149 research outputs found
Finite temperature Casimir effect of massive fermionic fields in the presence of compact dimensions
We consider the finite temperature Casimir effect of a massive fermionic
field confined between two parallel plates, with MIT bag boundary conditions on
the plates. The background spacetime is which has
dimensions compactified to a torus. On the compact dimensions, the field is
assumed to satisfy periodicity boundary conditions with arbitrary phases. Both
the high temperature and the low temperature expansions of the Casimir free
energy and the force are derived explicitly. It is found that the Casimir force
acting on the plates is always attractive at any temperature regardless of the
boundary conditions assumed on the compact torus. The asymptotic limits of the
Casimir force in the small plate separation limit are also obtained.Comment: 10 pages, accepted by Phys. Lett.
Quasiparticle excitations in superdeformed Hg192
For the first time, two excited superdeformed (SD) bands have been observed in the double closed shell superdeformed nucleus Hg192. One of the SD bands exhibits a pronounced peak in the dynamic moment of inertia which is interpreted as a crossing between two excited SD configurations involving the N=7 intruder and the [512]5/2 orbitals. This is only the second occurrence of such a crossing in a SD nucleus around A=190. The second excited SD band has near identical transition energies to an excited SD band in Hg191
Proton and neutron excitations in superdeformed Tb150
Two new superdeformed (SD) bands have been observed in Tb150 using the reaction P31+124Sn and the GAMMASPHERE detector array. These new bands are interpreted as being excited SD configurations involving a proton and a neutron particle-hole excitation, respectively. The configurations are discussed in terms of the occupancy of high-N intruder orbitals. These data are used to provide information on (i) the contribution to the dynamic moments of inertia due to the occupation of specific orbitals, (ii) the deformation driving effects of the particle-hole states, and (iii) the consequences of these effects on pairing and band-crossings
Lifetime measurement in excited and yrast superdeformed bands in Hg194
Nuclear level lifetimes have been measured in two superdeformed bands in Hg194 using the Doppler-shift attenuation method. Average transition quadrupole moments derived from the lifetimes of an excited and yrast superdeformed bands are Qt=17.6(30) and 17.2(20)eb, respectively. The Doppler shifts of the excited band relative to the yrast band indicate a slight difference in quadrupole moments [+4(5)%], assuming similar side feeding..ul2 These results imply that the second well is stable and rigid with respect to the particle excitation responsible for this excited band
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in âs = 7 TeV pp collisions with the ATLAS detector
A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fbâ1 of protonâproton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results
Jet size dependence of single jet suppression in lead-lead collisions at sqrt(s(NN)) = 2.76 TeV with the ATLAS detector at the LHC
Measurements of inclusive jet suppression in heavy ion collisions at the LHC
provide direct sensitivity to the physics of jet quenching. In a sample of
lead-lead collisions at sqrt(s) = 2.76 TeV corresponding to an integrated
luminosity of approximately 7 inverse microbarns, ATLAS has measured jets with
a calorimeter over the pseudorapidity interval |eta| < 2.1 and over the
transverse momentum range 38 < pT < 210 GeV. Jets were reconstructed using the
anti-kt algorithm with values for the distance parameter that determines the
nominal jet radius of R = 0.2, 0.3, 0.4 and 0.5. The centrality dependence of
the jet yield is characterized by the jet "central-to-peripheral ratio," Rcp.
Jet production is found to be suppressed by approximately a factor of two in
the 10% most central collisions relative to peripheral collisions. Rcp varies
smoothly with centrality as characterized by the number of participating
nucleons. The observed suppression is only weakly dependent on jet radius and
transverse momentum. These results provide the first direct measurement of
inclusive jet suppression in heavy ion collisions and complement previous
measurements of dijet transverse energy imbalance at the LHC.Comment: 15 pages plus author list (30 pages total), 8 figures, 2 tables,
submitted to Physics Letters B. All figures including auxiliary figures are
available at
http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2011-02
Identification of the unfavored N=7 superdeformed band in Hg191
A new superdeformed band has been identified in Hg191 bringing the total number of bands observed in this nucleus to four. The new band has properties similar to those of a superdeformed band reported recently in Hg193. Both bands are believed to be built on the unfavored signature of the j15/2 intruder configuration. Comparisons between the data and cranked Woods-Saxon calculations highlight the strengths and weaknesses of theory in describing high-N orbitals at large deformation
Test of ÎI = 2 staggering in the superdeformed bands of 194Hg
The presence of ÎI= 2 staggering in the three known superdeformed (SD) bands of 194Hg has been reexamined in a new experiment with Gammasphere. A relative precision of better than 60 eV was achieved for most transition energies. Staggering plots were extracted and their statistical significance was analyzed. No clear evidence was found for an extended regular ÎI = 2 staggering in the three SD bands of 194Hg. However, statistically significant deviations from a smooth reference were observed in the two excited SD bands. Different scenarios are discussed but no firm conclusion about the origin of the observed deviations can be drawn
Structure of superdeformed bands in 195Hg
Four new superdeformed bands have been observed with the Gammasphere array and have been assigned to the 195Hg nucleus. Two of the bands are interpreted as signature partners most likely based on Nosc6 neutron quasiparticles coupled to a superdeformed core, while the other two appear to be based on a j15/2 intruder orbital. These four bands do not exhibit a simple, ``identical bands'' relationship to other superdeformed bands in this mass region
New features of superdeformed bands in Hg194
Two new features of superdeformed (SD) bands in the A190 region emerge from a study of Hg194 with the Gammasphere detector array. A decrease of the dynamic moment of inertia is observed for rotational frequencies Latin small letter h with strokeÏ0.4 MeV, confirming long standing expectations based on mean field calculations with pairing. Evidence for a small staggering in the SD transition energies is also observed, suggesting the presence of terms with fourfold symmetry in the SD Hamiltonian
- âŠ