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Toubiana, A., Sberna, L., Caputo, A., Cusin, G., Marsat, S., Jani, K., et al. (2021). Detectable Environmental Effects in GW190521-like Black-Hole Binaries with LISA. Phys. Rev. Lett., 126(10), 101105–6pp.
Abstract: GW190521 is the compact binary with the largest masses observed to date, with at least one black hole in the pair-instability gap. This event has also been claimed to be associated with an optical flare observed by the Zwicky Transient Facility in an active galactic nucleus (AGN), possibly due to the postmerger motion of the merger remnant in the AGN gaseous disk. The Laser Interferometer Space Antenna (LISA) may detect up to ten such gas-rich black-hole binaries months to years before their detection by Laser Interferometer Gravitational Wave Observatory or Virgo-like interferometers, localizing them in the sky within approximate to 1 degrees(2). LISA will also measure directly deviations from purely vacuum and stationary waveforms arising from gas accretion, dynamical friction, and orbital motion around the AGN's massive black hole (acceleration, strong lensing, and Doppler modulation). LISA will therefore be crucial to enable us to point electromagnetic telescopes ahead of time toward this novel class of gas-rich sources, to gain direct insight on their physics, and to disentangle environmental effects from corrections to general relativity that may also appear in the waveforms at low frequencies.
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Caputo, A., Liu, H. W., Mishra-Sharma, S., Pospelov, M., Ruderman, J. T., & Urbano, A. (2021). Edges and Endpoints in 21-cm Observations from Resonant Photon Production. Phys. Rev. Lett., 127(1), 011102–7pp.
Abstract: We introduce a novel class of signatures-spectral edges and end points-in 21-cm measurements resulting from interactions between the standard and dark sectors. Within the context of a kinetically mixed dark photon, we demonstrate how resonant dark photon-to-photon conversions can imprint distinctive spectral features in the observed 21-cm brightness temperature, with implications for current, upcoming, and proposed experiments targeting the cosmic dawn and the dark ages. These signatures open up a qualitatively new way to look for physics beyond the Standard Model using 21-cm observations.
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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). Search for Displaced Leptons in root s=13 TeV pp Collisions with the ATLAS Detector. Phys. Rev. Lett., 127(5), 051802–21pp.
Abstract: A search for charged leptons with large impact parameters using 139 fb(-1) of root s = 13 TeV pp collision data from the ATLAS detector at the LHC is presented, addressing a long-standing gap in coverage of possible new physics signatures. Results are consistent with the background prediction. This search provides unique sensitivity to long-lived scalar supersymmetric lepton partners (sleptons). For lifetimes of 0.1 ns, selectron, smuon, and stau masses up to 720, 680, and 340 GeV, respectively, are excluded at 95% confidence level, drastically improving on the previous best limits from LEP.
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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. (2021). Observation of New Resonances Decaying to J=Psi K plus and J=Psi phi. Phys. Rev. Lett., 127(8), 082001–11pp.
Abstract: The first observation of exotic states with a new quark content ccus decaying to the J/Psi K+ final state is reported with high significance from an amplitude analysis of the B+-> J/ Psi phi K+ decay. The analysis is carried out using proton-proton collision data corresponding to a total integrated luminosity of 9 fb- 1 collected by the LHCb experiment at center-of-mass energies of 7, 8, and 13 TeV. The most significant state, Z(cs)(4000)+, has a mass of 4003 +/- 6 (-14) (+4) MeV, a width of 131 +/- 15 +/- 26 MeV, and spin parity J(P) = 1(+), where the quoted uncertainties are statistical and systematic, respectively. A new 1(+) X(4685) state decaying to the J/Psi phi final state is also observed with high significance. In addition, the four previously reported J/Psi phi states are confirmed and two more exotic states, Z(cs) (4220) (+) and X(4630), are observed with significance exceeding 5 standard deviations.
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Figueroa, D. G., Raatikainen, S., Rasanen, S., & Tomberg, E. (2021). Non-Gaussian Tail of the Curvature Perturbation in Stochastic Ultraslow-Roll Inflation: Implications for Primordial Black Hole Production. Phys. Rev. Lett., 127(10), 101302–7pp.
Abstract: We consider quantum diffusion in ultraslow-roll (USR) inflation. Using the Delta N formalism, we present the first stochastic calculation of the probability distribution P(R) of the curvature perturbation during USR. We capture the nonlinearity of the system, solving the coupled evolution of the coarse-grained background with random kicks from the short wavelength modes, simultaneously with the mode evolution around the stochastic background. This leads to a non-Markovian process from which we determine the highly non-Gaussian tail of P(R). Studying the production of primordial black holes in a viable model, we find that stochastic effects during USR increase their abundance by a factor of similar to 10(5) compared with the Gaussian approximation.
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LHCb Collaboration(Aaij, R. et al), Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., & Ruiz Vidal, J. (2021). Observation of the Mass Difference Between Neutral Charm-Meson Eigenstates. Phys. Rev. Lett., 127(11), 111801–12pp.
Abstract: A measurement of mixing and CP violation in neutral charm mesons is performed using data reconstructed in proton-proton collisions collected by the LHCb experiment from 2016 to 2018, corresponding to an integrated luminosity of 5.4 fb(-1). A total of 30.6 million D0 -> K-s(0)pi(+)pi(-) decays are analyzed using a method optimized for the measurement of the mass difference between neutral charmmeson eigenstates. Allowing for CP violation in mixing and in the interference between mixing and decay, the mass and decay-width differences are measured to be x(CP) = [3.97 +/- 0.46(stat) +/- 0.29(syst)] x 10(-3) and y(CP) = [4.59 +/- 1.20(stat) +/- 0.85(syst)] x 10(-3), respectively. The CP-violating parameters are measured as Delta x= [-0.27 +/- 0.18(stat)+/- 0.01(syst)] x 10 (-3) and Delta y = [0.20 +/- 0.36(stat) +/- 0.13(syst)] x 10(-3). This is the first observation of a nonzero mass difference in the D-0 meson system, with a significance exceeding seven standard deviations. The data are consistent with CP symmetry and improve existing constraints on the associated parameters.
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LHCb Collaboration(Aaij, R. et al), Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., & Ruiz Vidal, J. (2021). Branching Fraction Measurements of the Rare B-s(0) -> phi mu(+)mu(-) and B-s(0)-> f(2)' (1525)mu(+)mu(-) Decays. Phys. Rev. Lett., 127(15), 151801–11pp.
Abstract: The branching fraction of the rare B-s(0) -> phi mu(+)mu(-) decay is measured using data collected by the LHCb experiment at center-of-mass energies of 7, 8, and 13 TeV, corresponding to integrated luminosities of 1, 2, and 6 fb(-1), respectively. The branching fraction is reported in intervals of q(2), the square of the dimuon invariant mass. In the q(2) region between 1.1 and 6.0 GeV2/c(4) , the measurement is found to lie 3.6 standard deviations below a standard model prediction based on a combination of light cone sum rule and lattice QCD calculations. In addition, the first observation of the rare B-s(0)-> f(2)' (1525)mu(+)mu(-) decay is reported with a statistical significance of 9 standard deviations and its branching fraction is determined.
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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). Search for New Phenomena in Final States with Two Leptons and One or No b-Tagged Jets at root s=13 TeV Using the ATLAS Detector. Phys. Rev. Lett., 127(14), 141801–23pp.
Abstract: A search for new phenomena is presented in final states with two leptons and one or no b-tagged jets. The event selection requires the two leptons to have opposite charge, the same flavor (electrons or muons), and a large invariant mass. The analysis is based on the full run-2 proton-proton collision dataset recorded at a center-of-mass energy off root S = 13 TeV by the ATLAS experiment at the LHC, corresponding to an integrated luminosity of 139 fb(-1). No significant deviation from the expected background is observed in the data. Inspired by the B-meson decay anomalies, a four-fermion contact interaction between two quarks (b, s) and two leptons (ee or μmu) is used as a benchmark signal model, which is characterized by the energy scale and coupling, Lambda and g(*), respectively. Contact interactions with Lambda/g(*) lower than 2.0 (2.4) TeV are excluded for electrons (muons) at the 95% confidence level, still far below the value that is favored by the B-meson decay anomalies. Model-independent limits are set as a function of the minimum dilepton invariant mass, which allow the results to be reinterpreted in various signal scenarios.
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Belle II Collaboration(Abudinen, F. et al), & Marinas, C. (2021). Search for B+ -> K+nu(nu)over-bar Decays Using an Inclusive Tagging Method at Belle H. Phys. Rev. Lett., 127(18), 181802–10pp.
Abstract: A search for the flavor-changing neutral-current decay B+ -> K+nu(nu) over bar is performed at the Belle II experiment at the SuperKEKB asymmetric energy electron-positron collider. The data sample corresponds to an integrated luminosity of 63 fb(-1) collected at the Upsilon(4S) resonance and a sample of 9 fb(-1) collected at an energy 60 MeV below the resonance. Because the measurable decay signature involves only a single charged kaon, a novel measurement approach is used that exploits not only the properties of the B+ -> K+nu(nu) over bar decay, but also the inclusive properties of the other B meson in the Upsilon(4S) -> B (B) over bar event, to suppress the background from other B meson decays and light-quark pair production. This inclusive tagging approach offers a higher signal efficiency compared to previous searches. No significant signal is observed. An upper limit on the branching fraction of B+ -> K+nu(nu) over bar of 4.1 x 10(-5) is set at the 90% confidence level.
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Belle II Collaboration(Abudinen, F. et al), & Marinas, C. (2021). Precise Measurement of the D-0 and D+ Lifetimes at Belle II. Phys. Rev. Lett., 127(21), 211801–9pp.
Abstract: We report a measurement of the D-0 and D+ lifetimes using D-0 -> K-pi(+) and D+ -> K-pi(+)pi(+) decays reconstructed in e(+)e(-) -> c (c) over bar data recorded by the Belle II experiment at the SuperKEKB asymmetric-energy e(+)e(-) collider. The data, collected at center-of-mass energies at or near the (sic)(4S) resonance, correspond to an integrated luminosity of 72 fb(-1). The results, (tau)(D-0) = 410.5 +/- 1.1 (stat) +/- 0.8(syst) fs and tau(D-0) = 1030.4 +/- 4.7 (stat) +/- 3.1 (syst) fs, are the most precise to date and are consistent with previous determinations.
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