Showing papers by "Masaharu Nomachi published in 2020"
Book•
23 Feb 2020
TL;DR: The ATLAS detector as installed in its experimental cavern at point 1 at CERN is described in this paper, where a brief overview of the expected performance of the detector when the Large Hadron Collider begins operation is also presented.
Abstract: The ATLAS detector as installed in its experimental cavern at point 1 at CERN is described in this paper. A brief overview of the expected performance of the detector when the Large Hadron Collider begins operation is also presented.
3,111 citations
TL;DR: In this paper, a measurement of observables sensitive to spin correlations in tt¯ production is presented, using 36.1 fb - 1 of pp collision data at s=13 TeV recorded with the ATLAS detector at the Large Hadron Collider.
Abstract: A measurement of observables sensitive to spin correlations in tt¯ production is presented, using 36.1 fb - 1 of pp collision data at s=13 TeV recorded with the ATLAS detector at the Large Hadron Collider. Differential cross-sections are measured in events with exactly one electron and one muon with opposite-sign electric charge as a function of the azimuthal opening angle and the absolute difference in pseudorapidity between the electron and muon candidates in the laboratory frame. The azimuthal opening angle is also measured as a function of the invariant mass of the tt¯ system. The measured differential cross-sections are compared to predictions by several NLO Monte Carlo generators and fixed-order calculations. The observed degree of spin correlation is somewhat higher than predicted by the generators used. The data are consistent with the prediction of one of the fixed-order calculations at NLO, but agree less well with higher-order predictions. Using these leptonic observables, a search is performed for pair production of supersymmetric top squarks decaying into Standard Model top quarks and light neutralinos. Top squark masses between 170 and 230 GeV are largely excluded at the 95% confidence level for kinematically allowed values of the neutralino mass.
39 citations
TL;DR: In this article, multi-particle azimuthal cumulants are measured as a function of centrality and transverse momentum using 470 mu b(-1) of Pb+Pb collisions at root s(NN) = 5.02TeV with the ATLAS detector at the LHC.
Abstract: Multi-particle azimuthal cumulants are measured as a function of centrality and transverse momentum using 470 mu b(-1) of Pb+Pb collisions at root s(NN) = 5.02TeV with the ATLAS detector at the LHC ...
29 citations
TL;DR: In this paper, a measurement of the production of a prompt J/psi meson in association with a W-+/- boson with W−/- -> mu nu and J−psi -> mu(+)mu(-) is presented.
Abstract: A measurement of the production of a prompt J/psi meson in association with a W-+/- boson with W-+/- -> mu nu and J/psi -> mu(+)mu(-) is presented for J/psi transverse momenta in the range 8. ...
23 citations
TL;DR: In this article, the authors measured the jet energy scale, jet energy resolution, and their systematic uncertainties for jets reconstructed with the ATLAS detector in 2012 using proton-proton data produced at a centre-of-mass energy of 8 TeV with an integrated luminosity of 20fb−1.
Abstract: The jet energy scale, jet energy resolution, and their systematic uncertainties are measured for jets reconstructed with the ATLAS detector in 2012 using proton–proton data produced at a centre-of-mass energy of 8 TeV with an integrated luminosity of 20fb−1. Jets are reconstructed from clusters of energy depositions in the ATLAS calorimeters using the anti-kt algorithm. A jet calibration scheme is applied in multiple steps, each addressing specific effects including mitigation of contributions from additional proton–proton collisions, loss of energy in dead material, calorimeter non-compensation, angular biases and other global jet effects. The final calibration step uses several in situ techniques and corrects for residual effects not captured by the initial calibration. These analyses measure both the jet energy scale and resolution by exploiting the transverse momentum balance in γ + jet, Z + jet, dijet, and multijet events. A statistical combination of these measurements is performed. In the central detector region, the derived calibration has a precision better than 1% for jets with transverse momentum 150GeV
20 citations
01 Feb 2020
18 citations
TL;DR: In this article, the results from the measurement by ATLAS of long-range (|Delta eta|>2) dihadron angular correlations in root s=8 and 13 TeV pp collisions containing a Z boson are presented.
Abstract: Results are presented from the measurement by ATLAS of long-range (|Delta eta|>2) dihadron angular correlations in root s=8 and 13 TeV pp collisions containing a Z boson. The analysis is perform ...
12 citations
Journal Article•
7 citations
Joint Institute for Nuclear Research1, Academy of Sciences of Uzbekistan2, Kurchatov Institute3, University College London4, University of Manchester5, Comenius University in Bratislava6, National Research Nuclear University MEPhI7, University of Texas at Austin8, Czech Technical University in Prague9, Azerbaijan National Academy of Sciences10, University of Warwick11, Osaka University12, Saga University13, Imperial College London14, Institut Universitaire de France15, Charles University in Prague16
TL;DR: In this paper, a radiochemical method for producing 82 Se sources with an ultra-low level of contamination of natural radionuclides (40 K, decay products of 232 Th and 238 U) has been developed based on cation-exchange chromatographic purification with reverse removal of impurities.
Abstract: A radiochemical method for producing 82 Se sources with an ultra-low level of contamination of natural radionuclides ( 40 K, decay products of 232 Th and 238 U) has been developed based on cation-exchange chromatographic purification with reverse removal of impurities. It includes chromatographic separation (purification), reduction, conditioning (which includes decantation, centrifugation, washing, grinding, and drying), and 82 Se foil production. The conditioning stage, during which highly dispersed elemental selenium is obtained by the reduction of purified selenious acid (H 2 SeO 3 ) with sulfur dioxide (SO 2 ) represents the crucial step in the preparation of radiopure 82 Se samples. The natural selenium (600 g) was first produced in this procedure in order to refine the method. The technique developed was then used to produce 2.5 kg of radiopure enriched selenium ( 82 Se). The produced 82 Se samples were wrapped in polyethylene (12 μm thick) and radionuclides present in the sample were analyzed with the BiPo-3 detector. The radiopurity of the plastic materials (chromatographic column material and polypropylene chemical vessels), which were used at all stages, was determined by instrumental neutron activation analysis. The radiopurity of the 82 Se foils was checked by measurements with the BiPo-3 spectrometer, which confirmed the high purity of the final product. The measured contamination level for 208 Tl was 8–54 μBq/kg, and for 214 Bi the detection limit of 600 μBq/kg has been reached.
6 citations
International Pentecostal Holiness Church1, Centre national de la recherche scientifique2, Kurchatov Institute3, University of Manchester4, Comenius University in Bratislava5, National Research Nuclear University MEPhI6, Aix-Marseille University7, Idaho National Laboratory8, University of Bordeaux9, University of Texas at Austin10, University of Caen Lower Normandy11, University of Savoy12, Czech Technical University in Prague13, University of Warwick14, Boston University15, Osaka University16, Saga University17, Imperial College London18, Institut Universitaire de France19, Charles University in Prague20
TL;DR: In this article, the double-beta decay of 82Se to the 0 1 + excited state of 82Kr was studied with the NEMO-3 detector using 0.93 kg of enriched 82Se measured for 4.75 y, corresponding to an exposure of 4.42 kg⋅y.
5 citations
KEK1, Gwangju Institute of Science and Technology2, Chonnam National University3, Osaka University4, Soongsil University5, Dongshin University6, Tohoku University7, Japan Atomic Energy Agency8, University of Michigan9, Kitasato University10, Seoul National University of Science and Technology11, Chonbuk National University12, Seoul National University13, Kyungpook National University14, Kyoto Sangyo University15, University of Sussex16, University of Florida17, Sungkyunkwan University18, University of Alabama19, Brookhaven National Laboratory20
TL;DR: The JSNS2 (J-PARC Sterile Neutrino Search at J PARC Spallation Neutron Source) experiment aims to search for neutrino oscillations over a 24 m short baseline at JPARC, where the inner detector is filled with 17 tons of gadolinium-loaded liquid scintillator (LS) and both the intermediate γ-catcher and the optically separated outer veto are filled with unloaded LS as mentioned in this paper.
Abstract: The JSNS2 (J-PARC Sterile Neutrino Search at J-PARC Spallation Neutron Source) experiment aims to search for neutrino oscillations over a 24 m short baseline at J-PARC . The JSNS2 inner detector is filled with 17 tons of gadolinium-loaded liquid scintillator (LS) and both the intermediate γ-catcher and the optically separated outer veto are filled with un-loaded LS . Optical photons from scintillation are observed by 120 Photomultiplier Tubes (PMTs). A total of 130 PMTs for the JSNS2 experiment were either donated by other experiments or purchased from Hamamatsu. Donated PMTs were purchased around 10 years ago, therefore JSNS2 did pre-calibration of the PMTs including the purchased PMTs. 123 PMTs demonstrated acceptable performance for the JSNS2 experiment, and 120 PMTs were installed in the detector.
01 Jan 2020
TL;DR: In this paper, the neutrino-less double beta decay (0νββ) of 48Ca by using CaF2 scintillators was studied and a lower limit of (math) > 6.2 × 1022 year was given.
Abstract: We have studied the neutrino-less double beta decay(0νββ) of 48Ca by using CaF2(pure) scintillators. Analysis for rejection of backgrounds(212Bi→ 212Po events and 208Tl events) was effective to reduce backgrounds in Qββ-value region. No events are observed in the Qββ-value region for the data of 131 days × 86 kg. It gives a lower limit (90% confidence level) of (math) > 6.2 × 1022 year (preliminary) for the half-life of 0νββ of 48Ca.
TL;DR: This article studies the energy resolution of a neutrinoless double-beta decay experiment and improves the detector sensitivity for the CANDLES detector, which severely degrades the resolution at the $0
u \beta \beta $ value of Ca.
Abstract: In a neutrino-less double-beta-decay ($0
u\beta\beta$) experiment, an irremovable two-neutrino double-beta-decay ($2
u\beta\beta$) background surrounds the Q-value of the double beta decay isotope. The energy resolution must be improved to differentiate between $0
u\beta\beta$ and $2
u\beta\beta$ events. CAlcium fluoride for studies of Neutrino and Dark matters by Low Energy Spectrometer (CANDLES) discerns the $0
u\beta\beta$ of $^{48}$Ca using a CaF$_2$ scintillator as the detector and source. Photomultiplier tubes (PMTs) collect scintillation photons. Ideally, the energy resolution should equal the statistical fluctuation of the number of photoelectrons. At the Q-value of $^{48}$Ca, the current energy resolution (2.6%) exceeds this fluctuation (1.6%). Because of CaF$_2$'s long decay constant of 1000 ns, a signal integration in 4000 ns is used to calculate the energy. The baseline fluctuation ($\sigma_{\rm baseline}$) is accumulated in the signal integration, degrading the energy resolution. Therefore, this paper studies $\sigma_{\rm baseline}$ in the CANDLES detector, which has a severe effect (1%) at the Q-value of $^{48}$Ca. To avoid $\sigma_{\rm baseline}$, photon counting can be used to obtain the number of photoelectrons in each PMT; however, a significant photoelectron signal overlapping probability in each PMT causes missing photoelectrons in counting and reduces the energy resolution. "Partial photon counting" reduces $\sigma_{\rm baseline}$ and minimizes photoelectron loss. We thus obtain improved energy resolutions of 4.5--4.0% at 1460.8 keV ($\gamma$-ray of $^{40}$K), and 3.3--2.9% at 2614.5 keV ($\gamma$-ray of $^{208}$Tl). The energy resolution at the Q-value shows an estimated improvement of 2.2%, with improved detector sensitivity by factor 1.09 for the $0
u\beta\beta$ half-life of $^{48}$Ca.
KEK1, Gwangju Institute of Science and Technology2, Chonnam National University3, Osaka University4, Soongsil University5, Dongshin University6, Tohoku University7, Japan Atomic Energy Agency8, University of Michigan9, Kitasato University10, Seoul National University of Science and Technology11, Chonbuk National University12, Seoul National University13, Kyungpook National University14, Kyoto Sangyo University15, University of Sussex16, University of Florida17, Sungkyunkwan University18, University of Alabama19, Brookhaven National Laboratory20
TL;DR: The JSNS$^{2}$ (J-PARC Sterile Neutrino Search at J PARC Spallation Neutron Source) experiment as mentioned in this paper aims to search for neutrino oscillations over a 24\,m short baseline at JPARC.
Abstract: The JSNS$^{2}$ (J-PARC Sterile Neutrino Search at J-PARC Spallation Neutron Source) experiment aims to search for neutrino oscillations over a 24\,m short baseline at J-PARC. The JSNS$^{2}$ inner detector is filled with 17 tons of gadolinium-loaded liquid scintillator (LS) and both the intermediate $\gamma$-catcher and the optically separated outer veto are filled with un-loaded LS. Optical photons from scintillation are observed by 120 Photomultiplier Tubes (PMTs). A total of 130 PMTs for the JSNS2 experiment were both donated by other experiments and purchased from Hamamatsu. Donated PMTs were purchased around 10 years ago, therefore JSNS$^{2}$ did pre-calibration of the PMTs including the purchased PMTs. 123 PMTs demonstrated acceptable performance for the JSNS$^{2}$ experiment, and 120 PMTs were installed in the detector.
KEK1, Osaka University2, University of Michigan3, Soongsil University4, Dongshin University5, Tohoku University6, Chonnam National University7, Japan Atomic Energy Agency8, Gwangju Institute of Science and Technology9, Sungkyunkwan University10, Seoul National University of Science and Technology11, Kitasato University12, Chonbuk National University13, Seoul National University14, Kyungpook National University15, Kyoto Sangyo University16, University of Sussex17, University of Florida18, University of Alabama19, Brookhaven National Laboratory20
TL;DR: The JSNS$^{2}$ (J-PARC Sterile Neutrino Search at J PARC Spallation Neutron Source) experiment as discussed by the authors aims to search for neutrino oscillations over a 24 m short baseline at JPARC, where the inner detector is filled with 17 tons of gadolinium(Gd)-loaded liquid scintillator (LS) with an additional 31 tons of unloaded LS in the intermediate gamma-catcher and an optically separated outer veto volumes.
Abstract: The JSNS$^{2}$ (J-PARC Sterile Neutrino Search at J-PARC Spallation Neutron Source) experiment aims to search for neutrino oscillations over a 24 m short baseline at J-PARC. The JSNS$^{2}$ inner detector is filled with 17 tons of gadolinium(Gd)-loaded liquid scintillator (LS) with an additional 31 tons of unloaded LS in the intermediate $\gamma$-catcher and an optically separated outer veto volumes. A total of 120 10-inch photomultiplier tubes observe the scintillating optical photons and each analog waveform is stored with the flash analog-to-digital converters. We present details of the data acquisition, processing, and data quality monitoring system. We also present two different trigger logics which are developed for the beam and self-trigger.
TL;DR: In this article, the authors evaluate and compare the pulse shape discrimination (PSD) performance of multipixel photon counters (MPPCs) with that of a typical photomultiplier tube (PMT) when testing using CsI(Tl) scintillators.
Abstract: In this study, we evaluate and compare the pulse shape discrimination (PSD) performance of multipixel photon counters (MPPCs, also known as silicon photomultiphers - SiPMs) with that of a typical photomultiplier tube (PMT) when testing using CsI(Tl) scintillators. We use the charge comparison method, whereby we discriminate different types of particles by the ratio of charges integrated within two time-gates (the delayed part and the entire digitized waveform). For a satisfactory PSD performance, a setup should generate many photoelectrons (p.e.) and collect their charges efficiently. The PMT setup generates more p.e. than the MPPC setup does. With the same digitizer and the same long time-gate (the entire digitized waveform), the PMT setup is also better in charge collection. Therefore, the PMT setup demonstrates better PSD performance. We subsequently test the MPPC setup using a new data acquisition (DAQ) system. Using this new DAQ, the long time-gate is extended by nearly four times the length when using the previous digitizer. With this longer time-gate, we collect more p.e. at the tail part of the pulse and almost all the charges of the total collected p.e. Thus, the PSD performance of the MPPC setup is improved significantly. This study also provides an estimation of the short time-gate (the delayed part of the digitized waveform) that can give a satisfactory PSD performance without an extensive analysis to optimize this gate.