Mon·Dec 30, 2024Monday·December 30, 2024

1. 01*

   Improved measurements of neutron lifetime with cold neutron beam at J-PARC

   Y. Fuwa🇯🇵 · T. Hasegawa🇯🇵 · K. Hirota🇯🇵 · T. Hoshino🇯🇵 · R. Hosokawa🇯🇵 · G. Ichikawa🇯🇵 · S. Ieki🇯🇵 · T. Ino🇯🇵 · Y. Iwashita🇯🇵 · M. Kitaguchi🇯🇵 · R. Kitahara🇯🇵 · S. Makise🇯🇵 and 19 other authors

   The ``neutron lifetime puzzle'' arises from the discrepancy between neutron lifetime measurements obtained using the beam method, which measures decay products, and the bottle method, which measures the disappearance of neutrons. To resolve this puzzle, we conducted an experiment using a pulsed cold neutron beam at J-PARC. In this experiment, the neutron lifetime is determined from the ratio of neutron decay counts to ${}^3$He(n,p)${}^3$H reactions in a gas detector. This experiment belongs to the beam method but differs from previous experiments that measured protons, as it instead detects electrons, enabling measurements with distinct systematic uncertainties. By enlarging the beam transport system and reducing systematic uncertainties, we achieved a fivefold improvement in precision. Analysis of all acquired data yielded a neutron lifetime of ${\tau }_{\mathrm{n}}=877.2\pm 1.7_{(stat.)}{}_{-3.6}^{+4.0}{}_{(sys.)}$ s. This result is consistent with bottle method measurements but exhibits a 2.3$\sigma$ tension with the average value obtained from the proton-detection-based beam method.

   nucl-exhep-ex19 citations
2. 02*

   Hard Photon Triggered Jets in $p$-$p$ and $A$-$A$ Collisions

   C. Sirimanna🇺🇸 · Y. Tachibana🇯🇵 · A. Majumder🇺🇸 · A. Angerami🇺🇸 · R. Arora🇺🇸 · S. A. Bass🇺🇸 · Y. Chen🇺🇸 · R. Datta🇺🇸 · L. Du🇨🇦 · R. Ehlers🇺🇸 · H. Elfner🇩🇪 · R. J. Fries🇺🇸 and 40 other authors

   An investigation of high transverse momentum (high-$p_T$) photon triggered jets in proton-proton ($p$-$p$) and ion-ion ($A$-$A$) collisions at $\sqrt{s_{NN}}=0.2$ and $5.02\mathrm{TeV}$ is carried out, using the multistage description of in-medium jet evolution. Monte Carlo simulations of hard scattering and energy loss in heavy-ion collisions are performed using parameters tuned in a previous study of the nuclear modification factor ($R_{AA}$) for inclusive jets and high-$p_T$ hadrons. We obtain a good reproduction of the experimental data for photon triggered jet $R_{AA}$, as measured by the ATLAS detector, the distribution of the ratio of jet to photon $p_T$ ($X_{\mathrm{J}\gamma }$), measured by both CMS and ATLAS, and the photon-jet azimuthal correlation as measured by CMS. We obtain a moderate description of the photon triggered jet $I_{AA}$, as measured by STAR. A noticeable improvement in the comparison is observed when one goes beyond prompt photons and includes bremsstrahlung and decay photons, revealing their significance in certain kinematic regions, particularly at $X_{J\gamma }>1$. Moreover, azimuthal angle correlations demonstrate a notable impact of non-prompt photons on the distribution, emphasizing their role in accurately describing experimental results. This work highlights the success of the multistage model of jet modification to straightforwardly predict (this set of) photon triggered jet observables. This comparison, along with the role played by non-prompt photons, has important consequences on the inclusion of such observables in a future Bayesian analysis.

   ↳ hep-phnucl-exnucl-thPRC(2025)·8 citations
3. 03*

   The Felsenkeller shallow-underground laboratory for nuclear astrophysics

   Daniel Bemmerer🇩🇪 · Axel Boeltzig🇩🇪 · Marcel Grieger🇩🇪 · Katharina Gudat🇩🇪 · Thomas Hensel🇩🇪 · Eliana Masha🇩🇪 · Max Osswald🇩🇪 · Bruno Poser🇩🇪 · Simon Rümmler🇩🇪 · Konrad Schmidt🇩🇪 · José Luis Taín🇪🇸 · Ariel Tarifeño-Saldivia🇪🇸 and 3 other authors

   In the Felsenkeller shallow-underground site, protected from cosmic muons by a 45 m thick rock overburden, a research laboratory including a 5 MV Pelletron ion accelerator and a number of radioactivity-measurement setups is located. The laboratory and its installations are described in detail. The background radiation has been studied, finding suppression factors of 40 for cosmic-ray muons, 200 for ambient neutrons, and 100 for the background in germanium $\gamma$-ray detectors. Using an additional active muon veto, typically the background is just twice as high as in very deep underground laboratories. The properties of the accelerator including its external and internal ion sources and beam line are given. For the radioactivity counting setup, detection limits in the 10${}^{-4}$ Bq range have been obtained. Practical aspects for the usage of the laboratory by outside scientific users are discussed.

   ↳ physics.ins-detnucl-exEPJA(2025)·8 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.