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.
Spin precession of channeled particles in bent crystals has been observed for the first time. Polarized I"*" were channeled using bent Si crystals. These crystals provided an effective magnetic field of 45 T which resulted in a measured spin precession of 60° ±17°. This agrees with the prediction of 62° ± 2° using the world average of Z"*" magnetic moment measurements. This new technique gives a I"*" magnetic moment of (2.40 ± 0.46 ± 0.40)/X7v, where the quoted uncertainties are statistical and systematic, respectively. We see no evidence of depolarization in the channeling process. PACS numbers: 13.40.Fn, 14.20.Jn, 61.80.MkChanneling of high-energy particles in bent crystals has been observed in the momentum range [1-5] of 1.7-800 GeV/c. This technique has already found applications [3][4][5] in the deflection of high-energy beams. Another possibly important application of channeling is the precession of the spin of a polarized particle. This may allow the measurement of magnetic moments in distances of only a few cm. The lifetimes [6] of baryons containing charm quarks are so short that they travel only a few centimeters even at the highest available accelerator energies. Because of these short lifetimes, classical spin precession techniques using conventional magnets would produce negligibly small spin precession angles.It was pointed out by Baryshevskii [7] and Pondrom [8] that the magnetic moments of particles should precess if they were channeled in a bent crystal. The detailed precession theory has been developed by Lyuboshits [9] and Kim [10]. In a curved crystal the electrostatic field of the atomic planes deflecting the particle transforms into a magnetic field in the particle's rest frame. Thus the spin precession angle ^ is [9]
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
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