We review the present status of the determination of parton distribution functions (PDFs) in the light of the precision requirements for the LHC in Run 2 and other future hadron colliders. We provide ...brief reviews of all currently available PDF sets and use them to compute cross sections for a number of benchmark processes, including Higgs boson production in gluon–gluon fusion at the LHC. We show that the differences in the predictions obtained with the various PDFs are due to particular theory assumptions made in the fits of those PDFs. We discuss PDF uncertainties in the kinematic region covered by the LHC and on averaging procedures for PDFs, such as advocated by the PDF4LHC15 sets, and provide recommendations for the usage of PDF sets for theory predictions at the LHC.
A
bstract
The impact of measurements of heavy-flavour production in deep inelastic
ep
scattering and in
pp
collisions on parton distribution functions is studied in a QCD analysis at next-to-leading ...order. Recent combined results of inclusive and heavy-flavour produc- tion cross sections in deep inelastic scattering at HERA are investigated together with heavy-flavour production measurements at the LHC. Differential cross sections of charm- and beauty-hadron production measured by the LHCb collaboration at the centre-of-mass energies of 5, 7 and 13 TeV as well as the recent measurements of the ALICE experiment at the centre-of-mass energies of 5 and 7 TeV are explored. These data impose additional constraints on the gluon and the sea-quark distributions at low partonic fractions
x
of the proton momentum, down to
x ≈
10
−
6
. The impact of the resulting parton distribution function in the predictions for the prompt atmospheric-neutrino fluxes is studied.
We study the impact of the effect of multinucleon interactions in the reconstruction of the neutrino energy on the fit of the MiniBooNE data in terms of neutrino oscillations. We obtain some ...improvement of the fit of the MiniBooNE low-energy excess in the framework of two-neutrino oscillations and a shift of the allowed region in the sin super(2) 2vartheta-Deltam super(2) plane toward smaller values of sin super(2) 2vartheta and larger values of Deltam super(2). However, this effect is not enough to solve the problem of the appearance-disappearance tension in the global fit of short-baseline neutrino oscillation data.
A
bstract
We update predictions for lepton fluxes from the hadroproduction of charm quarks in the scattering of primary cosmic rays with the Earth’s atmosphere. The calculation of charm-pair ...hadroproduction applies the latest results from perturbative QCD through next-to-next-to-leading order and modern parton distributions, together with estimates on various sources of uncertainties. Our predictions for the lepton fluxes turn out to be compatible, within the uncertainty band, with recent results in the literature. However, by taking into account contributions neglected in previous works, our total uncertainties are much larger. The predictions are crucial for the interpretation of results from neutrino experiments like IceCube, when disentangling signals of neutrinos of astrophysical origin from the atmospheric background.
A
bstract
We present predictions for heavy-quark production at the Large Hadron Collider making use of the
MS
¯
and MSR renormalization schemes for the heavy-quark mass as alternatives to the widely ...used on-shell renormalization scheme. We compute single and double differential distributions including QCD corrections at next-to-leading order and investigate the renormalization and factorization scale dependence as well as the perturbative convergence in these mass renormalization schemes. The implementation is based on publicly available programs, MCFM and xFitter, extending their capabilities. Our results are applied to extract the top-quark mass using measurements of the total and differential
t
t
¯
production cross-sections and to investigate constraints on parton distribution functions, especially on the gluon distribution at low
x
values, from available LHC data on heavy-flavor hadro-production.
A
bstract
The hadroproduction of a
W
boson in association with a charm quark at the Large Hadron Collider is at the centre of current investigations due to its potential to probe the strangeness ...content of the proton. In this paper we present an implementation of the
W
+
c
production process in the PowHel event generator matched to the PYTHIA8 parton shower approach, allowing to obtain predictions for differential cross-sections with NLO QCD accuracy matched to the accuracy of the Shower Monte Carlo event generator. Effects of non-diagonal CKM matrix elements, finite charm quark mass and off-shell
W
decays including spin correlations are taken into account. We investigate the production of a leptonically decaying
W
boson in association with either a charmed meson (
W
±
+
D
∗∓
) or a charmed jet (
W
±
+
j
c
) and compare our predictions with particle-level measurements by the ATLAS and CMS collaborations at
s
= 7 and 13 TeV. The role of the so-called “opposite sign” and “same sign” contributions to the theoretical cross-sections is presented and discussed, pointing out the importance of including parton shower effects for a reliable estimate of the latter and a faithful comparison with experimental data.
A
bstract
We present predictions for the prompt-neutrino flux arising from the decay of charmed mesons and baryons produced by the interactions of high-energy cosmic rays in the Earth’s atmosphere, ...making use of a QCD approach on the basis of the general-mass variable-flavor-number scheme for the description of charm hadroproduction at NLO, complemented by a consistent set of fragmentation functions. We compare the theoretical results to those already obtained by our and other groups with different theoretical approaches. We provide comparisons with the experimental results obtained by the IceCube Collaboration in two different analyses and we discuss the implications for parton distribution functions.
Based on the OPP technique and the HELAC framework, HELAC-1LOOP is a program that is capable of numerically evaluating QCD virtual corrections to scattering amplitudes. A detailed presentation of the ...algorithm is given, along with instructions to run the code and benchmark results. The program is part of the HELAC-NLO framework that allows for a complete evaluation of QCD NLO corrections.
Program title:HELAC-1LOOP
Catalogue identifier: AEOC_v1_0
Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEOC_v1_0.html
Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland
Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html
No. of lines in distributed program, including test data, etc.: 290945
No. of bytes in distributed program, including test data, etc.: 3013326
Distribution format: tar.gz
Programming language: Fortran (gfortran(http://gcc.gnu.org/fortran/), lahey95 (http://www.lahey.com), ifort3(http://software.intel.com)).
Computer: Any.
Operating system: Linux, Unix, Mac OS.
Classification: 11.1.
Nature of problem:
The evaluation of virtual one-loop amplitudes for multi-particle scattering is a long-standing problem 1. In recent years the OPP reduction technique 2 opened the road for a fully numerical approach based on the evaluation of the one-loop amplitude for well-defined values of the loop momentum.
Solution method:
By using HELAC 3–5 and CutTools 6, HELAC-1LOOP is capable of evaluating QCD virtual corrections 7. The one-loop n-particle amplitudes are constructed as part of the n+2 tree-order ones, by using the basic recursive algorithm used in HELAC. A Les Houches Event (LHE) file is produced, combining the complete information from tree-order and virtual one-loop contributions. In conjunction with real corrections, obtained with the use of HELAC-DIPOLES 8, the full NLO corrections can be computed. The program has been successfully used in many applications.
Running time:
Depending on the number of particles and generated events from seconds to days.
References:
1R.K. Ellis, Z. Kunszt, K. Melnikov and G. Zanderighi, arXiv:1105.4319hepph.2G. Ossola, C. G. Papadopoulos and R. Pittau, Nucl. Phys. B 763 (2007) 147 arXiv:hep-ph/0609007.3A. Kanaki and C. G. Papadopoulos, Comput. Phys. Commun. 132 (2000) 306 arXiv:hep-ph/0002082.4C. G. Papadopoulos, Comput. Phys. Commun. 137 (2001) 247 arXiv:hepph/ 0007335.5A. Cafarella, C. G. Papadopoulos and M. Worek, Comput. Phys. Commun. 180 (2009) 1941 arXiv:0710.2427 hep-ph.6G. Ossola, C. G. Papadopoulos and R. Pittau, JHEP 0803 (2008) 042 arXiv:0711.3596 hep-ph.7A. van Hameren, C. G. Papadopoulos and R. Pittau, JHEP 0909, 106 (2009) arXiv:0903.4665 hep-ph.8M. Czakon, C. G. Papadopoulos and M. Worek, JHEP 0908, 085 (2009) arXiv:0905.0883 hep-ph.
The impact of recent measurements of heavy-flavour production in deep inelastic
ep
scattering and in
pp
collisions on parton distribution functions is studied in a QCD analysis in the fixed-flavour ...number scheme at next-to-leading order. Differential cross sections of charm- and beauty-hadron production measured by LHCb are used together with inclusive and heavy-flavour production cross sections in deep inelastic scattering at HERA. The heavy-flavour data of the LHCb experiment impose additional constraints on the gluon and the sea-quark distributions at low partonic fractions
x
of the proton momentum, down to
x
∼
5
×
10
-
6
. This kinematic range is currently not covered by other experimental data in perturbative QCD fits.
A
bstract
Effects on atmospheric prompt neutrino fluxes of present uncertainties affecting the nucleon composition are studied by using the PROSA fit to parton distribution functions (PDFs). The ...PROSA fit extends the precision of the PDFs to low
x
, which is the kinematic region of relevance for high-energy neutrino production, by taking into account LHCb data on charm and bottom hadroproduction collected at the center-of-mass energy of
s
=
7
TeV. In the range of neutrino energies explored by present Very Large Volume Neutrino Telescopes, it is found that PDF uncertainties are far smaller with respect to those due to renormalization and factorization scale variation and to assumptions on the cosmic ray composition, which at present dominate and limit our knowledge of prompt neutrino fluxes. A discussion is presented on how these uncertainties affect the expected number of atmospheric prompt neutrino events in the analysis of high-energy events characterized by interaction vertices fully contained within the instrumented volume of the detector, performed by the IceCube collaboration.
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