http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
Observation of the antimatter helium-4 nucleus
Agakishiev, H.,Aggarwal, M. M.,Ahammed, Z.,Alakhverdyants, A. V.,Alekseev, I.,Alford, J.,Anderson, B. D.,Anson, C. D.,Arkhipkin, D.,Averichev, G. S.,Balewski, J.,Beavis, D. R.,Behera, N. K.,Bellwied, Nature Publishing Group, a division of Macmillan P 2011 Nature Vol.473 No.7347
High-energy nuclear collisions create an energy density similar to that of the Universe microseconds after the Big Bang; in both cases, matter and antimatter are formed with comparable abundance. However, the relatively short-lived expansion in nuclear collisions allows antimatter to decouple quickly from matter, and avoid annihilation. Thus, a high-energy accelerator of heavy nuclei provides an efficient means of producing and studying antimatter. The antimatter helium-4 nucleus (), also known as the anti-慣 (), consists of two antiprotons and two antineutrons (baryon number B = ??4). It has not been observed previously, although the 慣-particle was identified a century ago by Rutherford and is present in cosmic radiation at the ten per cent level. Antimatter nuclei with B??<????1 have been observed only as rare products of interactions at particle accelerators, where the rate of antinucleus production in high-energy collisions decreases by a factor of about 1,000 with each additional antinucleon. Here we report the observation of , the heaviest observed antinucleus to date. In total, 18 counts were detected at the STAR experiment at the Relativistic Heavy Ion Collider (RHIC; ref. 6) in 10<SUP>9</SUP> recorded gold-on-gold (Au+Au) collisions at centre-of-mass energies of 200??GeV and 62??GeV per nucleon??nucleon pair. The yield is consistent with expectations from thermodynamic and coalescent nucleosynthesis models, providing an indication of the production rate of even heavier antimatter nuclei and a benchmark for possible future observations of in cosmic radiation.
STAR Collaboration,Agakishiev, G.,Aggarwal, M.M.,Ahammed, Z.,Alakhverdyants, A.V.,Alekseev, I.,Alford, J.,Anderson, B.D.,Anson, C.D.,Arkhipkin, D.,Averichev, G.S.,Balewski, J.,Beavis, D.R.,Behera, N.K North-Holland Pub. Co 2011 Physics letters: B Vol.704 No.5
We present first measurements of the evolution of the differential transverse momentum correlation function, C, with collision centrality in Au+Au interactions at s<SUB>NN</SUB>=200 GeV. This observable exhibits a strong dependence on collision centrality that is qualitatively similar to that of number correlations previously reported. We use the observed longitudinal broadening of the near-side peak of C with increasing centrality to estimate the ratio of the shear viscosity to entropy density, η/s, of the matter formed in central Au+Au interactions. We obtain an upper limit estimate of η/s that suggests that the produced medium has a small viscosity per unit entropy.
Single spin asymmetry A<sub>N</sub> in polarized proton-proton elastic scattering at s=200 GeV
STAR Collaboration,Adamczyk, L.,Agakishiev, G.,Aggarwal, M.M.,Ahammed, Z.,Alakhverdyants, A.V.,Alekseev, I.,Alford, J.,Anson, C.D.,Arkhipkin, D.,Aschenauer, E.,Averichev, G.S.,Balewski, J.,Banerjee, A North-Holland Pub. Co 2013 Physics letters: B Vol.719 No.1
We report a high precision measurement of the transverse single spin asymmetry A<SUB>N</SUB> at the center of mass energy s=200 GeV in elastic proton-proton scattering by the STAR experiment at RHIC. The A<SUB>N</SUB> was measured in the four-momentum transfer squared t range 0.003≤|t|≤0.035 (GeV/c)<SUP>2</SUP>, the region of a significant interference between the electromagnetic and hadronic scattering amplitudes. The measured values of A<SUB>N</SUB> and its t-dependence are consistent with a vanishing hadronic spin-flip amplitude, thus providing strong constraints on the ratio of the single spin-flip to the non-flip amplitudes. Since the hadronic amplitude is dominated by the Pomeron amplitude at this s, we conclude that this measurement addresses the question about the presence of a hadronic spin flip due to the Pomeron exchange in polarized proton-proton elastic scattering.
Adamczyk, L.,Adkins, J.K.,Agakishiev, G.,Aggarwal, M.M.,Ahammed, Z.,Ajitanand, N.N.,Alekseev, I.,Anderson, D.M.,Aoyama, R.,Aparin, A.,Arkhipkin, D.,Aschenauer, E.C.,Ashraf, M.U.,Attri, A.,Averichev, G North-Holland Pub. Co 2017 Physics letters. Section B Vol.771 No.-
<P><B>Abstract</B></P> <P>The inclusive J / ψ transverse momentum spectra and nuclear modification factors are reported at mid-rapidity ( | y | < 1.0 ) in Au+Au collisions at <SUB> s N N </SUB> = 39, 62.4 and 200 GeV taken by the STAR experiment. A suppression of J / ψ production, with respect to the production in p + p scaled by the number of binary nucleon–nucleon collisions, is observed in central Au+Au collisions at these three energies. No significant energy dependence of nuclear modification factors is found within uncertainties. The measured nuclear modification factors can be described by model calculations that take into account both suppression of direct J / ψ production due to the color screening effect and J / ψ regeneration from recombination of uncorrelated charm–anticharm quark pairs.</P>
Charged-to-neutral correlation at forward rapidity in Au + Au collisions at<sub>sNN</sub>=200GeV
Adamczyk, L.,Adkins, J. K.,Agakishiev, G.,Aggarwal, M. M.,Ahammed, Z.,Alekseev, I.,Alford, J.,Anson, C. D.,Aparin, A.,Arkhipkin, D.,Aschenauer, E. C.,Averichev, G. S.,Banerjee, A.,Beavis, D. R.,Bellwi American Physical Society 2015 PHYSICAL REVIEW C - Vol.91 No.3
Azimuthal Anisotropy inU+UandAu+AuCollisions at RHIC
Adamczyk, L.,Adkins, J. K.,Agakishiev, G.,Aggarwal, M. M.,Ahammed, Z.,Alekseev, I.,Alford, J.,Aparin, A.,Arkhipkin, D.,Aschenauer, E. C.,Averichev, G. S.,Banerjee, A.,Bellwied, R.,Bhasin, A.,Bhati, A. American Physical Society 2015 Physical review letters Vol.115 No.22
Adamczyk, L.,Adkins, J. K.,Agakishiev, G.,Aggarwal, M. M.,Ahammed, Z.,Ajitanand, N. N.,Alekseev, I.,Anderson, D. M.,Aoyama, R.,Aparin, A.,Arkhipkin, D.,Aschenauer, E. C.,Ashraf, M. U.,Attri, A.,Averic American Physical Society 2017 Physical Review D Vol.95 No.7
<P>We report the first measurement of the longitudinal double-spin asymmetry A(LL) for midrapidity dijet production in polarized pp collisions at a center-of-mass energy of root s = 200 GeV. The dijet cross section was measured and is shown to be consistent with next-to-leading order (NLO) perturbative QCD predictions. A(LL) results are presented for two distinct topologies, defined by the jet pseudorapidities, and are compared to predictions from several recent NLO global analyses. The measured asymmetries, the first such correlation measurements, support those analyses that find positive gluon polarization at the level of roughly 0.2 over the region of Bjorken-x > 0.05.</P>
Energy Dependence of Moments of Net-Proton Multiplicity Distributions at RHIC
Adamczyk, L.,Adkins, J. K.,Agakishiev, G.,Aggarwal, M. M.,Ahammed, Z.,Alekseev, I.,Alford, J.,Anson, C. D.,Aparin, A.,Arkhipkin, D.,Aschenauer, E. C.,Averichev, G. S.,Balewski, J.,Banerjee, A.,Barnovs American Physical Society 2014 Physical Review Letters Vol.112 No.3
<P>The first experimental study is presented of a corrugated wall device that uses wakefields to remove a linear energy correlation in a relativistic electron beam (a “dechirper”). Time-resolved measurements of both longitudinal and transverse wakefields of the device are presented and compared with simulations. This study demonstrates the feasibility to employ a dechirper for precise control of the beam phase space in the next generation of free-electron-lasers.</P>