Thu·Feb 1, 2024Thursday·February 1, 2024

1. 01*

   Abrasion-fission reactions at intermediate energies

   M. Bowry🇺🇸 · O. B. Tarasov🇺🇸 · J.S. Berryman🇺🇸 · V. Bader🇺🇸 · D. Bazin🇺🇸 · T. Chupp🇺🇸 · H.L. Crawford🇺🇸 · A. Gade🇺🇸 · E. Lunderberg · A. Ratkiewicz · F. Recchia🇮🇹 · B.M. Sherrill🇺🇸 and 7 other authors

   The availability of high-intensity, heavy-ion beams coupled to sensitive, large solid-angleacceptance spectrometers has enabled a detailed examination of the fission fragments produced in induced-fission reactions. The abrasion-fission process involves the formation of projectile-like prefragments in violent nuclear collisions at relative energies in excess of 100 MeV/u. At intermediate energies below this threshold, experiments suggest a change in the prefragment kinematic qualities. Information regarding the influence of this transitional phase upon the evolution of nuclei approaching the point of scission is scarce. In this article, data are presented for over 200 nuclei from nickel to palladium produced in abrasion-fission reactions of a 80 MeV/u 238U beam. Cross sections were obtained following yield measurements performed for the principal charge states of the identified fission fragments and a detailed analysis of the ion transmission. A full kinematic analysis of the fission fragments has been performed using the LISE++ software package, where the trajectory of an ion passing through a spectrometer can be reconstructed based upon measurements at the focal plane. The results obtained at the S800 spectrograph are compared with predictions obtained with a three-fission progenitor (3EER) model. Systematic studies of fission-fragment properties continue to provide a valuable experimental benchmark for theoretical efforts directed toward describing this complex decay channel, that is important in the context of planning experiments to explore the neutron-rich region of the nuclear chart at rare-isotope beam facilities.

   nucl-exPRC(2023)·2 citations
2. 02*

   Clarifying the Radiative Decay of the Hoyle State with Charged-Particle Spectroscopy

   D. Dell'Aquila🇮🇹 · I. Lombardo🇮🇹 · L. Redigolo · M. Vigilante🇮🇹 · F. Angelini🇮🇹 · L. Baldesi🇮🇹 · S. Barlini🇮🇹 · A. Best🇮🇹 · A. Camaiani🇮🇹 · G. Casini🇮🇹 · C. Ciampi🇫🇷 · M. Cicerchia🇮🇹 and 24 other authors

   A detailed knowledge of the decay properties of the so called Hoyle state in the ${}^{12}$C nucleus ($E_x=7.654$ MeV, $0^{+}$) is required to calculate the rate at which carbon is forged in typical red-giant stars. This paper reports on a new almost background-free measurement of the radiative decay branching ratio of the Hoyle state using advanced charged particle coincidence techniques. The exploitation, for the first time in a similar experiment, of a bidimensional map of the coincidence efficiency allows to reach an unitary value and, consequently, to strongly reduce sources of systematic uncertainties. The present results suggest a value of the radiative branching ratio of ${\Gamma }_{rad}/{\Gamma }_{tot}=4.2(6)\cdot 10^{-4}$. This finding helps to resolve the tension between recent data published in the literature.

   nucl-exSci.Rep.(2024)·12 citations
3. 03*

   Exclusive photoproduction of a photon-meson pair: A new class of observables to probe GPDs

   Goran Duplančić🇭🇷 · Saad Nabeebaccus🇫🇷 · Kornelija Passek-K.🇭🇷 · Bernard Pire🇫🇷 · Jakob Schönleber · Lech Szymanowski🇵🇱 · Samuel Wallon🇫🇷

   We discuss the exclusive photoproduction of a photon-meson pair with large $p_T$ as a channel to probe generalised parton distributions (GPDs). Like other $2\to 3$ exclusive processes, this channel allows us to better study the $x$-dependence of GPDs, in contrast to $2\to 2$ processes such as Deeply Virtual Compton Scattering (DVCS) which give only "moment-type" information. Moreover, it also gives the possibility to access, at leading twist, the chiral-odd GPDs, which are still completely unknown experimentally. In the first part of these proceedings, we present the computation of the amplitude at leading order and leading twist, for charged pions, and rho mesons of any charge and polarisation. These processes are sensitive to quark GPDs only. We also discuss the possibility of measuring such processes at various experiments, namely JLab, COMPASS, future EIC and LHC in ultra-peripheral collisions. In particular, in collider experiments, the dependence of GPDs at small skewness $(<10^{-3})$ can be extracted. For the second part, we report on our recent work on the exclusive photoproduction of ${\pi }^0\gamma$ pair, which, in addition to a quark GPD channel, also has a contribution from gluon GPDs. In the latter case, we demonstrate that a collinear factorisation of the process fails, due to the presence of a Glauber pinch. Our findings also imply that other similar processes, like ${\pi }^{0}N\to \gamma \gamma N$ also suffer from the same issue. On the other hand, we stress that the processes discussed earlier, which are sensitive to the quark GPD channels only, are safe from these factorisation breaking effects.

   ↳ hep-phhep-exnucl-exnucl-thPoS(2024)·4 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.