1,092 research outputs found

### Resummation and NLO Matching of Event Shapes with Effective Field Theory

The resummed differential thrust rate in e+e- annihilation is calculated
using Soft-Collinear Effective Theory (SCET). The resulting distribution in the
two-jet region T~1 is found to agree with the corresponding expression derived
by the standard approach. A matching procedure to account for finite
corrections at T < 1 is then described. There are two important advantages of
the SCET approach. First, SCET manifests a dynamical seesaw scale q = p^2/Q in
addition to the center-of-mass energy Q and the jet mass scale p ~ Q ~ sqrt(1 -
T). Thus, the resummation of logs of p/q can be cleanly distinguished from the
resummation of logs of Q/p. Second, finite parts of loop amplitudes appear in
specific places in the perturbative distribution: in the matching to the hard
function, at the scale Q, in matching to the jet function, at the scale p, and
in matching to the soft function, at the scale q. This allows for a consistent
merger of fixed order corrections and resummation. In particular, the total NLO
e+e- cross section is reproduced from these finite parts without having to
perform additional infrared regulation.Comment: 18 pages, 1 figure; notation updated and references adde

### A precise determination of alpha_s from LEP thrust data using effective field theory

Starting from a factorization theorem in Soft-Collinear Effective Theory, the
thrust distribution in e+e- collisions is calculated including resummation of
the next-to-next-to-next-to leading logarithms. This is a significant
improvement over previous calculations which were only valid to next-to-leading
logarithmic order. The fixed-order expansion of the resummed result approaches
the exact fixed-order distribution towards the kinematic endpoint. This close
agreement provides a verification of both the effective field theory expression
and recently completed next-to-next-to-leading fixed order event shapes. The
resummed distribution is then matched to fixed order, resulting in a
distribution valid over a large range of thrust. A fit to ALEPH and OPAL data
from LEP 1 and LEP 2 produces alpha_s(m_Z)= 0.1172 +/- 0.0010 +/- 0.0008
+/-0.0012 +/- 0.0012, where the uncertainties are respectively statistical,
systematic, hadronic, and perturbative. This is one of the world's most precise
extractions of alpha_s to date.Comment: 37 pages, 12 figures; v2: hadronization discussion and appendices
expande

### Threshold Hadronic Event Shapes with Effective Field Theory

Hadronic event shapes, that is, event shapes at hadron colliders, could
provide a great way to test both standard and non-standard theoretical models.
However, they are significantly more complicated than event shapes at e+e-
colliders, involving multiple hard directions, multiple channels and multiple
color structures. In this paper, hadronic event shapes are examined with
Soft-Collinear Effective Theory (SCET) by expanding around the dijet limit. A
simple event shape, threshold thrust, is defined. This observable is global and
has no free parameters, making it ideal for clarifying how resummation of
hadronic event shapes can be done in SCET. Threshold thrust is calculated at
next-to-leading fixed order (NLO) in SCET and resummed to
next-to-next-to-leading logarithmic accuracy (NNLL). The scale-dependent parts
of the soft function are shown to agree with what is expected from general
observations, and the factorization formula is explicitly shown to be
renormalization group invariant to 1-loop. Although threshold thrust is not
itself expected to be phenomenologically interesting, it can be modified into a
related observable which allows the jet pT distribution to be calculated and
resummed to NNLL+NLO accuracy. As in other processes, one expects resummation
to be important even for moderate jet momenta due to dynamical threshold
enhancement. A general discussion of threshold enhancement and non-global logs
in hadronic event shapes is also included.Comment: 38 pages, 2 figures; small typos corrected in v

### Seeing in Color: Jet Superstructure

A new class of observables is introduced which aims to characterize the
superstructure of an event, that is, features, such as color flow, which are
not determined by the jet four-momenta alone. Traditionally, an event is
described as having jets which are independent objects; each jet has some
energy, size, and possible substructure such as subjets or heavy flavor
content. This description discards information connecting the jets to each
other, which can be used to determine if the jets came from decay of a color
singlet object, or if they were initiated by quarks or gluons. An example
superstructure variable, pull, is presented as a simple handle on color flow.
It can be used on an event-by-event basis as a tool for distinguishing
previously irreducible backgrounds at the Tevatron and the LHC.Comment: 4 pages, 5 figures. Published version. Some clarifications and
references adde

### Reducing the Top Quark Mass Uncertainty with Jet Grooming

The measurement of the top quark mass has large systematic uncertainties
coming from the Monte Carlo simulations that are used to match theory and
experiment. We explore how much that uncertainty can be reduced by using jet
grooming procedures. We estimate the inherent ambiguity in what is meant by
Monte Carlo mass to be around 530 MeV without any corrections. This uncertainty
can be reduced by 60% to 200 MeV by calibrating to the W mass and a further 33%
to 140 MeV by applying soft-drop jet grooming (or by 20% more to 170 MeV with
trimming). At e+e- colliders, the associated uncertainty is around 110 MeV,
reducing to 50 MeV after calibrating to the W mass. By analyzing the tuning
parameters, we conclude that the importance of jet grooming after calibrating
to the W mass is to reduce sensitivity to the underlying event.Comment: 21 pages, 7 figure

### Quantum Field Theory and Unification in AdS5

We consider gauge bosons in the bulk of AdS5 in a two-brane theory that
addresses the hierarchy problem. We show such a theory can be consistent with
gauge coupling unification at a high scale. We discuss subtleties in this
calculation and show how to regulate consistently in a bounded AdS5 background.
Our regularization is guided by the holographic dual of the calculation.Comment: Published version, some typos correcte

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