arXiv subjects

S. Hasegawa

Publications and source records attributed to S. Hasegawa.

At least 91 records · Page 5Linked to original sources

arXiv2017

Nuclear dependence of the transverse-single-spin asymmetry for forward neutron production in polarized $p$$+$$A$ collisions at $\sqrt{s_{_{NN}}}=200$ GeV

During 2015 the Relativistic Heavy Ion Collider (RHIC) provided collisions of transversely polarized protons with Au and Al nuclei for the first time, enabling the exploration of transverse-single-spin asymmetries with heavy nuclei. Large single-spin asymmetries in very forward neutron production have been previously observed in transversely polarized $p$$+$$p$ collisions at RHIC, and the existing theoretical framework that was successful in describing the single-spin asymmetry in $p$$+$$p$ collisions predicts only a moderate atomic-mass-number ($A$) dependence. In contrast, the asymmetries observed at RHIC in $p$$+$$A$ collisions showed a surprisingly strong $A$ dependence in inclusive forward neutron production. The observed asymmetry in $p$$+$Al collisions is much smaller, while the asymmetry in $p$$+$Au collisions is a factor of three larger in absolute value and of opposite sign. The interplay of different neutron production mechanisms is discussed as a possible explanation of the observed $A$ dependence.

hep-ex↗

arXiv2017

Technical Design Report (TDR): Searching for a Sterile Neutrino at J-PARC MLF (E56, JSNS2)

In this document, the technical details of the JSNS$^2$ (J-PARC Sterile Neutrino Search at J-PARC Spallation Neutron Source) experiment are described. The search for sterile neutrinos is currently one of the hottest topics in neutrino physics. The JSNS$^2$ experiment aims to search for the existence of neutrino oscillations with $Δm^2$ near 1 eV$^2$ at the J-PARC Materials and Life Science Experimental Facility (MLF). A 1 MW beam of 3 GeV protons incident on a spallation neutron target produces an intense neutrino beam from muon decay at rest. Neutrinos come predominantly from $μ^+$ decay: $μ^{+} \to e^{+} + \barν_μ + ν_{e}$. The experiment will search for $\barν_μ$ to $\barν_{e}$ oscillations which are detected by the inverse beta decay interaction $\barν_{e} + p \to e^{+} + n$, followed by gammas from neutron capture on Gd. The detector has a fiducial volume of 17 tons and is located 24 meters away from the mercury target. JSNS$^2$ offers the ultimate direct test of the LSND anomaly. In addition to the sterile neutrino search, the physics program includes cross section measurements with neutrinos with a few 10's of MeV from muon decay at rest and with monochromatic 236 MeV neutrinos from kaon decay at rest. These cross sections are relevant for our understanding of supernova explosions and nuclear physics.

physics.ins-det↗

arXiv2017

Measurement of long-range angular correlations and azimuthal anisotropies in high-multiplicity $p$$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV

We present the first measurements of long-range angular correlations and the transverse momentum dependence of elliptic flow $v_2$ in high-multiplicity $p$$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV. A comparison of these results with previous measurements in high-multiplicity $d$$+$Au and $^3{\rm He}$$+$Au collisions demonstrates a relation between $v_2$ and the initial collision eccentricity $\varepsilon_2$, suggesting that the observed momentum-space azimuthal anisotropies in these small systems have a collective origin and reflect the initial geometry. Good agreement is observed between the measured $v_2$ and hydrodynamic calculations for all systems, and an argument disfavoring theoretical explanations based on momentum-space domain correlations is presented. The set of measurements presented here allows us to leverage the distinct intrinsic geometry of each of these systems to distinguish between different theoretical descriptions of the long-range correlations observed in small collision systems.

nucl-ex↗

arXiv2017

Missing-mass spectroscopy with the ${}^{6}$Li($π^{-}, K^{+}$)X reaction to search for ${}^{6}_Λ$H

We searched for the bound state of the neutron-rich $Λ$-hypernucleus ${}^{6}_Λ$H, using the ${}^{6}$Li($π^{-}, K^{+}$)X double charge-exchange reaction at a $π^{-}$ beam momentum of 1.2 GeV/c at J-PARC. A total of $1.4 \times 10^{12}$ $π^{-}$ was driven onto a ${}^{6}$Li target of 3.5-g/$\rm cm^2$ thickness. No event was observed below the bound threshold, i.e., the mass of ${}^{4}_Λ$H + 2n, in the missing-mass spectrum of the ${}^{6}$Li($π^{-}, K^{+}$)X reaction in the $2^{\circ}$ < $θ_{πK}$ < $20^{\circ}$ angular range. Furthermore, no event was found up to 2.8 MeV/$c^2$ above the bound threshold. We obtained the the double-differential cross section spectra of the ${}^{6}$Li($π^{-}, K^{+}$)X reaction in the angular range of $2^{\circ}$ < $θ_{πK}$ < $14^{\circ}$. An upper limit of 0.56 nb/sr (90% C.L.) was obtained for the production cross section of the ${}^{6}_Λ$H hypernucleus bound state. In addition, not only the bound state region, but also the $Λ$ continuum region and part of the $Σ^{-}$ quasi-free production region of the ${}^{6}$Li($π^{-}, K^{+}$)X reaction, were obtained with high statistics. The present missing-mass spectrum will facilitate the investigation of the $Σ^{-}$-nucleus optical potential for $Σ^{-}$-${}^{5}$He through spectrum shape analysis.

nucl-ex↗

arXiv2017

Measurement of the relative yields of $ψ(2S)$ to $ψ(1S)$ mesons produced at forward and backward rapidity in $p$$+$$p$, $p$$+$Al, $p$$+$Au, and $^{3}$He$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV

The PHENIX Collaboration has measured the ratio of the yields of $ψ(2S)$ to $ψ(1S)$ mesons produced in $p$$+$$p$, $p$$+$Al, $p$$+$Au, and $^{3}$He$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV over the forward and backward rapidity intervals $1.2<|y|<2.2$. We find that the ratio in $p$$+$$p$ collisions is consistent with measurements at other collision energies. In collisions with nuclei, we find that in the forward ($p$-going or $^{3}$He-going) direction, the relative yield of $ψ(2S)$ mesons to $ψ(1S)$ mesons is consistent with the value measured in \pp collisions. However, in the backward (nucleus-going) direction, the $ψ(2S)$ is preferentially suppressed by a factor of $\sim$2. This suppression is attributed in some models to breakup of the weakly-bound $ψ(2S)$ through final state interactions with comoving particles, which have a higher density in the nucleus-going direction. These breakup effects may compete with color screening in a deconfined quark-gluon plasma to produce sequential suppression of excited quarkonia states.

nucl-ex↗

arXiv2017

Measurements of double-helicity asymmetries in inclusive $J/ψ$ production in longitudinally polarized $p+p$ collisions at $\sqrt{s}=510$ GeV

We report the double helicity asymmetry, $A_{LL}^{J/ψ}$, in inclusive $J/ψ$ production at forward rapidity as a function of transverse momentum $p_T$ and rapidity $|y|$. The data analyzed were taken during $\sqrt{s}=510$ GeV longitudinally polarized $p$$+$$p$ collisions at the Relativistic Heavy Ion Collider (RHIC) in the 2013 run using the PHENIX detector. At this collision energy, $J/ψ$ particles are predominantly produced through gluon-gluon scatterings, thus $A_{LL}^{J/ψ}$ is sensitive to the gluon polarization inside the proton. We measured $A_{LL}^{J/ψ}$ by detecting the decay daughter muon pairs $μ^+ μ^-$ within the PHENIX muon spectrometers in the rapidity range $1.2<|y|<2.2$. In this kinematic range, we measured the $A_{LL}^{J/ψ}$ to be $0.012 \pm 0.010$~(stat)~$\pm$~$0.003$(syst). The $A_{LL}^{J/ψ}$ can be expressed to be proportional to the product of the gluon polarization distributions at two distinct ranges of Bjorken $x$: one at moderate range $x \approx 0.05$ where recent RHIC data of jet and $π^0$ double helicity spin asymmetries have shown evidence for significant gluon polarization, and the other one covering the poorly known small-$x$ region $x \approx 2\times 10^{-3}$. Thus our new results could be used to further constrain the gluon polarization for $x< 0.05$.

hep-ex↗

arXiv2016

Hayabusa-2 Mission Target Asteroid 162173 Ryugu (1999 JU3): Searching for the Object's Spin-Axis Orientation

The JAXA Hayabusa-2 mission was approved in 2010 and launched on December 3, 2014. The spacecraft will arrive at the near-Earth asteroid 162173 Ryugu in 2018 where it will perform a survey, land and obtain surface material, then depart in Dec 2019 and return to Earth in Dec 2020. We observed Ryugu with the Herschel Space Observatory in Apr 2012 at far-IR thermal wavelengths, supported by several ground-based observations to obtain optical lightcurves. We reanalysed previously published Subaru-COMICS and AKARI-IRC observations and merged them with a Spitzer-IRS data set. In addition, we used a large set of Spitzer-IRAC observations obtained in the period Jan to May, 2013. The data set includes two complete rotational lightcurves and a series of ten "point-and-shoot" observations. The almost spherical shape of the target together with the insufficient lightcurve quality forced us to combine radiometric and lightcurve inversion techniques in different ways to find the object's key physical and thermal parameters. We find that the solution which best matches our data sets leads to this C class asteroid having a retrograde rotation with a spin-axis orientation of (lambda = 310-340 deg; beta = -40+/-15 deg) in ecliptic coordinates, an effective diameter (of an equal-volume sphere) of 850 to 880 m, a geometric albedo of 0.044 to 0.050 and a thermal inertia in the range 150 to 300 Jm-2s-0.5K-1. Based on estimated thermal conductivities of the top-layer surface in the range 0.1 to 0.6 WK-1m-1, we calculated that the grain sizes are approximately equal to between 1 and 10 mm. The finely constrained values for this asteroid serve as a `design reference model', which is currently used for various planning, operational and modelling purposes by the Hayabusa2 team.

astro-ph.EP↗

arXiv2016

Status Report (22th J-PARC PAC): Searching for a Sterile Neutrino at J-PARC MLF (E56, JSNS2)

The JSNS$^2$ (J-PARC E56) experiment aims to search for a sterile neutrino at the J-PARC Materials and Life Sciences Experimental Facility (MLF). After the submission of a proposal to the J-PARC PAC, Stage-1 approval was granted to the JSNS$^2$ experiment on April 2015.This approval followed a series of background measurements which were performed in 2014. Recently, funding (the grant-in-aid for scientific research (S)) in Japan for building one 25~ton fiducial volume detector module was approved for the experiment. Therefore, we aim to start the experiment with one detector in JFY2018-2019. We are now working to produce precise cost estimates and schedule for construction, noting that most of the detector components can be produced within one year from the date of order. This will be reported at the next PAC meeting. In parallel to the detector construction schedule, JSNS$^2$ will submit a Technical Design report (TDR) to obtain the Stage-2 approval from the J-PARC PAC.The recent progress of the R$\&$D efforts towards this TDR are shown in this report. In particular, the R$\&$D status of the liquid scintillator, cosmic ray veto system, and software are shown. We have performed a test-experiment using 1.6~L of liquid scintillator at the 3rd floor of the MLF building in order to determine the identities of non-neutrino background particles coming to this detector location during the proton bunch. This is the so-called "MLF 2015AU0001" experiment. We briefly show preliminary results from this test-experiment.

physics.ins-det↗

arXiv2016

Interference effect between $ϕ$ and $Λ(1520)$ production channels in the $γp \rightarrow K^+K^-p$ reaction near threshold

The $ϕ$-$Λ(1520)$ interference effect in the $γp\to K^+K^-p$ reaction has been measured for the first time in the energy range from 1.673 to 2.173 GeV. The relative phases between $ϕ$ and $Λ(1520)$ production amplitudes were obtained in the kinematic region where the two resonances overlap. The measurement results support strong constructive interference when $K^+K^-$ pairs are observed at forward angles, but destructive interference for proton emission at forward angles. Furthermore, the observed interference effect does not account for the $\sqrt{s}=2.1$ GeV bump structure in forward differential cross sections for $ϕ$ photoproduction. This fact suggests possible exotic structures such as a hidden-strangeness pentaquark state, a new Pomeron exchange and rescattering processes via other hyperon states.

nucl-ex↗

arXiv2016

Status Report for the 21th J-PARC PAC : Searching for a Sterile Neutrino at J-PARC MLF (J-PARC E56, JSNS2)

The JSNS2 (J-PARC E56) experiment aims to search for sterile neutrinos at the J-PARC Materials and Life Sciences Experimental Facility (MLF).After the submission of a proposal to the J-PARC PAC, stage-1 approval was granted to the JSNS2 experiment. The approval followed a series of background measurements which were performed in 2014. Subsequent for stage-1 approval, the JSNS2 collaboration has made continuous efforts to write a Technical Design Report (TDR).This TDR will include two major items as discussed in the previous status report for the 20th J-PARC PAC: (1) A realistic detector location (2) Well understood and realistic detector performance using simulation studies, primarily in consideration of fast neutron rejection. Since August we have been in discussions with MLF staff regarding an appropriate detector location. We are also in the process of setting up a Monte Carlo (MC) simulation framework in order to study detector's performance in realistic conditions. In addition, we have pursued hardware R&D work for the liquid scintillator (LS) and to improve the dynamic range of the 10" photomultiplier tubes (PMTs). The LS R&D works includes Cherenkov studies inside the LS, and a Pulse Shape Discrimination (PSD) study with a test-beam, performed at Tohoku University. We also estimate the PSD performance of a full-sized detector using a detailed MC simulation. In this status report, we describe progress on this work.

physics.ins-det↗

arXiv2015

Direct Observation of Superconductivity in Calcium-Intercalated Bilayer Graphene by in situ Electrical Transport Measurements

We report the superconductivity in Ca-intercalated bilayer graphene C$_6$CaC$_6$, the thinnest limit of Ca graphite intercalation compound. We performed \textit{in situ} electrical transport measurements on pristine bilayer graphene, C$_6$LiC$_6$ and C$_6$CaC$_6$ fabricated on SiC substrate under zero and non-zero magnetic field. While both bilayer graphene and C$_6$LiC$_6$ show non-superconducting behavior, C$_6$CaC$_6$ exhibits the superconductivity with transition temperature ($T_{\rm c}$) of 4.0 K. The observed $T_{\rm c}$ in C$_6$CaC$_6$ and the absence of superconductivity in C$_6$LiC$_6$ show a good agreement with the theoretical prediction, suggesting the importance of a free-electron-like metallic band at the Fermi level to drive the superconductivity.

cond-mat.supr-con↗

arXiv2015

Observation of Spin-Dependent Charge Symmetry Breaking in $ΛN$ Interaction: Gamma-Ray Spectroscopy of $^4_{Λ}$He

The energy spacing between the ground-state spin doublet of $^4_Λ$He(1$^+$,0$^+$) was determined to be $1406 \pm 2 \pm 2$ keV, by measuring $γ$ rays for the $1^+ \to 0^+$ transition with a high efficiency germanium detector array in coincidence with the $^4$He$(K^-,π^-)$ $^4_Λ$He reaction at J-PARC. In comparison to the corresponding energy spacing in the mirror hypernucleus $^4_Λ$H, the present result clearly indicates the existence of charge symmetry breaking (CSB) in $ΛN$ interaction. It is also found that the CSB effect is large in the $0^+$ ground state but is by one order of magnitude smaller in the $1^+$ excited state, demonstrating that the $ΛN$ CSB interaction has spin dependence.

nucl-ex↗

arXiv2015

Status Report for the 20th J-PARC PAC : A Search for Sterile Neutrino at J-PARC MLF (J-PARC E56, JSNS2)

On April 2015, the J-PARC E56 (JSNS2: J-PARC Sterile Neutrino Search using neutrinos from J-PARC Spallation Neutron Source) experiment officially obtained stage-1 approval from J-PARC. We have since started to perform liquid scintillator R&D for improving energy resolution and fast neutron rejection. Also, we are studying Avalanche Photo-Diodes (SiPM) inside the liquid scintillator. In addition to the R&D work, a background measurement for the proton beam bunch timing using a small liquid scintillator volume was planned, and the safety discussions for the measurement have been done. This report describes the status of the R&D work and the background measurements, in addition to the milestones required before stage-2 approval.

physics.ins-det↗

arXiv2015

On-site Background Measurements for the J-PARC E56 Experiment: A Search for Sterile Neutrino at J-PARC MLF

The J-PARC E56 experiment aims to search for sterile neutrinos at the J-PARC Materials and Life Science Experimental Facility (MLF). In order to examine the feasibility of the experiment, we measured the background rates of different detector candidate sites, which are located at the third floor of the MLF, using a detector consisting of plastic scintillators with a fiducial mass of 500 kg. The result of the measurements is described in this article. The gammas and neutrons induced by the beam as well as the backgrounds from the cosmic rays were measured.

physics.ins-det↗

arXiv2015

Status Report (BKG measurement): A Search for Sterile Neutrino at J-PARC MLF

At the 17th J-PARC PAC, which was held on September 2013, we proposed the sterile neutrino search at J-PARC MLF. After reviewing the proposal, PAC recommended to have a background measurement at the detector's candidate site location in their report to investigate whether the background rates can be manageable for the real experiment or not. Therefore, we have performed the background measurements (MLF; 2013BU1301 test experiment) during the summer of 2014, also following the 18th J-PARC PAC recommendations, and the measurements results are described here.

physics.ins-det↗

arXiv2014

(25143) Itokawa: The Power of Radiometric Techniques for the Interpretation of Remote Thermal Observations in the Light of the Hayabusa Rendezvous Results

The near-Earth asteroid (25143) Itokawa was characterised in great detail by the Japanese Hayabusa mission. We revisited the available thermal observations in the light of the true asteroid properties with the goal to evaluate the possibilities and limitations of thermal model techniques. In total, we used 25 published ground-based mid-infrared photometric observations and 5 so far unpublished measurements from the Japanese infrared astronomical satellite AKARI in combination with improved H-G values. Our thermophysical model (TPM) approach allowed us to determine correctly the sense of rotation, to estimate the thermal inertia and to derive robust effective size and albedo values by only using a simple spherical shape model. A more complex shape model, derived from light-curve inversion techniques, improved the quality of the predictions considerably and made the interpretation of thermal light-curve possible. The radiometrically derived effective diameter value agrees within 2% of the true Itokawa size value. The combination of our TPM and the final Itokawa in-situ shape model was then used as a benchmark for deriving and testing radiometric solutions. The consolidated value for the surface-averaged thermal inertia is 700 $\pm$ 200 Jm$^{-2}$s$^{-0.5}$K$^{-1}$. We found that even the high resolution shape models still require additional small-scale roughness in order to explain the disk-integrated infrared measurements. Our description of the thermal effects as a function of wavelengths, phase angle, and rotational phase facilitates the planning of crucial thermal observations for sophisticated characterization of small bodies, including other potentially hazardous asteroids. Our analysis shows the power of radiometric techniques to derive the size, albedo, thermal inertia, and also spin-axis orientation from small sets of measurements at thermal infrared wavelengths.

astro-ph.EP↗

arXiv2014

Search for $^6_Λ$H hypernucleus by the $^6$Li$(π^-,K^+)$ reaction at $p_{π^-}$ = 1.2 GeV/$c$

We have carried out an experiment to search for a neutron-rich hypernucleus, $^6_Λ$H, by the $^6$Li($π^-,K^+$) reaction at $p_{π^-}$ =1.2 GeV/$c$. The obtained missing mass spectrum with an estimated energy resolution of 3.2 MeV (FWHM) showed no peak structure corresponding to the $^6_Λ$H hypernucleus neither below nor above the $^4_Λ$H$+2n$ particle decay threshold. An upper limit of the production cross section for the bound $^6_Λ$H hypernucleus was estimated to be 1.2 nb/sr at 90% confidence level.

nucl-ex↗

arXiv2014

Concept for an Electron Ion Collider (EIC) detector built around the BaBar solenoid

The PHENIX collaboration presents here a concept for a detector at a future Electron Ion Collider (EIC). The EIC detector proposed here, referred to as ePHENIX, will have excellent performance for a broad range of exciting EIC physics measurements, providing powerful investigations not currently available that will dramatically advance our understanding of how quantum chromodynamics binds the proton and forms nuclear matter.

nucl-ex↗