A
bstract
We consider QCD radiative corrections to Higgs boson pair production through gluon fusion in proton collisions. We combine the exact next-to-leading order (NLO) contribution, which features ...two-loop virtual amplitudes with the full dependence on the top quark mass
M
t
, with the next-to-next-to-leading order (NNLO) corrections computed in the large-
M
t
approximation. The latter are improved with different reweighting techniques in order to account for finite-
M
t
effects beyond NLO. Our reference NNLO result is obtained by combining one-loop double-real corrections with full
M
t
dependence with suitably reweighted real-virtual and double-virtual contributions evaluated in the large-
M
t
approximation. We present predictions for inclusive cross sections in
pp
collisions at
s
= 13, 14, 27 and 100 TeV and we discuss their uncertainties due to missing
M
t
effects. Our approximated NNLO corrections increase the NLO result by an amount ranging from +12% at
s
=
13
TeV to +7% at
s
=
100
TeV, and the residual uncertainty of the inclusive cross section from missing
M
t
effects is estimated to be at the few percent level. Our calculation is fully differential in the Higgs boson pair and the associated jet activity: we also present predictions for various differential distributions at
s
=
14
and 100 TeV, and discuss the size of the missing
M
t
effects, which can be larger, especially in the tails of certain observables. Our results represent the most advanced perturbative prediction available to date for this process.
A
bstract
We present next-to-leading order (NLO) predictions including QCD and electroweak (EW) corrections for the production and decay of off-shell electroweak vector bosons in association with up ...to two jets at the 13 TeV LHC. All possible dilepton final states with zero, one or two charged leptons that can arise from off-shell W and Z bosons or photons are considered. All predictions are obtained using the automated implementation of NLO QCD+EW corrections in the O
pen
Loops matrix-element generator combined with the Munich and Sherpa Monte Carlo frameworks. Electroweak corrections play an especially important role in the context of BSM searches, due to the presence of large EW Sudakov logarithms at the TeV scale. In this kinematic regime, important observables such as the jet transverse momentum or the total transverse energy are strongly sensitive to multijet emissions. As a result, fixed-order NLO QCD+EW predictions are plagued by huge QCD corrections and poor theoretical precision. To remedy this problem we present an approximate method that allows for a simple and reliable implementation of NLO EW corrections in the MePs@Nlo multijet merging framework. Using this general approach we present an inclusive simulation of vector-boson production in association with jets that guarantees NLO QCD+EW accuracy in all phase-space regions involving up to two resolved jets.
A
bstract
We present next-to-leading order (NLO) calculations including QCD and electroweak (EW) corrections for 2
ℓ
2
ν
diboson signatures with two opposite-charge leptons and two neutrinos. ...Specifically, we study the processes
pp
→
e
+
μ
−
ν
e
ν
¯
μ
and
pp
→
e
+
e
−
ν
ν
¯
, including all relevant off-shell diboson channels,
W
+
W
−
,
ZZ
, γ
Z
, as well as non-resonant contributions. Photon-induced processes are computed at NLO EW, and we discuss subtle differences related to the definition and the renormalisation of the coupling
α
for processes with initial- and final-state photons. All calculations are performed within the automated M
unich
/S
herpa
+O
pen
L
oops
frameworks, and we provide numerical predictions for the LHC at 13 TeV. The behaviour of the corrections is investigated with emphasis on the high-energy regime, where NLO EW effects can amount to tens of percent due to large Sudakov logarithms. The interplay between
W W
and
ZZ
contributions to the same-flavour channel,
pp
→
e
+
e
−
ν
ν
¯
, is discussed in detail, and a quantitative analysis of photon-induced contributions is presented. Finally, we consider approximations that account for all sources of large logarithms, at high and low energy, by combining virtual EW corrections with a YFS soft-photon resummation or a QED parton shower.
A
bstract
We present the first combination of NNLO QCD and NLO EW corrections for vector-boson pair production at the LHC. We consider all final states with two, three and four charged leptons, ...including resonant and non-resonant diagrams, spin correlations and off-shell effects. Detailed predictions are discussed for three representative channels corresponding to
W
+
W
−
,
W
±
Z
and
Z Z
production. Both QCD and EW corrections are very significant, and the details of their combination can play a crucial role to achieve the level of precision demanded by experimental analyses. In this context we point out nontrivial issues that arise at large transverse momenta, where the EW corrections are strongly enhanced by Sudakov logarithms and the QCD corrections can feature so-called giant
K
-factors. Our calculations have been carried out in the M
atrix
+O
pen
L
oops
framework and can be extended to the production of an arbitrary colour singlet in hadronic collisions, provided that the required two-loop QCD amplitudes are available. Combined NNLO QCD and NLO EW predictions for the full set of massive diboson processes will be made publicly available in the next release of M
atrix
and will be instrumental in advancing precision diboson studies and new-physics searches at the LHC and future hadron colliders.
A
bstract
We present the first NLO QCD+EW predictions for Higgs boson production in association with a
ℓν
ℓ
or
ℓ
+
ℓ
−
pair plus zero or one jets at the LHC. Fixed-order NLO QCD+EW calculations are ...combined with a QCD+QED parton shower using the recently developed resonance-aware method in the POWHEG framework. Moreover, applying the improved MiNLO technique to
Hℓν
ℓ
+jet and
Hℓ
+
ℓ
−
+jet production at NLO QCD+EW, we obtain predictions that are NLO accurate for observables with both zero or one resolved jet. This approach permits also to capture higher-order effects associated with the interplay of EW corrections and QCD radiation. The behavior of EW corrections is studied for various kinematic distributions, relevant for experimental analyses of Higgsstrahlung processes at the 13 TeV LHC. Exact NLO EW corrections are complemented with approximate analytic formulae that account for the leading and next-to-leading Sudakov logarithms in the high-energy regime. In the tails of transverse-momentum distributions, relevant for analyses in the boosted Higgs regime, the Sudakov approximation works well, and NLO EW effects can largely exceed the ten percent level. Our predictions are based on the POWHEG BOX RES+OpenLoops framework in combination with the Pythia 8.1 parton shower.
A
bstract
We present calculations of Higgs boson production via gluon-gluon fusion in association with one or two additional jets at next-to-leading order in QCD. The calculation of
H
+jet is exact ...in the treatment of the top-quark mass, whereas for the
H
+2 jets calculation the two-loop virtual amplitudes are approximated via a reweighting with leading-order mass effects, while keeping all top-quark mass effects in the real radiation contributions. For
H
+jet production, this study extends a previous calculation, revealing an error in the previous results. For total and differential cross sections, we present new results and compare the QCD corrections with the infinite top-mass limit, for which we find a strikingly good agreement if all amplitudes are rescaled by the leading-order mass dependence.
High-energy jets recoiling against missing transverse energy (MET) are powerful probes of dark matter at the LHC. Searches based on large MET signatures require a precise control of the
Z
(
ν
ν
¯
)
+
... jet background in the signal region. This can be achieved by taking accurate data in control regions dominated by
Z
(
ℓ
+
ℓ
-
)
+
jet,
W
(
ℓ
ν
)
+
jet and
γ
+
jet production, and extrapolating to the
Z
(
ν
ν
¯
)
+
jet background by means of precise theoretical predictions. In this context, recent advances in perturbative calculations open the door to significant sensitivity improvements in dark matter searches. In this spirit, we present a combination of state-of-the-art calculations for all relevant
V
+
jets processes, including throughout NNLO QCD corrections and NLO electroweak corrections supplemented by Sudakov logarithms at two loops. Predictions at parton level are provided together with detailed recommendations for their usage in experimental analyses based on the reweighting of Monte Carlo samples. Particular attention is devoted to the estimate of theoretical uncertainties in the framework of dark matter searches, where subtle aspects such as correlations across different
V
+
jet processes play a key role. The anticipated theoretical uncertainty in the
Z
(
ν
ν
¯
)
+
jet background is at the few percent level up to the TeV range.
A
bstract
The data taken in Run II at the Large Hadron Collider have started to probe Higgs boson production at high transverse momentum. Future data will provide a large sample of events with ...boosted Higgs boson topologies, allowing for a detailed understanding of electroweak Higgs boson plus two-jet production, and in particular the vector-boson fusion mode (VBF). We perform a detailed comparison of precision calculations for Higgs boson production in this channel, with particular emphasis on large Higgs boson transverse momenta, and on the jet radius dependence of the cross section. We study fixed-order predictions at next-to-leading order and next-to-next-to-leading order QCD, and compare the results to NLO plus parton shower (NLOPS) matched calculations. The impact of the NNLO corrections on the central predictions is mild, with inclusive scale uncertainties of the order of a few percent, which can increase with the imposition of kinematic cuts. We find good agreement between the fixed-order and matched calculations in non-Sudakov regions, and the various NLOPS predictions also agree well in the Sudakov regime. We analyze backgrounds to VBF Higgs boson production stemming from associated production, and from gluon-gluon fusion. At high Higgs boson transverse momenta, the ∆
y
jj
and/or
m
jj
cuts typically used to enhance the VBF signal over background lead to a reduced efficiency. We examine this effect as a function of the jet radius and using different definitions of the tagging jets. QCD radiative corrections increase for all Higgs production modes with increasing Higgs boson
p
T
, but the proportionately larger increase in the gluon fusion channel results in a decrease of the gluon-gluon fusion background to electroweak Higgs plus two jet production upon requiring exclusive two-jet topologies. We study this effect in detail and contrast in particular a central jet veto with a global jet multiplicity requirement.
A
bstract
We present next-to-leading order QCD and electroweak (EW) theory predictions for
V
+ 2 jet production, with
V
=
Z, W
±
, considering both the QCD and EW production modes and their ...interference. We focus on phase-space regions where
V
+ 2 jet production is dominated by vector-boson fusion, and where these processes yield the dominant irreducible backgrounds in searches for invisible Higgs boson decays. Predictions at parton level are provided together with detailed prescriptions for their implementation in experimental analyses based on the reweighting of Monte Carlo samples. The key idea is that, exploiting accurate data for
W
+ 2 jet production in combination with a theory-driven extrapolation to the
Z
+ 2 jet process can lead to a determination of the irreducible background at the few-percent level. Particular attention is devoted to the estimate of the residual theoretical uncertainties due to unknown higher-order QCD and EW effects and their correlation between the different
V
+ 2 jet processes, which is key to improve the sensitivity to invisible Higgs decays.
OBJECTIVE To compare minimally invasive endoscopic and open surgical procedures, to improve informed consent of parents, and to establish a baseline for further targeted improvement of surgical care, ...this study evaluated the complication rate and blood transfusion rate of craniosynostosis surgery in our department. METHODS A prospective complication registration database that contains a consecutive cohort of all pediatric neurosurgical procedures in the authors' neurosurgical department was used. All pediatric patients who underwent neurosurgical treatment for craniosynostosis between February 2004 and December 2014 were included. In total, 187 procedures were performed, of which 121 were endoscopically assisted minimally invasive procedures (65%). Ninety-three patients were diagnosed with scaphocephaly, 50 with trigonocephaly, 26 with plagiocephaly, 3 with brachycephaly, 9 with a craniosynostosis syndrome, and 6 patients were suffering from nonsyndromic multisutural craniosynostosis. RESULTS A total of 18 complications occurred in 187 procedures (9.6%, 95% CI 6.2-15), of which 5.3% (n = 10, 95% CI 2.9-10) occurred intraoperatively and 4.2% (n = 8, 95% CI 2.2-8.2) occurred postoperatively. In the open surgical procedure group, 9 complications occurred: 6 intraoperatively and 3 postoperatively. In the endoscopically assisted procedure group, 9 complications occurred: 4 intraoperatively and 5 postoperatively. Blood transfusion was needed in 100% (n = 66) of the open surgical procedures but in only 21% (n = 26, 95% CI 15-30) of the endoscopic procedures. One patient suffered a transfusion reaction, and 6 patients suffered infections, only one of which was a surgical site infection. A dural tear was the most common intraoperative complication that occurred (n = 8), but it never led to postoperative sequelae. Intraoperative bleeding from a sagittal sinus occurred in one patient with only minimal blood loss. There were no deaths, permanent morbidity, or neurological sequelae. CONCLUSIONS Complications during craniosynostosis surgery were relatively few and minor and were without permanent sequelae in open and in minimally invasive procedures. The blood transfusion rate was significantly reduced in endoscopic procedures compared with open procedures.
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