A. Ronzhin

Search for the decay

Abstract Data collected in Fermilab experiment E731 was used to perform the first search for the decay K L →π 0 ν ν . This decay is dominated by short distance effects and is almost entirely direct CP violating within the standard model. Cuts were developed to reject the background processes Λ→nπ0 and KL→π+e−γν. No candidate events were seen. We find BR (K L →π 0 ν ν ) −4 at the 90% confidence level.We report on a search for the rare decay K_L -> pi^0 nu nubar in the KTeV experiment at Fermilab. We searched for two-photon events whose kinematics were consistent with an isolated pi^0 coming from the decay K_L -> pi^0 nu nubar. One candidate event was observed, which was consistent with the expected level of background. An upper limit on the branching ratio was determined to be B(K_L -> pi^0 nu nubar) < 1.6E-6 at the 90% confidence level.We report on a search for the rare decay K_L -> pi^0 nu nubar in the KTeV experiment at Fermilab. We searched for two-photon events whose kinematics were consistent with an isolated pi^0 coming from the decay K_L -> pi^0 nu nubar. One candidate event was observed, which was consistent with the expected level of background. An upper limit on the branching ratio was determined to be B(K_L -> pi^0 nu nubar) < 1.6E-6 at the 90% confidence level.

Development of Picoseconds Time of Flight Systems in Meson Test Beam Facility at Fermilab

We describe here the development of a time of flight (TOF) system with 10–20 ps resolution for particle identification in a beam line. The detector resolution also was measured with the start and stop counters close together in the 120 GeV proton beam of the Fermilab Test Beam Facility. We tested both microchannel plate photomultipliers (MCP PMT) and silicon photomultipliers (SiPMs), in both cases using Cherenkov light produced in fused silica (quartz) radiators. Published by Elsevier B.V.

Radioactive source calibration technique for the CMS hadron calorimeter

Abstract Relative calibration of the scintillator tiles used in the hadronic calorimeter for the Compact Muon Solenoid detector at the CERN Large Hadron Collider is established and maintained using a radioactive source technique. A movable source can be positioned remotely to illuminate each scintillator tile individually, and the resulting photo-detector current is measured to provide the relative calibration. The unique measurement technique described here makes use of the normal high-speed data acquisition system required for signal digitization at the 40 MHz collider frequency. The data paths for collider measurements and source measurements are then identical, and systematic uncertainties associated with having different signal paths are avoided. In this high-speed mode, the source signal is observed as a Poisson photo-electron distribution with a mean that is smaller than the width of the electronics noise (pedestal) distribution. We report demonstration of the technique using prototype electronics for the complete readout chain and show the typical response observed with a 144 channel test beam system. The electronics noise has a root-mean-square of 1.6 least counts, and a 1 mCi source produces a shift of the mean value of 0.1 least counts. Because of the speed of the data acquisition system, this shift can be measured to a statistical precision better than a fraction of a percent on a millisecond time scale. The result is reproducible to better than 2% over a time scale of 1 month.

Front end readout electronics for the CMS Hadron Calorimeter

The front-end electronics for the CMS Hadron Calorimeter provides digitized data at the beam interaction rate of 40 MHz. Analog signals provided by hybrid photodiodes (HPDs) or photomultiplier tubes (PMTs) are digitized and the data is sent off board through serialized fiber optic links running at 1600 Mbps. In order to maximize the input signal, the front-end electronics are housed on the detector in close proximity to the scintillating fibers or phototubes. To fit the electronics into available space, custom crates, backplanes and cooling methods have had to be developed. During the expected ten-year lifetime, the front-end readout electronics will exist in an environment where radiation levels approach 330 rads and the neutron fluence will be 1.3E11 n/cm/sup 2/. For this reason, the design approach relies heavily upon custom radiation tolerant ASICs. This paper will present the system architecture of the front-end readout crates and describe our results with early prototypes.

Crosstalk properties of the CMS HCAL hybrid photodiode

The requirements of large dynamic range, 40 MHz readout and 4 T magnetic field of the CMS Hadronic calorimeter have led to the development of a custom Hybrid PhotoDiode (HPD). In the last 5 years many improvements have been made in cooperation with DEP 1 and Canberra 2 to the basic HPD concept to improve the performance. A 200-mm thick 19-channel PIN diode array with various surface treatments has been developed to ensure fast pulse behavior and low optical and capacitive crosstalk. r 2003 Elsevier Science B.V. All rights reserved.

Hybrid photodiode crosstalk due to backscattered electrons

Abstract The fraction of backscattering electrons are measured for 19 and 73 pixel Hybrid Photodiodes. The data obtained are in good agreement with calculations. A new method of HPD alignment is proposed and tested.

Study of timing properties of SiPMs at Fermilab

We continue our timing measurements of Silicon Photomultipliers (SiPM) at the picosecond level at Fermilab .. We using SiPMs readout based on Ortec system, also as on fast waveform digitizer DRS4 [1]. SiPMs signal pulse shape was investigated. The single photoelectron time resolution (SPTR) was measured for the signals coming from the SiPMs. Dependence of the SPTR on the SiPms size was measured. Results of the last test beam test with SiPMs are presented.

Production of optical decoder units for the CMS Hadron Calorimeter

The CMS Hadron Calorimeter (HCAL) will use optical decoder units (ODU) as a link between scintillating plastic tiles, arranged in megatile layers around the HCAL, and multi-channel hybrid photodiodes. Photons are produced in the scintillating tiles as sub-atomic particles pass through and deposit energy. Y-11 waveshifting fiber and cables of clear optical fiber serve as connecting transmission lines from scintillating tiles to the ODU. The ODU reorganizes light signals from layer geometry to tower geometry for particle energy measurement. The hybrid photodiode (HPD) converts the light signals to electrical signals that are amplified and digitized for the data acquisition system. This paper provides aspects of the production of optical decoder units.

New Fast Shower Max Detector Based on MCP as an Active Element

One possibility to make a fast and radiation resistant shower maximum (SM) detector is to use a secondary emitter as an active element. We present below test beam results, obtained with different types of photo detectors based on micro channel plates (MCP) as secondary emitter. The SM time resolution – we obtained for this new type of detector is at the level of 20-30 ps. We estimate that a significant contribution to the detector response originates from secondary emission of the MCP.

Single photoelectron time resolution (SPTR) of silicon photomultipliers (SiPMs) with large sensitive area

We continue Fermilab program to study timing properties of SiPMs. SPTR for SiPMs with large sensitive area were measured and results are presented.