Tue·Jul 28, 2009Tuesday·July 28, 2009

1. 01*

   J/$\psi$ Production in p+p and d+Au Collisions at $\sqrt{S_{NN}}$ = 200 GeV at STAR

   Chris Perkins (for the STAR Collaboration)🇺🇸

   We present analysis of J/$\psi$ production over the range $-1.0<\eta <4.2$ in p+p and d+Au collisions using di-electron data taken during the 2008 run with the STAR experiment at Brookhaven National Laboratory. STAR's unique forward capabilities, especially the Forward Meson Spectrometer electromagnetic calorimeter, allow us the possibility of investigating the intrinsic charm components of the proton wave function using high-$x_F$ forward particles produced in asymmetric partonic collisions. Mid-rapidity measurements in d+Au collisions extend our understanding of the mechanisms underlying heavy quarkonium production and its transport through cold nuclear matter.

   nucl-exNPA(2009)·7 citations
2. 02*

   Investigating Sources of Angular Correlations at High pT in Nucleon-Nucleon and Nucleus-Nucleus Collisions at the CERN SPS

   Marek Szuba (for the NA49 Collaboration)🇵🇱

   Angular correlations of high-pT hadrons can serve as a probe of interactions of partons with the dense medium produced in high-energy heavy-ion collisions but other effects may also be important at SPS energies. To study the various contributions, NA49 has performed an energy and system-size scan of two-particle azimuthal correlations in Pb+Pb, Si+Si and p+p collisions at sqrt(sNN) = 17.3 GeV, as well as central Pb+Pb collisions at 6.3, 7.6, 8.8 and 12.3 GeV. These results were compared to UrQMD simulations. NA49 results show a flattened away side of C2(dphi) in central Pb+Pb (Au+Au) collisions which depends weakly on collision energy even for low SPS energies. This is at odds with the standard scenario of parton energy loss. On the other hand, the near-side peak amplitude drops visibly with decreasing collision energy, turning into a depletion below sqrt(sNN) = 8.8 GeV. UrQMD describes the correlation functions on the away side but disagrees on the near side.

   nucl-exNPA(2009)·3 citations
3. 03*

   Jpsi and dielectron photoproduction measurements with PHENIX

   Zaida Conesa del Valle (for the PHENIX Collaboration)🇫🇷

   Jpsi and dielectron photoproduction measurements in ultra-peripheral Au+Au collisions at 200 GeV with the PHENIX experiment are presented. The triggered events correspond to those accompanied with forward neutron emission from the Au dissociation. Jpsi and high-mass dielectron cross sections and pT distributions are consistent with various theoretical calculations.

   nucl-exNPA(2009)·1 citation
4. 04*

   Measurement of ${\pi }^0$ and $\gamma$ in d+Au collisions at $\sqrt{s_{NN}}=$ 200 GeV by PHENIX experiment

   Ondrej Chvala (for the PHENIX collaboration)🇺🇸

   Previous results indicated that high $p_T$ particle suppression in Au+Au interactions is a final state effect, since R${}_{dA}$ ratios were compatible with unity, albeit within large experimental errors. It is important to test this conclusion to higher precision since the modification of structure functions may be involved. Recent d+Au data taken in 2008 improve the integrated luminosity by about a factor of thirty compared to the 2003 data. A more precise measurement of both ${\pi }^0$ and $\gamma$ at higher $p_T$ will shed new light on whether the initial state in the heavy nuclei is modified.

   nucl-exhep-exNPA(2009)·0 citations
5. 05*

   J/psi production in Au+Au and Cu+Cu collisions at sqrt(sNN) = 200 GeV at STAR

   Daniel Kikola (for the STAR Collaboration)🇺🇸

   J/psi production is considered to be a sensitive probe of the properties of quark gluon plasma created in nucleus+nucleus collisions at RHIC. In this article, the recent analysis of mid-rapidity (|y| < 1) J/psi production via the dielectron decay channel in Au+Au (year 2007) and Cu+Cu (year 2005) collisions at sqrt(sNN) = 200 GeV at STAR is reported. It is compared to STAR p+p results in order to study the nuclear modification factor as a function of transverse momentum and centrality. The results are compared to previously published data and available theoretical models.

   nucl-exhep-exNPA(2009)·2 citations
6. 06*

   Anomalous \phi Meson Suppression in Au+Au Collisions at \sqrt{s_{NN}}=200 GeV Measured by the PHENIX Experiment at RHIC

   Maxim Naglis (for the PHENIX collaboration)🇮🇱

   The PHENIX experiment at RHIC has measured the \phi-meson production at mid-rapidity in p+p, d+Au, Cu+Cu and Au+Au collisions at \sqrt{s_{NN}}=200 GeV via the K^+K^- decay mode. The transverse momentum spectra of the \phi-meson and the nuclear modification factor as a function of centrality are reviewed here.

   nucl-exhep-exNPA(2009)·9 citations
7. 07*

   QCD Phase Diagram: Phase Transition, Critical Point and Fluctuations

   Bedangadas Mohanty🇮🇳

   A summary of discussions on selected topics related to QCD phase diagram, phase transition, critical point, fluctuation and correlations at the Quark Matter 2009 conference are presented.

   nucl-exhep-phnucl-thNPA(2009)·98 citations
8. 08*

   Feasibility studies of the time-like proton electromagnetic form factor measurements with PANDA at FAIR

   M. Sudol🇫🇷 · M.C. Mora Espi🇩🇪 · E. Becheva🇫🇷 · J. Boucher🇫🇷 · T. Hennino🇫🇷 · R. Kunne🇫🇷 · D. Marchand🇫🇷 · S. Ong🇫🇷 · B. Ramstein🇫🇷 · J. Van de Wiele🇫🇷 · T. Zerguerras🇫🇷 · F. Maas🇩🇪 and 5 other authors

   The possibility of measuring the proton electromagnetic form factors in the time-like region at FAIR with the \PANDA detector is discussed. Detailed simulations on signal efficiency for the annihilation of $\bar{p}+p$ into a lepton pair as well as for the most important background channels have been performed. It is shown that precision measurements of the differential cross section of the reaction $\bar{p}+p\to e^{+}+e^{-}$ can be obtained in a wide angular and kinematical range. The individual determination of the moduli of the electric and magnetic proton form factors will be possible up to a value of momentum transfer squared of $q^2\simeq 14$ (GeV/c)${}^2$. The total $\bar{p}+p\to e^{+}+e^{-}$ cross section will be measured up to $q^2\simeq 28$ (GeV/c)${}^2$. The results obtained from simulated events are compared to the existing data. Sensitivity to the two photons exchange mechanism is also investigated.

   nucl-exEPJA(2010)·52 citations
9. 09*

   The NA61/SHINE Experiment at the CERN SPS

   Andras Laszlo (for the NA61/SHINE Collaboration)🇭🇺

   The physics goals, the detector and its performance as well as status and plans of the NA61/SHINE experiment at the CERN SPS accelerator are presented.

   nucl-exNPA(2009)·16 citations
10. 10*

    Highlights from STAR: probing the early medium in heavy ion collisions

    Gang Wang (for the STAR Collaboration)🇺🇸

    We present highlights of recent results from the STAR Collaboration at RHIC, focusing on the properties of the early medium created in heavy ion collisions. We emphasize the strangeness production including the observation of a hypernucleus (the hypertriton), the observation of reaction-plane-dependent angular correlation of charged particles searching for local strong parity violation effects in heavy ion collisions, and the evaluation of the medium viscosity from measurements of elliptic flow. We discuss STAR's plan for the "Critical Point Search" program at RHIC.

    nucl-exNPA(2009)·6 citations
11. 11*

    Footprints of the (Nearly) Perfect Liquid

    Aihong Tang🇺🇸

    In relativistic heavy-ion collisions, the system has gone through a series of evolution, almost at every stage of its evolution it leaves behind footprints in flow observable. Those footprints contain valuable information of the bulk property of the (nearly) perfect liquid. By examing footprints of the nearly perfect liquid, we address a few important issues, including the ideal hydrodynamic limit, estimation of $\eta /s$, testing the Number of Constituent Quark scaling at low energy, in small system, at large transverse momentum, and in forward region. Future prospect of flow study is discussed.

    nucl-exNPA(2009)·7 citations
12. 12*

    Exploration of jet energy loss via direct $\gamma$-charged particle azimuthal correlation measurements

    A. M. Hamed🇺🇸

    The multiplicities of charged particles azimuthally associated with direct photons and ${\pi }^0$ have been measured for Au+Au, p+p, and d+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV in the STAR experiment. Charged particles with transverse momentum 0.5 $<$ $p_T^{h^{\pm }}$ $<$ 16 GeV/c for p+p and d+Au, and 3 $<$ $p_T^{h^{\pm }}$ $<$ 16 GeV/c for Au+Au and pseudorapidity $\mid \eta \mid$ $\le$ 1.5 in coincidence with direct photons and ${\pi }^0$ of high transverse momentum 8 $<$ $p_T^{\gamma ,{\pi }^0}$ $<$ 16 GeV/c at $\mid \eta \mid$ $\le$ 0.9 have been used for this analysis. Within the considered range of kinematics, the observed suppressions of the associated yields per direct $\gamma$ in central Au+Au relative to p+p and d+Au are similar and constant with direct photon fractional energy $z_T$ ($z_T=p_T^{h^{\pm }}/p_T^{\gamma }$). The measured suppressions of the associated yields with direct $\gamma$ are comparable to those with ${\pi }^0$. The data are compared to theoretical predictions.

    nucl-exNPA(2009)·6 citations
13. 13*

    Strangeness Production in Heavy-Ion Collisions at STAR

    Anthony R Timmins (for the STAR Collaboration)🇺🇸

    We report an overview of strangeness production in Cu+Cu and Au+Au collisions at the energies $\sqrt{s_{NN}}=$ 62.4 and 200 GeV. We show new mid-rapidly $dN/dy$ results for the $K_S^0$, $\Lambda$, $\Xi$, $\Omega$ particles in Cu+Cu \sNN{62} collisions and compare to results in Au+Au \sNN{62} collisions. We show new results for mid-$p_T$ $\Lambda /K_S^0$ ratios in Cu+Cu \sNN{62} collisions and again compare to ratios in Au+Au \sNN{62} collisions. Finally, we show the high-$p_T$ ($\sim 6.2$ GeV/c) $R_{AA}(K_S^0)$ as a function of system size in Au+Au \sNN{200} collisions and compare to $R_{AA}(\pi )$.

    nucl-exNPA(2009)·11 citations
14. 14*

    Full Jet Reconstruction in Heavy Ion Collisions

    Sevil Salur🇺🇸

    Full jet reconstruction has traditionally been thought to be difficult in heavy ion events due to large multiplicity backgrounds. The search for new physics in high luminosity p+p collisions at the LHC similarly requires the precise measurement of jets over large backgrounds caused by pile up; this has motivated the development of a new generation of jet reconstruction algorithms which are also applicable in the heavy ion environment. We review the latest results on jet-medium interactions as seen in A+A collisions at RHIC, focusing on the new techniques for full jet reconstruction.

    nucl-exNPA(2009)·26 citations
15. 15*

    Upsilon production in d+Au collisions at STAR

    Haidong Liu (for the STAR Collaboration)🇨🇳

    We present the analysis of ${\rm Y}\to e^{+}{e}^{-}$ production in d+Au collisions at $\sqrt{s_{NN}}=200$ GeV from the STAR experiment. Using higher level dedicated ${\rm Y}$ triggers, STAR has sampled 32 nb${}^{-1}$ of integrated luminosity in year 2008 d+Au run. The cross section is found as $BR\times {(\frac{d\sigma }{dy})}_{y=0}^{{\rm Y}(1S+2S+3S)}=35\pm 4(stat.)\pm 5(sys.)$ nb and it is consistent with NLO CEM prediction with anti-shadowing effects. In addition we calculated the nuclear modification factor $R_{dAu}=0.98\pm 0.32(stat.)\pm 0.28(sys.)$, which suggests the ${\rm Y}(1S+2S+3S)$ production follows $N_{bin}$ scaling.

    nucl-exhep-exNPA(2009)·19 citations
16. 16*

    Study of the Fluctuations of Net-charge and Net-protons Using Higher Order Moments

    Tapan K. Nayak (for the STAR Collaboration)🇮🇳

    We present the STAR preliminary results on mid-rapidity and low transverse momentum mean, standard deviation, skewness, and kurtosis of net-charge and net-proton distributions in Au+Au and Cu+Cu collisions at $\sqrt{s_{NN}}$ = 200 GeV for various collision centralities. All the measured high moments of these distributions can be scaled by the number of participating nucleons, consistent with the soft process emissions. The ratios of fourth to second order cumulants of both the net-charge and net-proton distributions are consistent with models without QCD critical point.

    nucl-exNPA(2009)·24 citations
17. 17*

    Direct Photon-Hadron Correlations Measured with PHENIX

    Megan Connors (for the PHENIX Collaboration)🇺🇸

    Direct photon-hadron correlations greatly improve our ability to perform jet tomography in heavy-ion collisions because the momentum of the direct photon can be used to constrain the initial momentum of the opposing jet. By comparing the spectrum of away-side hadrons observed in heavy ion collisions to the spectrum seen in nucleon collisions we can quantify the medium modification to the fragmentation function due to energy loss of the away-side parton. High $p_T$ direct photon-hadron correlations have been measured with the PHENIX detector using a statistical subtraction method to remove the photon contribution from meson decays. The increased integrated luminosity in the most recent Au+Au RHIC run at $\sqrt{s_{NN}}$ = 200 GeV provides substantially improved statistical precision and enhances the kinematic reach. These measurements are compared to PHENIX p+p results and several theoretical models of energy loss. In addition, we compare direct photon-hadron and ${\pi }^0$-hadron correlations.

    nucl-exNPA(2009)·11 citations
18. 18*

    A GEANT4 Monte-Carlo Simulation Code for precision beta spectroscopy

    F. Wauters🇧🇪 · I. Kraev🇧🇪 · D. Zakoucky🇨🇿 · M. Beck🇧🇪 · V.V. Golovko🇧🇪 · V.Yu. Kozlov🇧🇪 · T. Phalet🇧🇪 · M. Tandecki🇧🇪 · E. Traykov🇧🇪 · S. Van Gorp🇧🇪 · N. Severijns🇧🇪

    The measurement of the beta asymmetry parameter in nuclear beta decay is a potentially very sensitive tool to search for non V-A components in the charge-changing weak interaction. To reach the required precision (percent level) all effects that modify the emission pattern of the beta radiation, i.e. the geometry of the setup, the effect of the magnetic field on the trajectories of beta particles as well as (back)scattering in the source, on the sample holder and on the detector, have to be correctly taken into account in the analysis of the data. A thorough study of these effects and a new method based on detailed GEANT4 Monte-Carlo simulations that was developed for this purpose is presented here. The code was developed for beta asymmetry measurements by means of the Low Temperature Nuclear Orientation (LTNO) method, but can in principle be generalized to other experimental setups using other polarization techniques.

    nucl-exNucl.Instrum.Meth.A(2009)·14 citations
19. 19*

    Status of ATLAS and Preparation for the Pb-Pb Run

    Jiri Dolejsi (for the ATLAS Collaboration)🇨🇿

    The ATLAS experiment took its first beam data in September 2008 and is actively preparing for the planned start of LHC collision data-taking in 2009. This preparation includes hardware and software commissioning, as well as calibration and cosmic data analysis. The status and performance of the ATLAS detector will be discussed, with a view towards the Pb+Pb run expected in 2010.

    nucl-exhep-exNPA(2009)·5 citations
20. 20*

    Measurements of soft and intermediate $p_T$ photons from hot and dense matter at RHIC-PHENIX

    Yorito Yamaguchi (for the PHENIX collaboration)🇯🇵

    The measurements of direct photons in $1.0<p_T<5.0$GeV/$c$ for p+p and Au+Au collisions have been made through the virtual photon method at PHENIX. The fraction of the virtual direct photon component to the inclusive $e^{+}{e}^{-}$ yield is determined by a shape analysis using the $e^{+}{e}^{-}$ mass spectra in $m_{ee}<300$MeV/$c^2$ for $1.0<p_T<5.0$GeV/$c$. The real direct photon spectra in p+p and Au+Au collisions are obtained from the virtual direct photon fractions, and a significant excess over a binary-scaled p+p result is seen in Au+Au collisions. Hydrodynamical models which reproduce the Au+Au result indicate the initial temperature of the matter is higher than the critical temperature of QGP. The d+Au data taken in 2008 are promising to evaluate the contribution of the nuclear effects because of its large statistics.

    nucl-exNPA(2009)·1 citation
21. 21*

    Open Heavy Flavor Production in Heavy Ion Collisions

    J.C. Dunlop🇺🇸

    The interaction of heavy partons, charm and beauty, with the matter created in heavy ion collisions has been of great interest in recent years. Heavy partons were predicted to interact less strongly with the matter than light partons. In apparent contrast to these predictions, unexpectedly strong suppression of non-photonic electrons from heavy flavor decays has been seen. However, significant experimental uncertainties remain, both in the measurements themselves and in the separation of the contribution from charm and beauty, which have complicated the interpretation of these results. The current experimental situation is critically reviewed and prospects for making these measurements more easily interpretable discussed.

    nucl-exhep-exNPA(2009)·4 citations
22. 22*

    Highlights from PHENIX-I: Initial State and Early Times

    Michael Leitch (for the PHENIX collaboration)🇺🇸

    We will review the latest physics developments from PHENIX concentrating on cold nuclear matter effects, the initial state for heavy-ion collisions, and probes of the earliest stages of the hot-dense medium created in those collisions. Recent physics results from p + p and d + Au collisions; and from direct photons, quarkonia and low-mass vector mesons in A+A collisions will be highlighted. Insights from these measurements into the characteristics of the initial state and about the earliest times in heavy-ion collisions will be discussed.

    nucl-exNPA(2009)·4 citations
23. 23*

    Jet Studies in STAR via Di-jet Triggered (2+1) Multi-hadron Correlations

    Kolja Kauder (for the STAR Collaboration)🇺🇸

    We explore jet-medium interactions via the recently developed multi-hadron correlation or "2+1" technique. We restrict the di-jet kinematics by selecting a pair of approximately back-to-back high pT hadron triggers and study associated particles. Here we present our study of di-jet systematics comparing the measurements of associate yields and spectra in 200 GeV Au+Au and d+Au collisions in two different scenarios. We present Sum(pT) as an estimate for energy loss. First findings indicate little to no energy loss in the symmetric "2+1" scenario whereas model predictions are about 2 GeV.

    nucl-exhep-exNPA(2009)·3 citations
24. 24*

    Quarkonia measurement in p+p and d+Au collisions at sqrt(s)=200 GeV by PHENIX Detector

    Cesar Luiz da Silva (PHENIX Collaboration)🇺🇸

    We report new quarkonia measurements necessary to understand production mechanisms and cold nuclear matter effects in the yields observed at RHIC energy. Results obtained in p+p collisions collected during the 2006 RHIC Run include J/psi, Psi' and Upsilon differential cross sections as well as J/psi polarization. Revisited interpretations of the published J/psi nuclear modification factors and statistically improved observations in d+Au collisions taken in the 2008 Run are also discussed in the view of the recent understanding of the initial state effects and breakup cross section.

    nucl-exhep-exNPA(2009)·26 citations
25. 25*

    NA60 results on phi production in the hadronic and leptonic channels in In-In collisions at 158 GeV

    Alessandro De Falco (for the NA60 Collaboration)🇮🇹

    The NA60 experiment at the CERN SPS studied phi meson production in In-In collisions at 158 A GeV via muon and kaon decay channels. Results in the hadronic channel are presented for the first time. These are discussed in the framework of the so-called phi puzzle through the comparison with the previous NA60 measurements in the muon channel. The yield and inverse m_T slopes observed in the two channels are compatible within errors, showing that the large discrepancies seen in Pb-Pb collisions between NA50 (muon pairs) and NA49 (kaon pairs) are not seen in the NA60 In-In data.

    nucl-exhep-exNPA(2009)·2 citations
26. 26*

    Results on angular distributions of thermal dileptons in nuclear collisions

    Gianluca Usai (for the NA60 collaboration)🇮🇹

    The NA60 experiment at the CERN SPS has studied dimuon production in 158 AGeV In-In collisions. The strong pair excess above the known sources found in the mass region $0.2<M<2.5$ GeV has been previously interpreted as thermal radiation. In this paper results on the associated angular distributions for $M<1$ GeV, as measured in the Collins-Soper reference frame, are presented. The structure function parameters $\lambda$, $\mu$, $\nu$ are consistent with zero and the projected polar and azimuth angle distributions are uniform. The absence of any polarization is consistent with the interpretation of the excess dimuons as thermal radiation from a randomized system.

    nucl-exhep-exNPA(2009)·0 citations
27. 27*

    Baryon Stopping in Au+Au and p+p collisions at 62 and 200 GeV

    Hans Hjersing Dalsgaard🇩🇰

    BRAHMS has measured rapidity density distributions of protons and antiprotons in both p+p and Au+Au collisions at 62 GeV and 200 GeV. From these distributions the yields of so-called "net-protons", that is the difference between the proton and antiproton yields, can be determined. The rapidity dependence of the net-proton yields from peripheral Au+Au collisions is found to have a similar behaviour to that found for the p+p results, while a quite different rapidity dependence is found for central Au+Au collisions. The net-proton distributions can be used together with model calculations to find the net-baryon yields as a function of rapidity, thus yielding information on the average rapidity loss of beam particles, the baryon transport properties of the medium, and the amount of "stopping" in these collisions.

    nucl-exhep-exNPA(2009)·1 citation
28. 28*

    Lessons from PHOBOS

    Wit Busza (for the PHOBOS collaboration)🇺🇸

    In June 2005 the PHOBOS Collaboration completed data taking at RHIC. In five years of operation PHOBOS recorded information for Au+Au at $\sqrt{s_{NN}}$ = 19.6, 62.4, 130, and 200 GeV, Cu+Cu at 22.4, 62.4 and 200 GeV, d+Au at 201 GeV, and p+p at 200 and 410 GeV, altogether more than one billion collisions. Using these data we have studied the energy and centrality dependence of the global properties of charged particle production over essentially the full 4$\pi$ solid angle and (for pions near mid rapidity) charged particle spectra down to transverse momenta below 30 MeV/c. We have also studied correlations of particles separated in pseudorapidity by up to 6 units. We find that the global properties of heavy ion collisions can be described in terms of a small number of simple dependencies on energy and centrality, and that there are strong correlations between the produced particles. To date no single model has been proposed which describes this rich phenomenology. In this talk I summarize what the data is explicitly telling us.

    nucl-exNPA(2009)·10 citations
29. 29*

    Experimental Studies of Hadronization and Parton Propagation in the Space-Time Domain

    W. K. Brooks🇨🇱 · H. Hakobyan🇨🇱

    Over the past decade, new data have become available from DESY, Jefferson Lab, Fermilab, and RHIC that connect to parton propagation and hadron formation. Semi-inclusive DIS on nuclei, the Drell-Yan reaction, and heavy-ion collisions all bring different kinds of information on parton propagation within a medium, while the most direct information on hadron formation comes from the DIS data. Over the next decade one can hope to begin to understand these data within a unified picture. We briefly survey the most relevant data and the common elements of the physics picture, then highlight the new Jefferson Lab data from CLAS, and close with prospects for the future.

    ↳ hep-exhep-phnucl-exNPA(2009)·22 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.