Automation of one-loop QCD computations Hirschi, Valentin; Frederix, Rikkert; Frixione, Stefano ...
The journal of high energy physics,
05/2011, Volume:
2011, Issue:
5
Journal Article
Peer reviewed
Open access
We present the complete automation of the computation of one-loop QCD corrections, including UV renormalization, to an arbitrary scattering process in the Standard Model. This is achieved by ...embedding the OPP integrand reduction technique, as implemented in CutTools, into the MadGraph framework. By interfacing the tool so constructed, which we dub MadLoop, with MadFKS, the fully automatic computation of any infrared-safe observable at the next-to-leading order in QCD is attained. We demonstrate the flexibility and the reach of our method by calculating the production rates for a variety of processes at the 7 TeV LHC.
A
bstract
We present a new calculation of the energy distribution of high-energy neutrinos from the decay of charm and bottom hadrons produced at the Large Hadron Collider (LHC). In the kinematical ...region of very forward rapidities, heavy-flavor production and decay is a source of tau neutrinos that leads to thousands of charged-current tau neutrino events in a 1 m long, 1 m radius lead neutrino detector at a distance of 480 m from the interaction region. In our computation, next-to-leading order QCD radiative corrections are accounted for in the production cross-sections. Non-perturbative intrinsic-
k
T
effects are approximated by a simple phenomenological model introducing a Gaussian
k
T
-smearing of the parton distribution functions, which might also mimic perturbative effects due to multiple initial-state soft-gluon emissions. The transition from partonic to hadronic states is described by phenomenological fragmentation functions. To study the effect of various input parameters, theoretical predictions for
D
s
±
production are compared with LHCb data on double-differential cross-sections in transverse momentum and rapidity. The uncertain- ties related to the choice of the input parameter values, ultimately affecting the predictions of the tau neutrino event distributions, are discussed. We consider a 3+1 neutrino mixing scenario to illustrate the potential for a neutrino experiment to constrain the 3+1 parameter space using tau neutrinos and antineutrinos. We find large theoretical uncertainties in the predictions of the neutrino fluxes in the far-forward region. Untangling the effects of tau neutrino oscillations into sterile neutrinos and distinguishing a 3+1 scenario from the standard scenario with three active neutrino flavours, will be challenging due to the large theoretical uncertainties from QCD.
A
bstract
New experiments dealing with neutrinos in the far-forward region at the Large Hadron Collider (LHC) are under design or already in preparation. Two of them, FASER
ν
and SND@LHC, are ...expected to be active during Run 3 and have the potential to detect the interactions of
ν
and
ν
¯
that come from high-energy collisions in one of the LHC interaction points, extracted along the direction tangent to the beam line. Tau neutrinos and antineutrinos come predominantly from
D
s
±
production in
pp
collisions, followed by the leptonic decay of these mesons. Neutrino pseudorapidities in the range of
η >
6
.
9 and
η >
8
.
9 are relevant to these future experiments. At such pseudorapidities at high energies, QCD theoretical predictions for the flux of
ν
τ
plus
ν
¯
τ
rely on parton distribution functions (PDFs) in a combination of very small and large parton
−x
values. We evaluate PDF un certainties affecting the flux of
ν
τ
+
ν
¯
τ
produced by
D
s
±
decay in the far forward region at the LHC. Next-to-leading order (NLO) QCD uncertainties are included in the calculation of
D
s
±
production and NLO PDF sets are used for consistency. The theoretical uncertainty associated with the 40 PDF sets of the PROSA19 group amounts to
±
(20
−
30)% for the (
ν
τ
+
ν
¯
τ
) number of charged-current (CC) events. Scale uncertainties are much larger, resulting in a range of CC event predictions from ~70% lower to ~90% higher than the central prediction. A comparison of the predictions with those obtained using as input the central PDFs from the 3-flavour NLO PDF sets of the CT14, ABMP16 and NNPDF3.1 collaborations show that far-forward neutrino energy distributions vary by as much as a factor of ~2 – 4 relative to the PROSA19 predictions at TeV neutrino energies. The Forward Physics Facility in the high luminosity LHC era will provide data capable of constraining NLO QCD evaluations with these PDF sets.
A
bstract
The high-energy atmospheric neutrino flux is dominated by neutrinos from the decays of charmed hadrons produced in the forward direction by cosmic ray interactions with air nuclei. We ...evaluate the charm contributions to the prompt atmospheric neutrino flux as a function of the center-of-mass energy
s
of the hadronic collision and of the center-of-mass rapidity
y
of the produced charm hadron. Uncertainties associated with parton distribution functions are also evaluated as a function of
y
. We find that the
y
coverage of LHCb for forward heavy-flavour production, complemented by the angular coverage of present and future forward neutrino experiments at the LHC, bracket the most interesting
y
regions for the prompt atmospheric neutrino flux. At
s
= 14 TeV foreseen for the HL-LHC phase, nucleon collisions in air contribute to the prompt neutrino flux prominently below
E
ν
~ 10
7
GeV. Measurements of forward charm and/or forward neutrinos produced in hadron collisions up to
s
= 100 TeV, which might become possible at the FCC, are relevant for the prompt atmospheric neutrino flux up to
E
ν
= 10
8
GeV and beyond.
The Forward Physics Facility (FPF) is a proposal to create a cavern with the space and infrastructure to support a suite of far-forward experiments at the Large Hadron Collider during the High ...Luminosity era. Located along the beam collision axis and shielded from the interaction point by at least 100 m of concrete and rock, the FPF will house experiments that will detect particles outside the acceptance of the existing large LHC experiments and will observe rare and exotic processes in an extremely low-background environment. In this work, we summarize the current status of plans for the FPF, including recent progress in civil engineering in identifying promising sites for the FPF and the experiments currently envisioned to realize the FPF’s physics potential. We then review the many Standard Model and new physics topics that will be advanced by the FPF, including searches for long-lived particles, probes of dark matter and dark sectors, high-statistics studies of TeV neutrinos of all three flavors, aspects of perturbative and non-perturbative QCD, and high-energy astroparticle physics.
Prospects for quarkonium-production studies accessible during the upcoming high-luminosity phases of the CERN Large Hadron Collider operation after 2021 are reviewed. Current experimental and ...theoretical open issues in the field are assessed together with the potential for future studies in quarkonium-related physics. This will be possible through the exploitation of the huge data samples to be collected in proton–proton, proton–nucleus and nucleus–nucleus collisions, both in the collider and fixed-target modes. Such investigations include, among others, those of: (i) J/ψ and Υ produced in association with other hard particles; (ii) χc,b and ηc,b down to small transverse momenta; (iii) the constraints brought in by quarkonia on gluon PDFs, nuclear PDFs, TMDs, GPDs and GTMDs, as well as on the low-x parton dynamics; (iv) the gluon Sivers effect in polarised-nucleon collisions; (v) the properties of the quark–gluon plasma produced in ultra-relativistic heavy-ion collisions and of collective partonic effects in general; and (vi) double and triple parton scatterings.
Phenomenology of tt¯j + X production at the LHC Alioli, Simone; Fuster, Juan; Garzelli, Maria Vittoria ...
The journal of high energy physics,
05/2022, Volume:
2022, Issue:
5
Journal Article
Peer reviewed
Open access
A
bstract
We present phenomenological results for
t
t
¯
j
+
X
production at the Large Hadron Collider, of interest for designing forthcoming experimental analyses of this process. We focus on those ...cases where the
t
t
¯
j
+
X
process is considered as a signal. We discuss present theoretical uncertainties and the dependence on relevant input parameters entering the computation. For the
R
distribution, which depends on the invariant mass of the
t
t
¯
j
-system, we present reference predictions in the on-shell,
MS
¯
and MSR top-quark mass renormalization schemes, applying the latter scheme to this process for the first time. Our conclusions are particularly interesting for those analyses aiming at extracting the top-quark mass from cross-section measurements.
A
bstract
We present the computation of the differential cross section for the process
p p
(
p
¯
) → (W
+
W
−
b
b
¯
→) e
+
ν
e
μ
−
ν
¯
μ
b
b
¯
+
X
at NLO QCD accuracy matched to Shower Monte Carlo ...(SMC) simulations using PowHel, on the basis of the interface between HELAC-NLO and POWHEG-BOX. We include all resonant and non-resonant contributions. This is achieved by fully taking into account the effect of off-shell t-quarks and off-shell W-bosons in the complex mass scheme. We also present a program called DECAYER that can be used to let the t-quarks present in the event files for
p p
(
p
¯
) → t
t
¯
X processes decay including both the finite width of the t-quarks and spin correlations. We present predictions for both the Tevatron and the LHC, with emphasis on differences emerging from three different W
+
W
−
b
b
¯
hadroproduction computations: (i) full implementation of the
p p
(
p
¯
) → W
+
W
−
b
b
¯
process, (ii) generating on-shell t-quarks pushed off-shell with a Breit-Wigner finite width and decayed by Decayer, and (iii) on-shell t-quark production followed by decay in the narrow width approximation, as described by the SMC.
PDF
