133 research outputs found
Jet Vetoes Interfering with H->WW
Far off-shell Higgs production in , is a particularly
powerful probe of Higgs properties, allowing one to disentangle Higgs width and
coupling information unavailable in on-shell rate measurements. These
measurements require an understanding of the cross section in the far off-shell
region in the presence of realistic experimental cuts. We analytically study
the effect of a jet veto on far off-shell cross sections, including
signal-background interference, by utilizing hard functions in the soft
collinear effective theory that are differential in the decay products of the
. Summing large logarithms of , we find that the
jet veto induces a strong dependence on the partonic centre of mass energy,
, and modifies distributions in or . The
example of is used to demonstrate these
effects at next to leading log order. We also discuss the importance of jet
vetoes and jet binning for the recent program to extract Higgs couplings and
widths from far off-shell cross sections.Comment: 31 pages, 8 figures. v2: Journal Versio
Convolved Substructure: Analytically Decorrelating Jet Substructure Observables
A number of recent applications of jet substructure, in particular searches
for light new particles, require substructure observables that are decorrelated
with the jet mass. In this paper we introduce the Convolved SubStructure (CSS)
approach, which uses a theoretical understanding of the observable to
decorrelate the complete shape of its distribution. This decorrelation is
performed by convolution with a shape function whose parameters and mass
dependence are derived analytically. We consider in detail the case of the
observable and perform an illustrative case study using a search for a
light hadronically decaying . We find that the CSS approach completely
decorrelates the observable over a wide range of masses. Our approach
highlights the importance of improving the theoretical understanding of jet
substructure observables to exploit increasingly subtle features for
performance.Comment: 20 pages, 11 figures. v2. Corrected typo in legend in Figure 5.
Updated Figure 11, minor modification to conclusions on discrimination power.
v3. Updated to published version. Minor typos correcte
Factorization and Resummation for Groomed Multi-Prong Jet Shapes
Observables which distinguish boosted topologies from QCD jets are playing an
increasingly important role at the Large Hadron Collider (LHC). These
observables are often used in conjunction with jet grooming algorithms, which
reduce contamination from both theoretical and experimental sources. In this
paper we derive factorization formulae for groomed multi-prong substructure
observables, focusing in particular on the groomed observable, which is
used to identify boosted hadronic decays of electroweak bosons at the LHC. Our
factorization formulae allow systematically improvable calculations of the
perturbative distribution and the resummation of logarithmically enhanced
terms in all regions of phase space using renormalization group evolution. They
include a novel factorization for the production of a soft subjet in the
presence of a grooming algorithm, in which clustering effects enter directly
into the hard matching. We use these factorization formulae to draw robust
conclusions of experimental relevance regarding the universality of the
distribution in both and collisions. In particular, we show that
the only process dependence is carried by the relative quark vs. gluon jet
fraction in the sample, no non-global logarithms from event-wide correlations
are present in the distribution, hadronization corrections are controlled by
the perturbative mass of the jet, and all global color correlations are
completely removed by grooming, making groomed a theoretically clean QCD
observable even in the LHC environment. We compute all ingredients to one-loop
accuracy, and present numerical results at next-to-leading logarithmic accuracy
for collisions, comparing with parton shower Monte Carlo simulations.
Results for collisions, as relevant for phenomenology at the LHC, are
presented in a companion paper.Comment: 66 pages, 18 figure
Non-Global Logarithms, Factorization, and the Soft Substructure of Jets
An outstanding problem in QCD and jet physics is the factorization and
resummation of logarithms that arise due to phase space constraints, so-called
non-global logarithms (NGLs). In this paper, we show that NGLs can be
factorized and resummed down to an unresolved infrared scale by making
sufficiently many measurements on a jet or other restricted phase space region.
Resummation is accomplished by renormalization group evolution of the objects
in the factorization theorem and anomalous dimensions can be calculated to any
perturbative accuracy and with any number of colors. To connect with the NGLs
of more inclusive measurements, we present a novel perturbative expansion which
is controlled by the volume of the allowed phase space for unresolved
emissions. Arbitrary accuracy can be obtained by making more and more
measurements so to resolve lower and lower scales. We find that even a minimal
number of measurements produces agreement with Monte Carlo methods for
leading-logarithmic resummation of NGLs at the sub-percent level over the full
dynamical range relevant for the Large Hadron Collider. We also discuss other
applications of our factorization theorem to soft jet dynamics and how to
extend to higher-order accuracy.Comment: 46 pages + appendices, 10 figures. v2: added current figures 4 and 5,
as well as corrected several typos in appendices. v3: corrected some typos,
added current figure 9, and added more discussion of fixed-order versus
dressed gluon expansions. v4: fixed an error in numerics of two-dressed
gluon; corrected figure 8, modified comparison to BMS. Conclusions unchanged.
v5: fixed minor typ
A Subleading Operator Basis and Matching for
The Soft Collinear Effective Theory (SCET) is a powerful framework for
studying factorization of amplitudes and cross sections in QCD. While
factorization at leading power has been well studied, much less is known at
subleading powers in the expansion. In SCET subleading soft and
collinear corrections to a hard scattering process are described by power
suppressed operators, which must be fixed case by case, and by well established
power suppressed Lagrangians, which correct the leading power dynamics of soft
and collinear radiation. Here we present a complete basis of power suppressed
operators for , classifying all operators which contribute to the
cross section at , and showing how helicity selection
rules significantly simplify the construction of the operator basis. We perform
matching calculations to determine the tree level Wilson coefficients of our
operators. These results are useful for studies of power corrections in both
resummed and fixed order perturbation theory, and for understanding the
factorization properties of gauge theory amplitudes and cross sections at
subleading power. As one example, our basis of operators can be used to
analytically compute power corrections for -jettiness subtractions for
induced color singlet production at the LHC.Comment: v2. JHEP version. Minor clarifications and typos fixe
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