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A. Bravar

Publications and source records attributed to A. Bravar.

188 records · Page 11Linked to original sources
arXiv2006

Strange baryon resonance production in $\sqrt{s_{NN}} = 200$ GeV $p+p$ and $Au+Au$ collisions

We report the measurements of $Σ(1385)$ and $Λ(1520)$ production in $p+p$ and $Au+Au$ collisions at $\sqrt{s_{NN}} = 200$ GeV from the STAR collaboration. The yields and the $p_{T}$ spectra are presented and discussed in terms of chemical and thermal freeze-out conditions and compared to model predictions. Thermal and microscopic models do not adequately describe the yields of all the resonances produced in central $Au+Au$ collisions. Our results indicate that there may be a time-span between chemical and thermal freeze-out during which elastic hadronic interactions occur.

nucl-ex↗
arXiv2005

Measurement of the Analyzing Power $A_N$ in $pp$ Elastic Scattering in the CNI Region with a Polarized Atomic Hydrogen Gas Jet Target

A precise measurement of the analyzing power $A_N$ in proton-proton elastic scattering in the region of 4-momentum transfer squared $0.001 < |t| < 0.032 ({\rm GeV}/c)^2$ has been performed using a polarized atomic hydrogen gas jet target and the 100 GeV/$c$ RHIC proton beam. The interference of the electromagnetic spin-flip amplitude with a hadronic spin-nonflip amplitude is predicted to generate a significant $A_N$ of 4--5%, peaking at $-t \simeq 0.003 ({\rm GeV}/c)^2$. This kinematic region is known as the Coulomb Nuclear Interference region. A possible hadronic spin-flip amplitude modifies this otherwise calculable prediction. Our data are well described by the CNI prediction with the electromagnetic spin-flip alone and do not support the presence of a large hadronic spin-flip amplitude.

hep-ex↗
arXiv2004

Measurement of the analyzing power of proton-carbon elastic scattering in the CNI region at RHIC

The single transverse spin asymmetry, A_N, of the p-carbon elastic scattering process in the Coulomb Nuclear Interference (CNI) region was measured using an ultra thin carbon target and polarized proton beam in the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL). In 2004, data were collected to calibrate the p-carbon process at two RHIC energies (24 GeV, 100 GeV). A_N was obtained as a function of momentum transfer -t. The results were fit with theoretical models which allow us to assess the contribution from a hadronic spin flip amplitude.

nucl-ex↗
arXiv2002

Diffraction at RHIC

The relativistic heavy ion collider (RHIC) offers many opportunities to study diffraction in pp, pA and AA collisions. Because both proton beams can be polarized, RHIC offers the unique possibility of studying polarization effects in diffraction. We will introduce diffraction at RHIC and present three compelling physics topics: hard diffraction with polarized beams, identification of exotic mesons (non-q q-bar states) in double-Pomeron collisions, and using diffraction to measure the low-x gluon density in $pA$ collisions, testing models of gluon saturation and the colored glass condensate. This note developed from discussion at a workshop on ``Diffraction and Glueball Production at RHIC'' at Brookhaven National Laboratory, May 17-18, 2002.

hep-ex↗
arXiv1997

Gluon polarization from correlated high-pT hadron pairs in polarized electro-production

We propose to measure the gluon distribution function Delta G(eta) at eta < 0.2 via pseudo jet production in polarized fixed target lepton nucleon scattering at typical lepton beam energies of 200 GeV. The measurement of the spin-asymmetry for the production of correlated charge conjugated hadrons of opposite transverse momentum can be directly related to Delta G(eta) through the photo-gluon fusion process. Wa also present a numerical analysis of the accuracy which can be obtained for different flavors and kinematics of the observed hadron pair.

hep-ph↗
arXiv1997

Gluon Polarization from Correlated High-p_T Hadron Pairs in Polarized l - N Scattering

We propose to access the gluon polarization $ΔG$ by measuring the cross section spin-asymmetry in semi-inclusive polarized lepton -- nucleon scattering. The photon-gluon fusion sub-process will be tagged by detecting high-$p_T$ correlated hadron pairs in the forward hemisphere. Selecting oppositely charged kaon pairs will allow to suppress the background coming from gluon radiation.

hep-ph↗
arXiv1997

Lambda and Lambda-bar Polarization in Lepton Induced Processes

The study of the longitudinal polarization of Lambda and Lambda-bar hyperons produced in polarized deep inelastic scattering, neutrino scattering, and in Z0 decays allows to access the spin dynamics of the quark fragmentation process. Different phenomenological spin transfer mechanisms are considered and predictions for the Lambda and Lambda-bar longitudinal polarization in various processes using unpolarized and polarized targets are made. Current and future semi-inclusive deep inelastic scattering experiments will provide soon accurate enough data to study these phenomena and distinguish between various models for the spin transfer mechanisms.

hep-ph↗