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XENON100 Collaboration(Aprile, E. et al), & Orrigo, S. E. A. (2014). First axion results from the XENON100 experiment. Phys. Rev. D, 90(6), 062009–7pp.
Abstract: We present the first results of searches for axions and axionlike particles with the XENON100 experiment. The axion-electron coupling constant, g(Ae), has been probed by exploiting the axioelectric effect in liquid xenon. A profile likelihood analysis of 224.6 live days x 34-kg exposure has shown no evidence for a signal. By rejecting g(Ae) larger than 7.7 x 10(-12) (90% C. L.) in the solar axion search, we set the best limit to date on this coupling. In the frame of the DFSZ and KSVZ models, we exclude QCD axions heavier than 0.3 and 80 eV/c(2), respectively. For axionlike particles, under the assumption that they constitute the whole abundance of dark matter in our galaxy, we constrain gAe to be lower than 1 x 10(-12) (90% C.L.) for masses between 5 and 10 keV/c(2).
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XENON Collaboration(Aprile, E. et al), & Orrigo, S. E. A. (2014). Conceptual design and simulation of a water Cherenkov muon veto for the XENON1T experiment. J. Instrum., 9, P11006–20pp.
Abstract: XENON is a dark matter direct detection project, consisting of a time projection chamber (TPC) filled with liquid xenon as detection medium. The construction of the next generation detector, XENON1T, is presently taking place at the Laboratori Nazionali del Gran Sasso (LNGS) in Italy. It aims at a sensitivity to spin-independent cross sections of 2.10(47) cm(2) for WIMP masses around 50 GeV/c(2), which requires a background reduction by two orders of magnitude compared to XENON100, the current generation detector. An active system that is able to tag muons and muon-induced backgrounds is critical for this goal. A water Cherenkov detector of similar to 10m height and diameter has been therefore developed, equipped with 8 inch photomultipliers and cladded by a reflective foil. We present the design and optimization study for this detector, which has been carried out with a series of Monte Carlo simulations. The muon veto will reach very high detection efficiencies for muons (> 99.5%) and showers of secondary particles from muon interactions in the rock (> 70%). Similar efficiencies will be obtained for XENONnT, the upgrade of XENON1T, which will later improve the WIMP sensitivity by another order of magnitude. With the Cherenkov water shield studied here, the background from muon-induced neutrons in XENON1T is negligible.
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Wendt, A. et al, & Algora, A. (2014). Isospin symmetry in the sd shell: Transition strengths in the neutron-deficient sd shell nucleus Ar-33. Phys. Rev. C, 90(5), 054301–7pp.
Abstract: Reduced transition strengths of the deexciting transitions from the first two excited states in Ar-33 were measured in a relativistic Coulomb excitation experiment at the GSI Helmholtz center. The radioactive ion beam was produced by fragmentation of a primary Ar-36 beam on a Be-9 target followed by the selection of the reaction product of interest via the GSI Fragment Separator. The (33A)r beam hit a secondary Au-197 target with an energy of approximately 145 MeV/nucleon. An array of high-purity germanium cluster detectors and large-volume BaF2 scintillator detectors were employed for gamma-ray spectroscopy at the secondary target position. The Lund-York-Cologne Calorimeter was used to track the outgoing ions and to identify the nuclear reaction channels. For the two lowest energy excited states of Ar-33 the reduced transition strengths have been determined. With these first results the T-z = -3/2 nucleus Ar-33 is now, together with Na-21 (T-z = -1/2), the only neutron-deficient odd-A sd shell nucleus in which experimental transition strengths are available. The experimental values are compared to results of shell-model calculations which describe simultaneously mirror-energy differences and transition-strength values of mirror pairs in the sd shell in a consistent way.
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Watanabe, H. et al, & Montaner-Piza, A. (2014). Monopole-Driven Shell Evolution below the Doubly Magic Nucleus Sn-132 Explored with the Long-Lived Isomer in Pd-126. Phys. Rev. Lett., 113(4), 042502–6pp.
Abstract: A new isomer with a half-life of 23.0(8) ms has been identified at 2406 keV in Pd-126 and is proposed to have a spin and parity of 10(+) with a maximally aligned configuration comprising two neutron holes in the 1h(11/2) orbit. In addition to an internal-decay branch through a hindered electric octupole transition, beta decay from the long-lived isomer was observed to populate excited states at high spins in Ag-126. The smaller energy difference between the 10(+) and 7(-) isomers in Pd-126 than in the heavier N = 80 isotones can be interpreted as being ascribed to the monopole shift of the 1h(11/2) neutron orbit. The effects of the monopole interaction on the evolution of single-neutron energies below Sn-132 are discussed in terms of the central and tensor forces.
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Wang, E., Xie, J. J., & Nieves, J. (2014). Regge signatures from forward CLAS Lambda(1520) photoproduction data. Phys. Rev. C, 90(6), 065203–10pp.
Abstract: The γp→K+Λ(1520) reaction mechanism is investigated within a Regge--effective Lagrangian hybrid approach based on our previous study of this reaction [Physical Review C89, 015203 (2014)]. Near threshold and for large K+ angles, both the CLAS and LEPS data can be successfully described by considering the contributions from the contact, t-channel K¯ exchange, u-channel Λ(1115) hyperon pole, and the s-channel nucleon pole and N∗(2120) resonance contributions. However, for higher energies and forward K+ angles, systematic discrepancies with data appear, which hint the possible existence of sizable quark-gluon string mechanism effects. We show how the inclusion of a K¯ Regge--trajectory exchange in the t-channel leads to an efficient description of the Λ(1520) photoproduction channel over the whole energy and angular ranges accessible in the CLAS experiment.
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