The scattering rate of multi-TeV and PeV energy neutrinos is fast becoming an interesting topic in (astro)particle-physics. This is due to experimental progress at Neutrino Telescopes such as IceCube ...which have begun to gain sensitivity to the flux of neutrinos in this energy range. In view of this, a precise calculation of the scattering rate of neutrinos upon atoms is presented. The two main components of the calculation are the differential cross-section predictions for neutrino scattering upon an atomic nucleus (such as that of water), as well as upon atomic electrons. In the first case, the predictions for neutrino-nucleus cross-sections in charged- and neutral-current scattering are refined by including resonant contributions generated within the photon field of the nucleus, which alter the considered distributions by ≈2%. In the latter case, radiative corrections are provided for all 2→2 scattering processes of the form νee−→ff¯′. For antineutrino energies of Eνe ≈ 6 PeV, where these processes become resonantly enhanced (the Glashow resonance) and dominate the total cross-section, these corrections amount to ≈−10%.
A
bstract
The LHCb collaboration has recently performed a measurement of the production rate of inclusive
B
hadron production (
pp
→
BX
) at both 7 and 13 TeV centre-of-mass (CoM) energies. As part ...of this measurement, the ratio of these two cross section measurements has been presented differentially in
B
hadron pseudorapidity within the range of
η
B
∈ 2
.
0
,
5
.
0. A large tension (4
σ
) is observed for the ratio measurement in the lower pseudorapidity range of
η
B
∈ 2
.
0
,
3
.
0, where the data is observed to exceed theoretical predictions, while consistency is found at larger
η
B
values. This behaviour is not expected within perturbative QCD, and can only be achieved by introducing ad-hoc features into the structure of the non-perturbative gluon PDF within the region of
x
∈ 10
−3
,
10
−4
. Specifically, the gluon PDF must grow extremely quickly with decreasing
x
within this kinematic range, closely followed by a period of decelerated growth. However, such behaviour is highly disfavoured by global fits of proton structure. Further studies of the available LHCb
B
and
D
hadron cross section data, available for a range of CoM energies, indicate systematic tension in the (pseudo)rapidity region of 2
.
0
,
2
.
5.
Neutrino telescopes as QCD microscopes Bertone, Valerio; Gauld, Rhorry; Rojo, Juan
The journal of high energy physics,
01/2019, Volume:
2019, Issue:
1
Journal Article
Peer reviewed
Open access
A
bstract
We present state-of-the-art predictions for the ultra-high energy (UHE) neutrino-nucleus cross-sections in charged- and neutral-current scattering. The calculation is performed in the ...framework of collinear factorisation at NNLO, extended to include the resummation of small-
x
BFKL effects. Further improvements are made by accounting for the free-nucleon PDF constraints provided by
D
-meson data from LHCb and assessing the impact of nuclear corrections and heavy-quark mass effects, which are treated at NLO. The calculations presented here should play an important role in the interpretation of future data from neutrino telescopes such as IceCube and KM3NeT, and highlight the opportunities that astroparticle experiments offer to study the strong interactions.
The prediction of differential cross-sections in hadron-hadron
scattering processes is typically performed in a scheme where the
heavy-flavour quarks (
c, b, t
c
,
b
,
t
)
are treated either as ...massless or massive partons. In this work, a
method to describe the production of colour-singlet processes which
combines these two approaches is presented. The core idea is that the
contribution from power corrections involving the heavy-quark mass can
be numerically isolated from the rest of the massive computation.
These power corrections can then be combined with a massless computation
(where they are absent), enabling the construction of differential
cross-section predictions in a massive variable flavour number scheme.
As an example, the procedure is applied to the low-mass Drell-Yan
process within the LHCb fiducial region, where predictions for the
rapidity and transverse-momentum distributions of the lepton pair are
provided. To validate the procedure, it is shown how the
n_f
n
f
-dependent
coefficient of a massless computation can be recovered from the massless
limit of the massive one. This feature is also used to differentially
extract the massless
N^3LO
N
3
L
O
coefficient of the Drell-Yan process in the gluon-fusion channel.
A
bstract
The recent observation by the IceCube experiment of cosmic neutrinos at energies up to a few PeV heralds the beginning of neutrino astronomy. At such high energies, the ‘conventional’ ...neutrino flux is suppressed and the ‘prompt’ component from charm meson decays is expected to become the dominant background to astrophysical neutrinos. Charm production at high energies is however theoretically uncertain, both since the scale uncertainties of the NLO calculation are large, and also because it is directly sensitive to the poorly-known gluon PDF at small-
x
. In this work we provide detailed perturbative QCD predictions for charm and bottom production in the forward region, and validate them by comparing with recent data from the LHCb experiment at 7 TeV. Finding good agreement between data and theory, we use the LHCb measurements to constrain the small-
x
gluon PDF, achieving a substantial reduction in its uncertainties. Using these improved PDFs, we provide predictions for charm and bottom production at LHCb at 13 TeV, as well as for the ratio of cross-sections between 13 and 7 TeV. The same calculations are used to compute the energy distribution of neutrinos from charm decays in
pA
collisions, a key ingredient towards achieving a theoretically robust estimate of charm-induced backgrounds at neutrino telescopes.
SMEFT at NNLO+PS: Vh production Gauld, Rhorry; Haisch, Ulrich; Schnell, Luc
The journal of high energy physics,
01/2024, Volume:
2024, Issue:
1
Journal Article
Peer reviewed
Open access
A
bstract
In the context of the Standard Model effective field theory (SMEFT) the next-to-next-to-leading (NNLO) QCD corrections to the Higgsstrahlungs (
Vh
) processes in hadronic collisions are ...calculated and matched to a parton shower (PS). NNLO+PS precision is achieved for the complete sets of SMEFT operators that describe the interactions between the Higgs and two vector bosons and the couplings of the Higgs, a
W
or a
Z
boson, and light fermions. A POWHEG-BOX implementation of the computed NNLO SMEFT corrections is provided that allows for a realistic exclusive description of
Vh
production at the level of hadronic events. This feature makes it an essential tool for future Higgs characterisation studies by the ATLAS and CMS collaborations. Utilising our new Monte Carlo code the numerical impact of NNLO+PS corrections on the kinematic distributions in
pp
→
Zh
→
ℓ
+
ℓ
−
h
production is explored, employing well-motivated SMEFT benchmark scenarios.
A
bstract
The recent observation of very high energy cosmic neutrinos by IceCube heralds the beginning of neutrino astronomy. At these energies, the dominant background to the astrophysical signal is ...the flux of ‘prompt’ neutrinos, arising from the decay of charmed mesons produced by cosmic ray collisions in the atmosphere. In this work we provide predictions for the prompt atmospheric neutrino flux in the framework of perturbative QCD, using state-of-the-art Monte Carlo event generators. Our calculation includes the constraints set by charm production measurements from the LHCb experiment at 7 TeV, recently validated with the corresponding 13 TeV data. Our result for the prompt flux is a factor of about 2 below the previous benchmark calculation, in general agreement with other recent estimates, but with an improved estimate of the uncertainty. This alleviates the existing tension between the theoretical prediction and IceCube limits, and suggests that a direct detection of the prompt flux is imminent.
We present an updated determination of nuclear parton distributions (nPDFs) from a global NLO QCD analysis of hard processes in fixed-target lepton-nucleus and proton-nucleus together with collider ...proton-nucleus experiments. In addition to neutral- and charged-current deep-inelastic and Drell–Yan measurements on nuclear targets, we consider the information provided by the production of electroweak gauge bosons, isolated photons, jet pairs, and charmed mesons in proton-lead collisions at the LHC across centre-of-mass energies of 5.02 TeV (Run I) and 8.16 TeV (Run II). For the first time in a global nPDF analysis, the constraints from these various processes are accounted for both in the nuclear PDFs and in the free-proton PDF baseline. The extensive dataset underlying the nNNPDF3.0 determination, combined with its model-independent parametrisation, reveals strong evidence for nuclear-induced modifications of the partonic structure of heavy nuclei, specifically for the small-
x
shadowing of gluons and sea quarks, as well as the large-
x
anti-shadowing of gluons. As a representative phenomenological application, we provide predictions for ultra-high-energy neutrino-nucleon cross-sections, relevant for data interpretation at neutrino observatories. Our results provide key input for ongoing and future experimental programs, from that of heavy-ion collisions in controlled collider environments to the study of high-energy astrophysical processes.
A
bstract
We present a phenomenological analysis of asymmetric bottom- and charm-quark production within the LHCb acceptance relevant for
pp
collisions at
s
=
13
TeV. Predictions are provided for ...both anti-
k
t
bottom- and charm-jet pairs, which are kept differentially with respect to the invariant mass of the jet pair. It is quantified how data in this region can provide sensitivity to the couplings of the
Z
boson to heavy quarks, and we investigate what precision is needed to compete with LEP. We also discuss how asymmetry and rate measurements can provide constraints on a particular class of new-physics models, which contains gauge bosons with small/moderate couplings to light/heavy quarks and masses of the order of 100GeV. Predictions are obtained including all relevant QCD and QED/weak contributions up to next-to-leading order, which have been implemented in a Fortran code which allows to directly compute the asymmetric cross sections. We provide all relevant analytic formulas for our computations.
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