669 research outputs found
Jet Veto Clustering Logarithms Beyond Leading Order
Many experimental analyses separate events into exclusive jet bins, using a
jet algorithm to cluster the final state and then veto on jets. Jet clustering
induces logarithmic dependence on the jet radius R in the cross section for
exclusive jet bins, a dependence that is poorly controlled due to the
non-global nature of the clustering. At jet radii of experimental interest, the
leading order (LO) clustering effects are numerically significant, but the
higher order effects are currently unknown. We rectify this situation by
calculating the most important part of the next-to-leading order (NLO)
clustering logarithms of R for any 0-jet process, which enter as
corrections to the cross section. The calculation blends
subtraction methods for NLO calculations with factorization properties of QCD
and soft-collinear effective theory (SCET). We compare the size of the known LO
and new NLO clustering logarithms and find that the impact of the NLO terms on
the 0-jet cross section in Higgs production is small. This brings clustering
effects under better control and may be used to improve uncertainty estimates
on cross sections with a jet veto.Comment: 39 pages, 5 figures. v2: journal version. v3: added missing term in
calculation, conclusions unchange
Catching a New Force by the Tail
The Large Hadron Collider (LHC) is sensitive to new heavy gauge bosons that
produce narrow peaks in the dilepton invariant mass spectrum up to about
TeV. s that are too heavy to produce directly can reveal
their presence through interference with Standard Model dilepton production. We
show that the LHC can significantly extend the mass reach for such s by
performing precision measurements of the shape of the dilepton invariant mass
spectrum. The high luminosity LHC can exclude, with 95 confidence, new
gauge bosons as heavy as TeV that couple with gauge
coupling strength of .Comment: 8 pages, 7 figure
Precision Probes of QCD at High Energies
New physics, that is too heavy to be produced directly, can leave measurable
imprints on the tails of kinematic distributions at the LHC. We use energetic
QCD processes to perform novel measurements of the Standard Model (SM)
Effective Field Theory. We show that the dijet invariant mass spectrum, and the
inclusive jet transverse momentum spectrum, are sensitive to a dimension 6
operator that modifies the gluon propagator at high energies. The dominant
effect is constructive or destructive interference with SM jet production. We
compare differential next-to-leading order predictions from POWHEG to public 7
TeV jet data, including scale, PDF, and experimental uncertainties and their
respective correlations. We constrain a New Physics (NP) scale of 3.5 TeV with
current data. We project the reach of future 13 and 100 TeV measurements, which
we estimate to be sensitive to NP scales of 8 and 60 TeV, respectively. As an
application, we apply our bounds to constrain heavy vector octet colorons that
couple to the QCD current. We project that effective operators will surpass
bump hunts, in terms of coloron mass reach, even for sequential couplings.Comment: 40 pages, 13 figures, 8 tables. Minor changes. Accepted on JHE
NLO QCD corrections to SM-EFT dilepton and electroweak Higgs boson production, matched to parton shower in POWHEG
We discuss the Standard Model Effective Field Theory (SM-EFT) contributions
to neutral- and charge-current Drell-Yan production, associated production of
the Higgs and a vector boson, and Higgs boson production via vector boson
fusion. We consider all the dimension-six SM-EFT operators that contribute to
these processes at leading order, include next-to-leading order QCD
corrections, and interface them with parton showering and hadronization in
Pythia8 according to the POWHEG method. We discuss existing constraints on the
coefficients of dimension-six operators and identify differential and angular
distributions that can differentiate between different effective operators,
pointing to specific features of Beyond-the-Standard-Model physics.Comment: 42 pages, 8 Figure
Underlying event sensitive observables in Drell-Yan production using GENEVA
We present an extension of the GENEVA Monte Carlo framework to include
multiple parton interactions (MPI) provided by PYTHIA8. This allows us to
obtain predictions for underlying-event sensitive measurements in Drell-Yan
production, in conjunction with GENEVA's fully-differential NNLO calculation,
NNLL' resummation for the 0-jet resolution variable (beam thrust), and NLL
resummation for the 1-jet resolution variable. We describe the interface with
the parton shower algorithm and MPI model of PYTHIA8, which preserves both the
precision of partonic N-jet cross sections in GENEVA as well as the shower
accuracy and good description of soft hadronic physics of PYTHIA8. We present
results for several underlying-event sensitive observables and compare to data
from ATLAS and CMS as well as to standalone PYTHIA8 predictions. This includes
a comparison with the recent ATLAS measurement of the beam thrust spectrum,
which provides a potential avenue to fully disentangle the physical effects
from the primary hard interaction, primary soft radiation, multiple parton
interactions, and nonperturbative hadronization.Comment: 23 pages, 11 figures. v3: version accepted by EPJ
Right-handed charged currents in the era of the Large Hadron Collider
We discuss the phenomenology of right-handed charged currents in the
framework of the Standard Model Effective Field Theory, in which they arise due
to a single gauge-invariant dimension-six operator. We study the manifestations
of the nine complex couplings of the to right-handed quarks in collider
physics, flavor physics, and low-energy precision measurements. We first obtain
constraints on the couplings under the assumption that the right-handed
operator is the dominant correction to the Standard Model at observable
energies. We subsequently study the impact of degeneracies with other
Beyond-the-Standard-Model effective interactions and identify observables, both
at colliders and low-energy experiments, that would uniquely point to
right-handed charged currents.Comment: 50 pages plus appendices and reference
Drell-Yan Production at NNLL'+NNLO Matched to Parton Showers
We present results for Drell-Yan production from the GENEVA Monte-Carlo
framework. We combine the fully-differential NNLO calculation with higher-order
resummation in the 0-jettiness resolution variable. The resulting parton-level
events are further combined with parton showering and hadronization provided by
PYTHIA8. The 0-jettiness resummation is carried out to NNLL', which
consistently incorporates all singular virtual and real NNLO corrections. It
thus provides a natural perturbative connection between the NNLO calculation
and the parton shower regime, including a systematic assessment of perturbative
uncertainties. In this way, inclusive observables are correct to NNLO, up to
small power corrections in the resolution cutoff. Furthermore, the perturbative
accuracy of 0-jet-like resummation variables is significantly improved beyond
the parton shower approximation. We provide comparisons with LHC measurements
of Drell-Yan production at 7 TeV from ATLAS, CMS, and LHCb. As already observed
in collisions, for resummation-sensitive observables, the agreement
with data is noticeably improved by using a lower value of .Comment: 26 pages, 20 figure
Top-quark pair-production with one jet and parton showering at hadron colliders
We present heavy-flavor production in association with one jet in hadronic
collisions matched to parton shower Monte Carlo predictions at next-to-leading
order QCD with account of top-quark decays and spin correlations. We use the
POWHEGBOX for the interface to the parton shower programs PYTHIA or HERWIG.
Phenomenological studies for the LHC and the Tevatron are presented with
particular emphasis on the inclusion of spin-correlation effects in top decay
and the impact of the parton shower on the top-quark charge asymmetries. As a
novel application of the present calculation the measurement of the top-quark
mass is discussed.Comment: 4 pages latex, 6 figures, Procs. of XX International Workshop on
Deep-Inelastic Scattering and Related Subjects (DIS 2012
W, Z and photon production in CMS
The production of electroweak bosons (photons, W and Z particles) in PbPb and
pp collisions at sqrt(s) = 2.76 TeV per interacting nucleon pair has been
measured with the CMS detector at the LHC. Direct photon production is studied
using samples of isolated photons. W and Z bosons are reconstructed through
their leptonic decay into muons. Their production rate in PbPb data is studied
as a function of the centrality of the collision and compared to that in pp
interactions, once normalized by the number of binary nucleon-nucleon
interactions. The results are also compared to next-to-leading-order
perturbative QCD calculations.Comment: Proceedings from Plenary Talk at 5th International Conference on Hard
and Electromagnetic Probes of High-Energy Nuclear Collisions (Hard Probes
2012) at Cagliari (Italia
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