Award Abstract #0079449
Collaborative Research: The MuLAN Project -- Development of Instrumentation for a New High-Precision Determination of the Fermi Coupling Constant

NSF Org:	PHY Division of Physics
Initial Amendment Date:	August 22, 2000
Latest Amendment Date:	July 20, 2004
Award Number:	0079449
Award Instrument:	Standard Grant
Program Manager:	Bradley D. Keister PHY Division of Physics MPS Directorate for Mathematical & Physical Sciences
Start Date:	August 15, 2000
Expires:	July 31, 2005 (Estimated)
Awarded Amount to Date:	$229680
Investigator(s):	Robert Carey carey@bu.edu (Principal Investigator)
Sponsor:	Trustees of Boston University 881 COMMONWEALTH AVE BOSTON, MA 02215 617/353-4365
NSF Program(s):	MAJOR RESEARCH INSTRUMENTATION
Field Application(s):
Program Reference Code(s):	OTHR, 0000
Program Element Code(s):	1189

ABSTRACT

0079449

Carey

The MuLan Project will develop the instrumentation needed to

measure the lifetime of the positive muon to unprecedented

precision, namely, a factor of 20 better than the current world

average. The muon lifetime fixes the value of the Fermi constant,

which governs the strength of all weak-interaction processes, just

as the fine structure constant governs the strength of all

electromagnetic-interaction processes. The Fermi constant is one

of the fundamental parameters of the Standard Model of particle

physics. A low-energy, continuous-wave muon beam at the Paul

Scherrer Institute (PSI) in Switzerland will be modified by a new

beam chopper system in order to create intense, short bursts of

muons, which will stop in thin targets. A positive muon stopped in

appropriate materials decays as if it were in vacuum. Such targets

will be surrounded by a nearly hermetic set of 180 fast-scintillator

timing detectors, each coupled to a state-of-the-art waveform

digitizer, and all readout by a high-speed data acquisition system.

Online analysis of the nearly 100 terabytes of data will take place

with a small array of fast microprocessors.

A second use of the instrumentation is in conjunction with an

ongoing effort at PSI to measure the negative muon lifetime in

hydrogen gas. The negative muon can decay exactly in the same

manner as the positive muon, or in hydrogen it can interact with a

proton by the weak-interaction process known as "capture." The

capture rate is predicted very accurately by theory; however,

current experiments, which have various interpretation problems, are

in disagreement with theory by a very significant amount. If this

disagreement is confirmed, this difference raises the exciting

possibility of pointing to new and unaccounted-for physics. By

measuring the difference between the positive and negative muon

lifetimes, we will determine the muon capture rate reliably and at a

precision more than four times better than current measurements.

The MuLan timing detectors, beamline and custom electronics are

expected to play a major role in this effort.

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