samples of Lambda, Sigma(1385) and Xi(1321) hyperons produced in deep-inelastic muon scattering off a ^6LiD target were collected with the COMPASS experimental setup at CERN. The relative yields of Sigma(1385)^+, Sigma(1385)^-, bar{Sigma}(1385)^-, bar{Sigma}(1385)^+, Xi(1321)^-, and bar{Xi}(1321)^+ hyperons decaying into Lambda(bar{Lambda})pi were measured. The heavy hyperon to Lambda and heavy antihyperon to bar{Lambda} yield ratios were found to be in the range 3.8% to 5.6% with a relative uncertainty of about 10%. They were used to tune the parameters relevant for strange particle production of the LEPTO Monte Carlo generator.
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We study the decays of the charmonium resonances $J/psi$ and $psi(3686)$ to the final states $Xi^{-}barXi^{+}$, $Sigma(1385)^{mp}barSigma(1385)^{pm}$ based on a single baryon tag method using data samples of $(223.7 pm 1.4) times 10^{6}$ $J/psi$ and $(106.4 pm 0.9) times 10^{6}$ $psi(3686)$ events collected with the BESIII detector at the BEPCII collider. The decay $psi(3686)rightarrowSigma(1385)^{mp}barSigma(1385)^{pm}$ is observed for the first time, and the measurements of the other processes, including the branching fractions and angular distributions, are in good agreement with and much more precise than the previously published results. Additionally, the ratios $frac{{cal{B}}(psi(3686)rightarrowXi^{-}barXi^{+})}{{cal{B}}(J/psirightarrowXi^{-}barXi^{+})}$, $frac{{cal{B}}(psi(3686)rightarrowSigma(1385)^{-}barSigma(1385)^{+})}{{cal{B}}(J/psirightarrowSigma(1385)^{-}barSigma(1385)^{+})}$ and $frac{{cal{B}}(psi(3686)rightarrowSigma(1385)^{+}barSigma(1385)^{-})}{{cal{B}}(J/psirightarrowSigma(1385)^{+}barSigma(1385)^{-})}$ are determined.
A semi-inclusive measurement of charged hadron multiplicities in deep inelastic muon scattering off an isoscalar target was performed using data collected by the COMPASS Collaboration at CERN. The following kinematic domain is covered by the data: photon virtuality $Q^{2}>1$ (GeV/$c$)$^2$, invariant mass of the hadronic system $W > 5$ GeV/$c^2$, Bjorken scaling variable in the range $0.003 < x < 0.4$, fraction of the virtual photon energy carried by the hadron in the range $0.2 < z < 0.8$, square of the hadron transverse momentum with respect to the virtual photon direction in the range 0.02 (GeV/$c)^2 < P_{rm{hT}}^{2} < 3$ (GeV/$c$)$^2$. The multiplicities are presented as a function of $P_{rm{hT}}^{2}$ in three-dimensional bins of $x$, $Q^2$, $z$ and compared to previous semi-inclusive measurements. We explore the small-$P_{rm{hT}}^{2}$ region, i.e. $P_{rm{hT}}^{2} < 1$ (GeV/$c$)$^2$, where hadron transverse momenta are expected to arise from non-perturbative effects, and also the domain of larger $P_{rm{hT}}^{2}$, where contributions from higher-order perturbative QCD are expected to dominate. The multiplicities are fitted using a single-exponential function at small $P_{rm{hT}}^{2}$ to study the dependence of the average transverse momentum $langle P_{rm{hT}}^{2}rangle$ on $x$, $Q^2$ and $z$. The power-law behaviour of the multiplicities at large $P_{rm{hT}}^{2}$ is investigated using various functional forms. The fits describe the data reasonably well over the full measured range.
We report a new measurement of the decay Omega^- to Xi^- pi^+ pi^- with 76 events and a first observation of the decay Omega^+ to Xi^+ pi^+ pi^- with 24 events, yielding a combined branching ratio (3.74 ^{+0.67}_{-0.56}) times 10^{-4}. This represents a factor 25 increase in statistics over the best previous measurement. No evidence is seen for CP violation, with B(Omega^- to Xi^- pi^+ pi^-)=4.04^{+0.83}_{-0.71} times 10^{-4} and B(Omega^+ to Xi^+ pi^+ pi^-)=3.15^{+1.12}_{-0.89} times 10^{-4}. Contrary to theoretical expectation, we see little evidence for the decays Omega^- to Xi_{1530}^{*0} pi^- and Omega^+ to Xi_{1530}^{*0} pi^+ and place a 90% C.L. upper limit on the combined branching ratio B(Omega^-(Omega^+) to Xi^{*0}_{1530}(Xi^{*0}_{1530}) pi^mp)<7.0 times 10^{-5}.
Precise measurements of charged-kaon multiplicities in deep inelastic scattering were performed. The results are presented in three-dimensional bins of the Bjorken scaling variable x, the relative virtual-photon energy y, and the fraction z of the virtual-photon energy carried by the produced hadron. The data were obtained by the COMPASS Collaboration by scattering 160 GeV muons off an isoscalar 6 LiD target. They cover the kinematic domain 1 (GeV/c)2 < Q2 < 60 (GeV/c)^2 in the photon virtuality, 0.004 < x < 0.4, 0.1 < y < 0.7, 0.20 < z < 0.85, and W > 5 GeV/c^2 in the invariant mass of the hadronic system. The results from the sum of the z-integrated K+ and K- multiplicities at high x point to a value of the non-strange quark fragmentation function larger than obtained by the earlier DSS fit.
The azimuthal asymmetry and the transverse momentum of forward produced charged hadrons in deep inelastic muon scattering have been studied as a function of the event kinematics and of the hadron variables. Primordial $k_T$ of the struck parton and O($alpha_s$) corrections to the cross-section are expected to contribute to the transverse momentum and the azimuthal asymmetry of hadrons. The data show some unexpected dependences not present in a Monte Carlo simulation which includes the theoretical parton-level azimuthal asymmetry.
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