ALICE is the heavy-ion experiment at the CERN Large Hadron Collider. The experiment continuously took data during the first physics campaign of the machine from fall 2009 until early 2013, using proton and lead-ion beams. In this paper we describe the running environment and the data handling procedures, and discuss the performance of the ALICE detectors and analysis methods for various physics observables.
Abstract. New results for the double beta decay of76 Ge are presented. They are extracted from Data obtained with the Heidelberg-Moscow experiment, which operates five enriched 76 Ge detectors in an extreme low-level environment in the Gran Sasso underground laboratory. The two neutrino accompanied double beta decay is evaluated for the first time for all five detectors with a statistical significance of 47.7 kg y resulting in a half life of T
Neutrinoless double beta decay is a process that violates lepton number conservation. It is predicted to occur in extensions of the standard model of particle physics. This Letter reports the results from phase I of the Germanium Detector Array (GERDA) experiment at the Gran Sasso Laboratory (Italy) searching for neutrinoless double beta decay of the isotope (76)Ge. Data considered in the present analysis have been collected between November 2011 and May 2013 with a total exposure of 21.6 kg yr. A blind analysis is performed. The background index is about 1 × 10(-2) counts/(keV kg yr) after pulse shape discrimination. No signal is observed and a lower limit is derived for the half-life of neutrinoless double beta decay of (76)Ge, T(1/2)(0ν) >2.1 × 10(25) yr (90% C.L.). The combination with the results from the previous experiments with (76)Ge yields T(1/2)(0ν)>3.0 × 10(25) yr (90% C.L.).
The Heidelberg-Moscow experiment gives the most stringent limit on the Majorana neutrino mass. After 24 kg yr of data with pulse shape measurements, we set a lower limit on the half-life of the 0νββ-decay in 76 Ge of T 0ν 1/2 ≥ 5.7 × 10 25 yr at 90% C.L., thus excluding an effective Majorana neutrino mass greater than 0.2 eV. This allows to set strong constraints on degenerate neutrino mass models.Neutrinoless double beta (0νββ) decay is an extremely sensitive tool to probe theories beyond the standard model (see [1]). While the standard model exactly conserves B-L, 0νββ-decay violates lepton number, and B-L, by two units. The simplest mechanism which can induce 0νββ-decay is the exchange of a Majorana neutrino between the decaying neutrons. Alternatively, any theory that contains lepton number violating interactions can lead to the process. Independently of the underlying mechanism, an observation of the 0νββ-decay would be an evidence for a nonzero Majorana neutrino mass [2]. There are several indications for nonzero neutrino masses, the most stringent ones come from solar and atmospheric neutrino experiments. In particular, the confirmation by Super Kamiokande of the atmospheric neutrino deficit [3], provides strong evidence for neutrino oscillations, although also other solutions are possible [4]. If a neutrino as a hot dark matter (HDM) component is taken into account, then fitting the atmospheric, solar and HDM scales with three neutrinos is only possible in the degenerate mass scenario, where all neutrinos have nearly the same mass, in the order of O(eV) [5]. This would lead to an amplitude for 0νββ-decay mediated by the neutrino mass which is accessible by the present sensitivity of the Heidelberg-Moscow experiment.The Heidelberg-Moscow experiment operates five p-type HPGe detectors in the Gran Sasso Underground Laboratory. The Ge crystals were grown out of 19.2 kg of 86% enriched 76 Ge material. The total active mass of the detectors is 10.96 kg, corresponding to 125.5 mol of 76 Ge, the presently largest source strength of all double beta experiments. Four detectors are placed in a common 30 cm thick lead shielding in a radon free nitrogen atmosphere, surrounded by 10 cm of boron-loaded polyethylene and with two layers of 1 cm thick scintillators on top. The remaining detector is situated in a separate box with 27 cm electrolytical copper and 20 cm lead shielding, flushed with gaseous nitrogen and with 10 cm of boron-loaded polyethylene below the box. A detailed description of the experiment and its background is given in [6]. For a further reduction of the already very low background of the experiment, a pulse shape analysis (PSA) method was developed [7]. The analysis distinguishes between multiple scattered interaction in the Ge crystal, so called multiple site events (MSE) and pointlike interactions, i.e. single site events (SSE). Since double beta decay events belong to the SSE category, the method allows to effectively reduce the background of multiple Compton scattered photons. The probability of...
ALICE is a general-purpose heavy-ion experiment designed to study the physics of strongly interacting matter and the quark–gluon plasma in nucleus–nucleus collisions at the LHC. It currently involves more than 900 physicists and senior engineers, from both the nuclear and high-energy physics sectors, from over 90 institutions in about 30 countries.The ALICE detector is designed to cope with the highest particle multiplicities above those anticipated for Pb–Pb collisions (dNch/dy up to 8000) and it will be operational at the start-up of the LHC. In addition to heavy systems, the ALICE Collaboration will study collisions of lower-mass ions, which are a means of varying the energy density, and protons (both pp and pA), which primarily provide reference data for the nucleus–nucleus collisions. In addition, the pp data will allow for a number of genuine pp physics studies.The detailed design of the different detector systems has been laid down in a number of Technical Design Reports issued between mid-1998 and the end of 2004. The experiment is currently under construction and will be ready for data taking with both proton and heavy-ion beams at the start-up of the LHC.Since the comprehensive information on detector and physics performance was last published in the ALICE Technical Proposal in 1996, the detector, as well as simulation, reconstruction and analysis software have undergone significant development. The Physics Performance Report (PPR) provides an updated and comprehensive summary of the performance of the various ALICE subsystems, including updates to the Technical Design Reports, as appropriate.The PPR is divided into two volumes. Volume I, published in 2004 (CERN/LHCC 2003-049, ALICE Collaboration 2004 J. Phys. G: Nucl. Part. Phys. 30 1517–1763), contains in four chapters a short theoretical overview and an extensive reference list concerning the physics topics of interest to ALICE, the experimental conditions at the LHC, a short summary and update of the subsystem designs, and a description of the offline framework and Monte Carlo event generators.The present volume, Volume II, contains the majority of the information relevant to the physics performance in proton–proton, proton–nucleus, and nucleus–nucleus collisions. Following an introductory overview, Chapter 5 describes the combined detector performance and the event reconstruction procedures, based on detailed simulations of the individual subsystems. Chapter 6 describes the analysis and physics reach for a representative sample of physics observables, from global event characteristics to hard processes.
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