74 research outputs found
pi-N charge exchange and pi(+)-pi(0) scattering at low energies
pi-N and pi-pi interactions near threshold are uniquely sensitive to the
chiral symmetry breaking part of the strong interaction. The pi-N sigma-term
value with its implications for nucleon quark structure and the recent
controversy concerning the size of the scalar quark condensate have renewed the
experimental interest in these two fundamental systems. We report new
differential cross sections for the reaction at 27.5 MeV
pion incident kinetic energy, measured between and
. Our results are in excellent agreement with the existing
comprehensive pi-N phase shift analysis. We also report on a Chew-Low analysis
of exclusive data at 260 MeV pion incident energy.Comment: Talk given by D. Pocanic at QULEN97, Osaka, 20-23 May 1997; 4 pages,
2 PostScript figures, writen in LaTeX 2e, uses packages "epsfig" and
"espcrc1
Measurement of stopping beam distributions in the PIBETA detector
Precise calculation of the geometrical acceptance of a large solid angle
detector with an integrated stopping target relies on precise knowledge of the
beam geometry. We describe four alternative methods that we used to measure the
beam stopping distributions in the PIBETA detector active target: (i) light
response of segmented target elements to incident beam particles, (ii)
back-tracking of charged particles from pi+ and mu+ decays using multi-wire
proportional chambers, (iii) volume distribution of the Dalitz decay
(pi0->gamma e+e-) event vertices, and (iv) the opening angle distribution of
two pi0 photons originating from the beta decay of pi+ at rest. We demonstrate
consistent results obtained by these four independent approaches and show how
particular beam stopping distributions affect the detector's geometrical
acceptance.Comment: 38 pages, 16 postscript figures, 2 tables, LaTeX, submitted to Nucl.
Instrum. Meth.
Impact of Neutron Decay Experiments on non-Standard Model Physics
This paper gives a brief overview of the present and expected future limits
on physics beyond the Standard Model (SM) from neutron beta decay, which is
described by two parameters only within the SM. Since more than two observables
are accessible, the problem is over-determined. Thus, precise measurements of
correlations in neutron decay can be used to study the SM as well to search for
evidence of possible extensions to it. Of particular interest in this context
are the search for right-handed currents or for scalar and tensor interactions.
Precision measurements of neutron decay observables address important open
questions of particle physics and cosmology, and are generally complementary to
direct searches for new physics beyond the SM in high-energy physics. Free
neutron decay is therefore a very active field, with a number of new
measurements underway worldwide. We present the impact of recent developments.Comment: 13 pages, 6 figures; Proceedings of the 5th International BEYOND 2010
Conference, Cape Town, South Africa (2010), World Scientific, accepted for
publication; Corrected typo
The automatic gain-matching in the PIBETA CsI calorimeter
Segmented electromagnetic calorimeters are used to determine both the total
energy and direction (momentum components) of charged particles and photons. A
trade off is involved in selecting the degree of segmentation of the
calorimeter as the spatial and energy resolutions are affected differently.
Increased number of individual detectors reduces accidental particle pile-up
per detector but introduces complications related to ADC pedestals and pedestal
variations, exacerbates the effects of electronic noise and ground loops, and
requires summing and discrimination of multiple analog signals. Moreover,
electromagnetic showers initiated by individual ionizing particles spread over
several detectors. This complicates the precise gain-matching of the detector
elements which requires an iterative procedure. The PIBETA calorimeter is a
240-module pure CsI non-magnetic detector optimized for detection of photons
and electrons in the energy range 5-100 MeV. We present the
computer-controlled, automatic, in situ gain-matching procedure that we
developed and used routinely in several rare pion and muon decay experiments
with the PIBETA detector.Comment: 28 pages, 13 postscript figures, LaTeX, submitted to Nucl. Instrum.
Meth.
Optics: general-purpose scintillator light response simulation code
We present the program optics that simulates the light response of an
arbitrarily shaped scintillation particle detector. Predicted light responses
of pure CsI polygonal detectors, plastic scintillator staves, cylindrical
plastic target scintillators and a Plexiglas light-distribution plate are
illustrated. We demonstrate how different bulk and surface optical properties
of a scintillator lead to specific volume and temporal light collection
probability distributions. High-statistics optics simulations are calibrated
against the detector responses measured in a custom-made cosmic muon tomography
apparatus. The presented code can also be used to track particles intersecting
complex geometrical objects.Comment: RevTeX LaTeX, 37 pages in e-print format, 12 Postscript Figures and 1
Table, also available at
http://pibeta.phys.virginia.edu/public_html/preprints/optics.p
Otpornost na zračenje dijelova detektora PIBETA
We have examined long-term changes in signal amplitude gain, energy resolution and detection efficiency of the active components of the PIBETA detector system. Beam-defining plastic scintillation counters were operated in a ∼ 1 MHz stopped π + beam for a period of 297 days, accumulating radiation doses of up to 2 · 106 rad. Detectors in the charged particle tracking system — a pair of cylindrical multi-wire proportional chambers and a thin plastic scintillation barrel-shaped hodoscope array — were irradiated during the same running period with an average dose of ∼ 4 · 104 rad. Individual CsI (undoped crystal) calorimeter detectors received an average dose of ∼ 120 rad, mainly from photons, positrons and protons originating from π + hadronic interactions as well as from π + and µ + weak decays at rest in the active target.Ispitivali smo trajne promjene amplitude, energijskog razlučivanja i učinkovitosti detekcije aktivnih dijelova detektorskog sustava PIBETA. Plastični scintilacijski detektori koji definiraju snop ozračeni su do 2 Mrad. Par višežičanih proporcionalnih komora i tanak valjak plastičnih scintilacijskih detektora ozračeni su do 40 krad. CsI kalorimetrijski detektori ozračeni su do 120 rad
Light response of pure CsI calorimeter crystals painted with wavelength-shifting lacquer
We have measured scintillation properties of pure CsI crystals used in the
shower calorimeter built for a precise determination of the pi+ -> pi0 e+ nu
decay rate at the Paul Scherrer Institute (PSI). All 240 individual crystals
painted with a special wavelength-shifting solution were examined in a
custom-build detection apparatus (RASTA=radioactive source tomography
apparatus) that uses a 137Cs radioactive gamma source, cosmic muons and a light
emitting diode as complementary probes of the scintillator light response. We
have extracted the total light output, axial light collection nonuniformities
and timing responses of the individual CsI crystals. These results predict
improved performance of the 3 pi sr PIBETA calorimeter due to the painted
lateral surfaces of 240 CsI crystals. The wavelength-shifting paint treatment
did not affect appreciably the total light output and timing resolution of our
crystal sample. The predicted energy resolution for positrons and photons in
the energy range of 10-100 MeV was nevertheless improved due to the more
favorable axial light collection probability variation. We have compared
simulated calorimeter ADC spectra due to 70 MeV positrons and photons with a
Monte Carlo calculation of an ideal detector light response.Comment: Elsevier LaTeX, 35 pages in e-print format, 15 Postscript Figures and
4 Tables, also available at
http://pibeta.phys.virginia.edu/~pibeta/subprojects/csipro/tomo/rasta.p
Theoretical Predictions for Pionium Searches
Characteristic properties of pionium and associated low energy
s--wave cross sections ,
and are
investigated with a coupled channels potential model. Some experimental results
and conclusions are to be reconsidered.Comment: 10 Pages REVTeX using epsfig.sty. Submitted to PR
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