Treatment of Heavy Quarks in Deeply Inelastic Scattering

We investigate a simplified version of the ACOT prescription for calculating deeply inelastic scattering from Q^2 values near the squared mass M_H^2 of a heavy quark to Q^2 much larger than M_H^2.Comment: 14 pages, 5 figure

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

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

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.

On The Injection Spectrum of Ultrahigh Energy Cosmic Rays in the Top-Down Scenario

We analyze the uncertainties involved in obtaining the injection spectra of UHECR particles in the top-down scenario of their origin. We show that the DGLAP $Q^2$ evolution of fragmentation functions (FF) to $Q=M_X$ (mass of the X particle) from their initial values at low $Q$ is subject to considerable uncertainties. We therefore argue that, for x\lsim 0.1 (the $x$ region of interest for most large $M_X$ values of interest, $x\equiv 2E/M_X$ being the scaled energy variable), the FF obtained from DGLAP evolution is no more reliable than that provided, for example, by a simple Gaussian form (in the variable $\ln(1/x)$) obtained under the Modified Leading Log Approximation (MLLA). Additionally, we find that for x\gsim0.1, the evolution in $Q^2$ of the singlet FF, which determines the injection spectrum, is ``minimal'' -- the singlet FF changes by barely a factor of 2 after evolving it over $\sim$ 14 orders of magnitude in $Q\sim M_X$. We, therefore, argue that as long as the measurement of the UHECR spectrum above \sim10^{20}\ev is going to remain uncertain by a factor of 2 or larger, it is good enough for most practical purposes to directly use any one of the available initial parametrisations of the FFs in the $x$ region x\gsim0.1 based on low energy data even without evolving them to the requisite $Q^2$ value.Comment: Minor changes, added a reference, version to appear 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

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.

Estimate of the Collins fragmentation function in a chiral invariant approach

We predict the features of the Collins function, which describes the fragmentation of a transversely polarized quark into an unpolarized hadron, by modeling the fragmentation process at a low energy scale. We use the chiral invariant approach of Manohar and Georgi, where constituent quarks and Goldstone bosons are considered as effective degrees of freedom in the non-perturbative regime of QCD. To test the approach we calculate the unpolarized fragmentation function and the transverse momentum distribution of a produced hadron, both of which are described reasonably well. In the case of semi-inclusive deep-inelastic scattering, our estimate of the Collins function in connection with the transversity distribution gives rise to a transverse single spin asymmetry of the order of 10%, supporting the idea of measuring the transversity distribution of the nucleon in this way. In the case of e+ e- annihilation into two hadrons, our model predicts a Collins azimuthal asymmetry of about 5%.Comment: 12 pages, 15 figures. Figs. 11-14 changed, minor changes in discussion, few typos fixed and some references added. Final version to appear in PR

Coefficient Functions and Open Charm Production in Deep Inelastic Scattering

It is shown that the problem of double counting in open charm production in DIS can be solved by using the expression for DIS coefficient functions in terms of 2PI diagramsComment: 11 pages, REVTeX, no figure

Nuclear parton distributions at next to leading order

We perform a next to leading order QCD global analysis of nuclear deep inelastic scattering and Drell-Yan data using the convolution approach to parameterize nuclear parton densities. We find both a significant improvement in the agreement with data compared to previous extractions, and substantial differences in the scale dependence of nuclear effects compared to leading order analyses.Comment: 9 pages, 10 figure