81 research outputs found
Search for the Rare Decay K_{L}\to\pi^{0}\pi^{0}\gamma
The KTeV E799 experiment has conducted a search for the rare decay
via the topology
(where ). Due to Bose
statistics of the pair and the real nature of the photon, the
decay is restricted to proceed at lowest order
by the CP conserving direct emission (DE) of an E2 electric quadrupole photon.
The rate of this decay is interesting theoretically since chiral perturbation
theory predicts that this process vanishes at level . Therefore, this
mode probes chiral perturbation theory at . In this paper we report a
determination of an upper limit of (90% CL) for
. This is approximately a factor of 20 lower than
previous results.Comment: six pages and six figures in the submission. Reformatted for Physics
Review
Search for the Rare Decays KL->pi0pi0mu+mu- and KL->pi0pi0X0->pi0pi0mu+mu-
The KTeV E799 experiment has conducted a search for the rare decays
KL->pi0pi0mu+mu- and KL->pi0pi0X0->pi0pi0mu+mu-, where the X0 is a possible new
neutral boson that was reported by the HyperCP experiment with a mass of (214.3
pm 0.5) MeV/c^{2}. We find no evidence for either decay. We obtain upper limits
of Br(KL->pi0pi0X0->pi0pi0mu+mu-) pi0pi0mu+mu-) <
9.2 x 10^{-11} at the 90% confidence level. This result rules out the
pseudoscalar X0 as an explanation of the HyperCP result under the scenario that
the \bar{d}sX0 coupling is completely real
Determination of the Parity of the Neutral Pion via the Four-Electron Decay
We present a new determination of the parity of the neutral pion via the
double Dalitz decay pi^0 -> e+ e- e+ e-. Our sample, which consists of 30511
candidate decays, was collected from K_L -> pi0 pi0 pi0 decays in flight at the
KTeV-E799 experiment at Fermi National Accelerator Laboratory. We confirm the
negative pi^0 parity, and place a limit on scalar contributions to the pi^0 ->
e+ e- e+ e- decay amplitude of less than 3.3% assuming CPT conservation. The
pi^0 gamma* gamma* form factor is well described by a momentum-dependent model
with a slope parameter fit to the final state phase space distribution.
Additionally, we have measured the branching ratio of this mode to be B(pi^0 ->
e+ e- e+ e-) = (3.26 +- 0.18) x 10^(-5).Comment: 5 pages, 4 figures. Typographical error in radiative branching ratio
(Eq. 6) correcte
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
Detailed Study of the KL -> 3pi0 Dalitz Plot
Using a sample of 68 million KL -> 3pi0 decays collected in 1996-1999 by the
KTeV (E832) experiment at Fermilab, we present a detailed study of the KL ->
3pi0 Dalitz plot density. We report the first observation of interference from
KL->pi+pi-pi0 decays in which pi+pi- rescatters to 2pi0 in a final-state
interaction. This rescattering effect is described by the Cabibbo-Isidori
model, and it depends on the difference in pion scattering lengths between the
isospin I=0 and I=2 states, a0-a2. Using the Cabibbo-Isidori model, we present
the first measurement of the KL-> 3pi0 quadratic slope parameter that accounts
for the rescattering effect.Comment: accepted by Phys. Rev
Dispersive analysis of K_{L mu3} and K_{L e3} scalar and vector form factors using KTeV data
Using the published KTeV samples of K_L --> pi^{\pm} e^{\mp} nu and K_L -->
pi^{\pm} mu^{\mp} nu decays [1], we perform a reanalysis of the scalar and
vector form factors based on the dispersive parameterization [2,3]. We obtain
phase space integrals I^e_K = 0.15446 \pm 0.00025 and I^{mu}_K = 0.10219 \pm
0.00025. For the scalar form factor parameterization, the only free parameter
is the normalized form factor value at the Callan-Treiman point (C); our best
fit results in ln C = 0.1915 \pm 0.0122. We also study the sensitivity of C to
different parametrizations of the vector form factor. The results for the phase
space integrals and C are then used to make tests of the Standard Model.
Finally, we compare our results with lattice QCD calculations of F_K/F_pi and
f_+(0).Comment: 9 pages, 3 figures, to be published in PR
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
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
Precise Measurements of Direct CP Violation, CPT Symmetry, and Other Parameters in the Neutral Kaon System
We present precise tests of CP and CPT symmetry based on the full dataset of
K to pipi decays collected by the KTeV experiment at Fermi National Accelerator
Laboratory during 1996, 1997, and 1999. This dataset contains 16 million K to
2pi0 and 69 million K to pi+pi- decays. We measure the direct CP violation
parameter Re(epsilon'/epsilon) = (19.2 pm 2.1)x10-4. We find the KL-KS mass
difference Deltam = (5270 pm 12)x10^6 hbar/s and the KS lifetime tauS = (89.62
pm 0.05)x10-12 s. We also measure several parameters that test CPT invariance.
We find the difference between the phase of the indirect CP violation
parameter, epsilon, and the superweak phase, phi_epsilon - phi_SW = (0.40 pm
0.56) degrees. We measure the difference of the relative phases between the CP
violating and CP conserving decay amplitudes for K to pi+pi- (phi+-) and for K
to 2pi0 (phi00), Delta phi = (0.30 pm 0.35) degrees. From these phase
measurements, we place a limit on the mass difference between K0 and K0bar,
DeltaM < 4.8 x 10-19 GeV/c^2 at 95% C.L. These results are consistent with
those of other experiments, our own earlier measurements, and CPT symmetry.Comment: 28 pages, 30 figures; removed extra figur
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
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