3,511 research outputs found
Recent STAR results in high-energy polarized proton-proton collisions at RHIC
The STAR experiment at the Relativistic Heavy-Ion Collider at Brookhaven
National Laboratory is carrying out a spin physics program in high-energy
polarized collisions at GeV to gain a
deeper insight into the spin structure and dynamics of the proton.
One of the main objectives of the spin physics program at RHIC is the
extraction of the polarized gluon distribution function based on measurements
of gluon initiated processes, such as hadron and jet production. The STAR
detector is well suited for the reconstruction of various final states
involving jets, , , e and , which allows to
measure several different processes. Recent results will be shown on the
measurement of jet production and hadron production at GeV. The
RHIC spin physics program has recently completed the first data taking period
in 2009 of polarized collisions at GeV. This
opens a new era in the study of the spin-flavor structure of the proton based
on the production of bosons. Recent STAR results on the first
measurement of boson production in polarized collisions
will be shown.Comment: 10 pages, 9 figures, Talk presented at the 26th Winter Workshop on
Nuclear Dynamics, Ocho Rios, Jamaica, January 2-9, 2010 to be published in
Journal of Physics: Conference Series (JPCS) The author may be contacted via:
[email protected]
The Hague Convention on the Protection of Children and Cooperation in Respect of Intercountry Adoption: the Need for a Uniform Standard for Intercountry Adoption by Homosexuals
Recent results from the STAR spin program at RHIC
The STAR experiment uses polarized p+p collisions at RHIC to determine the
contributions to the spin of the proton from gluon spin and from orbital
angular momentum of the quarks and gluons. Selective STAR measurements of the
longitudinal double spin asymmetry for inclusive jet and inclusive hadron
production are presented here. In addition, we report measurements of the
transverse spin asymmetry for di-jet production at mid-rapidity and the
transverse single-spin asymmetry for forward pi0 productionComment: 4 pages, 5 figures, presented at GHP06 conferenc
Overview on jet results from STAR
Full jet reconstruction allows access to the parton kinematics over a large
energy domain and can be used to constrain the mechanisms of energy loss in
heavy-ion collisions. Such measurements are challenging at RHIC, due to the
high-multiplicity environments created in heavy-ion collisions. In these
proceedings, we report an overview of the results on full jet reconstruction
obtained by the STAR experiment. Jet measurements in 200 GeV p+p show that jets
are calibrated pQCD probes and provide a baseline for jet measurements in Au+Au
collisions. Inclusive differential jet production cross sections and ratios are
reported for central 200 GeV Au+Au collisions and compared to p+p. We also
present measurements of fully reconstructed di-jets at mid-rapidity, and
compare spectra and fragmentation functions in p+p and central Au+Au
collisions.Comment: Proceedings for the 26th WWND conferenc
Recent high pT measurements in STAR
After five years of data taking, the STAR experiment at the Relativistic
Heavy Ion Collider (RHIC) at Brookhaven National Laboratory provides precise
measurements of particle production at high transverse momentum in p-p, d-Au,
and Au-Au collisions at sqrt(s) = 200 GeV. We review recent results on the
flavor dependence of high pT particle suppression and hadron particle spectra
at sqrt(s) = 62.4 GeV. New results on two-particle angular correlations for
identified trigger particles and for low momentum associated charged hadrons in
p-p and Au-Au as well as near-side correlations will be presented
and discussed.Comment: 5th International Conference on Physics and Astrophysics of Quark
Gluon Plasma, Calcutta. 8 pages, 10 figures, submitted to J. Phys. G: Nucl.
Part. Phy
Azimuth Quadrupole Systematics in Au-Au Collisions
We have measured -dependent two-particle number correlations on azimuth
and pseudorapidity for eleven centralities of and 200~GeV
Au-Au collisions at STAR. 2D fits to these angular correlations isolate the
azimuth quadrupole amplitude, denoted , from
localized same-side correlations. Event-plane measurements within
the STAR TPC acceptance can be expressed as a sum of the azimuth quadrupole and
the quadrupole component of the same-side peak. can be
transformed to reveal quadrupole spectra which are approximately
described by a fixed transverse boost and universal L\'evy form nearly
independent of centrality. A parametrization of can be
factored into centrality and -dependent pieces with a simple
dependence above 0.75 GeV/c. Results from STAR are compared to published data
and model predictions.Comment: Conference proceedings for Hot Quarks 201
Dissipation and fragmentation of low-Q^2 scattered partons in Au-Au collisions at RHIC
Two-particle correlations and event-wise fluctuations in transverse momentum
p_t are reported for Au-Au collisions at sqrt{s_{NN}} = 62 and 200 GeV on
pseudorapidity (eta) and azimuth (phi). Distributions of all pairs of particles
(no leading trigger particle) reveal jet-like correlations, or peaks at
pair-wise opening angles of order 1 radian or less. The width of this same-side
correlation peak increases dramatically on pseudorapidity and decreases on
azimuth for increasing collision centrality. Evolution of the same-side peak
with centrality suggests dissipation of low-Q^2 partons via strong coupling to
an expanding bulk medium. p_t correlations, which provide access to temperature
and/or velocity distributions in the colliding system, are also presented.Comment: 4 pages, 2 figures, conference poster write-u
Heavy ion collisions: Correlations and Fluctuations in particle production
Correlations and fluctuations (the latter are directly related to the
2-particle correlations) is one of the important directions in analysis of
heavy ion collisions. At the current stage of RHIC exploration, when the
details matter, basically any physics question is addressed with help of
correlation techniques. In this talk I start with a general introduction to the
correlation and fluctuation formalism and discuss weak and strong sides of
different type of observables. In more detail, I discuss the two-particle
correlations/\mpt fluctuations. In spite of not observing any dramatic
changes in the event-by-event fluctuations with energy, which would indicate a
possible phase transition, such correlations measurements remain an interesting
and important subject, bringing valuable information. Lastly, I show how radial
flow can generate characteristic azimuthal, transverse momentum and rapidity
correlations, which could qualitatively explain many of recently observed
phenomena in nuclear collisions.Comment: 8 pages, 8 figures. Invited talk at 5th International Conference on
Physics and Astrophysics of Quark Gluon Plasma, February 8-12, 2005, Salt
Lake City, Kolkata, Indi
Fluctuation and flow probes of early-time correlations in relativistic heavy ion collisions
Fluctuation and correlation observables are often measured using
multi-particle correlation methods and therefore mutually probe the origins of
genuine correlations present in multi-particle distribution functions. We
investigate the common influence of correlations arising from the spatially
inhomogeneous initial state on multiplicity and momentum fluctuations as well
as flow fluctuations. Although these observables reflect different aspects of
the initial state, taken together, they can constrain a correlation scale set
at the earliest moments of the collision. We calculate both the correlation
scale in an initial stage Glasma flux tube picture and the modification to
these correlations from later stage hydrodynamic flow and find quantitative
agreement with experimental measurements over a range of collision systems and
energies.Comment: Proceedings of the 28th Winter Workshop on Nuclear Dynamics, Dorado
del Mar, Puerto Rico, April 7-14, 201
Global polarization measurement in Au+Au collisions
The system created in non central relativistic nucleus-nucleus collisions
carries large angular orbital momentum. Due to spin-orbital coupling, produced
particles could be globally polarized along the direction of the system angular
momentum. We present results of a measurement of Lambda hyperon global
polarization in Au+Au collisions at the center of mass energies 62 and 200 GeV
with the STAR detector at RHIC. The observed global polarization of Lambda
hyperons in the STAR acceptance is consistent with zero within the precision of
the measurement. The obtained upper limit, |P_Lambda| < 0.01, is significantly
below the theoretical values discussed recently in the literature.Comment: Talk given at SQM 2006, International Conference on Strangeness in
Quark Matter, March 26-31, 2006, Los Angeles CA; 4 pages, 2 figure
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