4,071 research outputs found
Numerical evaluation of one-loop QCD amplitudes
We present the publicly available program NGluon allowing the numerical
evaluation of primitive amplitudes at one-loop order in massless QCD. The
program allows the computation of one-loop amplitudes for an arbitrary number
of gluons. The focus of the present article is the extension to one-loop
amplitudes including an arbitrary number of massless quark pairs. We discuss in
detail the algorithmic differences to the pure gluonic case and present cross
checks to validate our implementation. The numerical accuracy is investigated
in detail.Comment: Talk given at ACAT 2011 conference in London, 5-9 Septembe
Wafer test of the LHCb Outer Tracker TDC-Chip
The OTIS-TDC is the front end readout chip for the LHCb Outer Tracker. It is designed to measure drift times with a resolution better than 1 ns. As the chip will be directly mounted to its board, the test have to be performed on the wafer itself. As the testing period for 7 000 chips was only three weeks, many test routines have been implemented on a FPGA. Each chip is subjected to detailed probe testing to ensure the full functionality as well as a good performance. Overall 47 wafer have been tested. From the chips passing the test 2 000 have been used in the Outer Tracker front end electronic
High precision fundamental constants at the TeV scale
This report summarizes the proceedings of the 2014 Mainz Institute for
Theoretical Physics (MITP) scientific program on "High precision fundamental
constants at the TeV scale". The two outstanding parameters in the Standard
Model dealt with during the MITP scientific program are the strong coupling
constant and the top-quark mass . Lacking knowledge on the
value of those fundamental constants is often the limiting factor in the
accuracy of theoretical predictions. The current status on and
has been reviewed and directions for future research have been identified.Comment: 57 pages, 24 figures, pdflate
Electroweak effects in top-quark pair production at Hadron Colliders
Top-quark physics plays an important role at hadron colliders such as the
Tevatron collider at Fermilab or the upcoming Large Hadron Collider (LHC) at
CERN. Given the planned experimental precision, detailed theoretical
predictions are mandatory. In this article we present analytic results for the
complete electroweak corrections to gluon induced top-quark pair production,
completing our earlier results for the quark-induced reaction. As an
application we discuss top-quark pair production at Tevatron and at LHC. In
particular we show that, although small for inclusive quantities, weak
corrections can be sizeable for differential distribution
Aging Studies for the Large Honeycomb Drift Tube System of the Outer Tracker of HERA-B
The HERA-B Outer Tracker consists of drift tubes folded from polycarbonate
foil and is operated with Ar/CF4/CO2 as drift gas. The detector has to stand
radiation levels which are similar to LHC conditions. The first prototypes
exposed to radiation in HERA-B suffered severe radiation damage due to the
development of self-sustaining currents (Malter effect). In a subsequent
extended R&D program major changes to the original concept for the drift tubes
(surface conductivity, drift gas, production materials) have been developed and
validated for use in harsh radiation environments. In the test program various
aging effects (like Malter currents, gain loss due to anode aging and etching
of the anode gold surface) have been observed and cures by tuning of operation
parameters have been developed.Comment: 14 pages, 6 figures, to be published in the Proceedings of the
International Workshop On Aging Phenomena In Gaseous Detectors, 2-5 Oct 2001,
Hamburg, German
The Outer Tracker Detector of the HERA-B Experiment. Part II: Front-End Electronics
The HERA-B Outer Tracker is a large detector with 112674 drift chamber
channels. It is exposed to a particle flux of up to 2x10^5/cm^2/s thus coping
with conditions similar to those expected for the LHC experiments. The
front-end readout system, based on the ASD-8 chip and a customized TDC chip, is
designed to fulfil the requirements on low noise, high sensitivity, rate
tolerance, and high integration density. The TDC system is based on an ASIC
which digitizes the time in bins of about 0.5 ns within a total of 256 bins.
The chip also comprises a pipeline to store data from 128 events which is
required for a deadtime-free trigger and data acquisition system. We report on
the development, installation, and commissioning of the front-end electronics,
including the grounding and noise suppression schemes, and discuss its
performance in the HERA-B experiment
The SM and NLO multileg working group: Summary report
This report summarizes the activities of the SM and NLO Multileg Working
Group of the Workshop "Physics at TeV Colliders", Les Houches, France 8-26
June, 2009.Comment: 169 pages, Report of the SM and NLO Multileg Working Group for the
Workshop "Physics at TeV Colliders", Les Houches, France 8-26 June, 200
The Outer Tracker Detector of the HERA-B Experiment Part I: Detector
The HERA-B Outer Tracker is a large system of planar drift chambers with
about 113000 read-out channels. Its inner part has been designed to be exposed
to a particle flux of up to 2.10^5 cm^-2 s^-1, thus coping with conditions
similar to those expected for future hadron collider experiments. 13
superlayers, each consisting of two individual chambers, have been assembled
and installed in the experiment. The stereo layers inside each chamber are
composed of honeycomb drift tube modules with 5 and 10 mm diameter cells.
Chamber aging is prevented by coating the cathode foils with thin layers of
copper and gold, together with a proper drift gas choice. Longitudinal wire
segmentation is used to limit the occupancy in the most irradiated detector
regions to about 20 %. The production of 978 modules was distributed among six
different laboratories and took 15 months. For all materials in the fiducial
region of the detector good compromises of stability versus thickness were
found. A closed-loop gas system supplies the Ar/CF4/CO2 gas mixture to all
chambers. The successful operation of the HERA-B Outer Tracker shows that a
large tracker can be efficiently built and safely operated under huge radiation
load at a hadron collider.Comment: 28 pages, 14 figure
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