Fri·Sep 17, 2021Friday·September 17, 2021

1. 01*

   Probing the gluonic structure of the deuteron with $J/\psi$ photoproduction in d+Au ultra-peripheral collisions

   STAR Collaboration: M. S. Abdallah · B. E. Aboona · J. Adam · L. Adamczyk · J. R. Adams · J. K. Adkins · G. Agakishiev · I. Aggarwal · M. M. Aggarwal · Z. Ahammed · I. Alekseev · D. M. Anderson and 390 other authors

   Understanding gluon density distributions and how they are modified in nuclei are among the most important goals in nuclear physics. In recent years, diffractive vector meson production measured in ultra-peripheral collisions (UPCs) at heavy-ion colliders has provided a new tool for probing the gluon density. In this Letter, we report the first measurement of $J/\psi$ photoproduction off the deuteron in UPCs at the center-of-mass energy $\sqrt{s_{{}_{\mathrm{NN}}}}=200\mathrm{GeV}$ in d$+$Au collisions. The differential cross section as a function of momentum transfer $-t$ is measured. In addition, data with a neutron tagged in the deuteron-going Zero-Degree Calorimeter is investigated for the first time, which is found to be consistent with the expectation of incoherent diffractive scattering at low momentum transfer. Theoretical predictions based on the Color Glass Condensate saturation model and the gluon shadowing model are compared with the data quantitatively. A better agreement with the saturation model has been observed. With the current measurement, the results are found to be directly sensitive to the gluon density distribution of the deuteron and the deuteron breakup, which provides insights into the nuclear gluonic structure.

   nucl-exhep-exnucl-thPRL(2022)·30 citations
2. 02*

   Exclusive decay study of the 16.62\,MeV (2${}^{-}$, T=1) resonance in ${}^{12}$C

   Morten Kuhlwein · Kristian Lytje · Hans Otto Uldall Fynbo🇩🇰 · Andreas Gad · Erik Jensen · Oliver Sølund Kirsebom · Michael Munch · Jonas Refsgaard · Karsten Riisager🇩🇰

   The 3$\alpha$ decay of the 16.62\,MeV (2${}^{-}$, T=1) resonance in ${}^{12}$C has been studied for nearly a century starting with one of the first nuclear reaction studies at the Cavendish Laboratory in the 1930s. In the hitherto latest study published a decade ago a model based on earlier work from the 1960s was found to give a good account of a set of inclusive data. This model describes the decay as an l=3 $\alpha$-particle populating the 2${}^{+}$ state of ${}^8$Be. Here we provide new exclusive data on the 3$\alpha$ decay of the 16.62\,MeV resonance, and demonstrate that the decay is best described by a model with predominantly l=1 emission with an admixture of l=3.

   nucl-exPLB(2022)·4 citations
3. 03*

   Reconstruction of high-energy part of gamma-ray spectrum in thermal neutron capture by ${}^{113}$Cd

   V.A. Plujko🇺🇦 · O.M. Gorbachenko · K.M. Solodovnyk · V.M. Petrenko

   The average gamma-ray spectrum ${}^{114}$Cd after thermal neutron capture in ${}^{113}$Cd was evaluated in units of mb/MeV. Two approaches are considered for estimation of the average gamma-ray spectrum with normalization of the experimental data: mean spectra for all gamma-energies were found by averaging frequency polygon for experimental data histogram, and mean spectra were estimated as the combination of theoretical values at low gamma-ray energies and averaging experimental data in high-energy range. The experi mental spectra were evaluated from the gamma-intensities presented by Mheemeed et al. [A. Mheemeed et al., Nucl. Phys. A 412 (1984) 113] and Belgya et al [T. Belgya et al., EPJ Web of Conf. 146 (2017) 05009]. They were normalized to the average theoretical spectrum which was calculated using EMPIRE and TALYS codes. The procedure of normalization of the high-energy part of the spectrum was described. Estimated $\gamma$- spectra for ${}^{113}$Cd(n,{x$\gamma$}) reaction induced by thermal neutrons were presented.

   nucl-exnucl-thNucl.Phys.Atom.Energy(2021)·0 citations
4. 04*

   Mean-field update in the JAM microscopic model: Mean-field effects on collective flow in high-energy heavy-ion collisions at $\sqrt{s_{NN}}=2-20$ GeV energies

   Yasushi Nara🇯🇵 · Akira Ohnishi🇯🇵

   The beam energy dependence of the directed flow is a sensitive probe for the properties of strongly interacting matter. We consider different implementations of momentum-dependent hadronic mean fields in the relativistic quantum molecular dynamics (RQMD) framework. First, Lorentz scalar implementation of a Skyrme type potential is examined. Then, full implementation of the Skyrme type potential as a Lorentz vector in the RQMD approach is proposed. We find that scalar implementation of the Skyrme force is too weak to generate repulsion explaining observed data of sideward flows at $\sqrt{s_{NN}}<10$ GeV, while vector implementation gives collective flows compatible with the data for a wide range of beam energies $2.7<\sqrt{s_{NN}}<20$ GeV. We show that our approach reproduces the negative proton directed flow at $\sqrt{s_{NN}}>10$ GeV discovered by experiments. We discuss the dynamical generation mechanisms of the directed flow within a conventional hadronic mean field. A positive slope of proton directed flow is generated predominantly during compression stages of heavy-ion collisions by the strong repulsive interaction due to high baryon densities. In contrast, in the expansion stages of the collision, the negative directed flow is generated more strongly than the positive one by the tilted expansion and shadowing by the spectator matter. At lower collision energies $\sqrt{s_{NN}}<10$ GeV, the positive flow wins against the negative flow because of a long compression time. On the other hand, at higher energies $\sqrt{s_{NN}}>10$ GeV, negative flow wins because of shorter compression time and longer expansion time. A transition beam energy from positive to negative flow is highly sensitive to the strength of the interaction.

   ↳ nucl-thhep-phnucl-exPRC(2022)·64 citations
5. 05*

   The production of doubly charmed exotic hadrons in heavy ion collisions

   Yuanyuan Hu🇨🇳 · Jinfeng Liao🇺🇸 · Enke Wang🇨🇳 · Qian Wang🇨🇳 · Hongxi Xing🇨🇳 · Hui Zhang🇨🇳

   Hadron spectroscopy provides direct physical measurements that shed light on the non-perturbative behavior of quantum chromodynamics (QCD). In particular, various exotic hadrons such as the newly observed $T_{cc}^{+}$ by the LHCb collaboration, offer unique insights on the QCD dynamics in hadron structures. In this letter, we demonstrate how heavy ion collisions can serve as a powerful venue for hadron spectroscopy study of doubly charmed exotic hadrons by virtue of the extremely charm-rich environment created in such collisions. The yields of $T_{cc}^{+}$ as well as its potential isospin partners are computed within the molecular picture for Pb-Pb collisions at center-of-mass energy $2.76\mathrm{TeV}$. We find about three-order-of-magnitude enhancement in the production of $T_{cc}^{+}$ in Pb-Pb collisions as compared with the yield in proton-proton collisions, with a moderately smaller enhancement in the yields of the isospin partners $T_{cc}^0$ and $T_{cc}^{++}$. The $T_{cc}^{+}$ yield is comparable to that of the $X(3872)$ in the most central collisions while shows a considerably stronger decrease toward peripheral collisions, due to a "threshold" effect of the required double charm quarks for $T_{cc}^{+}$. Final results for their rapidity and transverse momentum $p_T$ dependence as well as the elliptic flow coefficient are reported and can be tested by future experimental measurements.

   ↳ hep-phhep-exnucl-exnucl-thPRD(2021)·56 citations
6. 06*

   Factorization breaking for higher moments of harmonic flow

   Piotr Bozek🇵🇱 · Rupam Samanta🇵🇱

   We study correlations between harmonic flow vectors squared measured at different transverse momenta. One of the flow harmonics squared is taken at a fixed transverse momentum and correlated to the momentum averaged harmonic flow squared of the same order. Such four particle correlators, dependent on transverse momentum, have been recently measured experimentally. Factorization coefficients based on the ratio of such four-particle correlators allow the independent measurement of the flow vector and flow magnitude factorization breaking coefficient. Moreover, the correlation of the angles of flow harmonics as a function of transverse momentum can be extracted. Results are compared to preliminary data of the ALICE Collaboration. We also present predictions for the momentum dependent factorization breaking coefficient between mixed flow harmonics. The correlators with squares of mixed harmonics can serve as a way to independently measure the flow vector, flow magnitude, and flow angle correlations, and could be used to gain additional information on the fluctuating initial state and the dynamics in heavy-ion collisions.

   ↳ nucl-thnucl-exPRC(2022)·18 citations
7. 07*

   Charmonium suppression in ultra-relativistic proton-proton collisions at LHC energies: A hint for QGP in small systems

   Captain R. Singh🇮🇳 · Suman Deb🇮🇳 · Raghunath Sahoo🇮🇳 · Jan-e Alam🇮🇳

   Proton-proton ($pp$) collision has been considered as a baseline to study the system produced in relativistic heavy-ion (AA) collisions with the basic assumption that no thermal medium is formed in $pp$ collisions. This warrants a cautious analysis of the system produced in $pp$ collisions at relativistic energies.In this work we investigate the charmonium suppression in $pp$ collisions at $\sqrt{s}=5.02,7$ and $13$ TeV energies. Further, charmonium suppression has been studied for various event multiplicities and transverse momenta by including the mechanisms of color screening, gluonic dissociation, collisional damping along with regeneration due to correlated $c\bar{c}$ pairs. Here we obtain a net suppression of charmonia at high-multiplicity events indicating the possibility of the formation of quark-gluon plasma in $pp$ collisions.

   ↳ hep-phhep-exnucl-exnucl-thEPJC(2022)·19 citations
8. 08*

   Measurement of $\mathrm{D}$-meson production as a function of charged-particle multiplicity in proton--proton collisions at $\sqrt{s}=13$ TeV with ALICE at the LHC

   Yoshini Bailung (for the ALICE Collaboration)🇮🇳

   Heavy quarks (charm and beauty) are produced in hard-scattering processes and the study of their production in proton--proton (pp) collisions is an important test for calculations based on perturbative Quantum Chromodynamics (pQCD). Heavy-flavor production as a function of charged-particle multiplicity provides insight into the processes occurring at the partonic level and the interplay between the hard and soft particle production mechanisms in pp collisions. In this contribution, measurements of open heavy-flavor production as a function of multiplicity, via the study of the $\mathrm{D}$-meson self-normalized yields in pp collisions at the center-of-mass energy of $\sqrt{s}=13$ TeV is presented. The $\mathrm{D}$-meson self-normalized yield is found to increase stronger than linearly with increasing charged-particle multiplicity. The measurements are compared to theoretical model calculations, and with the results at $\sqrt{s}=7$ TeV.

   ↳ hep-exnucl-exPoS(2021)·3 citations
9. 09*

   Characterization of Muon and Electron Beams in the Paul Scherrer Institute PiM1 Channel for the MUSE Experiment

   E. Cline🇺🇸 · W. Lin🇺🇸 · P. Roy🇮🇳 · P. E. Reimer🇺🇸 · K. E. Mesick🇺🇸 · A. Akmal🇺🇸 · A. Alie🇺🇸 · H. Atac🇺🇸 · A. Atencio🇺🇸 · C. Ayerbe Gayoso🇺🇸 · N. Benmouna🇺🇸 · F. Benmokhtar🇺🇸 and 48 other authors

   The MUon Scattering Experiment, MUSE, at the Paul Scherrer Institute, Switzerland, investigates the proton charge radius puzzle, lepton universality, and two-photon exchange, via simultaneous measurements of elastic muon-proton and electron-proton scattering. The experiment uses the PiM1 secondary beam channel, which was designed for high precision pion scattering measurements. We review the properties of the beam line established for pions. We discuss the production processes that generate the electron and muon beams, and the simulations of these processes. Simulations of the $\pi$/$\mu$/$e$ beams through the channel using TURTLE and G4beamline are compared. The G4beamline simulation is then compared to several experimental measurements of the channel, including the momentum dispersion at the IFP and target, the shape of the beam spot at the target, and timing measurements that allow the beam momenta to be determined. We conclude that the PiM1 channel can be used for high precision $\pi$, $\mu$, and $e$ scattering.

   ↳ physics.ins-detnucl-exPRC(2022)·15 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.