236 research outputs found
Observation of double radiative capture on pionic hydrogen
We report the first observation of double radiative capture on pionic
hydrogen. The experiment was conducted at the TRIUMF cyclotron using the RMC
spectrometer, and detected --ray coincidences following stops
in liquid hydrogen. We found the branching ratio for double radiative capture
to be . The measured
branching ratio and angle-energy distributions support the theoretical
prediction of a dominant contribution from the
annihilation mechanism.Comment: 4 Pages, 4 Figures. accepted for publication in Phys. Rev. Let
Polarized photons in radiative muon capture
We discuss the measurement of polarized photons arising from radiative muon
capture. The spectrum of left circularly polarized photons or equivalently the
circular polarization of the photons emitted in radiative muon capture on
hydrogen is quite sensitive to the strength of the induced pseudoscalar
coupling constant . A measurement of either of these quantities, although
very difficult, might be sufficient to resolve the present puzzle resulting
from the disagreement between the theoretical prediction for and the
results of a recent experiment. This sensitivity results from the absence of
left-handed radiation from the muon line and from the fact that the leading
parts of the radiation from the hadronic lines, as determined from the chiral
power counting rules of heavy-baryon chiral perturbation theory, all contain
pion poles.Comment: 10 pages, 6 figure
Muon capture by a proton in heavy baryon chiral perturbation theory
The matrix element for muon capture by a proton is calculated to O(p^3)
within heavy baryon chiral perturbation theory using the new O(p^3) Lagrangian
of Ecker and Mojzis. External nucleon fields are renormalized using the
appropriate definition of the wave function renormalization factor Z_N. Our
expression for Z_N differs somewhat from that found in existing literature, but
is the one which is consistent with the Lagrangian we use and the one which
ensures, within our approach, the nonrenormalization of the vector coupling as
required by the conserved vector current. Expressions for the standard muon
capture form factors are derived and compared to experimental data and we
determine three of the coefficients of the Ecker - Mojzis Lagrangian, namely,
b_7, b_{19}, and b_{23}.Comment: 14 pages, LaTeX, using revte
Capture rate and neutron helicity asymmetry for ordinary muon capture on hydrogen
Applying heavy-baryon chiral perturbation theory to ordinary muon capture
(OMC) on a proton, we calculate the capture rate and neutron helicity asymmetry
up to next-to-next-to-leading order. For the singlet hyperfine state, we obtain
the capture rate Gamma_0 = 695 sec^{-1} while, for the triplet hyperfine state,
we obtain the capture rate Gamma_1 = 11.9 sec^{-1} and the neutron asymmetry
alpha_1 = 0.93. If the existing formalism is used to relate these atomic
capture rates to Gamma_{liq}, the OMC rate in liquid hydrogen, then Gamma_{liq}
corresponding to our improved values of Gamma_0 and Gamma_1 is found to be
significantly larger than the experimental value, primarily due to the updated
larger value of g_A. We argue that this apparent difficulity may be correlated
to the specious anomaly recently reported for mu^- + p to n + nu_mu + gamma,
and we suggest a possibility to remove these two "problems" simply and
simultaneously by reexamining the molecular physics input that underlies the
conventional analysis of Gamma_{liq}.Comment: 14 pages, 1 figur
Radiative Muon Capture on Hydrogen and the Induced Pseudoscalar Coupling
The first measurement of the elementary process is reported. A photon pair spectrometer was used to measure
the partial branching ratio ( for photons of k >
60 MeV. The value of the weak pseudoscalar coupling constant determined from
the partial branching ratio is , where the first error is the quadrature sum of statistical
and systematic uncertainties and the second error is due to the uncertainty in
, the decay rate of the ortho to para molecule. This
value of g_p is 1.5 times the prediction of PCAC and pion-pole dominance.Comment: 13 pages, RevTeX type, 3 figures (encapsulated postscript), submitted
to Phys. Rev. Let
A new measurement of the properties of the rare decay K -> pi+ e+ e-
A large low-background sample of events (10300) has been collected for the
rare decay of kaons in flight K+ -> pi+ e+ e- by experiment E865 at the
Brookhaven AGS. The decay products were accepted by a broad band
high-resolution charged particle spectrometer with particle identification. The
branching ratio (2.94 +- 0.05(stat.) +- 0.13(syst.) +- 0.05(model))*10**{-7}
was determined normalizing to events from the decay chain K+ -> pi+ pi0; pi0 ->
e+ e- gamma. From the analysis of the decay distributions the vector nature of
this decay is firmly established now, and limits on scalar and tensor
contributions are deduced. From the (e+ e-) invariant mass distribution the
decay form factor f(z)=f0(1+ delta*z) (z=M(ee)**2/m(K)**2) is determined with
delta=2.14 +- 0.13 +- 0.15. Chiral QCD perturbation theory predictions for the
form factor are also tested, and terms beyond leading order O(p**4) are found
to be important.Comment: 4 pages, 5 figure
Recommended from our members
Conflict and Astroturfing in Niyamgiri: The Importance of National Advocacy Networks in Anti-Corporate Social Movements
Traditional models of transnational advocacy networks (TANs) and stakeholder management do not capture the nuance and dynamics of (counter-)organising processes around anti-corporate mobilisation. Based on the case of a resistance movement against a planned bauxite mine on tribal land in India, we develop a process theory of interactions between local, national and international actors within transnational advocacy networks. These encounters are not always friendly and are often characterised by conflict between actors with disparate goals and interests. We highlight the importance of national advocacy networks (NANs) in anti-corporate social movements and describe the conflicts and disruptions that result from ignoring them. Our findings also point to the role of corporate counter-mobilisation strategies in shaping resistance movements. Our narrative revolves around a particular focal actor in the anti-mining campaign: a young tribal man who emerged as a passionate spokesperson of the movement, but later became a supporter of the controversial mine. Our findings contribute to a richer understanding of the processes underlying transnational and national anti-corporate mobilisation
Induced pseudoscalar coupling of the proton weak interaction
The induced pseudoscalar coupling is the least well known of the weak
coupling constants of the proton's charged--current interaction. Its size is
dictated by chiral symmetry arguments, and its measurement represents an
important test of quantum chromodynamics at low energies. During the past
decade a large body of new data relevant to the coupling has been
accumulated. This data includes measurements of radiative and non radiative
muon capture on targets ranging from hydrogen and few--nucleon systems to
complex nuclei. Herein the authors review the theoretical underpinnings of
, the experimental studies of , and the procedures and uncertainties
in extracting the coupling from data. Current puzzles are highlighted and
future opportunities are discussed.Comment: 58 pages, Latex, Revtex4, prepared for Reviews of Modern Physic
Proportionate vs disproportionate distribution of wealth of two individuals in a tempered Paretian ensemble
We study the distribution P(\omega) of the random variable \omega = x_1/(x_1
+ x_2), where x_1 and x_2 are the wealths of two individuals selected at random
from the same tempered Paretian ensemble characterized by the distribution
\Psi(x) \sim \phi(x)/x^{1 + \alpha}, where \alpha > 0 is the Pareto index and
is the cut-off function. We consider two forms of \phi(x): a bounded
function \phi(x) = 1 for L \leq x \leq H, and zero otherwise, and a smooth
exponential function \phi(x) = \exp(-L/x - x/H). In both cases \Psi(x) has
moments of arbitrary order.
We show that, for \alpha > 1, P(\omega) always has a unimodal form and is
peaked at \omega = 1/2, so that most probably x_1 \approx x_2. For 0 < \alpha <
1 we observe a more complicated behavior which depends on the value of \delta =
L/H. In particular, for \delta < \delta_c - a certain threshold value -
P(\omega) has a three-modal (for a bounded \phi(x)) and a bimodal M-shape (for
an exponential \phi(x)) form which signifies that in such ensembles the wealths
x_1 and x_2 are disproportionately different.Comment: 9 pages, 8 figures, to appear in Physica
The Influence of Corporate Front-Group Stealth Campaigns
This research examined corporate front-group stealth campaigns. An experiment was conducted to examine the influence of front-group stealth campaigns on a variety of measures. It was anticipated that corporate front-group stealth campaigns, which feature names that mask the true interests of sponsors, positively affect public opinion, unless they are exposed as intentionally misleading, in which case they boomerang against sponsors. The experiment examined the potential of the inoculation strategy to preempt the influence of corporate front-group stealth campaigns. The pattern of results supported all of these expectations. Front-group stealth campaigns proved to be effective, at least in the short term. Front-group stealth campaigns eroded public attitudes toward the issue in question and boosted perceptions of the front group, but not the corporate sponsor. However, when front-group stealth campaigns were subsequently exposed, positive effects dissipated and perceptions of corporate sponsors boomeranged. Results revealed that inoculation can protect against the influence of front-group stealth campaigns.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline
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