Wed·Feb 4, 2015Wednesday·February 4, 2015

1. 01*

   Study of in-medium mass modification at J-PARC

   Kazuya Aoki (for the J-PARC E16 Collaboration)🇯🇵

   Study of in-medium mass modification has attracted interest in terms of the restoration of the spontaneously broken chiral symmetry, which is responsible for the generation of hadron mass. Many experiments were performed to measure in-medium property of hadrons but there is no consensus yet. J-PARC E16 has been proposed to study in-medium property of vector mesons via dilepton decay channel. The status of spectrometer R \& D is explained. Other related experiments planned at J-PARC are also introduced.

   nucl-ex21 citations
2. 02*

   Femtoscopic Proton-Lambda Correlations in Pb-Pb Collisions at sqrt(sNN) = 2.76 TeV with ALICE

   Hans Beck (for the ALICE Collaboration)🇩🇪

   Two-particle correlations at small relative momenta give insight into the size of the emitting source. Of particular interest is the test of hydrodynamic models which predict a universal, apparent decrease of the extent of the system with increasing transverse mass mT as a consequence of the strong radial flow in heavy-ion collisions at LHC energies. This contribution presents a study of correlations for protons and {\Lambda} particles in Pb-Pb collisions at sqrt(sNN) = 2.76 TeV measured with ALICE. The investigated particle species expand the experimental reach in mT due to their high rest mass. Residual impurities in the samples from misidentification and contributions from feed-down are corrected using data-driven techniques. Correlation functions are obtained in several centrality classes and mT intervals at large mT and show the expected decrease in volume of the strongly interacting fireball for more peripheral collisions. We observe the decrease of the source size with mT, predicted by hydrodynamical calculations, out to mean mT = 2.18 GeV/c2.

   nucl-ex1 citation
3. 03*

   Measurement of the Formation Rate of Muonic Hydrogen Molecules

   MuCap Collaboration: V. A. Andreev🇷🇺 · T. I. Banks🇺🇸 · R. M. Carey🇺🇸 · T. A. Case🇺🇸 · S. M. Clayton🇺🇸 · K. M. Crowe🇺🇸 · J. Deutsch🇧🇪 · J. Egger🇨🇭 · S. J. Freedman🇺🇸 · V. A. Ganzha🇷🇺 · T. Gorringe🇺🇸 · F. E. Gray🇺🇸 and 23 other authors

   Background: The rate \lambda_pp\mu\ characterizes the formation of pp\mu\ molecules in collisions of muonic p\mu\ atoms with hydrogen. In measurements of the basic weak muon capture reaction on the proton to determine the pseudoscalar coupling g_P, capture occurs from both atomic and molecular states. Thus knowledge of \lambda_pp\mu\ is required for a correct interpretation of these experiments. Purpose: Recently the MuCap experiment has measured the capture rate \Lambda_S from the singlet p\mu\ atom, employing a low density active target to suppress pp\mu\ formation (PRL 110, 12504 (2013)). Nevertheless, given the unprecedented precision of this experiment, the existing experimental knowledge in \lambda_pp\mu\ had to be improved. Method: The MuCap experiment derived the weak capture rate from the muon disappearance rate in ultra-pure hydrogen. By doping the hydrogen with 20 ppm of argon, a competing process to pp\mu\ formation was introduced, which allowed the extraction of \lambda_pp\mu\ from the observed time distribution of decay electrons. Results: The pp\mu\ formation rate was measured as \lambda_pp\mu = (2.01 +- 0.06(stat) +- 0.03(sys)) 10^6 s^-1. This result updates the \lambda_pp\mu\ value used in the above mentioned MuCap publication. Conclusions: The 2.5x higher precision compared to earlier experiments and the fact that the measurement was performed at nearly identical conditions to the main data taking, reduces the uncertainty induced by \lambda_pp\mu\ to a minor contribution to the overall uncertainty of \Lambda_S and g_P, as determined in MuCap. Our final value for \lambda_pp\mu\ shifts \Lambda_S and g_P by less than one tenth of their respective uncertainties compared to our results published earlier.

   nucl-exhep-exphysics.ins-detPRC(2015)·33 citations
4. 04*

   Collision Geometry and Flow in Uranium+Uranium Collisions

   Andy Goldschmidt🇺🇸 · Zhi Qiu🇺🇸 · Chun Shen🇨🇦 · Ulrich Heinz🇺🇸

   Using event-by-event viscous fluid dynamics to evolve fluctuating initial density profiles from the Monte-Carlo Glauber model for U+U collisions, we report a "knee"-like structure in the elliptic flow as a function of collision centrality, located near 0.5% centrality as measured by the final charged multiplicity. This knee is due to the preferential selection of tip-on-tip collision geometries by a high-multiplicity trigger. Such a knee structure is not seen in the STAR data. This rules out the two-component MC-Glauber model for initial energy and entropy production. An enrichment of tip-tip configurations by triggering solely on high-multiplicity in the U+U collisions thus does not work. On the other hand, using the Zero Degree Calorimeters (ZDCs) coupled with event-shape engineering, we identify the selection purity of body-body and tip-tip events in the full-overlap U+U collisions. With additional constraints on the asymmetry of the ZDC signals one can further increases the probability of selecting tip-tip events in U+U collisions.

   ↳ nucl-thnucl-ex13 citations
5. 05*

   Revisit of the neutron/proton ratio puzzle in intermediate-energy heavy-ion collisions

   Hai-Yun Kong · Yin Xia🇨🇳 · Jun Xu🇨🇳 · Lie-Wen Chen🇨🇳 · Bao-An Li🇺🇸 · Yu-Gang Ma🇨🇳

   Incorporating a newly improved isospin- and momentum-dependent interaction in the isospin-dependent Boltzmann-Uehling-Uhlenbeck transport model IBUU11, we have investigated relative effects of the density dependence of nuclear symmetry energy $E_{sym}(\rho )$ and the neutron-proton effective mass splitting $m_n^{\ast }-m_p^{\ast }$ on the neutron/proton ratio of free nucleons and those in light clusters. It is found that the $m_n^{\ast }-m_p^{\ast }$ has a relatively stronger effect than the $E_{sym}(\rho )$ and the assumption of $m_n^{\ast }\le m_p^{\ast }$ leads to a higher neutron/proton ratio. Moreover, this finding is independent of the in-medium nucleon-nucleon cross sections used. However, results of our calculations using the $E_{sym}(\rho )$ and $m_n^{\ast }-m_p^{\ast }$ both within their current uncertainty ranges are all too low compared to the recent NSCL/MSU double neutron/proton ratio data from central ${}^{124}$Sn+${}^{124}$Sn and ${}^{112}$Sn+${}^{112}$Sn collisions at 50 and 120 MeV/u, thus calling for new mechanisms to explain the puzzlingly high neutron/proton ratio observed in the experiments.

   ↳ nucl-thnucl-exPRC(2015)·30 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.