Scaled momentum distributions for $ K_S^0 $KS and $ \Lambda /\bar{\Lambda } $ in DIS at HERA

Abstract

Scaled momentum distributions for the strange hadrons K 0 S and Λ/Λ 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, Q 2 , was studied in the kinematic region 10 < Q 2 < 40000 GeV 2 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. Nextto-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 K 0 S and Λ/Λ strange hadrons.

Strangeness production at HERA

“…The HERA data have the potential to constrain these FFs over a wide kinematic range. Here a new measurement of ZEUS Collaboration of the scaled momentum distributions for K 0 S and Λ hadrons in DIS [9] is presented. The data used in this analysis were collected during the running period 2005-2007, when HERA operated with protons of energy E p = 920 GeV and electrons of energy E e = 27.5 GeV, and correspond to an integrated luminosity of 330 pb −1 .…”

“…In this report the new mesurements of K 0 s and Λ production performed by the H1 and ZEUS experiments at the electron-proton storage ring HERA are presented [7,8,9].…”