1,319 research outputs found
High energy solar neutrinos and p-wave contributions to ^3He(p,\nue^+)^4He
High energy solar neutrinos can come from the hep reaction ^3He(p,\nue^+)^4He
with a large end point energy of 18.8 MeV. Understanding the hep reaction may
be important for interpreting solar neutrino spectra. We calculate the
contribution of the axial charge transition to the hep
thermonuclear S factor using a one-body reaction model involving a nucleon
moving in optical potentials. Our result is comparable to or larger than
previous calculations of the s-wave Gamow Teller contribution. This indicates
that the hep reaction may have p-wave strength leading to an enhancement of the
S factor.Comment: 4 pages, 1 ps figure, very minor changes, Phys. Rev. C in pres
Single-inclusive production of large-pT charged particles in hadronic collisions at TeV energies and perturbative QCD predictions
The single inclusive spectrum of charged particles with transverse momenta
pT=3-150 GeV/c measured at midrapidity by the CDF experiment in
proton-antiproton (p-pbar) collisions at sqrt(s)=1.96 TeV is compared to
next-to-leading order (NLO) perturbative QCD calculations using the most recent
parametrizations of the parton distributions and parton-to-hadron fragmentation
functions. Above pT~20 GeV/c, there is a very sizeable disagreement of the
Tevatron data compared to the NLO predictions and to xT-scaling expectations,
suggesting a problem in the experimental data. We also present the predictions
for the pT-differential charged hadron spectra and the associated theoretical
uncertainties for proton-proton (p-p) collisions at LHC energies
(sqrt(s)=0.9-14 TeV). Two procedures to estimate the charged hadron spectra at
LHC heavy-ion collision energies (sqrt(s)=2.76,5.5 TeV) from p-p measurements
are suggested.Comment: 23 pages, 9 figures. A few text additions. Accepted for publication
in JHE
Infiltration from surface and buried point sources: The average wetting water content
The assumption in analytical solutions for flow from surface and buried point sources of an average water content, (θ) over bar, behind the wetting front is examined. Some recent work has shown that this assumption fitted some field data well. Here we calculated (θ) over bar using a steady state solution based on the work by Raats [1971] and an exponential dependence of the diffusivity upon the water content. This is compared with a constant value of (θ) over bar calculated from an assumption of a hydraulic conductivity at the wetting front of 1 mm day(-1) and the water content at saturation. This comparison was made for a wide range of soils. The constant (θ) over bar generally underestimated (θ) over bar at small wetted radii and overestimated (θ) over bar at large radii. The crossover point between under and overestimation changed with both soil properties and flow rate. The largest variance occurred for coarser texture soils at low-flow rates. At high-flow rates in finer-textured soils the use of a constant (θ) over bar results in underestimation of the time for the wetting front to reach a particular radius. The value of (θ) over bar is related to the time at which the wetting front reaches a given radius. In coarse-textured soils the use of a constant value of (θ) over bar can result in an error of the time when the wetting front reaches a particular radius, as large as 80% at low-flow rates and large radii
Bulk matter physics and its future at the Large Hadron Collider
Measurements at low transverse momentum will be performed at the LHC for
studying particle production mechanisms in and heavy-ion collisions. Some
of the experimental capabilities for bulk matter physics are presented,
focusing on tracking elements and particle identification. In order to
anticipate the study of baryon production for both colliding systems at
multi-TeV energies, measurements for identified species and recent model
extrapolations are discussed. Several mechanisms are expected to compete for
hadro-production in the low momentum region. For this reason, experimental
observables that could be used for investigating multi-parton interactions and
help understanding the "underlying event" content in the first collisions
at the LHC are also mentioned.Comment: 6 pages, 7 figures. To appear in the proceedings of Hot Quarks 2008,
Estes Park, Colorado, 18-23 August 200
Semidefinite Characterization and Computation of Real Radical Ideals
For an ideal given by a set of generators, a new
semidefinite characterization of its real radical is
presented, provided it is zero-dimensional (even if is not). Moreover we
propose an algorithm using numerical linear algebra and semidefinite
optimization techniques, to compute all (finitely many) points of the real
variety as well as a set of generators of the real radical
ideal. The latter is obtained in the form of a border or Gr\"obner basis. The
algorithm is based on moment relaxations and, in contrast to other existing
methods, it exploits the real algebraic nature of the problem right from the
beginning and avoids the computation of complex components.Comment: 41 page
Multiplicity dependence of jet-like two-particle correlations in p-Pb collisions at = 5.02 TeV
Two-particle angular correlations between unidentified charged trigger and
associated particles are measured by the ALICE detector in p-Pb collisions at a
nucleon-nucleon centre-of-mass energy of 5.02 TeV. The transverse-momentum
range 0.7 5.0 GeV/ is examined,
to include correlations induced by jets originating from low
momen\-tum-transfer scatterings (minijets). The correlations expressed as
associated yield per trigger particle are obtained in the pseudorapidity range
. The near-side long-range pseudorapidity correlations observed in
high-multiplicity p-Pb collisions are subtracted from both near-side
short-range and away-side correlations in order to remove the non-jet-like
components. The yields in the jet-like peaks are found to be invariant with
event multiplicity with the exception of events with low multiplicity. This
invariance is consistent with the particles being produced via the incoherent
fragmentation of multiple parton--parton scatterings, while the yield related
to the previously observed ridge structures is not jet-related. The number of
uncorrelated sources of particle production is found to increase linearly with
multiplicity, suggesting no saturation of the number of multi-parton
interactions even in the highest multiplicity p-Pb collisions. Further, the
number scales in the intermediate multiplicity region with the number of binary
nucleon-nucleon collisions estimated with a Glauber Monte-Carlo simulation.Comment: 23 pages, 6 captioned figures, 1 table, authors from page 17,
published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/161
Multi-particle azimuthal correlations in p-Pb and Pb-Pb collisions at the CERN Large Hadron Collider
Measurements of multi-particle azimuthal correlations (cumulants) for charged
particles in p-Pb and Pb-Pb collisions are presented. They help address the
question of whether there is evidence for global, flow-like, azimuthal
correlations in the p-Pb system. Comparisons are made to measurements from the
larger Pb-Pb system, where such evidence is established. In particular, the
second harmonic two-particle cumulants are found to decrease with multiplicity,
characteristic of a dominance of few-particle correlations in p-Pb collisions.
However, when a gap is placed to suppress such correlations,
the two-particle cumulants begin to rise at high-multiplicity, indicating the
presence of global azimuthal correlations. The Pb-Pb values are higher than the
p-Pb values at similar multiplicities. In both systems, the second harmonic
four-particle cumulants exhibit a transition from positive to negative values
when the multiplicity increases. The negative values allow for a measurement of
to be made, which is found to be higher in Pb-Pb collisions at
similar multiplicities. The second harmonic six-particle cumulants are also
found to be higher in Pb-Pb collisions. In Pb-Pb collisions, we generally find
which is indicative of a Bessel-Gaussian
function for the distribution. For very high-multiplicity Pb-Pb
collisions, we observe that the four- and six-particle cumulants become
consistent with 0. Finally, third harmonic two-particle cumulants in p-Pb and
Pb-Pb are measured. These are found to be similar for overlapping
multiplicities, when a gap is placed.Comment: 25 pages, 11 captioned figures, 3 tables, authors from page 20,
published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/87
Two-pion Bose-Einstein correlations in central Pb-Pb collisions at = 2.76 TeV
The first measurement of two-pion Bose-Einstein correlations in central Pb-Pb
collisions at TeV at the Large Hadron Collider is
presented. We observe a growing trend with energy now not only for the
longitudinal and the outward but also for the sideward pion source radius. The
pion homogeneity volume and the decoupling time are significantly larger than
those measured at RHIC.Comment: 17 pages, 5 captioned figures, 1 table, authors from page 12,
published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/388
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