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

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

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

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

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 $K_{L}\to\pi^{0}\pi^{0}\gamma$ via the topology $K_{L}\to\pi^{0}\pi^{0}_D\gamma$ (where $\pi^0_D\to\gamma e^+e^-$). Due to Bose statistics of the $\pi^0$ pair and the real nature of the photon, the $K_{L}\to\pi^{0}\pi^{0}\gamma$ 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 $O(p^4)$. Therefore, this mode probes chiral perturbation theory at $O(p^6)$. In this paper we report a determination of an upper limit of $2.43\times 10^{-7}$ (90% CL) for $K_{L}\to\pi^{0}\pi^{0}\gamma$. This is approximately a factor of 20 lower than previous results.Comment: six pages and six figures in the submission. Reformatted for Physics Review

Recent evolution of an ice‐cored moraine at the Gentianes Pass, Valais Alps, Switzerland

International audienceLateral moraines located in permafrost environments often preserve large amounts of both glacier and periglacial ice. To understand how ice‐cored moraines located in high alpine environments evolve in a context of both glacier retreat and permafrost degradation, we performed 11 terrestrial laser‐scanning measurement campaigns between 2007 and 2014 on a highly anthropogenic overprinted moraine prone to instability. Resulting comparison of the subsequent 3D models allowed to qualitatively and quantitatively analyze the morphological evolution of the moraine. The comparisons indicate a very high geomorphic activity of the moraine including large areas affected by downslope movements of blocks and 10 landslides with a volume between 24 ± 1 and 1,138 ± 47 m3. Data also indicated a very strong ice melt with a loss of ice thickness locally reaching 17.7 m at the foot of the moraine. These results, compared with resistivity and thermal measurements of the ground, suggest the combined role of ice loss at the foot of the moraine and the permafrost activity/warming in triggering these processes

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

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