5,426 research outputs found
Local dark matter searches with LISA
The drag-free satellites of LISA will maintain the test masses in geodesic
motion over many years with residual accelerations at unprecedented small
levels and time delay interferometry (TDI) will keep track of their
differential positions at level of picometers. This may allow investigations of
fine details of the gravitational field in the Solar System previously
inaccessible. In this spirit, we present the concept of a method to measure
directly the gravitational effect of the density of diffuse Local Dark Matter
(LDM) with a constellation of a few drag-free satellites, by exploiting how
peculiarly it would affect their relative motion. Using as test bed an
idealized LISA with rigid arms, we find that the separation in time between the
test masses is uniquely perturbed by the LDM, so that they acquire a
differential breathing mode. Such a LDM signal is related to the LDM density
within the orbits and has characteristic spectral components, with amplitudes
increasing in time, at various frequencies of the dynamics of the
constellation. This is the relevant result, in that the LDM signal is brought
to non-zero frequencies.Comment: 8 pages, 1 figure; v2: minor changes to match the version in press on
Classical and Quantum Gravity (special issue for the 7th International LISA
Symposium proceedings
Moments of the Proton F2 Structure Function at Low Q2
The Q^2 dependence of inclusive electron-proton scattering F_2 structure
function data in both the nucleon resonance region and the deep inelastic
region, at momentum transfers below 5 (GeV/c)^2, is investigated. Moments of
F_2 are constructed, down to momentum transfers of Q^2 ~ 0.1 (GeV/c)^2. The
second moment is only slowly varying with Q^2 down to Q^2 ~ 1 (GeV/c)^2, which
is a reflection of duality. Below Q^2 of 1 (GeV/c)^2, the Q^2 dependence of the
moments is predominantly governed by the elastic contribution, whereas the
inelastic channels still seem governed by local duality.Comment: 11 page paper, 1 LaTeX file, 10 postscript figure file
Structure and Production of Lambda Baryons
We discuss the quark parton structure of the baryon and the
fragmentation of quarks into baryons. We show that the hyperfine
interaction, responsible for the - and - mass
splittings, leads not only to sizeable SU(3) and SU(6) symmetry breaking in the
quark distributions of the , but also to significant polarized
non-strange quark distributions. The same arguments suggest flavor asymmetric
quark fragmentation functions and non-zero polarized non-strange quark
fragmentation functions. The calculated fragmentation functions give a good
description of all measured observables. We predict significant positive
polarization in semi-inclusive DIS experiments while models based on
SU(3) flavor symmetry predict zero or negative polarization. Our
approach also provides a natural explanation for the dependence of the maximum
of the spectrum on the mass of the particles produced in
annihilation.Comment: 24 pages, 9 figures, minor change
Limits on WWgamma and WWZ Couplings from W Boson Pair Production
The results of a search for W boson pair production in pbar-p collisions at
sqrt{s}=1.8 TeV with subsequent decay to emu, ee, and mumu channels are
presented. Five candidate events are observed with an expected background of
3.1+-0.4 events for an integrated luminosity of approximately 97 pb^{-1}.
Limits on the anomalous couplings are obtained from a maximum likelihood fit of
the E_T spectra of the leptons in the candidate events. Assuming identical
WWgamma and WWZ couplings, the 95 % C.L. limits are -0.62<Delta_kappa<0.77
(lambda = 0) and -0.53<lambda<0.56 (Delta_kappa = 0) for a form factor scale
Lambda = 1.5 TeV.Comment: 10 pages, 1 figure, submitted to Physical Review
Leading and higher twists in the proton polarized structure function at large Bjorken x
A phenomenological parameterization of the proton polarized structure
function has been developed for x > 0.02 using deep inelastic data up to ~ 50
(GeV/c)**2 as well as available experimental results on both photo- and
electro-production of proton resonances. According to the new parameterization
the generalized Drell-Hearn-Gerasimov sum rule is predicted to have a
zero-crossing point at Q**2 = 0.16 +/- 0.04 (GeV/c)**2. Then, low-order
polarized Nachtmann moments have been estimated and their Q**2-behavior has
been investigated in terms of leading and higher twists for Q**2 > 1
(GeV/c)**2. The leading twist has been treated at NLO in the strong coupling
constant and the effects of higher orders of the perturbative series have been
estimated using soft-gluon resummation techniques. In case of the first moment
higher-twist effects are found to be quite small for Q**2 > 1 (GeV/c)**2, and
the singlet axial charge has been determined to be a0[10 (GeV/c)**2] = 0.16 +/-
0.09. In case of higher order moments, which are sensitive to the large-x
region, higher-twist effects are significantly reduced by the introduction of
soft gluon contributions, but they are still relevant at Q**2 ~ few (GeV/c)**2
at variance with the case of the unpolarized transverse structure function of
the proton. Our finding suggests that spin-dependent correlations among partons
may have more impact than spin-independent ones. As a byproduct, it is also
shown that the Bloom-Gilman local duality is strongly violated in the region of
polarized electroproduction of the Delta(1232) resonance.Comment: revised version to appear in Phys. Rev. D; extended discussion on the
generalized DHG sum rul
Discovery of the Optical Transient of the Gamma Ray Burst 990308
The optical transient of the faint Gamma Ray Burst 990308 was detected by the
QUEST camera on the Venezuelan 1-m Schmidt telescope starting 3.28 hours after
the burst. Our photometry gives , , , and for times ranging from 3.28 to 3.47
hours after the burst. The colors correspond to a spectral slope of close to
. Within the standard synchrotron fireball model,
this requires that the external medium be less dense than , the
electrons contain of the shock energy, and the magnetic field energy
must be less than 24% of the energy in the electrons for normal interstellar or
circumstellar densities. We also report upper limits of at 132 s
(with LOTIS), from 132-1029s (with LOTIS), at 28.2 min
(with Super-LOTIS), and a 8.5 GHz flux of at 110 days (with the
Very Large Array). WIYN 3.5-m and Keck 10-m telescopes reveal this location to
be empty of any host galaxy to and . The lack of a host
galaxy likely implies that it is either substantially subluminous or more
distant than a red shift of .Comment: ApJ Lett submitted, 5 pages, 2 figures, no space for 12 coauthor
Measurement of the Boson Mass
A measurement of the mass of the boson is presented based on a sample of
5982 decays observed in collisions at
= 1.8~TeV with the D\O\ detector during the 1992--1993 run. From a
fit to the transverse mass spectrum, combined with measurements of the
boson mass, the boson mass is measured to be .Comment: 12 pages, LaTex, style Revtex, including 3 postscript figures
(submitted to PRL
The Azimuthal Decorrelation of Jets Widely Separated in Rapidity
This study reports the first measurement of the azimuthal decorrelation
between jets with pseudorapidity separation up to five units. The data were
accumulated using the D{\O}detector during the 1992--1993 collider run of the
Fermilab Tevatron at 1.8 TeV. These results are compared to
next--to--leading order (NLO) QCD predictions and to two leading--log
approximations (LLA) where the leading--log terms are resummed to all orders in
. The final state jets as predicted by NLO QCD
show less azimuthal decorrelation than the data. The parton showering LLA Monte
Carlo {\small HERWIG} describes the data well; an analytical LLA prediction
based on BFKL resummation shows more decorrelation than the data.Comment: 6 pages with 4 figures, all uuencoded and gzippe
Search for a Fourth Generation Charge -1/3 Quark via Flavor Changing Neutral Current Decay
We report on a search for pair production of a fourth generation charge -1/3
quark (b') in pbar p collisions at sqrt(s) = 1.8 TeV at the Fermilab Tevatron
using an integrated luminosity of 93 pb^-1. Both quarks are assumed to decay
via flavor changing neutral currents (FCNC). The search uses the signatures
gamma + 3 jets + mu-tag and 2 gamma + 2 jets. We see no significant excess of
events over the expected background. We place an upper limit on the production
cross section times branching fraction that is well below theoretical
expectations for a b' quark decaying exclusively via FCNC for b' quark masses
up to m(Z) + m(b).Comment: Eleven pages, two postscript figures, submitted to Physical Review
Letter
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