9,809 research outputs found
production and suppression in high energy proton-nucleus collisions
We apply a Color Glass Condensate+Non-Relativistic QCD (CGC+NRQCD) framework
to compute production in deuteron-nucleus collisions at RHIC and
proton-nucleus collisions at the LHC. Our results match smoothly at high
to a next-to-leading order perturbative QCD + NRQCD computation.
Excellent agreement is obtained for spectra at RHIC and LHC for
central and forward rapidities, as well as for the normalized ratio of
these results to spectra in proton-proton collisions. In particular, we observe
that the data is strongly bounded by our computations of the same for
each of the individual NRQCD channels; this result provides strong evidence
that our description is robust against uncertainties in initial conditions and
hadronization mechanisms.Comment: 7 pages, 4 figure
Fragmentation functions of polarized heavy quarkonium
Study of the polarized heavy quarkonium production in recently proposed QCD
factorization formalism requires knowledge of a large number of input
fragmentation functions (FFs) from a single parton or a heavy quark-antiquark
pair to a polarized heavy quarkonium. In this paper, we calculate these FFs at
the input scale in terms of nonrelativistic QCD (NRQCD) factorization. We
derive all relevant polarized NRQCD long-distance matrix elements based
symmetries and propose a self-consistent scheme to define them in arbitrary
dimensions. We then calculate polarized input FFs contributed from all -wave
and -wave NRQCD intermediate states. With our calculation of the polarized
input FFs, and the partonic hard part available in literatures, the QCD
factorization formalism is ready to be applied to polarized heavy quarkonium
production.Comment: 30 pages, 1 figur
versus suppression in proton-nucleus collisions from factorization violating soft color exchanges
We argue that the large suppression of the inclusive cross-section
relative to the inclusive cross-section in proton-nucleus (p+A)
collisions can be attributed to factorization breaking effects in the formation
of quarkonium. These factorization breaking effects arise from soft color
exchanges between charm-anticharm pairs undergoing hadronization and comoving
partons that are long-lived on time scales of quarkonium formation. We compute
the short distance pair production of heavy quarks in the Color Glass
Condensate (CGC) effective field theory and employ an improved Color
Evaporation model (ICEM) to describe their hadronization into quarkonium at
large distances. The combined CGC+ICEM model provides a quantitative
description of and data in proton-proton (p+p) collisions
from both RHIC and the LHC. Factorization breaking effects in hadronization,
due to additional parton comovers in the nucleus, are introduced heuristically
by imposing a cutoff , representing the momentum kick from soft color
exchanges, in the ICEM model. Such soft exchanges have no perceptible effect on
suppression in p+A collisions. In contrast, the interplay of the
physics of these soft exchanges at large distances, with the physics of
semi-hard rescattering at short distances, causes a significant additional
suppression of yields relative to that of the . A good fit
of all RHIC and LHC and data, for transverse momenta
GeV in p+p and p+A collisions, is obtained for
MeV.Comment: 16 pages, 12 figures. v2: version accepted for publication in PR
Color Behavior Of BL Lacertae Object OJ 287 During Optical Outburst
This paper aims to study the color behavior of the BL Lac object OJ 287
during optical outburst. According to the revisit of the data from the OJ-94
monitoring project and the analysis the data obtained with the 60/90 cm Schmidt
Telescope of NAOC, we found a bluer-when-brighter chromatism in this object.
The amplitude of variation tends to decrease with the decrease of frequency.
These results are consistent with the shock-in-jet model. We made some
simulations and confirmed that both amplitude difference and time delay between
variations at different wavelengths can result in the phenomenon of
bluer-when-brighter. Our observations confirmed that OJ 287 underwent a
double-peaked outburst after about 12 years from 1996, which provides further
evidence for the binary black hole model in this object.Comment: 25 pages, 13 figure
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