Physics prospects of the KTeV experiment at Fermilab Page: 3 of 6

Physics Prospects of the KTeV Experiment at Fermilab

J. Whitmore
Representing the KTeV Collaboration
Fermi National Accelerator Laboratory, Batavia, IL 60510, USA
KTeV is a new Fermilab fixed target experiment which will search for direct CP violation in the neutral kaon
system. In addition, we will make precision measurements of other CP and CPT violating parameters and make
high sensitivity studies of rare kaon decays. The detector has been commissioned and is currently taking data.
The physics goals and detector performance are presented.

1 CP Violation
Within the framework of the Standard Model, the
CP violating decay KL -* 2r arises primarily from
an asymmetry in the rate of K0 - K0 transitions.
This effect, known as "indirect" CP violation, can
be described by the standard K0 - K0 AS = 2
W-box diagrams and is parametrized by e. If we
define K7 : K2 + EK1, where the K2(K1) is a
CP-odd(CP-even) eigenstate, then indirect CP vi-
olation in the decay KL -+ 2w occurs because it
includes a small admixture of CP-even K1. By
contrast, "direct" CP violation occurs when the
K2 component of the K decays via a AS = 1
transition. The strength of this transition, which
can be described by strong and electromagnetic
penguin diagrams, is governed by the parameter
E'. The measured quantity, E'/E, can be expressed
through the double ratio
R -r(K7 - w+w--)/r(K, -+ 7r+7-)
r(KL -+ ?0r0)/'r(K? -+ 700) (1)
t 1 + 6Re(e'/e),
where 7+- ~ E+e' and 7oo = E-2E'. Calculations
of the Re(e'/E) depend on the interference between
the various penguin diagrams and are sensitive to
the top mass. Predictions 1 give a value of between
(-1 - 15) x 10-4. Other models, such as Super-
weak 2, account for CP violation only through di-
rect AS = 2 couplings, with the direct CP violat-
ing parameter E'= 0.
The NA31 experiment at CERN, has mea-
sured 3 a value of E'/E of (23 + 3.5 6) x 10-4.
while the Fermilab experiment E731 measured 4
(7.4 5.2 2.9) x 10-4. These numbers differ
by ~ 1.8a- and suggest different conclusions as to

whether there is a direct CP violating effect. It is
experimentally compelling to measure E'/E more
precisely to learn whether there is a contribution
from direct CP violation. There are three new
experiments being developed to precisely measure
e'/c: the KLOE detector at DA<DNE (1998), the
NA48 experiment at CERN (April 1997), and the
KTeV experiment at Fermilab, which came online
in August of this year.
2 Physics Goals
The Kaons at the TeVatron program a is a new
fixed target experiment at Fermilab designed to
study the properties of the neutral kaon sys-
tem. The experimental program has two distinct
phases. The first phase will focus on making a
high precision measurement of C'/E with a com-
bined statistical and systematic error of 1 x 10-4.
This measurement will be discussed in greater de-
tail in Section 4. In addition to determining E'/E.
KTeV will will precisely measure 0+ - 0oo, 0+-,
r~, Am, 7+-y, and 0+-., as well as other decays.
In the second phase, the experiment will col-
lect a large sample of rare K7 decays. Rare de-
cays provide windows into a variety of physics
topics such as lepton number violation, long and
short distance physics, and parity violation. The
rare decay modes which have the most poten-
tial to provide information about CP violation
are KL , 70+1-, where f = e, A, v. These de-
cays are predicted to have large direct CP vio-
lating contributions to their amplitudes. Unfor-
tunately, the branching fractions for these decay
modes are extremely small, of 0(10-11 - 10-12),
4KTeV is a collaboration of Arizona, Chicago, Colorado,
Elnhurst, Fermilab, Osaka, Rice, Rutgers, UCLA, UCSD,
Virginia and Wisconsin.

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Whitmore, J. & Collaboration, KTeV. Physics prospects of the KTeV experiment at Fermilab, article, October 1, 1996; Batavia, Illinois. (digital.library.unt.edu/ark:/67531/metadc679318/m1/3/ocr/: accessed October 15, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.

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