1,900 research outputs found
Jets in 200 GeV p+p and d+Au collisions from the STAR experiment at RHIC
Full jet reconstruction in heavy-ion collisions is a promising tool for the
quantitative study of properties of the dense medium produced at RHIC.
Measurements of d+Au collisions are important to disentangle initial state
nuclear effects from medium-induced kT broadening and jet quenching. Study of
jet production and properties in d+Au in combination with similar studies in
p+p is an important baseline measurement needed to better understand heavy-ion
results. We present mid-rapidity inclusive jet pT spectra and di-jet
correlations (kT) in 200 GeV p+p and d+Au collisions from the 2007-2008 RHIC
run. We discuss the methods used to correct the data for detector effects and
for background in d+Au collisions.Comment: 4 pages, 5 figures. To appear in Hot Quarks 2010 conference
proceeding
Charm-quark fragmentation with an effective coupling constant
We use a recently proposed non-perturbative model, based on an effective
strong coupling constant and free from tunable parameters, to study c-flavoured
hadron production in e+e- annihilation. Charm-quark production is described in
the framework of perturbative fragmentation functions, with NLO coefficient
functions, NLL non-singlet DGLAP evolution and NNLL large-x resummation. We
model hadronization effects by means of the effective coupling constant in the
NNLO approximation and compare our results with experimental data taken at the
Z0 pole and at the Upsilon(4S) resonance. We find that, within the experimental
and theoretical uncertainties, our model is able to give a reasonable
description of D*+-meson spectra from ALEPH for x<1-Lambda/m_c. More serious
discrepancies are instead present when comparing with D and D^* data from BELLE
and CLEO in x-space. Within the errors, our model is nonetheless capable of
reproducing the first ten Mellin moments of all considered data sets. However,
the fairly large theoretical uncertainties call for a full NNLO/NNLL analysis.Comment: 26 pages, 10 figures. Analysis in Mellin space and few references
adde
The RR Lyrae Period - K Luminosity relation for Globular Clusters: an observational approach
The Period - metallicity - K band luminosity (PLK) relation for RR Lyrae
stars in 15 Galactic globular clusters and in the LMC globular cluster
Reticulum has been derived. It is based on accurate near infrared (K)
photometry combined with 2MASS and other literature data. The PLK relation has
been calibrated and compared with the previous empirical and theoretical
determinations in literature. The zero point of the absolute calibration has
been obtained from the K magnitude of RR Lyr whose distance modulus has been
measured via trigonometric parallax with HST. Using this relation we obtain a
distance modulus to the LMC of (m-M)_0 = 18.54 \pm 0.15 mag, in good agreement
with recent determinations based on the analysis of Cepheid variable stars.Comment: 6 pages, 4 figures, accepted for publication by MNRA
Charm Cross Sections for the Tevatron Run II
We present a calculation of the D^{*+}, D^+ and D^0 meson single inclusive
production cross section for the Tevatron Run II. We use the FONLL approach in
perturbative QCD, which, besides including the known next-to-leading order
corrections, also provides for the resummation at the next-to-leading
logarithmic level of terms enhanced at large p_T by powers of log(p_T/m), where
m is the charm mass and p_T is its transverse momentum. Non-perturbative
effects in charm hadronization are extracted, in moment space, from recent
ALEPH data for D^* fragmentation in e^+e^- collisions.Comment: 11 pages, 5 figures, LaTe
Heavy-Quark Fragmentation
We study perturbative and non-perturbative aspects of heavy-quark fragmentation into hadrons, emphasizing the large-x region, where x is the energy fraction of the detected hadron. We first prove that when the moment index N and the quark mass m get large simultaneously with the ratio (N Lambda/m) fixed, the fragmentation function depends on this ratio alone. This opens up the way to formulate the non-perturbative contribution to the fragmentation function at large N as a shape function of m(1-x) which is convoluted with the Sudakov-resummed perturbative result. We implement this resummation and the parametrization of the corresponding shape function using Dressed Gluon Exponentiation. The Sudakov exponent is calculated in a process independent way from a generalized splitting function which describes the emission probability of an off-shell gluon off a heavy quark. Non-perturbative corrections are parametrized based on the renormalon structure of the Sudakov exponent. They appear in moment space as an exponential factor, with a leading contribution scaling as (N Lambda/m) and corrections of order (N Lambda/m)^3 and higher. Finally, we analyze in detail the case of B-meson production in e+e- collisions, confronting the theoretical predictions with LEP experimental data by fitting them in moment space
RR Lyrae variables in the globular cluster M3 (NGC5272). I. BVI CCD photometry
New BVI CCD photometry is presented for 60 RR Lyrae variables in the globular
cluster M3. Light curves have been constructed and ephemerides have been
(re)-derived for all of them. Four stars (i.e. V29, V136, V155 and V209),
although recognized as variables, had no previous period determinations. Also,
the period derived for V129 is significantly different from the one published
by Sawyer-Hogg (1973). Light curve parameters, i.e. mean magnitudes, amplitudes
and rise-times, have been derived. The discussion of these results in the
framework of the stellar evolution and pulsation theories will be presented in
a forthcoming paper.Comment: 19 pages, latex, uses mn.sty, 12 encapsulated figures, to be
published in MNRAS, text and figures also available at
http://www.bo.astro.it/bap/BAPhome.html or via anonymous ftp at
ftp://boas3.bo.astro.it/bap/files (bap98-12-textfig.ps
Charmonium Production via Fragmentation at DESY HERA
The cross section for the photoproduction of large-p_T J/psi mesons at HERA
is calculated at next-to-leading order, adopting a perturbative approach to
describe the fragmentation of charm quarks and gluons into J/psi mesons. We
treat the charm quark according to the massless factorization scheme, where it
is assumed to be one of the active flavours inside the proton and the resolved
photon. We present inclusive distributions in transverse momentum and rapidity,
including the contributions due to direct and resolved photons. The importance
of the colour-octet components of the J/psi wave function, which contribute to
the fragmentation process, is emphasized. In addition to prompt J/psi
production, we consider also the production of chi_{cJ} states followed by
radiative decays to J/psi mesons, both in the colour-singlet and colour-octet
channels.Comment: 32 pages (Latex), 12 figures (Postscript
Extraction of the x-dependence of the non-perturbative QCD b-quark fragmentation distribution component
Using recent measurements of the b-quark fragmentation distribution obtained
in events registered at the Z pole, the non-perturbative
QCD component of the distribution has been extracted independently of any
hadronic physics modelling. This distribution depends only on the way the
perturbative QCD component has been defined. When the perturbative QCD
component is taken from a parton shower Monte-Carlo, the non-perturbative QCD
component is rather similar with those obtained from the Lund or Bowler models.
When the perturbative QCD component is the result of an analytic NLL
computation, the non-perturbative QCD component has to be extended in a
non-physical region and thus cannot be described by any hadronic modelling. In
the two examples used to characterize these two situations, which are studied
at present, it happens that the extracted non-perturbative QCD distribution has
the same shape, being simply translated to higher-x values in the second
approach, illustrating the ability of the analytic perturbative QCD approach to
account for softer gluon radiation than with a parton shower generator.Comment: 13 page
D^* production from e^+e^- to ep collisions in NLO QCD
Fragmentation functions for D mesons, based on the convolution of a
perturbative part, related to the heavy quark perturbative showering, and a
non-perturbative model for its hadronization into the meson, are used to
describe D^* production in e^+e^- and ep collisions. The non-perturbative part
is determined by fitting the e^+e^- data taken by ARGUS and OPAL at 10.6 and
91.2 GeV respectively. When fitting with a non perturbative Peterson
fragmentation function and using next-to-leading evolution for the perturbative
part, we find an epsilon parameter sensibly different from the one commonly
used, which is instead found with a leading order fit. The use of this new
value is shown to increase considerably the cross section for D^* production at
HERA, suggesting a possible reconciliation between the next-to-leading order
theoretical predictions and the experimental data.Comment: 20 pages, LaTeX2e, 8 Postscript figure
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