3,641 research outputs found
Impact of future HERA data on the determination of proton parton distribution functions using the ZEUS QCD fit
The high precision and large kinematic coverage of the data from the HERA-I
running period (1994-2000) have already allowed precise extractions of proton
parton distribution functions (PDFs). The HERA-II running program is now
underway and is expected to provide a substantial increase in the luminosity
collected at HERA. In this paper, a study is presented which investigates the
potential impact of future data from HERA on the proton PDF uncertainties,
within the currently planned running scenario. In addition, the effect of a
possible future measurement of the longitudinal structure function, FL, on the
gluon distribution is investigated.Comment: 5 pages, 2 figures, in proceedings of the XIII International Workshop
on Deep Inelastic Scattering - DIS 2005, Madison, Wisconsin, 200
The race for supersymmetry: using mT2 for discovery
We describe how one may employ a very simple event selection, using only the
kinematic variable mT2, to search for new particles at the LHC. The method is
useful when searching for evidence of models (such as R-parity conserving
supersymmetry) which have a Z2 parity and a weakly-interacting lightest
parity-odd particle. We discuss the kinematic properties which make this
variable an excellent discriminant against the great majority of Standard Model
backgrounds. Monte Carlo simulations suggest that this approach could be used
to discover supersymmetry with somewhat smaller integrated luminosities (or
perhaps lower center-of-mass energies) than would be required for other
comparable analyses.Comment: 8 page
A comment on "Amplification of endpoint structure for new particle mass measurement at the LHC"
We present a comment on the kinematic variable recently proposed in
"Amplification of endpoint structure for new particle mass measurement at the
LHC". The variable is designed to be applied to models such as R-parity
conserving Supersymmetry (SUSY) when there is pair production of new heavy
particles each of which decays to a single massless visible and a massive
invisible component. It was proposed in "Amplification of endpoint structure
for new particle mass measurement at the LHC" that a measurement of the peak of
the distribution could be used to precisely constrain the masses of
the SUSY particles. We show that when Standard Model backgrounds are included
in simulations, the sensitivity of the variable to the SUSY particle
masses is more seriously impacted for than for other previously
proposed variables.Comment: 5 page
Tuning Monte Carlo Generators: The Perugia Tunes
We present 9 new tunes of the pT-ordered shower and underlying-event model in
PYTHIA 6.4. These "Perugia" tunes update and supersede the older "S0" family.
The data sets used to constrain the models include hadronic Z0 decays at LEP,
Tevatron minimum-bias data at 630, 1800, and 1960 GeV, Tevatron Drell-Yan data
at 1800 and 1960 GeV, and SPS min-bias data at 200, 546, and 900 GeV. In
addition to the central parameter set, called "Perugia 0", we introduce a set
of 8 related "Perugia Variations" that attempt to systematically explore soft,
hard, parton density, and colour structure variations in the theoretical
parameters. Based on these variations, a best-guess prediction of the charged
track multiplicity in inelastic, nondiffractive minimum-bias events at the LHC
is made. Note that these tunes can only be used with PYTHIA 6, not with PYTHIA
8. Note: this report was updated in March 2011 with a new set of variations,
collectively labeled "Perugia 2011", that are optimized for matching
applications and which also take into account some lessons from the early LHC
data. In order not to break the original text, these are described separately
in Appendix B. Note 2: a subsequent "Perugia 2012" update is described in
Appendix C.Comment: 46 page
Combined HERA Deep Inelastic Scattering Data and NLO QCD Fits
Previously published data on inclusive neutral and charged current e+p and
e-p deep inelastic scattering from HERA have been combined. The new,
model-independent method of combining the measured cross sections takes full
account of correlated systematics in a coherent way, leading to significantly
reduced uncertainties in the combined measurement across the (x, Q^2) plane.
The combined cross section data have been used as the sole input for a new
next-to-leading order QCD fit to extract the parton distribution functions
(PDFs) of the proton. The PDFs extracted have greatly reduced experimental
uncertainties, compared to separate QCD analyses on data from H1 and ZEUS.
Model uncertainties, including those arising from the parameterisation
dependence, have also been carefully considered. The resulting HERA PDFs have
impressive precision.Comment: 11 pages, 6 figures, prepared for the proceedings of the Ringberg
Workshop on "New Trends in HERA Physics 2008", Ringberg Castle, Tegernsee,
Oct 5-10, 200
Chemical Differentiation toward the Pipe Nebula Starless Cores
We used the new IRAM 30-m FTS backend to perform an unbiased ~15 GHz wide
survey at 3 mm toward the Pipe Nebula young diffuse starless cores. We found an
unexpectedly rich chemistry. We propose a new observational classification
based on the 3 mm molecular line emission normalized by the core visual
extinction (Av). Based on this classification, we report a clear
differentiation in terms of chemical composition and of line emission
properties, which served to define three molecular core groups. The "diffuse"
cores, Av<~15, show poor chemistry with mainly simple species (e.g. CS and
CCH). The "oxo-sulfurated" cores, Av~15--22, appear to be abundant in species
like SO and SO2, but also in HCO, which seem to disappear at higher densities.
Finally, the "deuterated" cores, Av>~22, show typical evolved chemistry prior
to the onset of the star formation process, with nitrogenated and deuterated
species, as well as carbon chain molecules. Based on these categories, one of
the "diffuse" cores (Core 47) has the spectral line properties of the
"oxo-sulfurated" ones, which suggests that it is a possible failed core.Comment: Accepted for publication in A&A. 5 pages, 2 figure
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