3,233 research outputs found
Diffraction at the LHC: a non-technical Introduction
In diffractive interactions of protons or nuclei a violent collision can
occur that leaves the forward going particle completely intact -with
probability determined by the structure of the proton or nucleus.
At very high energies these collisions also occur with both incident
particles remaining intact. This is called central exclusive production. If a
new particle, such as the Higgs boson, were produced exclusively this process
would give a precise measurement of its mass and test for expected properties
of the Higgs. Because of its unusual features this process is also a promising
discovery tool.
In this paper I focus on analogous electromagnetic processes because many
aspects apply to both- particularly the role of coherence. Also, topics in
diffraction with nuclear beams are based on electromagnetic interactions. I
also discuss two proposed measurements in ATLAS with Pb beams and with proton
beams (diffractive Higgs production).Comment: Review talk presented at XII Mexican Workshop on Particles and
Fields. 15 pages, 12 figures
R&D for a Dedicated Fast Timing Layer in the CMS Endcap Upgrade
The PhaseII Upgrades of CMS are being planned for the High Luminosity LHC
(HL-LHC) era when the mean number of interactions per beam crossing ("in-time
pileup") is expected to reach ~140-200. The potential backgrounds arising from
mis-associated jets and photon showers, for example, during event
reconstruction could be reduced if physics objects are tagged with an "event
time". This tag is fully complementary to the "event vertex" which is already
commonly used to reduce mis-reconstruction. Since the tracking vertex
resolution is typically ~10^{-3} (50 micron/4.8cm) of the rms vertex
distribution, whereas only ~10^{-1} (i.e. 20 vs.170 picoseconds (psec)) is
demonstrated for timing, it is often assumed that only photon (i.e. EM
calorimeter or shower-max) timing is of interest. We show that the optimal
solution will likely be a single timing layer which measures both charged
particle and photon time (a pre-shower layer).Comment: Proceedings of the 2014 Workshop on Picosecond Photon Sensors for
Physics and Medical Applications, Clermont Ferrand. 9 pages, 4 figure
Diffraction Dissociation - 50 Years Later
The field of Diffraction Dissociation, which is the subject of this workshop,
began 50 years ago with the analysis of deuteron stripping in low energy
collisions with nuclei. We return to the subject in a modern context- deuteron
dissociation in GeV d-Au collisions recorded during the
2003 RHIC run in the PHENIX experiment. At RHIC energy, dn+p proceeds
predominantly (90%) through Electromagnetic Dissociation and the remaining
fraction via the hadronic shadowing described by Glauber. Since the
dissociation cross section has a small theoretical error we adopt this process
to normalize other cross sections measured in RHIC.Comment: Submitted to: Proceedings of DIS05 conference, Diffraction and Vector
Meson Working Group. 5 pages,2 figure
- …