3,490 research outputs found
Non-global logarithms in jet and isolation cone cross sections
Starting from a factorization theorem in effective field theory, we derive a
parton-shower equation for the resummation of non-global logarithms. We have
implemented this shower and interfaced it with a tree-level event generator to
obtain an automated framework to resum the leading logarithm of non-global
observables in the large- limit. Using this setup, we compute gap
fractions for dijet processes and isolation cone cross sections relevant for
photon production. We compare our results with fixed-order computations and LHC
measurements. We find that naive exponentiation is often not adequate,
especially when the vetoed region is small, since non-global contributions are
enhanced due to their dependence on the veto-region size. Since our parton
shower is derived from first principles and based on renormalization-group
evolution, it is clear what ingredients will have to be included to perform
resummations at subleading logarithmic accuracy in the future.Comment: 39 pages, 13 figures. v2: journal version with new result (4.18) for
narrow isolation cone
Factorization and Resummation for Jet Processes
From a detailed analysis of cone-jet cross sections in effective field
theory, we obtain novel factorization theorems which separate the physics
associated with different energy scales present in such processes. The relevant
low-energy physics is encoded in Wilson lines along the directions of the
energetic particles inside the jets. This multi-Wilson-line structure is
present even for narrow-cone jets due to the relevance of small-angle soft
radiation. We discuss the renormalization-group equations satisfied by these
operators. Their solution resums all logarithmically enhanced contributions to
such processes, including non-global logarithms. Such logarithms arise in many
observables, in particular whenever hard phase-space constraints are imposed,
and are not captured with standard resummation techniques. Our formalism
provides the basis for higher-order logarithmic resummations of jet and other
non-global observables. As a nontrivial consistency check, we use it to obtain
explicit two-loop results for all logarithmically enhanced terms in cone-jet
cross sections and verify those against numerical fixed-order computations.Comment: 59 pages, 15 figures. v2: journal version; v3: corrected sign of
(5.11) and a few other typo
An Effective Field Theory for Jet Processes
Processes involving narrow jets receive perturbative corrections enhanced by
logarithms of the jet opening angle and the ratio of the energies inside and
outside the jets. Analyzing cone-jet processes in effective field theory, we
find that in addition to soft and collinear fields their description requires
degrees of freedom which are simultaneously soft and collinear to the jets.
These collinear-soft particles can resolve individual collinear partons,
leading to a complicated multi-Wilson-line structure of the associated
operators at higher orders. Our effective field theory provides, for the first
time, a factorization formula for a cone-jet process, which fully separates the
physics at different energy scales. Its renormalization-group equations control
all logarithmically enhanced higher-order terms, in particular also the
non-global logarithms.Comment: 9 pages, 1 figure. v2: PRL versio
Search for the signal of monotop production at the early LHC
We investigate the potential of the early LHC to discover the signal of
monotops, which can be decay products of some resonances in models such as
R-parity violating SUSY or SU(5), etc. We show how to constrain the parameter
space of the models by the present data of boson hadronic decay branching
ratio, mixing and dijet productions at the LHC. Then, we study
the various cuts imposed on the events, reconstructed from the hadronic final
states, to suppress backgrounds and increase the significance in detail. And we
find that in the hadronic mode the information from the missing transverse
energy and reconstructed resonance mass distributions can be used to specify
the masses of the resonance and the missing particle. Finally, we study the
sensitivities to the parameters at the LHC with =7 TeV and an
integrated luminosity of in detail. Our results show that the
early LHC may detect this signal at 5 level for some regions of the
parameter space allowed by the current data.Comment: 25 pages, 18 figures, 3 tables, version published in Phys.Rev.
Soft gluon resummation in the signal-background interference process of
We present a precise theoretical prediction for the signal-background
interference process of , which is useful to constrain the
Higgs boson decay width and to measure Higgs couplings to the SM particles. The
approximate NNLO -factor is in the range of (),
depending on , at the 8 (13) TeV LHC. And the soft gluon resummation
can increase the approximate NNLO result by about at both the 8 TeV and
13 TeV LHC. The theoretical uncertainties including the scale, uncalculated
multi-loop amplitudes of the background and PDF are roughly
at . We also confirm that the approximate
-factors in the interference and the pure signal processes are the same.Comment: 18 pages, 9 figures; v2 published in JHE
NLL resummation of jet mass
Starting from a factorization theorem in effective field theory, we present
resummed results for two non-global observables: the invariant-mass
distribution of jets and the energy distribution outside jets. Our results
include the full next-to-leading-order corrections to the hard, jet and soft
functions and are implemented in a parton-shower framework which generates the
renormalization-group running in the effective theory. The inclusion of these
matching corrections leads to an improved description of the data and reduced
theoretical uncertainties. They will have to be combined with two-loop running
in the future, but our results are an important first step towards the
higher-logarithmic resummation of non-global observables.Comment: 32 pages, 12 figures. v2: journal versio
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