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del Rio, A., Sanchis-Gual, N., Mewes, V., Agullo, I., Font, J. A., & Navarro-Salas, J. (2020). Spontaneous Creation of Circularly Polarized Photons in Chiral Astrophysical Systems. Phys. Rev. Lett., 124(21), 211301–6pp.
Abstract: This work establishes a relation between chiral anomalies in curved spacetimes and the radiative content of the gravitational field. In particular, we show that a flux of circularly polarized gravitational waves triggers the spontaneous creation of photons with net circular polarization from the quantum vacuum. Using waveform catalogs, we identify precessing binary black holes as astrophysical configurations that emit such gravitational radiation and then solve the fully nonlinear Einstein's equations with numerical relativity to evaluate the net effect. The quantum amplitude for a merger is comparable to the Hawking emission rate of the final black hole and small to be directly observed. However, the implications for the inspiral of binary neutron stars could be more prominent, as argued on symmetry grounds.
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Foffa, S., Mastrolia, P., Sturani, R., Sturm, C., & Bobadilla, W. J. T. (2019). Static Two-Body Potential at Fifth Post-Newtonian Order. Phys. Rev. Lett., 122(24), 241605–6pp.
Abstract: We determine the gravitational interaction between two compact bodies up to the sixth power in Newton's constant, G(N), in the static limit. This result is achieved within the effective field theory approach to general relativity, and exploits a manifest factorization property of static diagrams which allows us to derive static post Newtonian (PN) contributions of (2n + 1) order in terms of lower order ones. We recompute in this fashion the 1PN and 3PN static potential, and present the novel 5PN contribution.
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Figueroa, D. G., Lizarraga, J., Urio, A., & Urrestilla, J. (2023). Strong Backreaction Regime in Axion Inflation. Phys. Rev. Lett., 131(15), 151003–7pp.
Abstract: We study the nonlinear dynamics of axion inflation, capturing for the first time the inhomogeneity and full dynamical range during strong backreaction, till the end of inflation. Accounting for inhomogeneous effects leads to a number of new relevant results, compared to spatially homogeneous studies: (i) the number of extra efoldings beyond slow-roll inflation increases very rapidly with the coupling, (ii) oscillations of the inflaton velocity are attenuated, (iii) the tachyonic gauge field helicity spectrum is smoothed out (i.e., the spectral oscillatory features disappear), broadened, and shifted to smaller scales, and (iv) the nontachyonic helicity is excited, reducing the chiral asymmetry, now scale dependent. Our results are expected to impact strongly on the phenomenology and observability of axion inflation, including gravitational wave generation and primordial black hole production.
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ATLAS Collaboration(Aad, G. et al), Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Cantero, J., et al. (2023). Strong Constraints on Jet Quenching in Centrality-Dependent p plus Pb Collisions at 5.02 TeV from ATLAS. Phys. Rev. Lett., 131(7), 072301–21pp.
Abstract: Jet quenching is the process of color-charged partons losing energy via interactions with quark-gluon plasma droplets created in heavy-ion collisions. The collective expansion of such droplets is well described by viscous hydrodynamics. Similar evidence of collectivity is consistently observed in smaller collision systems, including pp and p+ Pb collisions. In contrast, while jet quenching is observed in Pb + Pb collisions, no evidence has been found in these small systems to date, raising fundamental questions about the nature of the system created in these collisions. The ATLAS experiment at the Large Hadron Collider has measured the yield of charged hadrons correlated with reconstructed jets in 0.36 nb-1 of p+ Pb and 3.6 pb-1 of pp collisions at 5.02 TeV. The yields of charged hadrons with p(T)(ch) > 0.5 GeV near and opposite in azimuth to jets with p(t)(je) T > 30 or 60 GeV, and the ratios of these yields between p+ Pb and pp collisions, IpPb, are reported. The collision centrality of p+ Pb events is categorized by the energy deposited by forward neutrons from the struck nucleus. The IpPb values are consistent with unity within a few percent for hadrons with p(T )(ch)> 4 GeV at all centralities. These data provide new, strong constraints that preclude almost any parton energy loss in central p+ Pb collisions.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2014). Study of Beauty Hadron Decays into Pairs of Charm Hadrons. Phys. Rev. Lett., 112(20), 202001–9pp.
Abstract: First observations of the decays A(b)(0) -> A(c)(+)D((s))(-) are reported using data corresponding to an integrated luminosity of 3 fb(-1) collected at 7 and 8 TeV center-of- ass energies in proton-proton collisions with the LHCb detector. In addition, the most precise measurement of the branching fraction B(B-s(0) -> D+Ds-) is made and a search is performed for the decays B-0((s)) -> A(c)(+)A(c)(-). The results obtained are B(A(b)(0) -> A(c)(+)D(-))/B(A(b)(0) -> A(c)(+)D(s)(-)) = 0.042 +/- 0.003 (stat) +/- 0.003 (syst), [B(A(b)(0) -> A(c)(+)D(s)(-))/B((B) over bar (0) -> D+Ds-)]/[B(A(b)(0) -> A(c)(+)pi(-))/B((B) over bar (0) -> D+pi(-))] = 0.96 +/- 0.02 (stat) +/- 0.06 (syst), B(B-s(0) -> D+Ds-)/B((B) over bar (0) -> D+Ds-) = 0.038 +/- 0.004 (stat) +/- (syst), B((B) over bar (0) -> A(c)(+)A(c)(-))/B((B) over bar (0) -> D+Ds-) < 0.0022[95% C.L.], B(B-s(0) -> A(c)(+)A(c)(-)) /B(B-s(0) -> D+Ds-) < 0.30[95% C.L.]. Measurement of the mass of the A(b)(0) baryon relative to the (B) over bar (0) meson gives M(A(b)(0)) – M((B) over bar (0)) = 339.72 +/- 0.24 (stat) +/- 0.18 (syst) MeV/c(2). This result provides the most precise measurement of the mass of the A(b)(0) baryon to date.
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BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., Oyanguren, A., & Villanueva-Perez, P. (2015). Study of CP Asymmetry in B-0-(B)over-bar(0) Mixing with Inclusive Dilepton Events. Phys. Rev. Lett., 114(8), 081801–8pp.
Abstract: We present a measurement of the asymmetry A(CP) between same- sign inclusive dilepton samples l(+) l(+) and l(-) l(-) ( l = e, mu) from semileptonic B decays in Y(4S) -> B (B) over bar events, using the complete data set recorded by the BABAR experiment near the Y(4S) resonance, corresponding to 471 x 10(6) B (B) over bar pairs. The asymmetry A(CP) allows comparison between the mixing probabilities P((B) over bar (0) -> B-0) and P(B-0 -> (B) over bar (0)) and therefore probes CP and T violation. The result, A(CP) = [-3.9 +/- 3.5(stat) +/- 1.9(syst)] x 10(-3), is consistent with the standard model expectation.
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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). Study of High-Transverse-Momentum Higgs Boson Production in Association with a Vector Boson in the qqbb Final State with the ATLAS Detector. Phys. Rev. Lett., 132(13), 131802–23pp.
Abstract: This Letter presents the first study of Higgs boson production in association with a vector boson (V = W or Z) in the fully hadronic qqbb final state using data recorded by the ATLAS detector at the LHC in ffiffiproton-proton collisions at root root s= 13 TeV and corresponding to an integrated luminosity of 137fb(-1). The vector bosons and Higgs bosons are each reconstructed as large-radius jets and tagged using jet substructure techniques. Dedicated tagging algorithms exploiting b-tagging properties are used to identify jets consistent with Higgs bosons decaying into b (b) over bar. Dominant backgrounds from multijet production are determined directly from the data, and a likelihood fit to the jet mass distribution of Higgs boson candidates is used to extract the number of signal events. The VH production cross section is measured inclusively and differentially in several ranges of Higgs boson transverse momentum: 250-450, 450-650, and greater than 650 GeV. The inclusive signal yield relative to the standard model expectation is observed to be μ= 1.4(-0.9)(+1.0) and the corresponding cross section is 3.1 +/- 1.3(stat)(-1.4)(+1.8) (syst) pb.
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LHCb Collaboration(Aaij, R. et al), Garcia Martin, L. M., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., Ruiz Valls, P., et al. (2017). Study of J/psi production in jets. Phys. Rev. Lett., 118(19), 192001–11pp.
Abstract: The production of J/psi mesons in jets is studied in the forward region of proton-proton collisions using data collected with the LHCb detector at a center-of-mass energy of 13 TeV. The fraction of the jet transverse momentum carried by the J/psi meson, z(J/psi) p(T) (J/psi) / p(T)(jet) is measured using jets with p(T)(jet) > 20 GeV in the pseudorapidity range 2.5 < eta(jet) < 4.0. The observed z(J/psi) distribution for J/psi mesons produced in b-hadron decays is consistent with expectations. However, the results for prompt J/psi production do not agree with predictions based on fixed-order nonrelativistic QCD. This is the first measurement of the p(T) fraction carried by prompt J/psi mesons in jets at any experiment.
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LHCb Collaboration(Aaij, R. et al), Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., & Ruiz Vidal, J. (2022). Study of Z Bosons Produced in Association with Charm in the Forward Region. Phys. Rev. Lett., 128(8), 082001–12pp.
Abstract: Events containing a Z boson and a charm jet are studied for the first time in the forward region of proton-proton collisions. The data sample used corresponds to an integrated luminosity of 6 fb(-1) collected at a center-of-mass energy of 13 TeV with the LHCb detector. In events with a Z boson and a jet, the fraction of charm jets is determined in intervals of Z-boson rapidity in the range 2.0 < y(Z) < 4.5. A sizable enhancement is observed in the forwardmost y(Z) interval, which could be indicative of a valencelike intrinsic-charm component in the proton wave function.
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AGATA Collaboration(Hadynska-Klek, K. et al), & Gadea, A. (2016). Superdeformed and Triaxial States in Ca-42. Phys. Rev. Lett., 117(6), 062501–7pp.
Abstract: Shape parameters of a weakly deformed ground-state band and highly deformed slightly triaxial sideband in Ca-42 were determined from E2 matrix elements measured in the first low-energy Coulomb excitation experiment performed with AGATA. The picture of two coexisting structures is well reproduced by new state-of-the-art large-scale shell model and beyond-mean-field calculations. Experimental evidence for superdeformation of the band built on 0(2)(+) has been obtained and the role of triaxiality in the A similar to 40 mass region is discussed. Furthermore, the potential of Coulomb excitation as a tool to study superdeformation has been demonstrated for the first time.
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