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An Observation Of Direct-CP Violation - E'/c Result From KTeV
Yee Bob Hsiunga*
aMS122, Fermilab, P. O. Box 500, Batavia, IL 60510
We report the first KTeV measurement for the search of direct-CP violation by using 23% of the data sample
collected in the 1996-97 fixed target run at Fermilab, . The result is, Re(c'/c) = (28.0 4.1) x 10-4, nearly 7a
above zero obtained by a blind analysis. This firmly establishes the long-sought "direct-CP violation" effect in
the two-pion system (7r+7- versus i-0i-0) of neutral kaon decays. Other new measurements of Am, -rs, A# and a
limit on the diurnal variation of #+- for testing CPT invariance from the same data sample are also presented.1. Introduction
One long lasting piece of puzzle in particle
physics is the origin of CP violation, where C
stands for the charge conjugation (exchange par-
ticle and anti-particle) and P stands for the parity
(space inversion). Thirty-five years after the first
unexpected discovery [1] of CP violation in KL -4
irir decays in 1964, we can only explain the dom-
inant effect as due to a small asymmetry of the
K - K mixing or admixture of wrong CP states
in the Ks and KL neutral kaons, parametrized by
E (about 0.0023). The question is "Does CP vi-
olation also occur in the K -* ww decay process
itself?" or "Can CP-odd component of neutral
kaon decay directly into CP-even final states?"
An effect referred as "direct-CP violation" [2],
parametrized by c' which contributes differently
to the rates of KL - 7+r-versus KL -+ 7r00 de-
cays (relative to the corresponding Ks decays),
and would be observed as a nonzero value in the
ratio of Re(E'/E).
Experimentally we measure the double ratio R,
R F(KL - 7r+7r)/F(Ks 7r+7r-)
F(KL -4 ir0ir0)/F(Ks - w0r0)
- I00 ~2 1 + 6Re(C'/E). (1)
ma 2
The standard Cabbibo-Kobayashi-Maskawa
(CKM) model [3] accomodates CP violation with
a complex phase in the quark mixing matrix,
*for KTeV Collaboration: Arizona, Chicago, Colorado,
Elmhurst, Fermilab, Osaka, Rice, Rutgers, UCLA, UCSD,
Virginia and Wisconsin.but the calculations of Re(C'/E) are still uncer-
tain depending on several input parameters and
on the method used to estimate the hadronic ma-
trix elements. Most recent estimates [4] [5] had
given non-zero values slightly below 10-3; how-
ever, another group [6] gave a somewhat larger
estimates. Alternatively, a "superweak" inter-
action [7] could also produce the observed CP-
violating mixing effect (E) but would give c'/E =
0. Therefore, a non-zero measurement of Re(E'/E)
would rule out the possibility that a superweak in-
teraction is the sole source of CP violation, and
would establish the "direct" CP violation from
the decay process itself.
The earlier two measurements of Re(E'/E) from
Fermilab-E731 [8] and CERN-NA31 [9] wereRe(C'/)
Re(C'/E)(7.4 + 5.9) x 10-4, (E731) (2)
(23.0 + 6.5) x 10-4, (NA31) (3)and the PDG average was (15 + 8) x 10-4 [10]
which gave inconclusive interpretations between
standard model or superweak CP-violation.
New experiments have been constructed at
Fermilab(KTeV), CERN(NA48) [11] and Fras-
cati(KLOE) to measure Re(E'/) with a precision
of ~ 1 x 10-4 for the search of "direct" CP vio-
lating effect and determining its magnitude.
We report here a new measurement of Re(E'/E)
from 23% of the data collected by the KTeV ex-
periment (E832 run period) during 1996-97 fixed
target run at Fermilab. This result has recently
been published in [12] after the first preliminary
announcement in February 24, 1999.
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Hsiung, Bob. An observation of direct-CP violation - {epsilon}{prime}{epsilon} result from KTeV, article, December 14, 1999; Batavia, Illinois. (https://digital.library.unt.edu/ark:/67531/metadc625570/m1/3/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.