86 research outputs found
Design and construction of the cylindrical drift chamber for the COMET Phase-I experiment
No full textSato A., Yoshida H., Moritsu M., et al. Design and construction of the cylindrical drift chamber for the COMET Phase-I experiment. Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 1069, 169926 (2024); https://doi.org/10.1016/j.nima.2024.169926.COMET is an experiment at J-PARC that searches for the charged lepton flavor violating process of neutrino-less muon-to-electron conversion (μ→e conversion) in a muonic atom. The COMET Phase-I experiment, which represents the first stage of its staged approach, utilizes the cylindrical drift chamber (CDC) as the main detector to measure the momentum of electrons emitted from μ→e conversion in a 1 T magnetic field. The CDC is designed for optimal performance to achieve the best momentum resolution and effectively separate the μ→e conversion electron signal from background signals. This design entails adapting He:i-C₄H₁₀ (90:10) as its chamber gas and employing an all-stereo wire configuration. This document provides a comprehensive overview of the CDC detector, encompassing design considerations, mechanical structure, construction methodologies, and results of performance evaluations conducted using cosmic-rays
Surcaudaphis supercauda Zhang, Chen, Zhong & Li
No full text<i>Surcaudaphis supercauda</i> Zhang, Chen, Zhong & Li, in Zhang 1999 = <i>Tuberocephalus misakurae</i> Moritsu & Hamasaki 1983 <p> The holotype and seven paratypes of <i>S. supercauda</i> were examined, and appear to be gynoparae of <i>T. misakurae</i>, which host­alternates between <i>Prunus</i> and <i>Dendranthema</i> in Japan and China.</p>Published as part of <i>Victor, Eastop, F. & Blackman, Roger L., 2005, Some new synonyms in Aphididae (Hemiptera: Sternorrhyncha), pp. 1-36 in Zootaxa 1089</i> on page 22, DOI: <a href="http://zenodo.org/record/273344">10.5281/zenodo.273344</a>
Measurement of the top-quark pole mass in dileptonic events at TeV with the ATLAS experiment
No full textA measurement of the top-quark pole mass is presented in ~events with an additional jet, , produced in collisions at TeV. The data sample, recorded with the ATLAS experiment during Run 2 of the LHC, corresponds to an integrated luminosity of 140 . Events with one electron and one muon of opposite electric charge in the final state are selected to measure the differential cross-section as a function of the inverse of the invariant mass of the system. Iterative Bayesian Unfolding is used to correct the data to enable comparison with fixed-order calculations at next-to-leading-order accuracy in the strong coupling. The process (), where top quarks are taken as stable particles, and the process (), which includes top-quark decays to the dilepton final state and off-shell effects, are considered. The top-quark mass is extracted using a fit of the unfolded normalized differential cross-section distribution. The results obtained with the and calculations are compatible within theoretical uncertainties, providing an important consistency check. The more precise determination is obtained for the measurement: GeV, which is in good agreement with other top-quark mass results.A measurement of the top-quark pole mass is presented in events with an additional jet, + 1-jet, produced in pp collisions at TeV. The data sample, recorded with the ATLAS experiment during Run 2 of the LHC, corresponds to an integrated luminosity of 140 fb. Events with one electron and one muon of opposite electric charge in the final state are selected to measure the + 1-jet differential cross-section as a function of the inverse of the invariant mass of the + 1-jet system. Iterative Bayesian Unfolding is used to correct the data to enable comparison with fixed-order calculations at next-to-leading-order accuracy in the strong coupling. The process , where top quarks are taken as stable particles, and the process , which includes top-quark decays to the dilepton final state and off-shell effects, are considered. The top-quark mass is extracted using a χ fit of the unfolded normalized differential cross-section distribution. The results obtained with the 2 → 3 and 2 → 7 calculations are compatible within theoretical uncertainties, providing an important consistency check. The more precise determination is obtained for the 2 → 3 measurement: GeV, which is in good agreement with other top-quark mass results.[graphic not available: see fulltext]A measurement of the top-quark pole mass is presented in events with an additional jet, , produced in collisions at TeV. The data sample, recorded with the ATLAS experiment during Run 2 of the LHC, corresponds to an integrated luminosity of . Events with one electron and one muon of opposite electric charge in the final state are selected to measure the differential cross-section as a function of the inverse of the invariant mass of the system. Iterative Bayesian Unfolding is used to correct the data to enable comparison with fixed-order calculations at next-to-leading-order accuracy in the strong coupling. The process (), where top quarks are taken as stable particles, and the process (), which includes top-quark decays to the dilepton final state and off-shell effects, are considered. The top-quark mass is extracted using a fit of the unfolded normalized differential cross-section distribution. The results obtained with the and calculations are compatible within theoretical uncertainties, providing an important consistency check. The more precise determination is obtained for the measurement: which is in good agreement with other top-quark mass results
Beam and SKS spectrometers at the K1.8 beam line
No full textHigh-resolution spectrometers for both incident beams and scattered particles have been constructed at the K1.8 beam line of the Hadron Experimental Facility at J-PARC. A point-to-point optics is realized between the entrance and exit of QQDQQ magnets for the beam spectrometer. Fine-pitch wire chamber trackers and hodoscope counters are installed in the beam spectrometer to accept a high rate beam up to 107 Hz. The superconducting kaon spectrometer for scattered particles was transferred from KEK with modifications to the cryogenic system and detectors. A missing-mass resolution of 1.9 ± 0.1 MeV/c2 (FWHM) was achieved for the Σ peaks of (π±,K+) reactions on a proton target in the first physics run of E19 in 2010
Search for a light charged Higgs boson in t → H±b decays, with H± → cs, in pp collisions at √s = 13 TeV with the ATLAS detector
No full textA search for a light charged Higgs boson produced in decays of the top quark, t → H±b with H± → cs,
is presented. This search targets the production of top-quark
pairs tt
¯ → WbH±b, with W → ν ( = e, μ), resulting in a lepton-plus-jets final state characterised by an isolated electron or muon and at least four jets. The search
exploits b-quark and c-quark identification techniques as well
as multivariate methods to suppress the dominant tt
¯ background. The data analysed correspond to 140 fb−1 of pp
collisions at √s = 13 TeV recorded with the ATLAS detector at the LHC between 2015 and 2018. Observed (expected)
95% confidence-level upper limits on the branching fraction
B(t → H±b), assuming B(t → W b) + B(t → H±(→
cs)b) = 1.0, are set between 0.066% (0.077%) and 3.6%
(2.3%) for a charged Higgs boson with a mass between 60
and 168 GeV
Study on Λ6H hypernucleus by the (π−, K+) reaction at J-PARC
No full textWe carried out an experiment to produce the neutron-rich hypernucleus Λ6H via the (π−, K+) reaction on 6Li target at the pion beam momentum of 1.2 GeV/c (J-PARC E10). In order to calibrate the scale of the missing-mass or of the Λ binding energy of the hypernucleus, we also measured the 12C(π+, K+) Λ12C, p(π−, K+)Σ− and p(π+, K+)Σ+reactions. The experiment was performed at the J-PARC Hadron Hall K1.8 beam line in December 2012 and January 2013. The overall collected data sample corresponds to an integrated beam intensity of 1.65 × 1012 pions
Search for the Θ^{+} Pentaquark via the π^{-}p→K^{-}X Reaction at 1.92 GeV/c
No full textThe Theta(+) pentaquark baryon was searched for via the pi(-) p -> K- X reaction with a missing mass resolution of 1.4 MeV/c(2) (FWHM) at the Japan Proton Accelerator Research Complex (J-PARC). pi(-) meson beams were incident on the liquid hydrogen target with a beam momentum of 1.92 GeV/c. No peak structure corresponding to the Theta(+) mass was observed. The upper limit of the production cross section averaged over the scattering angle of 2 degrees to 15 degrees in the laboratory frame is obtained to be 0.26 mu b/sr in the mass region of 1.51-1.55 GeV/c(2). The upper limit of the Theta(+) decay width is obtained to be 0.72 and 3.1 MeV for J(Theta)(P) = 1/2(+) and J(Theta)(P) = 1/2(-), respectively, using the effective Lagrangian approac
Combination of searches for singly produced vectorlike top quarks in pp collisions at √s = 13 TeV with the ATLAS detector
No full textA combination of searches for the single production of vectorlike top quarks (T) is presented.
These analyses are based on proton-proton collisions at √s = 13 TeV recorded in 2015–2018 with the
ATLAS detector at the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb−1. The
T decay modes considered in this combination are into a top quark and either a Standard Model Higgs
boson or a Z boson (T → Ht and T → Zt). The individual searches used in the combination are
differentiated by the number of leptons (e, μ) in the final state. The observed data are found to be in good
agreement with the Standard Model background prediction. Interpretations are provided for a range of
masses and couplings of the vectorlike top quark for benchmark models and generalized representations in
terms of 95% confidence level limits. For a benchmark signal prediction of a vectorlike top quark SU(2)
singlet with electroweak coupling, κ, of 0.5, masses below 2.1 TeV are excluded, resulting in the most
restrictive limits to date
Differential cross-section measurements of Higgs boson production in the H → τ+τ− decay channel in pp collisions at √s = 13 TeV with the ATLAS detector
No full textDiferential measurements of Higgs boson production in the τ -lepton-pair decay
channel are presented in the gluon fusion, vector-boson fusion (VBF), V H and ttH¯ associated
production modes, with particular focus on the VBF production mode. The data used to
perform the measurements correspond to 140 fb−1 of proton-proton collisions collected by the
ATLAS experiment at the LHC. Two methods are used to perform the measurements: the
Simplifed Template Cross-Section (STXS) approach and an Unfolded Fiducial Diferential
measurement considering only the VBF phase space. For the STXS measurement, events are
categorized by their production mode and kinematic properties such as the Higgs boson’s
transverse momentum (p
H
T
), the number of jets produced in association with the Higgs boson,
or the invariant mass of the two leading jets (mjj ). For the VBF production mode, the
ratio of the measured cross-section to the Standard Model prediction for mjj > 1.5 TeV and
p
H
T > 200 GeV (p
H
T < 200 GeV) is 1.29+0.39
−0.34 (0.12+0.34
−0.33). This is the frst VBF measurement for
the higher-p
H
T
criteria, and the most precise for the lower-p
H
T
criteria. The fducial cross-section
measurements, which only consider the kinematic properties of the event, are performed as
functions of variables characterizing the VBF topology, such as the signed ∆ϕjj between the
two leading jets. The measurements have a precision of 30%–50% and agree well with the
Standard Model predictions. These results are interpreted in the SMEFT framework, and
place the strongest constraints to date on the CP-odd Wilson coefcient cHW˜
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