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Departamento de Física
Renormalon-based resummation of Bjorken polarised sum rule in holomorphic QCD
2024-10-01, Ayala, Cesar, Castro-Arriaza, Camilo, Cvetic , Gorazd
Approximate knowledge of the renormalon structure of the Bjorken polarised sum rule (BSR) Γ\oline 1p‑n(Q2) leads to the corresponding BSR characteristic function that allows us to evaluate the leading-twist part of BSR. In our previous work [1], this evaluation (resummation) was performed using perturbative QCD (pQCD) coupling a(Q2)≡αs(Q2)/π in specific renormalisation schemes. In the present paper, we continue this work, by using instead holomorphic couplings [a(Q2)↦A(Q2)] that have no Landau singularities and thus require, in contrast to the pQCD case, no regularisation of the resummation formula. The D=2 and D=4 terms are included in the Operator Product Expansion (OPE) of inelastic BSR, and fits are performed to the available experimental data in a specific interval (Qmin2,Qmax2) where Qmax2=4.74GeV2. We needed relatively high Qmin2≈1.7GeV2 in the pQCD case since the pQCD coupling a(Q2) has Landau singularities at Q2≲1GeV2. Now, when holomorphic (AQCD) couplings A(Q2) are used, no such problems occur: for the 3δAQCD and 2δAQCD variants the preferred values are Qmin2≈0.6GeV2. The preferred values of αs in general cannot be unambiguously extracted, due to large uncertainties of the experimental BSR data. At a fixed value of αsMS\oline (MZ2), the values of the D=2 and D=4 residue parameters are determined in all cases, with the corresponding uncertainties.
Erratum to: Search for exclusive Higgs and Z boson decays to ϕγ and ργ with the ATLAS detector (Journal of High Energy Physics, (2018), 2018, 7, (127), 10.1007/JHEP07(2018)127)
2023-12-01, Aaboud, M., Aad, G., Abbott, B., Abdinov, O., Abeloos, B., Abidi, S. H., AbouZeid, O. S., Abraham, N. L., Abramowicz, H., Abreu, H., Abreu, R., Abulaiti, Y., Acharya, B. S., Adachi, S., Adamczyk, L., Adelman, J., Adersberger, M., Adye, T., Affolder, A. A., Afik, Y., Agatonovic-Jovin, T., Agheorghiesei, C., Aguilar-Saavedra, J. A., Ahlen, S. P., Ahmadov, F., Aielli, G., Akatsuka, S., Akerstedt, H., Åkesson, T. P.A., Akilli, E., Akimov, A. V., Alberghi, G. L., Albert, J., Albicocco, P., Alconada Verzini, M. J., Alderweireldt, S. C., Aleksa, M., Aleksandrov, I. N., Alexa, C., Alexander, G., Alexopoulos, T., Alhroob, M., Ali, B., Aliev, M., Alimonti, G., Alison, J., Alkire, S. P., Allbrooke, B. M.M., Allen, B. W., Allport, P. P., Aloisio, A., Alonso, A., Alonso, F., Alpigiani, C., Alshehri, A. A., Alstaty, M. I., Alvarez Gonzalez, B., Álvarez Piqueras, D., Alviggi, M. G., Amadio, B. T., Amaral Coutinho, Y., Amelung, C., Amidei, D., Amor Dos Santos, S. P., Amoroso, S., Amundsen, G., Anastopoulos, C., Ancu, L. S., Andari, N., Andeen, T., Anders, C. F., Anders, J. K., Anderson, K. J., Andreazza, A., Andrei, V., Angelidakis, S., Angelozzi, I., Angerami, A., Anisenkov, A. V., Anjos, N., Annovi, A., Antel, C., Antonelli, M., Antonov, A., Antrim, D. J., Anulli, F., Aoki, M., Aperio Bella, L., Arabidze, G., Arai, Y., Araque, J. P., Araujo Ferraz, V., Arce, A. T.H., Ardell, R. E., Arduh, F. A., Arguin, J. F., Argyropoulos, S., Arik, M., N. Viaux Maira, G.A. Vasquez, BROOKS, WILLIAM K., CARQUIN, EDSON, Kuleshov, S, Lopez, J. A., PEZOA, RAQUEL, Prokoshin, F., Javier Salazar Loyola, Tapia Araya, S., VASQUEZ GUERRA, ANDREA FERNANDA, TAPIA, SEBASTIAN
A search for the exclusive decays of the Higgs and Z bosons to a ϕ or ρ meson and a photon is performed with a pp collision data sample corresponding to an integrated luminosity of up to 35.6 fb−1 collected at s√=13 TeV with the ATLAS detector at the CERN Large Hadron Collider. These decays have been suggested as a probe of the Higgs boson couplings to light quarks. No significant excess of events is observed above the background, as expected from the Standard Model. Upper limits at 95% confidence level were obtained on the branching fractions of the Higgs boson decays to ϕγ and ργ of 5.0×10−4 and 10.4×10−4, respectively. The corresponding 95% confidence level upper limits for the Z boson decays are 0.7×10−6 and 4.0×10−6 for ϕγ and ργ, respectively.
Three-loop inverse scotogenic seesaw models
2024-05-01, Abada, Asmaa, Bernal, Nicolás, Carcamo Hernández, A.E., Kovalenko, Sergey, de Melo, Téssio B.
Abstract We propose a class of models providing an explanation of the origin of light neutrino masses, the baryon asymmetry of the Universe via leptogenesis and offering viable dark matter candidates. In these models the Majorana masses of the active neutrino are generated by the inverse seesaw mechanism with the lepton number violating right-handed Majorana neutrino masses μ arising at three loops. The latter is ensured by the preserved discrete symmetries, which also guarantee the stability of the dark matter candidate. We focus on one of these models and perform a detailed analysis of the phenomenology of its leptonic sector. The model can successfully accommodate baryogenesis through leptogenesis in both weak and strong washout regimes. The lightest heavy fermion turns out to be a viable dark matter candidate, provided that the entries of the Majorana submatrix μ are in the keV to MeV range. The solutions are consistent with the experimental constraints, accommodating both mass orderings for active neutrinos, in particular charged-lepton flavor violating decays μ → eγ, μ → eee, and the electron-muon conversion processes get sizable rates within future sensitivity reach.
A search for an unexpected asymmetry in the production of e+μ− and e−μ+ pairs in proton–proton collisions recorded by the ATLAS detector at s=13 TeV
2022-07-10, Aad, G., Abbott, B., Abbott, D. C., Abed Abud, A., Abeling, K., Abhayasinghe, D. K., Abidi, S. H., Aboulhorma, A., Abramowicz, H., Abreu, H., Abulaiti, Y., Abusleme Hoffman, A. C., Acharya, B. S., Achkar, B., Adam, L., Adam Bourdarios, C., Adamczyk, L., Adamek, L., Addepalli, S. V., Adelman, J., Adiguzel, A., Adorni, S., Adye, T., Affolder, A. A., Afik, Y., Agapopoulou, C., Agaras, M. N., Agarwala, J., Aggarwal, A., Agheorghiesei, C., Aguilar-Saavedra, J. A., Ahmad, A., Ahmadov, F., Ahmed, W. S., Ai, X., Aielli, G., Aizenberg, I., Akatsuka, S., Akbiyik, M., Åkesson, T. P.A., Akimov, A. V., Al Khoury, K., Alberghi, G. L., Albert, J., Albicocco, P., Alconada Verzini, M. J., Alderweireldt, S., Aleksa, M., Aleksandrov, I. N., Alexa, C., Alexopoulos, T., Alfonsi, A., Alfonsi, F., Alhroob, M., Ali, B., Ali, S., Aliev, M., Alimonti, G., Allaire, C., Allbrooke, B. M.M., Allport, P. P., Aloisio, A., Alonso, F., Alpigiani, C., Alunno Camelia, E., Alvarez Estevez, M., Alviggi, M. G., Amaral Coutinho, Y., Ambler, A., Ambroz, L., Amelung, C., Amidei, D., Amor Dos Santos, S. P., Amoroso, S., Amos, K. R., Amrouche, C. S., Ananiev, V., Anastopoulos, C., Andari, N., Andeen, T., Anders, J. K., Andrean, S. Y., Andreazza, A., Angelidakis, S., Angerami, A., Anisenkov, A. V., Annovi, A., Antel, C., Anthony, M. T., Antipov, E., Antonelli, M., Antrim, D. J.A., Anulli, F., Brooks, William K., CARQUIN, EDSON, Pezoa, Raquel, C.M. Robles Gajardo, Viaux Maira, Nicolas, Araujo Ferraz, V., Arcangeletti, C.
This search, a type not previously performed at ATLAS, uses a comparison of the production cross sections for e+μ− and e−μ+ pairs to constrain physics processes beyond the Standard Model. It uses 139 fb−1 of proton–proton collision data recorded at √s = 13 TeV at the LHC. Targeting sources of new physics which prefer final states containing e+μ− to e−μ+, the search contains two broad signal regions which are used to provide model-independent constraints on the ratio of cross sections at the 2% level. The search also has two special selections targeting supersymmetric models and leptoquark signatures. Observations using one of these selections are able to exclude, at 95% confidence level, singly produced smuons with masses up to 640 GeV in a model in which the only other light sparticle is a neutralino when the Rparity-violating coupling λ 231 is close to unity. Observations using the other selection exclude scalar leptoquarks with masses below 1880 GeV when geu 1R = g μc 1R = 1, at 95% confidence level. The limit on the coupling reduces to geu 1R = g μc 1R = 0.46 for a mass of 1420 GeV.
Long-lived light neutralinos at Belle II
2021-02-01, Dey, Sourav, Dib Venturelli, Claudio Omar, Helo, Juan Carlos, Nayak, Minakshi, Neill, Nicolás A., Soffer, Abner, Wang, Zeren Simon
Abstract We consider light neutralinos of mass about 1 GeV, produced from τ lepton rare decays at Belle II, in the context of R-parity-violating (RPV) supersymmetry. With large and clean samples of τ leptons produced at the Belle II experiment, excellent sensitivity to such light neutralinos with the exotic signatures of displaced vertices is expected. We focus on two benchmark scenarios of single RPV operators, $$ {\lambda}_{311}^{\prime }{L}_3{Q}_1{\overline{D}}_1 $$ λ 311 ′ L 3 Q 1 D ¯ 1 and $$ {\lambda}_{312}^{\prime }{L}_3{Q}_1{\overline{D}}_2 $$ λ 312 ′ L 3 Q 1 D ¯ 2 , which induce both the production and decay of the lightest neutralino. For the reconstruction of a displaced vertex, we require at least two charged pions in the final states. We perform Monte-Carlo simulations for both signal and background events, and find that Belle II can explore regions in the parameter space competitive with other probes. In particular, for the $$ {\lambda}_{311}^{\prime } $$ λ 311 ′ scenario, it can put limits up to two orders of magnitude stronger than the current bounds.
Quantum model for the effect of thiols adsorption on resistivity of gold ultrathin films
2019-12-01, Henríquez, Ricardo, Gonzalez-Fuentes, Claudio, del Campo, Valeria, Correa-Puerta, Jonathan, Parra, Carolina, Marín, Francisca, Häberle, Patricio
The predominant role of surface scattering, in electronic transport through nanoscale thin films, was examined by measuring and modeling the change in resistivity induced by the adsorption of thiols on the surface. For this purpose, gold ultrathin films on sapphire, using chromium as surfactant, were prepared through thermal evaporation, seeking to maximize the surface induced dispersion. A maximum resistivity increase of 13.5% was observed, in an 8 nm Au/Cr/Sapphire sample. This is the highest reported value for such films to date. The morphology of the samples was measured by STM and characterized through height-difference correlation function. A fractal self-affine representation of the surface was found, and it was modified to account the thiol effect: the scattering center due to the adsorption of a molecule was modeled as a void in the surface. This change was related to the electrical transport of the film through two quantum models: the Palasantzas and Barnas (PB) theory and the Sheng, Xing and Wang theory, extended by Munoz et al. (mSXW). For our samples, the mSXW theory did not predict a resistivity change, while the PB theory provides a good description of the experimental resistivity increase due to thiols adsorption as function of thickness.
SDSS J124043.01+671034.68: The partially burned remnant of a low-mass white dwarf that underwent thermonuclear ignition?
2020-08-01, Gänsicke, Boris T., Koester, Detlev, Raddi, Roberto, Toloza, Odette, Kepler, S. O.
ABSTRACT The white dwarf SDSS J124043.01+671034.68 (SDSS J1240+6710) was previously found to have an oxygen-dominated atmosphere with significant traces of neon, magnesium, and silicon. A possible origin via a violent late thermal pulse or binary interactions has been suggested to explain this very unusual photospheric composition. We report the additional detection of carbon, sodium, and aluminium in far-ultraviolet and optical follow-up spectroscopy. No iron-group elements are detected, with tight upper limits on titanium, iron, cobalt, and nickel, suggesting that the star underwent partial oxygen burning, but failed to ignite silicon burning. Modelling the spectral energy distribution and adopting the distance based on the Gaia parallax, we infer a low white dwarf mass, $M_\mathrm{wd}=0.41\pm 0.05\, \mathrm{M}_\odot$. The large space velocity of SDSS J1240+6710, computed from the Gaia proper motion and its radial velocity, is compatible with a Galactic rest-frame velocity of ≃ 250 km s−1 in the opposite direction with respect to the Galactic rotation, strongly supporting a binary origin of this star. We discuss the properties of SDSS J1240+6710 in the context of the recently identified survivors of thermonuclear supernovae, the D6 and LP 40−365 stars, and conclude that it is unlikely related to either of those two groups. We tentatively suggest that SDSS J1240+6710 is the partially burned remnant of a low-mass white dwarf that underwent a thermonuclear event.
Surface roughness of thin gold films and its effects on the proton energy loss straggling
2006-01-01, Celedón, C., M. Flores, Häberle, Patricio, Valdés, J. E.
We present a description of the effect of the surface roughness on the energy straggling associated to the energy loss distributions of protons transmitted through a self supported metallic thin foil. For this purpose we prepared a polycrystalline gold thin films using the standard sputtering method with different deposition rates. The statistics of the surface height distribution induced in these thin films were determined using Atomic Force Microscopy. The measured surface roughness allowed us to quantify the ion energy loss straggling in these samples for different deposition parameters and as a function of the incident ion energy.
Bounds on lepton flavor violating physics and decays of neutral mesons from τ (μ) →3â.,", â.,"γγ -decays
2019-02-01, DIB VENTURELLI, CLAUDIO OMAR, Gutsche, Thomas, Kovalenko, Sergey G., Lyubovitskij, Valery E., SCHMIDT, IVAN
We study two- and three-body lepton flavor violating (LFV) decays involving leptons and neu- tral vector bosons V = ρ0, ω, φ, J/ψ, Υ, Z0, as well as pseudoscalar P = π0, η, η′, ηc and scalar S = f0(500), f0(980), a0(980), χc0(1P ) mesons, without referring to a specific mechanism of LFV realization. In particular, we relate the rates of the three-body LFV decays τ (μ) → 3`, where ` = μ or e, to the two-body LFV decays (V, P ) → τ μ(τ e, μe), where V and P play the role of intermediate resonances in the decay process τ (μ) → 3`. From the experimental upper bounds for the branching ratios of τ (μ) → 3` decays, we derive upper limits for the branching ratios of (V, P ) → τ μ(τ e, μe). We compare our results to the available experimental data and known theoretical upper limits from previous studies of LFV processes and find that some of our limits are several orders of magnitude more stringent. Using the idea of quark-hadron duality, we extract limits on various quark-lepton dimension-six LFV operators from data on lepton decays. Some of these limits are either new or stronger than those existing in the literature.
Composite Resonances effects on EWPT and Higgs diphoton decay rate
2015-01-01, Cárcamo Hernández, A. E., DIB VENTURELLI, CLAUDIO OMAR, ZERWEKH, ALFONSO
In scenarios of strongly coupled electroweak symmetry breaking, heavy composite particles of different spin and parity may arise and cause observable effects on signals that appear at loop levels. The recently observed process of Higgs to γγ at the LHC is one of such signals. We study the new constraints that are imposed on composite models from , together with the existing constraints from the high precision electroweak tests. We use an effective chiral Lagrangian to describe the effective theory that contains the Standard Model spectrum and the extra composites below the electroweak scale. Considering the effective theory cutoff at , consistency with the T and S parameters and the newly observed can be found for a rather restricted range of masses of vector and axial-vector composites from 1.5 TeV to 1.7 TeV and 1.8 TeV to 1.9 TeV, respectively, and only provided a non-standard kinetic mixing between the and fields is included.