3,125 research outputs found
Retention capacity of random surfaces
We introduce a "water retention" model for liquids captured on a random
surface with open boundaries, and investigate it for both continuous and
discrete surface heights 0, 1, ... n-1, on a square lattice with a square
boundary. The model is found to have several intriguing features, including a
non-monotonic dependence of the retention on the number of levels in the
discrete case: for many n, the retention is counterintuitively greater than
that of an n+1-level system. The behavior is explained using percolation
theory, by mapping it to a 2-level system with variable probability. Results in
1-dimension are also found.Comment: 5 page
First operation and performance of a 200 lt double phase LAr LEM-TPC with a 40x76 cm^2 readout
In this paper we describe the design, construction, and operation of a first
large area double-phase liquid argon Large Electron Multiplier Time Projection
Chamber (LAr LEM-TPC). The detector has a maximum drift length of 60 cm and the
readout consists of a cm LEM and 2D projective anode to
multiply and collect drifting charges. Scintillation light is detected by means
of cryogenic PMTs positioned below the cathode. To record both charge and light
signals, we have developed a compact acquisition system, which is scalable up
to ton-scale detectors with thousands of charge readout channels. The
acquisition system, as well as the design and the performance of custom-made
charge sensitive preamplifiers, are described. The complete experimental setup
has been operated for a first time during a period of four weeks at CERN in the
cryostat of the ArDM experiment, which was equipped with liquid and gas argon
purification systems. The detector, exposed to cosmic rays, recorded events
with a single-channel signal-to-noise ratio in excess of 30 for minimum
ionising particles. Cosmic muon tracks and their -rays were used to
assess the performance of the detector, and to estimate the liquid argon purity
and the gain at different amplification fields.Comment: 23 pages, 21 figure
Contributions of order to form factors and unitarity of the CKM matrix
The form factors for the semileptonic decay are computed to
order in generalized chiral perturbation theory. The main difference
with the standard expressions consists in contributions quadratic in
quark masses, which are described by a single divergence-free low-energy
constant, . A new simultaneous analysis is presented for the CKM matrix
element , the ratio , decay rates and the
scalar form factor slope . This framework easily accommodates the
precise value for deduced from superallowed nuclear -decays
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
Giant Liquid Argon Observatory for Proton Decay, Neutrino Astrophysics and CP-violation in the Lepton Sector (GLACIER)
GLACIER (Giant Liquid Argon Charge Imaging ExpeRiment) is a large underground
observatory for proton decay search, neutrino astrophysics and CP-violation
studies in the lepton sector. Possible underground sites are studied within the
FP7 LAGUNA project (Europe) and along the JPARC neutrino beam in collaboration
with KEK (Japan). The concept is scalable to very large masses.Comment: 4 pages, 1 figure, Contribution to the Workshop "European Strategy
for Future Neutrino Physics", CERN, Oct. 200
Contribution of higher meson resonances to the electromagnetic -meson mass difference
Modifications of the DGMLY relation for calculation of electromagnetic
-meson mass difference based on the Chiral Symmetry Restoration phenomenon
at high energies as well as the Operator Product Expansion of quark densities
for vector () and axial-vector () meson fields difference are
proposed. In the calculations higher meson resonances in vector and
axial-vector channels are taken into account. It is shown that the inclusion of
the first and radial excitations improves the results for
electromagnetic -meson mass difference as compared with the previous ones.
Estimations on the electromagnetic and -meson decay constants and
the constant of effective chiral Lagrangian are obtained from the
generalized Weinberg sum rules.Comment: Latex2e, 10 pages, submitted to Yad. Phy
Chiral Symmetry Breaking without Bilinear Condensates, Unbroken Axial Z_N Symmetry, and Exact QCD Inequalities
An alternative pattern of the chiral symmetry breaking, suggested recently by
Stern, is investigated. It could be self-consistent provided that the chiral
symmetry is broken spontaneously down to rather than to . The discrete axial then
would play a custodial role preventing the quark bilinears from condensation.
It is shown that this pattern of the chiral symmetry breaking is ruled out in
QCD by exact inequalities. It is not ruled out, however, in other gauge
theories with scalar quarks and/or Yukawa couplings.Comment: 9 pages, Latex, clarifying comments and several references adde
ArDM: first results from underground commissioning
The Argon Dark Matter experiment is a ton-scale double phase argon Time
Projection Chamber designed for direct Dark Matter searches. It combines the
detection of scintillation light together with the ionisation charge in order
to discriminate the background (electron recoils) from the WIMP signals
(nuclear recoils). After a successful operation on surface at CERN, the
detector was recently installed in the underground Laboratorio Subterr\'aneo de
Canfranc, and the commissioning phase is ongoing. We describe the status of the
installation and present first results from data collected underground with the
detector filled with gas argon at room temperature.Comment: 6 pages, 3 figures, Light Detection In Noble Elements (LIDINE 2013
Stable operation with gain of a double phase Liquid Argon LEM-TPC with a 1 mm thick segmented LEM
In this paper we present results from a test of a small Liquid Argon Large
Electron Multiplier Time Projection Chamber (LAr LEM-TPC). This detector
concept provides a 3D-tracking and calorimetric device capable of charge
amplification, suited for next-generation neutrino detectors and possibly
direct Dark Matter searches. During a test of a 3~lt chamber equipped with a
1010~cm readout, cosmic muon data was recorded during three weeks
of data taking. A maximum gain of 6.5 was achieved and the liquid argon was
kept pure enough to ensure 20~cm drift (O(ppb)~O equivalent).Comment: 7 pages, 6 figures, to appear in Proc. of 1st International Workshop
towards the Giant Liquid Argon Charge Imaging Experiment (GLA2010), Tsukuba
(Japan), March 201
Hadronic light-by-light scattering contribution to the muon g-2: an effective field theory approach
The hadronic light-by-light contribution to a_{mu}, the anomalous magnetic
moment of the muon, is discussed from the point of view of an effective
low-energy theory. As an application, the coefficient of the leading logarithm
arising from the two-loop graphs involving two anomalous vertices is computed,
and found to be positive. This corresponds to a positive sign for the pion-pole
contribution to the hadronic light-by-light correction to a_{mu}, and to a
sizeable reduction of the discrepancy between the present experimental value of
a_{mu} and its theoretical counterpart in the standard model.Comment: 4 pages, 1 figure. v2: published versio
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