M. Mikuz

First direct observation of time-reversal non-invariance in the neutral-kaon system

Abstract We report on the first observation of time-reversal symmetry violation through a comparison of the probabilities of K 0 transforming into K0 and K0 into K 0 as a function of the neutral-kaon eigentime t. The comparison is based on the analysis of the neutral-kaon semileptonic decays recorded in the CPLEAR experiment. There, the strangeness of the neutral kaon at time t=0 was tagged by the kaon charge in the reaction p p → K ± π ∓ K 0 ( K 0 ) at rest, whereas the strangeness of the kaon at the decay time t=τ was tagged by the lepton charge in the final state. An average decay-rate asymmetry 〈 R( K 0 t=0 → e + π − ν t=τ )−R( K 0 t=0 → e − π + ν t=τ ) R( K 0 t=0 → e + π − ν t=τ )+R( K 0 t=0 → e − π + ν t=τ ) 〉=(6.6±1.3 stat ±1.0 syst )×10 −3 was measured over the interval 1 τ S τ S , thus leading to evidence for time-reversal non-invariance.

Investigation of Irradiated Silicon Detectors by Edge-TCT

A Transient Current Technique (TCT) utilizing an IR laser with 100 ps pulse width and beam diameter of FWHM = 8 μm was used to evaluate non-irradiated and irradiated p-type silicon micro-strip detectors. The beam was parallel with the surface and perpendicular to the strips (Edge-TCT) so that the electron hole pairs were created at known depth in the detector. Induced current pulses were measured in one of the strips. The pulse shapes were analyzed in a new way, which does not require the knowledge of effective trapping times, to determine drift velocity, charge collection and electric field profiles in heavily irradiated silicon detectors. The profiles were studied at different laser beam positions (depth of carrier generation), voltages and fluences up to 5·1015 neutrons cm-2. A strong evidence for charge multiplication at high voltages was found with the detector irradiated to the highest fluence.

Tests of CPT symmetry and quantum mechanics with experimental data from CPLEAR

Abstract We use fits to recent published CPLEAR data on neutral kaon decays to π + π − and πeν to constrain the CPT-violation parameters appearing in a formulation of the neutral kaon system as an open quantum-mechanical system. The obtained upper limits of the CPT-violation parameters are approaching the range suggested by certain ideas concerning quantum gravity.

Design and performance of the ABCD chip for the binary readout of silicon strip detectors in the ATLAS semiconductor tracker

The ABCD design is a single chip implementation of the binary readout architecture for silicon strip detectors in the ATLAS semiconductor tracker. The prototype chip has been manufactured successfully in the DMILL process. In the paper we present the design of the chip and the measurement results. The basic analogue performance of the ABCD design has been evaluated using a prototype SCT module equipped with the ABCD chips. The digital performance has been evaluated using a general purpose IC tester. The measurements confirmed that all blocks of the ABCD design are fully functional and the chips meet all basic requirements of the SCT. Wafer screening has been performed using a customised wafer tester.

Bulk damage in DMILL npn bipolar transistors caused by thermal neutrons versus protons and fast neutrons

DMILL bipolar transistors (npn) were exposed to 24 GeV protons and fast and thermal neutrons to fluences up to 6/spl middot/10/sup 14/ n/cm/sup 2/. Transistor common emitter current gain (/spl beta/=I/sub collector//I/sub base/) was measured after irradiations. It was found that /spl beta/ degradation scales as /spl Delta/(1//spl beta/)=k/sub T//spl middot//spl Phi//sub T/ where /spl Phi//sub T/ is the fluence of thermal neutrons and as /spl Delta/(1//spl beta/)=k/sub eq//spl middot//spl Phi//sub eq/, with /spl Phi//sub eq/ 1-MeV equivalent fluence, if transistors are irradiated with protons or fast neutrons. Large damage factor k/sub T//spl sim/3/spl middot/k/sub eq/ was measured. Thermal neutrons do not have sufficient energy to displace a Si atom. Their damage mechanism is, therefore, identified with /sup 10/B(n,/spl alpha/)/sup 7/Li reaction from which energetic /spl alpha/ and Li particles produce bulk damage in the base of the device. Boron is used as the base dopant in these transistors having also highly doped regions below base contacts. Irradiations with neutrons with energies distributed from thermal to fast show that gain degradation adds up as /spl Delta/(1//spl beta/)=k/sub T//spl middot//spl Phi//sub T/+k/sub eq//spl middot//spl Phi//sub eq/.

Determination of the T and CPT violation parameters in the neutral kaon system using the Bell-Steinberger relation and data from CPLEAR

Abstract Data from the CPLEAR experiment, together with the most recent world averages for some of the neutral-kaon parameters, were constrained with the Bell–Steinberger (or unitarity) relation, allowing the T-violation parameter Re( ϵ ) and the CPT-violation parameter Im( δ ) of the neutral-kaon mixing matrix to be determined with an increased accuracy: Re( ϵ )=(164.9±2.5)×10 −5 , Im( δ )=(2.4±5.0)×10 −5 . Moreover, the constraint allows the CPT-violation parameter for the neutral-kaon semileptonic decays, Re( y ), to be determined for the first time. The ΔS ≠ ΔQ parameters Re( x − ) and Im( x + ) are given with an increased accuracy. The quantity Re( y + x − ), which enters the T-violation CPLEAR asymmetry previously published, is determined to be (−0.2±0.3)×10 −3 . The value obtained for Re( δ ) is in agreement with the one resulting from a previous unconstrained fit and has a slightly smaller error.

Influence of trapping on silicon microstrip detector design and performance

New systematic measurements of effective carrier trapping times were used as an input to simulate the operation of an irradiated silicon strip detector. The dependence of charge-collection efficiency (CCE) on bias voltage, magnetic field, irradiation particle type, fluence, and detector design was investigated. It was observed that irradiated detectors processed on standard n-silicon material with n/sup +/ strips performed better than those with p/sup +/ strips. At /spl Phi//sub eq/=2/spl times/10/sup 14/ cm/sup -2/, the difference in CCE was around 10% at voltages well above V/sub FD/ and even larger for lower voltages. A few percent difference in CCE for different track paths across the strip was observed. The effective Lorentz angle was found to be independent of the irradiation level. A nonnegligible amount of charge also appears on neighboring strips as a consequence of charge trapping. The influence of detector thickness and strip width on induced charge was also studied.

Online Integrating Radiation Monitoring System for the ATLAS Detector at the Large Hadron Collider

Detectors and electronics inside the ATLAS detector at the large hadron collider will be exposed to high fluxes of photons, charged particles, and neutrons. Damage caused by radiation will influence the performance of the detector. It will therefore be important to continuously monitor the radiation dose to follow the level of detector degradation. It will also be important to have information about the radiation field in the detector early in the life of the experiment in order to check the simulations and to correctly predict future radiation damage. An online radiation monitoring system with semiconductor radiation sensors will monitor the dose at several locations in the ATLAS detector. It will measure ionizing dose in SiO with RadFETs, displacement damage in silicon in terms of 1-MeV(Si) equivalent neutron fluence with p-i-n diodes and fluence of thermal neutrons from current gain degradation in dedicated bipolar transistors. The design of the system and its response to various types of radiation is described.

Performance of a 128 channel analogue front-end chip for read-out of Si strip detector modules for LHC experiments

We present a 128-channel analogue front-end chip, SCT128A-HC, for readout of silicon strip detectors employed in the inner tracking detectors of the LHC experiment. The chip is produced in the radiation hard DMILL technology. The architecture of the chip and critical design issues are discussed. The performance of the chip has been evaluated in details in the test bench and is presented in the paper. The chip is used to read out prototype analogue modules compatible in size, functionality and performance with the ATLAS SCT base line modules. Several full size detector modules equipped with SCT128A-HC chips has been built and tested successfully in the lab with /spl beta/ particles as well as in the test beam. The results concerning the signal-to-noise ratio, noise occupancy, efficiency and spatial resolution are presented. The radiation hardness issues are discussed.

Last Results of a First Compton Probe Demonstrator

A first prostate probe prototype based on the Compton imaging technique has been developed, with a scatter detector composed of a stack of five thick silicon pad detectors, and a scintillator as absorption detector. The silicon sensors are 4 cm times 1 cm, 1 mm thick, with 1.4 mm times 1.4 mm pad dimensions. The scatter detector performance has been optimized, and an energy resolution about 1.4 keV FWHM is obtained. The absorption detector consists of three Nal(Tl) scintillators that are placed around the scatter detector. A spatial resolution of 5 mm FWHM has been measured reconstructing an image of a point-like 133 Ba source placed at 11 cm distance from the scatter detector. Additional studies show the improvement of the detector resolution with increasing incident photon energy and relative distance from the scatter to the absorption detector. Simulations have also been performed for a complete understanding of the data, and to predict the expected resolution at near field operation of the device. The prototype construction is the first step in the development of a Compton probe for prostate imaging.