Orbifold projection in supersymmetric QCD at N_f\leq N_c

Supersymmetric orbifold projection of N=1 SQCD with relatively small number of flavors (not larger than the number of colors) is considered. The purpose is to check whether orbifolding commutes with the infrared limit. On the one hand, one considers the orbifold projection of SQCD and obtains the low-energy description of the resulting theory. On the other hand, one starts with the low-energy effective theory of the original SQCD, and only then perfoms orbifolding. It is shown that at finite N_c the two low-energy theories obtained in these ways are different. However, in the case of stabilized run-away vacuum these two theories are shown to coincide in the large N_c limit. In the case of quantum modified moduli space, topological solitons carrying baryonic charges are present in the orbifolded low-energy theory. These solitons may restore the correspondence between the two theories provided that the soliton mass tends to zero in the large N_c limit.Comment: 10 pages; misprint corrected, reference adde

γ spectroscopy of states in Cl 32 relevant for the S 31 (p,γ) Cl 32 reaction rate

Background: The S31(p,γ)Cl32 reaction becomes important for sulfur production in novae if the P31(p,α)Si28 reaction rate is somewhat greater than currently accepted. The rate of the S31(p,γ)Cl32 reaction is uncertain, primarily due to the properties of resonances at Ec.m.=156 and 549 keV. Purpose: We precisely determined the excitation energies of states in Cl32 through high-resolution γ spectroscopy including the two states most important for the S31(p,γ)Cl32 reaction at nova temperatures. Method: Excited states in Cl32 were populated using the B10(Mg24,2n)Cl32 reaction with a Mg24 beam from the ATLAS facility at Argonne National Laboratory. The reaction channel of interest was selected using recoils in the Fragment Mass Analyzer, and precise level energies were determined by detecting γ rays with Gammasphere. Results: We observed γ rays from the decay of six excited states in Cl32. The excitation energies for two unbound levels at Ex=1738.1 (6) keV and 2130.5 (10) keV were determined and found to be in agreement with a previous high-precision measurement of the S32(He3,t)Cl32 reaction [1]. Conclusions: An updated S31(p,γ)Cl32 reaction rate is presented. With the excitation energies of important levels firmly established, the dominant uncertainty in the reaction rate at nova temperatures is due to the strength of the resonance corresponding to the 2131-keV state in Cl32

Cross-shell excitations in Si 31

The Si31 nucleus was produced through the O18(O18, αn) fusion-evaporation reaction at Elab=24MeV. Evaporated α particles from the reaction were detected and identified in the Microball detector array for channel selection. Multiple γ-ray coincidence events were detected in Gammasphere. The energy and angle information for the α particles was used to determine the Si31 recoil kinematics on an event-by-event basis for a more accurate Doppler correction. A total of 22 new states and 52 new γ transitions were observed, including 14 from states above the neutron separation energy. The positive-parity states predicted by the shell-model calculations in the sd model space agree well with experiment. The negative-parity states were compared with shell-model calculations in the psdpf model space with some variations in the N=20 shell gap. The best agreement was found with a shell gap intermediate between that originally used for A≈20 nuclei and that previously adapted for P32,34. This variation suggests the need for a more universal cross-shell interaction

Design of SECAR a recoil mass separator for astrophysical capture reactions with radioactive beams

A recoil mass separator SECAR has been designed for the purpose of studying low-energy (p,γ) and (α,γ) reactions in inverse kinematics with radioactive beams for masses up to about A = 65. Their reaction rates are of importance for our understanding of the energy production and nucleosynthesis during explosive hydrogen and helium burning. The radiative capture reactions take place in a windowless hydrogen or He gas target at the entrance of the separator, which consists of four Sections. The first Section selects the charge state of the recoils. The second and third Sections contain Wien Filters providing high mass resolving power to separate efficiently the intense beam from the few reaction products. In the following fourth Section, the reaction products are guided into a detector system capable of position, angle and time-of-flight measurements. In order to accept the complete kinematic cone of recoil particles including multiple scattering in the target in the center of mass energy range of 0.2 MeV to 3.0 MeV, the system must have a large polar angle acceptance of ± 25 mrad. This requires a careful minimization of higher order aberrations. The present system will be installed at the NSCL ReA3 accelerator and will be used with the much higher beam intensities of the FRIB facility when it becomes available

Probing the role of proton cross-shell excitations in Ni 70 using nucleon knockout reactions

The neutron-rich Ni isotopes have attracted attention in recent years because of the occurrence of shape or configuration coexistence. We report on the difference in population of excited final states in Ni70 following γ-ray tagged one-proton, one-neutron, and two-proton knockout from Cu71, Ni71, and Zn72 rare-isotope beams, respectively. Using variations observed in the relative transition intensities, signaling the changed population of specific final states in the different reactions, the role of neutron and proton configurations in excited states of Ni70 is probed schematically, with the goal of identifying those that carry, as leading configuration, proton excitations across the Z=28 shell closure. Such states are suggested in the literature to form a collective structure associated with prolate deformation. Adding to the body of knowledge for Ni70, 29 new transitions are reported, of which 15 are placed in its level scheme

Study of the fusion reaction \u3csup\u3e12\u3c/sup\u3eC + \u3csup\u3e12\u3c/sup\u3eC at low beam energy

In this article we discuss two aspects related to the 12C + 12C fusion reaction at low energies for carbon burning in supermassive stars. First we present plausible arguments for the notion that the observed resonance structures at the lowest measured energies arise from the relatively large spacing and narrow width of 24Mg compound levels at the corresponding excitation energy region. We thus point out that the Incoming Wave Boundary Condition is inappropriate for calculating the fusion cross section under these situations. Secondly, we report on a particle-γ coincidence technique that has been used for the first time to measure the fusion cross section in the system 12C + 12C at low beam energies. Based on these results, it should be possible to measure this important fusion cross section down to the 10 pb level within a reasonable length of time

Search for Nova Presolar Grains: γ -Ray Spectroscopy of Ar 34 and its Relevance for the Astrophysical Cl 33 (p,γ) Reaction

The discovery of presolar grains in primitive meteorites has initiated a new era of research in the study of stellar nucleosynthesis. However, the accurate classification of presolar grains as being of specific stellar origins is particularly challenging. Recently, it has been suggested that sulfur isotopic abundances may hold the key to definitively identifying presolar grains with being of nova origins and, in this regard, the astrophysical Cl33(p,γ)Ar34 reaction is expected to play a decisive role. As such, we have performed a detailed γ-ray spectroscopy study of Ar34. Excitation energies have been measured with high precision and spin-parity assignments for resonant states, located above the proton threshold in Ar34, have been made for the first time. Uncertainties in the Cl33(p,γ) reaction have been dramatically reduced and the results indicate that a newly identified ℓ =0 resonance at Er=396.9(13) keV dominates the entire rate for T=0.25-0.40 GK. Furthermore, nova hydrodynamic simulations based on the present work indicate an ejected S32/S33 abundance ratio distinctive from type-II supernovae and potentially compatible with recent measurements of a presolar grain

Level structure of the Tz=-1 nucleus Ar 34 and its relevance for nucleosynthesis in ONe novae

The Mg24+C12 fusion reaction was used to perform a detailed γ-ray spectroscopy study of the astrophysically important nucleus Ar34. In particular, an experimental setup, coupling the advanced γ-ray tracking array GRETINA with the well-established Argonne fragment mass analyzer (FMA), was employed to obtain excitation energies and spin-parity assignments for excited states in Ar34, both above and below the proton separation energy. For the first time, an angular distribution analysis of in-beam γ rays from fusion-evaporation reactions, using a tracking array, has been performed and Coulomb energy differences of analog states in the T=1, A=34 mirror system, explored from 0 to 6 MeV. Furthermore, we present a comprehensive discussion of the astrophysical Cl33(p,γ) stellar reaction rate, together with implications for the identification of nova presolar grains from sulfur isotopic abundances