294 research outputs found
Spin precession in a quadrupole lens
No full textIn transporting a polarized proton beam through a channel consisting of dipole magnets and quadrupoles, one needs to calculate the depolarization effects due to the magnetic fields. Usually the dipole magnet has a homogeneous field and the spin precession is calculated straightforwardly. But an equation of motion of spin in a quadrupole lens has not yet been solved analytically. The author proposes here such a solution and the result obtained is applied to some interesting practical cases. (5 refs)
About extraction of 70-GeV protons by a bent crystal from the IHEP accelerator to the PROZA setup
No full text
Crystal-assisted extraction of Au ions from RHIC and application of the Au beam for the search of anomalous Cherenkov radiation
No full textJet-like correlations with direct-photon and neutral-pion triggers at sNN=200 GeV
No full textAbstractAzimuthal correlations of charged hadrons with direct-photon (γdir) and neutral-pion (π0) trigger particles are analyzed in central Au+Au and minimum-bias p+p collisions at sNN=200 GeV in the STAR experiment. The charged-hadron per-trigger yields at mid-rapidity from central Au+Au collisions are compared with p+p collisions to quantify the suppression in Au+Au collisions. The suppression of the away-side associated-particle yields per γdir trigger is independent of the transverse momentum of the trigger particle (pTtrig), whereas the suppression is smaller at low transverse momentum of the associated charged hadrons (pTassoc). Within uncertainty, similar levels of suppression are observed for γdir and π0 triggers as a function of zT (≡pTassoc/pTtrig). The results are compared with energy-loss-inspired theoretical model predictions. Our studies support previous conclusions that the lost energy reappears predominantly at low transverse momentum, regardless of the trigger energy
POLARIZATION EFFECTS IN CHARGE-EXCHANGE REACTION AT 40 GeV/c
No full textNous présentons des résultats obtenus dans l'étude des réactions π-p → π°n, π-p → ηn, π-p → η'(958)n, π-p → f (1270)n à 40 GeV/c. Nous avons observé quelques nouveaux phénomènes dans le comportement de ces réactions.The results on measuring the asymmetries in the reactions π-p → π°n, π-p → ηn, π-p → η'(958)n, π-p → f (1270)n at 40 GeV/c are presented. Some new phenomena have been discovered in the asymmetry behaviour in these reactions
Single transverse-spin asymmetry in very forward and very backward neutral particle production for polarized proton collisions at s=200 GeV
No full textAbstractIn the 2001–2002 running period of the Relativistic Heavy Ion Collider (RHIC), transversely polarized protons were accelerated to 100 GeV for the first time, with collisions at s=200 GeV. We present results from this run for single transverse-spin asymmetries for inclusive production of neutral pions, photons and neutrons of the energy region 20–100 GeV for forward and backward production for angles between 0.3 mrad and 2.2 mrad with respect to the polarized proton direction. An asymmetry of AN=(−0.090±0.006±0.009)×(1.0−0.24+0.47) was observed for forward neutron production, where the errors are statistical and systematic, and the scale error is from the beam polarization uncertainty. The forward photon and π0, and backward neutron, photon, and π0 asymmetries were consistent with zero. The large neutron asymmetry indicates a strong interference between a spin–flip amplitude, such as one pion exchange which dominates lower energy neutron production, and remaining spin–non-flip amplitudes such as reggeon exchange
Observation of meson nuclear modifications in Au+Au collisions at = 200 GeV
No full text7 pages including author list, 4 figures ; see paper for full list of authorsWe report the first measurement of charmed-hadron () production via the hadronic decay channel () in Au+Au collisions at = 200\,GeV with the STAR experiment. The charm production cross-section per nucleon-nucleon collision at mid-rapidity scales with the number of binary collisions, , from + to central Au+Au collisions. The meson yields in central Au+Au collisions are strongly suppressed compared to those in + scaled by , for transverse momenta p_{T}>3 GeV/, demonstrating significant energy loss of charm quarks in the hot and dense medium. An enhancement at intermediate is also observed. Model calculations including strong charm-medium interactions and coalescence hadronization describe our measurements
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