981 research outputs found
Threshold corrections to rapidity distributions of Z and W^\pm bosons beyond N^2 LO at hadron colliders
Threshold enhanced perturbative QCD corrections to rapidity distributions of
and bosons at hadron colliders are presented using the Sudakov
resummed cross sections at NLO level. We have used renormalisation group
invariance and the mass factorisation theorem that these hard scattering cross
sections satisfy to construct the QCD amplitudes. We show that these higher
order threshold QCD corrections stabilise the theoretical predictions for
vector boson production at the LHC under variations of both renormalisation and
factorisation scales.Comment: 17 pages, 8 eps figures. This paper is dedicated to the memory of
W.L.G.A.M. van Neerve
Soft Resummation of Quark Anomalous Dimensions and Coefficient Functions in MS-bar Factorization
The asymptotic behaviour at large N of the MS-bar quark anomalous dimensions
is derived to all orders assuming only MS-bar factorization and standard
results for the exponentiation of soft logarithms in the quark initiated bare
cross sections for deep inelastic scattering and Drell-Yan. The result is then
used to write the MS-bar quark coefficient functions in a form in which all
terms of are resummed.Comment: 12 page
Parton distribution functions from the precise NNLO QCD fit
We report the parton distribution functions (PDFs) determined from the NNLO
QCD analysis of the world inclusive DIS data with account of the precise NNLO
QCD corrections to the evolution equations kernel. The value of strong coupling
constant \alpha_s^{NNLO}(M_Z)=0.1141(14), in fair agreement with one obtained
using the earlier approximate NNLO kernel by van Neerven-Vogt. The intermediate
bosons rates calculated in the NNLO using obtained PDFs are in agreement to the
latest Run II results.Comment: 8 pages, LATEX, 2 figures (EPS
Threshold Corrections in Precision LHC Physics: QED otimes QCD
With an eye toward LHC processes in which theoretical precisions of 1 percent
are desired, we introduce the theory of the simultaneous YFS resummation of QED
and QCD to compute the size of the expected resummed soft radiative threshold
effects in precision studies of heavy particle production at the LHC. Our
results show that both QED and QCD soft threshold effects must be controlled to
be on the conservative side to achieve such precision goals.Comment: 4 pages, no figures; presented by B.F.L. Ward in DPF200
Resummation of Hadroproduction Cross-sections at High Energy
We reconsider the high energy resummation of photoproduction,
electroproduction and hadroproduction cross-sections, in the light of recent
progress in the resummation of perturbative parton evolution to NLO in
logarithms of Q^2 and x. We show in particular that the when the coupling runs
the dramatic enhancements seen at fixed coupling, due to infrared singularities
in the partonic cross-sections, are substantially reduced, to the extent that
they are largely accounted for by the usual NLO and NNLO perturbative
corrections. This leads to a novel explanation of the large K-factors commonly
found in perturbative calculations of hadroproduction cross-sections. We give
numerical estimates of high energy resummation effects for inclusive
B-production, inclusive jets, Drell-Yan and vector boson production, along with
their rapidity distributions. We find that resummation modifies the
B-production cross-section at the LHC by at most 15%, but that the enhancement
of gluonic W-production may be as large as 50% at large rapidities.Comment: 49 pages, 25 figures, version to be published in Nucl Phys
Complexity of the Ruminococcus flavefaciens FD-1 cellulosome reflects an expansion of family-related protein-protein interactions
This work was supported in part by the European Union, Area NMP.2013.1.1â2: Self-assembly of naturally occurring nanosystems: CellulosomePlus Project number: 604530, and by the EU Seventh Framework Programme (FP7 2007â2013) under the WallTraC project (Grant Agreement no 263916), and BioStruct-X (grant agreement no 283570). This paper reflects the authorâs views only. The European Community is not liable for any use that may be made of the information contained herein. CMGAF is also supported by Fundação para a CiĂȘncia e a Tecnologia (Lisbon, Portugal) through grants PTDC/BIA-PRO/103980/2008 and EXPL/BIA-MIC/1176/2012. EAB is also funded by a grant (No. 1349/13) from the Israel Science Foundation (ISF), Jerusalem, Israel and by a grant (No. 2013284) from the U.S.-Israel Binational Science Foundation (BSF). E.A.B. is the incumbent of The Maynard I. and Elaine Wishner Chair of Bio-organic Chemistry.Peer reviewedPublisher PD
at Hadron Colliders
We study the observability for a lepton flavor-changing decay of a Higgs
boson at hadron colliders. Flavor-changing couplings of a Higgs
boson exist at tree level in models with multiple Higgs doublets. The
coupling is particularly motivated by the favorable intepretation of
oscillation. We find that at the Tevatron Run II the unique
signature could serve as the Higgs discovery channel, surpassing
expectations for Higgs boson searches in the SM and in a large parameter region
of the MSSM. The sensitivity will be greatly improved at the LHC, beyond the
coverage at a muon collider Higgs factory.Comment: Version to appear in PR
Observational tests of interstellar methanol formation
Context. It has been established that the classical gas-phase production of interstellar methanol (CH3OH) cannot explain observed abundances. Instead it is now generally thought that the main formation path has to be by successive hydrogenation of solid CO on interstellar grain surfaces.
Aims: While theoretical models and laboratory experiments show that methanol is efficiently formed from CO on cold grains, our aim is to test this scenario by astronomical observations of gas associated with young stellar objects (YSOs).
Methods: We have observed the rotational transition quartets J = 2K - 1K of 12CH3OH and 13CH3OH at 96.7 and 94.4 GHz, respectively, towards a sample of massive YSOs in different stages of evolution. In addition, the J = 1-0 transitions of 12C18O and 13C18O were observed towards some of these sources. We use the 12C/13C ratio to discriminate between gas-phase and grain surface origin: If methanol is formed from CO on grains, the ratios should be similar in CH3OH and CO. If not, the ratio should be higher in CH3OH due to 13C fractionation in cold CO gas. We also estimate the abundance ratios between the nuclear spin types of methanol (E and A). If methanol is formed on grains, this ratio is likely to have been thermalized at the low physical temperature of the grain, and therefore show a relative over-abundance of A-methanol.
Results: We show that the 12C/13C isotopic ratio is very similar in gas-phase CH3OH and C18O, on the spatial scale of about 40", towards four YSOs. For two of our sources we find an overabundance of A-methanol as compared to E-methanol, corresponding to nuclear spin temperatures of 10 and 16 K. For the remaining five sources, the methanol E/A ratio is less than unity.
Conclusions: While the 12C/13C ratio test is consistent with methanol formation from hydrogenation of CO on grain surfaces, the result of the E/A ratio test is inconclusive
Oblique Corrections To The W Width
The lowest-order expression for the partial width to , has no oblique radiative
corrections from new physics if the measured mass is used. Here GeV/ is the muon decay constant. For
the present value of GeV/, and with
GeV, one expects MeV. The total
width is also expected to lack oblique corrections from
new physics, so that . Present data are consistent with this prediction.Comment: 15 pages (LaTeX), one PostScript figure not included (available upon
request
Anomalous dimension of the gluon operator in pure Yang-Mills theory
We present new one loop calculations that confirm the theorems of Joglekar
and Lee on the renormalization of composite operators. We do this by
considering physical matrix elements with the operators inserted at non-zero
momentum. The resulting IR singularities are regulated dimensionally. We show
that the physical matrix element of the BRST exact gauge variant operator which
appears in the energy- momentum tensor is zero. We then show that the physical
matrix elements of the classical energy-momentum tensor and the gauge invariant
twist two gluon operator are independent of the gauge fixing parameter. A
Sudakov factor appears in the latter cases. The universality of this factor and
the UV finiteness of the energy-momentum tensor provide another method of
finding the anomalous dimension of the gluon operator. We conjecture that this
method applies to higher loops and takes full advantage of the triangularity of
the mixing matrix.Comment: submitted to Phys. Rev. D, 18 pages LaTEX uses psfig and revtex
macros, figures appended as uuencoded Postscript file (complete Postsript
version including figures available via anonymous ftp from
ftp://max.physics.sunysb.edu/preprints/harris/paper.ps.Z), ITP-SB-94-3
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