38 research outputs found
Next-to-leading order QCD corrections to top quark spin correlations at hadron colliders: the reactions and
We have computed the cross section for production by gluon-gluon
fusion at next-to-leading order (NLO) in the QCD coupling, keeping the full
dependence on the spins. Furthermore we have determined to the same
order the spin dependent cross sections for the processes . Together with our previous results for these results allow for predictions, at NLO QCD, of the
hadronic production of pairs in a general spin configuration. As an
application we have determined the degree of correlation of the and spins at NLO, using various spin quantisation axes.Comment: 10 pages, 8 figure
Factorization Approach for Inclusive Production of Doubly Heavy Baryon
We study inclusive production of doubly heavy baryon at a collider
and at hadron colliders through fragmentation. We study the production by
factorizing nonpertubative- and perturbative effects. In our approach the
production can be thought as a two-step process: A pair of heavy quarks can be
produced perturbatively and then the pair is transformed into the baryon. The
transformation is nonperturbative. Since a heavy quark moves with a small
velocity in the baryon in its rest frame, we can use NRQCD to describe the
transformation and perform a systematic expansion in the small velocity. At the
leading order we find that the baryon can be formed from two states of the
heavy-quark pair, one state is with the pair in state and in color
, another is with the pair in state and in color . Two matrix elements are defined for the transformation from the two
states, their perturbative coefficients in the contribution to the
cross-section at a collider and to the function of heavy quark
fragmentation are calculated. Our approach is different than previous
approaches where only the pair in state and in color is
taken into account. Numerical results for colliders at the two
-factories and for hadronic colliders LHC and Tevatron are given.Comment: Add results for large p_t, minor change
Mixed QCD and weak corrections to top quark pair production at hadron colliders
The order mixed QCD and weak corrections to top quark
pair production by quark antiquark annihilation are computed, keeping the full
dependence on the and spins. We determine the contributions to the
cross section and to single and double top spin asymmetries at the parton
level. These results are necessary ingredients for precise standard model
predictions of top quark observables, in particular of top spin-induced
parity-violating angular correlations and asymmetries at hadron colliders.Comment: 12 pages, 9 figure
QCD corrections to top quark spin correlations at hadron colliders
Future hadron collider experiments will allow for a detailed investigation of
spin correlation effects. In this talk, recent progress in the
theoretical description of these effects is reported. In particular,
next-to-leading order results for the spin correlations in
are presented, using various spin quantization axes.Comment: 5 pages, 5 figures. Talk presented at the conference `QCD 00',
Montpellier, 6-13th July 2000, to appear in the proceeding
QCD-corrected spin analysing power of jets in decays of polarized top quarks
We present results for the differential distributions of jets from
non-leptonic decays of polarized top quarks within the Standard Model,
including QCD radiative corrections. Our work extends existing results which
are only available for semileptonic top quark decays at the parton level. For
-> b-jet + 2 light jets we compute in particular the
QCD-corrected top-spin analysing power of the b-quark jet and the least
energetic light jet. The dependence of the results on the choice of the jet
recombination scheme is found to be small. In addition we compute the spin
analysing power of the thrust axis. Our results constitute a so far missing
ingredient to analyse top quark production and subsequent non-leptonic decay at
next-to-leading order in alpha_s, keeping the full information on the top quark
polarization.Comment: 11 page
Next-to-leading order QCD corrections to top quark spin correlations at hadron colliders: the reactions
Future hadron collider experiments are expected to record large to huge
samples of events. The analysis of these data with respect to spin-spin correlations requires precise predictions of the production of
these quark pairs in a general spin configuration. Therefore we have computed,
at next-to-leading order (NLO) in the QCD coupling, the spin density matrices
describing production by quark antiquark annihilation, which is the
dominant production process at the Tevatron. Moreover we have computed the
strength of the spin correlation at NLO, using various spin
quantization axes.Comment: 14 pages, 5 figure
Top quark pair production and decay at hadron colliders
In ongoing and upcoming hadron collider experiments, top quark physics will
play an important role in testing the Standard Model and its possible
extensions. In this work we present analytic results for the differential cross
sections of top quark pair production in hadronic collisions at next-to-leading
order in the QCD coupling, keeping the full dependence on the spins of the top
quarks. These results are combined with the corresponding next-to-leading order
results for the decay of polarized top quarks into dilepton, lepton plus jets,
and all jets final states. As an application we predict double differential
angular distributions which are due to the QCD-induced top quark spin
correlations in the intermediate state. In addition to the analytic results, we
give numerical results in terms of fit functions that can easily be used in an
experimental analysis.Comment: 58 pages, 12 figure
Search for the Chiral Magnetic Effect in Au+Au collisions at GeV with the STAR forward Event Plane Detectors
A decisive experimental test of the Chiral Magnetic Effect (CME) is
considered one of the major scientific goals at the Relativistic Heavy-Ion
Collider (RHIC) towards understanding the nontrivial topological fluctuations
of the Quantum Chromodynamics vacuum. In heavy-ion collisions, the CME is
expected to result in a charge separation phenomenon across the reaction plane,
whose strength could be strongly energy dependent. The previous CME searches
have been focused on top RHIC energy collisions. In this Letter, we present a
low energy search for the CME in Au+Au collisions at
GeV. We measure elliptic flow scaled charge-dependent correlators relative to
the event planes that are defined at both mid-rapidity and at
forward rapidity . We compare the results based on the
directed flow plane () at forward rapidity and the elliptic flow plane
() at both central and forward rapidity. The CME scenario is expected
to result in a larger correlation relative to than to , while
a flow driven background scenario would lead to a consistent result for both
event planes[1,2]. In 10-50\% centrality, results using three different event
planes are found to be consistent within experimental uncertainties, suggesting
a flow driven background scenario dominating the measurement. We obtain an
upper limit on the deviation from a flow driven background scenario at the 95\%
confidence level. This work opens up a possible road map towards future CME
search with the high statistics data from the RHIC Beam Energy Scan Phase-II.Comment: main: 8 pages, 5 figures; supplementary material: 2 pages, 1 figur
Myosin light chain kinase is necessary for post-shock mesenteric lymph drainage enhancement of vascular reactivity and calcium sensitivity in hemorrhagic-shocked rats
Vascular hyporeactivity is an important factor in irreversible shock, and post-shock mesenteric lymph (PSML) blockade improves vascular reactivity after hemorrhagic shock. This study explored the possible involvement of myosin light chain kinase (MLCK) in PSML-mediated vascular hyporeactivity and calcium desensitization. Rats were divided into sham (n=12), shock (n=18), and shock+drainage (n=18) groups. A hemorrhagic shock model (40±2 mmHg, 3 h) was established in the shock and shock+drainage groups. PSML drainage was performed from 1 to 3 h from start of hypotension in shock+drainage rats. Levels of phospho-MLCK (p-MLCK) were determined in superior mesenteric artery (SMA) tissue, and the vascular reactivity to norepinephrine (NE) and sensitivity to Ca2+ were observed in SMA rings in an isolated organ perfusion system. p-MLCK was significantly decreased in the shock group compared with the sham group, but increased in the shock+drainage group compared with the shock group. Substance P (1 nM), an agonist of MLCK, significantly elevated the decreased contractile response of SMA rings to both NE and Ca2+ at various concentrations. Maximum contractility (Emax) in the shock group increased with NE (from 0.179±0.038 to 0.440±0.177 g/mg, P<0.05) and Ca2+ (from 0.515±0.043 to 0.646±0.096 g/mg, P<0.05). ML-7 (0.1 nM), an inhibitor of MLCK, reduced the increased vascular response to NE and Ca2+ at various concentrations in the shock+drainage group (from 0.744±0.187 to 0.570±0.143 g/mg in Emax for NE and from 0.729±0.037 to 0.645±0.056 g/mg in Emax for Ca2+, P<0.05). We conclude that MLCK is an important contributor to PSML drainage, enhancing vascular reactivity and calcium sensitivity in rats with hemorrhagic shock