Reactor Neutrino Flux Uncertainty Suppression on Multiple Detector Experiments

This publication provides a coherent treatment for the reactor neutrino flux uncertainties suppression, specially focussed on the latest $\theta_{13}$ measurement. The treatment starts with single detector in single reactor site, most relevant for all reactor experiments beyond $\theta_{13}$. We demonstrate there is no trivial error cancellation, thus the flux systematic error can remain dominant even after the adoption of multi-detector configurations. However, three mechanisms for flux error suppression have been identified and calculated in the context of Double Chooz, Daya Bay and RENO sites. Our analysis computes the error {\it suppression fraction} using simplified scenarios to maximise relative comparison among experiments. We have validated the only mechanism exploited so far by experiments to improve the precision of the published $\theta_{13}$. The other two newly identified mechanisms could lead to total error flux cancellation under specific conditions and are expected to have major implications on the global $\theta_{13}$ knowledge today. First, Double Chooz, in its final configuration, is the only experiment benefiting from a negligible reactor flux error due to a $\sim$90\% geometrical suppression. Second, Daya Bay and RENO could benefit from their partial geometrical cancellation, yielding a potential $\sim$50\% error suppression, thus significantly improving the global $\theta_{13}$ precision today. And third, we illustrate the rationale behind further error suppression upon the exploitation of the inter-reactor error correlations, so far neglected. So, our publication is a key step forward in the context of high precision neutrino reactor experiments providing insight on the suppression of their intrinsic flux error uncertainty, thus affecting past and current experimental results, as well as the design of future experiments

Design studies for the double chooz trigger

The main characteristic of the neutrino mixing effect is assumed to be the coupling between the flavor and the mass eigenstates. Three mixing angles (theta12, theta23 and theta13) are describing the magnitude of this effect. Still unknown, theta13 is considered very small, in principal based on the measurement done by the CHOOZ experiment. The next generation reactor neutrino experiments will explore the theta13 region allowed by CHOOZ using multiple detectors in order to reduce the uncertainties related to the neutrino production and interaction. A leading experiment will be Double Chooz, placed in the Ardennes region (northwest of France), on the same site used by CHOOZ. The goal of Double Chooz is the exploration of ~80% from the current allowed theta13 region, in relatively short time and with low costs. Double Chooz will use two similar detectors, placed at different distances from the reactor cores: a near one at ~150 m where no oscillations are expected and a far one at 1.05 km distance, close to the first oscillation maximum. The measurement foresees a precise comparison of neutrino rates and spectra between both detectors. The detection mechanism is based on the inverse beta decay. The detectors have been designed to minimize the rate of random background. An simplified overview can consider two optically separated regions. The target, filled with Gd-doped liquid scintillator, is the main antineutrino interaction volume. Surrounding the target, the inner veto region aims to tag the atmospheric muon background which hits the detector. Both regions are monitored by photomultipliers tubes. The Double Chooz trigger system has to be highly efficient for antineutrino events as well as for several types of background. The trigger analyses discriminated signals from target and inner veto photomultipliers. The trigger logic is fully programmable and can combine any input signals. The trigger conditions are based on the total energy released in event and on the PMT groups multiplicity. For redundancy, two independent trigger boards will be used for target, each of them receiving signals from half of photomultipliers. In this way, the hardware failures are easily detected and will not result in a loss of events. A third trigger board will handle the inner veto signals and the additional trigger inputs. This PhD research establishes the trigger algorithm as result of the trigger efficiency optimization. The efficiency parameters are obtained from fits of Monte Carlo simulation data. Various possible influences are considered, the resulted algorithm being able to sustain the trigger goals for all kinds of events. In my work, I developed a method for measuring the trigger efficiency based on the redundancy of the two target boards. This method will use experimental and simulated Double Chooz data. Atmospheric muons are the dominant source of the Double Chooz triggered events. For the near detector, the foreseen muon rate is ~250Hz. The DAQ system is unable to sustain the full detector read-out at such high frequency. As consequence, the triggered events are treated differently, regarding their importance for future analysis. For physics events, the full available information is saved, the offline data for background muons will contain only summary information. An important concern is related to muons which stop in the target region. They can generate late beta decaying products such as 9Li or 8He, a source of correlated background. The trigger algorithm is able to identify "special" muons classes, for which the full detector read-out is performed. The recognition of the muon classes is based on the energy depositions from all detector regions and on the "topological" information provided by groups of photomultipliers

Track Reconstruction with Cosmic Ray Data at the Tracker Integration Facility

The subsystems of the CMS silicon strip tracker were integrated and commissioned at the Tracker Integration Facility (TIF) in the period from November 2006 to July 2007. As part of the commissioning, large samples of cosmic ray data were recorded under various running conditions in the absence of a magnetic field. Cosmic rays detected by scintillation counters were used to trigger the readout of up to 15\,\% of the final silicon strip detector, and over 4.7~million events were recorded. This document describes the cosmic track reconstruction and presents results on the performance of track and hit reconstruction as from dedicated analyses