Mon·Nov 27, 2023Monday·November 27, 2023

1. 01*

   Emergence of long-range angular correlations in low-multiplicity proton-proton collisions

   ALICE Collaboration

   This Letter presents the measurement of near-side associated per-trigger yields, denoted ridge yields, from the analysis of angular correlations of charged hadrons in proton-proton collisions at $\sqrt{s}$ = 13 TeV. Long-range ridge yields are extracted for pairs of charged particles with a pseudorapidity difference of $1.4<|\Delta \eta |<1.8$ and a transverse momentum of $1<p_{\mathrm{T}}<2$ GeV/$c$, as a function of the charged-particle multiplicity measured at midrapidity. This study extends the measurements of the ridge yield to the low multiplicity region, where in hadronic collisions it is typically conjectured that a strongly-interacting medium is unlikely to be formed. The precision of the new low multiplicity results allows for the first direct quantitative comparison with the results obtained in ${\mathrm{e}}^{+}{\mathrm{e}}^{-}$ collisions at $\sqrt{s}$ = 91 GeV and $\sqrt{s}$ = 183$-$209 GeV, where initial-state effects such as pre-equilibrium dynamics and collision geometry are not expected to play a role. In the multiplicity range $8\lesssim ⟨N_{\mathrm{ch}}⟩\lesssim 24$ where the ${\mathrm{e}}^{+}{\mathrm{e}}^{-}$ results have good precision, the measured ridge yields in pp collisions are substantially larger than the limits set in ${\mathrm{e}}^{+}{\mathrm{e}}^{-}$ annihilations. Consequently, the findings presented in this Letter suggest that the processes involved in ${\mathrm{e}}^{+}{\mathrm{e}}^{-}$ annihilations do not contribute significantly to the emergence of long-range correlations in pp collisions.

   nucl-exhep-exPRL(2024)·42 citations
2. 02*

   Measurement of fragment-correlated $\gamma$-ray emission from ${}^{252}$Cf(sf)

   Stefano Marin🇨🇭 · Ivan A. Tolstukhin🇺🇸 · Nathan P. Giha🇺🇸 · Fredrik Tovesson🇺🇸 · Vladimir Protopopescu🇺🇸 · Sara A. Pozzi🇮🇹

   This paper presents recent experimental results on the yield of prompt fission $\gamma$ rays from the spontaneous fission of ${}^{252}$Cf. We use an ionization chamber to tag fission events and measure the masses and kinetic energies of the fission fragments and trans-stilbene organic scintillators to measure the neutrons and $\gamma$ rays emitted by the fission fragments. The combination of the ionization chamber and trans-stilbene scintillators allows us to determine the properties of neutrons and $\gamma$ rays in coincidence with the fragments. The yield of $\gamma$ rays is known to be influenced by the angular momenta (AM) of the fission fragments. We present new experimental evidence that indicates that the total $\gamma$-ray multiplicity, i.e., the sum of both fragments' emission, saturates at sufficiently high internal fragment excitation energies. We also observe distinct behaviors for the yield of $\gamma$ rays from the light and heavy fragment, which for certain mass and total kinetic energy (TKE) regions are weakly or anti-correlated, indicating the presence of complex AM generation modes. We also observed a mass- and TKE-dependent anisotropy of the $\gamma$ rays, which challenges and expands on the conventional notion that the fragments' AM are always aligned perpendicularly to the fission axis. Moreover, the dependence of the anisotropy on mass and TKE indicates a dependence of these properties on the specific fission channels, thus providing an insight into the deformations and dynamics in fission and their connection with experimentally observable quantities.

   nucl-exPRC(2024)·5 citations
3. 03*

   Systematics of the low-energy electric dipole strength in the Sn isotopic chain

   M. Markova (1)🇳🇴 · P. von Neumann-Cosel (2)🇩🇪 · E. Litvinova (3,4,5) ((1) Department of Physics, University of Oslo, Oslo, Norway, (2) Institut fuer Kernphysik, Technische Universitaet Darmstadt, Darmstadt, Germany, (3) Department of Physics, Western Michigan University, Kalamazoo, Michigan, USA, (4) National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan, USA, (5) GANIL, CEA/DRF-CNRS/IN2P3, Caen, France)🇺🇸

   We present a systematic study of the mass dependence of the low-energy electric dipole strength (LEDS) in Sn isotopes in the range $A=111-124$ based on data obtained with the Oslo method and with relativistic Coulomb excitation in forward-angle ($p,p^{\prime }$) scattering. The combined data cover an energy range of $2-20$ MeV which permits, with minimal assumptions, a decomposition of the total strength into the contribution from the low-energy tail of the isovector giant dipole resonance (IVGDR) and possible resonance-like structures on top of it. In all cases, a resonance peaked at about 8.3 MeV is observed, exhausting an approximately constant fraction of the Thomas-Reiche-Kuhn (TRK) sum rule with a local maximum at ${}^{120}$Sn which might be related to shell structure effects. For heavier isotopes ($A\ge 118$) a consistent description of the data requires the inclusion of a second resonance centered at 6.5 MeV, representing the isovector response of the pygmy dipole resonance (PDR). Its strength corresponds to a small fraction of the total LEDS only and shows an approximately linear dependence on mass number. The experimental results are also compared to ab initio-based microscopic calculations to investigate the importance of an inclusion of quasiparticle vibration coupling (qPVC) for a realistic description of the LEDS. A possible interpretation of the experimentally observed two-bump structure is given.

   nucl-exnucl-thPLB(2025)·15 citations
4. 04*

   Impact of two-body currents on magnetic dipole moments of nuclei

   T. Miyagi🇩🇪 · X. Cao · R. Seutin🇩🇪 · S. Bacca🇩🇪 · R. F. Garcia Ruiz🇺🇸 · K. Hebeler🇩🇪 · J. D. Holt🇨🇦 · A. Schwenk🇩🇪

   We investigate the effects of two-body currents on magnetic dipole moments of medium-mass and heavy nuclei using the valence-space in-medium similarity renormalization group with chiral effective field theory interactions and currents. Focusing on near doubly magic nuclei from oxygen to bismuth, we have found that the leading two-body currents globally improve the agreement with experimental magnetic moments. Moreover, our results show the importance of multi-shell effects for ${}^{41}$Ca, which suggest that the $Z=N=20$ gap in ${}^{40}$Ca is not as robust as in ${}^{48}$Ca. The increasing contribution of two-body currents in heavier systems is explained by the operator structure of the center-of-mass dependent Sachs term.

   ↳ nucl-thnucl-exPRL(2024)·58 citations
5. 05*

   Common femtoscopic hadron-emission source in pp collisions at the LHC

   ALICE Collaboration

   The femtoscopic study of pairs of identical pions is particularly suited to investigate the effective source function of particle emission, due to the resulting Bose-Einstein correlation signal. In small collision systems at the LHC, pp in particular, the majority of the pions are produced in resonance decays, which significantly affect the profile and size of the source. In this work, we explicitly model this effect in order to extract the primordial source in pp collisions at $\sqrt{s}=13$ TeV from charged $\pi -\pi$ correlations measured by ALICE. We demonstrate that the assumption of a Gaussian primordial source is compatible with the data and that the effective source, resulting from modifications due to resonances, is approximately exponential, as found in previous measurements at the LHC. The universality of hadron emission in pp collisions is further investigated by applying the same methodology to characterize the primordial source of K$-$p pairs. The size of the primordial source is evaluated as a function of the transverse mass ($m_{\mathrm{T}}$) of the pairs, leading to the observation of a common scaling for both $\pi -\pi$ and K$-$p, suggesting a collective effect. Further, the present results are compatible with the $m_{\mathrm{T}}$ scaling of the p$-$p and p$-\Lambda$ primordial source measured by ALICE in high multiplicity pp collisions, providing additional evidence for the presence of a common emission source for all hadrons in small collision systems at the LHC. This will allow the determination of the source function for any hadron-hadron pairs with high precision, granting access to the properties of the possible final-state interaction among pairs of less abundantly produced hadrons, such as strange or charmed particles.

   ↳ hep-phhep-exnucl-exEPJC(2025)·44 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.