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Register a new userScaled momentum distributions for K0s and Lambda/bar Lambda in DIS at HERA
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Scaled momentum distributions for the strange hadrons K0s and Lambda/bar Lambda were measured in deep inelastic ep scattering with the ZEUS detector at HERA using an integrated luminosity of 330 pb-1. The evolution of these distributions with the photon virtuality, Q2, was studied in the kinematic region 10<Q2<40000 GeV2 and 0.001<x<0.75, where x is the Bjorken scaling variable. Clear scaling violations are observed. Predictions based on different approaches to fragmentation were compared to the measurements. Leading-logarithm parton-shower Monte Carlo calculations interfaced to the Lund string fragmentation model describe the data reasonably well in the whole range measured. Next-to-leading-order QCD calculations based on fragmentation functions, FFs, extracted from e+e- data alone, fail to describe the measurements. The calculations based on FFs extracted from a global analysis including e+e-, ep and pp data give an improved description. The measurements presented in this paper have the potential to further constrain the FFs of quarks, anti-quarks and gluons yielding K0s and Lambda/bar Lambda strange hadrons.
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We report the first observation of the spontaneous polarization of $Lambda$ and $bar{Lambda}$ hyperons transverse to the production plane in $e^+e^-$ annihilation, which is attributed to the effect arising from a polarizing fragmentation function. For inclusive $Lambda/bar{Lambda}$ production, we also report results with subtracted feed-down contributions from $Sigma^0$ and charm. This measurement uses a dataset of 800.4 fb$^{-1}$ collected by the Belle experiment at or near a center-of-mass energy of 10.58 GeV. We observe a significant polarization that rises with the fractional energy carried by the $Lambda/bar{Lambda}$ hyperon.
We report the first observation of the polarization of $Lambda/bar{Lambda}$ hyperons transverse to its production plane in $e^+e^-$ annihilation. We observe a significant polarization that rises with the fractional energy carried by the hyperon as well as its transverse momentum. To define the production plane, we use the direction of the hyperon momentum together with either the thrust axis in the event or the momentum vector of a hadron in the opposite hemisphere. Furthermore, we investigate the contributions to the hyperon polarization from the feed-down from $Sigma^0/bar{Sigma}^0$ and $Lambda_c^{pm}$ decays. This measurement uses a dataset of 800.4~fb$^{-1}$ collected by the Belle experiment at or near a center-of-mass energy of 10.58 GeV.
Preliminary results for the longitudinal polarization of $Lambda$ and ${bar Lambda}$ hyperons in longitudinally polarized proton-proton collisions at $sqrt s$ = 200 GeV are presented. The $Lambda$($bar Lambda$) candidates are reconstructed at mid-rapidity ($|eta|<1$) with the time projection chamber of the STAR experiment at RHIC, using 0.5 pb$^{-1}$ collected in 2003 and 2004 with beam polarizations of up to 45%. Their mean longitudinal momentum fraction $x_F$ is about 8 $times$$10^{-3}$ and their mean transverse momentum $p_T$ is about 1.5 GeV. The analysis uses asymmetries of counts for different spin states of the colliding proton beams and does not require detailed knowledge of the detector acceptance. The preliminary $Lambda$(${bar Lambda}$) polarization values are consistent with zero within their statistical uncertainties of 0.05.
This contribution reports on a proof-of-principle measurement of the longitudinal spin transfer $D_{LL}$ in inclusive $Lambda$ and $bar Lambda$ production in polarized proton-proton collisions at a center of mass energy $sqrt{s}$ = 200 GeV. The data sample consists of about 3 $times$ $10^6$ minimum bias events collected in the year 2005 by the STAR experiment at RHIC with proton beam polarizations of up to 50%. The $Lambda$($bar Lambda$) candidates are reconstructed at mid-rapidity ($|eta|<1$) using the STAR Time Projection Chamber via the dominant decay channel $Lambdato p pi^-$ ($bar Lambda to bar p pi^+$). Their mean transverse momentum $p_T$ is about 1.3 GeV/c and longitudinal momentum fraction $x_F = 7.5 times 10^{-3}$ . The longitudinal $Lambda$($bar Lambda$) polarization is determined using a method in which the detector acceptance mostly cancels.
Using 121.4 fb^{-1} of data collected with the Belle detector at the Y(5S) resonance at the KEKB asymmetric-energy e^+e^- collider, we report evidence for the B_s^0 -> Lambda_c^+ Lambda-bar pi^- decay mode with a measured branching fraction (3.6 +- 1.1[stat.] {+0.3 -0.5}[syst.] +- 0.9[Lambda_c^+] +- 0.7[N_{Bs}]) * 10^{-4} and a significance of 4.4 standard deviations. This is the first evidence for a baryonic B_s^0 decay.
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