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488
result(s) for
"Sako, H"
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The v31/3/v21/2 ratio in PbAu collisions at sNN= 17.3 GeV: a hint of a hydrodynamic behavior
The Fourier harmonics,
v
2
and
v
3
of negative pions are measured at center-of-mass energy per nucleon pair of
s
NN
= 17.3 GeV around midrapidity by the CERES/NA45 experiment at the CERN SPS in 0–30% central PbAu collisions with a mean centrality of 5.5%. The analysis is performed in two centrality bins as a function of the transverse momentum
p
T
from 0.05 GeV/
c
to more than 2 GeV/
c
. This is the first measurement of the
v
3
1
/
3
/
v
2
1
/
2
ratio as a function of transverse momentum at SPS energies, that reveals, independently of the hydrodynamic models, hydrodynamic behavior of the formed system. For
p
T
above 0.5 GeV/
c
, the ratio is nearly flat in accordance with the hydrodynamic prediction and as previously observed by the ATLAS and ALICE experiments at the much higher LHC energies. The results are also compared with the SMASH-vHLLE hybrid model predictions, as well as with the SMASH model applied alone.
Journal Article
The$$v^{1/3}_{3}/v^{1/2}_{2}$$ratio in PbAu collisions at$$\\sqrt{s_{\\textrm{NN}}} = $$17.3 GeV: a hint of a hydrodynamic behavior
The Fourier harmonics,$$v_2$$v 2 and$$v_3$$v 3 of negative pions are measured at center-of-mass energy per nucleon pair of$$\\sqrt{s_{\\textrm{NN}}}$$s NN = 17.3 GeV around midrapidity by the CERES/NA45 experiment at the CERN SPS in 0–30% central PbAu collisions with a mean centrality of 5.5%. The analysis is performed in two centrality bins as a function of the transverse momentum$$\\mathrm {p_{\\textrm{T}}}$$p T from 0.05 GeV/ c to more than 2 GeV/ c . This is the first measurement of the$$v^{1/3}_{3}/v^{1/2}_{2}$$v 3 1 / 3 / v 2 1 / 2 ratio as a function of transverse momentum at SPS energies, that reveals, independently of the hydrodynamic models, hydrodynamic behavior of the formed system. For$$\\mathrm {p_{\\textrm{T}}}$$p T above 0.5 GeV/ c , the ratio is nearly flat in accordance with the hydrodynamic prediction and as previously observed by the ATLAS and ALICE experiments at the much higher LHC energies. The results are also compared with the SMASH-vHLLE hybrid model predictions, as well as with the SMASH model applied alone.
Journal Article
Measurement of Λ Polarization in the π ¯ p → K0 Λ Reaction at pπ¯ = 1.33 GeV/c toward a New Λ p Scattering Experiment
Understanding the spectrum and dynamics of excited nucleon states (\\(N^{*}\\) resonances) remains a central challenge in hadron physics, as these resonances emerge in intermediate states of \\(\\pi N\\) and \\(\\gamma N\\) interactions. The dynamical coupled-channel models addressing this problem rely critically on experimental inputs for partial wave analyses. However, polarization observables of hyperons, which serve as sensitive probes of reaction mechanisms, have so far been limited in precision. To address this, we aim to provide high-precision measurements of the polarization of the \\(\\Lambda\\) hyperon produced in the \\(\\pi ^- p \\rightarrow K^0 \\Lambda\\) reaction. The data were obtained with the Japan Proton Accelerator Research Complex (J-PARC) E40 experiment at the K1.8 beamline of the J-PARC Hadron Experimental Facility. The polarization of the \\(\\Lambda\\) was precisely measured in the angular range \\(0.6 < \\cos {\\theta ^{K^0}_{\\rm CM}}< 1.0\\) with a fine bin width of \\(0.6 < \\cos {\\theta ^{K^0}_{\\rm CM}}< 1.0\\). The observed average polarization in the region \\(0.6 < \\cos {\\theta ^{K^0}_{\\rm CM}}< 1.0\\) was \\(0.932 \\pm 0.058 (\\text{stat.}) \\pm 0.028 (\\text{syst.})\\). These results provide essential input for partial wave analyses of dynamical coupled-channel models, contributing to a deeper understanding of \\(N^{*}\\) resonance dynamics. Furthermore, the strong \\(\\Lambda\\) polarization observed indicates the feasibility of developing a highly polarized \\(\\Lambda\\) beam, opening prospects for future \\(\\Lambda p\\) scattering experiments such as J-PARC E86.
Journal Article
Study of ∑N interaction from the ∑p scattering experiment at J-PARC
A high statistics ∑p scattering experiment has been performed at the K1.8 beamline in the J-PARC Hadron Experimental Facility. Data for momentum-tagged ∑− beam running in a liquid hydrogen target were accumulated by detecting the π−p→K+∑− reaction with a high intensity π− beam of 20 M/spill. The number of the Σ− beam was about 1.7 × 107 in total. The ∑−ρ elastic scattering and the ∑−p → Λn inelastic scattering events were successfully observed with about 100 times larger statistics than that in past experiments.
Journal Article
Ξ − atomic X-ray spectroscopy using a counter-emulsion hybrid method
Ξ− atomic X-ray spectroscopy is one of the most useful methods for investigation of the Ξ–nucleus strong interaction. Since the X-ray energy is shifted and/or broadened due to the Ξ–nucleus strong interaction compared to those calculated from electromagnetic interaction alone, the measurement of the energy shift, ΔE, and the width, Γ, give us information on the Ξ–nucleus potential. A serious problem in the measurement is the significant background derived from in-flight Ξ− decay. A novel method of identifying stopped Ξ− events using the nuclear emulsion was developed to realize the first Ξ− atomic X-ray spectroscopy experiment as the J-PARC E07 experiment, which also aimed at searching for ΛΛ and Ξ− hypernuclei in the emulsion. The X-rays emitted from Ξ− Br and Ξ− Ag atoms were measured using germanium detectors. No clear peaks were observed in the obtained spectra. However, we succeeded in reducing the background to 1/170 by this method employing coincidence measurements using nuclear emulsion and X-ray detectors.
Journal Article
e + e--pair production in Pb-Au collisions at 158 GeV per nucleon
We present the combined results on electron-pair production in 158 GeV/n Pb-Au (\\(\\sqrt{s}\\) = 17.2 GeV) collisions taken at the CERN SPS in 1995 and 1996, and give a detailed account of the data analysis. The enhancement over the reference of neutral meson decays amounts to a factor of 2.31 \\(\\pm0.19 (stat.)\\pm0.55 (syst.)\\pm0.69 (decays)\\) for semi-central collisions (28\\(\\%\\)\\(\\sigma/\\sigma_{geo}\\)) when yields are integrated over m > 200 MeV/c2 in invariant mass. The measured yield, its stronger-than-linear scaling with \\(N_{\\rm ch}\\), and the dominance of low pair pt strongly suggest an interpretation as thermal radiation from pion annihilation in the hadronic fireball. The shape of the excess centring at \\(m\\approx\\) 500 MeV/c2, however, cannot be described without strong medium modifications of the \\(\\rho\\) meson. The results are put into perspective by comparison to predictions from Brown-Rho scaling governed by chiral symmetry restoration, and from the spectral-function many-body treatment in which the approach to the phase boundary is less explicit.
Journal Article
Recent progress and future prospects of hyperon nucleon scattering experiment
A new hyperon-proton scattering experiment, dubbed J-PARC E40, was performed to measure differential cross sections of the Σ + p , Σ − p elastic scatterings and the Σ − p → Λ n scattering by identifying a lot of Σ particles in the momentum ranging from 0.4 to 0.8 GeV/ c produced by the π ± p → K + Σ ± reactions. We successfully measured the differential cross sections of these three channels with a drastically improved accuracy with a fine angular step. These new data will become important experimental constraints to improve the theories of the two-body baryon-baryon interactions. Following this success, we proposed a new experiment to measure the differential cross sections and spin observables by using a highly polarized Λ beam for providing quantitative information on the Λ N interaction. The results of three Σ p channels and future prospects of the Λ p scattering experiment are described.
Journal Article
Study of Neutron-Rich Hypernuclei by the (π−, K+) Reaction at J-PARC
We are planning to perform an experiment at J-PARC and produce new neutron-rich Λ hypernuclei by using the (
π
−
,
K
+
) reaction (J-PARC E10). As the first step, we are planning to produce
hypernuclei with a
6
Li target. To conduct this experiment, we are developing new detectors, those are scintillating fiber tracker, and silicon strip detector, for high rate operation to aim at increasing beam intensity up to 10
7
/spill. As a result of beam test in Jun 2012, we are going to use high-rate beam at least 10
7
/spill.
Journal Article
J-PARC E27 Experiment to Search for a Nuclear Kaon Bound State K−pp
In the J-PARC E27 experiment, we search for a
K
−
pp
bound state via the
d
(
π
+
,
K
+
) reaction at 1.7 GeV/
c
at the K1.8 beam line. The binding energy and decay width of the
K
−
pp
bound state can be obtained in the missing mass measurement with a good energy resolution of 2 MeV/
c
2
. A range counter array (RCA) was constructed to detect the two high-momentum protons from the
K
−
pp
decay and to reduce the background such as quasi-free hyperon production. Recently, we have carried out a pilot run in June, 2012. The
d
(
π
+
,
K
+
) missing-mass spectrum has been obtained for the first time. In this report, an overview of the E27 experiment and a preliminary result on this pilot run are presented.
Journal Article