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ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Bouchhar, N., Cabrera Urban, S., Cantero, J., et al. (2025). Observation of t(t)over-bar Production in Pb plus Pb Collisions at √sNN = 5.02 TeV with the ATLAS Detector. Phys. Rev. Lett., 134(14), 142301–22pp.
Abstract: Top-quark pair production is observed in lead-lead (Pb + Pb) collisions at root s(NN) = 5.02 TeV at the Large Hadron Collider with the ATLAS detector. The data sample was recorded in 2015 and 2018, amounting to an integrated luminosity of 1.9 nb(-1). Events with exactly one electron and one muon and at least two jets are selected. Top-quark pair production is measured with an observed (expected) significance of 5.0 (4.1) standard deviations. The measured top-quark pair production cross section is sigma(t (t) over bar) = 3.6(-0.09)(+1.0) (stat)(-0.5)(+0.8) (syst) μb, with a total relative uncertainty of 31%, and is consistent with theoretical predictions using a range of different nuclear parton distribution functions. The observation of this process consolidates the evidence of the existence of all quark flavors in the preequilibrium stage of the quark-gluon plasma at very high energy densities, similar to the conditions present in the early Universe.
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Albaladejo, M., Feijoo, A., Vidaña, I., Nieves, J., & Oset, E. (2025). Inverse problem in femtoscopic correlation functions: the Tcc(3875)+ state. Eur. Phys. J. A, 61(8), 187–15pp.
Abstract: We study the inverse problem of analyzing femtoscopic correlation functions with an efficient tool to extract the maximum information possible about the interaction between the involved coupled-channel hadrons, and derive the existence of possible bound states. The method is flexible enough to accommodate non-molecular components and the effect of missing channels relevant for the interaction. We apply the method to realistic correlation functions for the D*+D0 and D*0D+ pairs derived consistently from the properties of the Tcc(3875)+. We can extract the existence of a bound state, its D*+D0-D*0D+ molecular nature, the probabilities of each channel, as well as scattering lengths and effective ranges, together with the size of the source function, all of these quantities with relatively good precision. We analyze (pseudo) data generated with source sizes of 1fm and 5fm, and observe that the uncertainties are larger for the second case.
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Baeza-Ballesteros, J., HernAndez, P., & Romero-Lopez, F. (2025). The ππ scattering amplitude at large Nc. J. High Energy Phys., 08(8), 110–65pp.
Abstract: We study the scaling of meson-meson scattering amplitudes with the number of colors, N-c. We use lattice calculations in a theory with N-f= 4 degenerate flavors, with N-c= 3-6a nd pion mass M-pi approximate to 560 MeV. We focus on three different scattering channels, two of which have the same quantum numbers as some tetraquark candidates recently found at LHCb: the T-cs0(0)(2900),T-c s0(++)(2900),T-c s0(0)(2900) and T-cs1(0)(2900)states. Finite-volume energies are extracted using a large set of operators, containing two-particle operators with the form of two pions or two vector mesons, and local tetraquark operators. The resulting energy spectra is used to constrain the infinite-volume scattering amplitude by means of Luscher'squantization condition. We consider polynomial parametrizations of the phase shift, as well as one-loop chiral perturbation theory (ChPT) predictions. We find that our lattice results follow the expected N-c scaling and are sensitive to sub leading Nc corrections. In addition, we constrain the scaling of different combinations of low-energy constants from matching to large N-c ChPT. The results for the channel corresponding to a(pi D-+(s)+-K+D+)state show evide Nce of a virtual bound state with energy Evirtual= 1.63(10)M pi for N-c= 3, while this pole disappears atN(c)>3. This may be connected to the exotic states found in experiment
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Sanchis, H., Barenboim, G., & Perez-Gonzalez, Y. F. (2025). Neutrino emission and plasma heating from primordial black holes: an improved approach to Neff constraints. J. Cosmol. Astropart. Phys., 08(8), 049–29pp.
Abstract: We investigate the impact of neutrino emission via Hawking radiation from primordial black holes (PBHs) on the cosmological effective number of neutrino species, Neff, after neutrino decoupling. By comparing this effect with observational limits, we derive bounds on the abundance of light PBHs. Our analysis incorporates two previously unaccounted-for effects: the emission of secondary neutrinos from unstable particles, which increases Neff, and the modification of the neutrino-photon temperature ratio due to particle emission heating the photon plasma, which lowers Neff. Overall, including these effects allows us to impose constraints on PBHs with initial masses in the range 109 g <= Mini <= 1013 g. However, our limits remain less stringent than those derived from Big Bang Nucleosynthesis.
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Perez-Gonzalez, Y. F., & Shergold, J. D. (2025). Cosmic neutrino background detection in the minimally extended Standard Model. J. Cosmol. Astropart. Phys., 08(8), 033–34pp.
Abstract: We investigate the sensitivity of relic neutrino detection methods within the Standard Model, extended to include right-chiral neutrino singlets with Majorana mass terms. In particular, we study neutrino capture on unstable nuclei, the Stodolsky effect, coherent scattering, and an accelerator experiment. We demonstrate that the sensitivity transitions smoothly between Dirac and Majorana regimes, depending on the scale of lepton number violation. Importantly, neutral current interactions lead to transitions between the light and heavy neutrino states, necessitating the use of a density matrix formalism for accurate sensitivity calculations. As the oldest source of neutrinos in the universe, relic neutrinos would be able to provide an ultimate constraint on the lepton number violating scale, mR greater than or similar to 10-33 eV, below which neutrinos would behave as Dirac fermions for all practical purposes.
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