5,907 research outputs found
Early Electroweak and Top Quark Physics with CMS
The Large Hadron Collider is an ideal place for precision measurements of the
properties of the electroweak gauge bosons W^\pm, Z^0, as well as of the top
quark. In this article, a few highlights of the prospects for performing such
measurements with the CMS detector are summarized, with an emphasis on the
first few 1/fb of data.Comment: 4 pages, to appear in the proceedings of DIS 2007, Munich, April 200
Diffractive DIS Cross Sections and Parton Distributions
Highlights are presented mainly from two recent measurements of the
diffractive Deep Inelastic Scattering cross section at HERA. In the first, the
process is studied by tagging the leading final state proton. In
the second, events of this type are selected by requiring a large rapidity gap
devoid of hadronic activity in the proton direction. The two measurements are
compared in detail and the kinematic dependences are interpreted within the
framework of a factorisable diffractive exchange. Diffractive parton
distributions are determined from a next-to-leading order QCD analysis of the
large rapidity gap data, which can be applied to the prediction of diffractive
processes, also at the TEVATRON and the LHC.Comment: to appear in the proceedings of the 33rd Intl. Conference on High
Energy Physics, ICHEP 2006 (Moscow, July 2006
Status and Commissioning of the CMS Experiment
After a brief overview of the Compact Muon Solenoid (CMS) experiment, the
status of construction and installation is described in the first part of the
note. The second part of the document is devoted to a discussion of the general
commissioning strategy of the CMS experiment, with a particular emphasis on
trigger, calibration and alignment. Aspects of b-physics, as well as examples
for early physics with CMS are also presented. CMS will be ready for data
taking in time for the first collisions in the Large Hadron Collider (LHC) at
CERN in late 2007.Comment: Talks given at the 11th Intl. Conference on B-Physics at Hadron
Machines BEAUTY 2006, Oxford (UK), September 200
Inclusive Diffraction at HERA
New precision measurements of inclusive diffractive deep-inelastic ep
scattering interactions, performed by the H1 and ZEUS collaborations at the
HERA collider, are discussed. A new set of diffractive parton distributions,
determined from recent high precision H1 data, is presented.Comment: 5 pages, to appear in the proceedings of the 31st Intl. Conference on
High Energy Physics ICHEP 2002, Amsterdam, July 200
Microscopic theory of glassy dynamics and glass transition for molecular crystals
We derive a microscopic equation of motion for the dynamical orientational
correlators of molecular crystals. Our approach is based upon mode coupling
theory. Compared to liquids we find four main differences: (i) the memory
kernel contains Umklapp processes, (ii) besides the static two-molecule
orientational correlators one also needs the static one-molecule orientational
density as an input, where the latter is nontrivial, (iii) the static
orientational current density correlator does contribute an anisotropic,
inertia-independent part to the memory kernel, (iv) if the molecules are
assumed to be fixed on a rigid lattice, the tensorial orientational correlators
and the memory kernel have vanishing l,l'=0 components. The resulting mode
coupling equations are solved for hard ellipsoids of revolution on a rigid
sc-lattice. Using the static orientational correlators from Percus-Yevick
theory we find an ideal glass transition generated due to precursors of
orientational order which depend on X and p, the aspect ratio and packing
fraction of the ellipsoids. The glass formation of oblate ellipsoids is
enhanced compared to that for prolate ones. For oblate ellipsoids with X <~ 0.7
and prolate ellipsoids with X >~ 4, the critical diagonal nonergodicity
parameters in reciprocal space exhibit more or less sharp maxima at the zone
center with very small values elsewhere, while for prolate ellipsoids with 2 <~
X <~ 2.5 we have maxima at the zone edge. The off-diagonal nonergodicity
parameters are not restricted to positive values and show similar behavior. For
0.7 <~ X <~ 2, no glass transition is found. In the glass phase, the
nonergodicity parameters show a pronounced q-dependence.Comment: 17 pages, 12 figures, accepted at Phys. Rev. E. v4 is almost
identical to the final paper version. It includes, compared to former
versions v2/v3, no new physical content, but only some corrected formulas in
the appendices and corrected typos in text. In comparison to version v1, in
v2-v4 some new results have been included and text has been change
Track Based Alignment of Composite Detector Structures
An iterative algorithm for track based alignment is presented. The algorithm can be applied to rigid composite detector structures or to individual modules. The iterative process involves track reconstruction and alignment, in which the chi-2 function of the hit residuals of each alignable object is minimized. Six alignment parameters per structure or per module, three for location and three for orientation, can be computed. The method is computationally light and easily parallelizable. The performance of the method is demonstrated with simulated tracks in the CMS pixel detector and tracks reconstructed from experimental data recorded with a test beam setup
Osmotic compression of droplets of hard rods: A computer simulation study
By means of computer simulations we study how droplets of hard, rod-like
particles optimize their shape and internal structure under the influence of
the osmotic compression caused by the presence of spherical particles that act
as depletion agents. At sufficiently high osmotic pressures the rods that make
up the drops spontaneously align to turn them into uniaxial nematic liquid
crystalline droplets. The nematic droplets or "tactoids" that are formed this
way are not spherical but elongated, resulting from the competition between the
anisotropic surface tension and the elastic deformation of the director field.
In agreement with recent theoretical predictions we find that sufficiently
small tactoids have a uniform director field, whilst large ones are
characterized by a bipolar director field. From the shape and director-field
transformation of the droplets we are able to estimate the surface anchoring
strength and an average of the elastic constants of the hard-rod nematic
Dynamic Glass Transition in Two Dimensions
The question about the existence of a structural glass transition in two
dimensions is studied using mode coupling theory (MCT). We determine the
explicit d-dependence of the memory functional of mode coupling for
one-component systems. Applied to two dimensions we solve the MCT equations
numerically for monodisperse hard discs. A dynamic glass transition is found at
a critical packing fraction phi_c^{d=2} = 0.697 which is above phi_c^{d=3} =
0.516 by about 35%. phi^d_c scales approximately with phi^d_{\rm rcp} the value
for random close packing, at least for d=2, 3. Quantities characterizing the
local, cooperative 'cage motion' do not differ much for d=2 and d=3, and we
e.g. find the Lindemann criterion for the localization length at the glass
transition. The final relaxation obeys the superposition principle, collapsing
remarkably well onto a Kohlrausch law. The d=2 MCT results are in qualitative
agreement with existing results from MC and MD simulations. The mean squared
displacements measured experimentally for a quasi-two-dimensional binary system
of dipolar hard spheres can be described satisfactorily by MCT for monodisperse
hard discs over four decades in time provided the experimental control
parameter Gamma (which measures the strength of dipolar interactions) and the
packing fraction phi are properly related to each other.Comment: 14 pages, 15 figure
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