Thu·Apr 2, 2015Thursday·April 2, 2015

1. 01*

   Coherent ${\rho }^0$ photoproduction in ultra-peripheral Pb-Pb collisions at $\sqrt{{\text{s}}_{\mathrm{NN}}}=2.76$ TeV

   ALICE Collaboration

   We report the first measurement at the LHC of coherent photoproduction of ${\rho }^0$ mesons in ultra-peripheral Pb-Pb collisions. The invariant mass and transverse momentum distributions for ${\rho }^0$ production are studied in the ${\pi }^{+}{\pi }^{-}$ decay channel at mid-rapidity. The production cross section in the rapidity range $|y|<0.5$ is found to be $\mathrm{d}\sigma /\mathrm{d}y=425\pm 10(stat.)$ ${}_{-50}^{+42}(sys.)$ mb. Coherent ${\rho }^0$ production is studied with and without requirement of nuclear breakup, and the fractional yields for various breakup scenarios are presented. The results are compared with those from lower energies and with model predictions.

   nucl-exhep-exJHEP(2015)·118 citations
2. 02*

   Measurement of pion, kaon and proton production in proton-proton collisions at $\sqrt{s}=7$ TeV

   ALICE Collaboration

   The measurement of primary ${\pi }^{\pm }$, K${}^{\pm }$, p and $\overline{p}$ production at mid-rapidity ($|y|<$ 0.5) in proton-proton collisions at $\sqrt{s}=7$ TeV performed with ALICE (A Large Ion Collider Experiment) at the Large Hadron Collider (LHC) is reported. Particle identification is performed using the specific ionization energy loss and time-of-flight information, the ring-imaging Cherenkov technique and the kink-topology identification of weak decays of charged kaons. Transverse momentum spectra are measured from 0.1 up to 3 GeV/$c$ for pions, from 0.2 up to 6 GeV/$c$ for kaons and from 0.3 up to 6 GeV/$c$ for protons. The measured spectra and particle ratios are compared with QCD-inspired models, tuned to reproduce also the earlier measurements performed at the LHC. Furthermore, the integrated particle yields and ratios as well as the average transverse momenta are compared with results at lower collision energies.

   nucl-exhep-exEPJC(2015)·241 citations
3. 03*

   Curvature of the critical line on the plane of quark chemical potential and pseudo scalar meson mass for three-flavor QCD

   Xiao-Yong Jin🇯🇵 · Yoshinobu Kuramashi🇯🇵 · Yoshifumi Nakamura🇯🇵 · Shinji Takeda🇯🇵 · Akira Ukawa🇯🇵

   We investigate the phase structure of three-flavor QCD in the presence of finite quark chemical potential $\mu /T\lesssim 1.2$ by using the non-perturbatively $O(a)$ improved Wilson fermion action on lattices with a fixed temporal extent $N_{\mathrm{t}}=6$ and varied spatial linear extents $N_{\mathrm{s}}=8,10,12$. Especially, we focus on locating the critical end point that characterizes the phase structure, and extracting the curvature of the critical line on the $\mu$-$m_{\pi }$ plane. For Wilson-type fermions, the correspondence between bare parameters and physical parameters is indirect. Hence we present a strategy to transfer the bare parameter phase structure to the physical one, in order to obtain the curvature. Our conclusion is that the curvature is positive. This implies that, if one starts from a quark mass in the region of crossover at zero chemical potential, one would encounter a first-order phase transition when one raises the chemical potential.

   ↳ hep-latnucl-exPRD(2015)·11 citations
4. 04*

   Effect of neutron skin thickness on projectile fragmentation

   Z. T. Dai · D. Q. Fang🇨🇳 · Y. G. Ma🇨🇳 · X. G. Cao🇨🇳 · G. Q. Zhang🇨🇳 · W. Q. Shen🇨🇳

   The fragment production in collisions of ${}^{48,50}$Ca+${}^{12}$C at 50 MeV/nucleon are simulated via the Isospin-Dependent Quantum Molecular Dynamics (IQMD) model followed by the {GEMINI code}. {By changing the diffuseness parameter of neutron density distribution to obtain different neutron skin size, the effects of neutron skin thickness (${\delta }_{np}$) on projectile-like fragments (PLF) are investigated. The sensitivity of isoscaling behavior to neutron skin size is studied, from which it is found that the isoscaling parameter $\alpha$ has a linear dependence on ${\delta }_{np}$. A linear dependence between ${\delta }_{np}$ and the mean $N/Z$ [N(Z) is neutron(proton) number] of PLF is obtained as well.} The results show that thicker neutron skin will lead to smaller {isoscaling parameter} $\alpha$ and N/Z. Therefore, it may be probable to extract information of neutron skin thickness from {isoscaling parameter} $\alpha$ and N/Z.

   ↳ nucl-thnucl-exPRC(2015)·16 citations
5. 05*

   Energy Dependence of Direct-Quarkonium Production in pp Collisions from Fixed-Target to LHC Energies: Complete One-Loop Analysis

   Yu Feng🇨🇳 · Jean-Philippe Lansberg🇫🇷 · Jian-Xiong Wang🇨🇳

   We compute the energy dependence of the P_T-integrated cross section of directly produced quarkonia in pp collisions at next-to-leading order (NLO), namely up to alpha_s^3, within nonrelativistic QCD (NRQCD). Our analysis is based on the idea that the P_T-integrated and the P_T-differential cross sections can be treated as two different observables. The colour-octet NRQCD parameters needed to predict the P_T-integrated yield can thus be extracted from the fits of the P_T-differential cross sections at mid and large P_T. For the first time, the total cross section is evaluated in NRQCD at full NLO accuracy using the recent NLO fits of the P_T-differential yields at RHIC, the Tevatron and the LHC. Both the normalisation and the energy dependence of the J/psi, psi' and Upsilon(1S), we obtained, are in disagreement with the data irrespective of the fit method. The same is true if one uses CEM-like colour-octet NRQCD parameters. If, on the contrary, one disregards the colour-octet contribution, the existing data in the TeV range are well described by the alpha_s^3 contribution in the colour-singlet model --which, at alpha_s^4, however shows an unphysical energy dependence. A similar observation is made for eta(c,b). This calls for a full NNLO or for a resummation of the initial-state radiation in this channel. In any case, past claims that colour-octet transitions are dominantly responsible for low-P_T quarkonium production are not supported by our results. This may impact the interpretation of quarkonium suppression in high-energy proton-nucleus and nucleus-nucleus collisions.

   ↳ hep-phhep-exnucl-exnucl-thEPJC(2015)·65 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.