共查询到20条相似文献,搜索用时 921 毫秒
1.
A. D. Martin W. J. Stirling R. S. Thorne G. Watt 《The European Physical Journal C - Particles and Fields》2009,64(4):653-680
We determine the uncertainty on the strong coupling α
S
due to the experimental errors on the data fitted in global analysis of hard-scattering data, within the standard framework
of leading-twist fixed-order collinear factorisation in the
[`(MS)]\overline{\mathrm{MS}}
scheme, finding that α
S
(M
Z
2)=0.1202−0.0015+0.0012 at next-to-leading order (NLO) and α
S
(M
Z
2)=0.1171−0.0014+0.0014 at next-to-next-to-leading order (NNLO). We do not address in detail the issue of the additional theory uncertainty on α
S
(M
Z
2), but an estimate is ±0.003 at NLO and at most ±0.002 at NNLO. We investigate the interplay between uncertainties on α
S
and uncertainties on parton distribution functions (PDFs). We show, for the first time, how both these sources of uncertainty
can be accounted for simultaneously in calculations of cross sections, and we provide eigenvector PDF sets with different
fixed α
S
values to allow further studies by the general user. We illustrate the application of these PDF sets by calculating cross
sections for W, Z, Higgs boson and inclusive jet production at the Tevatron and LHC. 相似文献
2.
A.D. Martin R.G. Roberts W.J. Stirling R.S. Thorne 《The European Physical Journal C - Particles and Fields》2000,14(1):133-145
W and Z bosons will be produced copiously at the LHC proton-proton collider. We study the parton distribution dependence of the total
production cross sections and rapidity distributions, paying particular attention to the uncertainties arising from uncertainties
in the parton distributions themselves. Variations in the gluon, the strong coupling, the sea quarks and the overall normalisation
are shown to lead to small but non-negligible variations in the cross section predictions. Ultimately, therefore, the measurement
of these cross sections will provide a powerful cross check on our knowledge of parton distributions and their evolution.
Received: 23 November 1999 / Published online: 6 April 2000 相似文献
3.
The inclusive production cross sections for W+,W− and Z0-bosons form important benchmarks for the physics at hadron colliders. We perform a detailed comparison of the predictions for these standard candles based on recent next-to-next-to-leading order (NNLO) parton parameterizations and new analyses including the combined HERA data, compare to all available experimental results, and discuss the predictions for present and upcoming RHIC, SPS, Tevatron and LHC energies. The rates for gauge boson production at the LHC can be rather confidently predicted with an accuracy of better than about 10% at NNLO. We also present detailed NNLO predictions for the Higgs boson production cross sections for Tevatron and LHC energies (1.96, 7, 8, 14 TeV), and propose a possible method to monitor the gluon distribution experimentally in the kinematic region close to the mass range expected for the Higgs boson. The production cross sections of the Higgs boson at the LHC are presently predicted with an accuracy of about 10–17%. The inclusion of the NNLO contributions is mandatory for achieving such accuracies since the total uncertainties are substantially larger at NLO. 相似文献
4.
A.D. Martin R.G. Roberts W.J. Stirling R.S. Thorne 《The European Physical Journal C - Particles and Fields》2003,28(4):455-473
We determine the uncertainties on observables arising from the errors on the experimental data that are fitted in the global
MRST2001 parton analysis. By diagonalizing the error matrix we produce sets of partons suitable for use within the framework
of linear propagation of errors, which is the most convenient method for calculating the uncertainties. Despite the potential
limitations of this approach we find that it can be made to work well in practice. This is confirmed by our alternative approach
of using the more rigorous Lagrange multiplier method to determine the errors on physical quantities directly. As particular
examples we determine the uncertainties on the predictions of the charged-current deep-inelastic structure functions, on the
cross-sections for W production and for Higgs boson production via gluon-gluon fusion at the Tevatron and the LHC, on the ratio of W- to W+ production at the LHC and on the moments of the non-singlet quark distributions. We discuss the corresponding uncertainties
on the parton distributions in the relevant x,Q2 domains. Finally, we briefly look at uncertainties related to the fit procedure, stressing their importance and using , and extractions of as examples. As a by-product of this last point we present a slightly updated set of parton distributions, MRST2002.
Received: 13 November 2002 / Published online: 5 May 2003
RID="a"
ID="a" Royal Society University Research Fellow 相似文献
5.
M.C. Kumar Prakash Mathews V. Ravindran 《The European Physical Journal C - Particles and Fields》2007,49(2):599-611
In the extra dimension models of ADD and RS we study the dependence of the various parton distribution functions on observables
of Drell–Yan processes to NLO in QCD at LHC and Tevatron energies. Uncertainties at LHC due to factorisation scales in going
from leading to next-to-leading order in QCD for the various distributions get reduced by about 2.75 times for a μF range 0.5Q<μF<1.5Q. Further uncertainties arising from the error on the experimental data are estimated using the MRST parton distribution
functions. 相似文献
6.
In this paper we consider soft processes at LHC energies in the framework of the constituent quark model. We show that this
rather naive model is able to describe all available soft process data at lower energies and to predict the behavior of the
total cross section, the elastic and diffractive cross sections at LHC energy. It turns out that the “input” pomeron that
has been used in this approach has parameters that are close to the so called “hard” pomeron with rather large intercept Δ≈0.12
and small value of the slope α′
P≈0.08 GeV-2. We show that the elastic amplitude has a minimum at impact parameter b=0 and a maximum at b≈2 GeV-1. Such a behavior is the result of overlapping of the parton clouds that belong to the different quarks in the hadron. 相似文献
7.
C.A. Nelson 《The European Physical Journal C - Particles and Fields》2001,19(2):323-337
Due to the absence of hadronization effects and the large mass, top quark decay will be uniquely sensitive to fundamental electroweak physics at the Tevatron, at the LHC, and at a
future linear collider. A “complete measurement” of the four helicity amplitudes in decay is possible by the combined use of andW polarimetry in stage-two spin-correlation functions (S2SC). In this paper, the most general Lorentz-invariant decay density
matrix is obtained for the decay sequence where and [or ], and likewise for . These density matrices are expressed in terms of b-polarimetry helicity parameters which enable a unique determination of the relative phases among the amplitudes. Thereby, S2SC distributions and single-sided b-W-interference distributions are expressed in terms of these parameters. The four b-polarimetry helicity parameters involving the amplitude are considered in detail. polarimetry signatures will not be suppressed in top quark analyses when final angles-and-energy variables are used for .
Received: 26 January 2001 / Published online: 15 March 2001 相似文献
8.
9.
J.?G.?Due?as N.?Gutierrez R.?Martínez F.?Ochoa 《The European Physical Journal C - Particles and Fields》2009,60(4):653-659
We analyse the possibilities to detect a new Z
′ boson in di-electron events at Tevatron and LHC in the framework of the 331 model with right-handed neutrinos. We also study
other fermions and Higgs events as final state at LHC. Using
collision data collected by the CDF II detector at Fermilab Tevatron, we find that the 331 Z
′ boson is excluded with masses below 920 GeV. For an integrated luminosity of 100 fb−1 at LHC, and considering a central value
GeV, we obtain the invariant-mass distribution in the process pp→Z
′→e
+
e
−, where a huge peak, corresponding to 800 signal events/(20 GeV), is found above the SM background. The number of di-electron
events vary from 50000 to 2400 in the mass range of
–2000 GeV. We also obtain branching ratios and cross sections in other fermion and Higgs channels at LHC, where a heavy top
quark T exhibits the biggest ratio with m
T
=300 GeV. 相似文献
10.
M. Carena S. Heinemeyer C. E. M. Wagner G. Weiglein 《The European Physical Journal C - Particles and Fields》2006,45(3):797-814
The Higgs boson search has shifted from LEP2 to the Tevatron and will subsequently move to the LHC. The current limits from
the Tevatron and the prospective sensitivities at the LHC are often interpreted in specific MSSM scenarios. For heavy Higgs
boson production and subsequent decay into
or τ+τ–, the present Tevatron data allow one to set limits in the MA–tan β plane for small MA and large tan β values. Similar channels have been explored for the LHC, where the discovery reach extends to higher values
of MA and smaller tan β. Searches for MSSM charged Higgs bosons, produced in top decays or in association with top quarks, have
also been investigated at the Tevatron and the LHC. We analyze the current Tevatron limits and prospective LHC sensitivities.
We discuss how robust they are with respect to variations of the other MSSM parameters and possible improvements of the theoretical
predictions for Higgs boson production and decay. It is shown that the inclusion of supersymmetric radiative corrections to
the production cross sections and decay widths leads to important modifications of the present limits on the MSSM parameter
space. The impact on the region where only the lightest MSSM Higgs boson can be detected at the LHC is also analyzed. We propose
to extend the existing benchmark scenarios by including additional values of the higgsino mass parameter μ. This affects only
slightly the search channels for a SM-like Higgs boson, while having a major impact on the searches for non-standard MSSM
Higgs bosons. 相似文献
11.
S. Alekhin J. Blümlein S. Moch 《The European Physical Journal C - Particles and Fields》2011,71(8):1723
The constraints of fixed-target DIS data in fits of parton distributions including QCD corrections to next-to-next-to leading
order are studied. We point out a potential problem in the analysis of the NMC data which can lead to inconsistencies in the
extracted value for α
s
(M
Z
) and the gluon distribution at higher orders in QCD. The implications for predictions of rates for Standard Model Higgs boson
production at hadron colliders are investigated. We conclude that the current range of excluded Higgs boson masses at the
Tevatron appears to be much too large. 相似文献
12.
Nikolaos Kidonakis 《Physics of Particles and Nuclei》2014,45(4):714-722
I discuss threshold resummation at NNLL accuracy in the standard moment-space approach in perturbative QCD for top-pair and single-top production. For top quark pair production I present new approximate NNLO results for the total cross section and for the top quark transverse momentum and rapidity distributions at 8 TeV LHC energy. I discuss the accuracy of the soft-gluon approximation and show that the NLO and NNLO approximate results from resummation are practically indistinguishable from exact NLO and partial NNLO results. For single top production I present new approximate NNLO results for the total cross sections in all three channels at the LHC and also for the top quark transverse momentum distributions in t-channel production and in top-quark associated production with a W boson. For both \(t\bar t\) and single-top production the agreement of theoretical results with LHC and Tevatron data is excellent. 相似文献
13.
M. Heyssler 《Zeitschrift fur Physik C Particles and Fields》1997,73(2):299-308
We give predictions for diffractive heavy flavour production at the Tevatron and the LHC in leading-order approximation. In the framework of these studies we use three different models for the partonic structure of the Pomeron recently proposed by Stirling and Kunszt. These Pomeron models are, despite being fitted to the same diffractive deep inelastic HERA data, very different in their parton content and taken together provide a powerful tool to probe the structure of the Pomeron. All models satisfy GLAP evolution and show a significant Q2 dependence. We give numerical predictions for single as well as double diffractive cross sections assuming a Donnachie-Landshoff-type Pomeron flux factor. 相似文献
14.
Z. Kunszt S. Moretti W. J. Stirling 《Zeitschrift fur Physik C Particles and Fields》1997,74(3):479-491
New theoretical and experimental information motivates a re-examination of the Standard Model Higgs production rates at the LHC pp collider. We present calculations of the relevant cross sections and branching ratios, including recently calculated QCD next-to-leading order corrections, new parton distributions fitted to recent HERA structure function data, and new values for electroweak input parameters, in particular for the top quark mass. Cross sections are calculated at two collider energies, √s = 10 TeV and 14 TeV. 相似文献
15.
A. Cafarella C. Corianò M. Guzzi J. Smith 《The European Physical Journal C - Particles and Fields》2006,47(3):703-721
We present a detailed study of the total pp cross section for scalar Higgs production to next-to-next-to-leading order in
αs at LHC energies, and of the pp̄ cross section at the Tevatron, combining an implementation of the solutions of the parton
evolution equations at the three-loop order with the corresponding hard scatterings, evaluated at the same perturbative order.
Our solutions of the DGLAP equations are implemented directly in x-space and allow for the study of the dependence of the
results on the factorization (μF) and renormalization scales (μR) typical of a given process, together with the stability of the perturbative expansion. The input sets for the parton evolutions
are those given by Martin, Roberts, Stirling and Thorne and by Alekhin. Results for K-factors are also presented. The NNLO
corrections can be quite sizeable at typical collider energies. The stability region of the perturbative expansion is found
when μR>mH∼μF. 相似文献
16.
17.
A.D. Martin R.G. Roberts W.J. Stirling R.S. Thorne 《The European Physical Journal C - Particles and Fields》2000,18(1):117-126
We use the recent estimates of NNLO splitting functions, made by van Neerven and Vogt, to perform exploratory fits to deep
inelastic and related hard scattering data. We investigate the hierarchy of parton distributions obtained at LO, NLO and NNLO,
and, more important, the stability of the resulting predictions for physical observables. We use the longitudinal structure
function and the cross sections for W and Z hadroproduction as examples. For we find relatively poor convergence, with increasing order, at small x; whereas are much more reliably predicted.
Received: 7 September 2000 / Published online: 13 November 2000 相似文献
18.
A. Arbey M. Battaglia F. Mahmoudi 《The European Physical Journal C - Particles and Fields》2012,72(1):1847
We study the implications of LHC searches on SUSY particle spectra using flat scans of the 19-parameter pMSSM phase space.
We apply constraints from flavour physics, g
μ
−2, dark matter and earlier LEP and Tevatron searches. The sensitivity of the LHC SUSY searches with jets, leptons and missing
energy is assessed by reproducing with fast simulation the recent CMS analyses after validation on benchmark points. We present
results in terms of the fraction of pMSSM points compatible with all the constraints which are excluded by the LHC searches
with 1 fb−1 and 15 fb−1 as a function of the mass of strongly and weakly interacting SUSY particles. We also discuss the suppression of Higgs production
cross sections for the MSSM points not excluded and contrast the region of parameter space tested by the LHC data with the
constraints from dark matter direct detection experiments. 相似文献
19.
Lepton-pair production from deep inelastic scatteringin peripheral relativistic heavy ion collisions
U. Dreyer T. Baier K. Hencken D. Trautmann 《The European Physical Journal C - Particles and Fields》2006,45(3):783-795
We calculate the inelastic electron- and muon-pair production in peripheral relativistic heavy ion collisions in the region
of large Q2 of one of the photons. This offers a possibility to study the quark distribution functions in ions in "ultraperipheral heavy
ion collisions". The calculations are compared with those making use of the equivalent photon and the equivalent lepton approximation.
We compare the results for Pb-Pb and Pb-p collisions at RHIC (γ ≈ 100) and LHC (γ ≈ 3000) energies. Furthermore we include nuclear modifications to the parton distribution
functions in our calculations to study their effect on the cross sections. 相似文献
20.
C.-X. Yue L. Zhou S. Yang 《The European Physical Journal C - Particles and Fields》2006,48(1):243-249
We investigate the corrections of the “littlest” Higgs (LH) model and the SU(3) simple group model to single top production at the CERN Large Hadron Collider (LHC). We find that the new gauge bosons WH
± predicted by the LH model can generate significant contributions to single top production via the s-channel process. The correction terms for the tree-level Wqq’ couplings coming from the SU(3) simple group model can give large contributions to the cross sections of the t-channel single top production process. We expect that the effects of the LH model and the SU(3) simple group model on single top production can be detected at the LHC experiments. 相似文献