J/psi production at HERA Artoisenet, P; Campbell, J; Maltoni, F ...
Physical review letters,
04/2009, Letnik:
102, Številka:
14
Journal Article
Recenzirano
We consider the J/psi photoproduction data collected at the DESY ep collider HERA in the light of next-to-leading order predictions for the color-singlet yield and polarization. We find that, while ...the shapes of inclusive distributions in the transverse momentum and inelasticity are well reproduced, the experimental rates are larger than those given by the color-singlet contribution alone. Furthermore, the next-to-leading order calculation predicts the J/psi's to be mostly longitudinally polarized at high transverse momentum in contrast with the trend of the preliminary data from the ZEUS Collaboration.
This Letter details and discusses the next-to-leading order QCD corrections to t-channel electro-weak W+bj production, where finite top-width effects are consistently taken into account. The ...computation is done within the aMC@NLO framework and includes both resonant and non-resonant contributions as well as interferences between the two. Results are presented for the LHC and compared to those of the narrow-width approximation and effective theory approaches.
We present an update of the Binoth Les Houches Accord (BLHA) to standardise the interface between Monte Carlo programs and codes providing one-loop matrix elements.
We study the phenomenology of same sign top pair production at the LHC in a model-independent way. The complete set of dimension six operators involving two top (or anti-top) quarks is introduced and ...the connection with all possible t- or s-channel heavy particle exchanges is established. Only in the former case, same and opposite sign top pair production can be related. We find that while current Tevatron data disfavor t-channel models, other production mechanisms are viable and can be tested at the LHC.
Is Vtb≃1? Alwall, J.; Frederix, R.; Gérard, J.-M. ...
The European physical journal. C, Particles and fields,
2/2007, Letnik:
49, Številka:
3
Journal Article
Recenzirano
Odprti dostop
The strongest constraint on Vtb presently comes from the 3×3 unitarity of the CKM matrix, which fixes Vtb to be very close to one. If unitarity is relaxed, current information from top production at ...Tevatron still leaves open the possibility that Vtb is sizably smaller than one. In minimal extensions of the standard model with extra heavy quarks, the unitarity constraints are much weaker, and the EW precision parameters entail the strongest bounds on Vtb. We discuss the experimental perspectives of discovering and identifying such new physics models at the Tevatron and the LHC, through a precise measurement of Vtb from the single top cross sections and by the study of processes where the extra heavy quarks are produced.
Many highly developed Monte Carlo tools for the evaluation of cross sections based on tree matrix elements exist and are used by experimental collaborations in high energy physics. As the evaluation ...of one-loop matrix elements has recently been undergoing enormous progress, the combination of one-loop matrix elements with existing Monte Carlo tools is on the horizon. This would lead to phenomenological predictions at the next-to-leading order level. This note summarises the discussion of the next-to-leading order multi-leg (NLM) working group on this issue which has been taking place during the workshop on Physics at TeV Colliders at Les Houches, France, in June 2009. The result is a proposal for a standard interface between Monte Carlo tools and one-loop matrix element programs.
Dedicated to the memory of, and in tribute to, Thomas Binoth, who led the effort to develop this proposal for Les Houches 2009. Thomas led the discussions, set up the subgroups, collected the contributions, and wrote and edited this paper. He made a promise that the paper would be on the arXiv the first week of January, and we are faithfully fulfilling his promise. In his honour, we would like to call this the Binoth Les Houches Accord.
A
bstract
We study the jets plus missing energy signature at the LHC in a scenario where the gravitino is very light and the gluino is the next-to-lightest supersymmetric particle and promptly decays ...into a gluon and a gravitino. We consider both associated gravitino production with a gluino and gluino pair production. By merging matrix elements with parton showers, we generate inclusive signal and background samples and show how information on the gluino and gravitino masses can be obtained by simple final state observables.
Current methods to extract the quark-mixing matrix element |
V
tb
| from single-top-production measurements assume that |
V
tb
|≫|
V
td
|,|
V
ts
|: top quarks decay into
b
quarks with 100 % branching ...fraction,
s
-channel single-top production is always accompanied by a
b
quark and initial-state contributions from
d
and
s
quarks in the
t
-channel production of single top quarks are neglected. Triggered by a recent measurement of the ratio
performed by the D0 collaboration, we consider a |
V
tb
| extraction method that takes into account non zero
d
- and
s
-quark contributions both in production and decay. We propose a strategy that allows to extract consistently and in a model-independent way the quark-mixing matrix elements |
V
td
|, |
V
ts
|, and |
V
tb
| from the measurement of
R
and from single-top measured event yields. As an illustration, we apply our method to the Tevatron data using a CDF analysis of the measured single-top event yield with two jets in the final state, one of which is identified as a
b
-quark jet. We constrain the |
V
tq
| matrix elements within a four-generation scenario by combining the results with those obtained from direct measurements in flavor physics and determine the preferred range for the top-quark decay width within different scenarios.
PDF
