Wed·May 28, 2025Wednesday·May 28, 2025

1. 01*

   Performance of the prototype Silicon Tracking System of the CBM experiment tested with heavy-ion beams at SIS18

   The CBM Collaboration

   The Compressed Baryonic Matter (CBM) experiment at the future Facility for Antiproton and Ion Research (FAIR) is a heavy-ion experiment designed to study nuclear matter at the highest baryonic density. For high-statistics measurements of rare probes, event rates of up to 10 MHz are targeted. The experiment, therefore, requires fast and radiation-hard detectors, self-triggered detector front-ends, free-streaming readout architecture, and online event reconstruction. The Silicon Tracking System (STS) is the main tracking detector of CBM, designed to reconstruct the trajectories of charged particles with efficiency larger than 95%, a momentum resolution better than 2% for particle momenta larger than 1 GeV/c inside a 1 Tm magnetic field, and to identify complex decay topologies. It comprises 876 double-sided silicon strip modules arranged in 8 tracking stations. A prototype of this detector, consisting of 12 modules arranged in three tracking stations, is installed in the mini-CBM demonstrator. This experimental setup is a small-scale precursor to the full CBM detector, composed of sub-units of all major CBM systems installed on the SIS18 beamline. In various beam campaigns taken between 2021 and 2024, heavy ion collisions at 1-2 AGeV with an average collision rate of 500 kHz have been measured. This allows for the evaluation of the operational performance of the STS detector, including time and position resolution, hit reconstruction efficiency, charge distribution, signal-to-noise ratio, and its potential for track and vertex reconstruction.

   ↳ physics.ins-detnucl-exNucl.Instrum.Meth.A(2026)·11 citations
2. 02*

   Radial excitations and their potential impact on Fermi $\beta$-decay rates

   L. Xayavong🇰🇷 · Y. Lim🇰🇷 · N. A. Smirnova🇫🇷 · Calvin W. Johnson🇺🇸

   We investigate the contribution of radial excitations to Fermi $\beta$-decay matrix element. To this end, exact no-core shell model calculations are performed for the mirror $\beta$ decay of tritium, where full convergence can be achieved on an ordinary computer. The differences between the isospin-mixing correction values obtained in the full and in a restricted model spaces are matched to the radial overlap correction term, analogous to that required in the shell-model approach, where the configuration space is extremely limited. We examine this complementary correction term using a nonorthogonal harmonic-oscillator basis, generated by slightly differentiating the oscillator frequencies between the initial and final nuclei, while all desirable properties, including translational invariance, are still preserved. For $N_{\max }\le 8$, we find that the radial excitation contribution is negative, with a typical magnitude of approximately 10\,\% to 20\,\% of the radial diagonal contribution. This effect becomes more pronounced as the model space increases. Therefore, the ${\delta }_{C2}$ values obtained in the shell model approach, where radial excitations are not explicitly included, are likely overestimated. Based on experimental $ft$ data and the corrective terms adopted in the survey by Hardy and Towner [Phys. Rev. C {\bf 102}, 045501 (2020)], we show that the incorporation of radial excitations for the superallowed $0^{+}\to 0^{+}$ nuclear $\beta$ decay tends however to worsen agreement with the Standard Model.

   ↳ nucl-thnucl-exPRC(2026)·3 citations
3. 03*

   Electromagnetic tomography of radial flow in the quark-gluon plasma

   Lipei Du🇺🇸 · Ulrich Heinz🇺🇸

   We present a novel multimessenger approach to extract the effective radial flow of the quark-gluon plasma (QGP) by jointly analyzing thermal photon and dilepton spectra in heavy-ion collisions. A key feature of this method is that it circumvents the need for a directly unmeasurable reference -- the photon temperature in the absence of flow -- by establishing, within a calibrated model framework, a stable, approximately linear correlation with the dilepton-inferred temperature. This construction defines an experimentally constructible quantity, $v_r^{\mathrm{eff}}$, which reflects early-time collectivity and exhibits a strong correlation with the spacetime-averaged radial velocity of the QGP. Together with previous results linking dilepton slopes to the initial QGP temperature, our work establishes a consistent framework for electromagnetic tomography of the QGP. Our framework quantifies the experimental precision target, thereby providing a concrete roadmap for future measurements at RHIC and the LHC and opening a new avenue to probe the early-time dynamics of hot QCD matter.

   ↳ hep-phnucl-exnucl-thPRL(2026)·6 citations
4. 04*

   On chirality and chiral neutrino oscillations

   Evgeny Akhmedov🇩🇪

   It has been claimed in a number of publications that neutrinos can exhibit chirality oscillations. In this note we discuss the notion of chirality and show that chiral neutrino oscillations in vacuum do not occur. We argue that the incorrect claims to the contrary resulted from a failure to clearly discriminate between quantum fields, states and wave functions. We also emphasize the role played in the erroneous claims on the possibility of chirality oscillations by the widely spread misconceptions about negative energies.

   ↳ hep-phhep-exnucl-ex4 citations
5. 05*

   The anomalous magnetic moment of the muon in the Standard Model: an update

   R. Aliberti🇩🇪 · T. Aoyama🇯🇵 · E. Balzani🇮🇹 · A. Bashir🇲🇽 · G. Benton🇺🇸 · J. Bijnens🇸🇪 · V. Biloshytskyi🇩🇪 · T. Blum🇺🇸 · D. Boito🇧🇷 · M. Bruno🇮🇹 · E. Budassi🇮🇹 · S. Burri🇨🇭 and 223 other authors

   We present the current Standard Model (SM) prediction for the muon anomalous magnetic moment, $a_{\mu }$, updating the first White Paper (WP20) [1]. The pure QED and electroweak contributions have been further consolidated, while hadronic contributions continue to be responsible for the bulk of the uncertainty of the SM prediction. Significant progress has been achieved in the hadronic light-by-light scattering contribution using both the data-driven dispersive approach as well as lattice-QCD calculations, leading to a reduction of the uncertainty by almost a factor of two. The most important development since WP20 is the change in the estimate of the leading-order hadronic-vacuum-polarization (LO HVP) contribution. A new measurement of the $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}$ cross section by CMD-3 has increased the tensions among data-driven dispersive evaluations of the LO HVP contribution to a level that makes it impossible to combine the results in a meaningful way. At the same time, the attainable precision of lattice-QCD calculations has increased substantially and allows for a consolidated lattice-QCD average of the LO HVP contribution with a precision of about 0.9%. Adopting the latter in this update has resulted in a major upward shift of the total SM prediction, which now reads $a_{\mu }^{\text{SM}}=116592033(62)\times 10^{-11}$ (530 ppb). When compared against the current experimental average based on the E821 experiment and runs 1-6 of E989 at Fermilab, one finds $a_{\mu }^{\text{exp}}-a_{\mu }^{\text{SM}}=38(63)\times 10^{-11}$, which implies that there is no tension between the SM and experiment at the current level of precision. The final precision of E989 (127 ppb) is the target of future efforts by the Theory Initiative. The resolution of the tensions among data-driven dispersive evaluations of the LO HVP contribution will be a key element in this endeavor.

   ↳ hep-phhep-exhep-latnucl-ex+1Phys.Rept.(2025)·354 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.