604 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
Radiative Decay Width Measurements of Neutral Kaon Excitations Using the Primakoff Effect
We produce a sample consisting of 147 candidate events, with minimal
backgrounds, of the mixed axial vector pair K1(1270)-K1(1400) by exciting Kl's
in the Coulomb field of lead and report the first measurements of the radiative
widths Gamma_r(K1(1400)) = 280.8+-23.2(stat)+-40.4(syst) keV and
Gamma_r(K1(1270)) = 73.2+- 6.1(stat)+-28.3(syst) keV. We also place 90% CL
upper limits Gamma_r(K*(1410)) < 52.9 keV for the vector state and
Gamma_r(K2*(1430)) < 5.4 keV for the tensor state. These measurements allow for
significant tests of quark-model predictions of radiative widths for the
low-lying vector mesons.Comment: PRL-size article, 4 figure
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
First Observation of the decay KL -> pi0 e e gamma
We report on the first observation of the decay KL -> pi0 ee gamma by the
KTeV E799 experiment at Fermilab. Based upon a sample of 48 events with an
estimated background of 3.6 +/- 1.1 events, we measure the KL -> pi0 ee gamma
branching ratio to be (2.34 +/- 0.35 +/- 0.13)x10^{-8}. Our data agree with
recent O(p^6) calculations in chiral perturbation theory that include
contributions from vector meson exchange through the parameter a_V. A fit was
made to the KL -> pi0 ee gamma data for a_V with the result -0.67 +/- 0.21 +/-
0.12, which is consistent with previous results from KTeV.Comment: Submitted to Physical Review Letters, 5 pages, 5 figure
Light Gluino Search for Decays Containing pi+pi- or pi0 from a Neutral Hadron Beam at Fermilab
We report on two null searches, one for the spontaneous appearance of
pairs, another for a single , consistent with the decay of
a long-lived neutral particle into hadrons and an unseen neutral particle. For
the lowest level gluon-gluino bound state, known as the , we exclude the
decays and for
the masses of and in the theoretically allowed range. In
the most interesting mass range, , we exclude
lifetimes from seconds to as high as seconds,
assuming perturbative QCD production for the .Comment: 15 pages, 7 figure
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
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
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
Measurements of the rare decay K_{L} -> e^{+} e^{-} e^{+} e^{-}
We observe 441 K_{L} -> e^{+} e^{-} e^{+} e^{-} candidate events with a
background of 4.2 events and measure B(K_{L} -> e^{+} e^{-} e^{+} e^{-}) =
(3.72 \pm 0.18(stat) \pm 0.23(syst)) \times 10^{-8} in the KTeV/E799II
experiment at Fermilab. Using the distribution of the angle between the planes
of the e^{+} e^{-} pairs, we measure the CP parameters beta_{CP} = -0.23 \pm
0.09(stat) \pm 0.02(syst) and gamma_{CP} = -0.09 \pm 0.09(stat) \pm 0.02(syst).
We also present the first detailed study of the e^{+} e^{-} invariant mass
spectrum in this decay mode.Comment: 14 pages, 4 figure
Search for the Decay Kl -> pi0 e+ e-
We report on a search for the decay Kl -> pi0 e+ e- carried out by the
KTeV/E799 experiment at Fermilab. This decay is expected to have a significant
CP violating contribution and the measurement of its branching ratio could
support the CKM mechanism for CP violation or could point to new physics. Two
events were observed in the 1997 data with an expected background of 1.06
+-0.41 events, and we set an upper limit Br(Kl -> pi0 e+ e-) < 5.1 x 10^-10 at
the 90% confidence level.Comment: 13 pages, 2 figure
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