1,839 research outputs found
Partons and Jets at the LHC
I review some issues related to short distance QCD and its relation to the
experimental program of the Large Hadron Collider (LHC) now under construction
in Geneva.Comment: Talk at the conference QCD2002 at IIT Kanpur, India, November 2002.
Ten pages with 12 figure
Liquid-liquid coexistence in the phase diagram of a fluid confined in fractal porous materials
Multicanonical ensemble sampling simulations have been performed to calculate
the phase diagram of a Lennard-Jones fluid embedded in a fractal random matrix
generated through diffusion limited cluster aggregation. The study of the
system at increasing size and constant porosity shows that the results are
independent from the matrix realization but not from the size effects. A
gas-liquid transition shifted with respect to bulk is found. On growing the
size of the system on the high density side of the gas-liquid coexistence curve
it appears a second coexistence region between two liquid phases. These two
phases are characterized by a different behaviour of the local density inside
the interconnected porous structure at the same temperature and chemical
potential.Comment: 5 pages, 4 figures. To be published in Europhys. Letter
Transverse momentum dependence in gluon distribution and fragmentation functions
We investigate the twist two gluon distribution functions for spin 1/2
hadrons, emphasizing intrinsic transverse momentum of the gluons. These
functions are relevant in leading order in the inverse hard scale in scattering
processes such as inclusive leptoproduction or Drell-Yan scattering, or more
general in hard processes in which at least two hadrons are involved. They show
up in azimuthal asymmetries. For future estimates of such observables, we
discuss specific bounds on these functions.Comment: 14 pages, revtex, 7 Postscript figure
X-ray Diffraction and Molecular Dynamics Study of Medium-range Order in Ambient and Hot Water
We have developed x-ray diffraction measurements with high energy-resolution
and accuracy to study water structure at three different temperatures (7, 25
and 66 C) under normal pressure. Using a spherically curved Ge crystal an
energy resolution better than 15 eV has been achieved which eliminates
influence from Compton scattering. The high quality of the data allows a
precise oxygen-oxygen pair correlation function (PCF) to be directly derived
from the Fourier transform of the experimental data resolving shell structure
out to ~12 {\AA}, i.e. 5 hydration shells. Large-scale molecular dynamics (MD)
simulations using the TIP4P/2005 force-field reproduce excellently the
experimental shell-structure in the range 4-12 {\AA} although less agreement is
seen for the first peak in the PCF. The Local Structure Index [J. Chem. Phys.
104, 7671 (1996)] identifies a tetrahedral minority giving the
intermediate-range oscillations in the PCF and a disordered majority providing
a more featureless background in this range. The current study supports the
proposal that the structure of liquid water, even at high temperatures, can be
described in terms of a two-state fluctuation model involving local structures
related to the high-density and low-density forms of liquid water postulated in
the liquid-liquid phase transition hypothesis.Comment: Submitted to Phys. Chem. Chem. Phy
Two-hadron interference fragmentation functions. Part I: general framework
We investigate the properties of interference fragmentation functions
measurable from the distribution of two hadrons produced in the same jet in the
current fragmentation region of a hard process. We discuss the azimuthal
angular dependences in the leading order cross section of two-hadron inclusive
lepton-nucleon scattering as an example how these interference fragmentation
functions can be addressed separately.Comment: RevTeX, 7 figures, first part of a work split in two, second part
forthcoming in few day
Bounds on transverse momentum dependent distribution and fragmentation functions
We give bounds on the distribution and fragmentation functions that appear at
leading order in deep inelastic 1-particle inclusive leptoproduction or in
Drell-Yan processes. These bounds simply follow from positivity of the defining
matrix elements and are an important guidance in estimating the magnitude of
the azimuthal and spin asymmetries in these processes.Comment: 5 pages, Revtex, 3 Postscript figures, version with minor changes, to
be published in Physical Review Letter
Purification and preconcentration of genomic DNA from whole cell lysates using photoactivated polycarbonate (PPC) microfluidic chips
We discuss the use of a photoactivated polycarbonate (PPC) microfluidic chip for the solid-phase, reversible immobilization (SPRI) and purification of genomic DNA (gDNA) from whole cell lysates. The surface of polycarbonate was activated by UV radiation resulting in a photo-oxidation reaction, which produced a channel surface containing carboxylate groups. The gDNA was selectively captured on this photoactivated surface in an immobilization buffer, which consisted of 3% polyethylene glycol, 0.4 M NaCl and 70% ethanol. The methodology reported herein is similar to conventional SPRI in that surface-confined carboxylate groups are used for the selective immobilization of DNA; however, no magnetic beads or a magnetic field are required. As observed by UV spectroscopy, a load of ∼7.6 ± 1.6 µg/ml of gDNA was immobilized onto the PPC bed. The recovery of DNA following purification was estimated to be 85 ± 5%. The immobilization and purification assay using this PPC microchip could be performed within ∼25 min as follows: (i) DNA immobilization ∼6 min, (ii) chip washout with ethanol 10 min, and (iii) drying and gDNA desorption ∼6 min. The PPC microchip could also be used for subsequent assays with no substantial loss in recovery, no observable carryover and no need for ‘reactivation’ of the PC surface with UV light
Accessing transversity with interference fragmentation functions
We discuss in detail the option to access the transversity distribution
function by utilizing the analyzing power of interference
fragmentation functions in two-pion production inside the same current jet. The
transverse polarization of the fragmenting quark is related to the transverse
component of the relative momentum of the hadron pair via a new azimuthal
angle. As a specific example, we spell out thoroughly the way to extract
from a measured single spin asymmetry in two-pion inclusive
lepton-nucleon scattering. To estimate the sizes of observable effects we
employ a spectator model for the fragmentation functions. The resulting
asymmetry of our example is discussed as arising in different scenarios for the
transversity.Comment: 17 pages, 15 figures in .eps format included, typesetted in RevTeX
and epsfig.sty, submitted to Phys. Rev.
Solutions to the R_b, R_c and alpha_s puzzles by Vector Fermions
We propose two minimal extensions of Standard Model, both of which can easily
accommodate the recent puzzling observations about the excess in , the
deficit in and the discrepancy in the low energy and high energy
determinations of . Each model requires three additional heavy
vectorial fermions in order to resolve the puzzles. The current
phenomenological constraints and the new potential phenomena are also
discussed.Comment: 12 pages, in LaTeX, postscript file also appear
http://www.uic.edu/~keung/pub/rbrc.p
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