5,909 research outputs found
Sleptogenesis
We propose that the observed baryon asymmetry of the Universe can naturally
arise from a net asymmetry generated in the sleptonic sector at fairly low
reheat temperatures. The best candidate is indeed the right-handed sneutrino.
The initial asymmetry in the sneutrino sector can be produced from the decay of
the inflaton, and is subsequently transferred into the Standard Model (s)lepton
doublet via the decay of the sneutrino. The active sphalerons then reprocess
the leptonic asymmetry into the baryonic asymmetry. The marked feature of this
scenario is that the lepton asymmetry is decoupled from the neutrino Yukawa
sector. We exhibit that our scenario can be embedded within models which seek
the origin of a tiny mass for neutrinos.Comment: 7 revtex pages, 2 figures (uses axodraw). Minor changes for better
clarification and updated references. Final version to appear in Phys. Rev.
Summary of the Activities of the Working Group I on High Energy and Collider Physics
This is a summary of the projects undertaken by the Working Group I on High
Energy Collider Physics at the Eighth Workshop on High Energy Physics
Phenomenology (WHEPP8) held at the Indian Institute of Technology, Mumbai,
January 5-16, 2004. The topics covered are (i) Higgs searches (ii)
supersymmetry searches (iii) extra dimensions and (iv) linear collider.Comment: summary of Working Group I at the Eighth Workshop on High Energy
Physics Phenomenology (WHEPP8), I.I.T., Mumbai, January 5-16, 200
Towards an Observational Appraisal of String Cosmology
We review the current observational status of string cosmology when
confronted with experimental datasets. We begin by defining common
observational parameters and discuss how they are determined for a given model.
Then we review the observable footprints of several string theoretic models,
discussing the significance of various potential signals. Throughout we comment
on present and future prospects of finding evidence for string theory in
cosmology, and on significant issues for the future.Comment: Review accepted for publication in the CQG focus issue on string
cosmology. Minor clarifications and references adde
Spin alignment measurements of the and vector mesons at RHIC
We present the first spin alignment measurements for the and
vector mesons produced at mid-rapidity with transverse momenta up
to 5 GeV/c at = 200 GeV at RHIC. The diagonal spin density
matrix elements with respect to the reaction plane in Au+Au collisions are
= 0.32 0.04 (stat) 0.09 (syst) for the
( GeV/c) and = 0.34 0.02 (stat) 0.03
(syst) for the ( GeV/c), and are constant with transverse
momentum and collision centrality. The data are consistent with the unpolarized
expectation of 1/3 and thus no evidence is found for the transfer of the
orbital angular momentum of the colliding system to the vector meson spins.
Spin alignments for and in Au+Au collisions were also measured
with respect to the particle's production plane. The result,
= 0.41 0.02 (stat) 0.04 (syst), is consistent with that in p+p
collisions, = 0.39 0.03 (stat) 0.06 (syst), also
measured in this work. The measurements thus constrain the possible size of
polarization phenomena in the production dynamics of vector mesons.Comment: 7 pages, 4 figures. fig.1 updated; one more reference added, one typo
corrected, published in PRC.77.06190
System-Size Independence of Directed Flow Measured at the BNL Relativistic Heavy-Ion Collider
We measure directed flow (ν_1) for charged particles in Au+Au and Cu+Cu collisions at √S_(NN)=200 and 62.4 GeV, as a function of pseudorapidity (η), transverse momentum (p_t), and collision centrality, based on data from the STAR experiment. We find that the directed flow depends on the incident energy but, contrary to all available model implementations, not on the size of the colliding system at a given centrality. We extend the validity of the limiting fragmentation concept to ν_1 in different collision systems, and investigate possible explanations for the observed sign change in ν_1(p_t)
Measurements of meson production in relativistic heavy-ion collisions at RHIC
We present results for the measurement of meson production via its
charged kaon decay channel in Au+Au collisions at
, 130, and 200 GeV, and in and +Au collisions
at GeV from the STAR experiment at the BNL Relativistic
Heavy Ion Collider (RHIC). The midrapidity () meson transverse
momentum () spectra in central Au+Au collisions are found to be well
described by a single exponential distribution. On the other hand, the
spectra from , +Au and peripheral Au+Au collisions show power-law tails
at intermediate and high and are described better by Levy
distributions. The constant yield ratio vs beam species, collision
centrality and colliding energy is in contradiction with expectations from
models having kaon coalescence as the dominant mechanism for production
at RHIC. The yield ratio as a function of is consistent
with a model based on the recombination of thermal quarks up to GeV/, but disagrees at higher transverse momenta. The measured nuclear
modification factor, , for the meson increases above unity at
intermediate , similar to that for pions and protons, while is
suppressed due to the energy loss effect in central Au+Au collisions. Number of
constituent quark scaling of both and for the meson
with respect to other hadrons in Au+Au collisions at =200 GeV
at intermediate is observed. These observations support quark
coalescence as being the dominant mechanism of hadronization in the
intermediate region at RHIC.Comment: 22 pages, 21 figures, 4 table
Growth of Long Range Forward-Backward Multiplicity Correlations with Centrality in Au+Au Collisions at = 200 GeV
Forward-backward multiplicity correlation strengths have been measured with
the STAR detector for Au+Au and collisions at =
200 GeV. Strong short and long range correlations (LRC) are seen in central
Au+Au collisions. The magnitude of these correlations decrease with decreasing
centrality until only short range correlations are observed in peripheral Au+Au
collisions. Both the Dual Parton Model (DPM) and the Color Glass Condensate
(CGC) predict the existence of the long range correlations. In the DPM the
fluctuation in the number of elementary (parton) inelastic collisions produces
the LRC. In the CGC longitudinal color flux tubes generate the LRC. The data is
in qualitative agreement with the predictions from the DPM and indicates the
presence of multiple parton interactions.Comment: 6 pages, 3 figures The abstract has been slightly modifie
Longitudinal Spin Transfer to and Hyperons in Polarized Proton-Proton Collisions at = 200 GeV
The longitudinal spin transfer, , from high energy polarized protons
to and hyperons has been measured for the first time
in proton-proton collisions at with the STAR
detector at RHIC. The measurements cover pseudorapidity, , in the range
and transverse momenta, , up to . The longitudinal spin transfer is found to be for inclusive
and for
inclusive hyperons with and . The dependence on and is presented.Comment: 5 pages, 4 figure
Inclusive pi^0, eta, and direct photon production at high transverse momentum in p+p and d+Au collisions at sqrt(s_NN) = 200 GeV
We report a measurement of high-p_T inclusive pi^0, eta, and direct photon
production in p+p and d+Au collisions at sqrt(s_NN) = 200 GeV at midrapidity (0
gamma gamma were detected in the
Barrel Electromagnetic Calorimeter of the STAR experiment at the Relativistic
Heavy Ion Collider. The eta -> gamma gamma decay was also observed and
constituted the first eta measurement by STAR. The first direct photon cross
section measurement by STAR is also presented, the signal was extracted
statistically by subtracting the pi^0, eta, and omega(782) decay background
from the inclusive photon distribution observed in the calorimeter. The
analysis is described in detail, and the results are found to be in good
agreement with earlier measurements and with next-to-leading order perturbative
QCD calculations.Comment: 28 pages, 30 figures, 6 tables, the updated version that was accepted
by Phys. Rev.
Charged and strange hadron elliptic flow in Cu+Cu collisions at = 62.4 and 200 GeV
We present the results of an elliptic flow analysis of Cu+Cu collisions
recorded with the STAR detector at 62.4 and 200GeV. Elliptic flow as a function
of transverse momentum is reported for different collision centralities for
charged hadrons and strangeness containing hadrons , ,
, in the midrapidity region . Significant reduction in
systematic uncertainty of the measurement due to non-flow effects has been
achieved by correlating particles at midrapidity, , with those at
forward rapidity, . We also present azimuthal correlations in
p+p collisions at 200 GeV to help estimating non-flow effects. To study the
system-size dependence of elliptic flow, we present a detailed comparison with
previously published results from Au+Au collisions at 200 GeV. We observe that
() of strange hadrons has similar scaling properties as were
first observed in Au+Au collisions, i.e.: (i) at low transverse momenta,
, scales with transverse kinetic energy, , and
(ii) at intermediate , , it scales with the number of
constituent quarks, . We have found that ideal hydrodynamic calculations
fail to reproduce the centrality dependence of () for
and . Eccentricity scaled values, , are larger
in more central collisions, suggesting stronger collective flow develops in
more central collisions. The comparison with Au+Au collisions which go further
in density shows depend on the system size, number of
participants . This indicates that the ideal hydrodynamic limit is
not reached in Cu+Cu collisions, presumably because the assumption of
thermalization is not attained.Comment: 18 pages, 14 figure
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