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.Comment: 13 pages, 10 figures, Proceedings of Ringberg Workshop: New Trends in HERA Physics 2001, Munich, German

Neutrino Dimuon Production and the Strangeness Asymmetry of the Nucleon

We have performed the first global QCD analysis to include the CCFR and NuTeV dimuon data, which provide direct constraints on the strange and anti-strange parton distributions, $s(x)$ and $\bar{s}(x)$. To explore the strangeness sector, we adopt a general parametrization of the non-perturbative $s(x), \bar{s}(x)$ functions satisfying basic QCD requirements. We find that the strangeness asymmetry, as represented by the momentum integral $[S^{-}]\equiv \int_0^1 x [s(x)-\bar{s}(x)] dx$, is sensitive to the dimuon data provided the theoretical QCD constraints are enforced. We use the Lagrange Multiplier method to probe the quality of the global fit as a function of $[S^-]$ and find $-0.001 < [S^-] < 0.004$. Representative parton distribution sets spanning this range are given. Comparisons with previous work are made.Comment: 23 pages, 4 figures; expanded version for publicatio

Heavy Quark Production and PDF's Subgroup Report

We present a status report of a variety of projects related to heavy quark production and parton distributions for the Tevatron Run II.Comment: Latex. 8 pages, 7 eps figures. Contribution to the Physics at Run II Workshops: QCD and Weak Boson Physic

Heavy Quark Initiated Contributions to Deep Inelastic Structure Functions

We present O(alpha_s^1) corrections to deep inelastic scattering amplitudes on massive quarks obtained within the scheme of Aivazis, Collins, Olness and Tung (ACOT). After identifying the correct subtraction term the convergence of these contributions towards the analogous coefficient functions for massless quarks, obtained within the modified minimal subtraction scheme (MSbar), is demonstrated. Furthermore, the quantitative relevance of the contributions to neutral current (NC) and charged current (CC) structure functions is investigated for several choices of the factorization scale.Comment: 29 pages, 6 figures; uses epsfig.sty, amssymb.sty, axodraw.sty; minor changes for publication in Phys. Rev.

Cortical hypertrophy with a short, curved uncemented hip stem does not have any clinical impact during early follow-up

Background: Short stems have become more and more popular for cementless total hip arthroplasty in the past few years. While conventional, uncemented straight stems for primary total hip arthroplasty (THA) have shown high survival rates in the long term, it is not known whether uncemented short stems represent a reasonable alternative. As cortical hypertrophy has been reported for short stems, the aim of this study was to determine the radiographic prevalence of cortical hypertrophy and to assess the clinical outcome of a frequently used short, curved hip stem. Methods: We retrospectively studied the clinical and radiographic results of our first 100 consecutive THAs (97 patients) using the Fitmore® hip stem. Mean age at the time of index arthroplasty was 59 years (range, 19 – 79 years). Clinical outcome and radiographic results were assessed with a minimum follow-up of 2 years, and Kaplan-Meier survivorship analysis was used to estimate survival for different endpoints. Results: After a mean follow-up of 3.3 years (range, 2.0 – 4.4 years), two patients (two hips) had died, and three patients (four hips) were lost to follow-up. Kaplan-Meier analysis estimated a survival rate of 100 % at 3.8 years, with revision for any reason as the endpoint. No femoral component showed radiographic signs of loosening. No osteolysis was detected. Cortical hypertrophy was found in 50 hips (63 %), predominantly in Gruen zone 3 and 5. In the cortical hypertrophy group, two patients (two hips; 4 %) reported some thigh pain in combination with pain over the greater trochanter region during physical exercise (UCLA Score 6 and 7). There was no significant difference concerning the clinical outcome between the cortical hypertrophy and no cortical hypertrophy group. Conclusions: The survival rate and both clinical and the radiographic outcome confirm the encouraging results for short, curved uncemented stems. Postoperative radiographs frequently displayed cortical hypertrophy but it had no significant effect on the clinical outcome in the early follow-up. Further clinical and radiographic follow-up is necessary to detect possible adverse, long-term, clinical effects of cortical hypertrophy

Parton Distributions Working Group

The main focus of this working group was to investigate the different issues associated with the development of quantitative tools to estimate parton distribution functions uncertainties. In the conclusion, we introduce a "Manifesto" that describes an optimal method for reporting data.Comment: Report of the Parton Distributions Working Group of the 'QCD and Weak Boson Physics workshop in preparation for Run II at the Fermilab Tevatron'. Co-Conveners: L. de Barbaro, S.A. Keller, S. Kuhlmann, H. Schellman, and W.-K. Tun

Tomography of cold and hot QCD matter : tools and diagnosis

The probability distribution D(epsilon) in the energy loss incurred by incoming and outgoing hard quarks in a QCD medium is computed numerically from the BDMPS gluon spectrum. It is shown to follow an empirical log-normal behavior which allows us to give the quenching weight a simple analytic parameterization. The dependence of our results under the infrared and ultraviolet sensitivity of the gluon spectrum is investigated as well. Finally, as an illustration, we discuss and compare estimates for the quenching of hadron spectra in nuclear matter and in a quark-gluon plasma to HERA and RHIC preliminary data.Comment: 29 pages, 11 figures. Typo corrected in Eq.(4.17

Scheme Independence of g1p(x,Q2)g_1^p (x, Q^2)

We work with two general factorization schemes in order to explore the consequences of imposing scheme independence on $g_1^p (x, Q^2)$. We see that although the light quark sector is indifferent to the choice of a particular scheme, the extension of the calculations to the heavy quark sector indicates that a scheme like the $\bar{MS}$ is preferable.Comment: 11 pages, 2 figures. To appear in the Brief Reports of Phys. Rev.

Leading log radiative corrections to polarized heavy flavour leptoproduction

O(\alpha) QED radiative corrections to polarized neutral current leptoproduction of heavy quark flavours are calculated in the leading log approximation for HERMES, COMPASS, and HERA kinematics. Besides the inclusive case, we derive general $z_h$-differential formulae for the polarized boson gluon fusion process and use them to calculate radiative corrections to semi-inclusive polarized heavy flavour production in the case of HERA kinematics.Comment: 22 pages, 5 figures, 1 fig. removed, 1 formula added, several additions and changes in the text and the abstrac