Measurement of charm production in neutrino charged-current interactions

Abstract

The nuclear emulsion target of the CHORUS detector was exposed to the wide-band neutrino beam of the CERN SPS of 27 GeV average neutrino energy from 1994 to 1997. In total about 100000 charged-current neutrino interactions with at least one identified muon were located in the emulsion target and fully reconstructed, using newly developed automated scanning systems. Charmed particles were searched for by a program recognizing particle decays. The observation of the decay in nuclear emulsion makes it possible to select a sample with very low background and minimal kinematical bias. 2013 charged-current interactions with a charmed hadron candidate in the final state were selected and confirmed through visual inspection. The charm production rate induced by neutrinos relative to the charged-current cross-section is measured to be σ(ν µ N → µ − CX)/σ(CC) = (5.75 ± 0.32(stat) ± 0.30(syst))%. The charm production cross-section as a function of the neutrino energy is also obtained. The results are in good agreement with previous measurements. The charm-quark hadronization produces the following charmed hadrons with relative fractions (in %): f D 0 = 43.7 ± 4.5, f Λ + c = 19.2 ± 4.2, f D + = 25.3 ± 4.2, and f D + s = 11.8 ± 4.7.

Determination of strange sea quark distributions from fixed-target and collider data

“…Note, that the DIS data for light nuclear targets can discriminate these two approaches. Indeed, the JLAB data for 3 He, 4 He, and 9 Be are well described by the KP model, in contrast to the ones based on the global properties of nuclei [39,42]. Furthermore, the number of fitted parameters describing the nuclear PDFs should be essentially the same as for the ordinary PDFs.…”

“…The E531 experiment [35] collected 120 ν-induced inclusive charm events and measured the complete decay and event kinematics, allowing for a determination of the charm production fractions, f h ðE ν Þ. The recent measurement by the CHORUS experiment [4] collected a total of 2013 inclusive charm events, although only the visible neutrino energy and the charm decay length were measured. The CHORUS experiment has also measured separately the yields of neutral (D 0 ) and charged charmed hadrons as a function of the neutrino energy.…”

“…The new precision measurement of charm di-muon production in neutrino-iron DIS interactions by NOMAD [3] has substantially reduced both experimental and model uncertainties with respect to the NuTeV and CCFR measurements. In addition, the CHORUS experiment [4] has released a new direct measurement of inclusive charm production in nuclear emulsions insensitive to B μ . Furthermore, improved theoretical descriptions in perturbative QCD for some of the underlying hard scattering reactions have become available.…”

“…Section II also summarizes briefly the new improvements in QCD theory for CC DIS charm quark production with a running c-quark mass. Section III gives a brief description of the new data sets from CHORUS, NOMAD [2][3][4] and the LHC W þ c data [12,13]. Section IV contains the results of the analysis including a new study of the energy dependence of the semileptonic branching ratio B μ of charmed hadrons.…”

“…Section IV contains the results of the analysis including a new study of the energy dependence of the semileptonic branching ratio B μ of charmed hadrons. Starting from a fit to the combined data of NuTeV, CCFR, CHORUS and NOMAD [2][3][4] the impact of individual data sets is quantified and the resulting shifts in the strange quark distributions are documented. Particular care is also taken to control potential correlations with the u-and d-quark sea distributions.…”