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FERMILAB-Conf-00/344-E CKM January 2001
CKM - Charged Kaons at the Main Injector
Peter S. Cooper
Fermi National Accelerator Laboratory
P.O.Box 500, Batavia IL, USA, 60510
aFor the CKM Collaboration
Web Address: http://www.fnal.gov/projects/ckm/Welcome.html
The CKM experiment is a proposal to measure the branching ratio of the rare decay K+ 4 7r+vp at the Main
Injector at Fermilab using a decay in flight technique. The goal is to observe ~ 100 events, for a Standard Model
branching ratio of 1 x 10-10 with a background of less than 10 events.
The branching ratio for the decay K+ 4 1r+vj
was first calculated by Inami and Lim  as an
isospin rotation from K+ -+ roe+v. The mea-
surement of the branching ratio of K+ -+ 1r+vj
alone will allow one to obtain the magnitude
of Vtd, the element in the Cabbibo Kobayashi
Maskawa matrix, which controls CP violation in
the Standard Model. In conjunction with the
neutral channel decay K0 -+ ir0v and measure-
ments in the B sector, this will provide an over-
constrained measurement of both the real (p) and
the imaginary (ii) parts of Vtd. Figure 1 illustrates
the proposed sensitivity of experiments that will
measure p and 9.
The critical question is: Are all CP phenom-
ena described by just p and ? Lincoln Wolfen-
stein, who invented p and il, says he doesn't care
what their actual values are - we shouldn't ei-
ther. The four observables of Figure 1 are the
only ones with sufficiently robust theoretical pre-
dictions that an inconsistency among them would
require contributions to CP violation beyond the
The present Standard Model branching ra-
tio prediction for the K+ -+ 1r+vv decay is
[0.8 + 0.3] x 10-10 . One event, correspond-
ing to a branching ratio of 1.5+3.4 x 10-10, has
been observed by the BNL experiment E787 us-
ing stopped K+ . We propose  to measure
the decay in flight of K+ -+ 1r+vv and obtain
-50sin(2>=+ 06 /
Figure 1. Experiments proposed sensitivity in the
measurement of the CP violating parameters of
the Standard Model.
>70 events in two years of data taking . This will
match the precision suggested by the theoretical
uncertainty. An intermediate stage, the observa-
tion of 5-10 events, is the goal of an approved
BNL experiment E949, which is the continuation
of E787. Some members of the CKM and E949
are now working in collaboration with each other
as two stages of a physics program.
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Cooper, P.S. CKM--Charged Kaons at the Main Injector, article, January 16, 2001; Batavia, Illinois. (digital.library.unt.edu/ark:/67531/metadc720171/m1/1/: accessed July 21, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.