Thu·Jul 7, 2016Thursday·July 7, 2016

1. 01*

   Direct virtual photon production in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV

   STAR Collaboration

   We report the direct virtual photon invariant yields in the transverse momentum ranges $1<p_T<3$ GeV/$c$ and $5<p_T<10$ GeV/$c$ at mid-rapidity derived from the dielectron invariant mass continuum region $0.10<M_{ee}<0.28$ GeV/$c^2$ for 0-80\% minimum-bias Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV. A clear excess in the invariant yield compared to the number-of-binary-collisions ($N_{bin}$) scaled $p+p$ reference is observed in the $p_T$ range $1<p_T<3$ GeV/$c$. For $p_T>6$ GeV/$c$ the production follows $N_{bin}$ scaling. Model calculations with contributions from thermal radiation and initial hard parton scattering are consistent within uncertainties with the direct virtual photon invariant yield.

   nucl-exhep-exhep-phnucl-thPLB(2017)·96 citations
2. 02*

   Challenges in QCD matter physics - The Compressed Baryonic Matter experiment at FAIR

   CBM Collaboration: T. Ablyazimov🇷🇺 · A. Abuhoza🇩🇪 · R.P. Adak🇮🇳 · M. Adamczyk🇵🇱 · K. Agarwal🇩🇪 · M.M. Aggarwal🇮🇳 · Z. Ahammed🇮🇳 · F. Ahmad · N. Ahmad · S. Ahmad · A. Akindinov🇷🇺 · P. Akishin🇷🇺 and 575 other authors

   Substantial experimental and theoretical efforts worldwide are devoted to explore the phase diagram of strongly interacting matter. At LHC and top RHIC energies, QCD matter is studied at very high temperatures and nearly vanishing net-baryon densities. There is evidence that a Quark-Gluon-Plasma (QGP) was created at experiments at RHIC and LHC. The transition from the QGP back to the hadron gas is found to be a smooth cross over. For larger net-baryon densities and lower temperatures, it is expected that the QCD phase diagram exhibits a rich structure, such as a first-order phase transition between hadronic and partonic matter which terminates in a critical point, or exotic phases like quarkyonic matter. The discovery of these landmarks would be a breakthrough in our understanding of the strong interaction and is therefore in the focus of various high-energy heavy-ion research programs. The Compressed Baryonic Matter (CBM) experiment at FAIR will play a unique role in the exploration of the QCD phase diagram in the region of high net-baryon densities, because it is designed to run at unprecedented interaction rates. High-rate operation is the key prerequisite for high-precision measurements of multi-differential observables and of rare diagnostic probes which are sensitive to the dense phase of the nuclear fireball. The goal of the CBM experiment at SIS100 (sqrt(s_NN) = 2.7 - 4.9 GeV) is to discover fundamental properties of QCD matter: the phase structure at large baryon-chemical potentials (mu_B > 500 MeV), effects of chiral symmetry, and the equation-of-state at high density as it is expected to occur in the core of neutron stars. In this article, we review the motivation for and the physics programme of CBM, including activities before the start of data taking in 2022, in the context of the worldwide efforts to explore high-density QCD matter.

   nucl-exEPJA(2017)·458 citations
3. 03*

   Transverse single-spin asymmetry of weak bosons and Drell-Yan production in p+p collisions at STAR: present and future

   Salvatore Fazio🇺🇸

   Accessing the Sivers TMD function in proton+proton collisions through the measurement of transverse single spin asymmetries (TSSAs) in Drell-Yan and weak boson production is an effective path to test the fundamental QCD prediction of the non-universality of the Sivers function. Furthermore, it provides data to study the spin-flavor structure of valence and sea quarks inside the proton and to test the evolution of parton distributions. The TSSA amplitude, $A_N$, has been measured at STAR in proton+proton collisions at $\sqrt{s}=500$ GeV, with a recorded integrated luminosity of 25 pb${}^{-1}$. Within relatively large statistical uncertainties, the current data favor theoretical models that include a change of sign for the Sivers function relative to observations in SIDIS measurements, if TMD evolution effects are small. RHIC plans to run proton+proton collisions of transversely polarized beams at $\sqrt{s}=510$ GeV in 2017, delivering an integrated luminosity of 400 pb${}^{-1}$. This will allow STAR to perform a precise measurement of TSSAs in both Drell-Yan and weak boson production. The present status and future plans for the Sivers function program at STAR will be discussed as well as other observables sensitive to the non-universality of the Sivers function in the Twist-3 framework, e.g. the TSSA of direct photons.

   nucl-exhep-exPoS(2016)·1 citation
4. 04*

   Studying photon structure at an EIC

   Xiaoxuan Chu🇨🇳 · Elke-Caroline Aschenauer🇺🇸 · Jeong-Hun Lee🇺🇸

   A future Electron-Ion Collider (EIC) will deliver luminosities of $10^{33}-10^{34}$ cm${}^{-2}$s${}^{-1}$ for collisions of polarized electrons and protons and heavy ions over a wide range of center-of-mass energies (40 $\mathrm{GeV}$ to 145 $\mathrm{GeV}$). One of its promising physics programs is to study the partonic structure of quasi-real photons. Measuring di-jet in photoproduction events, one can effectively access the underlying parton dynamics of the photons through the selection of the resolved photon processes. In this paper, we discuss the feasibility of tagging resolved photon processes and measuring the di-jet cross section as a function of jet transverse momentum in ranges of $x_{\gamma }^{rec}$ at an EIC. These studies show that parton distributions in the photon can be extracted at an EIC.

   nucl-exhep-phPoS(2016)·1 citation
5. 05*

   Axial form factor of the nucleon at large momentum transfers

   I.V. Anikin🇷🇺 · V.M. Braun🇩🇪 · N. Offen🇩🇪

   Motivated by the emerging possibilities to study threshold pion electroproduction at large momentum transfers at Jefferson Laboratory following the 12 GeV upgrade, we provide a short theory summary and an estimate of the nucleon axial form factor for large virtualities in the $Q^2=1-10{\text{GeV}}^2$ range using next-to-leading order light-cone sum rules.

   ↳ hep-phnucl-exnucl-thPRD(2016)·27 citations
6. 06*

   Measurement of forward direct photon production in p-A at the LHC with ALICE - A probe for nuclear PDFs and saturation

   Thomas Peitzmann (for the ALICE FoCal Collaboration)🇳🇱

   Probes for the small-x parton densities and predicted effects of gluon saturation are discussed. At very low x and intermediate Q, only results on hadronic observables at the LHC are available, which do not provide unambiguous information. It is shown that the measurement of direct photons at forward rapidity at the LHC is particularly promising to provide a unique signal. We further discuss the possibilities to perform such measurements with a detector upgrade in the ALICE experiment and present the R&D activities ongoing.

   ↳ hep-exnucl-exPoS(2016)·7 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.