120412772
Renormalization-group approach to the lattice massive Schwinger model
Using Migdal-type recursion relations, the long-distance Coulomb force is found to be screened in the massive Schwinger model on a lattice. (AIP)
115620347
The Schwinger mechanisms in non-abelian gauge theories
Abstract An alternative to the Higgs-Kibble mechanism for the formulation of spontaneously broken gauge theories has been recently proposed. It is shown how the new procedures can be generalised to the case when non-Abelian gauge groups are present.
120645598
Spectroscopy of Nb 90 at high spin
Excited states of {sup 90}Nb were investigated via prompt and delayed {gamma} decays and the recoil-isomer tagging technique. The level scheme of {sup 90}Nb has been extended up to J=19({Dirac_h}/2{pi}) and E{sub x}=8.4 MeV. Half-lives of the 11{sup -} and 17/2{sup -} isomeric levels in {sup 90,91}Nb were measured to be 0.47{+-}0.01 and 3.3{+-}0.4 {mu}s, respectively. The results are compared with the predictions of large-basis shell model calculations. The effects of truncation of the valence model space on the calculated results are discussed.
118268033
Astrophysical implication of low E(21+) in neutron‐rich Sn isotopes
The observation and prediction of unusually depressed first excited 21+ states in even‐A neutron—rich isotopes of semi‐magic Sn above 132Sn provide motivations for reviewing the problems related to the nuclear astrophysics in general. In the present work, the β‐decay rates of the exotic even Sn isotopes (134,136Sn) above the 132Sn core have been calculated as a function of temperature (T). In order to get the necessary ft values, B(GT) values corresponding to allowed Gamow Teller (GT—) β‐decay have been theoretically calculated using shell model. The total decay rate shows decrease with increasing temperature as the ground state population is depleted and population of excited states with slower decay rates increases. The abundance at each Z value is inversely proportional to the decay constant of the waiting point nucleus for that particular Z. So the increase in half‐life of isotopes of Sn, like 136Sn, might have substantial impact on the r‐process nucleosynthesis.
53492385
Mechanical prototype of tracking chamber in station 2 in dimuon spectrometer of ALICE
To explore the physics of ultra-relativistic heavy-ion collision, a large ion collider experiment (ALICE) [1] is proposed to carry out at large hadron collider (LHC). Forward muon spectrometer (FMS) [2] is included in ALICE to look for the signals of quark gluon plasma (QGP) using dileptonic decay of heavy quarkonia (J=ψ , γ) produced in the collision as a probe. The production of these states will be suppressed in a deconfined medium of QGP which can be estimated from the invariant mass spectrum of dimuonic decay channel. The spectrometer is designed to track down the flight path of the dimuons with the help of five tracking stations from which the opening angle of the pair can be known by reconstruction and extrapolation of their tracks. The momenta of the pairs can be obtained from the deviation of the tracks in a dipole magnetic field. The invariant mass of the pair can be determined from the opening angle and momenta of dimuon pairs. Each of the five tracking stations is equipped with two planes of cathode pad chamber each divided into four quadrants to detect the position of the dimuon passing through them and reconstruct their tracks from their positions. The tracking chambers are designed following the basic feature of a position sensitive multi-wire proportional counter (MWPC) where an anode wire plane is interposed between two cathode planes and a high electric field is maintained near the anode with respect to the cathodes. The chambers are capable of providing X, Y position readout of an event from the charge distribution induced over the cathode planes equipped with pad matrices due to the avalanche produced in the gaseous medium. However, the mechanical design of the large chamber (diameter 2 m) for the second tracking station is a challenging task as it concerns good surface planarity to achieve position resolution better than 100 μm (necessary to meet mass resolution about 100 MeV) as well as minimum usage of material to keep radiation length low (2–3% of X0) in order to minimise the energy loss and scattering of the incident lepton. The calculation was carried out at IPN, Orsay to simulate a full scale quadrant with different design parameters and materials to study its mechanical characteristics [3,4]. In the simulation, various options in material and design aspects were studied to seek an optimum design for the chamber to enhance its mechanical
119169856
New shell closure for neutron-rich Sn isotopes
The evolution of shell structure away from stability [1]has been a topic of intense theoretical [2, 3] and experi-mental [4–6] studies since last decade. Theoretical stud-ies have identiﬁed diﬀerent reasons for the phenomenonof shell evolution with neutron or proton excess. Amongthe various components of the nucleon - nucleon interac-tion, the spin-orbit, tensor part and three - body eﬀectplay important roles in the shell evolutions [1]. Due totensor interactions, nuclear mean ﬁeld undergoes varia-tions with neutron excess. This leads to monopole mi-gration [2]. It is observed for both proton-rich as well asneutron-rich nuclei. While approaching the neutron dripline, the neutron density becomes very diﬀused [3] whichcan also lead to shell quenching. For exotic light nucleithe well established magic numbers for the stable nu-clei are found to be modiﬁed or new magic numbers haveevolved. At least four doubly magic oxygen isotopes havebeen observed [6–8]. They are
201072483
Corrections to the Bekenstein-Hawking entropy in the brick wall approach
The brick wall model is a semi-classical approach to underst and he microscopic origin of black hole entropy. In this approach, the entropy of the black hole arises due to the canonical entropy of matter fields outside the black hole event horizon, evaluate d the Hawking temperature. Usually, in the brick wall model, the density of states and the resulti ng canonical entropy of the matter fields are calculated at the leading order (in terms of h̄) in the WKB approximation. We extend this approach and compute the brick wall entropy of a quantum scalar field around static and spherically symmetric black holes at the higher orders in th e WKB approximation. We find that the brick wall model generally predicts corrections to the B kenstein-Hawking entropy in all spacetime dimensions. We compare our results with the sub-l eading contributions to the black hole entropy that has been obtained from various other appro ches.