573 research outputs found
The Spin Structure of the Nucleon
The present status of the nucleon's spin structure is reviewed with emphasis
on new experimental results.Comment: Invited talk presented at the XIX International Symposium on Lepton
and Photon Interactions, Stanford University, August 9-14, 1999, 16 pages, 15
figure
Why there is no crisis of the "spin crisis"
In a recent eprint [1] it is argued that the experimental determinations of
the spin-dependent structure function g1 have been done incorrectly and that a
reanalysis of those data suggests that the original motivation to argue fora
"spin crisis", namely the small contribution of quark spins to the nucleon
spin, is invalid. In a subsequent note [2] the theoretical understanding, as it
has evolved from almost 30 years of theoretical and experimental scrutiny, has
been shortly summarised. In this short note, arguments are presented that the
line of reasoning in Ref. [1] does not apply, at least not for the Compass
data.Comment: 2 pages, no figure
Spin Physics with COMPASS
The recently proposed COMPASS experiment at CERN attempts a measurement of the gluon polarisation with a precision of delta(Delta g/g) = 0.1. The experiment uses open charm muoproduction to tag the photon-gluon fusion process
Measurements of Delta G/G
Our present information on the gluon polarisation Delta g/g is reviewed. The
data from fixed-target lepton-nucleon experiments are in context with the
recent data from the RHIC polarised pp collider. The main tools to study Delta
g/g in lepton-nucleon scattering are scaling violations of the g_1 structure
functions and longitudinal spin asymmetries in hadron production. Results from
high-p_T hadron pairs, inclusive hadrons as well as open-charm production are
discussed. At RHIC the most precise data presently came from inclusive pi^0 and
jet production. All data indicate that the gluon polarisation is small compared
to earlier expectations, but still can make a major contribution to the nucleon
spin.Comment: Proceedings for SPIN2006, Kyot
Distinguishing Supersymmetry From Universal Extra Dimensions or Little Higgs Models With Dark Matter Experiments
There are compelling reasons to think that new physics will appear at or
below the TeV-scale. It is not known what form this new physics will take,
however. Although The Large Hadron collider is very likely to discover new
particles associated with the TeV-scale, it may be difficult for it to
determine the nature of those particles, whether superpartners, Kaluza-Klein
modes or other states. In this article, we consider how direct and indirect
dark matter detection experiments may provide information complementary to
hadron colliders, which can be used to discriminate between supersymmetry,
models with universal extra dimensions, and Little Higgs theories. We find
that, in many scenarios, dark matter experiments can be effectively used to
distinguish between these possibilities.Comment: 23 pages, 7 figures, references added in version
Kaluza-Klein Dark Matter: Direct Detection vis-a-vis LHC
We explore the phenomenology of Kaluza-Klein (KK) dark matter in very general
models with universal extra dimensions (UEDs), emphasizing the complementarity
between high-energy colliders and dark matter direct detection experiments. In
models with relatively small mass splittings between the dark matter candidate
and the rest of the (colored) spectrum, the collider sensitivity is diminished,
but direct detection rates are enhanced. UEDs provide a natural framework for
such mass degeneracies. We consider both 5-dimensional and 6-dimensional
non-minimal UED models, and discuss the detection prospects for various KK dark
matter candidates: the KK photon , the KK -boson , the KK
Higgs boson and the spinless KK photon . We combine collider
limits such as electroweak precision data and expected LHC reach, with
cosmological constraints from WMAP, and the sensitivity of current or planned
direct detection experiments. Allowing for general mass splittings, we show
that neither colliders, nor direct detection experiments by themselves can
explore all of the relevant KK dark matter parameter space. Nevertheless, they
probe different parameter space regions, and the combination of the two types
of constraints can be quite powerful. For example, in the case of in
5D UEDs the relevant parameter space will be almost completely covered by the
combined LHC and direct detection sensitivities expected in the near future.Comment: 52 pages, 29 figure
Gluon polarization in the proton
We combine heavy-quark renormalization group arguments with our understanding
of the nucleon's wavefunction to deduce a bound on the gluon polarization Delta
g in the proton. The bound is consistent with the values extracted from spin
experiments at COMPASS and RHIC.Comment: 4 page
Kaluza-Klein Dark Matter
We propose that cold dark matter is made of Kaluza-Klein particles and
explore avenues for its detection. The lightest Kaluza-Klein state is an
excellent dark matter candidate if standard model particles propagate in extra
dimensions and Kaluza-Klein parity is conserved. We consider Kaluza-Klein gauge
bosons. In sharp contrast to the case of supersymmetric dark matter, these
annihilate to hard positrons, neutrinos and photons with unsuppressed rates.
Direct detection signals are also promising. These conclusions are generic to
bosonic dark matter candidates.Comment: 4 pages, 3 figures, discussion of spin-independent cross section
clarified, references added, published versio
Exploring the polarization of gluons in the nucleon
We give an overview of the current status of investigations of the
polarization of gluons in the nucleon. We describe some of the physics of the
spin-dependent gluon parton distribution and its phenomenology in high-energy
polarized hadronic scattering. We also review the recent experimental results.Comment: 10 pages, 13 figures. Talk presented at the "Second Meeting of the
APS Topical Group on Hadronic Physics", Nashville, Tennessee, October 22-24,
2006. Reference adde
On dark matter search after DAMA with Ge-73
The Weakly Interacting Massive Particle (WIMP) is one of the main candidates
for the relic dark matter (DM).In the effective low-energy minimal
supersymmetric standard model (effMSSM) the neutralino-nucleon spin and scalar
cross sections in the low-mass regime were calculated. The calculated cross
sections are compared with almost all experimental currently available
exclusion curves for spin-dependent WIMP-proton and WIMP-neutron cross
sections. It is demonstrated that in general about two-orders-of-magnitude
improvement of the current DM experiment sensitivities is needed to reach the
(effMSSM) SUSY predictions. At the current level of accuracy it looks
reasonable to safely neglect sub-dominant spin WIMP-nucleon contributions
analyzing the data from spin-non-zero targets. To avoid misleading
discrepancies between data and SUSY calculations it is, however, preferable to
use a mixed spin-scalar coupling approach.This approach is applied to estimate
future prospects of experiments with the odd-neutron high-spin isotope Ge-73.
It is noticed that the DAMA evidence favors the light Higgs sector in the
effMSSM, a high event rate in a Ge-73 detector and relatively high upgoing muon
fluxes from relic neutralino annihilations in the Earth and the Sun.Comment: 29 pages, 12 figures, 124 reference
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