Fri·Apr 11, 2025Friday·April 11, 2025

1. 01*

   Measurement of coincident photon-initiated processes in ultra-peripheral Pb+Pb collisions with the ATLAS detector

   ATLAS Collaboration

   The Lorentz-contracted electromagnetic fields of the ions in ultra-relativistic heavy-ion collisions generate intense quasi-real photon fluxes. These lead to photon-induced interactions that are observed in ultra-peripheral collisions (UPCs), such as vector meson and lepton-pair production. The high photon flux also enables the occurrence of multiple photon-induced processes in a single collision. Presented is the first measurement of the coincident production of $\gamma \gamma \to {\mu }^{+}{\mu }^{-}$ and $\gamma +A\to {\rho }^0+A$ in UPC Pb+Pb collisions at centre-of-mass energies of 5.02 TeV and 5.36 TeV with the ATLAS detector at the Large Hadron Collider. The rate of the coincident process relative to the exclusive $\gamma \gamma \to {\mu }^{+}{\mu }^{-}$ process is measured differentially in intervals of forward event activity, quantified by the Zero Degree Calorimeters. The relative rate, summed over forward event activity, for the coincident ${\rho }^0$ production is measured to be $(9.3\pm 0.4(stat.)\pm 0.2(syst.))\times 10^{-3}$. Correlations between the dimuon kinematic properties, such as its mass, and the coincident ${\rho }^0$ meson production rate, are also presented. These measurements confirm the presence of multi photon-induced processes in UPC collisions, and can provide new insight into the impact parameter dependence of photon-induced vector meson production.

   nucl-exhep-ex14 citations
2. 02*

   Probing fluctuating protons using forward neutrons in soft and hard inelastic proton-nucleus scattering

   M. Alvioli (CNR IRPI, Perugia and INFN, Perugia)🇮🇹 · V. Guzey (Jyvaskyla U. and Helsinki Inst. of Phys., Helsinki U.)🇫🇮 · M. Strikman (Penn State U.)🇺🇸

   We present a model for the distribution of the number of forward neutrons emitted in soft (minimum bias) and hard inelastic proton-nucleus ($pA$) scattering at the LHC. It is based on the Gribov-Glauber model for the distribution over the number of inelastic collisions (wounded nucleons) combined with a parametrization of cross section (color) fluctuations in the projectile proton, which depend on the parton momentum fraction $x_p$, and the assumption of independent neutron emissions. We observe that while the effect of soft color fluctuations is modest, a reduction of the interaction strength with increasing $x_p$ provides the dominant effect. It allows us to qualitatively describe the trend of the ATLAS data on the ZDC energy spectra of forward neutrons emitted in dijet production in inelastic $pA$ scattering at $\sqrt{s_{NN}}=8.16$ TeV.

   ↳ hep-phhep-exnucl-exPRC(2025)·2 citations
3. 03*

   Radiative $\alpha$ capture on ${}^{12}$C in cluster effective field theory: short review

   Shung-Ichi Ando🇰🇷

   Study of radiative $\alpha$ capture on ${}^{12}$C, ${}^{12}$C($\alpha$,$\gamma$)${}^{16}$O, in cluster effective field theory (EFT) is reviewed. A low energy EFT for ${}^{12}$C($\alpha$,$\gamma$)${}^{16}$O at the Gamow-peak energy, $E_G=0.3$~MeV, is constructed, and the theory is first applied to the study of elastic $\alpha$-${}^{12}$C scattering at low energies. The effective range parameters are fitted to the precise phase shift data of the elastic scattering and the astrophysical $S_{E1}$ factor of the $E1$ transition of ${}^{12}$C($\alpha$,$\gamma$)${}^{16}$O at $E_G$ is estimated. For the study of the $E2$ transition of ${}^{12}$C($\alpha$,$\gamma$)${}^{16}$O, we discuss a difficulty to determine the asymptotic normalization coefficient (ANC) of the subthreshold $2_1^{+}$ state of ${}^{16}$O from the elastic scattering data, and demonstrate the difficulty with the estimate of the astrophysical $S_{E2}$ factor of ${}^{12}$C($\alpha$,$\gamma$)${}^{16}$O at $E_G$. We discuss the uncertainty in the estimate of the $S$ factors at $E_G$ in the present approach.

   ↳ nucl-thnucl-exNPA(2025)·3 citations
4. 04*

   Schottky detection techniques for ultra-rare short-lived ions in heavy ion storage rings

   Shahab Sanjari🇩🇪 · Yuri A. Litvinov🇩🇪 · George Hudson-Chang🇬🇧 · Sarah Naimi🇫🇷 · Dmytro Dmytriiev🇩🇪 · Jan Glorius🇩🇪 · Esther Menz🇩🇪 · Tetsuya Ohnishi🇯🇵 · Zsolt Podolyak🇬🇧 · Thomas Stöhlker🇩🇪 · Takayuki Yamaguchi🇯🇵 · Yoshitaka Yamaguchi🇯🇵 · Asahi Yano🇯🇵

   Non-destructive Schottky detectors are indispensable devices widely used in experiments at heavy-ion storage rings. In particular, they can be used to accurately determine the masses and lifetimes of short-lived exotic nuclear species. Single-ion sensitivity -- which enables highest sensitivity -- has been regularly achieved in the past utilizing resonant cavity detectors. Recent designs and analysis methods aim at pushing the limits of measurement accuracy by increasing the dimensionality of the acquired data, namely the position of the particle as well as the phase difference between several detectors. This work describes current methods and future perspectives of Schottky detection techniques focusing at their application for mass and lifetime measurements of the most rare and simultaneously short-lived radio nuclides.

   ↳ physics.ins-detnucl-exCPC(2025)·0 citations
5. 05*

   Off-line Commissioning of the St. Benedict Radiofrequency Quadrupole Cooler-Buncher

   D.P. Burdette🇺🇸 · R. Zite🇺🇸 · M. Brodeur🇺🇸 · A.A. Valverde🇺🇸 · O. Bruce🇺🇸 · R. Bualuan · A. Cannon · J.A. Clark🇺🇸 · C. Davis🇨🇦 · T. Florenzo · A.T. Gallant🇺🇸 · J. Harkin🇮🇪 and 11 other authors

   The St. Benedict ion trapping system, which aims to measure the $\beta -\nu$ angular correlation parameter in superallowed-mixed mirror transitions, is under construction at the University of Notre Dame. These measurements will provide much-needed data to improve the accuracy of the $V_{ud}$ element of the CKM matrix. One of the major components of this system is the radio frequency quadrupole cooler-buncher, which is necessary to create low-emittance ion bunches for injection into the measurement Paul trap. The off-line commissioning of the cooler-buncher, using a potassium ion source, determined that the device could produce cooled ion bunches characterized by a 50-ns full-width-half-maximum time width. The commissioning results also determined the trapping efficiency to be 93(1)$\%$ and the trapping half-life to be 20.0(5) s.

   ↳ physics.ins-detnucl-exNucl.Instrum.Meth.A(2026)·6 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.