arXiv subjects

Stefan Kretzer

Publications and source records attributed to Stefan Kretzer.

7 recordsLinked to original sources

arXiv2005

Heavy Quark Parton Distribution Functions

We present the CTEQ6HQ parton distribution set which is determined in the general variable flavor number scheme which incorporates heavy flavor mass effects; hence, this set provides advantages for precision observables which are sensitive to charm and bottom quark masses. We describe the analysis procedure, examine the predominant features of the new distributions, and compare with previous distributions. We also examine the uncertainties of the strange quark distribution and how the the recent NuTeV dimuon data constrains this quantity.

hep-ph↗

arXiv2004

Fragmentation of Partons

The concept of parton fragmentation in QCD hard scattering phenomenology as well as NLO pQCD analysis of fragmentation functions are outlined. Hadroproduction of pions of a few GeV pT is discussed through the example of recent measurements at \sqrt{S_{RHIC}}=200 GeV.

hep-ph↗

arXiv2004

QCD Aspects of the NuTeV Anomaly

The weak mixing angle measured in neutrino scattering differs from the world average of other measurements by about 3 sigma. I discuss QCD corrections of perturbative and nonperturbative (parton structure) origin to the underlying neutrino observables.

hep-ph↗

arXiv2004

QCD Hard Scattering and the Sign of the Spin Asymmetry A_LL^pi

Recent preliminary PHENIX data are consistent with a negative and sizable longitudinal double-spin asymmetry A_LL^pi for pi^0 production at moderate transverse momentum p_perp \simeq 1 - 4 GeV and central rapidity. By means of a systematic investigation of the relevant degrees of freedom we show that the perturbative QCD framework at leading power in p_perp produces at best a very small negative asymmetry in this kinematic range.

hep-ph↗

arXiv2002

Mass Corrections and Neutrino DIS

Including the effects of the ${\cal{O}}(\gtrsim 1 {\rm GeV})$ masses of the charm quark, $τ$ lepton and target nucleon in DIS phenomenology is discussed with applications to CC neutrino DIS: Neutrino data for $F_2$ are revisited within the global analysis framework. A fully differential calculation refines the CC charm production process as a gate to extract $\{s(x), {\bar s} (x) \}$. New results are presented for a "heavy quark" version of the CTEQ6 set of PDFs and for ($ν_μ \to ν_τ$ oscillation-signal) $τ$ neutrino cross sections.

hep-ph↗

arXiv2001

Open Heavy Flavor Production in QCD -- Conceptual Framework and Implementation Issues

Heavy flavor production is an important QCD process both in its own right and as a key component of precision global QCD analysis. Apparent disagreements between fixed-flavor scheme calculations of b-production rate with experimental measurements in hadro-, lepto-, and photo-production provide new impetus to a thorough examination of the theory and phenomenology of this process. We review existing methods of calculation, and place them in the context of the general PQCD framework of Collins. A distinction is drawn between scheme dependence and implementation issues related to quark mass effects near threshold. We point out a so far overlooked kinematic constraint on the threshold behavior, which greatly simplifies the variable flavor number scheme. It obviates the need for the elaborate existing prescriptions, and leads to robust predictions. It can facilitate the study of current issues on heavy flavor production as well as precision global QCD analysis.

hep-ph↗

arXiv2001

Ultrahigh-Energy Neutrino-Nucleon Cross Sections and Perturbative Unitarity

Unitarity relates the total cross section for neutrino-nucleon scattering to the neutrino-nucleon forward scattering amplitude. Assuming the validity of the perturbative expansion of the forward amplitude in the {\em weak} coupling constant, we derive a unitarity bound on the inelastic cross section. The inelastic cross section saturates this bound at a typical neutrino energy $E_ν\simeq 10^8 {\rm GeV}$. This implies that calculations of the inelastic cross section that use current parton distribution functions and lowest order weak perturbation theory are unreliable above this energy.

hep-ph↗