M. Mannelli

The value of $\frac{{\ensuremath{\epsilon}}^{\ensuremath{'}}}{\ensuremath{\epsilon}}$, a measure of the $\mathrm{CP}$-nonconserving direct transition from the ${K}_{L}^{0}$ state to the isospin-2 state of two pions, was determined to be 0.0017\ifmmode\pm\else\textpm\fi{}0.0082, a result that excludes interesting models of $\mathrm{CP}$ nonconservation.

A pair of small angle silicon-tungsten (Si-W) calorimeters has been built to measure the luminosity to a precision better than 0.1% in the OPAL experiment at the Large Electron Positron (LEP) collider at CERN near Geneva. Each calorimeter contains 19 layers of tungsten (W) plates and silicon (Si) detectors, corresponding to a total of 22 radiation lengths, sampled by about 1 m/sup 2/ of detectors divided into 304/spl times/64 independently read out channels. A complete electronics system has been developed, from the preamplifier up to the VME read out and control interface. It includes a fast trigger based on analogue sums. This paper describes how a large number of channels have been implemented in a dense environment, thanks to the use of ASIC's directly bonded on the detector.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The High Luminosity phase of the Large Hadron Collider will deliver 10 times more integrated luminosity than the existing collider, posing significant challenges for radiation tolerance and event pileup on detectors, especially for forward calorimetry. As part of its upgrade program, the Compact Muon Solenoid collaboration is designing a high-granularity calorimeter (HGCAL) to replace the existing endcap calorimeters. It will feature unprecedented transverse and longitudinal readout and triggering segmentation for both electromagnetic and hadronic sections. The electromagnetic section and a large fraction of the hadronic section will be based on hexagonal silicon sensors of 0.5–1 cm2 cell size, with the remainder of the hadronic section being based on highly-segmented scintillators with silicon photomultiplier readout. The intrinsic high-precision timing capabilities of the silicon sensors will add an extra dimension to event reconstruction, especially in terms of pileup rejection. First hexagonal silicon modules, using the existing Skiroc2 front-end ASIC developed for CALICE, have been tested in beams at Fermilab and CERN in 2016. We present results from these tests, in terms of system stability, calibration with minimum-ionizing particles and resolution (energy, position and timing) for electrons, and the comparisons of these quantities with GEANT4-based simulation.

The Compact Muon Solenoid (CMS) is one of the experiments at the Large Hadron Collider (LHC) under construction at CERN. Its inner tracking system consist of the world largest Silicon Strip Tracker (SST). In total it implements 24,244 silicon sensors covering an area of 206m2. To construct a large system of this size and ensure its functionality for the full lifetime of 10 years under LHC condition, the CMS collaboration developed an elaborate design and a detailed quality assurance program. This paper describes the strategy and shows first results on sensor qualification.

The high luminosity upgraded LHC or Phase-II is expected to increase the instantaneous luminosity by a factor of 10 beyond the LHC's design value, expecting to deliver 250 fb−1 per year for a further 10 years of operation. Under these conditions the performance degradation due to integrated radiation dose will need to be addressed. The CMS collaboration is planning to upgrade the forward calorimeters. The replacement is called the High Granularity Calorimeter (HGC) and it will be realized as a sampling calorimeter with layers of silicon detectors interleaved. The sensors will be realized as pad detectors with sizes of less that ∼1.0 cm2 and an active thickness between 100 and 300 μm depending on the position, respectively, the expected radiation levels. For an integrated luminosity of 3000 fb−1, the electromagnetic calorimetry will sustain integrated doses of 1.5 MGy (150 Mrads) and neutron fluences up to 1016 neq/cm2. A radiation tolerance study after neutron irradiation of 300, 200, and 100 μm n-on-p and p-on-n silicon pads irradiated to fluences up to 1.6×1016 neq/cm2 is presented. The properties of these diodes studied before and after irradiation were leakage current, capacitance, charge collection efficiency, annealing effects and timing capability. The results of these measurements validate these sensors as candidates for the HGC system.

In the context of the development of radiation hard silicon microstrip detectors for the CMS Tracker, we have investigated the dependence of interstrip and backplane capacitance as well as depletion and breakdown voltage on the design parameters and substrate characteristics of the devices. Measurements have been made for strip pitches between 60 and 240μm and various strip implants and metal widths, using multi-geometry devices, fabricated on wafers of either 〈111〉 or 〈100〉 crystal orientation, of resistivities between 1 and 6kΩcm and of thicknesses between 300 and 410μm. The effect of irradiation on properties of devices has been studied with 24GeV/c protons up to a fluence of 4.3×1014cm−2.

We report on a search for the flavor-changing neutral-current decays ${K}_{L}^{0}$\ensuremath{\rightarrow}\ensuremath{\mu}+e and ${K}_{L}^{0}$\ensuremath{\rightarrow}e+e. Limits obtained for these processes are B(${K}_{L}^{0}$\ensuremath{\rightarrow}\ensuremath{\mu}+e)6.7\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}9}$ and B(${K}_{L}^{0}$\ensuremath{\rightarrow}e+e)4.5\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}9}$ (90% confidence level).

Interstrip and backplane capacitances on silicon microstrip detectors with p+ strip on n substrate of 320μm thickness were measured for pitches between 60 and 240μm and width over pitch ratios between 0.13 and 0.5. Parametrisations of capacitance w.r.t. pitch and width were compared with data. The detectors were measured before and after being irradiated to a fluence of 4×1014protons/cm2 of 24GeV/c momentum. The effect of the crystal orientation of the silicon has been found to have a relevant influence on the surface radiation damage, favouring the choice of a 〈100〉 substrate. Working at high bias (up to 500 V in CMS) might be critical for the stability of detector, for a small width over pitch ratio. The influence of having a metal strip larger than the p+ implant has been studied and found to enhance the stability.

We report on a search for the flavor-changing neutral-current decays ${K}_{L}^{0}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}{e}^{+}{e}^{\ensuremath{-}}$ and ${K}_{L}^{0}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}}$. Limits obtained for these processes are $B({K}_{L}^{0}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}{e}^{+}{e}^{\ensuremath{-}})&lt;3.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$ and $B({K}_{L}^{0}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}})&lt;1.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$.

We report on the signal timing capabilities of thin silicon sensors when traversed by multiple simultaneous minimum ionizing particles (MIP). Three different planar sensors, with depletion thicknesses 133, 211, and 285 µm, have been exposed to high energy muons and electrons at CERN. We describe signal shape and timing resolution measurements as well as the response of these devices as a function of the multiplicity of MIPs. We compare these measurements to simulations where possible. We achieve better than 20 ps timing resolution for signals larger than a few tens of MIPs.

The high luminosity LHC (HL-LHC or Phase-II) is expected to increase the instantaneous luminosity of the LHC by a factor of about five, delivering 0∼25 fb −1 per year between 2025 and 2035. Under these conditions the performance degradation of detectors due to integrated radiation dose/fluence will need to be addressed. The CMS collaboration is planning to upgrade many detector components, including the forward calorimeters. The replacement for the existing endcap preshower, electromagnetic and hadronic calorimeters is called the High Granularity Calorimeter (HGCAL) and it will be realized as a sampling calorimeter, including 40 layers of silicon detectors totalling 600 m2. The sensors will be realized as pad detectors with cell size between 0.5 and 1.0 cm2 and an active thickness between 100 μm and 300 μm depending on their location in the endcaps. The thinner sensors will be used in the highest radiation environment. For an integrated luminosity of 3000 fb −1, the electromagnetic calorimeter will have to sustain a maximum integrated dose of 1.5 MGy and neutron fluences of 1.0×1016 neq/cm2. A tolerance study after neutron irradiation of 300 μm, 200 μm, 100 μm and 50 μm n-on-p and p-on-n silicon pads irradiated to fluences up to 1.6×1016 neq/cm2 is presented. The main properties of these diodes have been studied before and after irradiation: leakage current, capacitance, charge collection efficiency with laser and sensitivity to minimum ionizing particles with radioactive source (90Sr). The results show a good performance even after the most extreme irradiation.

We report on a search for the lepton-generation-number-violating decay ${K}_{L}^{0}\ensuremath{\rightarrow}\ensuremath{\mu}e$. We find $B({K}_{L}^{0}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{\ifmmode\pm\else\textpm\fi{}}{e}^{\ifmmode\pm\else\textpm\fi{}})&lt;1.9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$ (90% confidence level).

We present results obtained with full-size wedge silicon microstrip detectors bonded to APV6 (Raymond et al., Proceedings of the 3rd Workshop on Electronics for LHC Experiments, CERN/LHCC/97-60) readout chips. We used two identical modules, each consisting of two crystals bonded together. One module was irradiated with 1.7×1014neutrons/cm2. The detectors have been characterized both in the laboratory and by exposing them to a beam of minimum ionizing particles. The results obtained are a good starting point for the evaluation of the performance of the “ensemble” detector plus readout chip in a version very similar to the final production one. We detected the signal from minimum ionizing particles with a signal-to-noise ratio ranging from 9.3 for the irradiated detector up to 20.5 for the non-irradiated detector, provided the parameters of the readout chips are carefully tuned.

The replacement of the existing endcap calorimeter in the Compact Muon Solenoid (CMS) detector for the high-luminosity LHC (HL-LHC), scheduled for 2027, will be a high granularity calorimeter. It will provide detailed position, energy, and timing information on electromagnetic and hadronic showers in the immense pileup of the HL-LHC. The High Granularity Calorimeter (HGCAL) will use 120-, 200-, and 300-μm-thick silicon (Si) pad sensors as the main active material and will sustain 1 MeV neutron equivalent fluences up to about 1016 neq cm−2. In order to address the performance degradation of the Si detectors caused by the intense radiation environment, irradiation campaigns of test diode samples from 8-inch and 6-inch wafers were performed in two reactors. Characterization of the electrical and charge collection properties after irradiation involved both bulk polarities for the three sensor thicknesses. Since the Si sensors will be operated at −30oC to reduce increasing bulk leakage current with fluence, the charge collection investigation of 30 irradiated samples was carried out with the infrared-TCT setup at −30oC. TCAD simulation results at the lower fluences are in close agreement with the experimental results and provide predictions of sensor performance for the lower fluence regions not covered by the experimental study. All investigated sensors display 60% or higher charge collection efficiency at their respective highest lifetime fluences when operated at 800 V, and display above 90% at the lowest fluence, at 600 V. The collected charge close to the fluence of 1016 neq cm−2 exceeds 1 fC at voltages beyond 800 V.

This paper describes the main achievements in the development of radiation resistant silicon detectors to be used in the CMS tracker. After a general description of the basic requirements for the operation of large semiconductor systems in the LHC environment, the issue of radiation resistance is discussed in detail. Advantages and disadvantages of the different technological options are presented for comparison. Laboratory measurements and test beam data are used to check the performance of several series of prototypes fabricated by different companies. The expected performance of the final detector modules are presented together with preliminary test beam results on system prototypes.

The CMS experiment at the LHC will comprise a large silicon strip tracker. This article highlights some of the results obtained in the R&D studies for the optimization of its silicon sensors. Measurements of the capacitances and of the high voltage stability of the devices are presented before and after irradiation to the dose expected after the full lifetime of the tracker.

This note is a short summary of the workshop on "Energy and time measurements with high-granular silicon devices" that took place on the 13/6/16 and the 14/6/16 at DESY/Hamburg in the frame of the first AIDA-2020 Annual Meeting. This note tries to put forward trends that could be spotted and to emphasise in particular open issues that were addressed by the speakers.

The CMS Silicon tracker consists of 70m2 of microstrip sensors which design will be finalized at the end of 1999 on the basis of systematic studies of device characteristics as function of the most important parameters. A fundamental constraint comes from the fact that the detector has to be operated in a very hostile radiation environment with full efficiency. We present an overview of the current results and prospects for converging on a final set of parameters for the silicon tracker sensors.

For the construction of the silicon microstrip detectors for the Tracker of the CMS experiment, two different substrate choices were investigated: A high-resistivity (6 k cm) substrate with (111) crystalorientation and a low-resistivity (2k cm) one with (100) crystalorientation. The interstrip and backplane capacitances were measured before and after the exposure to radiation in a range of strip pitches from 60 μm to 240 μm and for values of the width-over-pitch ratio between 0.1 and 0.5.

Abstract A large quantity of silicon microstrip detectors is foreseen to be used as part of the CMS tracker. A specific research and development program has been carried out with the aim of defining layouts and technological solutions suitable for the use of silicon detectors in high radiation environment. Results presented here summarise this work on many research areas such as techniques for device manufacturing, pre- and post-irradiation electrical characterization, silicon bulk defects analysis and simulations, system performance analytical calculations and simulations and test beam analysis. As a result of this work we have chosen to use single-sided, AC-coupled, poly silicon biased, 300 μm thick, p + on n substrate detectors. We feel confident that these devices will match the required performances for the CMS tracker provided they can be operated at bias voltages as high as 500 V. Such high-voltage devices have been succesfully manufactured and we are now concentrating our efforts in enhancing yield and reliability.

The breakdown performance of CMS barrelmodule prototype detectors and test devices with single and multi-guard structures were studied before and after neutron irradiation up to 2·1014 1 MeV equivalent neutrons. Before irradiation avalanche breakdown occurred at the guard ring implant edges. We measured 100–300 V higher breakdown voltage values for the devices with multi-guard than for devices with single-guard ring. After irradiation and type inversion the breakdown was smoother than before irradiation and the breakdown voltage value increased to 500–600 V for most of the devices.

We review the prospects, strategies and technologies for the High Luminosity (HL-LHC) upgrades of the ATLAS and CMS detectors, in the light of a very successful two year-long first physics run, and the discovery of a new 126 GeV boson with properties consistent with those of the Standard Model Higgs boson.

This paper describes the Silicon microstrip Tracker of the CMS experiment at LHC. It consists of a barrel part with 5 layers and two endcaps with 10 disks each. About 10 000 single-sided equivalent modules have to be built, each one carrying two daisy-chained silicon detectors and their front-end electronics. Back-to-back modules are used to read-out the radial coordinate. The tracker will be operated in an environment kept at a temperature of T=−10°C to minimize the Si sensors radiation damage. Heavily irradiated detectors will be safely operated due to the high-voltage capability of the sensors. Full-size mechanical prototypes have been built to check the system aspects before starting the construction.

The CMS silicon strip tracker is the largest device of its kind ever built, and is the first instance of a large collider detector relying exclusively on this all-silicon technology for tracking. With an instrumented surface of over 200 m 2 , and over nine million readout channels, it is two orders of magnitude larger than the silicon vertex detectors of the LEP experiments, and 30–40 times larger than the silicon inner detectors of the CDF and D0 experiments at the Tevatron. It makes use of microelectronics technology, but deploys it at the macroscale. The photograph below shows the completed CMS silicon tracker, ready for installation in the experiment, side by side with the silicon strip vertex detector of the OPAL experiment at LEP. Approximately a decade and more than two orders of magnitude in scale separate these two silicon strip detectors. [Formula: see text] In the following we motivate the choice of an all-silicon tracker for the CMS experiment, and discuss the reasons for the major design choices that define the system.

We report on the design, simulation and test of Low Gain Avalanche Diodes (LGADs) which utilize a buried gain layer. The buried layer is formed by patterned implantation of a 50-micron thick float zone substrate wafer-bonded to a low resistivity carrier. This is then followed by epitaxial deposition of a ≈ 3 micron-thick high resistivity amplification region. The topside is then processed with junction edge termination and guard ring structures and incorporates an AC-coupled cathode implant. This design allows for independent adjustment of gain layer depth and density, increasing design flexibility. A higher gain layer dopant density can also be achieved by controlling the process thermal budget, improving radiation hardness. A first set of demonstration devices has been fabricated, including a variety of test structures. We report on TCAD design and simulation, fabrication process flow, and preliminary measurements of prototype devices.

The silicon detectors at the future Large Hadron Collider (LHC) at CERN have to survive large particle fluxes up to a few 1014 particles per cm2. These high fluxes cause dramatic changes in the behaviour of the silicon detectors, like inversion of n-type silicon to p-type silicon. Here, we report on the high-voltage behaviour of silicon mictrostrip detectors up to doses of about 1014 particles/cm2, and the changes in the depletion voltage and inter-strip capacitance. The CMS baseline choice for the biasing element of the AC-coupled microstrip detectors is a polysilicon resistor. The silicon detectors, tested here, are Foxfet biased. We measured the changes in the Foxfet characteristics. Such detectors have been reported to show, after irradiation, a noise which is higher than expected. Using a fast amplifier (PREMUX chip), we also measure a higher noise.

Abstract A large use of silicon microstrip detectors is foreseen for the intermediate part of the CMS tracker. A specific research and development program has been carried out with the aim of finding design layouts and technological solutions for allowing silicon microstrip detectors to be reliably used on a high radiation level environment. As a result of this work single sided, AC-coupled, polysilicon biased, 300 μ m thick, p + on n substrate detectors were chosen. Irradiation tests have been performed on prototypes up to fluence 2×10 14  n/cm 2 . The detector performances do not significantly change if the detectors are biased well above the depletion voltage. S / N is reduced by less than 20%, still enough to insure a good efficiency and space resolution. Multiguard structures has been developed in order to reach high voltage operation (above 500 V).

We report selected results of laboratory measurements and beam tests of heavily irradiated microstrip silicon detectors. The detectors were single-sided devices, produced by different manufacturers and irradiated with different sources, for several total ionizing doses and fluences up to 4 /spl times/10/sup 14/ 1-MeV-equivalent neutrons per cm/sup 2/. Strip resistance and capacitance, detector leakage currents and breakdown performance were measured before and after irradiations. Signal-to-noise ratio and detector efficiency were studied in beam tests, for different values of the detector temperature and of the read-out pitch, as a function of the detector bias voltage. The goal of these test is to optimise the design of the final prototypes for the Silicon Strip Tracker of the CMS experiment at the CERN LHC collider.

This note is intended to describe the main features of the first engineered versions of the basic singlesided detector modules for the barrel and forward silicon tracker of CMS.

Abstract The new silicon tracker layout (V4) is presented. The system aspects of the construction are discussed together with the expected tracking performance. Because of the high radiation environment in which the detectors will operate, particular care has been devoted to the study of the characteristics of heavily irradiated detectors. This includes studies on performance (charge collection, cluster size, resolution, efficiency) as a function of the bias voltage, integrated fluence, incidence angle and temperature.

The CMS silicon strip tracker involves about 70 m2 of instrumented silicon, with approximately 18500 microstrip detectors read out by 5 × 106 electronics channels. It has to satisfy a set of stringent requirements imposed by the environment and by the physics expected at the LHC: low cell occupancy and good resolution, radiation hardness aided by adequate cooling, low mass combined with high stability. These conditions have been incorporated in a highly modular design of the detector modules and their support structures, chosen to facilitate construction and to allow for easy assembly and maintenance.

The paper describes the Silicon Tracking System of the Compact Muon Solenoid (CMS) experiment that is foreseen to collect events from p–p collision at the Ecm=14 TeV at the CERN future Large Hadron Collider (LHC). The proposed system consists of four layers of silicon microstrip detectors placed between the two inner layers of the pixel detector and the outer microstrip gas chamber system. The barrel part covers the η region up to 1.8, instrumenting the central radial region between 20 and 50 cm. The forward–backward disks extend the coverage up to η=2.6. This paper will review the main characteristics and performances of the system, the actual status of the R&D activities that we are carrying on, and the status of the milestones we have to fulfill in view of the Technical Design Report expected at the end of the year.

This paper describes the silicon microstrip tracker of the CMS experiment at the future LHC. The silicon tracker consists of a barrel part with 5 layers and two endcaps with 10 disks each. About 6500 modules will have to be built, each one carrying two daisy-chained silicon sensors and their front-end electronics. The modules have been designed to be as simple and robust as possible. Radiation damage in the silicon sensors is minimized by cooling the whole system down to -10°C. Safe operation after heavy irradiation will be possible due to the high-voltage capability of the sensors. We expect the sensors to have a signal-to-noise ratio of 10 at the end of 10years of LHC running, which still gives an efficiency of almost 100%.

Experiment 780 is a search for the rare K decays K/sub L//sup 0/ ..-->.. ..mu..e and K/sub L//sup 0/ ..-->.. e/sup +/e/sup -/. We will be sensitive to these decays if the branching ratio is above 10/sup -10/. To achieve this in a 1000 hr experiment will require an intense beam with about 2 x 10/sup 5/ K decays/sec in the three meter decay region and over 10/sup 7/ counts/m/sup 2//sec in the apparatus. We will need a multilevel event selection sequence which will accept good events with high efficiency but quickly reject most of the background events. 1 ref.

After twenty years of intense scrutiny CP violation is apparently still well described, if not explained, by the superweak hypothesis, in which absolute values ..delta..S = 2 (T-violating) transitions between the K/sup 0/, anti K/sup 0/ states induce CP violating impurities in the K/sub L//sup 0/, K/sub S//sup 0/ states. CP-violating effects observed in the K/sup 0/ - anti K/sup 0/ system can be described in terms of one parameter, absolute values epsilon approx. = 2 x 10/sup -3/, which defines the portion of the CP-even state K/sub 1//sup 0/ found in the predominantly CP-odd K/sub L//sup 0/ state: K/sub L//sup 0/ proportional to K/sub 2//sup 0/ + epsilon K/sub 1//sup 0/. A precise measurement of the relative rates for the CP-violating decays K/sub L//sup 0/ ..-->.. ..pi../sup +/..pi../sup -/ and K/sub S//sup 0/ ..-->.. ..pi../sup 0/..pi../sup 0/ in principle provides a test for absolute values ..delta..S = 1 CP-violating amplitudes which result in deviations from the superweak predictions: eta /sup 00/ = eta /sup + -/ = epsilon, where eta /sup + -/ and eta /sup 00/ are the ratios of K/sub L/ to K/sub S/ decay amplitudes into ..pi../sup +/..pi../sup -/ and ..pi../sup 0/..pi../sup 0/ final states. Gaugemore » theory models of CP-violation are in general constructed to nearly mimic superweak predictions by having the dominant contribution to CP-violation arise from complex terms in the K/sup 0/ - anti K/sup 0/ mixing amplitudes. However, there are usually additional contributions in the form of direct CP violating absolute values ..delta..S = 1 decay amplitudes, parametrized by epsilon', which are not identical for the weak transitions into isospin I = 0 and 2 ..pi pi.. final states. The Yale-BNL group has recently completed a measurement of R and thus epsilon'/epsilon at the Brookhaven AGS. Results are presented.« less

We report on a search for the flavor-changing neutral-current decays K/sub L/ e e , K/sub L/ e e and K/sub L/ /sup +-/e/sup /minus plus//. Limits obtained for these processes are BR(K/sub L/ e e ) < 3.2 x 10 X, BR(K/sub L/ e e ) < 1.2 x 10 Z, BR(K/sub L/ /sup +-/e/sup /minus plus//) < 1.9 x 10 Z. 10 refs., 8 figs.

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We report on the progress of a search for the rare decays K/sub L//sup 0/ ..-->.. ..mu.. + e and K/sub L//sup 0/ ..-->.. e + e underway at the Brookhaven National Laboratory AGS. Analysis of data collected in February and May of 1987 yields the preliminary limit: BR(K/sub L//sup 0/ ..-->.. ..mu.. + e), BR(K/sub L//sup 0/ ..-->.. e + e) < 7 x 10/sup -9/. Prospects are discussed for the running period scheduled to begin in January of 1988.

We report on a search for the flavor-changing neutral-current decays K/sub L//sup 0/ ..-->.. ..pi../sup 0/e/sup +/e/sup /minus//, K/sub L//sup 0/ ..-->.. e/sup +/e/sup /minus// and K/sub L//sup 0/ ..-->.. ..mu../sup +-/e/sup /minus plus//. Limits obtained for these processes are BR(K/sub L//sup 0/ ..-->.. ..pi../sup 0/e/sup +/e/sup /minus//) .. e/sup +/e/sup /minus//) .. ..mu../sup +-/e/sup /minus plus//) < 1.9 /times/ 10/sup /minus/9/. 10 refs., 9 figs.

We report on a search for the flavor-changing neutral-current decays KL0 → π0e+e−, KL0 → e+e−, and KL0 → μ±e∓. 90% confidence limits obtained for these processes are BR(KL0 → π0e+e−) < 3.2 · 10−7, BR (KL0 → e+e−) < 1.2 · 10−9. and BR(KL0 → μ±e∓) < 1.9 · 10−9.

We report on a search for the rare decays K/sub L//sup 0/ ..-->.. ..mu../sup +-/e/sup /minus plus//, K/sub L//sup 0/ ..-->.. e/sup +/e/sup /minus//, and K/sub L//sup 0/ ..-->.. ..pi../sup 0/e/sup +/e/sup /minus// at the Brookhaven AGS. Limits obtained for these processes are BR(K/sub L//sup 0/ ..-->.. ..mu../sup +-/e/sup /minus plus//) .. e/sup +/e/sup /minus//) .. ..pi../sup 0/e/sup +/e/sup /minus//) < 3.2 /times/ 10/sup /minus/7/. 4 refs., 2 figs.