Wed·Jul 29, 2009Wednesday·July 29, 2009

1. 01*

   Heavy Ion Physics Program in CMS Experiment

   Olga Kodolova🇷🇺 · Michael Murray (for the CMS collaboration)🇺🇸

   We present the capabilities of the CMS experiment to explore the heavy-ion physics program offered by the CERN Large Hadron Collider (LHC). The prime goal of this research is to test the fundamental theory of the strong interaction (QCD) in extreme conditions of temperature, density and parton momentum fraction by colliding nuclei at energies of sqrt(s_NN) = 5.5 TeV. This presentation will give the overview of the potential of the CMS to carry out a full set of representative Pb-Pb measurements both in "soft" and "hard" regimes. Measurements include "bulk" observables -- charged hadron multiplicity, low pT inclusive hadron identified spectra and elliptic flow -- which provide information on the collective properties of the system; as well as perturbative processes - such as quarkonia, heavy-quarks, jets, gamma-jet, and high pT hadrons -- which yield "tomographic" information of the hottest and densest phases of the reaction.

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

   Is the ridge formed by aligned jet propagation and medium flow?

   Joshua Robert Konzer (For STAR Collaboration)🇺🇸

   Motivated by the recent observation that the ridge decreases with trigger particle angle (${\varphi }_s$) relative to the event plane, it is theorized that the ridge is formed by interplay between jet propagation and medium flow. Such interplay may produce asymmetry in the ridge azimuthal correlation at a fixed ${\varphi }_s$. We present an analysis of this asymmetry from STAR data. We found an asymmetric ridge with maximum asymmetry at ${\varphi }_s\approx 45^{\circ }$ concurrent with a symmetric jet at all ${\varphi }_s$.

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

   SPS energy scan results and physics prospects at FAIR

   C. Hohne🇩🇪

   Experimental studies of nucleus-nucleus collisions in the whole SPS energy range are reviewed. Selected topics such as statistical properties of the hadronic phase, strangeness production, fluctuations and correlations are discussed with regard to information on the onset of deconfinement and the critical point of strongly interacting matter. In spite of the very interesting results obtained in particular at the low SPS energies, additional data including rare probes such as charmed particles and di-leptons are required for a precise understanding of the underlying physics. An outlook about prospects and capabilities of upcoming experiments in this interesting energy region at RHIC, SPS, and in particular with CBM at FAIR, is given.

   nucl-exNPA(2009)·11 citations
4. 04*

   Probing medium-induced energy loss with direct jet reconstruction in p+p and Cu+Cu collisions at PHENIX

   Yue-Shi Lai (for the PHENIX collaboration)🇺🇸

   We present the application of a new jet reconstruction algorithm that uses a Gaussian filter to locate and reconstruct the jet energy to p+p and heavy ion data from the PHENIX detector. This algorithm is combined with a fake jet rejection scheme that provides efficient jet reconstruction with an acceptable fake rate. We show our first results on the measured jet spectra, jet--jet angular correlation in p+p and Cu+Cu collisions.

   nucl-exhep-exNPA(2009)·43 citations
5. 05*

   Highlights from PHENIX II: Exploring the QCD medium

   Carla M. Vale (for the PHENIX Collaboration)🇺🇸

   Much of the present experimental effort at RHIC is now directed towards understanding the properties of the hot and dense colored medium created in A+A collisions. Recent results from PHENIX on the dynamical evolution of the medium and its response to high momentum probes are presented, and their impact on our overall understanding of heavy-ion collisions is discussed.

   nucl-exNPA(2009)·3 citations
6. 06*

   D^0 measurements in Au+Au Collisions at \sqrt{s_{NN}} = 200 GeV using the STAR Silicon Inner Tracker

   Sarah LaPointe (for the STAR Collaboration)🇺🇸

   We present preliminary results from D^0 meson measurements through the hadronic decay channel in minimum bias Au+Au collisions at \sqrt{s_{NN}} = 200 GeV at STAR. The measurements are performed using a secondary vertexing technique that exploits the resolution given by the Silicon detectors available in STAR.

   nucl-exNPA(2009)·5 citations
7. 07*

   Estimation of shear viscosity based on transverse momentum correlations

   Monika Sharma (for the STAR Collaboration)🇰🇼

   Event anisotropy measurements at RHIC suggest the strongly interacting matter created in heavy ion collisions flows with very little shear viscosity. Precise determination of "shear viscosity-to-entropy" ratio is currently a subject of extensive study. We present preliminary results of measurements of the evolution of transverse momentum correlation function with collision centrality of $Au+Au$ interactions at $\sqrt{s_{NN}}$ = 200 GeV. We compare two differential correlation functions, namely {\it inclusive} and a differential version of the correlation measure $\tilde{C}$ introduced by Gavin $et.al.$. These observables can be used for the experimental study of the shear viscosity per unit entropy.

   nucl-exNPA(2009)·11 citations
8. 08*

   Forward-rapidity azimuthal and radial flow of identified particles for $\sqrt{s_{NN}}$ = 200 GeV Au+Au collisions

   S.J. Sanders (for the BRAHMS Collaboration)🇺🇸

   A strong azimuthal flow signature at RHIC suggests rapid system equilibration leading to an almost perfect fluid state. The longitudinal extent of the flow behavior depends on how this state is formed and can be studied by measuring the pseudorapidity and transverse momentum dependence of the second Fourier component ($v_2(p_T)$) of the azimuthal angular distribution. We report on a measurement of identified-particle $v_2$ as a function of $p_T$ (0.5-2.0 GeV/c), centrality (0-25%, 25-50%), and pseudorapidity ($0\le \eta <3.2$) for $\sqrt{s_{NN}}=200\mathrm{GeV}$ Au+Au collisions. The BRAHMS spectrometers are used for particle identification ($\pi$, K, p) and momentum determination and the BRAHMS global detectors are used to determine the corresponding reaction-plane angles. The results are discussed in terms of the rapidity dependence of constituent quark scaling and in terms of models that develop the complete (azimuthal and radial) hydrodynamic aspects of the forward dynamics at RHIC.

   nucl-exNPA(2009)·1 citation
9. 09*

   Overview and Recent Results from BRAHMS

   F. Videbaek (for the BRAHMS Collaboration)🇺🇸

   The BRAHMS experiment was designed to measure and characterize in particular the properties of rapidity dependence of particle production in heavy ion collisions. The data-taking is now over, results of several years of analysis have been published and demonstrates several important features of the rapidity dependence, not envisioned from the start of the RHIC program. The bulk properties of the system formed at high rapidity resemble that of systems at lower energies at mid-rapidity when referenced via the baryo-chemical potential. New physics in AA are essentially observed at mid-rapidity including the demonstration that high-\pT suppression is a final state effect. Another key result is that in d+A collisions at forward rapidities where the very low-x region of the nucleus was probed, a strong suppression of pion production was observed consistent with the picture of gluon saturation. The latest results examines the centrality and rapidity dependence of nuclear stopping, the particle production of pions, collective expansion vs. rapidity, and the baryon enhancement at intermediate values of \pT .

   nucl-exNPA(2009)·23 citations
10. 10*

    Addressing the physics of the ridge by 2- and 3-particle correlations at STAR

    Pawan Kumar Netrakanti (for the STAR Collaboration)🇮🇳

    We present new results on 2-particle azimuthal ($\Delta \varphi$) correlation relative to event plane and 3-particle pseudorapidity ($\Delta \eta$) correlation at mid-rapidity in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV, measured by the STAR experiment. While jet-like correlation is symmetric, ridge is found to be asymmetric when trigger particle azimuth is between in- and out-of-plane. The charge ordering properties between associated and trigger particles are exploited to separate jet-like and ridge contributions in 3-particle $\Delta \eta$-$\Delta \eta$ correlations. We found that like-sign triplets are dominated by ridge. The separated ridge, while narrow in $\Delta \varphi$, is extremely broad in $\Delta \eta$. The ridge particles are not only uncorrelated to the trigger particle in $\Delta \eta$, but also uncorrelated between themselves.

    nucl-exnucl-thNPA(2009)·6 citations
11. 11*

    Positrons at Jefferson Laboratory

    A. W. Thomas🇺🇸

    We review the compelling case for establishing a capability to accelerate positrons at Jefferson Lab. The potential appplications range from the study of two-photon exchange and deeply-virtual Compton scattering to exploiting the charge current weak interaction to probe the flavor structure of hadrons and nuclei. There are also fascinating ideas for using such a capability to discover new physics beyond the Standard Model of nuclear and particle physics.

    nucl-exhep-exhep-phAIP Conf.Proc.(2009)·2 citations
12. 12*

    Open Heavy Flavor at PHENIX

    Alan Dion (for the PHENIX collaboration)🇺🇸

    We report on two new measurements by the PHENIX collaboration regarding open heavy flavor. The first is an additional contribution to the background in the measurement of the yield of electrons at mid-rapidity from open heavy flavor decays. We found that the $J/\Psi$ can contribute substantially to the yield at high $p_T$. PHENIX has also measured the spectrum of muons at forward rapidity from open heavy flavor decays in Cu+Cu collisions at $\sqrt{s_{NN}}$ = 200 GeV.

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

    The rapidity dependence of the proton-to-pion ratio in Au+Au and p+p collisions at sqrt(sNN) = 62.4 and 200 GeV

    P. Staszel (for the BRAHMS collaboration)🇵🇱

    The BRAHMS measured proton-to-pion ratios in Au+Au and p+p collisions at \rootsnn{62.4} and \rootsnn{200} are presented as a function of transverse momentum and collision centrality within the pseudo-rapidity range 0 < eta < 3.8 The results for Au+Au at sqrt(sNN) = 200 GeV are compared with predictions from models which incorporate hydro-dynamics, hadron rescattering and jet production, in the eta interval covered. In Au+Au collisions at sqrt(sNN) = 200 GeV, eta ~ 2.2, and at sqrt(sNN) = 62.4 GeV, eta = 0, the bulk medium can be characterized by the common value of \mi_B ~ 65 MeV. The p/pi ratios measured for these two selections display a striking agreement in the pT range covered (up to 2.2 GeV/c). At a collision energy of 62.4 GeV and at forward pseudo-rapidity we found a crossing point of p/pi+ ratios measured in central and semi-peripheral Au+Au and in p+p reactions. The crossing occurs in the narrow eta bin around value of 3.2, simultaneously in the whole covered pT range (0.3 GeV/c < pT < 2 GeV/c).

    nucl-exNPA(2009)·2 citations
14. 14*

    J/psi Elliptic Flow, High pT Suppression and Upsilon Measurements in A+A Collisions by the PHENIX Experiment

    Ermias T. Atomssa (for the PHENIX Collaboration)🇫🇷

    Three measurements that broaden the scope of the experimental investigation of quarkonia modifications in heavy ion collisions are presented. Although the current statistical precision on the first two measurements does not allow one to draw significant conclusions, J/$\psi$ elliptic flow and high pT suppression results are important proofs of principle measurements, and make the case for higher luminosities at RHIC. Finally, the first measurement of an upper limit on the nuclear modification R_AA of dielectrons in the ${\rm Y}$ mass region in Au+Au collisions is presented. The results show a significant suppression with an upper limit of 0.64 at 90% CL.

    nucl-exNPA(2009)·21 citations
15. 15*

    Measurements of jet structure and fragmentation from full jet reconstruction in heavy ion collisions at RHIC

    Elena Bruna (STAR Collaboration)🇺🇸

    Measurements of inclusive hadron suppression and di-hadron azimuthal correlations have provided important insights into jet quenching in hot QCD matter. However, they do not provide access to the energy of the hard scattering and are limited in their sensitivity since they can be affected by biases toward hard fragmentation and small energy loss. Full jet reconstruction in heavy-ion collisions enables a complete study of the modification of jet structure due to energy loss, but is challenging due to the high-multiplicity environment. We present measurements of fully reconstructed di-jets at mid-rapidity in 200 GeV p+p and central Au+Au collisions performed with the STAR detector. We compare fragmentation functions measured in 200 GeV p+p and central Au+Au collisions and assess the systematic uncertainties of their ratio.

    nucl-exNPA(2009)·39 citations
16. 16*

    Dilepton radiation measured in PHENIX probing the strongly interacting matter created at RHIC

    Y. Akiba (for the PHENIX Collaboration)🇺🇸

    PHENIX has measured $e^{+}{e}^{-}$ pairs from p+p and Au+Au collisions as function of mass and $p_T$. The data can be used to probe the properties of dense matter formed in Au+Au collision. The relation between electron pairs and virtual photons is discussed.

    nucl-exNPA(2009)·4 citations
17. 17*

    Single Particle Probes of d+Au Collisions in PHENIX

    Zvi Citron (PHENIX Collaboration)🇺🇸

    Deuteron-gold collisions provide insights into the nuclear structure function and a valuable baseline for Au+Au collisions. Measurement of the nuclear modification factor, R_{dAu}, in d+Au in the PHENIX central arms for hadrons and photons allows us to disentangle cold nuclear matter effects from the hot medium effects that are important in Au+Au collisions. In addition, the d+Au system can yield important insights into the gluonic structure of the Au nucleus. RHIC experiments have previously measured suppression of forward rapidity particle production relative to p+p scaled by the number of binary N-N collisions, but a definitive explanation of these data is thus far elusive. Correlations between hadrons with a large rapidity gap are a particularly sensitive probe of gluon saturation. We will discuss probing this physics via particle production in events tagged with high momentum particles at different rapidities, along with R_{dAu} in new forward rapidity regions.

    nucl-exNPA(2009)·4 citations
18. 18*

    Muon Production in Relativistic Cosmic-Ray Interactions

    Spencer R. Klein🇺🇸

    Cosmic-rays with energies up to $3\times 10^{20}$ eV have been observed. The nuclear composition of these cosmic rays is unknown but if the incident nuclei are protons then the corresponding center of mass energy is $\sqrt{s_{nn}}=700$ TeV. High energy muons can be used to probe the composition of these incident nuclei. The energy spectra of high-energy ($>$ 1 TeV) cosmic ray induced muons have been measured with deep underground or under-ice detectors. These muons come from pion and kaon decays and from charm production in the atmosphere. Terrestrial experiments are most sensitive to far-forward muons so the production rates are sensitive to high-$x$ partons in the incident nucleus and low-$x$ partons in the nitrogen/oxygen targets. Muon measurements can complement the central-particle data collected at colliders. This paper will review muon production data and discuss some non-perturbative (soft) models that have been used to interpret the data. I will show measurements of TeV muon transverse momentum ($p_T$) spectra in cosmic-ray air showers from MACRO, and describe how the IceCube neutrino observatory and the proposed Km3Net detector will extend these measurements to a higher $p_T$ region where perturbative QCD should apply. With a 1 km${}^2$ surface area, the full IceCube detector should observe hundreds of muons/year with $p_T$ in the pQCD regime.

    nucl-exastro-ph.HEhep-phNPA(2009)·7 citations
19. 19*

    Centrality Dependence of Two-Particle Correlations in Heavy Ion Collisions

    George S.F. Stephans (for the PHOBOS collaboration)🇺🇸

    Data from the PHOBOS detector have been used to study two-particle correlations over a broad range of pseudorapidity. A simple cluster model parameterization has been applied to inclusive two-particle correlations over a range of centrality for both Cu+Cu and Au+Au collisions at sqrt(s_NN)=200GeV. Analysis of the data for Au+Au has recently been extended to more peripheral collisions showing that the previously-observed rise in cluster size with decreasing system size eventually reaches a maximum value. Model studies have been used to quantify the significant effect of limited detector acceptance on the extracted cluster parameters. In the case of Au+Au, correlations between a trigger particle with pT>2.5GeV and inclusive associated particles have also been studied. These reveal the presence of a `ridge' at small relative azimuthal angle which extends with roughly constant amplitude out to the largest relative pseudorapidity studied. The large phase-space coverage of the PHOBOS detector has enabled a quantitative understanding of the so-called `ZYAM' parameter used in the subtraction of the contribution of elliptic flow to these triggered correlations.

    nucl-exNPA(2009)·3 citations
20. 20*

    Heavy Flavor Production and Energy Loss with Two-Particle Correlations at PHENIX

    Tatia Engelmore (for the PHENIX Collaboration)🇺🇸

    Heavy quarks are a valuable probe of the hot, dense medium created in a heavy ion collision, and are an important test of proposed mechanisms of energy loss. It was discovered that single non-photonic electrons are suppressed at a similar level to light hadrons, implying a comparable level of energy loss between light and heavy partons. Because theory has had a difficult time explaining the level of heavy quark energy loss, it is crucial to better understand charm and bottom suppression. Electron-hadron correlations have been used at PHENIX to study heavy flavor in both p+p and Au+Au collisions. In p+p the ratio of charm to bottom production has been measured using mass correlations through a partial reconstruction of the D meson. Electron-hadron angular correlations have also been used to study medium modification of heavy flavor, and we see hints of energy loss effects. A complementary study of correlated electron-muon pairs provides a clean measurement of heavy flavor production in a rapidity range not yet studied.

    nucl-exNPA(2009)·3 citations
21. 21*

    High $p_T$ Parton Energy Loss from Jet Pair Correlation Observables in the PHENIX Experiment

    Chin-Hao Chen (for the PHENIX collaboration)🇺🇸

    By tuning several experimental observables, such as momentum and reaction plane, the PHENIX experiment has performed a systematic study of high $p_T$ parton energy loss in hot nuclear matter, as well as jet induced medium modifications, such as the ridge and shoulder. Baseline d+Au measurements are also studied to provide the comparison as control of cold nuclear matter effect.

    nucl-exNPA(2009)·1 citation
22. 22*

    Measurements of Fragmentation Photons with the PHENIX Detector

    Ali Hanks (for the PHENIX Collaboration)🇺🇸

    Direct photons associated with jets provide a direct measurement of the effects of energy loss on the fragmentation of the parton as it propagates through the medium. Perturbative QCD calculations describe the direct photon cross section well at next-to-leading order, predicting a significant contribution from photons produced through parton fragmentation. Non-perturbative quantities such as the photon fragmentation function, which is poorly constrained, lead to large theoretical uncertainties. The measurement of photons correlated with jets in p+p collisions serves as an important test of these calculations and is an essential baseline measurement for comparison to A+A collisions. A natural way of selecting such photons is to study hadron-photon correlations. Results for the production of photons associated with high pT hadron triggers are presented for PHENIX p+p data at 200 GeV center-of-mass energy.

    nucl-exNPA(2009)·3 citations
23. 23*

    Energy Loss and Flavor Dynamics from Single Particle Measurements in PHENIX

    R. Belmont (for the PHENIX Collaboration)🇺🇸

    The transverse momentum spectra, yields, and ratios of charged pions, protons, and antiprotons have been studied up to 5 GeV/c in $p_T$ in 5 different centrality classes in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. These results are compared and contrasted with the observables calculated in recombination models of hadronization. They are also used to examine the color charge dependence of parton energy loss in the medium.

    nucl-exNPA(2009)·2 citations
24. 24*

    Probing High Parton Densities at Low-$x$ in d+Au Collisions at PHENIX Using the New Forward and Backward Muon Piston Calorimeters

    Beau Meredith🇺🇸

    The new forward Muon Piston Calorimeters allow PHENIX to explore low-$x$ parton distributions in d+Au collisions with hopes of observing gluon saturation. We present a two-particle azimuthal $\Delta \varphi$ correlation measurement made between a mid-rapidity particle ($|{\eta }_1|<0.35$) and a forward ${\pi }^0$ ($3.1<{\eta }_2<3.9$) wherein we compare correlation widths in d+Au to p+p and compute $I_{dA}$.

    nucl-exNPA(2009)·17 citations
25. 25*

    Using two- and Three-particle correlations to probe strongly interacting partonic matter

    Wolf G. Holzmann (for the PHENIX Collaboration)🇺🇸

    The latest two- and three-particle correlation measurements obtained by the PHENIX collaboration are presented. Three-particle correlations are consistent with the presence of conical emission patterns in the data. Two-particle correlations relative to the collision geometry reveal strong shape and yield modifications of the away-side jet, that depend on the orientation of the trigger particle with respect to the event plane. A difference in the geometry dependence of the per trigger yields in the regions around $\Delta \varphi \approx \pi$ and $\Delta \varphi \approx \pi \pm 1.1$ can be understood by a different geometry dependence of jet energy loss and the medium response to the deposited energy.

    nucl-exNPA(2009)·12 citations
26. 26*

    Ultra-peripheral Au+Au collisions at PHENIX

    Mate Csanad (for the PHENIX Collaboration)🇭🇺

    Ultra-peripheral collisions (UPC) of heavy-ions involve long range electromagnetic interactions at impact parameters twice larger than the nuclear radius, where no nucleon-nucleon collisions occur. The first measurement of photoproduction of $J/\psi$ and of two-photon production of high-mass $e^{+}{e}^{-}$ pairs in ultra-peripheral nucleus-nucleus interactions will be presented, using Au+Au data at $\sqrt{s_{{}_{NN}}}$ = 200 GeV. The measured cross sections at midrapidity are consistent with various theoretical predictions.

    nucl-ex0 citations
27. 27*

    Jet-Medium Interactions with Identified Particles

    Anne M. Sickles🇺🇸

    Identified particles have long been of great interest at RHIC in large part because of the baryon/meson differences observed at intermediate $p_T$ and the implications for hadronization via quark coalescence. With recent high statistics data identified particles are also now central to understanding the details of the jet-medium interactions and energy loss and hadron formation at intermediate and high $p_T$. In particular, high $p_T$ identified particle spectra along with two-particle correlations triggered with direct photons, neutral pions or electrons from heavy flavor decay with hadrons can provide information about how medium modifications to jet fragmentation depend on parton type. I will review recent results with identified particles both in heavy ion systems and the reference measurements in p+p collisions.

    nucl-exNPA(2009)·6 citations
28. 28*

    Elucidating Jet Energy Loss Using Jets: Prospects from ATLAS

    N. Grau (for the ATLAS Collaboration)🇺🇸

    Jets at the LHC are expected to provide the testing ground for studying QCD energy loss. In this contribution, we briefly outline the strategy that will be used to measure jets in ATLAS and how we will go about studying energy loss. We describe the utility of measuring the jet $R_{AA}$, the fragmentation function, and heavy flavor jets. Utilizing the collision energy provided by the LHC and the nearly hermetic and highly segmented calorimeter, ATLAS is expected to make important contributions to the understanding of parton energy loss using fully reconstructed jets.

    nucl-exNPA(2009)·4 citations
29. 29*

    Jet quenching and the gravity dual

    Mohammed Mia🇨🇦 · Charles Gale🇨🇦

    We compute the momentum broadening of an energetic parton as it moves through strongly interacting matter, using the gravity dual of a non conformal gauge theory with matter in the fundamental representation. Our approach defines a family of theories, all of which have logarithmic running of the couplings in the far IR but becomes almost conformal in the far UV. For a given set of degrees of freedom, we obtain average transverse momentum square of the parton as a function of temperature and compare with results obtained from the AdS/CFT correspondence.

    ↳ hep-phhep-thnucl-exnucl-thNPA(2009)·6 citations
30. 30*

    An Electron-Ion Collider at Jefferson lab

    Anthony W. Thomas🇺🇸

    Long term plans for the investigation of the quark and gluon structure of matter have for some time focussed on the possibility of an electron-ion collider, with the nuclear physics communities associated with JLab and BNL being particularly active. We briefly outline the current thinking on this subject at Jefferson lab.

    ↳ hep-exhep-phnucl-exphysics.acc-ph11 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.