291 research outputs found
Hadron production from quark coalescence and jet fragmentation in intermediate energy collisions at RHIC
Transverse momentum spectra of pions, protons and antiprotons in Au+Au
collisions at intermediate RHIC energy of GeV are studied in
a model that includes both quark coalescence from the dense partonic matter and
fragmentation of the quenched perturbative minijet partons. The resulting
baryon to meson ratio at intermediate transverse momenta is predicted to be
larger than that seen in experiments at higher center of mass energies.Comment: 6 pages, 2 figures. Figures replaced to differentially address the
high-pT behavior of baryon versus antibaryon to meson ratio
Dihadron Correlation in Jets Produced in Heavy-Ion Collisions
The difference between the structures of jets produced in heavy-ion and
hadronic collisions can best be exhibited in the correlations between particles
within those jets. We study the dihadron correlations in jets in the framework
of parton recombination. Two types of triggers, and proton, are
considered. It is shown that the recombination of thermal and shower partons
makes the most important contribution to the spectra of the associated
particles at intermediate . In collisions the only significant
contribution arises from shower-shower recombination, which is negligible in
heavy-ion collisions. Moments of the associated-particle distributions are
calculated to provide simple summary of the jet structures for easy comparison
with experiments.Comment: 24 pages in Latex + 5 figure
Compatibility of various approaches to heavy-quark fragmentation
We find that the definition of the heavy-quark fragmentation function given
by Jaffe and Randall differs by a factor of the longitudinal-momentum fraction
z from the standard Collins-Soper definition. Once this factor is taken into
account, the explicit calculation of Braaten et al. is found to be in agreement
with the general analysis of Jaffe and Randall. We also examine the model of
Peterson et al. for heavy-quark fragmentation and find that the quoted values
of the width and of the value of at the maximum are in error. The corrected
values are in agreement with the analysis of Jaffe and Randall.Comment: 4 pages late
Inclusive B-Meson Production in e^+ e^- and p p-bar Collisions
We provide nonperturbative fragmentation functions for B mesons, both at
leading and next-to-leading order in the MS-bar factorization scheme with five
massless quark flavors. They are determined by fitting the fractional energy
distribution of B mesons inclusively produced in e^+ e^- annihilation at CERN
LEP1. Theoretical predictions for the inclusive production of B mesons with
high transverse momenta in p p-bar scattering obtained with these fragmentation
functions nicely agree, both in shape and normalization, with data recently
taken at the Fermilab Tevatron.Comment: 20 pages (Latex), 6 figures (Postscript
Fragmentation or Recombination at High p_T?
All hadronization processes, including fragmentation, are shown to proceed
through recombination. The shower partons in a jet turn out to play an
important role in describing the p_T spectra of hadrons produced in heavy-ion
collisions. Due to the recombination of the shower partons with the soft
thermal partons, the structure of jets produced in AA collisions is not the
same as that of jets produced in pp collisions.Comment: Talk given at Quark Matter 200
Phenomenology of single spin asymmetries in p(transv. polarized)-p -> pion + X
A phenomenological description of single transverse spin effects in
hadron-hadron inclusive processes is proposed, assuming a generalized
factorization scheme and pQCD hard interactions. The transverse momentum, k_T,
of the quarks inside the hadrons and of the hadrons relatively to the
fragmenting quark, is taken into account in distribution and fragmentation
functions, and leads to possible non zero single spin asymmetries. The role of
k_T and spin dependent quark fragmentations -- the so-called Collins effect --
is investigated in details in p(transv. polarized)-p -> pion + X processes: it
is shown how the experimental data could be described, obtaining an explicit
expression for the spin asymmetry of a polarized fragmenting quark, on which
some comments are made. Predictions for other processes, possible further
applications and experimental tests are discussed.Comment: 20+1 pages, LaTeX, 6 eps figures, uses epsfig.sty. Version v2: Some
sentences rephrased and comments added throughout the paper; one reference
added; no changes in results and figures. Final version to be published in
Phys. Rev.
Do we understand the single-spin asymmetry for inclusive production in pp collisions?
The cross section data for inclusive production in collisions is
considered in a rather broad kinematic region in energy , Feynman
variable and transverse momentum . The analysis of these data is
done in the perturbative QCD framework at the next-to-leading order. We find
that they cannot be correctly described in the entire kinematic domain and this
leads us to conclude that the single-spin asymmetry, for this process,
observed several years ago at FNAL by the experiment E704 and the recent result
obtained at BNL-RHIC by STAR, are two different phenomena. This suggests that
STAR data probes a genuine leading-twist QCD single-spin asymmetry for the
first time and finds a large effect.Comment: text modified, version to be published in Eur. Phys. J. C, 6 pages, 5
figure
Inclusive J/psi and psi(2S) Production from B Decay in p p-bar Collisions
Using information on B-meson fragmentation functions from CERN LEP 1 and
adopting the nonrelativistic QCD factorization formalism proposed by Bodwin,
Braaten, and Lepage, we predict the transverse-momentum distribution of J/psi
mesons originating from the inclusive decays of b hadrons produced in p p-bar
collisions at the Fermilab Tevatron. We determine the relevant colour-octet
charmonium matrix elements from fits to CDF data on prompt charmonium
hadroproduction and to CLEO data on charmonium production from B-meson decay.
Our predictions are found to agree well with recent CDF and D0 data.Comment: 27 pages (Latex), 9 figures (Postscript
Two-Photon Doppler cooling of alkaline-earth-metal and ytterbium atoms
A new possibility of laser cooling of alkaline-earth-metal and Ytterbium
atoms using a two-photon transition is analyzed. We consider a -
transition, with excitation in near resonance with the
level. This greatly increases the two-photon transition rate, allowing an
effective transfer of momentum. The experimental implementation of this
technique is discussed and we show that for Calcium, for example, two-photon
cooling can be used to achieve a Doppler limit of 123 microKelvin. The
efficiency of this cooling scheme and the main loss mechanisms are analyzed.Comment: 7 pages, 5 figure
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