Nuclear Experiment

This paper presents an automatic method for data classification in nuclear physics experiments based on evolutionary computing and vector quantization. The major novelties of our approach are the fully automatic mechanism and the use of analytical models to provide physics constraints, yielding to a fast and physically reliable classification with nearly-zero human supervision. Our method is successfully validated by using experimental data produced by stacks of semiconducting detectors. The resulting classification is highly satisfactory for all explored cases and is particularly robust to noise. The algorithm is suitable to be integrated in the online and offline analysis programs of existing large complexity detection arrays for the study of nucleus-nucleus collisions at low and intermediate energies.

The proposed measurement is a dedicated study of the exclusive electroproduction process,1H(e,e'p)pi0, in the backward-angle regime (u-channel process) above the resonance region. The produced pi0 is emitted 180 degrees opposite to the virtual-photon momentum. This study also aims to apply the well-known Rosenbluth separation technique that provides the model-independent differential cross-sections at the never explored u-channel kinematics region. Currently, the "soft-hard transition" in u-channel meson production remains an interesting and unexplored subject. The available theoretical frameworks offer competing interpretations for the observed backward-angle cross section peaks. In a "soft" hadronic Regge exchange description, the backward meson production comes from the interference between nucleon exchange and the meson produced via re-scattering within the nucleon. Whereas in the "hard" GPD-like backward collinear factorization regime, the scattering amplitude factorizes into a hard subprocess amplitude and baryon to meson transition distribution amplitudes (TDAs), otherwise known as super skewed parton distributions (SuperSPDs). Both TDAs and SPDs are universal non-perturbative objects of nucleon structure accessible only through backward-angle kinematics. The separated cross sections:sigma_T,sigma_L and T/L ratio at Q2=2-6 GeV2, provide a direct test of two predictions from the TDA model. The magnitude and u-dependence of the separated cross sections also provide a direct connection to the re-scattering Regge picture. The extracted interaction radius (from u-dependence) at different Q2 can be used to study the soft-hard transition in the u-channel kinematics. The acquisition of these data will be an important step forward in validating the existence of a backward factorization scheme of the nucleon structure function and establishing its applicable kinematic range.

The measurements of particle multiplicity distributions have generated considerable interest in understanding the fluctuations of conserved quantum numbers in the Quantum Chromodynamics (QCD) hadronization regime, in particular near a possible critical point and near the chemical freeze-out. We report the measurement of efficiency and centrality bin width corrected cumulant ratios ( C 2 / C 1 , C 3 / C 2 ) of net- Λ distributions, in the context of both strangeness and baryon number conservation, as a function of collision energy, centrality and rapidity. The results are for Au + Au collisions at five beam energies ( s NN − − − − √ = 19.6, 27, 39, 62.4 and 200 GeV) recorded with the Solenoidal Tracker at RHIC (STAR). We compare our results to the Poisson and negative binomial (NBD) expectations, as well as to Ultra-relativistic Quantum Molecular Dynamics (UrQMD) and Hadron Resonance Gas (HRG) model predictions. Both NBD and Poisson baselines agree with data within the statistical and systematic uncertainties. The ratios of the measured cumulants show no features of critical fluctuations. The chemical freeze-out temperatures extracted from a recent HRG calculation, which was successfully used to describe the net-proton, net-kaon and net-charge data, indicate Λ freeze-out conditions similar to those of kaons. However, large deviations are found when comparing to temperatures obtained from net-proton fluctuations. The net- Λ cumulants show a weak, but finite, dependence on the rapidity coverage in the acceptance of the detector, which can be attributed to quantum number conservation.

We present a measurement of the first-order azimuthal anisotropy, v 1 (y) , of deuterons from Au+Au collisions at s NN − − − − √ = 7.7, 11.5, 14.5, 19.6, 27, and 39 GeV recorded with the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). The energy dependence of the v 1 (y) slope, d v 1 /dy | y=0 , for deuterons, where y is the rapidity, is extracted for semi-central collisions (10-40\% centrality) and compared to that of protons. While the v 1 (y) slopes of protons are generally negative for s NN − − − − √ > 10 GeV, those for deuterons are consistent with zero, a strong enhancement of the v 1 (y) slope of deuterons is seen at the lowest collision energy (the largest baryon density) at s NN − − − − √ = 7.7 GeV. In addition, we report the transverse momentum dependence of v 1 for protons and deuterons. The experimental results are compared with transport and coalescence models.

We report on a new measurement of the beam-normal single spin asymmetry A n in the elastic scattering of 570 MeV transversely polarized electrons off 28 Si and 90 Zr at Q 2 =0.04 GeV 2 / c 2 . The studied kinematics allow for a comprehensive comparison with former results on 12 C. No significant mass dependence of the beam-normal single spin asymmetry is observed in the mass regime from 12 C to 90 Zr.

Recent measurements and hydrodynamic model calculations suggest that the higher-order flow coefficients v 4 and v 5 have two contributions: a linear contribution driven by the initial-state eccentricities, ε n , and a mode-coupled contribution derived from the lower-order eccentricity coefficients ε 2 and ε 3 . Measurements of these two contributions to v 4 and v 5 provide crucial insights to discern initial-state models and to constrain the temperature-dependent specific shear viscosity, η/s , of the plasma produced in heavy-ion collisions. In this work, we have employed the two-subevents cumulant technique to provide the first beam-energy and collision-system dependence of the linear and mode-coupled contributions to the higher-order flow harmonics. Our results are shown and discussed for several centrality intervals for U+U collisions at s NN − − − √ = 193 GeV, Au+Au collisions at s NN − − − √ =200, and 54.4 GeV and Cu+Au collisions at s NN − − − √ =200 GeV. The results are compared with similar studies performed by the ALICE experiment at LHC.

In this manuscript, various beauty production measurements using the ALICE detector will be presented. We will show new measurements of non-prompt D 0 mesons in pp collisions at s √ =5.02 TeV and beauty-tagged jet production in p--Pb collisions at s NN − − − √ =5.02 TeV. The R AA of beauty-hadron decay electrons in central Pb--Pb collisions and the v 2 of beauty-hadron decay electrons in semi-central Pb--Pb collisions at s NN − − − √ =5.02 TeV will also be discussed.

We used a high-resolution magnetic spectrograph to study neutron pair-correlated 0 + states in 136 Ba, produced via the 138 Ba(p,t) reaction. In conjunction with state-of-the-art shell model calculations, these data benchmark part of the dominant Gamow-Teller component of the nuclear matrix element (NME) for 136 Xe neutrinoless double beta ( 0νββ ) decay. We demonstrate for the first time an evaluation of part of a 0νββ decay NME by use of an experimental observable, presenting a new avenue of approach for more accurate calculations of 0νββ decay matrix elements.

The beta decay of tritium in the form of molecular TT is the basis of sensitive experiments to measure neutrino mass. The final-state electronic, vibrational, and rotational excitations modify the beta spectrum significantly, and are obtained from theory. We report measurements of the branching ratios to specific ionization states for the isotopolog HT. Two earlier, concordant measurements gave branching ratios of HT to the bound HHe + ion of 89.5% and 93.2%, in sharp disagreement with the theoretical prediction of 55-57%, raising concerns about the theory's reliability in neutrino mass experiments. Our result, 56.5(6)%, is compatible with the theoretical expectation and disagrees strongly with the previous measurements.

We report here the results of a study of the β decay of the proton-rich Ge isotopes, 60 Ge and 62 Ge, produced in an experiment at the RIKEN Nishina Center. We have improved our knowledge of the half-lives of 62 Ge (73.5(1) ms), 60 Ge (25.0(3) ms) and its daughter nucleus, 60 Ga (69.4(2) ms). We measured individual β -delayed proton and γ emissions and their related branching ratios. Decay schemes and absolute Fermi and Gamow-Teller transition strengths have been determined. The mass excesses of the nuclei under study have been deduced. A total β -delayed proton-emission branching ratio of 67(3)% has been obtained for 60 Ge. New information has been obtained on the energy levels populated in 60 Ga and on the 1/2 − excited state in the βp daughter 59 Zn. We extracted a ground state to ground state feeding of 85.3(3)% for the decay of 62 Ge. Eight new γ lines have been added to the de-excitation of levels populated in the 62 Ga daughter.