611 research outputs found
Improved KL->pi e nu Form Factor and Phase Space Integral with Reduced Model Uncertainty
Using the published KTeV sample of 2 million KL-> pi e nu decays and a new
form factor expansion with a rigorous bound on higher order terms, we present a
new determination of the KL->pi e nu form factor and phase space integral.
Compared to the previous KTeV result, the uncertainty in the new form factor
expansion is negligible and results in an overall uncertainty in the phase
space integral (IKe) that is a factor of two smaller: IKe = 0.15392 +- 0.00048
\.Comment: 3 pages, 2 figures, submitted to PRD Rapid Communicatio
A Measurement of the K0 Charge Radius and a CP Violating Asymmetry Together with a Search for CP Violating E1 Direct Photon Emission in the Rare Decay KL->pi+pi-e+e-
Using the complete KTeV data set of 5241 candidate KL->pi+pi-e+e- decays
(including an estimated background of 204+-14 events), we have measured the
coupling gCR=0.163+- 0.014(stat)+-0.023(syst) of the CP conserving charge
radius process and from it determined a K0 charge radius of
(K0)=(-0.077+-0.007(stat)+-0.011(syst)) fm**2. We have also determined a
first experimental upper limit of 0.04 (90% CL) for the ratio |g_{E1}|/|g_{M1}|
of the coupling for the E1 direct photon emission process relative to the
coupling for M1 direct photon emission process. We also report the measurement
of its associated vector form factor |gM1`|(1+
(a_1/a_2)/(M(rho)**2-M(K)**2)+2M(K)E(gamma*)) where |gM1`|=(1.11+-
0.12(stat)+-0.08(syst) and a_1/a_2 = (-0.744+-0.027(stat)0.032(syst))
GeV**2/c**2. In addition, a measurement of the manifestly CP violating
asymmetry of magnitude (13.6+- 1.4+-(stat)+-1.5(syst))% in the CP and T odd
angle phi between the decay planes of the e+e- and pi+pi- pairs in the KL
center of mass system is reported
Measurement of the rare decay pi0 -> e+ e-
The branching ratio of the rare decay pi0 -> e+ e- has been measured
precisely, using the complete data set from the KTeV E799-II experiment at
Fermilab. We observe 794 candidate pi0 -> e+ e- events using K0_L -> 3pi0 as a
source of tagged pi0's. The expected background is 52.7 +- 11.2 events,
predominantly from high e+ e- mass pi0 -> e+ e- gamma decays. We have measured
B[(pi0 -> e+ e-), (m_e+e-/m_pi0)^2 > 0.95] = 6.44 +- 0.25(stat) +- 0.22(syst)
x10^(-8), which is above the unitary bound from pi0 -> gamma gamma and within
the range of theoretical expectations from the standard model.Comment: 6 pages, 4 figure
Measurements of KL Branching Fractions and the CP Violation Parameter |eta+-|
We present new measurements of the six largest branching fractions of the KL
using data collected in 1997 by the KTeV experiment (E832) at Fermilab. The
results are B(KL -> pi e nu) = 0.4067 +- 0.0011 B(KL -> pi mu nu) = 0.2701 +-
0.0009 B(KL -> pi+ pi- pi0) = 0.1252 +- 0.0007 B(KL -> pi0 pi0 pi0) = 0.1945 +-
0.0018 B(KL -> pi+ pi-) = (1.975 +- 0.012)E-3, and B(KL -> pi0 pi0) = (0.865 +-
0.010)E-3, where statistical and systematic errors have been summed in
quadrature. We also determine the CP violation parameter |eta+-| to be (2.228
+- 0.010)E-3. Several of these results are not in good agreement with averages
of previous measurements.Comment: Submitted to Phys. Rev. D; 20 pages, 22 figure
Measurement of Direct Emission in the KL->pi+pi-gamma Decay Mode
In this paper the KTeV collaboration reports the analysis of 112.1*10^3
candidate KL->pi+pi-gamma decays including a background of 671+/-41 events with
the objective of determining the photon production mechanisms intrinsic to the
decay process. These decays have been analyzed to extract the relative
contributions of the CP violating bremsstrahlung process and the CP conserving
M1 and CP violating E1 direct photon emission processes. The M1 direct photon
emission amplitude and its associated vector form factor parameterized as
|g_M1|(1+ (a_1/a_2)/(M(rho)^2-M(K)^2+2M(K)*E(gamma)) have been measured to be
|g_M1|=1.198 +/- 0.035(stat) +/- 0.086(syst) and a_1/a_2 = -0.738 +/-
0.007(stat) +/- 0.018 (syst) GeV^2/c^2 respectively. An upper limit for the CP
violating E1 direct emission amplitude |g_E1| < 0.21 (90% CL) has been found.
The overall ratio of direct photon emission (DE) to total photon emission
including the bremsstrahlung process (IB) has been determined to be DE/(DE +IB)
= 0.689 +/- 0.021 for E(gamma) > 20 MeV.Comment: REVTeX 3.1, 4 pages, 4 figures submitted to Physical Review Letter
Search for the Decay K_L -> pi^0 nu nubar using pi^0 -> e^+ e^- gamma
We report on a search for the decay K_L -> pi^0 nu nubar, carried out as a
part of E799-II, a rare K_L decay experiment at Fermilab. Within the Standard
Model, the K_L -> pi^0 nu nubar decay is dominated by direct CP violating
processes, and thus an observation of the decay implies confirmation of direct
CP violation. Due to theoretically clean calculations, a measurement of B(K_L
-> pi^0 nu nubar) is one of the best ways to determine the CKM parameter eta.
No events were observed, and we set an upper limit B(K_L -> pi^0 nu nubar) <
5.9 times 10^-7 at the 90% confidence level.Comment: 5 pages, 4 figure
Cascade and anti-Cascade Polarization Measurements at 800 GeV/c
The polarization of neutral Cascade and anti-Cascade hyperons produced by 800
GeV/c protons on a BeO target at a fixed targeting angle of 4.8 mrad is
measured by the KTeV experiment at Fermilab. Our result of 9.7% for the neutral
Cascade polarization shows no significant energy dependence when compared to a
result obtained at 400 GeV/c production energy and at twice our targeting
angle. The polarization of the neutral anti-Cascade is measured for the first
time and found to be consistent with zero. We also examine the dependence of
polarization on transverse production momentum.Comment: 4 page PR
Search for Light Gluinos via the Spontaneous Appearance of pi+pi- Pairs with an 800 GeV/c Proton Beam at Fermilab
We searched for the appearance of pi+pi- pairs with invariant mass greater
than 648 MeV in a neutral beam. Such an observation could signify the decay of
a long-lived light neutral particle. We find no evidence for this decay. Our
null result severely constrains the existence of an R0 hadron, which is the
lightest bound state of a gluon and a light gluino, and thereby also the
possibility of a light gluino. Depending on the photino mass, we exclude the R0
in the mass and lifetime ranges of 1.2 -- 4.6 GeV and 2E-10 -- 7E-4 seconds,
respectively. (To Appear in Phys. Rev. Lett.)Comment: Documentstyle aps,epsfig,prl (revtex), 6 pages, 7 figure
Observation of the Decay
We have observed the decay at the KTeV
experiment at Fermilab. This decay presents a formidable background to the
search for new physics in . The 1997 data yielded a
sample of 4 signal events, with an expected background of 0.155 0.081
events. The branching ratio is )
with
, consistent with a QED calculation
which predicts .Comment: See also the paper "Search for the Decay ", also by the KTeV collaboratio
Search for the Decay
We report on a search for the decay \klpimumu carried out as a part of the
KTeV experiment at Fermilab. This decay is expected to have a significant
violating contribution and a direct measurement will either support the CKM
mechanism for CP violation or point to new physics. Two events were observed in
the 1997 data with an expected background of events, and we set
an upper limit \BR{\klpimumu} at the 90% confidence
level.Comment: See also "Observation of the Decay ", also by the KTeV collaboratio
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