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ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Bouchhar, N., et al. (2024). Improving topological cluster reconstruction using calorimeter cell timing in ATLAS. Eur. Phys. J. C, 84(5), 455–42pp.
Abstract: Clusters of topologically connected calorimeter cells around cells with large absolute signal-to-noise ratio (topo-clusters) are the basis for calorimeter signal reconstruction in the ATLAS experiment. Topological cell clustering has proven performant in LHC Runs 1 and 2. It is, however, susceptible to out-of-time pile-up of signals from soft collisions outside the 25 ns proton-bunch-crossing window associated with the event's hard collision. To reduce this effect, a calorimeter-cell timing criterion was added to the signal-to-noise ratio requirement in the clustering algorithm. Multiple versions of this criterion were tested by reconstructing hadronic signals in simulated events and Run 2 ATLAS data. The preferred version is found to reduce the out-of-time pile-up jet multiplicity by similar to 50% for jet p(T) similar to 20 GeV and by similar to 80% for jet p(T) greater than or similar to 50 GeV, while not disrupting the reconstruction of hadronic signals of interest, and improving the jet energy resolution by up to 5% for 20 < p(T) < 30 GeV. Pile-up is also suppressed for other physics objects based on topo-clusters (electrons, photons, tau -leptons), reducing the overall event size on disk by about 6% in early Run 3 pileup conditions. Offline reconstruction for Run 3 includes the timing requirement.
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Batool, A., Malik Sultan, A., Olmo, G. J., & Rubiera-Garcia, D. (2024). Stellar structure in f(R,T) gravity: Some exact solutions. Phys. Rev. D, 110(6), 064059–6pp.
Abstract: We find some exact solutions for constant-density and quark matter equations of state in stellar structure models framed within the f(R, T) = R + lambda(KT)-T-2 theory of gravity, where R is the curvature scalar, T the trace of the stress-energy tensor, and lambda some constant. These solutions correspond to specific values of the constant lambda and represent different compactness states of the corresponding stars, though only those made of quark matter can be regarded as physical. The latter modify the compactness (Buchdahl) limit of neutron stars upward for lambda > 0 until saturating the one of black holes. Our results show that it is possible to find useful insights on stellar structure in this class of theories, a fact that could be used for obtaining constraints on limiting masses such as the minimum hydrogen burning mass.
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Kamenik, J. F., Kosnik, N., & Novoa-Brunet, M. (2024). CP-odd window into long distance dynamics in rare semileptonic B decays. Phys. Rev. D, 110(5), 054013–8pp.
Abstract: We consider the combined measurements of -averaged decay rates and direct asymmetries of (+/-) -> (+/-)l(+)l(-) and (+/-) -> (+/-)l(+)l(-) to probe (nonlocal) four-quark operator matrix element contributions to rare semileptonic meson decays. We also explore how their effects could be in principle disentangled from possible local new physics effects using -spin relations. To this end, we construct a ratio of -odd decay rate differences which are exactly predicted within the standard model in the -spin limit, while the leading -spin breaking effects can also be systematically calculated. Our results motivate binned measurements of the direct asymmetry in (+/-) -> (+/-)l(+)l(-) as well as dedicated theoretical estimates of -spin breaking both in local form factors as well as in four-quark matrix elements.
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Neri, N. et al, Jaimes Elles, S. J., Libralon, S., Martinez-Vidal, F., Mazorra de Cos, J., Sanderswood, I., et al. (2024). Advancements in experimental techniques for measuring dipole moments of short-lived particles at the LHC. Nucl. Instrum. Methods Phys. Res. A, 1069, 169875–5pp.
Abstract: ALADDIN is a proposed fixed-target experiment at the LHC for the direct measurement of charm baryon dipole moments. The detector features a spectrometer and a Cherenkov detector, while the experimental technique is based on the phenomena of particle channelling and spin precession in bent crystals. TWOCRYST, a proof-of- principle test at the LHC for the proposed experiment, is planned during the LHC Run 3. Recent channelling efficiency measurements performed at the CERN SPS of bent crystals developed at INFN are presented, marking significant progress towards its realisation. The silicon pixel detector for TWOCRYST is under construction. It will work in the secondary vacuum of a Roman Pot positioned inside the LHC beam pipe. The design, construction and integration of the pixel detector inside the Roman Pot will be discussed, along with the design and perspectives for the proposed ALADDIN experiment.
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Casanovas-Hoste, A. (2024). Shedding Light on the Origin of Pb-204, the Heaviest s-Process-Only Isotope in the Solar System. Phys. Rev. Lett., 133(5), 052702–8pp.
Abstract: Asymptotic giant branch stars are responsible for the production of most of the heavy isotopes beyond Sr observed in the solar system. Among them, isotopes shielded from the r-process contribution by their stable isobars are defined as s-only nuclei. For a long time the abundance of (204) Pb, the heaviest s-only isotope, has been a topic of debate because state-of-the-art stellar models appeared to systematically underestimate its solar abundance. Besides the impact of uncertainties from stellar models and galactic chemical evolution simulations, this discrepancy was further obscured by rather divergent theoretical estimates for the neutron capture cross section of its radioactive precursor in the neutron-capture flow, 204 Tl ( t( 1/2)=2 1 / 4 3.78 . 78 yr), and by the lack of experimental data on this reaction. We present the first ever neutron capture measurement on (204) Tl, conducted at the CERN neutron time-of-flight facility n_TOF, employing a sample of only 9 mg of 204 Tl produced at the Institute Laue Langevin high flux reactor. By complementing our new results with semiempirical calculations we obtained, at the s-process temperatures of kT approximate to 8 keV and kT approximate to 30 keV, Maxwellian-averaged cross sections (MACS) of 580(168) mb and 260(90) mb, respectively. These figures are about 3% lower and 20% higher than the corresponding values widely used in astrophysical calculations, which were based only on theoretical calculations. By using the new Tl-204 MACS, the uncertainty arising from the( 204) Tl ( n ; gamma) cross section on the s-process abundance of Pb-204 has been reduced from similar to 30% down to & thorn;8%= = – 6% , and the s-process calculations are in agreement with the latest solar system abundance of Pb-204 reported by K. Lodders in 2021.
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