Wed·Nov 3, 2021Wednesday·November 3, 2021

1. 01*

   Centrality determination in heavy-ion collisions with the LHCb detector

   LHCb collaboration: R. Aaij · C. Abellán Beteta · T. Ackernley · B. Adeva · M. Adinolfi · H. Afsharnia · C.A. Aidala · S. Aiola · Z. Ajaltouni · S. Akar · J. Albrecht · F. Alessio and 941 other authors

   The centrality of heavy-ion collisions is directly related to the medium created therein. A procedure to determine the centrality of collisions with the LHCb detector is implemented for lead-lead collisions at $\sqrt{s_{\text{NN}}}=5\mathrm{TeV}$ and lead-neon fixed-target collisions at $\sqrt{s_{\text{NN}}}=69\mathrm{GeV}$. The energy deposits in the electromagnetic calorimeter are used to determine and define the centrality classes. The correspondence between the number of participants and the centrality for the lead-lead collisions is in good agreement with the correspondence found in other experiments, and the centrality measurements for the lead-neon collisions presented here are the first performed in fixed-target collisions at the LHC.

   nucl-exhep-exJINST(2022)·47 citations
2. 02*

   The $\eta$- and ${\eta }^{\prime }$-nucleus interactions and the search for $\eta$, ${\eta }^{\prime }$- mesic states

   Steven D. Bass🇵🇱 · Volker Metag🇩🇪 · Pawel Moskal🇵🇱

   The isoscalar $\eta$ and ${\eta }^{\prime }$ mesons are special in QCD, being linked both to chiral symmetry and to non-perturbative glue associated with the axial anomaly. The properties of these mesons in medium are sensitive to how these dynamics work in the nuclear environment. In contrast to pionic and kaonic atoms which are mainly bound by the Coulomb interaction with some corrections due to the strong force (Coulomb assisted binding), the $\eta$ and ${\eta }^{\prime }$ as neutral mesons can only be bound by the strong interaction. Is this interaction strong enough? This topic has inspired a vigorous program of experiments, conducted in close contact with theory, One has to determine the complex $\eta$, ${\eta }^{\prime }$-nucleus potential. Does the real part $V$ provide a sufficiently deep potential? Is the imaginary part $W$ small enough to allow for narrow states that can more easily be detected experimentally, i.e. $|W|\ll |V|$? The ${\eta }^{\prime }$ effective mass is observed to be suppressed by $\approx -40$ MeV at nuclear matter density. Bound state searches are ongoing. This article gives an overview of the status of knowledge in this field together with an outlook to future experiments.

   ↳ hep-phnucl-exnucl-thIn: Tanihata, I., Toki, H., Kajino, T. (e…·11 citations
3. 03*

   Searching for Hidden Neutrons with a Reactor Neutrino Experiment: Constraints from the STEREO Experiment

   H. Almazán🇩🇪 · L. Bernard🇫🇷 · A. Blanchet🇫🇷 · A. Bonhomme🇩🇪 · C. Buck🇩🇪 · P. del Amo Sanchez🇫🇷 · I. El Atmani🇫🇷 · L. Labit🇫🇷 · J. Lamblin🇫🇷 · A. Letourneau🇫🇷 · D. Lhuillier🇫🇷 · M. Licciardi🇫🇷 and 16 other authors

   Different extensions of the standard model of particle physics, such as braneworld or mirror matter models, predict the existence of a neutron sterile state, possibly as a dark matter candidate. This Letter reports a new experimental constraint on the probability $p$ for neutron conversion into a hidden neutron, set by the STEREO experiment at the high flux reactor of the Institut Laue-Langevin. The limit is $p<3.1\times 10^{-11}$ at $95\%$ C.L. improving the previous limit by a factor 13. This result demonstrates that short-baseline neutrino experiments can be used as competitive passing-through-walls neutron experiments to search for hidden neutrons.

   ↳ hep-exnucl-exPRL(2022)·25 citations
4. 04*

   Modification of $Z^0$ leptonic invariant mass in ultrarelativistic heavy ion collisions as a measure of the electromagnetic field

   Yifeng Sun🇮🇹 · Vincenzo Greco🇮🇹 · Xin-Nian Wang🇺🇸

   An extraordinary strong magnetic field, $e{B}_0\approx 10^{18}$ Gauss, is expected to be generated in non-central ultrarelativistic heavy ion collisions and it is envisaged to induce several effects on hot QCD matter including the possibility of local parity and local parity and charge conjugation symmetry violations. A direct signature of such e.m. fields and a first quantitative measurement of its strength and lifetime are still missing. We point out that both the mean value of leptonic invariant mass of $Z^0$ boson, reconstructed by its decaying lepton pairs, and the relative width are modified in relativistic heavy ion collisions due to the presence of strong initial e.m. fields. We propose a measurement of the leptonic invariant mass of $Z^0$ as a novel probe of the strength of the $B_y$. Both shifts could be up to about few hundred MeV and are found to depend on the integral of $B_y$ over the time duration quadratically (approximate). Hence it provides a novel and clear probe of electromagnetic fields, which can be tested experimentally.

   ↳ nucl-thhep-phnucl-exPLB(2022)·9 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.