28797376
Parton distributions extracted from data on deep-inelastic lepton scattering, prompt photon production, and the Drell-Yan process.
We present a next-to-leading-order QCD structure-function analysis of deep-inelastic muon and neutrino scattering data. In particular, we incorporate new $\frac{{F}_{2}^{\ensuremath{\mu}n}}{{F}_{2}^{\ensuremath{\mu}p}}$ data and take account of a recent reanalysis of SLAC data. The fit is performed simultaneously with next-to-leading-order fits to recent prompt photon and Drell-Yan data. As a result we are able to place tighter constraints on the quark and gluon distributions. Two definitive sets of parton distributions are presented according to whether the European Muon Collaboration or Bologna-CERN-Dubna-Munich-Saclay Collaboration muon data are included in the global fit. Comparisons with distributions obtained in earlier analyses are made and the consistency of data sets is investigated.
15108358
Off-diagonal parton distributions and their evolution
We construct off-diagonal parton distributions defined on the interval 0 ≤ X ≤ 1 starting from the off-forward distributions defined by Ji. We emphasize the particular role played by the symmetry relations in the “ERBL-like” region. We find the evolution equations for the off-diagonal distributions which conserve these symmetries. We present numerical results of the evolution, and verify that the analytic asymptotic forms of the parton distributions are reproduced. We also compare the constructed off-diagonal distributions with the non-forward distributions defined by Radyushkin and comment on the singularity structure of the basic amplitude written in terms of the off-diagonal distributions.
118665854
Diffraction and correlations at the LHC: definitions and observables
We note that the definition of diffractive events is a matter of convention. We discuss two possible “definitions”: one based on unitarity and the other on Large Rapidity Gaps (LRG) or Pomeron exchange. LRG can also arise from fluctuations and we quantify this effect and some of the related uncertainties. We find care must be taken in extracting the Pomeron contribution from LRG events. We show that long-range correlations in multiplicities can arise from the same multi-Pomeron diagrams that are responsible for LRG events, and we explain how early LHC data can illuminate our understanding of ‘soft’ interactions.
126229857
Structure Function Analysis and psi, Jet, W, Z Production: Pinning Down the Gluon
117807416
Diffractive deep inelastic scattering
A new approach to the analysis of diffractive deep inelastic data is presented. We show that the collinear factorisation theorem, which holds for diffractive DIS, has important modifications in the sub‐asymptotic HERA regime, which can be quantified by using perturbative QCD. In fact the diffractive parton densities are shown to satisfy an inhomogeneous evolution equation. Moreover it is necessary to include both the gluonic and sea‐quark t‐channel components of the perturbative Pomeron.
123328618
Proton-proton scattering and the pomeron
Abstract We describe various attempts to fit the data on pp and p p elastic scattering and total cross sections, including the recent ISR data, with a variety of Regge pole and cut models. Only two types of model are able to explain the data over the whole energy range satisfactorily. The simplest of these has no cuts, but a pomeron pole with trajectory α p(0) = 1.06 + 0.25 t , and a non-shrinking “core” term at large | t |. The other has a flat trajectory, α p( t ) = 1.06 for all t , and strong eikonal-model cuts which explain both the shrinkage at low | t |, and the lack of it at larger | t |. We also briefly review various speculations which relate the fact that α p(0) > 1 to the small triple-pomeron coupling.
33800044
Finite-size and dynamical effects in pair production by an external field.
We evaluate the rate of pair production in a uniform electric field confined to a bounded region in space. Using the Balian-Bloch expansion of Green's functions we obtain explicit expressions for finite-size corrections to Schwinger's formula. The case of a time-dependent boundary, relevant to describe energy deposition by quark-antiquark pair production in ultrarelativistic collisions, is also investigated. We find that finite-size effects are important in nuclear collisions. They decrease when the strength of the chromoelectric field between the nuclei is large. As a result, the rate of energy deposition increases sharply with the mass number {ital A} of the colliding nuclei.
41996012
Stability of systems of three arbitrary charges: General properties.
The stability of systems consisting of a negative charge {minus}{ital q}{sub 1} and two positive charges {ital q}{sub 2} and {ital q}{sub 3} is discussed as a function of the values of the charges {ital q}{sub {ital i}} and of the constituent masses {ital m}{sub {ital i}}. We give general results and list some open questions of interest, which hopefully will stimulate further investigations.
17368592
Raising the unification scale in supersymmetry.
In the minimal supersymmetric standard model, the three gauge couplings appear to unify at a mass scale near 2{times}10{sup 16} GeV. We investigate the possibility that intermediate scale particle thresholds modify the running couplings so as to increase the unification scale. By requiring consistency of this scenario, we derive some constraints on the particle content and locations of the intermediate thresholds. There are remarkably few acceptable solutions with a single cleanly defined intermediate scale far below the unification scale.
11226857
Dynamical electroweak symmetry breaking with top-quark and neutrino condensates.
Recently it has been suggested that electroweak symmetry is broken by a top-quark vacuum condensate. In that model, the prediction for the top-quark mass seems to be in conflict with indirect experimental upper bounds. We propose a new scenario in which electroweak symmetry is broken by a combination of top-quark and third-generation neutrino condensates, involving a right-handed gauge-singlet neutrino. We show that the top-quark mass comes out smaller in this model and can easily lie in the experimentally favored window. The resulting neutrino spectrum is phenomenologically acceptable if we make the natural assumption that the right-handed neutrino has a large Majorana mass.
28650811
Crossing intrinsic depolarizing resonances by varying a partial Siberian snake.
We recently forced a 140 MeV polarized proton beam to cross intrinsic depolarizing resonances by varying a partial Siberian snake{close_quote}s strength for different values of the vertical and horizontal betatron tunes {nu}{sub {ital y}} and {nu}{sub {ital x}}. A weak second-order intrinsic resonance was observed in the {nu}{sub {ital x}} sweep; moreover, an unexpected partial spin flip was found in the {nu}{sub {ital y}} sweep. We also varied the snake ramp time to identify the {nu}{sub {ital y}} and {nu}{sub {ital x}} regions where the resonance crossings occurred during the snake variation; in these crossings the polarization partially deviated from Froissart-Stora behavior. {copyright} {ital 1996 The American Physical Society.}