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Title: Global polarization measurement in Au+Au collisions.

Abstract

The system created in noncentral relativistic nucleus-nucleus collisions possesses large orbital angular momentum. Because of spin-orbit coupling, particles produced in such a system could become globally polarized along the direction of the system angular momentum. We present the results of {Lambda} and {bar {Lambda}} hyperon global polarization measurements in Au+Au collisions at {radical}s{sub NN} = 62.4 and 200 GeV performed with the STAR detector at the BNL Relativistic Heavy Ion Collider (RHIC). The observed global polarization of {Lambda} and {bar {Lambda}} hyperons in the STAR acceptance is consistent with zero within the precision of the measurements. The obtained upper limit, |P{Lambda},{bar {Lambda}}| {le} 0.02, is compared with the theoretical values discussed recently in the literature.

Authors:
; ; ; ; ; ; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC); National Science Foundation (NSF); Swiss NSF
OSTI Identifier:
966340
Report Number(s):
ANL-HEP-PR-09-99
Journal ID: ISSN 0556-2813; PRVCAN; TRN: US0903946
DOE Contract Number:
DE-AC02-06CH11357
Resource Type:
Journal Article
Resource Relation:
Journal Name: Phys. Rev. C; Journal Volume: 76; Journal Issue: 2007
Country of Publication:
United States
Language:
ENGLISH
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; 74 ATOMIC AND MOLECULAR PHYSICS; ACCURACY; ANGULAR MOMENTUM; BNL; HEAVY IONS; HYPERONS; ORBITAL ANGULAR MOMENTUM; POLARIZATION

Citation Formats

Abelev, B. I., Aggarwal, M. M., Ahammed, Z., Anderson, B. D., Arkhipkin, D., Krueger, K., Spinka, H. M., Underwood, D. G., STAR Collaboration, High Energy Physics, Univ. of Illinois, Panjab Univ., Variable Energy Cyclotron Centre, Kent State Univ., and Particle Physics Lab. Global polarization measurement in Au+Au collisions.. United States: N. p., 2007. Web. doi:10.1103/PhysRevC.76.024915.
Abelev, B. I., Aggarwal, M. M., Ahammed, Z., Anderson, B. D., Arkhipkin, D., Krueger, K., Spinka, H. M., Underwood, D. G., STAR Collaboration, High Energy Physics, Univ. of Illinois, Panjab Univ., Variable Energy Cyclotron Centre, Kent State Univ., & Particle Physics Lab. Global polarization measurement in Au+Au collisions.. United States. doi:10.1103/PhysRevC.76.024915.
Abelev, B. I., Aggarwal, M. M., Ahammed, Z., Anderson, B. D., Arkhipkin, D., Krueger, K., Spinka, H. M., Underwood, D. G., STAR Collaboration, High Energy Physics, Univ. of Illinois, Panjab Univ., Variable Energy Cyclotron Centre, Kent State Univ., and Particle Physics Lab. Mon . "Global polarization measurement in Au+Au collisions.". United States. doi:10.1103/PhysRevC.76.024915.
@article{osti_966340,
title = {Global polarization measurement in Au+Au collisions.},
author = {Abelev, B. I. and Aggarwal, M. M. and Ahammed, Z. and Anderson, B. D. and Arkhipkin, D. and Krueger, K. and Spinka, H. M. and Underwood, D. G. and STAR Collaboration and High Energy Physics and Univ. of Illinois and Panjab Univ. and Variable Energy Cyclotron Centre and Kent State Univ. and Particle Physics Lab.},
abstractNote = {The system created in noncentral relativistic nucleus-nucleus collisions possesses large orbital angular momentum. Because of spin-orbit coupling, particles produced in such a system could become globally polarized along the direction of the system angular momentum. We present the results of {Lambda} and {bar {Lambda}} hyperon global polarization measurements in Au+Au collisions at {radical}s{sub NN} = 62.4 and 200 GeV performed with the STAR detector at the BNL Relativistic Heavy Ion Collider (RHIC). The observed global polarization of {Lambda} and {bar {Lambda}} hyperons in the STAR acceptance is consistent with zero within the precision of the measurements. The obtained upper limit, |P{Lambda},{bar {Lambda}}| {le} 0.02, is compared with the theoretical values discussed recently in the literature.},
doi = {10.1103/PhysRevC.76.024915},
journal = {Phys. Rev. C},
number = 2007,
volume = 76,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • The system created in non-central relativisticnucleus-nucleus collisions possesses large orbital angular momentum. Dueto spin-orbit coupling, particles produced in such a system could becomeglobally polarized along the direction of the system angular momentum. Wepresent the results of Lambda and anti-Lambda hyperon global polarizationmeasurements in Au+Au collisions at sqrt sNN=62.4 GeV and 200 GeVperformed with the STAR detector at RHIC. The observed globalpolarization of Lambda and anti-Lambda hyperons in the STAR acceptance isconsistent with zero within the precision of the measurements. Theobtained upper limit, lbar P Lambda, anti-Lambda rbar<= 0.02, iscompared to the theoretical values discussed recently in theliterature.
  • Signatures of collective effects are studied in the quark gluon string model and in the fluid dynamical model for Au+Au collisions at 11.6[ital A] GeV/[ital c]. In the fluid dynamical model the dependence of observables on the quark-gluon plasma (QGP) formation in the equation of state is pointed out although the maximal total amount of pure QGP formed is only about 8 fm[sup 3] in these reactions. In contrast to the baryon rapidity distribution, the in-plane transverse flow and especially the squeeze-out effect are particularly sensitive to the EOS. In the QGSM the lifetime and extent of baryon density inmore » strings are studied. The QGSM picture is very similar to the one obtained in the fluid dynamical model with a pure hadronic EOS.« less
  • Charged particles produced in Cu+Cu collisions at {radical}(s{sub NN}) = 200 and 62.4 GeV have been measured in the PHOBOS experiment at RHIC. The comparison of the results for Cu+Cu and Au+Au for the most central collisions at the same energy reveals that the particle density per nucleon participant pair and the extended longitudinal scaling behavior are similar in both systems. This implies that for the most central events in symmetric nucleus-nucleus collisions the particle density per nucleon participant pair does not depend on the size of the two colliding nuclei but only on the collision energy. Also the extendedmore » longitudinal scaling seems independent of the colliding energy and species for central collisions. In addition, there is an overall factorization of dNch/d{eta} shapes as a function of collision centraliry between Au+Au and Cu+Cu collisions at the same energy.« less
  • Three possible scenarios of the statistical hadronization model are reexamined with the use of the p{sub T} spectra of the PHENIX and very low p{sub T} PHOBOS measurements at {radical}(s{sub NN})=200 GeV. These scenarios are as follows: (a) full chemical nonequilibrium, (b) strangeness chemical nonequilibrium, and (c) chemical equilibrium. Fits to the spectra are done within the Cracow single-freeze-out model, which takes into account both the expansion and resonance decays. Predictions for spectra of {phi},K(892){sup *0}, and {pi}{sup 0} are also given. Global variables such as the transverse energy at midrapidity, the charged particle multiplicity at midrapidity, and the totalmore » multiplicity of charged particles are evaluated and their predicted values agree qualitatively well with the experimental data. The thorough analysis within this model suggests that the chemical full nonequilibrium case is the least likely and both other cases are of similar likelihood. It is also shown that if the full chemical nonequilibrium freeze-out took place it could manifest itself in the enhancement of the {pi}{sup 0} production at very low transverse momenta.« less
  • The authors report on a measurement of inclusive photon production in the P{sub T} range from a few MeV/c to a few GeV/c in 10.8 A-GeV/c Au-Au collisions at the AGS. Measurements were made using a high resolution photon detector, consisting of a 5 x 6 array of undoped CsI crystals located at a polar angle of 4.8{degrees} in the E877 forward spectrometer, and 35 meters downstream from the target. The measured photon spectrum shows that at high P{sub T} (P{sub T}>200 MeV/c), the spectrum can be described assuming that all photons originate from {pi}{sup 0} decays, in agreement qualitativelymore » with the {pi}{sup 0} spectrum generated by RQMD. Quantitative comparisons will be shown. At low P{sub T}, the data exhibit a very large excess above the contribution expected from {pi}{sup 0} decays. The background from external bremsstrahlung also rises rapidly in this range. The authors used the predictions from RQMD coupled with the simulation code GEANT to determine this background quantitatively. They will discuss the sensitivity of the present data to anomalous low P{sub T} photon production.« less