Many neutron star properties, such as the proton fraction, reflect the symmetry energy contributions to the equation of state that dominate when neutron and proton densities differ strongly. To ...constrain these contributions at suprasaturation densities, we measure the spectra of charged pions produced by colliding rare isotope tin (Sn) beams with isotopically enriched Sn targets. Using ratios of the charged pion spectra measured at high transverse momenta, we deduce the slope of the symmetry energy to be 42<L<117 MeV. This value is slightly lower but consistent with the L values deduced from a recent measurement of the neutron skin thickness of ^{208}Pb.
In the past two decades, pions created in the high density regions of heavy ion collisions have been predicted to be sensitive at high densities to the symmetry energy term in the nuclear equation of ...state, a property that is key to our understanding of neutron stars. In a new experiment designed to study the symmetry energy, the multiplicities of negatively and positively charged pions have been measured with high accuracy for central 132Sn+124Sn, 112Sn+124Sn, and 108Sn+112Sn collisions at E/A=270 MeV with the SπRIT Time Projection Chamber. While individual pion multiplicities are measured to 4% accuracy, those of the charged pion multiplicity ratios are measured to 2% accuracy. We compare these data to predictions from seven major transport models. The calculations reproduce qualitatively the dependence of the multiplicities and their ratios on the total neutron and proton number in the colliding systems. However, the predictions of the transport models from different codes differ too much to allow extraction of reliable constraints on the symmetry energy from the data. This finding may explain previous contradictory conclusions on symmetry energy constraints obtained from pion data in Au+Au system. These new results call for still better understanding of the differences among transport codes, and new observables that are more sensitive to the density dependence of the symmetry energy.
In proton therapy, positron emitter nuclei are generated via the target nuclear fragmentation reactions between irradiated proton and nuclei constituting a human body. The proton-irradiated volume ...can be confirmed with measurement of annihilation γ-rays from the generated positron emitter nuclei. To achieve the high accuracy of proton therapy, in vivo dosimetry, i.e., evaluation of the irradiated dose during the treatment is important. To convert the measured activity distribution to irradiated dose, cross-sectional data for positron emitter production is necessary, which is currently insufficient in the treatment area. The purpose of this study is to collect cross-sectional data of C12(p,pn)C11 and C12(p,p2n)C10 reactions between the incident proton and carbon nuclei, which are important target nuclear fragmentation reactions, to estimate the range and exposure dose distribution in the patient's body. Using planar-type PET capable of measuring annihilation γ-rays at high positional resolution and thick polyethylene target, we measured cross-sectional data in continuous wide energy range. The cross section of C12(p,pn)C11 is in good agreement with existing experimental data. The cross section of C12(p,p2n)C10 is reported for the first data in the low-energy range of 67.6–10.5 MeV near the Bragg peak of proton beam.
•Cross sections for C11 and C10 productions in proton-induced target fragmentation were measured.•Cross sections of C12(p,pn)11C were in good agreement with previous studies.•The first data of cross sections of C12(p,p2n)10C for range of 67.6–10 MeV were obtained.•Cross sections of continuous energy were measured using planar-type PET and thick target.
The MEG II experiment, based at the Paul Scherrer Institut in Switzerland, reports the result of a search for the decay
μ
+
→
e
+
γ
from data taken in the first physics run in 2021. No excess of ...events over the expected background is observed, yielding an upper limit on the branching ratio of
B
(
μ
+
→
e
+
γ
)
<
7.5
×
10
-
13
(90% CL). The combination of this result and the limit obtained by MEG gives
B
(
μ
+
→
e
+
γ
)
<
3.1
×
10
-
13
(90% CL), which is the most stringent limit to date. A ten-fold larger sample of data is being collected during the years 2022–2023, and data-taking will continue in the coming years.
Operation and performance of the MEG II detector Afanaciev, K.; Baldini, A. M.; Ban, S. ...
The European physical journal. C, Particles and fields,
02/2024, Letnik:
84, Številka:
2
Journal Article
Recenzirano
Odprti dostop
The MEG II experiment, located at the Paul Scherrer Institut (PSI) in Switzerland, is the successor to the MEG experiment, which completed data taking in 2013. MEG II started fully operational data ...taking in 2021, with the goal of improving the sensitivity of the
μ
+
→
e
+
γ
decay down to
∼
6
×
10
-
14
almost an order of magnitude better than the current limit. In this paper, we describe the operation and performance of the experiment and give a new estimate of its sensitivity versus data acquisition time.
Properties of the nuclear equation of state (EoS) can be probed by measuring the dynamical properties of nucleus-nucleus collisions. In this study, we present the directed flow (v1), elliptic flow ...(v2) and stopping (VarXZ) measured in fixed target Sn + Sn collisions at ▪ with the SπRIT Time Projection Chamber. We perform Bayesian analyses in which EoS parameters are varied simultaneously within the Improved Quantum Molecular Dynamics-Skyrme (ImQMD-Sky) transport code to obtain a multivariate correlated constraint. The varied parameters include symmetry energy, S0, and slope of the symmetry energy, L, at saturation density, isoscalar effective mass, ms⁎/mN, isovector effective mass, mv⁎/mN and the in-medium cross-section enhancement factor η. We find that the flow and VarXZ observables are sensitive to the splitting of proton and neutron effective masses and the in-medium cross-section. Comparisons of ImQMD-Sky predictions to the SπRIT data suggest a narrow range of preferred values for ms⁎/mN, mv⁎/mN and η.
The NEUT intranuclear cascade model is described and fit to a large body of π± -nucleus scattering data. Methods are developed to deal with deficiencies in the available historical data, and robust ...uncertainty estimates are produced. The results are compared to a variety of simulation packages and the data. This work provides a method for tuning final state interaction models, which are of particular interest to neutrino experiments that operate in the few-GeV energy region, and provides results which can be used directly by the T2K and Super-Kamiokande Collaborations, for whom NEUT is the primary simulation package.
•We measured the production cross sections for a variety of radioactive isotopes.•They were produced from 124Xe, 48Ca, and 238U beams at 345MeV/nucleon using BigRIPS.•The measured production cross ...sections were compared with the EPAX formulae.•We discovered four new isotopes 85,86Ru and 81,82Mo produced by 124Xe+Be.•103Sb is particle unbound with an upper limit of 49ns for the half-life.
We have measured the production rates and production cross sections for a variety of radioactive isotopes which were produced from 124Xe, 48Ca, and 238U beams at an energy of 345MeV/nucleon using the BigRIPS separator at the RIKEN Nishina Center RI Beam Factory (RIBF). Proton-rich isotopes with atomic numbers Z=40–52 and neutron-rich isotopes with Z=5–16 were produced by projectile fragmentation of the 124Xe and 48Ca beam on Be targets, respectively. Neutron-rich isotopes with Z=20–59 were produced by in-flight fission of the 238U beam, in which both Be and Pb were used as production targets. The measured production rates and production cross sections were compared with those of the LISE++ calculations, and overall fairly good agreement has been obtained. Furthermore, in the measurements with the 124Xe beam, we have discovered four new isotopes on the proton-drip line, 85,86Ru and 81,82Mo, and obtained the clear evidence that 103Sb is particle unbound with an upper limit of 49ns for the half-life. The measurements of projectile-fragment momentum distributions have been also performed with the 124Xe beam, in which the low-momentum tails of the distributions have been measured for the first time at the energy of 345MeV/nucleon.
The rapidity distributions of hydrogen isotopes emitted from central collisions of neutron-rich 132Sn+124Sn and neutron-deficient 108Sn+112Sn systems at 270 MeV/nucleon were investigated at ...RIKEN-RIBF. The data are compared with antisymmetrized molecular dynamics (AMD) calculations and the rapidity distributions can be reproduced after adjusting the in-medium nucleon-nucleon cross sections. The double ratios between the two reaction systems taken for the relative yields of deuteron to proton (d/p) and triton to proton (t/p) are further examined in the midrapidity domain, where the adjustments in the AMD calculations do not affect much on them. The d/p and t/p double ratios at midrapidity agree well with the ratio of the system neutron numbers and its squared value, respectively, and the rapidity dependence of these double ratios is consistent with a picture of partial mixing of colliding nuclei. By comparing with the AMD model which shows a strong symmetry energy dependence of the t/p double ratio, the experimental result in the midrapidity domain favors the calculation with a symmetry-energy slope parameter around L=46 MeV rather than L=108 MeV.
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