Fri·Feb 3, 2017Friday·February 3, 2017

1. 01*

   Centrality Issues In Asymmetric Collisions: Direct Photons To The Rescue?

   Gabor David🇺🇸

   Methods to classify events experimentally according to collision geometry are well established and non-controversial when collisions of large ions are studied. However, high luminosity data from $p/d$+A collisions at RHIC and LHC provided some surprising results that either call for new physics or question the applicability of the established methods of event classification for them. So far there is no consensus in the community what is the proper model and procedure to determine centrality, how to connect observed event activity with collision geometry in very asymmetric, $p/d$+A collisions in the same sense and with the same accuracy as was done in A+A. We argue that high $p_T$ direct photons offer an {\it a posteriori} test of any method suggested to categorize $p/d$+A -- and in general, very asymmetric -- collisions: the method is only viable if the nuclear modification factor for high $p_T$ direct photons is about unity for all centrality classes.

   nucl-exPoS(2017)·3 citations
2. 02*

   K${}^{\ast }(892{)}^0$ and $\varphi (1020)$ meson production at high transverse momentum in pp and Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV

   ALICE Collaboration

   The production of K${}^{\ast }(892{)}^0$ and $\varphi (1020)$ mesons in proton-proton (pp) and lead-lead (Pb-Pb) collisions at $\sqrt{s_{\mathrm{NN}}}=$ 2.76 TeV has been analyzed using a high luminosity data sample accumulated in 2011 with the ALICE detector at the Large Hadron Collider (LHC). Transverse momentum ($p_{\mathrm{T}}$) spectra have been measured for K${}^{\ast }(892{)}^0$ and $\varphi (1020)$ mesons via their hadronic decay channels for $p_{\mathrm{T}}$ up to 20 GeV/$c$. The measurements in pp collisions have been compared to model calculations and used to determine the nuclear modification factor and particle ratios. The K${}^{\ast }(892{)}^0$/K ratio exhibits significant reduction from pp to central Pb-Pb collisions, consistent with the suppression of the K${}^{\ast }(892{)}^0$ yield at low $p_{\mathrm{T}}$ due to rescattering of its decay products in the hadronic phase. In central Pb-Pb collisions the $p_{\mathrm{T}}$ dependent $\varphi (1020)/\pi$ and K${}^{\ast }(892{)}^0$/$\pi$ ratios show an enhancement over pp collisions for $p_{\mathrm{T}}$ $\sim$3 GeV/$c$, consistent with previous observations of strong radial flow. At high $p_{\mathrm{T}}$, particle ratios in Pb-Pb collisions are similar to those measured in pp collisions. In central Pb-Pb collisions, the production of K${}^{\ast }(892{)}^0$ and $\varphi (1020)$ mesons is suppressed for $p_{\mathrm{T}}>8$ GeV/$c$. This suppression is similar to that of charged pions, kaons and protons, indicating that the suppression does not depend on particle mass or flavor in the light quark sector.

   nucl-exhep-exPRC(2017)·179 citations
3. 03*

   Selective decay from a candidate of the $\sigma$-bond linear-chain state in ${}^{14}$C

   J. Li🇨🇳 · Y.L. Ye🇨🇳 · Z.H. Li · C.J. Lin🇺🇸 · Q.T. Li🇨🇳 · Y.C. Ge🇨🇳 · J.L. Lou🇨🇳 · Z.Y. Tian · W. Jiang🇨🇳 · Z.H. Yang🇯🇵 · J. Feng · P.J. Li and 14 other authors

   A cluster-transfer experiment ${}^9$Be(${}^9$Be,${}^{14}$C${}^{\ast }\to \alpha$+${}^{10}$Be)$\alpha$ was carried out using an incident beam energy of 45 MeV. This reaction channel has a large $Q$-value that favors populating the high-lying states in ${}^{14}$C and separating various reaction channels. A number of resonant states are reconstructed from the forward emitting ${}^{10}$Be + $\alpha$ fragments with respect to three sets of well discriminated final states in ${}^{10}$Be, most of which agree with the previous observations. A state at 22.5(1) MeV in ${}^{14}$C is found to decay predominantly into the states around 6 MeV in ${}^{10}$Be daughter nucleus, in line with the unique property of the predicted band head of the $\sigma$-bond linear-chain molecular states. A new state at 23.5(1) MeV is identified which decays strongly into the first excited state of ${}^{10}$Be.

   nucl-exPRC(2017)·46 citations
4. 04*

   Re-evaluation of the Beck et al. data to constrain the energy of the Th-229 isomer

   Georgy A. Kazakov · Thorsten Schumm · Simon Stellmer

   The presently accepted value of the energy splitting of the Th-229 ground-state doublet has been obtained on the basis of undirect gamma spectroscopy measurements by Beck et al., Phys. Rev. Lett. 98, 142501 (2007). Since then, a number of experiments set out to measure the isomer energy directly, however none of them resulted in an observation of the transition. Here we perform an analysis to identify the parameter space of isomer energy and branching ratio that is consistent with the Beck et al. experiment.

   nucl-ex2 citations
5. 05*

   Subthreshold resonances and resonances in the $R$-matrix method for binary reactions and in the Trojan Horse method

   A. M. Mukhamedzhanov · Shubhchintak · C. A. Bertulani

   In this paper we discuss the $R$-matrix approach to treat the subthreshold resonances for the single-level and one channel, and for the single-level and two channel cases. In particular, the expression relating the ANC with the observable reduced width, when the subthreshold bound state is the only channel or coupled with an open channel, which is a resonance, is formulated. Since the ANC plays a very important role in nuclear astrophysics, these relations significantly enhance the power of the derived equations. We present the relationship between the resonance width and the ANC for the general case and consider two limiting cases: wide and narrow resonances. Different equations for the astrophysical S-factors in the $R$-matrix approach are presented. After that we discuss the Trojan Horse Method (THM) formalism. The developed equations are obtained using the surface-integral formalism and the generalized $R$-matrix approach for the three-body resonant reactions. It is shown how the Trojan Horse (TH) double differential cross section can be expressed in terms of the on-the-energy-shell astrophysical S-factor for the binary sub-reaction. Finally, we demonstrate how the THM can be used to calculate the astrophysical S-factor for the neutron generator ${}^{13}\mathrm{C}(\alpha ,n{)}^{16}\mathrm{O}$ in low-mass AGB stars. At astrophysically relevant energies this astrophysical S-factor is controlled by the threshold level $1/2^{+},E_x=6356$ keV. Here, we reanalyzed recent TH data taking into account more accurately the three-body effects and using both assumptions that the threshold level is a subthreshold bound state or it is a resonance state.

   ↳ nucl-thnucl-exPRC(2017)·14 citations
6. 06*

   The $x$ and $Q^2$ dependence of $\hat{q}$, quasi-particles and the JET puzzle

   Evan Bianchi🇺🇸 · Jacob Elledge🇺🇸 · Amit Kumar🇺🇸 · Abhijit Majumder🇺🇸 · Guang-You Qin🇨🇳 · Chun Shen🇺🇸

   We present the first attempt to extract the "$x$" dependence of the parton distribution function (PDF) of the quark gluon plasma (QGP). In the absence of knowledge regarding the mass of a QGP constituent, we define the new variable $x_N$, the nucleonic momentum fraction, which represents the ratio of the momentum of the parton to that of a self-contained section of the plasma that has the mass of a nucleon. Calculations are compared to data for single hadron suppression in terms of the nuclear modification factor $R_{AA}$ and the azimuthal anisotropy parameter $v_2$, as a function of transverse momentum $p_T$, centrality and energy of the collision. It is demonstrated that the scale evolution of the QGP-PDF is responsible for the reduction in normalization of the jet transport coefficient $\hat{q}$, between fits to Relativistic Heavy-Ion Collider (RHIC) and Large Hadron Collider (LHC) data; a puzzle, first discovered by the JET collaboration. Best fits to data are suggestive of the presence of quasi-particles with wide dispersion relations in the QGP.

   ↳ nucl-thhep-phnucl-ex33 citations
7. 07*

   Exotic Hadrons from Heavy Ion Collisions

   ExHIC Collaboration: Sungtae Cho🇰🇷 · Tetsuo Hyodo🇯🇵 · Daisuke Jido🇯🇵 · Che Ming Ko🇺🇸 · Su Houng Lee🇰🇷 · Saori Maeda🇯🇵 · Kenta Miyahara🇯🇵 · Kenji Morita🇯🇵 · Marina Nielsen🇧🇷 · Akira Ohnishi🇯🇵 · Takayasu Sekihara🇯🇵 · Taesoo Song🇩🇪 · Shigehiro Yasui🇯🇵 · Koichi Yazaki🇯🇵

   Heavy ion collisions (HIC) at high energies are excellent ways for producing heavy hadrons and composite particles. With upgraded detectors at RHIC and LHC, it has become possible to measure hadrons beyond their ground states. Therefore, HIC provide a new method for studying exotic hadrons that are either hadronic molecular states or compact multiquark systems. Because their structures are related to the fundamental properties of QCD, studying exotic hadrons is currently one of the most active areas of research in hadron physics. Experiments carried out at various accelerator facilities have indicated that some exotic hadrons may have already been produced. The present review is a summary of the current understanding of a selected set of exotic particle candidates that can be potentially measured in HIC. It also includes discussions on the production of exotic hadrons in HIC based on the coalescence and statistical models. A more detailed discussion leads to the conclusion that the yield of a hadron is typically an order of magnitude smaller when it is a compact multiquark state than that of an excited hadronic state with normal quark numbers and/or a molecular configuration. Attention is also given to some of the proposed heavy exotic hadrons that could be produced with sufficient abundance in HIC because of the significant numbers of charm and bottom quarks produced at RHIC and LHC, making it possible to study them in these experiments. Further included in the discussion are the general formalism for the coalescence model that involves resonance particles and its implication on the present estimated yield for resonance production. Finally, a review is given on recent studies to constrain the hadron-hadron interaction through correlation measurements in HIC and their implications on the interpretation and the possible existence of exotic states in hadronic interactions.

   ↳ nucl-thhep-phnucl-exPPNP(2017)·203 citations
8. 08*

   Energy dependence of forward-rapidity J/$\psi$ and $\psi (2S)$ production in pp collisions at the LHC

   ALICE Collaboration

   We present results on transverse momentum ($p_{\mathrm{T}}$) and rapidity ($y$) differential production cross sections, mean transverse momentum and mean transverse momentum square of inclusive J/$\psi$ and $\psi (2S)$ at forward rapidity ($2.5<y<4$) as well as $\psi (2S)$-to-J/$\psi$ cross section ratios. These quantities are measured in pp collisions at center of mass energies $\sqrt{s}=5.02$ and 13 TeV with the ALICE detector. Both charmonium states are reconstructed in the dimuon decay channel, using the muon spectrometer. A comprehensive comparison to inclusive charmonium cross sections measured at $\sqrt{s}=2.76$, 7 and 8 TeV is performed. A comparison to non-relativistic quantum chromodynamics and fixed-order next-to-leading logarithm calculations, which describe prompt and non-prompt charmonium production respectively, is also presented. A good description of the data is obtained over the full $p_{\mathrm{T}}$ range, provided that both contributions are summed. In particular, it is found that for $p_{\mathrm{T}}>15$ GeV/$c$ the non-prompt contribution reaches up to 50% of the total charmonium yield.

   ↳ hep-exnucl-exEPJC(2017)·109 citations
9. 09*

   Measurement of jet fragmentation in Pb+Pb and $pp$ collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV with the ATLAS detector

   ATLAS Collaboration

   The distributions of transverse momentum and longitudinal momentum fraction of charged particles in jets are measured in Pb+Pb and pp collisions with the ATLAS detector at the LHC. The distributions are measured as a function of jet transverse momentum and rapidity. The analysis utilises an integrated luminosity of 0.14 nb${}^{-1}$ of Pb+Pb data and 4.0 pb${}^{-1}$ of pp data collected in 2011 and 2013, respectively, at the same centre-of-mass energy of 2.76 TeV per colliding nucleon pair. The distributions measured in pp collisions are used as a reference for those measured in Pb+Pb collisions in order to evaluate the impact on the internal structure of jets from the jet energy loss of fast partons propagating through the hot, dense medium created in heavy-ion collisions. Modest but significant centrality-dependent modifications of fragmentation functions in Pb+Pb collisions with respect to those in pp collisions are seen. No significant dependence of modifications on jet $p_{\mathrm{T}}$ and rapidity selections is observed except for the fragments with the highest transverse momenta for which some reduction of yields is observed for more forward jets.

   ↳ hep-exnucl-exEPJC(2017)·115 citations
10. 10*

    Corrections of alpha- and proton-decay energies in implantation experiments

    Wenjia Huang🇫🇷 · Georges Audi🇫🇷

    Energies from alpha- and proton-decay experiments yield information of capital importance for deriving the atomic masses of superheavy and exotic nuclides. We present a procedure to correct the published decay energies in case the recoiling daughter nuclides were not considered properly in implantation experiments. A program has been developed based on Lindhard's integral theory, which can accurately predict the energy deposition of heavy atomic projectiles in matter.

    ↳ physics.ins-detnucl-exEPJ Web Conf.(2017)·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.