6062 research outputs found
Sort by
Search for high-mass exclusive diphoton production with tagged protons in proton-proton collisions at <math display="inline"><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>13</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math>
No full textA search is presented for high-mass exclusive diphoton production via photon-photon fusion in proton-proton collisions at s=13 TeV in events where both protons survive the interaction. The analysis utilizes data corresponding to an integrated luminosity of 103 fb-1 collected in 2016–2018 with the central CMS detector and the CMS and TOTEM precision proton spectrometer (PPS). Events that have two photons with high transverse momenta (pTγ>100 GeV), back-to-back in azimuth, and with a large diphoton invariant mass (mγγ>350 GeV) are selected. To remove the dominant inclusive diphoton backgrounds, the kinematic properties of the protons detected in PPS are required to match those of the central diphoton system. Only events having opposite-side forward protons detected with a fractional momentum loss between 0.035 and 0.15 (0.18) for the detectors on the negative (positive) side of CMS are considered. One exclusive diphoton candidate is observed for an expected background of 1.1 events. Limits at 95% confidence level are derived for the four-photon anomalous coupling parameters |ζ1|<0.073 TeV-4 and |ζ2|<0.15 TeV-4, using an effective field theory. Additionally, upper limits are placed on the production of axionlike particles with coupling strength to photons f-1 that varies from 0.03 TeV-1 to 1 TeV-1 over the mass range from 500 to 2000 GeV
Search for a third-generation leptoquark coupled to a τ lepton and a b quark through single, pair, and nonresonant production in proton-proton collisions at = 13 TeV
No full textA search is presented for a third-generation leptoquark (LQ) coupled exclusively to a τ lepton and a b quark. The search is based on proton-proton collision data at a center-of-mass energy of 13 TeV recorded with the CMS detector, corresponding to an integrated luminosity of 138 fb. Events with τ leptons and a varying number of jets originating from b quarks are considered, targeting the single and pair production of LQs, as well as nonresonant t-channel LQ exchange. An excess is observed in the data with respect to the background expectation in the combined analysis of all search regions. For a benchmark LQ mass of 2 TeV and an LQ-b-τ coupling strength of 2.5, the excess reaches a local significance of up to 2.8 standard deviations. Upper limits at the 95% confidence level are placed on the LQ production cross section in the LQ mass range 0.5–2.3 TeV, and up to 3 TeV for t-channel LQ exchange. Leptoquarks are excluded below masses of 1.22–1.88 TeV for different LQ models and varying coupling strengths up to 2.5. The study of nonresonant ττ production through t-channel LQ exchange allows lower limits on the LQ mass of up to 2.3 TeV to be obtained.[graphic not available: see fulltext
Determination of Dead Layer Parameters of Semiconductor Germanium Detectors Using Machine Learning for the Legend Experiment
No full textThe search for neutrinoless double-beta decay remains today one of the most important areas in particle and nuclear physics. Germanium detectors are an excellent technology for this search because of their state-of-the-art energy resolution, but a dead layer in a germanium crystal can reduce the active volume, which can affect both exposure and half-life sensitivity. In this work, we used machine learning methods to study the dead layer in enriched germanium crystals. 1000 sets of events were simulated with various combinations of dead layer parameters. A fully connected neural network was used to determine these parameters from the energy spectra of a germanium detector exposed to a gamma calibration source Barium-133
Dust Collapse in Asymptotic Safety: A Path to Regular Black Holes
No full textRegular black hole spacetimes are obtained from an effective Lagrangian for quantum Einstein gravity. The interior matter is modeled as a dust fluid, which interacts with the geometry through a multiplicative coupling function denoted as χ. The specific functional form of χ is deduced from asymptotically safe gravity, under the key assumption that the Reuter fixed point remains minimally affected by the presence of matter. As a consequence the gravitational coupling vanishes at high energies. The static exterior geometry of the black hole is entirely determined by the junction conditions at the boundary surface. Consequently, the resulting global spacetime geometry remains devoid of singularities at all times. This outcome offers a new perspective on how regular black holes are formed through gravitational collapse
Full-magnetic implementation of a classical Toffoli gate
No full textThe Toffoli gate is the essential ingredient for reversible computing, an energy-efficient classical computational paradigm that evades the energy dissipation resulting from Landauer's principle. In this paper, we analyze different setups to realize a magnetic implementation of the Toffoli gate using three interacting classical spins, each one embodying one of the three bits needed for the Toffoli gate. In our scheme, different control-spin configurations produce an effective field capable of conditionally flipping the target spin. We study what the experimental requirements are for the realization of our scheme, focusing on the degree of local control, the ability to dynamically switch the spin-spin interactions, and the required single-spin anisotropies to make the classical spin stable, showing that these are compatible with current technology
Search for non-resonant Higgs boson pair production in the final state in pp collisions at = 13 TeV with the ATLAS detector
No full textA search for non-resonant Higgs boson pair (HH) production is presented, in which one of the Higgs bosons decays to a b-quark pair () and the other decays to WW, ZZ, or ττ, with in each case a final state with ℓℓ+ neutrinos (ℓ = e, μ). The analysis targets separately the gluon-gluon fusion and vector boson fusion production modes. Data recorded by the ATLAS detector in proton-proton collisions at a centre-of-mass energy of 13 TeV at the Large Hadron Collider, corresponding to an integrated luminosity of 140 fb, are used in this analysis. Events are selected to have exactly two b-tagged jets and two leptons with opposite electric charge and missing transverse momentum in the final state. These events are classified using multivariate analysis algorithms to separate the HH events from other Standard Model processes. No evidence of the signal is found. The observed (expected) upper limit on the cross-section for non-resonant Higgs boson pair production is determined to be 9.7 (16.2) times the Standard Model prediction at 95% confidence level. The Higgs boson self-interaction coupling parameter κ and the quadrilinear coupling parameter κ are each separately constrained by this analysis to be within the ranges [−6.2, 13.3] and [−0.17, 2.4], respectively, at 95% confidence level, when all other parameters are fixed.[graphic not available: see fulltext
Test of CP-invariance of the Higgs boson in vector-boson fusion production and in its decay into four leptons
No full textA search for CP violation in the decay kinematics and vector-boson fusion production of the Higgs boson is performed in the H → ZZ → 4ℓ (ℓ = e, μ) decay channel. The results are based on proton-proton collision data produced at the LHC at a centre-of-mass energy of 13 TeV and recorded by the ATLAS detector from 2015 to 2018, corresponding to an integrated luminosity of 139 fb. Matrix element-based optimal observables are used to constrain CP-odd couplings beyond the Standard Model in the framework of Standard Model effective field theory expressed in the Warsaw and Higgs bases. Differential fiducial cross-section measurements of the optimal observables are also performed, and a new fiducial cross-section measurement for vector-boson-fusion production is provided. All measurements are in agreement with the Standard Model prediction of a CP-even Higgs boson.[graphic not available: see fulltext
Search for the Exclusive <math display="inline"><mi>W</mi></math> Boson Hadronic Decays <math display="inline"><mrow><msup><mrow><mi>W</mi></mrow><mrow><mo>±</mo></mrow></msup><mo stretchy="false">→</mo><msup><mrow><mi>π</mi></mrow><mrow><mo>±</mo></mrow></msup><mi>γ</mi></mrow></math>, <math display="inline"><mrow><msup><mrow><mi>W</mi></mrow><mrow><mo>±</mo></mrow></msup><mo stretchy="false">→</mo><msup><mrow><mi>K</mi></mrow><mrow><mo>±</mo></mrow></msup><mi>γ</mi></mrow></math> and <math display="inline"><mrow><msup><mrow><mi>W</mi></mrow><mrow><mo>±</mo></mrow></msup><mo stretchy="false">→</mo><msup><mrow><mi>ρ</mi></mrow><mrow><mo>±</mo></mrow></msup><mi>γ</mi></mrow></math> with the ATLAS Detector
No full textA search for the exclusive hadronic decays W±→π±γ, W±→K±γ, and W±→ρ±γ is performed using up to 140 fb-1 of proton-proton collisions recorded with the ATLAS detector at a center-of-mass energy of s=13 TeV. If observed, these rare processes would provide a unique test bench for the quantum chromodynamics factorization formalism used to calculate cross sections at colliders. Additionally, at future colliders, these decays could offer a new way to measure the W boson mass through fully reconstructed decay products. The search results in the most stringent upper limits to date on the branching fractions B(W±→π±γ)<1.9×10-6, B(W±→K±γ)<1.7×10-6, B(W±→ρ±γ)<5.2×10-6 at 95% confidence level
First Measurement of the <math display="inline"><mo stretchy="false">|</mo><mi>t</mi><mo stretchy="false">|</mo></math> Dependence of Incoherent <math display="inline"><mi>J</mi><mo>/</mo><mi>ψ</mi></math> Photonuclear Production
No full textThe first measurement of the cross section for incoherent photonuclear production of J/ψ vector mesons as a function of the Mandelstam |t| variable is presented. The measurement was carried out with the ALICE detector at midrapidity, |y|<0.8, using ultraperipheral collisions of Pb nuclei at a center-of-mass energy per nucleon pair of sNN=5.02 TeV. This rapidity interval corresponds to a Bjorken-x range (0.3–1.4)×10-3. Cross sections are given in five |t| intervals in the range 0.04<|t|<1 GeV2 and compared to the predictions by different models. Models that ignore quantum fluctuations of the gluon density in the colliding hadron predict a |t| dependence of the cross section much steeper than in data. The inclusion of such fluctuations in the same models provides a better description of the data
Measurements of inclusive J/ψ production at midrapidity and forward rapidity in Pb–Pb collisions at <math altimg="si1.svg"><msqrt><mrow><msub><mrow><mi>s</mi></mrow><mrow><mi mathvariant="normal">NN</mi></mrow></msub></mrow></msqrt></math> = 5.02 TeV
No full textThe measurements of the inclusive J/ψ yield at midrapidity (|y|<0.9) and forward rapidity (2.5 <y< 4) in Pb–Pb collisions at sNN=5.02 TeV with the ALICE detector at the LHC are reported. The inclusive J/ψ production yields and nuclear modification factors, RAA, are measured as a function of the collision centrality, J/ψ transverse momentum (pT), and rapidity. The J/ψ average transverse momentum and squared transverse momentum (〈pT〉 and 〈pT2〉) are evaluated as a function of the centrality at midrapidity. Compared to the previous ALICE publications, here the entire Pb–Pb collisions dataset collected during the LHC Run 2 is used, which improves the precision of the measurements and extends the pT coverage. The pT-integrated RAA shows a hint of an increasing trend towards unity from semicentral to central collisions at midrapidity, while it is flat at forward rapidity. The pT-differential RAA shows a strong suppression at high pT with less suppression at low pT where it reaches a larger value at midrapidity compared to forward rapidity. The ratio of the pT-integrated yields of J/ψ to those of D<sup>0</sup> mesons is reported for the first time for the central and semicentral event classes at midrapidity. Model calculations implementing charmonium production via the coalescence of charm quarks and antiquarks during the fireball evolution (transport models) or in a statistical approach with thermal weights are in good agreement with the data at low pT. At higher pT, the data are well described by transport models and a model based on energy loss in the strongly-interacting medium produced in nuclear collisions at the LHC