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## Nuclear Experiment (nucl-ex) updates on the arXiv.org e-print archive

Published: 2017-09-19T20:30:00-05:00

Stopping powers and energy loss straggling for MeV protons in a kapton polyimide thin film. (arXiv:1709.06083v1 [physics.ins-det])

The energy loss and energy loss straggling widths have been measured in transmission for MeV protons traversing a thin kapton polyimide foil. In a prior step, the thickness and non-uniformity of the target foil were carefully investigated. The overall relative uncertainties in the stopping power and energy loss straggling variance data amount, respectively, to less than 2% and 8%. The experimental data show to be in excellent agreement with available previous ones and with those compiled in the ICRU-49 report. They are fully consistent with the predictions of Sigmund-Schinner's binary collision theory of electronic stopping over the whole proton energy range explored. An average deviation of ~2.5% relative to values calculated by the SRIM-2008 code, likely due to effects of valence electrons involving the , and bonds, is however observed at low proton velocities. The measured energy loss straggling data, which are unique to our knowledge, are found to be in good agreement with values derived by the classical Bohr formula for keV but they significantly exceed Bohr's collisional energy loss straggling at lower proton velocities where target electrons can no longer be considered as free. They also show to be consistent with the predictions of the Bethe-Livingston and Sigmund-Schinner theories over the low proton velocity region ( keV). However, they are significantly overestimated by these theories over the intermediate and high proton velocity regions, which may be due to bunching effect by inner shell electrons of the polymer target. Besides, our energy loss straggling data are in better overall consistency with the Yang, O'Connor and Wang empirical formula for keV, while deviations above the latter amounting up to ~18% are observed at lower proton velocities.

Keywords: Swift protons; Kapton polyimide; Stopping power; Energy loss straggling; Binary collision theory.

Disentangling the role of vibration, rotation, and neutron transfer in the fusion of neutron-rich mid-mass nuclei. (arXiv:1709.06167v1 [nucl-ex])

We report the first measurement of the fusion excitation functions for $^{39,47}$K + $^{28}$Si at near-barrier energies. Evaporation residues resulting from the fusion process were identified by direct measurement of their energy and time-of-flight with high geometric efficiency. At the lowest incident energy, the cross-section measured for the neutron-rich $^{47}$K induced reaction is ~6 times larger than that of the $\beta$-stable system. The experimental data are compared with both a dynamical deformation model and coupled channels calculations (CCFULL).

Development of a compact ExB microchannel plate detector for beam imaging. (arXiv:1709.06177v1 [physics.ins-det])

A beam imaging detector was developed by coupling a multi-strip anode with delay line readout to an E$\times$B microchannel plate (MCP) detector. This detector is capable of measuring the incident position of the beam particles in one-dimension. To assess the spatial resolution, the detector was illuminated by an $\alpha$-source with an intervening mask that consists of a series of precisely-machined slits. The measured spatial resolution was 520$\mu$m FWHM, which was improved to 413$\mu$m FWHM by performing an FFT of the signals, rejecting spurious signals on the delay line, and requiring a minimum signal amplitude. This measured spatial resolution of 413$\mu$m FWHM corresponds to an intrinsic resolution of 334$\mu$m FWHM when the effect of the finite slit width is de-convoluted. To understand the measured resolution, the performance of the detector is simulated with the ion-trajectory code SIMION.

Role of Multi-Parton Interactions on $J/\psi$ production in $p+p$ collisions at LHC Energies. (arXiv:1709.06358v1 [hep-ph])

The production mechanism of quarkonia states in hadronic collisions is still to be understood by the scientific community. In high-multiplicity $p+p$ collisions, Underlying Event (UE) observables are of major interest. The Multi-Parton Interactions (MPI) is a UE observable, where several interactions occur at the partonic level in a single $p+p$ event. This leads to dependence of particle production on event multiplicity. If the MPI occurs in a harder scale, there will be a correlation between the yield of quarkonia and total charged particle multiplicity. The ALICE experiment at the Large Hadron Collider (LHC) in $p+p$ collisions at $\sqrt{s}$ = 7 and 13 TeV has observed an approximate linear increase of relative $J/\psi$ yield ($\frac{dN_{J/\psi}/dy}{}$) with relative charged particle multiplicity density ($\frac{dN_{ch}/dy}{}$). In our present work we have performed a comprehensive study of the production of charmonia as a function of charged particle multiplicity in $p+p$ collisions at LHC energies using pQCD-inspired multiparton interaction model, PYTHIA8 tune 4C, with and without Color Reconnection (CR) scheme. A detail multiplicity and energy dependent study is performed to understand the effects of MPI on $J/\psi$ production. The ratio of $\psi(2S)$ to $J/\psi$ is also studied as a function of charged particle multiplicity at LHC energies.

First direct mass measurements of hot-fusion transuranium isotopes with an MRTOF-MS. (arXiv:1709.06468v1 [nucl-ex])

Masses of $^{246}$Es, $^{251}$Fm and the transfermium nuclei $^{249-252}$Md, and $^{254}$No, produced by hot- and cold-fusion reactions, in the vicinity of the deformed $N=152$ neutron shell closure, have been directly measured using a multi-reflection time-of-flight mass spectrograph. The masses of $^{246}$Es and $^{249,250,252}$Md were measured for the first time. Using the masses of $^{249,250}$Md as anchor points for $\alpha$ decay chains, the masses of heavier nuclei, up to $^{261}$Bh and $^{266}$Mt, were determined. These new masses were compared with theoretical global mass models and demonstrated to be in good agreement with macroscopic-microscopic models in this region. The empirical shell gap parameter $\delta_{2n}$ derived from three isotopic masses was updated with the new masses and corroborate the existence of the deformed $N=152$ neutron shell closure for Md and Lr.

Hyperfine splitting in ordinary and muonic hydrogen. (arXiv:1709.06544v1 [hep-ph])

We provide an accurate evaluation of the two-photon exchange correction to the hyperfine splitting of S energy levels in muonic hydrogen exploiting the corresponding measurements in electronic hydrogen. The proton structure uncertainty in the calculation of $\alpha^5$ contribution is reduced from $100~\mathrm{ppm}$ level to $16~\mathrm{ppm}$.

On the existence of Rydberg nuclear molecules. (arXiv:1706.01150v2 [nucl-th] UPDATED)

Present nuclear detection techniques prevents us from determining if the analogue of a Rydberg molecule exists for the nuclear case. But nothing in nature disallows their existence. As in the atomic case, Rydberg nuclear molecules would be a laboratory for new aspects and applications of nuclear physics. We propose that Rydberg nuclear molecules, which represent the exotic, halo nuclei version, such as 11Be + 11Be, of the well known quasimolecules observed in stable nuclei such as 12C + 12C, might be common structures that could manifest their existence along the dripline. A study of possible candidates and the expected structure of such exotic clustering of two halo nuclei: the Rydberg nuclear molecules, is made on the basis of three diferent methods. It is shown that such cluster structures might be stable and unexpectedly common.

Importance of d-wave contributions in the charge symmetry breaking reaction $dd \to {}^4\text{He}\pi^0$. (arXiv:1709.01060v2 [nucl-ex] UPDATED)

This letter reports the first measurement of the contribution of higher partial waves in the charge symmetry breaking reaction $dd \to {}^4\text{He}\pi^0$ using the WASA-at-COSY detector setup at an excess energy of $Q = 60$ MeV. The determined differential cross section can be parametrized as $\text{d}\sigma/\text{d}\Omega = a + b\cos^{2}\theta^*$, where $\theta^*$ is the production angle of the pion in the center-of-mass coordinate system, and the results for the parameters are $a = \left(1.55 \pm 0.46 (\text{stat}) ^{+0.32}_{-0.8} (\text{syst}) \right) \text{pb/sr}$ and $b = \left(13.1 \pm 2.1 (\text{stat}) ^{+1.0}_{-2.7} (\text{syst})\right) \text{pb/sr}$. The data are compatible with vanishing p-waves and a sizable d-wave contribution. This finding should strongly constrain the contribution of the $\Delta$ isobar to the $dd \to {}^4\text{He}\pi^0$ reaction and is therefore crucial for a quantitative understanding of quark mass effects in nuclear production reactions.

Experimental techniques and performance of $\Lambda$-hypernuclear spectroscopy with the $(e,e^{\prime}K^{+})$ reaction. (arXiv:1709.05682v2 [physics.ins-det] UPDATED)

The missing-mass spectroscopy of $\Lambda$ hypernuclei via the $(e,e^{\prime}K^{+})$ reaction has been developed through experiments at JLab Halls A and C in the last two decades. For the latest experiment, E05-115 in Hall C, we developed a new spectrometer system consisting of the HKS and HES; resulting in the best energy resolution ($E_{\Lambda} \simeq0.5$-MeV FWHM) and $B_{\Lambda}$ accuracy ($B_{\Lambda}\leq0.2$ MeV) in $\Lambda$-hypernuclear reaction spectroscopy. This paper describes the characteristics of the $(e,e^{\prime}K^{+})$ reaction compared to other reactions and experimental methods. In addition, the experimental apparatus, some of the important analyses such as the semi-automated calibration of absolute energy scale, and the performance achieved in E05-115 are presented.

Electromagnetic fields in small systems from a multiphase transport model. (arXiv:1709.05962v2 [hep-ph] UPDATED)

We calculate the electromagnetic fields generated in small systems by using the a multiphase transport (AMPT) model. Compared to A+A collisions, we find that the absolute electric and magnetic fields are not small in p+Au and d+Au collisions at RHIC energy and in p+Pb collisions at the LHC energy. We study the centrality dependences and the spatial distributions of electromagnetic fields. We further investigate the azimuthal fluctuations of magnetic field and its correlation with the fluctuating geometry using event-by-event simulations. We find that the azimuthal correlation $$between the magnetic field direction and the second harmonic participant plane is almost zero in small systems with high multiplicities, but not in those with low multiplicities. This indicates that the charge azimuthal correlation,$$, is not a valid probe to study Chiral Magnetic Effect (CME) in small systems with high multiplicities. However, we suggest to search for possible CME effects in small systems with low multiplicities.

The MCUCN simulation code for ultracold neutron physics. (arXiv:1709.05974v2 [physics.ins-det] UPDATED)

Ultracold neutrons (UCN) have very low kinetic energies 0-300 neV, thereby can be stored in specific material or magnetic confinements for many hundreds of seconds. This makes them a very useful tool in probing fundamental symmetries of nature (for instance charge-parity violation by neutron electric dipole moment experiments) and contributing important parameters for the Big Bang nucleosynthesis (neutron lifetime measurements). Improved precision experiments are in construction at new and planned UCN sources around the world. MC simulations play an important role in the optimization of such systems with a large number of parameters, but also in the estimation of systematic effects, in benchmarking of analysis codes, or as part of the analysis. The MCUCN code written at PSI has been extensively used for the optimization of the UCN source optics and in the optimization and analysis of (test) experiments within the nEDM project based at PSI. In this paper we present the main features of MCUCN and interesting benchmark and application examples.