We consider the impact of a weakly coupled environment comprising a light scalar field on the open dynamics of a quantum probe field, resulting in a master equation for the probe field that features corrections to the coherent dynamics, as well as decoherence and momentum diffusion. The light scalar is assumed to couple to matter either through a nonminimal coupling to gravity or, equivalently, through a Higgs portal. Motivated by applications to experiments such as atom interferometry, we assume that the probe field can be initialized, by means of external driving, in a state that is not an eigenstate of the light scalar-field–probe system, and we derive the master equation for single-particle matrix elements of the reduced density operator of a toy model. We comment on the possibilities for experimental detection and the related challenges, and highlight possible pathways for further improvements. This derivation of the master equation requires techniques of nonequilibrium quantum field theory, including the Feynman-Vernon influence functional and thermo field dynamics, used to motivate a method of Lehmann-Symanzik-Zimmermann-like reduction. In order to obtain cutoff-independent results for the probe-field dynamics, we find that it is necessary to use a time-dependent renormalization procedure. Specifically, we show that non-Markovian effects following a quench, namely the violation of time-translational invariance due to finite-time effects, lead to a time-dependent modulation of the usual vacuum counterterms.
Following Krotov and Polyakov [ Nucl. Phys. B849 410 (2011)], we show that in global de Sitter space its isometry is broken by the loop IR divergences for any invariant vacuum state of the massive scalars. We derive a kinetic equation in global de Sitter space that follows from the Dyson-Schwinger equation of the Schwinger-Keldysh diagrammatic technique in the IR limit and allows us to understand the physical meaning and consequences of the loop IR divergences. In many respects, the isometry breaking in global de Sitter space is similar to the one in the contracting Poincaré patch of de Sitter space. Hence, as a warm-up exercise we study the kinetic equation and properties of its solutions in the expanding and contracting Poincaré patches of de Sitter space. Quite unexpectedly, we find that under some initial conditions there is an explosive production of massive particles in the expanding Poincaré patch.
We report measurements of the lifetimes of the Λ+c, Ξ+c and Ξ0c charm baryons using proton-proton collision data at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3.0 fb−1, collected by the LHCb experiment. The charm baryons are reconstructed through the decays Λ+c→pK−π+, Ξ+c→pK−π+ and Ξ0c→pK−K−π+, and originate from semimuonic decays of beauty baryons. The lifetimes are measured relative to that of the D+ meson, and are determined to be τΛ+c=203.5±1.0±1.3±1.4 fs, τΞ+c=456.8±3.5±2.9±3.1 fs, τΞ0c=154.5±1.7±1.6±1.0 fs, where the uncertainties are statistical, systematic, and due to the uncertainty in the D+ lifetime. The measurements are approximately 3–4 times more precise than the current world average values. The Λ+c and Ξ+c lifetimes are in agreement with previous measurements; however, the Ξ0c baryon lifetime is approximately 3.3 standard deviations larger than the world average value.
We measure the inclusive production cross sections of hyperons and charmed baryons from e+e- annihilation using a 800 fb-1 data sample taken near the (4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. The feed-down contributions from heavy particles are subtracted using our data, and the direct production cross sections are presented for the first time. The production cross sections divided by the number of spin states for S=-1 hyperons follow an exponential function with a single slope parameter except for the Σ(1385)+ resonance. Suppression for Σ(1385)+ and Ξ(1530)0 hyperons is observed. Among the production cross sections of charmed baryons, a factor of 3 difference for Λc+ states over Σc states is observed. This observation suggests a diquark structure for these baryons. © 2018 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the »https://creativecommons.org/licenses/by/4.0/» Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3.
Additional scalar fields from scalar-tensor, modified gravity or higher dimensional theories beyond general relativity may account for dark energy and the accelerating expansion of the Universe. These theories have led to proposed models of screening mechanisms, such as chameleon and symmetron fields, to account for the tight experimental bounds on fifth-force searches. Cold atom systems have been very successfully used to constrain the parameters of these screening models, and may in the future eliminate the interesting parameter space of some models entirely. In this paper, we show how to manipulate a Bose-Einstein condensate to simulate the effect of any scalar field model coupled conformally to the metric. We give explicit expressions for the simulation of various common models. This result may be useful for investigating the computationally challenging evolution of particles on a screened scalar field background, as well as for testing the metrology scheme of an upcoming detector proposal.
The core of this work is an old and broadly discussed problem concerning electromagnetic radiation in the case of hyperbolic motion. We prove that radiation is nonzero in the lab (Minkowski) frame. Further, we attempt to understand this subject better by using comoving noninertial frames of reference, investigating other types of uniformly accelerated motion, and, finally, using scalar waves instead of pointlike particles as sources of radiation.
We report the results of a first search for a doubly-charged DDK bound state, denoted the R++, in Υ(1S) and Υ(2S) inclusive decays and via direct production in e+e− collisions at s√ = 10.520, 10.580, and 10.867 GeV. The search uses data accumulated with the Belle detector at the KEKB asymmetric-energy e+e− collider. No significant signals are observed in the D+D∗+s invariant-mass spectra of all studied modes. The 90\% credibility level upper limits on their product branching fractions in Υ(1S) and Υ(2S) inclusive decays (B(Υ(1S,2S)→R+++anything)×B(R++→D+D∗+s)), and the product values of Born cross section and branching fraction in e+e− collisions (σ(e+e−→R+++anything)×B(R++→D+D∗+s)) at s√ = 10.520, 10.580, and 10.867 GeV under different assumptions of R++ masses varying from 4.13 to 4.17 GeV/c2, and widths varying from 0 to 5 MeV are obtained.
We report searches for B0→invisible and B0→invisible+γ decays, where the energy of the photon is required to be larger than 0.5 GeV. These results are obtained from a 711 fb-1 data sample that contains 772×106BB¯ pairs and was collected near the ϒ(4S) resonance with the Belle detector at the KEKB e+e- collider. We observe no significant signal for either decay and set upper limits on their branching fractions at 90% confidence level of B(B0→invisible)<7.8×10-5 and B(B0→invisible+γ)<1.6×10-5. © 2020 authors.
We report the results of a search for the decay B0→X(3872)(→J/ψπ+π-)γ. The analysis is performed on a data sample corresponding to an integrated luminosity of 711 fb-1 and containing 772×106BB pairs, collected with the Belle detector at the KEKB asymmetric-energy e+e- collider running at the (4S) resonance energy. We find no evidence for a signal and place an upper limit of B(B0→X(3872)γ)×B(X(3872)→J/ψπ+π-)<5.1×10-7 at 90% confidence level. © 2019 authors. Published by the American Physical Society.
A search for CP violation in the Λ0b→pπ−π+π− decay is performed using LHCb data corresponding to an integrated luminosity of 6.6 fb−1 collected in pp collisions at center-of-mass energies of 7, 8 and 13 TeV. The analysis uses both triple product asymmetries and the unbinned energy test method. The highest significances of CP asymmetry are 2.9 standard deviations from triple product asymmetries and 3.0 standard deviations for the energy test method. Once the global p-value is considered, all results are consistent with no CP violation. Parity violation is observed at a significance of 5.5 standard deviations for the triple product asymmetry method and 5.3 standard deviations for the energy test method. The reported deviations are given in regions of phase space.
We search for CP violation in the singly-Cabibbo-suppressed decay D0→K+K-π+π- using data corresponding to an integrated luminosity of 988 fb-1 collected by the Belle detector at the KEKB e+e- collider. We measure a set of five kinematically dependent CP asymmetries, of which four asymmetries are measured for the first time. The set of asymmetry measurements can be sensitive to CP violation via interference between the different partial-wave contributions to the decay and performed on other pseudoscalar decays. We find no evidence of CP violation. © 2019 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the »https://creativecommons.org/licenses/by/4.0/» Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3.
Dijet events are studied in the proton-proton collision data set recorded at s=13 TeV with the ATLAS detector at the Large Hadron Collider in 2015 and 2016, corresponding to integrated luminosities of 3.5 fb−1 and 33.5 fb−1 respectively. Invariant mass and angular distributions are compared to background predictions and no significant deviation is observed. For resonance searches, a new method for fitting the background component of the invariant mass distribution is employed. The data set is then used to set upper limits at a 95% confidence level on a range of new physics scenarios. Excited quarks with masses below 6.0 TeV are excluded, and limits are set on quantum black holes, heavy W′ bosons, W* bosons, and a range of masses and couplings in a Z′ dark matter mediator model. Model-independent limits on signals with a Gaussian shape are also set, using a new approach allowing factorization of physics and detector effects. From the angular distributions, a scale of new physics in contact interaction models is excluded for scenarios with either constructive or destructive interference. These results represent a substantial improvement over those obtained previously with lower integrated luminosity.
We report the results of a search for the B→Y(4260)K, Y(4260)→J/ψπ+π− decays. This study is based on a data sample corresponding to an integrated luminosity of 711~fb−1 , collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e− collider. We investigate the J/ψπ+π− invariant mass distribution in the range 4.0 to 4.6 GeV/c2 using both B+→J/ψπ+π−K+ and B0→J/ψπ+π−K0S decays. We find excesses of events above the background levels, with a significances of 2.1 and 0.9 standard deviations for charged and neutral B→Y(4260)K decays, respectively, taking into account the systematic uncertainties. These correspond to upper limits on the product of branching fractions, B(B+→Y(4260)K+)×B(Y(4260)→J/ψπ+π−)<1.4×10−5 and B(B0→Y(4260)K0)×B(Y(4260)→J/ψπ+π−)<1.7×10−5 at the 90\% confidence level.
We have searched for the lepton-flavor-violating decay B0→K∗0μ±e using a data sample of 711 fb-1 that contains 772×106 BB̄ pairs. The data were collected near the (4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. No signals were observed, and we set 90% confidence level upper limits on the branching fractions of B(B0→K∗0μ+e-)<1.2×10-7, B(B0→K∗0μ-e+)<1.6×10-7, and, for both decays combined, B(B0→K∗0μ±e)<1.8×10-7. These are the most stringent limits on these decays to date. © 2018 authors. Published by the American Physical Society.
We present the result of the search for the rare B meson decay of B+→+νγ with =e,μ. For the search the full data set recorded by the Belle experiment of 711 fb-1 integrated luminosity near the (4S) resonance is used. Signal candidates are reconstructed for photon energies Eγ larger than 1 GeV using a novel multivariate tagging algorithm. The novel algorithm fully reconstructs the second B meson produced in the collision using hadronic modes and was specifically trained to recognize the signal signature in combination with hadronic tag-side B meson decays. This approach greatly enhances the performance. Background processes that can mimic this signature, mainly charmless semileptonic decays and continuum processes, are suppressed using multivariate methods. The number of signal candidates is determined by analyzing the missing mass squared distribution as inferred from the signal side particles and the kinematic properties of the tag-side B meson. No significant excess over the background-only hypothesis is observed and upper limits on the partial branching fraction ΔB with Eγ>1 GeV individually for electron and muon final states as well as for the average branching fraction of both lepton final states are reported. We find a Bayesian upper limit of ΔB(B+→+νγ)<3.0×10-6 at 90% CL and also report an upper limit on the first inverse moment of the light-cone distribution amplitude of the B meson of λB>0.24 GeV at 90% CL. © 2018 authors. Published by the American Physical Society.
A search for the flavor-changing neutral-current decay Λ c+→ p μ+ μ− is reported using a data set corresponding to an integrated luminosity of 3.0 fb− 1 collected by the LHCb Collaboration. No significant signal is observed outside of the dimuon mass regions around the ϕ and ω resonances, and an upper limit is placed on the branching fraction of B (Λ c+→ p μ+ μ−)< 7.7 (9.6)× 10− 8 at 90%(95%) confidence level. A significant signal is observed in the ω dimuon mass region for the first time.
A search for the Standard Model Higgs boson produced in association with a top-quark pair, tt¯H, is presented. The analysis uses 36.1 fb-1 of pp collision data at √s = 13 TeV, collected with the ATLAS detector at the Large Hadron Collider in 2015 and 2016. The search targets the H→bb¯ decay mode. The selected events contain either one or two electrons or muons from the top-quark decays, and are then categorized according to the number of jets and how likely these are to contain b-hadrons. Multivariate techniques are used to discriminate between signal and background events, the latter being dominated by tt¯ + jets production. For a Higgs boson mass of 125 GeV, the ratio of the measured tt¯H signal cross-section to the Standard Model expectation is found to be μ=0.84+0.64−0.61. A value of μ greater than 2.0 is excluded at 95% confidence level while the expected upper limit is μ<1.2 in the absence of a tt¯H signal.
Using data collected in the Belle experiment at the KEKB asymmetric-energy e+e− collider we search for transitions Υ(4S)→ηb(1S)ω, Υ(5S)→ηb(1S)ω and Υ(5S)→ηb(2S)ω. No significant signals are observed and we set 90\% confidence level upper limits on the corresponding visible cross sections: 0.2 pb,0.4 pb and 1.9 pb, respectively.
A search is presented for the production of two Higgs bosons in final states containing two photons and two bottom quarks. Both resonant and nonresonant hypotheses are investigated. The analyzed data correspond to an integrated luminosity of 19.7 fb−1 of proton-proton collisions at s√=8 TeVcollected with the CMS detector. Good agreement is observed between data and predictions of the standard model (SM). Upper limits are set at 95% confidence level on the production cross section of new particles and compared to the prediction for the existence of a warped extra dimension. When the decay to two Higgs bosons is kinematically allowed, assuming a mass scale ΛR=1 TeV for the model, the data exclude a radion scalar at masses below 980 GeV. The first Kaluza-Klein excitation mode of the graviton in the RS1 Randall-Sundrum model is excluded for masses between 325 and 450 GeV. An upper limit of 0.71 pb is set on the nonresonant two-Higgs-boson cross section in the SM-like hypothesis. Limits are also derived on nonresonant production assuming anomalous Higgs-boson couplings.
Investigations of the existence of pentaquark states containing a single b (anti)quark decaying weakly into four specific final states J/ψK+π−p, J/ψK−π−p, J/ψK−π+p, and J/ψϕ(1020)p are reported. The data sample corresponds to an integrated luminosity of 3.0 fb−1 in 7 and 8 TeV pp collisions acquired with the LHCb detector. Signals are not observed and upper limits are set on the product of the production cross section times branching fraction with respect to that of the Λ0b.
We report a search for X(3872) and X(3915) in B+→χc1π0K+ decays. We set an upper limit of B(B+→X(3872)K+)×B(X(3872)→χc1π0) <8.1×10−6 and B(B+→X(3915)K+)×B(X(3915)→χc1π0) <3.8×10−5 at 90\% confidence level. We also measure B(X(3872)→χc1π0)/B(X(3872)→J/ψπ+π−)<0.97 at 90\% confidence level. The results reported here are obtained from 772×106 BB¯¯¯¯ events collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e− collider.