680 research outputs found
Detection of K+ mesons in segmented electromagnetic calorimeters
The combination of the CrystalBall and TAPS electromagnetic calorimeters were installed in the MAMI A2 hall in 2003. Here they are able to detect the reaction products from photo-induced reactions in combination with the Glasgow photon tagger. In the last two years the MAMI facility was upgraded from 885 MeV to 1.5 GeV, the A2 photon tagger underwent a similar upgrade crossing the threshold for strangeness photoproduction. For the CrystalBall this created a new challenge, to identify K+ mesons above the large background from other charged hadrons, in a situation where the detector setup does not benefit from a magnetic field to help separate particle species. These proceedings outline a novel technique which uses the decay products of the K+ as a strangeness tag
Viscous instabilities in flowing foams: A Cellular Potts Model approach
The Cellular Potts Model (CPM) succesfully simulates drainage and shear in
foams. Here we use the CPM to investigate instabilities due to the flow of a
single large bubble in a dry, monodisperse two-dimensional flowing foam. As in
experiments in a Hele-Shaw cell, above a threshold velocity the large bubble
moves faster than the mean flow. Our simulations reproduce analytical and
experimental predictions for the velocity threshold and the relative velocity
of the large bubble, demonstrating the utility of the CPM in foam rheology
studies.Comment: 10 pages, 3 figures. Replaced with revised version accepted for
publication in JSTA
Kaon Photoproduction and the Decay Parameter
The weak decay parameter of the is an important quantity
for the extraction of polarization observables in various experiments.
Moreover, in combination with from decay it provides a
measure for matter-antimatter asymmetry. The weak decay parameter also affects
the decay parameters of the and baryons and, in general, any
quantity in which the polarization of the is relevant. The recently
reported value by the BESIII collaboration of is significantly
larger than the previous PDG value of that had been accepted and
used for over 40 years. In this work we make an independent estimate of
, using an extensive set of polarization data measured in kaon
photoproduction in the baryon resonance region and constraints set by spin
algebra. The obtained value is 0.721(6)(5). The result is corroborated by
multiple statistical tests as well as a modern phenomenological model, showing
that our new value yields the best description of the data in question. Our
analysis supports the new BESIII finding that is significantly
larger than the previous PDG value. Any experimental quantity relying on the
value of should therefore be re-considered.Comment: 6 pages, 1 figure
Mechanical probing of liquid foam aging
We present experimental results on the Stokes experiment performed in a 3D
dry liquid foam. The system is used as a rheometric tool : from the force
exerted on a 1cm glass bead, plunged at controlled velocity in the foam in a
quasi static regime, local foam properties are probed around the sphere. With
this original and simple technique, we show the possibility of measuring the
foam shear modulus, the gravity drainage rate and the evolution of the bubble
size during coarsening
Machine Learned Particle Detector Simulations
The use of machine learning algorithms is an attractive way to produce very
fast detector simulations for scattering reactions that can otherwise be
computationally expensive. Here we develop a factorised approach where we deal
with each particle produced in a reaction individually: first determine if it
was detected (acceptance) and second determine its reconstructed variables such
as four momentum (reconstruction). For the acceptance we propose using a
probability classification density ratio technique to determine the probability
the particle was detected as a function of many variables. Neural Network and
Boosted Decision Tree classifiers were tested for this purpose and we found
using a combination of both, through a reweighting stage, provided the most
reliable results. For reconstruction a simple method of synthetic data
generation, based on nearest neighbour or decision trees was developed. Using a
toy parameterised detector we demonstrate that such a method can reliably and
accurately reproduce kinematic distributions from a physics reaction. The
relatively simple algorithms allow for small training overheads whilst
producing reliable results. Possible applications for such fast simulated data
include Toy-MC studies of parameter extraction, preprocessing expensive
simulations or generating templates for background distributions shapes
Coarsening in the q-State Potts Model and the Ising Model with Globally Conserved Magnetization
We study the nonequilibrium dynamics of the -state Potts model following a
quench from the high temperature disordered phase to zero temperature. The time
dependent two-point correlation functions of the order parameter field satisfy
dynamic scaling with a length scale . In particular, the
autocorrelation function decays as . We illustrate these
properties by solving exactly the kinetic Potts model in . We then analyze
a Langevin equation of an appropriate field theory to compute these correlation
functions for general and . We establish a correspondence between the
two-point correlations of the -state Potts model and those of a kinetic
Ising model evolving with a fixed magnetization . The dynamics of this
Ising model is solved exactly in the large q limit, and in the limit of a large
number of components for the order parameter. For general and in any
dimension, we introduce a Gaussian closure approximation and calculate within
this approximation the scaling functions and the exponent . These
are in good agreement with the direct numerical simulations of the Potts model
as well as the kinetic Ising model with fixed magnetization. We also discuss
the existing and possible experimental realizations of these models.Comment: TeX, Vanilla.sty is needed. [Admin note: author contacted regarding
missing figure1 but is unable to supply, see journal version (Nov99)
Measurement of Spin Density Matrix Elements in Λ(1520) Photoproduction at 8.2-8.8 GeV
We report on the measurement of spin density matrix elements of the Λ(1520) in the photoproduction reaction γp→Λ(1520)K+, via its subsequent decay to K−p. The measurement was performed as part of the GlueX experimental program in Hall D at Jefferson Laboratory using a linearly polarized photon beam with Eγ = 8.2 GeV–8.8 GeV. These are the first such measurements in this photon energy range. Results are presented in bins of momentum transfer squared, − (t − t0). We compare the results with a Reggeon exchange model and determine that natural exchange amplitudes are dominant in Λ(1520) photoproduction
Photoproduction of K+ K- Meson Pairs on the Proton
The exclusive reaction γp → pK+K− was studied in the photon energy range 3.0–3.8 GeV and momentum transfer range 0.6 \u3c −t\u3c 1.3 GeV2. Data were collected with the CLAS detector at the Thomas Jefferson National Accelerator Facility. In this kinematic range the integrated luminosity was approximately 20 pb−1. The reaction was isolated by detecting the K+ and the proton in CLAS, and reconstructing the K− via the missing-mass technique. Moments of the dikaon decay angular distributions were extracted from the experimental data. Besides the dominant contribution of the ϕ meson in the P wave, evidence for S − P interference was found. The differential production cross sections dσ=dt for individual waves in the mass range of the ϕ resonance were extracted and compared to predictions of a Regge-inspired model. This is the first time the t-dependent cross section of the S-wave contribution to the elastic K+K− photoproduction has been measured
Professionalism, Golf Coaching and a Master of Science Degree: A commentary
As a point of reference I congratulate Simon Jenkins on tackling the issue of professionalism in coaching. As he points out coaching is not a profession, but this does not mean that coaching would not benefit from going through a professionalization process. As things stand I find that the stimulus article unpacks some critically important issues of professionalism, broadly within the context of golf coaching. However, I am not sure enough is made of understanding what professional (golf) coaching actually is nor how the development of a professional golf coach can be facilitated by a Master of Science Degree (M.Sc.). I will focus my commentary on these two issues
Mass-dependent cuts in longitudinal phase space
Longitudinal phase space analyses as introduced by van Hove provided a
simplified method of separating different reaction production mechanisms. Cuts
in the longitudinal phase space can help to select specific reaction kinematics
but also induce nonflat acceptance effects in angular distributions. We show
that in photoproduction reactions dominated by t-channel exchanges, selection
of meson or baryon production over a large mass range can be optimized through
calculating mass-dependent cut limits compared to cuts on a van Hove plot
sector alone. A cut is presented that improves this selection of one type of
hadron production by rejecting another. In addition we demonstrate that using
cuts in longitudinal phase space preserves sufficient information to reliably
extract observables from the angular distribution of the final state particles.Comment: 9 pages, 9 figures, copyright AP
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