6062 research outputs found
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Investigation of the <math display="inline"><mi mathvariant="normal">Δ</mi><mi>I</mi><mo>=</mo><mn>1</mn><mo>/</mo><mn>2</mn></math> Rule and Test of <math display="inline"><mi>C</mi><mi>P</mi></math> Symmetry through the Measurement of Decay Asymmetry Parameters in <math display="inline"><msup><mi mathvariant="normal">Ξ</mi><mo>-</mo></msup></math> Decays
No full textUsing (10087±44)×106 J/ψ events collected with the BESIII detector, numerous Ξ- and Λ decay asymmetry parameters are simultaneously determined from the process J/ψ→Ξ-Ξ¯+→Λ(pπ-)π-Λ¯(n¯π0)π+ and its charge-conjugate channel. The precisions of αΛ0 for Λ→nπ0 and α¯Λ0 for Λ¯→n¯π0 compared to world averages are improved by factors of 4 and 1.7, respectively. The ratio of decay asymmetry parameters of Λ→nπ0 to that of Λ→pπ-, ⟨αΛ0⟩/⟨αΛ-⟩, is determined to be 0.873±0.012-0.010+0.011, where the first and the second uncertainties are statistical and systematic, respectively. The ratio is smaller than unity more than 5σ, which signifies the existence of the ΔI=3/2 transition in Λ for the first time. Besides, we test for CP symmetry in Ξ-→Λπ- and in Λ→nπ0 with the best precision to date
Probing the CP nature of the top–Higgs Yukawa coupling in <math altimg="si1.svg"><mi>t</mi><mover accent="true"><mrow><mi>t</mi></mrow><mrow><mo stretchy="false">¯</mo></mrow></mover><mi>H</mi></math> and tH events with <math altimg="si2.svg"><mi>H</mi><mo stretchy="false">→</mo><mi>b</mi><mover accent="true"><mrow><mi>b</mi></mrow><mrow><mo stretchy="false">¯</mo></mrow></mover></math> decays using the ATLAS detector at the LHC
No full textThe CP properties of the coupling between the Higgs boson and the top quark are investigated using 139 fb<sup>−1</sup> of proton–proton collision data recorded by the ATLAS experiment at the LHC at a centre-of-mass energy of s=13 TeV. The CP structure of the top quark–Higgs boson Yukawa coupling is probed in events with a Higgs boson decaying into a pair of b-quarks and produced in association with either a pair of top quarks, tt¯H, or a single top quark, tH. Events containing one or two electrons or muons are used for the measurement. Multivariate techniques are used to select regions enriched in tt¯H and tH events, where dedicated CP-sensitive observables are exploited. In an extension of the Standard Model (SM) with a CP-odd admixture in the top–Higgs Yukawa coupling, the mixing angle between CP-even and CP-odd couplings is measured to be α=11−73∘∘+52∘, compatible with the SM prediction corresponding to α=0
Search for a new resonance decaying into two spin-0 bosons in a final state with two photons and two bottom quarks in proton-proton collisions at = 13 TeV
No full textA search for a new boson X is presented using CERN LHC proton-proton collision data collected by the CMS experiment at = 13 TeV in 2016–2018, and corresponding to an integrated luminosity of 138 fb. The resonance X decays into either a pair of Higgs bosons HH of mass 125 GeV or an H and a new spin-0 boson Y. One H subsequently decays to a pair of photons, and the second H or Y, to a pair of bottom quarks. The explored mass ranges of X are 260–1000 GeV and 300–1000 GeV, for decays to HH and to HY, respectively, with the Y mass range being 90–800 GeV. For a spin-0 X hypothesis, the 95% confidence level upper limit on the product of its production cross section and decay branching fraction is observed to be within 0.90–0.04 fb, depending on the masses of X and Y. The largest deviation from the background-only hypothesis with a local (global) significance of 3.8 (below 2.8) standard deviations is observed for X and Y masses of 650 and 90 GeV, respectively. The limits are interpreted using several models of new physics.[graphic not available: see fulltext
Revealing phase transition in dense matter with gravitational wave spectroscopy of binary neutron star mergers
No full textWe use numerical relativity simulations of binary neutron star mergers to show that high density deconfinement phase transitions to quark matter can be probed using multimodal postmerger gravitational wave (GW) spectroscopy. Our simulations suggest that hadron-quark phase transitions may suppress the one-armed spiral instability in the remnant. This is manifested in an anticorrelation between the energy carried in the ℓ=2, m=1 GW mode and energy density gap which separates the two phases. Our work demonstrates a potential connection between features of the postmerger GW spectrum and microphysical features of the high-density equation of state
Spin decoherence and off-resonance behavior of radio-frequency-driven spin rotations in storage rings
No full textHigh-frequency driven resonant spin rotators are routinely used as standard instruments in polarization experiments in particle and nuclear physics. Maintaining the continuous exact parametric spin resonance condition of the equality of the spin rotator and the spin precession frequency during operation is one of the challenges. We present a detailed analytical description of the effects of detuning the exact spin resonance on the precessing vertical and in-plane components of the polarization. An important part of the formalism presented here is the consideration of experimentally relevant spin decoherence effects. Within the developed formalism, we address the impact of feedback via pilot-bunch-based comagnetometry on continuous spin flips and on the related interpretation of charged-particle electric dipole moment searches using storage rings. We propose a spin-flip-based tomography of the longitudinal profile of polarization in a bunch, which is important for the evaluation of the polarization-dependent luminosity in collider experiments. We emphasize the potential importance of the previously unexplored phase of the horizontal polarization of the envelope as an indicator of the stability of radio-frequency-driven spin rotations in storage rings and as a testing ground for spin decoherence mechanisms
Atacama Cosmology Telescope: High-resolution component-separated maps across one third of the sky
No full textObservations of the millimeter sky contain valuable information on a number of signals, including the blackbody cosmic microwave background (CMB), Galactic emissions, and the Compton-y distortion due to the thermal Sunyaev-Zel'dovich (tSZ) effect. Extracting new insight into cosmological and astrophysical questions often requires combining multiwavelength observations to spectrally isolate one component. In this work, we present a new arc-minute-resolution Compton-y map, which traces out the line-of-sight-integrated electron pressure, as well as maps of the CMB in intensity and E-mode polarization, across a third of the sky (around 13,000 deg2). We produce these through a joint analysis of data from the Atacama Cosmology Telescope (ACT) data release 4 and 6 at frequencies of roughly 93, 148, and 225 GHz, together with data from the Planck satellite at frequencies between 30 and 545 GHz. We present detailed verification of an internal linear combination pipeline implemented in a needlet frame that allows us to efficiently suppress Galactic contamination and account for spatial variations in the ACT instrument noise. These maps provide a significant advance, in noise levels and resolution, over the existing Planck component-separated maps and will enable a host of science goals including studies of cluster and galaxy astrophysics, inferences of the cosmic velocity field, primordial non-Gaussianity searches, and gravitational lensing reconstruction of the CMB
Search for dark matter annual modulation with DarkSide-50
No full textDark matter may induce an event in an Earth-based detector, and its event rate is predicted to show an annual modulation as a result of the Earth's orbital motion around the Sun. We searched for this modulation signature using the ionization signal of the DarkSide-50 liquid argon time projection chamber. No significant signature compatible with dark matter is observed in the electron recoil equivalent energy range above 40 eVee, the lowest threshold ever achieved in such a search
Study of the decay <math display="inline"><mrow><mi>J</mi><mo>/</mo><mi>ψ</mi><mo stretchy="false">→</mo><mi>ϕ</mi><msup><mrow><mi>π</mi></mrow><mrow><mn>0</mn></mrow></msup><mi>η</mi></mrow></math>
No full textBased on (10.09±0.04)×109 J/ψ events collected with the BESIII detector operating at the BEPCII collider, a partial wave analysis of the decay J/ψ→ϕπ0η is performed. We observe for the first time two new structures on the ϕη invariant mass distribution, with significances exceeding 27σ and 13σ; the first with JPC=1+-, mass M=(1908±6(stat) -4+8(sys)) MeV/c2, and width Γ=(175±13(stat) -16+7(sys)) MeV, the second with JPC=1--, mass M=(1992±12(stat) -6+15(sys)) MeV/c2, and width Γ=(132±22(stat) -4+17(sys)) MeV. These measurements provide important input for the strangeonium spectrum. In addition, the f0(980)-a0(980)0 mixing signal in J/ψ→ϕf0(980)→ϕa0(980)0 and the corresponding electromagnetic decay J/ψ→ϕa0(980)0 are measured with improved precision, providing crucial information to understand the nature of a0(980)0 and f0(980)
Electron and photon efficiencies in LHC Run 2 with the ATLAS experiment
No full textPrecision measurements of electron reconstruction, identification, and isolation efficiencies and photon identification efficiencies are presented. They use the full Run 2 data sample collected by the ATLAS experiment in pp collisions at a centre-of-mass energy of 13 TeV during the years 2015–2018, corresponding to an integrated luminosity of 139 fb. The measured electron identification efficiencies have uncertainties that are around 30%–50% smaller than the previous Run 2 results due to an improved methodology and the inclusion of more data. A better pile-up subtraction method leads to electron isolation efficiencies that are more independent of the amount of pile-up activity. Updated photon identification efficiencies are also presented, using the full Run 2 data. When compared to the previous measurement, a 30%–40% smaller uncertainty is observed on the photon identification efficiencies, thanks to the increased amount of available data.[graphic not available: see fulltext
Measurement of prompt D and production in pPb collisions at = 5.02 TeV
No full textThe production of prompt D and mesons is studied in proton-lead collisions at a centre-of-mass energy of = 5.02 TeV. The data sample corresponding to an integrated luminosity of (1.58 ± 0.02)nb is collected by the LHCb experiment at the LHC. The differential production cross-sections are measured using D and candidates with transverse momentum in the range of 0 < p< 14 GeV/c and rapidities in the ranges of 1.5 < y< 4.0 and –5.0 < y< –2.5 in the nucleon-nucleon centre-of-mass system. For both particles, the nuclear modification factor and the forward-backward production ratio are determined. These results are compared with theoretical models that include initial-state nuclear effects. In addition, measurements of the cross-section ratios between D, and D mesons are presented, providing a baseline for studying the charm hadronization in lead-lead collisions at LHC energies.[graphic not available: see fulltext