Measurement of the very rare K+→π+ννˉK^+ \to \pi^+ \nu \bar\nu decay

The decay K+→π+νν¯ , with a very precisely predicted branching ratio of less than 10−10 , is among the best processes to reveal indirect effects of new physics. The NA62 experiment at CERN SPS is designed to study the K+→π+νν¯ decay and to measure its branching ratio using a decay-in-flight technique. NA62 took data in 2016, 2017 and 2018, reaching the sensitivity of the Standard Model for the K+→π+νν¯ decay by the analysis of the 2016 and 2017 data, and providing the most precise measurement of the branching ratio to date by the analysis of the 2018 data. This measurement is also used to set limits on BR(K+→π+X ), where X is a scalar or pseudo-scalar particle. The final result of the BR(K+→π+νν¯ ) measurement and its interpretation in terms of the K+→π+X decay from the analysis of the full 2016-2018 data set is presented, and future plans and prospects are reviewed

K+→π+νν‾K^+ \to \pi^+ \nu \overline{\nu} - NA62 First Result

The CERN NA62 experiment uses a novel "kaon decay-in-flight" technique to observe $K^+ \to \pi^+ \nu \overline{\nu}$. The preliminary result based on the analysis of the full 2016 dataset will be presented. In agreement with the Standard Model prediction, one candidate was observed. Under the background hypothesis, an upper limit of $14 \times 10^{-10}$ at 95 % C.L. was placed on the branching ratio

Development and Commissioning of the Silicon Pixel GigaTracker for the NA62 Experiment at CERN

This dissertation focuses on the development and commissioning of the Giga- Tracker. The project is part of a larger research programme dedicated to the measurement of the rare $K^{+} \to \pi^{+} \nu \bar\nu$ decay branching ratio. The text is organized as follow: in Chapter 1 we review the unique characteristics of the rare $K^{+} \to \pi^{+} \nu \bar\nu$ decay as well as the NA62 experimental setup. Silicon pixel detectors are discussed in Chapter 2; we collect the important formulae we need for the discussion. A special emphasis is put on radiation damage and on the time resolution of silicon sensors. The aspects of this work related to the GigaTracker development are grouped in Chapter 3. Finally, the Chapter 4 is mostly dedicated to the study of the GigaTracker performances. We close the text with a firrst exploration of the NA62 2014 pilot run data

Development and commissioning of the silicon pixel GigaTracker for the NA62 experiment at CERN

The standard model of particle physics describes the microscopic interactions of elementary particles with an unprecedented accuracy over a wide range of energies. However, observations such as the neutrino oscillations or the matter-antimatter asymmetry in the Universe do not fit the current description. In addition, some theoretical features of the model are unsatisfactory. In a complementary manner to the direct searches, accurate measurements of the branching fraction of rare processes like the K → πνν̅ decay could potentially reveal hints of beyond the standard model physics. Doing such a measurement using a decay-in-flight technique requires the active tracking of a high-intensity hadron beam. This brings new challenges in terms of detector temporal resolution, radiation hardness, material budget and data processing capabilities. This dissertation focuses on the development and commissioning of a silicon pixel tracker with a hit time resolution below 150 ps for the NA62 experiment at CERN. The GigaTracker is the result of more than ten years of research and development. Important aspects of the project are covered in this work. The main outcomes are the characterisation of the sensors radiation hardness; the implementation of a detailed Monte Carlo simulation of the GigaTracker; the assessment of the impact of the tracker material on the other detectors and the elaboration of innovative solutions for the spatial-temporal alignment and calibration of the GigaTracker stations. In parallel, a GigaTracker prototype, and later the final detector, were thoughtfully studied. We report an unmatched time resolution for this kind of detectors. To conclude, a first survey of the performance of the global NA62 setup was conducted.(SC - Sciences) -- UCL, 201

K±→π±γγK^{\pm} \rightarrow \pi^{\pm}\gamma\gamma studies at NA48/2 and NA62-RK experiments at CERN

Final results from an analysis of about 400K±→π±γγ rare decay candidates collected by the NA48/2 and NA62-RK experiments at CERN during low intensity runs with minimum bias trigger configurations are presented. The results include a model-independent decay rate measurement and fits to Chiral Perturbation Theory (ChPT) description. The data support the ChPT prediction for a cusp in the di-photon invariant mass spectrum at the two pion threshold

Test-beam results of a silicon pixel detector with Time-over-Threshold read-out having ultra-precise time resolution

A time-tagging hybrid silicon pixel detector developed for beam tracking in the NA62 experiment has been tested in a dedicated test-beam at CERN with 10 GeV/c hadrons. Measurements include time resolution, detection efficiency and charge sharing between pixels, as well as effects due to bias voltage variations. A time resolution of less than 150 ps has been measured with a 200 μm thick silicon sensor, using an on-pixel amplifier-discriminator and an end-of-column DLL-based time-to-digital converter

NA62 Liquid Krypton Purity Monitor

A system for determining the purity of liquid krypton employed in the NA62 rare kaon decay experiment at CERN was developed based on the use of a time projection chamber. The attenuation of drifting ionization electrons from absorption of 511 keV gamma rays in liquid krypton was measured to estimate the purity. The setup was tested with krypton purified from commercial sources.A system for determining the purity of liquid krypton employed in the NA62 rare kaon decay experiment at CERN was developed based on the use of a time projection chamber. The attenuation of drifting ionization electrons from absorption of 511 keV gamma rays in liquid krypton was measured to estimate the purity. The setup was tested with krypton purified from commercial sources

High rate particle tracking and ultra-fast timing with a thin hybrid silicon pixel detector

The Gigatracker (GTK) is a hybrid silicon pixel detector designed for the NA62 experiment at CERN. The beam spectrometer, made of three GTK stations, has to sustain high and non-uniform particle rate (∼1 GHz in total) and measure momentum and angles of each beam track with a combined time resolution of 150 ps. In order to reduce multiple scattering and hadronic interactions of beam particles, the material budget of a single GTK station has been fixed to 0.5% X0. The expected fluence for 100 days of running is 2 × 10 14 1 MeV neq/cm2, comparable to the one foreseen in the inner trackers of LHC detectors during 10 years of operation. To comply with these requirements, an efficient and very low-mass (<0:15% X0) cooling system is being constructed, using a novel microchannel cooling silicon plate. Two complementary read-out architectures have been produced as small-scale prototypes: one is based on a Time-over-Threshold circuit followed by a TDC shared by a group of pixels, while the other makes use of a constant-fraction discriminator followed by an on-pixel TDC. The read-out ASICs are produced in 130 nm IBM CMOS technology and will be thinned down to 100 μm or less. An overview of the Gigatracker detector system will be presented. Experimental results from laboratory and beam tests of prototype bump-bonded assemblies will be described as well. These results show a time resolution of about 170 ps for single hits from minimum ionizing particles, using 200 μm thick silicon sensors. © 2012 Elsevier B.V. All rights reserved

GigaTracker, the NA62 Beam Tracker

The GigaTracker measures the momentum, the direction and the crossing time of all the NA62 secondary beam particles. It is composed of three hybrid silicon pixel stations and four achromatic magnets. All the stations have a rate capability above 750 MHz, a single hit time resolution better than 200 ps and a thickness less than 0.5 % of X = X 0 . The stations’ sensor is read out by ten custom TDCpix ASICs. An innovative microchannel cooling solution is used to keep the sensor temperature below 0 °C. The stations are operated in vacuum and are easily swappabl