22 research outputs found
Systematic Improvement of Parton Showers with Effective Theory
We carry out a systematic classification and computation of next-to-leading
order kinematic power corrections to the fully differential cross section in
the parton shower. To do this we devise a map between ingredients in a parton
shower and operators in a traditional effective field theory framework using a
chain of soft-collinear effective theories. Our approach overcomes several
difficulties including avoiding double counting and distinguishing
approximations that are coordinate choices from true power corrections.
Branching corrections can be classified as hard-scattering, that occur near the
top of the shower, and jet-structure, that can occur at any point inside it.
Hard-scattering corrections include matrix elements with additional hard
partons, as well as power suppressed contributions to the branching for the
leading jet. Jet-structure corrections require simultaneous consideration of
potential 1 -> 2 and 1 -> 3 branchings. The interference structure induced by
collinear terms with subleading powers remains localized in the shower.Comment: 54 pages, 24 figures, plus a few appendices. v2: included a parameter
"eta" to account for energy loss, title improved, journal versio
Jet Shapes and Jet Algorithms in SCET
Jet shapes are weighted sums over the four-momenta of the constituents of a
jet and reveal details of its internal structure, potentially allowing
discrimination of its partonic origin. In this work we make predictions for
quark and gluon jet shape distributions in N-jet final states in e+e-
collisions, defined with a cone or recombination algorithm, where we measure
some jet shape observable on a subset of these jets. Using the framework of
Soft-Collinear Effective Theory, we prove a factorization theorem for jet shape
distributions and demonstrate the consistent renormalization-group running of
the functions in the factorization theorem for any number of measured and
unmeasured jets, any number of quark and gluon jets, and any angular size R of
the jets, as long as R is much smaller than the angular separation between
jets. We calculate the jet and soft functions for angularity jet shapes \tau_a
to one-loop order (O(alpha_s)) and resum a subset of the large logarithms of
\tau_a needed for next-to-leading logarithmic (NLL) accuracy for both cone and
kT-type jets. We compare our predictions for the resummed \tau_a distribution
of a quark or a gluon jet produced in a 3-jet final state in e+e- annihilation
to the output of a Monte Carlo event generator and find that the dependence on
a and R is very similar.Comment: 62 pages plus 21 pages of Appendices, 13 figures, uses JHEP3.cls. v2:
corrections to finite parts of NLO jet functions, minor changes to plots,
clarified discussion of power corrections. v3: Journal version. Introductory
sections significantly reorganized for clarity, classification of logarithmic
accuracy clarified, results for non-Mercedes-Benz configurations adde
Tracker Operation and Performance at the Magnet Test and Cosmic Challenge
During summer 2006 a fraction of the CMS silicon strip tracker was operated in a comprehensive slice test called the Magnet Test and Cosmic Challenge (MTCC). At the MTCC, cosmic rays detected in the muon chambers were used to trigger the readout of all CMS sub-detectors in the general data acquisition system and in the presence of the 4 T magnetic field produced by the CMS superconducting solenoid. This document describes the operation of the Tracker hardware and software prior, during and after data taking. The performance of the detector as resulting from the MTCC data analysis is also presented
Tracker Operation and Performance at the Magnet Test and Cosmic Challenge
During summer 2006 a fraction of the CMS silicon strip tracker was operated in a comprehensive slice test called the Magnet Test and Cosmic Challenge (MTCC). At the MTCC, cosmic rays detected in the muon chambers were used to trigger the readout of all CMS sub-detectors in the general data acquisition system and in the presence of the 4 T magnetic field produced by the CMS superconducting solenoid. This document describes the operation of the Tracker hardware and software prior, during and after data taking. The performance of the detector as resulting from the MTCC data analysis is also presented