Dear colleagues,
Here is my proposed abstract for a muCap talk at the APS/JPS Hawaii
meeting in September. I welcome your comments; the deadline for
submitting it is Wednesday afternoon, so please let me know tomorrow
if there are any concerns.
The TeX is below; the attachment shows how it is rendered by the
APS system.
Thanks,
-- Fred
-- Fred Gray / Visiting Postdoctoral Researcher --
-- Department of Physics / University of California, Berkeley --
-- fegray@berkeley.edu / phone 510-642-2438 / fax 510-642-9811 --
The $\mu$Cap collaboration$^{1}$ is measuring the rate of muon capture on
the proton in hydrogen. Muons are stopped in a time projection chamber (TPC)
filled with isotopically pure protium gas that contains of order
$10^{-6}$ deuterium and $10^{-8}$ higher-$Z$ impurity contamination.
This active target allows the muon to be tracked to its stopping point so that
only those stopping within the chamber, well away from the walls, are included
in the data set. The effective lifetime of the negative muon is measured in
this environment from the time spectrum of decay electrons. It is compared
with the positive muon lifetime to determine the capture rate, which in turn
gives $g_p$, the induced weak pseudoscalar form factor of the proton.
Precise theoretical predictions of $g_p$ have been made using heavy baryon
chiral perturbation theory, with uncertainties at the level of $3\%$.
The current experimental situation is confusing, with significant ambiguity
introduced by the formation of $p \mu p$ molecular states in the liquid
hydrogen targets that were used in these experiments, a difficulty that is
avoided with a lower-density gas target. A precise measurement to compare
with theory will provide a sensitive test of the chiral symmetry of QCD.
A ``blind'' analysis of the data collected in fall 2004 (a $\sim 15\%$
measurement of $g_p$) is in progress. Data collection will continue in 2005
and 2006, with an eventual precision goal of $7\%$.
$^{1}$ PNPI - PSI - UC Berkeley -
UI Urbana-Champaign - UC de Louvain - Boston University -
UK Lexington - TU M\"unchen
Attachment:
mucap_abstract.jpg
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