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Hernandez, P., Kekic, M., Lopez-Pavon, J., Racker, J., & Salvado, J. (2016). Testable baryogenesis is in seesaw models. J. High Energy Phys., 08(8), 157–29pp.
Abstract: We revisit the production of baryon asymmetries in the minimal type I seesaw model with heavy Majorana singlets in the GeV range. In particular we include “washout” effects from scattering processes with gauge bosons, Higgs decays and inverse decays, besides the dominant top scatterings. We show that in the minimal model with two singlets, and for an inverted light neutrino ordering, future measurements from SHiP and neutrinoless double beta decay could in principle provide sufficient information to predict the matter-antimatter asymmetry in the universe. We also show that SHiP measurements could provide very valuable information on the PMNS CP phases.
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ATLAS Collaboration(Aad, G. et al), Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Cardillo, F., Castillo, F. L., et al. (2021). Test of the universality of τ and μ lepton couplings in W-boson decays with the ATLAS detector. Nat. Phys., 17, 813–818.
Abstract: The standard model of particle physics encapsulates our best current understanding of physics at the smallest scales. A fundamental axiom of this theory is the universality of the couplings of the different generations of leptons to the electroweak gauge bosons. The measurement of the ratio of the decay rate of W bosons to t leptons and muons, R(tau/mu), constitutes an important test of this axiom. Using 139 fb(-1) of proton-proton collisions recorded with the ATLAS detector at a centre-of-mass energy of 13 TeV, we report a measurement of this quantity from di-leptonic tt events where the top quarks decay into a W boson and a bottom quark. We can distinguish muons originating from W bosons and those originating from an intermediate t lepton through the muon transverse impact parameter and differences in the muon transverse momentum spectra. The measured value of R(tau/mu) is 0.992 +/- 0.013 [+/- 0.007(stat) +/- 0.011(syst)] and is in agreement with the hypothesis of universal lepton couplings as postulated in the standard model. This is the only such measurement from the Large Hadron Collider, so far, and obtains twice the precision of previous measurements.
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MiniBooNE Collaboration(Aguilar-Arevalo, A. A. et al), & Sorel, M. (2013). Test of Lorentz and CPT violation with short baseline neutrino oscillation excesses. Phys. Lett. B, 718(4-5), 1303–1308.
Abstract: The sidereal time dependence of MiniBooNE nu(e) and (nu) over bar (e) appearance data is analyzed to search for evidence of Lorentz and CPT violation. An unbinned Kolmogorov-Smirnov (K-S) test shows both the nu(e) and (nu) over bar (e) appearance data are compatible with the null sidereal variation hypothesis to more than 5%. Using an unbinned likelihood fit with a Lorentz-violating oscillation model derived from the Standard Model Extension (SME) to describe any excess events over background, we find that the nu(e) appearance data prefer a sidereal time-independent solution, and the (nu) over bar (e) appearance data slightly prefer a sidereal time-dependent solution. Limits of order 10(-20) GeV are placed on combinations of SME coefficients. These limits give the best limits on certain SME coefficients for nu(mu) -> nu(e) and (nu) over bar (mu) -> (nu) over bar (e) oscillations. The fit values and limits of combinations of SME coefficients are provided.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., et al. (2020). Test of lepton universality with Lambda(0)(b) -> pK(-) l(+)l(-). J. High Energy Phys., 05(5), 40–27pp.
Abstract: The ratio of branching fractions of the decays -> pK(-)mu(+)mu(-),RpK-1}, is measured for the first time using proton-proton collision data corresponding to an integrated luminosity of 4.7 fb(-1) recorded with the LHCb experiment at center-of-mass energies of 7, 8 and 13 TeV. In the dilepton mass-squared range 0.1 < q(2)< 6.0 GeV2/c(4) and the pK(-) mass range m(pK(-)) < 2600 MeV/c(2), the ratio of branching fractions is measured to be RpK-1=1.17-0.16+0.18 +/- 0.0$$ {R}{pK}<^>{-1}={1.17}{-0.16}<^>{+0.18}\pm 0.07 $$\end{document}, where the first uncertainty is statistical and the second systematic. This is the first test of lepton universality with b baryons and the first observation of the decay -> pK(-)e(+)e(-).
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Henry, L., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., et al. (2017). Test of lepton universality with B-0 -> K*(0)l(+)l(-) decays. J. High Energy Phys., 08(8), 055–31pp.
Abstract: A test of lepton universality, performed by measuring the ratio of the branching fractions of the B-0 -> K*(0)mu(+) mu(-) and B-0 -> K*e(+)e(-) decays, R-K*0, is presented. The K*(0) meson is reconstructed in the final state K+pi(-), which is required to have an invariant mass within 100 MeV/c(2) of the known K*(892)(0) mass. The analysis is performed using proton-proton collision data, corresponding to an integrated luminosity of about 3 fb(-1), collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The ratio is measured in two regions of the dilepton invariant mass squared, q(2), to be R-K*0 – {0.66(-0.007)(+0.11)(stat) +/- 0.03(syst) for 0.045 < q(2) < GeV2/c(4), 0.69(-0.07)(+0.11)(stat) +/- 0.05(syst) for 1.1 < q(2) < 6.0 GeV2/c(4). The corresponding 95.4% confidence level intervals are [0.52, 0.89] and [0.53, 0.94]. The results, which represent the most precise measurements of R-K*0 to date, are compatible with the Standard Model expectations at the level of 2.1-2.3 and 2.4-2.5 standard deviations in the two q(2) regions, respectively.
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LHCb Collaboration(Aaij, R. et al), Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., et al. (2022). Test of lepton universality in beauty-quark decays. Nat. Phys., 18(3), 277–282.
Abstract: The standard model of particle physics currently provides our best description of fundamental particles and their interactions. The theory predicts that the different charged leptons, the electron, muon and tau, have identical electroweak interaction strengths. Previous measurements have shown that a wide range of particle decays are consistent with this principle of lepton universality. This article presents evidence for the breaking of lepton universality in beauty-quark decays, with a significance of 3.1 standard deviations, based on proton–proton collision data collected with the LHCb detector at CERN's Large Hadron Collider. The measurements are of processes in which a beauty meson transforms into a strange meson with the emission of either an electron and a positron, or a muon and an antimuon. If confirmed by future measurements, this violation of lepton universality would imply physics beyond the standard model, such as a new fundamental interaction between quarks and leptons.
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Luo, X. L. et al, Agramunt, J., Egea, F. J., Gadea, A., & Huyuk, T. (2014). Test of digital neutron-gamma discrimination with four different photomultiplier tubes for the NEutron Detector Array (NEDA). Nucl. Instrum. Methods Phys. Res. A, 767, 83–91.
Abstract: A comparative study of the neutron-gamma discrimination performance of a liquid scintillator detector BC501A coupled to four different 5 in photomultiplier tubes (ET9390kb, R11833-100, XP4512 and R4144) was carried out Both the Charge Comparison method and the Integrated Rise-Time method were implemented digitally to discriminate between neutrons and gamma rays emitted by a Cf-252 source. In both methods, the neutron-gamma discrimination capabilities of the four photomultiplier tubes were quantitatively compared by evaluating their figure-of-merit values at different energy regions between 50 keVee and 1000 keVee. Additionally, the results were further verified qualitatively using time-of-flight to distinguish gamma rays and neutrons. The results consistently show that photomultiplier tubes R11833-100 and ET9390kb generally perform best regarding neutron-gamma discrimination with only slight differences in figure-of-merit values. This superiority can be explained by their relatively higher photoelectron yield, which indicates that a scintillator detector coupled to a photomultiplier tube with higher photoelectron yield tends to result in better neutron-gamma discrimination performance. The results of this work will provide reference for the choice of photomultiplier tubes for future neutron detector arrays like NEDA.
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ATLAS Collaboration(Aad, G. et al), Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Castillo, F. L., Castillo Gimenez, V., et al. (2020). Test of CP invariance in vector-boson fusion production of the Higgs boson in the H -> tau tau channel in proton-proton collisions at root s=13 TeV with the ATLAS detector. Phys. Lett. B, 805, 135426–25pp.
Abstract: A test of CP invariance in Higgs boson production via vector-boson fusion is performed in the H -> tau tau decay channel. This test uses the Optimal Observable method and is carried out using 36.1 fb(-1) of root s = 13 TeV proton-proton collision data collected by the ATLAS experiment at the LHC. Contributions from CP-violating interactions between the Higgs boson and electroweak gauge bosons are described by an effective field theory, in which the parameter (d) over tilde governs the strength of CP violation. No sign of CP violation is observed in the distributions of the Optimal Observable, and (d) over tilde is constrained to the interval [-0.090, 0.035] at the 68% confidence level (CL), compared to an expected interval of (d) over tilde is an element of [ -0.035, 0.033] based upon the Standard Model prediction. No constraints can be set on (d) over tilde at 95% CL, while an expected 95% CL interval of (d) over tilde is an element of [ -0.21, 0.15] for the Standard Model hypothesis was expected.
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Degiovanni, A., Amaldi, U., Bonomi, R., Garlasche, M., Garonna, A., Verdu-Andres, S., et al. (2011). TERA high gradient test program of RF cavities for medical linear accelerators. Nucl. Instrum. Methods Phys. Res. A, 657(1), 55–58.
Abstract: The scientific community and the medical industries are putting a considerable effort into the design of compact, reliable and cheap accelerators for hadrontherapy. Up to now only circular accelerators are used to deliver beams with energies suitable for the treatment of deep seated tumors. The TERA Foundation has proposed and designed a hadrontherapy facility based on the cyclinac concept: a high gradient linear accelerator placed downstream of a cyclotron used as an injector. The overall length of the linac, and therefore its final cost, is almost inversely proportional to the average accelerating gradient achieved in the linac. TERA, in collaboration with the CLIC RF group, has started a high gradient test program. The main goal is to study the high gradient behavior of prototype cavities and to determine the appropriate linac operating frequency considering important issues such as machine reliability and availability of distributed power sources. A preliminary test of a 3 GHz cavity has been carried out at the beginning of 2010, giving encouraging results. Further investigations are planned before the end of 2011. A set of 5.7 GHz cavities is under production and will be tested in a near future. The construction and test of a multi-cell structure is also foreseen.
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Beltran Jimenez, J., Heisenberg, L., & Olmo, G. J. (2015). Tensor perturbations in a general class of Palatini theories. J. Cosmol. Astropart. Phys., 06(6), 026–16pp.
Abstract: We study a general class of gravitational theories formulated in the Palatini approach and derive the equations governing the evolution of tensor perturbations. In the absence of torsion, the connection can be solved as the Christoffel symbols of an auxiliary metric which is non-trivially related to the space-time metric. We then consider background solutions corresponding to a perfect fluid and show that the tensor perturbations equations (including anisotropic stresses) for the auxiliary metric around such a background take an Einstein-like form. This facilitates the study in a homogeneous and isotropic cosmological scenario where we explicitly establish the relation between the auxiliary metric and the spacetime metric tensor perturbations. As a general result, we show that both tensor perturbations coincide in the absence of anisotropic stresses.
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