Systematic investigation of projectile fragmentation using beams of unstable B and C isotopes

Background: Models describing nuclear fragmentation and fragmentation fission deliver important input for planning nuclear physics experiments and future radioactive ion beam facilities. These models are usually benchmarked against data from stable beam experiments. In the future, two-step fragmentation reactions with exotic nuclei as stepping stones are a promising tool for reaching the most neutron-rich nuclei, creating a need for models to describe also these reactions. Purpose: We want to extend the presently available data on fragmentation reactions towards the light exotic region on the nuclear chart. Furthermore, we want to improve the understanding of projectile fragmentation especially for unstable isotopes. Method: We have measured projectile fragments from (10,12-18C) and B10-15 isotopes colliding with a carbon target. These measurements were all performed within one experiment, which gives rise to a very consistent data set. We compare our data to model calculations. Results: One-proton removal cross sections with different final neutron numbers (1 pxn) for relativistic C-10,C-12-18 and B10-15 isotopes impinging on a carbon target. Comparing model calculations to the data, we find that the EPAX code is not able to describe the data satisfactorily. Using ABRABLA07 on the other hand, we find that the average excitation energy per abraded nucleon needs to be decreased from 27 MeV to 8.1 MeV. With that decrease ABRABLA07 describes the data surprisingly well. Conclusions: Extending the available data towards light unstable nuclei with a consistent set of new data has allowed a systematic investigation of the role of the excitation energy induced in projectile fragmentation. Most striking is the apparent mass dependence of the average excitation energy per abraded nucleon. Nevertheless, this parameter, which has been related to final-state interactions, requires further study.

Measurement of the muon neutrino inclusive charged-current cross section in the energy range of 1–3 GeV with the T2K INGRID detector

We report a measurement of the νµ-nucleus inclusive charged current cross section (=σ cc) on ironusing data from exposed to the J-PARC neutrino beam. The detector consists of 14 modules in total, which are spread over a range of off-axis angles from 0◦ to 1.1◦. The variation in the neutrino energy spectrum as a function of the off-axis angle, combined with event topology information, is used to calculate this cross section as a function of neutrino energy. The cross section is measured to be σcc(1.1 GeV) = 1.10±0.15 (10^−38cm^2/nucleon), σcc(2.0 GeV) = 2.07±0.27 (10^−38cm^2/nucleon), and σcc(3.3 GeV) = 2.29 ± 0.45 (10^−38cm^2/nucleon), at energies of 1.1, 2.0, and 3.3 GeV, respectively. These results are consistent with the cross section calculated by the neutrino interaction generators currently used by T2K. More importantly, the method described here opens up a new way to determine the energy dependence of neutrino-nucleus cross sections.

(p,p) and (n,p) data listing : 0-750 MeV /

"UCRL-50426."

Effects of nuclear ground state correlations on pion scattering /

"LA-UR-76-1844."

Measurement of single spin asymmetry and fifth structure function for the p( e&ar; ,e'K +)Λ reaction with CEBAF Large Acceptance Spectrometer (CLAS)

The single spin asymmetry, ALT ′, and the polarized structure function, σ LT′, for the p( e&ar; , e′K +)Λ reaction in the resonance region have been measured and extracted using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. Data were taken at an electron beam energy of 2.567 GeV. The large acceptance of CLAS allows for full azimuthal angle coverage over a large range of center-of-mass scattering angles. Results were obtained that span a range in Q 2 from 0.5 to 1.3 GeV2 and W from threshold up to 2.1 GeV and were compared to existing theoretical calculations. The polarized structure function is sensitive to the interferences between various resonant amplitudes, as well as to resonant and non-resonant amplitudes. This measurement is essential for understanding the structure of nucleons and searching for previously undetected nucleon excited states (resonances) predicted by quark models. The W dependence of the σ LT′ in the kinematic regions dominated by s and u channel exchange (cos qcmk = −0.50, −0.167, 0.167) indicated possible resonance structures not predicted by theoretical calculations. The σLT ′ behavior around W = 1.875 GeV could be the signature of a resonance predicted by the quark models and possibly seen in photoproduction. In the very forward angles where the reaction is dominated by the t-channel, the average σLT ′ was zero. There was no indication of the interference between resonances or resonant and non-resonant amplitudes. This might be indicating the dominance of a single t-channel exchange. Study of the sensitivity of the fifth structure function data to the resonance around 1900 MeV showed that these data were highly sensitive to the various assumptions of the models for the quantum number of this resonance. This project was part of a larger CLAS program to measure cross sections and polarization observables for kaon electroproduction in the nucleon resonance region. ^

Coherent rho meson electroproduction off deuteron

QCD predicts Color Transparency (CT), which refers to nuclear medium becoming transparent to a small color neutral object produced in high momentum transfer reactions, due to reduced strong interaction. Despite several studies at BNL, SLAC, FNAL, DESY and Jefferson Lab, a definitive signal for CT still remains elusive. In this dissertation, we present the results of a new study at Jefferson Lab motivated by theoretical calculations that suggest fully exclusive measurement of coherent rho meson electroproduction off the deuteron is a favorable channel for studying CT. Vector meson production has a large cross section at high energies, and the deuteron is the best understood and simplest nuclear system. Exclusivity allows the production and propagation to be controlled separately by controlling Q 2, lf (formation length), lc (coherence length) and t. This control is important as the rapid expansion of small objects increases their interaction probability and masks CT. The CT signal is investigated in a ratio of cross sections at high t (where re-scattering is significant) to low t (where single nucleon reactions dominate). The results are presented over a Q2 range of 1 to 3 GeV2 based on the data taken with beam energy of 6 GeV.

Spectroscopy of Electroproduced Light to Medium Mass Lambda Hypernuclei

The E01-011 experiment at Jefferson Laboratory (JLab) studied light-to-medium mass Λ hypernuclei via the AZ + e → [special characters omitted] + e' + K+ electroproduction reaction. Precise measurement of hypernuclear ground state masses and excitation energies provides information about the nature of hyperon-nucleon interactions. Until recently, hypernuclei were studied at accelerator facilities with intense π+ and K- meson beams. The poor quality of these beams limited the resolution of the hypernuclear excitation energy spectra to about 1.5 MeV (FWHM). This resolution is not sufficient for resolving the rich structure observed in the excitation spectra. By using a high quality electron beam and employing a new high resolution spectrometer system, this study aims to improve the resolution to a few hundred keV with an absolute precision of about 100 keV for excitation energies. In this work the high-resolution excitation spectra of [special characters omitted], and [special characters omitted] hypernuclei are presented. In an attempt to emphasize the presence of the core-excited states we introduced a novel likelihood approach to particle identification (PID) to serve as an alternative to the commonly used standard hard-cut PID. The new method resulted in almost identical missing mass spectra as obtained by the standard approach. An energy resolution of approximately 400–500 keV (FWHM) has been achieved, an unprecedented value in hypernuclear reaction spectroscopy. For [special characters omitted] the core-excited configuration has been clearly observed with significant statistics. The embedded Λ hyperon increases the excitation energies of the 11B nuclear core by 0.5–1 MeV. The [special characters omitted] spectrum has been observed with significant statistics for the first time. The ground state is bound deeper by roughly 400 keV than currently predicted by theory. Indication for the core-excited doublet, which is unbound in the core itself, is observed. The measurement of [special characters omitted] provides the first study of a d-shell hypernucleus with sub-MeV resolution. Discrepancies of up to 2 MeV between measured and theoretically predicted binding energies are found. Similar disagreement exists when comparing to the [special characters omitted] mirror hypernucleus. Also the core-excited structure observed between the major s-, p- and d-shell Λ orbits is not consistent with the available theoretical calculations. In conclusion, the discrepancies found in this study will provide valuable input for the further development of theoretical models.

QCD structure of nuclear interactions

The research presented in this dissertation investigated selected processes involving baryons and nuclei in hard scattering reactions. These processes are characterized by the production of particles with large energies and transverse momenta. Through these processes, this work explored both, the constituent (quark) structure of baryons (specifically nucleons and Δ-Isobars), and the mechanisms through which the interactions between these constituents ultimately control the selected reactions. The first of such reactions is the hard nucleon-nucleon elastic scattering, which was studied here considering the quark exchange between the nucleons to be the dominant mechanism of interaction in the constituent picture. In particular, it was found that an angular asymmetry exhibited by proton-neutron elastic scattering data is explained within this framework if a quark-diquark picture dominates the nucleon’s structure instead of a more traditional SU(6) three quarks picture. The latter yields an asymmetry around 90o center of mass scattering with a sign opposite to what is experimentally observed. The second process is the hard breakup by a photon of a nucleon-nucleon system in light nuclei. Proton-proton (pp) and proton-neutron (pn) breakup in 3He, and ΔΔ-isobars production in deuteron breakup were analyzed in the hard rescattering model (HRM), which in conjunction with the quark interchange mechanism provides a Quantum Chromodynamics (QCD) description of the reaction. Through the HRM, cross sections for both channels in 3He photodisintegration were computed without the need of a fitting parameter. The results presented here for pp breakup show excellent agreement with recent experimental data. In ΔΔ-isobars production in deuteron breakup, HRM angular distributions for the two ΔΔ channels were compared to the pn channel and to each other. An important prediction fromthis study is that the Δ++Δ- channel consistently dominates Δ+Δ0, which is in contrast with models that unlike the HRM consider a ΔΔ system in the initial state of the interaction. For such models both channels should have the same strength. These results are important in developing a QCD description of the atomic nucleus.

A precise measurement of the two -photon exchange effect

The two-photon exchange phenomenon is believed to be responsible for the discrepancy observed between the ratio of proton electric and magnetic form factors, measured by the Rosenbluth and polarization transfer methods. This disagreement is about a factor of three at Q 2 of 5.6 GeV2. The precise knowledge of the proton form factors is of critical importance in understanding the structure of this nucleon. The theoretical models that estimate the size of the two-photon exchange (TPE) radiative correction are poorly constrained. This factor was found to be directly measurable by taking the ratio of the electron-proton and positron-proton elastic scattering cross sections, as the TPE effect changes sign with respect to the charge of the incident particle. A test run of a modified beamline has been conducted with the CEBAF Large Acceptance Spectrometer (CLAS) at Thomas Jefferson National Accelerator Facility. This test run demonstrated the feasibility of producing a mixed electron/positron beam of good quality. Extensive simulations performed prior to the run were used to reduce the background rate that limits the production luminosity. A 3.3 GeV primary electron beam was used that resulted in an average secondary lepton beam of 1 GeV. As a result, the elastic scattering data of both lepton types were obtained at scattering angles up to 40 degrees for Q2 up to 1.5 GeV2. The cross section ratio displayed an &epsis; dependence that was Q2 dependent at smaller Q2 limits. The magnitude of the average ratio as a function of &epsis; was consistent with the previous measurements, and the elastic (Blunden) model to within the experimental uncertainties. Ultimately, higher luminosity is needed to extend the data range to lower &epsis; where the TPE effect is predicted to be largest.

Proton Form Factor Puzzle and the CEBAF Large Acceptance Spectrometer (CLAS) two-photon exchange experiment

The electromagnetic form factors are the most fundamental observables that encode information about the internal structure of the nucleon. The electric (GE) and the magnetic ( GM) form factors contain information about the spatial distribution of the charge and magnetization inside the nucleon. A significant discrepancy exists between the Rosenbluth and the polarization transfer measurements of the electromagnetic form factors of the proton. One possible explanation for the discrepancy is the contributions of two-photon exchange (TPE) effects. Theoretical calculations estimating the magnitude of the TPE effect are highly model dependent, and limited experimental evidence for such effects exists. Experimentally, the TPE effect can be measured by comparing the ratio of positron-proton elastic scattering cross section to that of the electron-proton [R = σ(e +p)/σ(e+p)]. The ratio R was measured over a wide range of kinematics, utilizing a 5.6 GeV primary electron beam produced by the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab. This dissertation explored dependence of R on kinematic variables such as squared four-momentum transfer (Q2) and the virtual photon polarization parameter (&epsis;). A mixed electron-positron beam was produced from the primary electron beam in experimental Hall B. The mixed beam was scattered from a liquid hydrogen (LH2) target. Both the scattered lepton and the recoil proton were detected by the CEBAF Large Acceptance Spectrometer (CLAS). The elastic events were then identified by using elastic scattering kinematics. This work extracted the Q2 dependence of R at high &epsis;(&epsis; > 0.8) and the $&epsis; dependence of R at ⟨Q 2⟩ approx 0.85 GeV2. In these kinematics, our data confirm the validity of the hadronic calculations of the TPE effect by Blunden, Melnitchouk, and Tjon. This hadronic TPE effect, with additional corrections contributed by higher excitations of the intermediate state nucleon, largely reconciles the Rosenbluth and the polarization transfer measurements of the electromagnetic form factors.

Experimental deuteron momentum distributions with reduced final state interactions

This dissertation presents a study of the D( e, e′p)n reaction carried out at the Thomas Jefferson National Accelerator Facility (Jefferson Lab) for a set of fixed values of four-momentum transfer Q 2 = 2.1 and 0.8 (GeV/c)2 and for missing momenta pm ranging from pm = 0.03 to pm = 0.65 GeV/c. The analysis resulted in the determination of absolute D(e,e′ p)n cross sections as a function of the recoiling neutron momentum and it's scattering angle with respect to the momentum transfer [vector] q. The angular distribution was compared to various modern theoretical predictions that also included final state interactions. The data confirmed the theoretical prediction of a strong anisotropy of final state interaction contributions at Q2 of 2.1 (GeV/c)2 while at the lower Q2 value, the anisotropy was much less pronounced. At Q2 of 0.8 (GeV/c)2, theories show a large disagreement with the experimental results. The experimental momentum distribution of the bound proton inside the deuteron has been determined for the first time at a set of fixed neutron recoil angles. The momentum distribution is directly related to the ground state wave function of the deuteron in momentum space. The high momentum part of this wave function plays a crucial role in understanding the short-range part of the nucleon-nucleon force. At Q2 = 2.1 (GeV/c)2, the momentum distribution determined at small neutron recoil angles is much less affected by FSI compared to a recoil angle of 75°. In contrast, at Q2 = 0.8 (GeV/c)2 there seems to be no region with reduced FSI for larger missing momenta. Besides the statistical errors, systematic errors of about 5–6 % were included in the final results in order to account for normalization uncertainties and uncertainties in the determi- nation of kinematic veriables. The measurements were carried out using an electron beam energy of 2.8 and 4.7 GeV with beam currents between 10 to 100 &mgr; A. The scattered electrons and the ejected protons originated from a 15cm long liquid deuterium target, and were detected in conicidence with the two high resolution spectrometers of Hall A at Jefferson Lab.^

A Measurement of the Proton Structure Function g2p at Low Q2

Experiments at Jefferson Lab have been conducted to extract the nucleon spin-dependent structure functions over a wide kinematic range. Higher moments of these quantities provide tests of QCD sum rules and predictions of chiral perturbation theory ($\chi$PT). While precise measurements of $g_{1}^n$, $g_{2}^n$, and $g_1^p$ have been extensively performed, the data of $g_2^p$ remain scarce. Discrepancies were found between existing data related to $g_2$ and theoretical predictions. Results on the proton at large $Q^2$ show a significant deviation from the Burkhardt-Cottingham sum rule, while results for the neutron generally follow this sum rule. The next-to-leading order $\chi$PT calculations exhibit discrepancy with data on the longitudinal-transverse polarizability $\delta_{LT}^n$. Further measurements of the proton spin structure function $g_2^p$ are desired to understand these discrepancies.

Experiment E08-027 (g2p) was conducted at Jefferson Lab in experimental Hall A in 2012. Inclusive measurements were performed with polarized electron beam and a polarized ammonia target to obtain the proton spin-dependent structure function $g_2^p$ at low Q$^2$ region (0.02$<$Q$^2$$<$0.2 GeV$^2$) for the first time. The results can be used to test the Burkhardt-Cottingham sum rule, and also allow us to extract the longitudinal-transverse spin polarizability of the proton, which will provide a benchmark test of $\chi$PT calculations. This thesis will present and discuss the very preliminary results of the transverse asymmetry and the spin-dependent structure functions $g_1^p$ and $g_2^p$ from the data analysis of the g2p experiment .

van der Waals coefficients for positronium interactions with atoms

The random-phase approximation with exchange (RPAE) is used with a B-spline basis to compute dynamic dipole polarizabilities of noble-gas atoms and several other closed-shell atoms (Be, Mg, Ca, Zn, Sr, Cd, and Ba). From these, values of the van der Waals C₆ constants for positronium interactions with these atoms are determined and compared with existing data. After correcting the RPAE polarizabilities to fit the most accurate static polarizability data, our best predictions of C₆ for Ps–noble-gas pairs are expected to be accurate to within 1%, and to within a few percent for the alkaline-earth metals. We also used accurate dynamic dipole polarizabilities from the literature to compute the C₆ coefficients for the alkali-metal atoms. Implications of increased C₆ values for Ps scattering from more polarizable atoms are discussed.

The role of nuclear physics in supernovae and the evolution of neutron stars, Neutrino Opacities, Equation of State, Transport Coefficients, and Dark Matter Production

Thesis (Ph.D.)--University of Washington, 2016-08

Outer crust of a cold non-accreting magnetar

The outer-crust structure and composition of a cold, non-accreting magnetar are studied. We model the outer crust to be made of fully equilibrated matter where ionized nuclei form a Coulomb crystal embedded in an electron gas. The main effects of the strong magnetic field are those of quantizing the electron motion in Landau levels and of modifying the nuclear single-particle levels producing, on average, an increased binding of nucleons in nuclei present in the Coulomb lattice. The effect of a homogeneous and constant magnetic field on nuclear masses has been predicted by using a covariant density functional in which induced currents and axial deformation due to the presence of a magnetic field that breaks time-reversal symmetry have been included self-consistently in the nucleon and meson equations of motion. Although not yet observed, for Ba 1016 G both effects contribute to produce different compositions - odd-mass nuclei are frequently predicted - and to increase the neutron-drip pressure as compared to a typical neutron star. Specifically, in such a regime, the magnetic-field effects on nuclei favor the appearance of heavier nuclei at low pressures. As B increases, such heavier nuclei are also preferred up to larger pressures. For the most extreme magnetic field considered, B=1018 G, and for the models studied, almost the whole outer crust is made of 4092Zr52.