Wed·Jun 16, 2021Wednesday·June 16, 2021

1. 01*

   Constraining baryon annihilation in the hadronic phase of heavy-ion collisions via event-by-event fluctuations

   Oleh Savchuk🇩🇪 · Volodymyr Vovchenko🇺🇸 · Volker Koch🇺🇸 · Jan Steinheimer🇩🇪 · Horst Stoecker🇩🇪

   We point out that the variance of net-baryon distribution normalized by the Skellam distribution baseline, ${\kappa }_2[B-\bar{B}]/⟨B+\bar{B}⟩$, is sensitive to the possible modification of (anti)baryon yields due to $B\bar{B}$ annihilation in the hadronic phase. The corresponding measurements can thus place stringent limits on the magnitude of the $B\bar{B}$ annihilation and its inverse reaction. We perform Monte Carlo simulations of the hadronic phase in Pb-Pb collisions at the LHC via the recently developed subensemble sampler + UrQMD afterburner and show that the effect survives in net-proton fluctuations, which are directly accessible experimentally. The available experimental data of the ALICE Collaboration on net-proton fluctuations disfavors a notable suppression of (anti)baryon yields in $B\bar{B}$ annihilations predicted by the present version of UrQMD if only global baryon conservation is incorporated. On the other hand, the annihilations improve the data description when local baryon conservation is imposed. The two effects can be disentangled by measuring ${\kappa }_2[B+\bar{B}]/⟨B+\bar{B}⟩$, which at the LHC is notably suppressed by annihilations but virtually unaffected by baryon number conservation.

   ↳ hep-phnucl-exnucl-thPLB(2022)·24 citations
2. 02*

   Imprints of high-momentum nucleons in nuclei on hard photons from heavy-ion collisions around the Fermi Energy

   Wen-Mei Guo🇨🇳 · Bao-An Li🇺🇸 · Gao-Chan Yong🇨🇳

   The short-range correlation (SRC) induced by the tensor force in the isosinglet neutron-proton interaction channel leads to a high-momentum tail (HMT) in the single-nucleon momentum distributions n(k) in nuclei. Owing to the remaining uncertainties about the tensor force, the shape of the nucleon HMT may be significantly different from the dilute interacting Fermi gas model prediction $n(k)\sim 1/k^4$ similar to the HMT in cold atoms near the unitary limit. Within an isospin- and momentum-dependent Boltzmann-Uehling-Uhlenbeck transport model incorporating approximately the nucleon HMT, we investigate hard photon emissions in ${}^{14}$N+${}^{12}$C and ${}^{48}$Ca+${}^{124}$Sn reactions at beam energies around the Fermi energy. Imprints of different shapes of the HMT on the energy spectrum, angular distribution and transverse momentum spectrum of hard photons are studied. While the angular distribution does not carry any information about the shape of the nucleon HMT, the energy spectra and especially the mid-rapidity transverse momentum spectra of hard photons are found to bare strong imprints of the shapes of nucleon HMTs in the two colliding nuclei.

   ↳ nucl-thnucl-exPRC(2021)·37 citations
3. 03*

   Characterization of stilbene-d12 for neutron spectroscopy without time of flight

   N. Gaughan · J. Zhou🇨🇳 · F. D. Becchetti · R. O. Torres-Isea · M. Febbraro🇺🇸 · N. Zaitseva · A. Di Fulvio

   We have experimentally characterized the light-output response of a deuterated trans-stilbene (stilbene-d12) crystal to quasi-monoenergetic neutrons in the 0.8 to 4.4 MeV energy range. These data allowed us to perform neutron spectroscopy measurements of a DT 14.1 MeV source and a PuBe-239 source by unfolding the impinging neutron spectrum from the measured light-output response. The stilbene-d12 outperforms a H1-stilbene of similar size when comparing the shape of the unfolded spectra and the reference ones. These results confirm the viability of non-hygroscopic stilbene-d12 crystal for direct neutron spectroscopy without need for time-of-flight measurements. This capability makes stilbene-d12 a well suited detector for fast-neutron spectroscopy in many applications including nuclear reaction studies, radiation protection, nuclear non-proliferation, and space travel.

   ↳ physics.ins-detnucl-exNucl.Instrum.Meth.A(2021)·3 citations
4. 04*

   RTP Pockels Cell with Nanometer-Level Position Control

   Caryn Palatchi🇺🇸 · Kent Paschke🇺🇸

   MOLLER is a future experiment designed to measure parity violation in Moller scattering to extremely high precision. MOLLER will measure the right-left scattering differential cross-section parity-violating asymmetry APV , in the elastic scattering of polarized electrons off an unpolarized LH2 target to extreme ppb precision. To make this measurement, the polarized electron source, generated with a circularly polarized laser beam, must have the ability to switch quickly between right and left helicity polarization states. The polarized source must also maintain minimal right-left helicity correlated beam asymmetries, including energy changes, position changes, intensity changes, or spot-size changes. These requirements can be met with appropriate choice and design of the Pockels cell used to generate the circularly polarized light. Rubidium Titanyl Phosphate (RTP) has been used in recent years for ultra-fast Pockels cell switches due to its lack of piezo-electric resonances at frequencies up to several hundred MHz. However, crystal non-uniformity in this material leads to poorer extinction ratios than in commonly used KD*P Pockels cells when used in hald-wave configuration. It leads to voltage dependent beam steering when used in quarter-wave configuration. Here we present an innovative RTP Pockels cell design which uses electric field gradients to counteract crystal non-uniformities and control beam steering down to the nm-level. We demonstrate this RTP Pockels cell design is capable of producing precisely controlled polarized electron beam at Jefferson Laboratory, a national accelerator facility, for current experiments, including the recent PREX II measurement, as well as the future MOLLER experiment.

   ↳ physics.ins-detnucl-exphysics.acc-phphysics.optics4 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.