17472486
On the Manifestations of Particles
The mathematical description of stable particle-like systems appearing in relativistic quantum field theory at large, respectively small scales or non-zero temperatures is discussed.
2708024
An algebraic characterization of vacuum states in Minkowski space
An algebraic characterization of vacuum states on nets ofC*-algebras over Minkowski space is given and space-time translations are reconstructed with the help of the modular structures associated with such states. The result suggests that a “condition of geometrical modular action” might hold in quantum field theories on a wider class of spacetime manifolds.
122078833
Dirac versus wigner. Towards a universal particle concept in local quantum field theory
Abstract Based on the concept of particle weight a unified description of stable particle-like systems in local quantum field theory is given which applies also to so called infraparticles. Particle weights carry definite charge, four momentum and spin and give rise to characteristic mass shell singularities. A collision theory for these weights is proposed which allows to calculate transition probabilities directly from local gauge invariant operators.
1870101
Local temperature in curved spacetime
A physically meaningful local concept of temperature is introduced in quantum field theory on curved spacetime and applied to the example of a massless field on de Sitter space. It turns out in this model that the equilibrium (Gibbs) states which can be prepared by a geodesic observer have in general a varying temperature distribution in the neighbourhood of the geodesic and may not even allow for a consistent thermal interpretation close to the horizon. This result, which can be traced back to the Unruh effect, illustrates the failure of a global notion of temperature in curved spacetime and reveals the need for a local concept, as presented here.
16799561
Quantum Delocalization of the Electric Charge
The classical Maxwell–Dirac and Maxwell–Klein–Gordon theories admit solutions of the field equations where the corresponding electric current vanishes in the causal complement of some bounded region of Minkowski space. This poses the interesting question of whether states with a similarly well localized charge density also exist in quantum electrodynamics. For a large family of charged states, the dominant quantum corrections at spacelike infinity to the expectation values of local observables are computed. It turns out that certain moments of the charge density decrease no faster than the Coulomb field in spacelike directions. In contrast to the classical theory, it is therefore impossible to define the electric charge support of these states in a meaningful way.
15385756
There are no causality problems for Fermi's two-atom system.
A repeatedly discussed gedanken expeirment, proposed by Fermi to check Einstein causality, is reconsidered. It is shown that, contrary to a recent statement made by Hegerfeldt, there appears no causality paradox in a proper theoretical description of the experiment.
123787086
$D^0$ hot topics
The authors present recent D0 results based on approximately 1 fb{sup -1} of p{bar p} collisions at {radical}s = 1.96 TeV recorded at the Fermilab Tevatron. Preliminary results on a search for the flavor changing neutral current process D{sup +} {yields} {pi}{sup +}{mu}{sup +}{mu}{sup -}, a measurement of the Cp violation parameter in B mixing, {epsilon}{sub B}, and a two sided limit on the B{sub s} oscillation frequency {Delta}m{sub s} are presented. The limits on {epsilon}{sub B} and {Beta}(D{sup +} {yields} {pi}{sup +}{mu}{sup +}{mu}{sup -}) are the world's best limits. The two sided bound on {Delta}m{sub s} is the first direct indication by a single experiment that {Delta}m{sub s} is bounded from above.
121765828
Pion pion phase shift and form-factors in the decays k+- ---> pi+ pi- e+- nu(e)
119779374
Neural network based neutral particles reconstruction with the E687 hadron calorimeter
Abstract We present a neutral particle reconstruction algorithm based on a neural network approach applied to the E687 hadron calorimeter. A measurement of the invariant mass of the Σ ± → nπ ± is presented to verify the reliability of the reconstruction. The reconstructed invariant mass of the charmed meson D + → K L 0 π + π + π − is also presented to show the possible application of this technique to charmed particles decaying into a neutral hadron. An example of this would be Λ c + → n K − π + π + .
120539815
Experimental tests of discrete symmetries in the decays k+- ---> pi+ pi- e+- nu(e)
118465845
Recent results on charm from Fermilab experiment E-687
About 10{sup 4} charm decays have been reconstructed from first-run data of Fermilab experiment E687 using the Fermilab Wide-Band Photon Spectrometer with the world's highest energy photon beam. The success of techniques for isolating and reconstructing charm event samples based on two complementary vertexing strategies is illustrated. Preliminary results are presented. These include lifetime value of (0.50 {plus minus} 0.06 {plus minus} 0.03)ps for the D{sub s}{sup +}, and (0.20 {plus minus} 0.03 {plus minus} 0.03)ps for the {Lambda}{sub c}{sup +}. Preliminary values for the D{sup +} and D{sup 0} lifetimes are consistent with currently accepted world averages. Signals for the Cabibbo-suppressed decays D{sup 0} {yields} {pi}{sup +}{pi}{sup {minus}}{pi}{sup +}{pi}{sup {minus}}, D{sup +} {yields} K{sup +}K{sup {minus}}{pi}{sup +}, and D{sup +} {yields} {phi}{pi}{sup +} are shown; for B(D{sup 0} {yields} {pi}{sup +}{pi}{sup {minus}}{pi}{sup +}{pi}{sup {minus}})/B(D{sup 0} {yields} K{sup {minus}}{pi}{sup +}{pi}{sup +}{pi}{sup {minus}}) our preliminary value is 0.10 {plus minus} 0.02 {plus minus} 0.02. Preliminary values for ratios B(D{sup 0} {yields} {ovr K}{sup 0}K{sup +}K{sup {minus}})/B(D{sup 0} {yields} {ovr K}{sup 0}{pi}{sup +}{pi}{sup {minus}}) and B(D{sup 0} {yields} {ovr K}{sup 0}{phi})/B(D{sup 0} {yields} {ovr K}{sup 0}{pi}{sup +}{pi}{sup {minus}}) are 0.20 {plus minus} 0.06 and 0.16 {plus minus} 0.06. Preliminary results are givenmore » for cross sections of D*{sup {plus minus}} and D{sup {plus minus}} photoproduction on a Be target for the p{sup 2}{sub {tau}} dependence of D{sup {minus plus}} photoproduction and for the ratios D{double prime}/D*{sup +} and D*{sup {minus}}/D{sup {minus plus}}. The energy dependence of the total open charm photoproduction cross section is compared with model predictions for photon energies up to 350 GeV. 18 refs., 5 figs.« less