Transverse Momentum and Centrality Dependence of High-pT Nonphotonic Electron Suppression in Au+Au Collisions at √sNN=200 GeV.

The STAR collaboration at the BNL Relativistic Heavy-Ion Collider (RHIC) reports measurements of the inclusive yield of nonphotonic electrons, which arise dominantly from semileptonic decays of heavy flavor mesons, over a broad range of transverse momenta (1.2<pT<10  GeV/c) in p+p, d+Au, and Au+Au collisions at √sNN=200  GeV. The nonphotonic electron yield exhibits an unexpectedly large suppression in central Au+Au collisions at high pT, suggesting substantial heavy-quark energy loss at RHIC. The centrality and pT dependences of the suppression provide constraints on theoretical models of suppression

Forward Λ production and nuclear stopping power in d+Au collisions at √sNN=200 GeV

We report the measurement of Λ and Λ¯ yields and inverse slope parameters in d+Au collisions at √sNN=200 GeV at forward and backward rapidities (y=±2.75), using data from the STAR forward time projection chambers. The contributions of different processes to baryon transport and particle production are probed exploiting the inherent asymmetry of the d+Au system. Comparisons to model calculations show that baryon transport on the deuteron side is consistent with multiple collisions of the deuteron nucleons with gold participants. On the gold side, HIJING-based models without a hadronic rescattering phase do not describe the measured particle yields, while models that include target remnants or hadronic rescattering do. The multichain model can provide a good description of the net baryon density in d+Au collisions at energies currently available at the BNL Relativistic Heavy Ion Collider, and the derived parameters of the model agree with those from nuclear collisions at lower energies

Spin-dependent Forward Particle Correlations in p+p Collisions at s=200\sqrt{s} = 200 GeV

The STAR collaboration has reported precision measurements of the transverse single spin asymmetries for the production of the $\pi^0$ mesons from polarized proton collisions at $\sqrt{s} = 200$ GeV. These measurements were obtained using modular forward detectors. The Forward Meson Spectrometer (FMS), covering a region of $2.5 < \eta < 4.0$, and its engineering prototype, provide increased acceptance, as needed for spin-dependent correlation studies that could disentangle contributions to the forward \$pi^0$ asymmetries. We report on the status of the analysis.Comment: 4 pages, 2 figures, to be published in the proceedings of the 18th International Spin Physics Symposium (SPIN2008), October 6-11, 2008, Charlottesville, Virginia, US

Long range rapidity correlations and jet production in high energy nuclear collisions

The STAR Collaboration at the Relativistic Heavy Ion Collider presents a systematic study of high-transverse-momentum charged-di-hadron correlations at small azimuthal pair separation Δϕ in d+Au and central Au+Au collisions at √sNN=200 GeV. Significant correlated yield for pairs with large longitudinal separation Δη is observed in central Au+Au collisions, in contrast to d+Au collisions. The associated yield distribution in Δη×Δϕ can be decomposed into a narrow jet-like peak at small angular separation which has a similar shape to that found in d+Au collisions, and a component that is narrow in Δϕ and depends only weakly on Δη, the “ridge.” Using two systematically independent determinations of the background normalization and shape, finite ridge yield is found to persist for trigger pt>6 GeV/c, indicating that it is correlated with jet production. The transverse-momentum spectrum of hadrons comprising the ridge is found to be similar to that of bulk particle production in the measured range (2<pt<4 GeV/c)

Beam-energy and system-size dependence of dynamical net charge fluctuations

We present measurements of net charge fluctuations in Au+Au collisions at √sNN=19.6, 62.4, 130, and 200 GeV, Cu+Cu collisions at √sNN=62.4 and 200 GeV, and p+p collisions at √s=200 GeV using the dynamical net charge fluctuations measure ν+−,dyn. We observe that the dynamical fluctuations are nonzero at all energies and exhibit a modest dependence on beam energy. A weak system size dependence is also observed. We examine the collision centrality dependence of the net charge fluctuations and find that dynamical net charge fluctuations violate 1/Nch scaling but display approximate 1/Npart scaling. We also study the azimuthal and rapidity dependence of the net charge correlation strength and observe strong dependence on the azimuthal angular range and pseudorapidity widths integrated to measure the correlation

Stem cell highways: signalling beats trafficking?

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Production of Σ(1385)± and Ξ(1530)0 in proton-proton collisions at √s = 7 TeV

The production of the strange and double-strange baryon resonances (Sigma (1385)(+/-), Xi (1530)(0)) has been measured at mid-rapidity (vertical bar y vertical bar < 0.5) in proton-proton collisions at root s = 7 TeV with the ALICE detector at the LHC. Transverse momentum spectra for inelastic collisions are compared to QCD-inspired models, which in general underpredict the data. A search for the phi (1860) pentaquark, decaying in the Xi pi channel, has been carried out but no evidence is seen

Event-by-event mean pT fluctuations in pp and Pb-Pb collisions at the LHC

Event-by-event fluctuations of the mean transverse momentum of charged particles produced in pp collisions at s√ = 0.9, 2.76 and 7 TeV, and Pb–Pb collisions at sNN‾‾‾‾√ = 2.76 TeV are studied as a function of the charged-particle multiplicity using the ALICE detector at the LHC. Dynamical fluctuations indicative of correlated particle emission are observed in all systems. The results in pp collisions show little dependence on collision energy. The Monte Carlo event generators PYTHIA and PHOJET are in qualitative agreement with the data. Peripheral Pb–Pb data exhibit a similar multiplicity dependence as that observed in pp. In central Pb–Pb, the results deviate from this trend, featuring a significant reduction of the fluctuation strength. The results in Pb–Pb are in qualitative agreement with previous measurements in Au–Au at lower collision energies and with expectations from models that incorporate collective phenomena

Elliptic flow of identified hadrons in Pb-Pb collisions at root(NN)-N-s=2.76 Tev

The elliptic flow coefficient (v(2)) of identified particles in Pb-Pb collisions at root s(NN) = 2.76 TeV was measured with the ALICE detector at the Large Hadron Collider (LHC). The results were obtained with the Scalar Product method, a two-particle correlation technique, using a pseudo-rapidity gap of |Delta eta| > 0.9 between the identified hadron under study and the reference particles. The v (2) is reported for pi(+/-), K-+/-, K-S(0), p+(p) over bar, phi, Lambda+(Lambda) over bar, Xi+(Xi) over bar (+) and Omega(-)+(Omega) over bar (+) in several collision centralities. In the low transverse momentum (p(T)) region, p(T) 3 GeV/c

Measurement of visible cross sections in proton- lead collisions at √sNN = 5.02 TeV in van der Meer scans with the ALICE detector

In 2013, the Large Hadron Collider provided proton-lead and lead-proton collisions at the center-of-mass energy per nucleon pair √ sNN = 5.02 TeV. Van der Meer scans were performed for both configurations of colliding beams, and the cross section was measured for two reference processes, based on particle detection by the T0 and V0 detectors, with pseudo-rapidity coverage 4.6 &lt; η &lt; 4.9, −3.3 &lt; η &lt; −3.0 and 2.8 &lt; η &lt; 5.1, −3.7 &lt; η &lt; −1.7, respectively. Given the asymmetric detector acceptance, the cross section was measured separately for the two configurations. The measured visible cross sections are used to calculate the integrated luminosity of the proton-lead and lead-proton data samples, and to indirectly measure the cross section for a third, configuration-independent, reference process, based on neutron detection by the Zero Degree Calorimeters