32 research outputs found
How important are next-to-leading order models in predicting strange particle spectra in p+p collisions at STAR ?
STAR has measured a variety of strange particle species in p + p collisions
at = 200 GeV. These high statistics data are ideal for comparing to
existing leading- and next-to-leading order perturbative QCD (pQCD) models.
Next-to-leading (NLO) models have been successful in describing inclusive
hadron production using parameterized fragmentation functions (FF) for quarks
and gluons. However, in order to describe identied strange particle spectra at
NLO, knowledge of flavor separated FF is essential. Such FF have recently been
parameterized using data by the OPAL experiment and allow for the first time to
perform NLO calculation for strange baryons. In fact, comparing the STAR Lambda
data with these calculations allow to put a constraint on the gluon
fragmentation function. We show that the Leading-order (LO) event generator
PYTHIA has to be tuned significantly to reproduce the STAR identified strange
particle data. In particular, it fails to describe the observed enhancement of
baryon-to-meson ratio at intermediate pT (2-6 GeV/c). In heavy-ion (HI)
collisions this observable has been extensively compared with models and shows
a strong dependency on collision centrality or parton density. In the HI
context the observed enhancement has been explained by recent approaches in
terms of parton coalescense and recombination models.Comment: 5 pages, HotQuarks 2006 conference proceeding
Recommended from our members
Experimental search for W/Z pairs and Higgs bosons at very high energy hadron-hadron colliders
We study, from an experimental point of view, the main ways to detect standard high mass Higgs bosons (from 300 GeV up to about 1 TeV) when they decay into W- and Z-pairs at the SSC. We also consider the corresponding W- and Z/sup 0/-pair continuum which may itself provide interesting physics, and we pay some attention to the case of an intermediate mass charged Higgs decaying into tau..nu../sub tau/ (m/sub H+-/ = 300 GeV). We first explain why and how high energy pp colliders may search for Higgs' and we compare their possible performances to those of the e/sup +/e/sup -/ and ep colliders at all possible mass scale (from few tens of GeV's up to 1 TeV). We then estimate the rates of the signals and the main backgrounds. We define the main characteristics of these events as reproduced by M.C. generators (especially implemented with these processes) and simulated through an idealized 4..pi.. fine-grained calorimeter. A trigger strategy for W- and Z-pairs is derived from this study. 26 refs., 28 figs
High-p_T Higgs Boson Production at Hadron Colliders to Order(alpha_s G_Fermi^3)
We study high-- Higgs boson production at hadron colliders to
order( ) in hadron collisions. In particular, we investigate
the process g+q/\bar{q}\ra q/\bar{q}+H, where or , for the
LHC (a 14~TeV, proton--proton collider). Our results are compared to
the order( ) calculation. The associated production of a
high-- Higgs boson with a --quark or anti--quark is comparable to the
order( ) calculation because of the large top quark mass and
the additional contribution of electroweak gauge and Goldstone bosons. The
associated production of light quarks, however, is not significant. We also
comment on new physics effects in the framework of the electroweak chiral
Lagrangian.Comment: Latex file,16 pages, 2 figures, uses psfig.sty, postscript file
available at ftp://cithe502.cithep.caltech.edu/pub/mrenna/cp0.ps or at
http://www.cithep.caltech.edu/~mrenn
Searching for a Light Stop at the Tevatron
We describe a method to help the search for a light stop squark [M(stop) +
M(LSP) < M(top)] at the Fermilab Tevatron. Traditional search methods rely upon
a series of stringent background-reducing cuts which, unfortunately, leave very
few signal events given the present data set. To avoid this difficulty, we
instead suggest using a milder set of cuts, combined with a "superweight,"
whose purpose is to discriminate between signal and background events. The
superweight consists of a sum of terms, each of which are either zero or one.
The terms are assigned event-by-event depending upon the values of various
observables. We suggest a method for choosing the observables as well as the
criteria used to assign the values such that the superweight is "large" for the
supersymmetric signal and "small" for the standard model background. For
illustration, we mainly consider the detection of stops coming from top decay,
making our analysis especially relevant to the W+2 jets top sample.Comment: 45 pages, revtex, 15 figures included. Final version, as will appear
in Phys. Rev. D. Contains an expanded introduction plus a few additional
reference
Antiprotons in cosmic rays from neutralino annihilation
We calculate the antiproton flux due to relic neutralino annihilations, in a
two-dimensional diffusion model compatible with stable and radioactive cosmic
ray nuclei. We find that the uncertainty in the primary flux induced by the
propagation parameters alone is about two orders of magnitude at low energies,
and it is mainly determined by the lack of knowledge on the thickness of the
diffusive halo. On the contrary, different dark matter density profiles do not
significantly alter the flux: a NFW distribution produces fluxes which are at
most 20% higher than an isothermal sphere. The most conservative choice for
propagation parameters and dark matter distribution normalization, together
with current data on cosmic antiprotons, cannot lead to any definitive
constraint on the supersymmetric parameter space, neither in a low-energy
effective MSSM, or in a minimal SUGRA scheme. However, if the best choice for
propagation parameters - corresponding to a diffusive halo of L=4 kpc - is
adopted, some supersymmetric configurations with the neutralino mass of about
100 GeV should be considered as excluded. An enhancement flux factor - due for
instance to a clumpy dark halo or to a higher local dark matter density - would
imply a more severe cut on the supersymmetric parameters.Comment: 23 pages, 2 tables and 19 figures, typeset with ReVTeX4. The paper
may also be found at http://www.to.infn.it/~fornengo/papers/pbar03.ps.gz or
through http://www.to.infn.it/astropart/index.html A subsection added. Final
version to appear in PR
Recommended from our members
Detecting W/Z pairs and Higgs at high energy pp colliders: Main experimental issues
The main detection issues implied by the search for W and Z/sup 0/ pairs and Higgs in a high energy pp collider context are discussed here. It includes: precise electron identification, missing energy measurement, multilepton recognition, sophisticated jet pattern recognition, and pile-up. The study uses, as much as possible, a ''realistic simulation of life.'