282 research outputs found
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 evolution of fragmentation functions (FF) to (mass of the X
particle) from their initial values at low is subject to considerable
uncertainties. We therefore argue that, for x\lsim 0.1 (the region of
interest for most large values of interest, 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 ) obtained under the Modified Leading Log Approximation
(MLLA). Additionally, we find that for x\gsim0.1, the evolution in 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 14
orders of magnitude in . 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 region x\gsim0.1 based on low energy data even without
evolving them to the requisite 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
We work with two general factorization schemes in order to explore the
consequences of imposing scheme independence on . 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 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
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