No abstract

No abstract

Current models of antineutrino production in nuclear reactors predict detection rates and spectra at odds with the existing body of direct reactor antineutrino measurements. High-resolution antineutrino detectors operated close to compact research reactor cores can produce new precision measurements useful in testing explanations for these observed discrepancies involving underlying nuclear or new physics. Absolute measurement of the 235 U-produced antineutrino spectrum can provide additional constraints for evaluating the accuracy of current and future reactor models, while relative measurements of spectral distortion between differing baselines can be used to search for oscillations arising from the existence of eV-scale sterile neutrinos. Such a measurement can be performed in the United States at several highly-enriched uranium fueled research reactors using near-surface segmented liquid scintillator detectors. We describe here the conceptual design and physics potential of the PROSPECT experiment, a U.S.-based, multi-phase experiment with reactor-detector baselines of 7-20 meters capable of addressing these and other physics and detector development goals. Current R&D status and future plans for PROSPECT detector deployment and data-taking at the High Flux Isotope Reactor at Oak Ridge National Laboratory will be discussed.

The narrow widths of highly excited A single-particie states are discussed in comparison with large widths of nucleon deep hole states.Recoilless (K, m ) reactions have produced a A particle in various single-particle orbits and disclosed basic properties of the A single-particle potential. ' Figure 1 shows the experimental data on~Ca. Let us look at the widths of the peaks. The width of the (Od)~orbit [the peaks corresponding to the (d5~2 +d572'") and (dy2 Adg2'") configurations] looks to be 3-4 MeV, while the energy resolution of the m measurement is 2-3 MeV. This indicates that the physical width 1~(Od) is quite narrow. It is noticed that the (Od)õ rbit is in 2h QA = 20 MeV excitation. A good contrast to this is the nucleon deep hole, for example, the (Os)N and (Gp)N holes of Ca have very large widths, I' N(0s) =22 MeV and I' N(Op) = 12 MeV. ' The (Os)N hole state is also in 2tAN excitation of Ca. The situation is schematically shown in Fig. 2. We try to understand how such a big difference arises between the widths of the A particle and nucleon-hole states.Let us consider the second-order contribution to the single-particle (hole) energy Ass (a) (8 = A or N) as shown in Fig. 3. The width I s(a) due to this diagram process is given by -21mAes(a), which is expressed explicitly as and I A(aA) = g g (4MNkp) I I f"~g(&~b~pN&N;LST) I [Ll [Sj[6 2 A &N"W kp /2MN = EA(aA) + EN(AN) 6g(~g) I N(~N) = 2 X X (4MNkp) g I rNN(~N&NPN~NiLST) I [L1 [%[ T1 . z a' &~"N LST a N N (2) (3) k& /2MN = EN(AN) + CN(AN ) CN(&N)where [Lj = 2L + 1, etc. ,~(LST) is the particle-hole coupling interaction matrix elements with orbital angular momentum L, spin S, and isospin T.~NN here is defined as Q(1+5,~)(1+5""i)/4 times the normalized and antisymmetrized matrix element and the factor 2 in front of the right-hand side of Eq. (3) takes account for the exchange term. Equations (2) and (4) are the energy conserving conditions in the intermediate states of Fig. 3,~here the momentum k" is associated with the nucleon particle state p brought up into the continuum. The wave function of p is normalized as sin(k, r + . )/k"r asymptotically.Before going to numerical calculations, we make some qualitative discussions on what can be different between I A of Eq. (1) and I'N of Eq. (3).(a) Difference in the spin-isospin (ST) of excited nucleon particle hole. The A particle with zero isospin excites only isoscalar ( T = 0) pN -hN mode and furthermore, since AN spin-spin interaction is weak, the spin vector (S = 1) pN -AN mode is weakly excited. Thus, if we take only S = T =0 in Eq. (1), we have »o MeV/c, 8=o

No abstract