In this paper we describe the development, testing, and characterization of three low-emission rate AmLi neutron sources. The sources are used to calibrate the nuclear recoil response of the LUX-ZEPLIN (LZ) dark matter experiment. The sources' neutron emission rate was measured using $^{3}$He proportional tubes. The sources' gamma emissions were characterized using a high-purity germanium (HPGe) detector. Source-validated GEANT4 Monte Carlo simulations allowed to calibrate the Ge and neutron detector responses.

This article describes the setup and performance of the near and far detectors in the Double Chooz experiment. The electron antineutrinos of the Chooz nuclear power plant were measured in two identically designed detectors with different average baselines of about 400 m and 1050 m from the two reactor cores. Over many years of data taking the neutrino signals were extracted from interactions in the detectors with the goal of measuring a fundamental parameter in the context of neutrino oscillation, the mixing angle θ13. The central part of the Double Chooz detectors was a main detector comprising four cylindrical volumes filled with organic liquids. From the inside towards the outside there were volumes containing gadolinium-loaded scintillator, gadolinium-free scintillator, a buffer oil and, optically separated, another liquid scintillator acting as veto system. Above this main detector an additional outer veto system using plastic scintillator strips was installed. The technologies developed in Double Chooz were inspiration for several other antineutrino detectors in the field. The detector design allowed implementation of efficient background rejection techniques including use of pulse shape information provided by the data acquisition system. The Double Chooz detectors featured remarkable stability, in particular for the detected photons, as well as high radiopurity of the detector components.

We present a search for signatures of neutrino mixing of electron anti-neutrinos with additional hypothetical sterile neutrino flavors using the Double Chooz experiment. The search is based on data from 5 years of operation of Double Chooz, including 2 years in the two-detector configuration. The analysis is based on a profile likelihood, i.e.\ comparing the data to the model prediction of disappearance in a data-to-data comparison of the two respective detectors. The analysis is optimized for a model of three active and one sterile neutrino. It is sensitive in the typical mass range $5 \cdot 10^{-3} $ eV$^2 \lesssim \Delta m^2_{41} \lesssim 3\cdot 10^{-1} $ eV$^2$ for mixing angles down to $\sin^2 2\theta_{14} \gtrsim 0.02$. No significant disappearance additionally to the conventional disappearance related to $\theta_{13} $ is observed and correspondingly exclusion bounds on the sterile mixing parameter $\theta_{14} $ as function of $ \Delta m^2_{41} $ are obtained.

A bstract A θ 13 oscillation analysis based on the observed antineutrino rates at the Double Chooz far and near detectors for different reactor power conditions is presented. This approach provides a so far unique simultaneous determination of θ 13 and the total background rates without relying on any assumptions on the specific background contributions. The analysis comprises 865 days of data collected in both detectors with at least one reactor in operation. The oscillation results are enhanced by the use of 24.06 days (12.74 days) of reactor-off data in the far (near) detector. The analysis considers the $$ {\overline{\nu}}_e $$ ν ¯ e interactions up to a visible energy of 8.5 MeV, using the events at higher energies to build a cosmogenic background model considering fast-neutrons interactions and 9 Li decays. The background-model-independent determination of the mixing angle yields sin 2 (2 θ 13 ) = 0 . 094 ± 0 . 017, being the best-fit total background rates fully consistent with the cosmogenic background model. A second oscillation analysis is also performed constraining the total background rates to the cosmogenic background estimates. While the central value is not significantly modified due to the consistency between the reactor-off data and the background estimates, the addition of the background model reduces the uncertainty on θ 13 to 0.015. Along with the oscillation results, the normalization of the anti-neutrino rate is measured with a precision of 0.86%, reducing the 1.43% uncertainty associated to the expectation.

We report measurements of the inclusive production of heavy quarkonium states in Z decays based on the analysis of 3.6 million hadronic events collected by the L3 detector at LEP. The measurement of inclusive J production and an improved 95% confidence level upper limit on F production are presented. In addition, two independent measurements of the ratio, f of prompt J mesons to those from B decay are made using two different isolation cuts to separate prompt J mesons from J mesons produced in the decays of b hadrons. The results are: Br(Z TM J + X) = (3.21 + 0.21 (stat.) J^1/ (sys.)) X 10 y 3, Br(Z TM F(1S) + X) < 4.4 X 10 y 5, fp = (7.1 + 2.1 (stat.) + 1.2(sys.) qjg (theo.)) X 10 y 2 . © 1999 Published by Elsevier Science B.V. All rights reserved. 1 Also supported by CONICET and Universidad Nacional de La Plata, CC 67, 1900 La Plata, Argentina. 2 Also supported by Panjab University, Chandigarh-160014, India. 3 Supported by Deutscher Akademischer Austauschdienst. 4 Also supported by the Hungarian OTKA fund under contract numbers T22238 and T026178. 5 Supported by the German Bundesministerium fur Bildung, Wissenschaft, Forschung und Technologie. 6 Supported by the National Natural Science Foundation of China. 7 Supported by the Hungarian OTKA fund under contract num­ bers T019181, F023259 and T024011. 8 Supported also by the Comisión Interministerial de Ciencia y Tecnología.

A search for unstable neutral and charged heavy leptons as well as for stable charged heavy leptons has been made at center-of-mass energies fi = 161 GeV and 6 = 172 GeV with the L3 detector at LEP. No evidence for their existence was found. We exclude unstable neutral leptons of Dirac (Majorana) type for masses below 78.0 (66.7), 78.0 (66.7) and 72.2 (58.2) GeV, if the heavy neutrino couples to the electron, muon or tau family, respectively. We exclude unstable charged heavy leptons for masses below 81.0 GeV for a wide mass range of the associated neutral heavy lepton. The production of stable charged heavy leptons with a mass less than 84.2 GeV is also excluded. If the unstable charged heavy lepton decays via mixing into a massless neutrino, we exclude masses below 78.7 GeV.

The inclusive semileptonic branching ratios b —► e u X , uX , r vX and vX have been measured at LEP with a Supported by the German Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie b Supported by the Hungarian OTKA fund under contract number T 14459 c Supported also by the Comisión Interministerial de Ciencia y Technologia d Also supported by CONICET and Universidad Nacional de La Plata, CC 67, 1900 La Plata, Argentina e Also supported by Panjab University, Chandigarh-160014, India the L3 detector. The analysis is based on 2-jet hadronic Z decays obtained in the data collected between 1991 and 1992. Three separate event samples are analysed, contain­ ing electrons, muons and large missing energy (neutrinos), respectively. From the electron sample, we measure Br(b —> ez/X) (10.89±0.20=b0.51)% and, from the muon sam­ ple, Br(b —► ¡jl vX ) = (10.82±0.15±0.59)%, where the first error is statistical and the second is systematic. From

We have studied the structure of hadronic events with a hard, isolated photon in the final state (e+e_—> Z -» hadrons + y) in the 3.6 million hadronic events collected with the L3 detector at centre-of-mass energies around 91 GeV. The centre-of-mass energy of the hadronic system is in the range 30 GeV to 86 GeV. Event shape variables have been measured at these reduced centre-of-mass energies and have been compared with the predictions of different QCD Monte Carlo programs. The event shape variables and the energy dependence of their mean values are well reproduced by QCD models. 5 Supported by the Hungarian OTKA fund under contract numbers T14459 and T24011. 6 Supported also by the Comisión Interministerial de Ciencia y Technologia. p Massachusetts Institute of Technology, Cambridge, MA 02139, USA q INFN Sezione di Firenze and University of Florence, 1-50125 Florence, Italy r European Laboratory for Particle Physics, CERN, CH-1211 Geneva 23, Switzerland s World Laboratory, FBLJA Project, CH-1211 Geneva 23, Switzerland 1 University of Geneva, CH-1211 Geneva 4, Switzerland u Chinese University of Science and Technology, USTC, Hefei, Anhui 230 029, China 4 v SEFT, Research Institute for High Energy Physics, P.O. Box 9, SF-00014 Helsinki, Finland w University of Lausanne, CH-1015 Lausanne, Switzerland x INFN-Sezione di Lecce and Università Degli Studi di Lecce, 1-73100 Lecce, Italy y Los Alamos National Laboratory, Los Alamos, NM 87544, USA L Institut de Physique Nucléaire de Lyon, IN2P3-CNRS, Università Claude Bernard, F-69622 Villeurbanne, France “““ Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas, CIEMAT, E-28040 Madrid, Spain 6 ab INFN-Sezione di Milano, 1-20133 Milan, Italy ac Institute of Theoretical and Experimental Physics, ITEP, Moscow, Russia ad INFN-Sezione di Napoli and University of Naples, I-80I25 Naples, Italy “ Department of Natural Sciences, University of Cyprus, Nicosia, Cyprus af University of Nijmegen and NIKHEF, NL-6525 ED Nijmegen, The Netherlands a* Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA * California Institute of Technology, Pasadena, CA 91125, USA “ INFN-Sezione di Perugia and Università Degli Studi di Perugia, 1-06100 Perugia, Italy “j Camegie Mellon University, Pittsburgh, PA 15213, USA ak Princeton University, Princeton, NJ 08544, USA al INFN-Sezione di Roma and University of Rome, “La Sapienza”, 1-00185 Rome, Italy am Nuclear Physics Institute, St. Petersburg, Russia a" University and INFN, Salerno, 1-84100 Salerno, Italy a° University of California, San Diego, CA 92093, USA ap Dept, de Fisica de Partículas Elementales, Univ, de Santiago, E-15706 Santiago de Compostela, Spain Bulgarian Academy of Sciences, Central Lab. of Mechatronics and Instrumentation, BU-1113 Sofia, Bulgaria “ Center for High Energy Physics, Korea Adv. Inst, of Sciences and Technology, 305-701 Taejon, South Korea as University of Alabama, Tuscaloosa, AL 35486, USA “ Utrecht University and NIKHEF, NL-3584 CB Utrecht, The Netherlands “ Purdue University, West Lafayette, IN 47907, USA av Paul Scherrer Institut, PSI, CH-5232 Villigen, Switzerland aw DESY-Institut für Hochenergiephysik, D-15738 Zeuthen, FRG “ Eidgenössische Technische Hochschule, ETH Zürich, CH-8093 Zürich, Switzerland ay University of Hamburg, D-22761 Hamburg, FRG az High Energy Physics Group, Taiwan, ROC Received 23 June 1997 Editor: K. Winter M. Acciarri et al./Physics Letters B 411 (1997) 339-353 343 We fit distributions of several global event shape variables to resummed calculations to determine the strong coupling constant as over a wide range of energies. We find that the strong coupling constant as decreases with increasing energy, as expected from QCD. © 1997 Elsevier Science B.V.

Liquid scintillators are a common choice for neutrino physics experiments, but their capabilities to perform background rejection by scintillation pulse shape discrimination is generally limited in large detectors. This paper describes a novel approach for a pulse shape based event classification developed in the context of the Double Chooz reactor antineutrino experiment. Unlike previous implementations, this method uses the Fourier power spectra of the scintillation pulse shapes to obtain event-wise information. A classification variable built from spectral information was able to achieve an unprecedented performance, despite the lack of optimization at the detector design level. Several examples of event classification are provided, ranging from differentiation between the detector volumes and an efficient rejection of instrumental light noise, to some sensitivity to the particle type, such as stopping muons, ortho-positronium formation, alpha particles as well as electrons and positrons. In combination with other techniques the method is expected to allow for a versatile and more efficient background rejection in the future, especially if detector optimization is taken into account at the design level.

A bstract The yields and production rates of the radioisotopes 9 Li and 8 He created by cosmic muon spallation on 12 C, have been measured by the two detectors of the Double Chooz experiment. The identical detectors are located at separate sites and depths, which means that they are subject to different muon spectra. The near (far) detector has an overburden of ∼120 m.w.e. (∼300 m.w.e.) corresponding to a mean muon energy of 32.1 ± 2.0 GeV (63.7 ± 5.5 GeV). Comparing the data to a detailed simulation of the 9 Li and 8 He decays, the contribution of the 8 He radioisotope at both detectors is found to be compatible with zero. The observed 9 Li yields in the near and far detectors are 5.51 ± 0.51 and 7.90 ± 0.51, respectively, in units of 10 −8 μ −1 g −1 cm 2 . The shallow overburdens of the near and far detectors give a unique insight when combined with measurements by KamLAND and Borexino to give the first multi-experiment, data driven relationship between the 9 Li yield and the mean muon energy according to the power law $$ Y = {Y}_0{\left(\left\langle {E}_{\mu}\right\rangle /1\ GeV\right)}^{\overline{\alpha}} $$ Y = Y 0 E μ / 1 GeV α ¯ , giving $$ \overline{\alpha} = 0.72 \pm 0.06 $$ α ¯ = 0.72 ± 0.06 and Y 0 = (0.43 ± 0.11) × 10 −8 μ −1 g −1 cm 2 . This relationship gives future liquid scintillator based experiments the ability to predict their cosmogenic 9 Li background rates.

The LZ dark matter detector, like many other rareevent searches, will suffer from backgrounds due to the radioactive decay of radon daughters. In order to achieve its science goals, the concentration of radon within the xenon should not exceed 2 mu B /kg, or 20 mBq total within its 10 tonnes. The LZ collaboration is in the midst of a program to screen all significant components in contact with the xenon. The four institutions involved in this effort have begun sharing two crosscalibration sources to ensure consistent measurement results across multiple distinct devices. We present here five preliminary screening results, some mitigation strategies that will reduce the amount of radon produced by the most problematic components, and a summary of the current estimate of radon emanation throughout the detector. This best estimate totals < 17 : 3 mBq, sufficiently low to meet the detector's science goals.

A study on cosmic muons has been performed for the two identical near and far neutrino detectors of the Double Chooz experiment, placed at similar to 120 and similar to 300 m. w.e. underground respectively, including the corresponding simulations using the MUSIC simulation package. This characterization has allowed us to measure the muon flux reaching both detectors to be (3.64 +/- 0.04) x 10(-4) cm(-2) s(-1) for the near detector and (7.00 +/- 0.05) x 10(-5) cm(-2) s(-1) for the far one. The seasonal modulation of the signal has also been studied observing a positive correlation with the atmospheric temperature, leading to an effective temperature coefficient of alpha(T) = 0.212 +/- 0.024 and 0.355 +/- 0.019 for the near and far detectors respectively. These measurements, in good agreement with expectations based on theoretical models, represent one of the first measurements of this coefficient in shallow depth installations.

Using the Double Chooz detector, designed to measure the neutrino mixing angle theta(13), the products of mu(-) capture on C-12, C-13, N-14, and O-16 have been measured. Over a period of 489.5 days, 2.3 x 10(6) stopping cosmic mu(-) have been collected, of which 1.8 x 10(5) captured on carbon, nitrogen, or oxygen nuclei in the inner detector scintillator or acrylic vessels. The resulting isotopes were tagged using prompt neutron emission (when applicable), the subsequent beta decays, and, in some cases, beta-delayed neutrons. The most precise measurement of the rate of C-12(mu(-), nu)B-12 to date is reported: 6.57(-0.21)(+0.11) x 10(3) s(-1), or (17.35(-0.59)(+0.35))% of nuclear captures. By tagging excited states emitting gamma s, the ground state transition rate to B-12 has been determined to be 5.68(-0.23)(+0.14) x 10(3) s(-1). The heretofore unobserved reactions C-12(mu(-), nu alpha)Li-8, C-13(mu(-), nu n alpha)Li-8, and C-13(mu(-), nu n)B-12 are measured. Further, a population of beta n decays following stopping muons is identified with 5.5 sigma significance. Statistics limit our ability to identify these decays definitively. Assuming negligible production of He-8, the reaction C-13(mu(-), nu alpha)Li-9 is found to be present at the 2.7 sigma level. Limits are set on a variety of other processes.

The Double Chooz collaboration presents a measurement of the neutrino mixing angle θ13 using reactor νe observed via the inverse beta decay reaction in which the neutron is captured on hydrogen. This measurement is based on 462.72 live days data, approximately twice as much data as in the previous such analysis, collected with a detector positioned at an average distance of 1050 m from two reactor cores. Several novel techniques have been developed to achieve significant reductions of the backgrounds and systematic uncertainties. Accidental coincidences, the dominant background in this analysis, are suppressed by more than an order of magnitude with respect to our previous publication by a multi-variate analysis. These improvements demonstrate the capability of precise measurement of reactor νe without gadolinium loading. Spectral distortions from the νe reactor flux predictions previously reported with the neutron capture on gadolinium events are confirmed in the independent data sample presented here. A value of sin 2θ13 = 0.095 +0.038 −0.039(stat+syst) is obtained from a fit to the observed event rate as a function of the reactor power, a method insensitive to the energy spectrum shape. A simultaneous fit of the hydrogen capture events and of the gadolinium capture events yields a measurement of sin 2θ13 = 0.088± 0.033(stat+syst).

During the commissioning of the first of the two detectors of the Double Chooz experiment, an unexpected and dominant background caused by the emission of light inside the optical volume has been observed. A specific study of the ensemble of phenomena called Light Noise has been carried out in-situ, and in an external laboratory, in order to characterize the signals and to identify the possible processes underlying the effect. Some mechanisms of instrumental noise originating from the PMTs were identified and it has been found that the leading one arises from the light emission localized on the photomultiplier base and produced by the combined effect of heat and high voltage across the transparent epoxy resin covering the electric components. The correlation of the rate and the amplitude of the signal with the temperature has been observed. For the first detector in operation the induced background has been mitigated using online and offline analysis selections based on timing and light pattern of the signals, while a modification of the photomultiplier assembly has been implemented for the second detector in order to blacken the PMT bases.

The Double Chooz experiment presents improved measurements of the neutrino mixing angle θ 13 using the data collected in 467.90 live days from a detector positioned at an average distance of 1050 m from two reactor cores at the Chooz nuclear power plant. Several novel techniques have been developed to achieve significant reductions of the backgrounds and systematic uncertainties with respect to previous publications, whereas the efficiency of the ν_e signal has increased. The value of θ 13 is measured to be sin 2 2 θ 13 = 0.090 − 0.029 + 0.032 from a fit to the observed energy spectrum. Deviations from the reactor ν_e prediction observed above a prompt signal energy of 4 MeV and possible explanations are also reported. A consistent value of θ 13 is obtained from a fit to the observed rate as a function of the reactor power independently of the spectrum shape and background estimation, demonstrating the robustness of the θ 13 measurement despite the observed distortion.

The Double Chooz experiment measures the neutrino mixing angle theta(13) by detecting reactor (nu) over bar (e) via inverse beta decay. The positron-neutron space and time coincidence allows for a sizable background rejection, nonetheless liquid scintillator detectors would profit from a positron/electron discrimination, if feasible in large detector, to suppress the remaining background. Standard particle identification, based on particle dependent time profile of photon emission in liquid scintillator, can not be used given the identical mass of the two particles. However, the positron annihilation is sometimes delayed by the orthopositronium (o-Ps) metastable state formation, which induces a pulse shape distortion that could be used for positron identification. In this paper we report on the first observation of positronium formation in a large liquid scintillator detector based on pulse shape analysis of single events. The o-Ps formation fraction and its lifetime were measured, finding the values of 44 +/- 12 % (sys.) +/- 5 % (stat.) and 3.68 ns +/- 0.17 ns (sys.) +/- 0.15 ns (stat.) respectively, in agreement with the results obtained with a dedicated positron annihilation lifetime spectroscopy setup.

We describe here the recent activities of our two groups over the first year of this award (effectively November 2010 through January 2012) and our proposed activities and associated budgets for the coming grant year. Both of our groups are collaborating on the Double Chooz reactor neutrino experiment and are playing major roles in calibration and analysis. A major milestone was reached recently: the collaboration obtained the first result on the search for θ13 based on 100 days of data from the far detector. Our data indicates that θ13 is not zero; specifically the best fit of the neutrino oscillation hypothesis to our data gives sin2(2θ13) = 0.086 ± 0.041 (stat) ± 0.030 (syst). The null oscillation hypothesis is excluded at the 94.6% C.L. This result has been submitted to Physical Review Letters. As we continue to take data with the far detector in the coming year, in parallel with completing the construction of the near lab and installing the near detector, we expect the precision of our measurement to improve as we gather significantly more statistics, gain better control of backgrounds through use of partial power data and improved event selection, and better understand the detector energy scale and detection efficiency from calibration data. With both detectors taking data starting in the second half of 2013, we expect to further drive down the uncertainty on our measurement of sin2(2θ13) to less than 0.02. Stancu’s group is also collaborating on the MiniBooNE experiment. Data taking is scheduled to continue through April, by which time 1.18 × 1021 POT is projected. The UA group is playing a leading role in the measurement of antineutrino cross sections, which should be the subject of a publication later this year as well as of Ranjan Dharmapalan’s Ph.D. thesis, which he is expected to defend by the end of this year. It is time to begin working on projects which will eventually succeed Double Chooz and MiniBooNE as the main foci of our efforts. The Stancu group plans to become re–involved in LBNE and possibly also to join NO A, and the Busenitz group has begun to explore joining a direct dark matter search.

We describe a muon track reconstruction algorithm for the reactor anti-neutrino experiment Double Chooz. The Double Chooz detector consists of two optically isolated volumes of the liquid scintillator viewed by PMTs, and an Outer Veto above these made of crossed scintillator strips. Muons are reconstructed by their Outer Veto hit positions along with timing information from the other two detector volumes. All muons are fit under the hypothesis that they are through-going and ultrarelativistic. If the energy depositions suggest that the muon may have stopped, the reconstruction fits also for this hypothesis and chooses between the two via the relative goodness-of-fit. In the ideal case of a through-going muon intersecting the center of the detector, the resolution is ~40mm in each transverse dimension. High quality muon reconstruction is an important tool for reducing the impact of the cosmogenic isotope background in Double Chooz.