We report on a search for the decay K(L)-->pi(0)&mgr;(+)&mgr;(-) carried out as a part of the KTeV experiment at Fermilab. This decay is expected to have a significant CP violating contribution and a direct measurement will either support the Cabibbo-Kobayashi-Maskawa mechanism for CP violation or point to new physics. Two events were observed in the 1997 data with an expected background of 0.87+/-0.15 events, and we set an upper limit B(K(L)-->pi(0)&mgr;(+)&mgr;(-))<3. 8x10(-10) at the 90% confidence level.
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+/-0.18(stat)+/-0.23(syst)]x10(-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+/-0.09(stat)+/-0.02(syst) and gamma(CP) = -0.09+/-0.09(stat)+/-0.02(syst). We also present the first detailed study of the e(+)e(-) invariant mass spectrum in this decay mode.
We searched for the appearance of p 1 p 2 pairs with invariant mass $648 MeV͞c 2 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 R 0 hadron, which is the lightest bound state of a gluon and a light gluino ͑gg͒, and thereby also the existence of a light gluino. Depending on the photino mass, we exclude the R 0 in the mass and lifetime ranges of 1.2 4.6 GeV͞c 2 and 2 3 10 210 7 3 10 24 s, respectively. [S0031-9007(97)04573-0] PACS numbers: 13.85. Rm, 13.25.Es, 14.40.Aq, 14.80.Ly This Letter is motivated by recent discussions [1] of the possible existence of long-lived hadrons that contain light gluinos. In some theories where the breaking of supersymmetry is communicated to ordinary particles by the exchange of very heavy states, gauginos have small tree-level masses and are light compared to the squarks. The gluino ͑g͒ and photino ͑g͒ masses are expected to be &1.0 GeV͞c 2 . The gluons ͑g͒, gluinos, and quarks can form bound states, the lightest of which is a spin-1͞2 gg combination called the R 0 . The approximate degeneracy of R 0 with the 0 11 gluonia [1] suggests that the R 0 mass could be of the order of 1.3 2.2 GeV͞c 2 . The stable photino in this theory is a cold dark matter candidate [2]. Estimates from particle physics [1] and cosmology [2] place the R 0 lifetime in the 10 210 10 25 s range. The R 0 decays into ag and hadrons. Because of the approximate C invariance of supersymmetric QCD, the R 0 decay into rg is expected to be the dominant decay mode [1]; depending on the extent of C violation, the R 0 may also decay into p 0g or hg. The existence of a light gluino can have an impact on the running of the strong coupling constant a s . A phenomenological analysis of the perturbative running of a s [3], in conjunction with the multijet analysis at the CERN Large Electron-Positron Collider [4] has claimed an indirect exclusion of the light gluino scenario. However, a debate over the extent of this exclusion [5] underlines the necessity of a direct search for hadrons containing light gluinos.The R 0 's can be produced in pN collisions by processes such as quark-antiquark annihilation, gluon fusion, etc. Since squarks need not be involved, the R 0 production is in the realm of conventional QCD. Dawson, Eichten, and Quigg [6] have calculated cross sections for gluino production in tree approximation. Their calculations suggest an order-of-magnitude cross section estimate [7] of ϳ10 mb per nucleon for the production of an R 0 0031-9007͞97͞79(21)͞4083(5)$10.00
We present a measurement of the charge asymmetry δ L in the mode K L → π ± e ∓ ν based on 298 million analyzed decays. We measure a value of δ L = (3322 ± 58(stat) ± 47(sys)) · 10 −6 , in good agreement with previous measurements and 2.4 times more precise than the current best published result. The result is used to place more stringent limits on CPT and ∆S = ∆Q violation in the neutral kaon system. PACS numbers: 11.30. Er, 13.25.Es, The charge asymmetry in K L semileptonic decays is deeply related to CP violation through neutral kaon mixing. TheBR(e + π − ) + BR(e − π + ) . Assuming ∆S = ∆Q and no CPT violation in the decayTo first order in the parameters that violate CP and CPT,The terms Y and Re(x −x) parameterize CPT violation in the ∆S = ∆Q and ∆S = −∆Q transitions respectively[1, 2]:In the Standard Model, the ∆S = ∆Q violation is CPTconserving and occurs in 2nd order weak decays. Estimates for |x| are in the range 10 −7 [3]. δ L is modified to order |x| 2 and will not be considered in this letter.
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