OPUS 4 | Search

Evidence for an exotic S=-2, Q=-2 baryon resonance in proton-proton collisions at the CERN SPS (2004)

Christopher Alt L. Betev Anja Billmeier Christoph Blume Roland Bramm P. Buncic Peter Dinkelaker Dominik Bernhard Flierl Marek Gazdzicki Stefan Kniege Thorsten Kollegger Christine Meurer Michael Kosta Mitrovski R. Renfordt Reinhard Stock Herbert Ströbele Alexander Albert Wetzler Jacek Zaranek et al. NA49 Collaboration

Results of resonance searches in the Xi - pi -, Xi - pi +, Xi -bar+ pi -, and Xi -bar+ pi + invariant mass spectra in proton-proton collisions at sqrt[s]=17.2 GeV are presented. Evidence is shown for the existence of a narrow Xi - pi - baryon resonance with mass of 1.862±0.002 GeV/c2 and width below the detector resolution of about 0.018 GeV/c2. The significance is estimated to be above 4.2 sigma . This state is a candidate for the hypothetical exotic Xi --3/2 baryon with S=-2, I=3 / 2, and a quark content of (dsdsu-bar). At the same mass, a peak is observed in the Xi - pi + spectrum which is a candidate for the Xi 03/2 member of this isospin quartet with a quark content of (dsusd-bar). The corresponding antibaryon spectra also show enhancements at the same invariant mass.

Azimuthal anisotropy and correlations in the hard scattering regime at RHIC (2003)

Clemens Adler Jens Berger Thomas Dietel Dominik Bernhard Flierl Jens Sören Lange Reinhard Stock Christof Struck et al. STAR Collaboration

Azimuthal anisotropy (v2) and two-particle angular correlations of high pT charged hadrons have been measured in Au+Au collisions at sqrt[sNN]=130 GeV for transverse momenta up to 6 GeV/c, where hard processes are expected to contribute significantly. The two-particle angular correlations exhibit elliptic flow and a structure suggestive of fragmentation of high pT partons. The monotonic rise of v2(pT) for pT<2 GeV/c is consistent with collective hydrodynamical flow calculations. At pT>3 GeV/c, a saturation of v2 is observed which persists up to pT=6 GeV/c.

Erratum: Midrapidity antiproton-to-proton ratio from Au+Au collisions at sqrt[sNN]=130 GeV [Phys. Rev. Lett. 86, 4778 (2001)] (2003)

Clemens Adler Z. Ahammed C. Allgower Jens Berger Dominik Bernhard Flierl Jens Sören Lange Reinhard Stock Herbert Ströbele Christof Struck et al. STAR Collaboration

Centrality Dependence of High-pT Hadron Suppression in Au+Au Collisions at sqrt[sNN]=130 GeV (2002)

Clemens Adler Z. Ahammed C. Allgower Jens Berger Thomas Dietel Dominik Bernhard Flierl Jens Sören Lange Reinhard Stock Christof Struck et al. STAR Collaboration

Inclusive transverse momentum distributions of charged hadrons within 0.2<pT<6.0 GeV/c have been measured over a broad range of centrality for Au+Au collisions at sqrt[sNN]=130 GeV. Hadron yields are suppressed at high pT in central collisions relative to peripheral collisions and to a nucleon-nucleon reference scaled for collision geometry. Peripheral collisions are not suppressed relative to the nucleon-nucleon reference. The suppression varies continuously at intermediate centralities. The results indicate significant nuclear medium effects on high-pT hadron production in heavy-ion collisions at high energy.

Coherent rho 0 production in ultraperipheral heavy-ion collisions (2002)

Clemens Adler Z. Ahammed C. Allgower Jens Berger Thomas Dietel Dominik Bernhard Flierl Jens Sören Lange Reinhard Stock Christof Struck et al. STAR Collaboration

The STAR Collaboration reports the first observation of exclusive rho 0 photoproduction, AuAu-->AuAu rho 0, and rho 0 production accompanied by mutual nuclear Coulomb excitation, AuAu-->Au [star] Au [star] rho 0, in ultraperipheral heavy-ion collisions. The rho 0 have low transverse momenta, consistent with coherent coupling to both nuclei. The cross sections at sqrt[sNN]=130 GeV agree with theoretical predictions treating rho 0 production and Coulomb excitation as independent processes.

Azimuthal anisotropy of K0S and Lambda + Lambda -bar production at midrapidity from Au+Au collisions at sqrt[sNN]=130 GeV (2002)

Clemens Adler Z. Ahammed C. Allgower Jens Berger Thomas Dietel Dominik Bernhard Flierl Jens Sören Lange Reinhard Stock Christof Struck et al. STAR Collaboration

We report STAR results on the azimuthal anisotropy parameter v2 for strange particles K0S, Lambda , and Lambda -bar at midrapidity in Au+Au collisions at sqrt[sNN]=130 GeV at the Relativistic Heavy Ion Collider. The value of v2 as a function of transverse momentum, pt, of the produced particle and collision centrality is presented for both particles up to pt~3.0 GeV/c. A strong pt dependence in v2 is observed up to 2.0 GeV/c. The v2 measurement is compared with hydrodynamic model calculations. The physics implications of the pt integrated v2 magnitude as a function of particle mass are also discussed.

Disappearance of back-to-back high-pT hadron correlations in central Au+Au collisions at sqrt[sNN]=200 GeV (2003)

Clemens Adler Z. Ahammed C. Allgower Jens Berger Thomas Dietel Dominik Bernhard Flierl Thorsten Kollegger Jens Sören Lange Reinhard Stock Christof Struck et al. STAR Collaboration

Azimuthal anisotropy (v2) and two-particle angular correlations of high pT charged hadrons have been measured in Au+Au collisions at sqrt[sNN]=130 GeV for transverse momenta up to 6 GeV/c, where hard processes are expected to contribute significantly. The two-particle angular correlations exhibit elliptic flow and a structure suggestive of fragmentation of high pT partons. The monotonic rise of v2(pT) for pT<2 GeV/c is consistent with collective hydrodynamical flow calculations. At pT>3 GeV/c, a saturation of v2 is observed which persists up to pT=6 GeV/c.

Azimuthally sensitive Hanbury Brown-Twiss interferometry in Au+Au collisions at sqrt[sNN]=200 GeV (2004)

J. Adams Clemens Adler Jens Berger Thomas Dietel Dominik Bernhard Flierl Thorsten Kollegger Jens Sören Lange Reinhard Stock Christof Struck et al. STAR Collaboration

We present the results of a systematic study of the shape of the pion distribution in coordinate space at freeze-out in Au+Au collisions at BNL RHIC using two-pion Hanbury Brown-Twiss (HBT) interferometry. Oscillations of the extracted HBT radii versus emission angle indicate sources elongated perpendicular to the reaction plane. The results indicate that the pressure and expansion time of the collision system are not sufficient to completely quench its initial shape.

Photon and neutral pion production in Au + Au collisions at sqrt[sNN ]=130 GeV (2004)

J. Adams Clemens Adler Jens Berger Thomas Dietel Dominik Bernhard Flierl Thorsten Kollegger Jens Sören Lange Reinhard Stock Christof Struck et al. STAR Collaboration

We report inclusive photon measurements about midrapidity ( |y| <0.5 ) from 197 Au + 197 Au collisions at sqrt[sNN ]=130 GeV at RHIC. Photon pair conversions were reconstructed from electron and positron tracks measured with the Time Projection Chamber (TPC) of the STAR experiment. With this method, an energy resolution of Delta E/E ~ 2% at 0.5 GeV has been achieved. Reconstructed photons have also been used to measure the transverse momentum ( pt ) spectra of pi 0 mesons about midrapidity ( |y| <1 ) via the pi 0 --> gamma gamma decay channel. The fractional contribution of the pi 0 --> gamma gamma decay to the inclusive photon spectrum decreases by 20%±5% between pt =1.65 GeV/c and pt =2.4 GeV/c in the most central events, indicating that relative to pi 0 --> gamma gamma decay the contribution of other photon sources is substantially increasing.

Rapidity and centrality dependence of proton and antiproton production from 197Au + 197Au collisions at sqrt[SNN ]=130 GeV (2004)

J. Adams Clemens Adler Jens Berger Thomas Dietel Dominik Bernhard Flierl Thorsten Kollegger Jens Sören Lange Reinhard Stock Christof Struck et al. STAR Collaboration

We report on the rapidity and centrality dependence of proton and antiproton transverse mass distributions from 197Au + 197Au collisions at sqrt[sNN ]=130 GeV as measured by the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). Our results are from the rapidity and transverse momentum range of |y| <0.5 and 0.35< pt <1.00 GeV/c . For both protons and antiprotons, transverse mass distributions become more convex from peripheral to central collisions demonstrating characteristics of collective expansion. The measured rapidity distributions and the mean transverse momenta versus rapidity are flat within |y| <0.5 . Comparisons of our data with results from model calculations indicate that in order to obtain a consistent picture of the proton (antiproton) yields and transverse mass distributions the possibility of prehadronic collective expansion may have to be taken into account.

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