Double Chooz project: Status of a reactor experiment aimed at searches for neutrino oscillations

Double Chooz is an experiment that is devoted to searches for reactor-antineutrino oscillations at the CHOOZ nuclear power plant. This project is aimed at measuring the unknown mixing angle θ ₁₃. It is assumed that the value of θ ₁₃ will be extracted from an analysis of the distortion of the antineutrino spectra obtained in relative measurements at two distances from the nuclear reactors by means of two identical detectors. The method makes it possible to minimize systematic errors of the experiment and to improve the sensitivity to the sought parameter. To date, the most stringent constraint on the parameter θ ₁₃ was obtained from the CHOOZ experiment in 1995–1997 [sin²(2θ ₁₃) < 0.19, with the difference of the squares of the neutrino masses being Δm ₁₃ ² = 2.5 × 10^?3 eV²].     

Non-standard interaction effects at reactor neutrino experiments

We study non-standard interactions (NSIs) at reactor neutrino experiments, and in particular, the mimicking effects on θ₁₃${\theta }_{13}$. We present generic formulas for oscillation probabilities including NSIs from sources and detectors. Instructive mappings between the fundamental leptonic mixing parameters and the effective leptonic mixing parameters are established. In addition, NSI corrections to the mixing angles θ₁₃${\theta }_{13}$ and θ₁₂${\theta }_{12}$ are discussed in detailed. Finally, we show that, even for a vanishing θ₁₃${\theta }_{13}$, an oscillation phenomenon may still be observed in future short baseline reactor neutrino experiments, such as Double Chooz and Daya Bay, due to the existences of NSIs.     

Towards a θ 13 measurement

Reactor-based antineutrino experiments hold the promise of providing an unambiguous determination of the neutrino mixing angle ?? ₁₃. At present, Daya Bay, Double Chooz and RENO are such experiments being set up for this purpose. In this paper, the status and prospects of these three initiatives are presented.     

Solar neutrino oscillation parameters after KamLAND

We explore the impact of the data from the KamLAND experiment in constraining neutrino mass and mixing angles involved in solar neutrino oscillations. In particular, we discuss the precision with which we can determine the mass squared difference Δm _⊙ ² and the mixing angle θ_⊙ from combined solar and KamLAND data. We show that the precision with which Δm _⊙ ² can be determined improves drastically with the KamLAND data, but the sensitivity of KamLAND to the mixing angle is not as good. We study the effect of enhanced statistics in KamLAND as well as reduced systematics in improving the precision. We also show the effect of the SNO salt data in improving the precision. Finally, we discuss how a dedicated reactor experiment with a baseline of 70 km can improve the θ_⊙ sensitivity by a large amount.     

Systematic impact of spent nuclear fuel on θ13 sensitivity at reactor neutrino experiment

Reactor neutrino oscillation experiments, such as Daya Bay, Double Chooz and RENO are designed to determine the neutrino mixing angle θ13 with a sensitivity of 0.01--0.03 in sin2 2θ13 at 90% confidence level, an improvement over the current limit by more than one order of magnitude. The control of systematic uncertainties is critical to achieving the sin2 2θ13 sensitivity goal of these experiments. Antineutrinos emitted from spent nuclear fuel (SNF) would distort the soft part of energy spectrum and may introduce a non-negligible systematic uncertainty. In this article, a detailed calculation of SNF neutrinos is performed taking account of the operation of a typical reactor and the event rate in the detector is obtained. A further estimation shows that the event rate contribution of SNF neutrinos is less than 0.2% relative to the reactor neutrino signals. A global χ2 analysis shows that this uncertainty will degrade the θ13 sensitivity at a negligible level.     

Present status of Double Chooz experiment

The goal of the Double Chooz experiment is to measure the value of sin²(2ϑ ₁₃), which is of great interest at the moment in neutrino physics. To overcome the existing limit coming from the CHOOZ experiment, we are going to use two identical detectors that will be placed at a distance of 150 m and 1.05 km from the reactor cores. This setup will allow us to decrease systematic error down to the level of a percent. In this paper, we discuss the details of the proposed experiment and the ways in which we plan to achieve the announced sensitivity. on behalf of Double Chooz Collaboration The text was submitted by the author in English.     

Indication of reactor ν(e) disappearance in the Double Chooz experiment

The Double Chooz experiment presents an indication of reactor electron antineutrino disappearance consistent with neutrino oscillations. An observed-to-predicted ratio of events of 0.944±0.016(stat)±0.040(syst) was obtained in 101 days of running at the Chooz nuclear power plant in France, with two 4.25 GW(th) reactors. The results were obtained from a single 10 m(3) fiducial volume detector located 1050 m from the two reactor cores. The reactor antineutrino flux prediction used the Bugey4 flux measurement after correction for differences in core composition. The deficit can be interpreted as an indication of a nonzero value of the still unmeasured neutrino mixing parameter sin(2)2θ(13). Analyzing both the rate of the prompt positrons and their energy spectrum, we find sin(2)2θ(13)=0.086±0.041(stat)±0.030(syst), or, at 90% C.L., 0.017相似文献   

Lithium experiment on solar neutrinos to weight the CNO cycle

The measurement of the flux of beryllium neutrinos with an accuracy of about 10% and CNO neutrinos with an accuracy of 20–30% will enable one to find the flux of pp neutrinos in the source with an accuracy better than 1% using the luminosity constraint. The future experiments on νe^? scattering will enable one to measure with very good accuracy the flux of beryllium and pp neutrinos on the Earth. The ratio of the flux of pp neutrinos on the Earth and in the source will enable one to find with very good accuracy a mixing angle θ_⊙. A lithium detector has high sensitivity to CNO neutrinos and can find the contribution of the CNO cycle to the energy generated in the Sun. This will be a stringent test of the theory of stellar evolution and combined with other experiments will provide a precise determination of the flux of pp neutrinos in the source and a mixing angle θ_⊙. The work on the development of the technology of a lithium experiment is now in progress.     

Employing low-power reactors in studying the mixing parameter sin<Superscript>2</Superscript>(2<Emphasis Type="Italic">θ</Emphasis><Subscript>13</Subscript>)

Measurement of the mixing parameter sin²(2θ₁₃) is one of the pressing problems in neutrino physics. Projects of reactor experiments characterized by a sensitivity of sin²(2θ₁₃)≈0.01 are being presently discussed. Almost all of them are based on the one reactor-two detectors scheme. Within this methodological approach, one employs an NPP reactor of power about a few GW for an antineutrino source and two detectors of identical configurations that are arranged at different distances from the reactor. In such experiments, the systematic error may be about 1%, which ensures a precision of about 0.01. In the present study, it is proposed to use, in a measurement of sin²(2θ₁₃), the existing SuperKamiokande (SK) detector combined with its own antineutrino source, a nuclear reactor of low thermal power, about 300 MW (low-power reactor, or LPR). Such an experiment can be performed within a rather short time. An analysis that studied various detection mechanisms revealed that the LPR-SK combination would make it possible to attain a sensitivity of sin²(2θ₁₃)≈0.002.     

Measurement of polarization angular coefficients in <Emphasis Type="Italic">Z</Emphasis> boson leptonic decays with ATLAS at the LHC

This paper presents the complete set of polarization angular coefficients A _0?7 describing lepton angular distributions in Z boson decay, which were measured at the ATLAS experiment in proton–proton collisions with the energy √s = 8 TeV. Theoretical values for the difference A ₀ ? A ₂ calculated in the fixed-order QCD perturbation theory O(α _s ² ), demonstrate significant deviation from the measured data, which indicates the necessity of taking into account higher order corrections. The evidence of nonzero coefficients A _5,6,7 was obtained for the first time, in accordance with theoretical calculations in O(α _s ² ) approximation. Measurement of the polarization angular coefficients A _i is important for subsequent precision measurement of parameters of the electroweak model at the LHC, such as the sine of Weinberg electroweak mixing angle sin² θ _W and the W boson mass.     

Future neutrino long baseline experiments

Very soon a new generation of reactor and accelerator neutrino oscillation experiments—Double Chooz, Daya Bay, Reno and T2K—will seek for oscillation signals generated by the mixing parameter θ₁₃. The knowledge of this angle is a fundamental milestone to optimize further experiments aimed at detecting CP violation in the neutrino sector. Leptonic CP violation is a key phenomenon that has profound implications in particle physics and cosmology but it is clearly out of reach for the aforementioned experiments. Since late 90’s, a worldwide activity is in progress to design facilities that can access CP violation in neutrino oscillation and perform high precision measurements of the lepton counterpart of the Cabibbo-Kobayashi-Maskawa matrix.     

C2GT: intercepting CERN neutrinos to Gran Sasso in the Gulf of Taranto to measure θ13

Today’s greatest challenge in accelerator-based neutrino physics is to measure the mixing angle θ₁₃ which is known to be much smaller than the solar mixing angle θ₁₂ and the atmospheric mixing angle θ₂₃. A non-zero value of the angle θ₁₃ is a prerequisite for observing CP violation in neutrino mixing. In this paper, we discuss a deep-sea neutrino experiment with 1.5 Mt fiducial target mass in the Gulf of Taranto with the prime objective of measuring θ₁₃. The detector is exposed to the CERN neutrino beam to Gran Sasso in off-axis geometry. Monochromatic muon neutrinos of ≈ 800 MeV energy are the dominant beam component. Neutrinos are detected through quasi-elastic, charged-current reactions in sea water; electrons and muons are detected in a large-surface, ring-imaging Cherenkov detector. The profile of the seabed in the Gulf of Taranto allows for a moveable experiment at variable distances from CERN, starting at 1100 km. From the oscillatory pattern of the disappearance of muon neutrinos, the experiment will measure sin²θ₂₃ and especially Δm² ₂₃ with high precision. The appearance of electron neutrinos will be observed with a sensitivity to P(ν_μ→ν_e) as small as 0.0035 (90% CL) and sin²θ₁₃ as small as 0.0019 (90% CL; for a CP phase angle δ=0° and for normal neutrino mass hierarchy).     

Neutrino mixing matrices with relatively large <Emphasis Type="Italic">θ</Emphasis><Subscript>13</Subscript> and with texture one-zero

The recent T2K, MINOS and Double Chooz oscillation data hint at a relatively large θ ₁₃, which can be accommodated by some general modification of the tribimaximal/bimaximal/democratic mixing matrices. Using such matrices we analyze several Majorana mass matrices with texture one-zero and show whether they satisfy the normal or the inverted mass hierarchy and are phenomenologically viable or not.     

The mass hierarchy with atmospheric neutrinos at INO

We study the neutrino mass hierarchy at the magnetized Iron CALorimeter (ICAL) detector at India-based Neutrino Observatory with atmospheric neutrino events generated by the Monte Carlo event generator Nuance. We judicially choose the observables so that the possible systematic uncertainties can be reduced. The resolution as a function of both energy and zenith angle simultaneously is obtained for neutrinos and anti-neutrinos separately from thousand years un-oscillated atmospheric neutrino events at ICAL to migrate number of events from neutrino energy and zenith angle bins to muon energy and zenith angle bins. The resonance ranges in terms of directly measurable quantities like muon energy and zenith angle are found using this resolution function at different input values of θ₁₃${\theta }_{13}$. Then, the marginalized χ²s${\chi }^2\mathrm{s}$ are studied for different input values of θ₁₃${\theta }_{13}$ with its resonance ranges taking input data in muon energy and zenith angle bins. Finally, we find that the mass hierarchy can be explored up to a lower value of θ₁₃≈5°${\theta }_{13}\approx 5°$ with confidence level >95% in this set up.     

Measuring the weak charge of the proton at Jefferson Lab: A search for physics beyond the standard model

The JLab Q _weak Collaboration is designing and constructing an experiment to measure the proton’s weak charge, Q _W ^p , by measuring the parity violating asymmetry in elastic electron-proton scattering at very low momentum transfer. The standard model predicts Q _W ^p = 1 ? 4 sin² θ _w from the running of the weak mixing angle sin² θ _w , corresponding to a 10σ effect in the experiment. The experiment will determine Q _W ^p with 4% combined statistical and systematic uncertainties, which leads to 0.3% uncertainty in sin² θ _w . Installation of the experiment will begin in September 2009.     

A lithium experiment in the program of solar neutrino research

Experiments sensitive to pp neutrinos from the Sun are very promising for precise measurement of the mixing angle ϑ ₁₂. A νe ⁻ scattering experiment (XMASS) and/or a charged-current experiment (indium detector) can measure the flux of electron pp neutrinos. One can find the total flux of pp neutrinos from a luminosity constraint after the contributions of ⁷Be and CNO neutrinos to the total luminosity of the Sun are measured. A radiochemical experiment utilizing a lithium target has high sensitivity to the CNO neutrinos; thus, it has a good promise for precise measurement of the mixing angle and for a test of the current theory of evolution of the stars. The text was submitted by the authors in English.     

Coefficient of ultrasound transmission from liquid helium to aluminum in the intermediate state at <Emphasis Type="Italic">T</Emphasis> ≈ 0.1 K

The coefficient α(θ) of ultrasound transmission from liquid ⁴He to an aluminum single crystal in intermediate, superconducting, and normal states at a temperature T ≈ 0.1 K is measured as a function of the polar angle θ at the azimuthal angle φ = 0. The experimental technique is based on the measurement of the Kapitza temperature jump at the interface between two media. The dependences of the transmission coefficient for the Rayleigh modes on the sound frequency (in the range 13–194 MHz) and the magnetic field strength are determined. It is demonstrated that the integrated transmission coefficient of the aluminum single crystal in the intermediate state at an angle θ_R larger than the critical value increases with an increase in the magnetic field strength. The integrals of the transmission coefficient in magnetic fields close to the field H _c are independent of the frequency. In the vicinity of H = 0, the transmission coefficient at ν > 39 MHz increases only slightly with increasing frequency. At the lowest frequencies, the transmission coefficient increases anomalously as the frequency decreases. The experimental data are compared with the results obtained in the framework of the Andreev theory. Numerical calculations are performed and the dependences α(θ, φ) for bulk modes in the range corresponding to angles smaller than the critical value are constructed for the three principal planes of the crystal, i.e., the (001), (011), and (111) planes. The dependence α(θ) is obtained for the azimuthal angle φ = 0. The width of the Rayleigh peak is estimated.     

Status of the Chorus experiment

The CHORUS experiment at CERN searches for ν_μ ? ν_τ oscillations by looking for τ decays from charged-current ν_τ interactions. The emulsion target of the detector, having a resolution of about a micron, enables the detection of the decay topology of the τ. After having analyzed a sample of 126000 events containing an identified muon and 7500 purely hadronic events, no ν_τ candidate has been found. This result translates in a limit on the mixing angle sin²2θ_μτ < 8 × 10^?4 at 90% C.L. for large Δm _μτ ² .     

The Qweak: Precision Measurement of the Proton’s Weak Charge by Parity Violating Experiment

The Qweak experiment at the Thomas Jefferson National Accelerator Facility measures the parity violating asymmetry in longitudinally polarized electron scattering from the proton at very low momentum transfer, Q ² = 0.026 (GeV/c)², at an incident electron beam energy of 1.16 GeV. With this measurement and the earlier results of the parity violating elastic scattering experiments, the Qweak experiment determines the weak charge of the proton, ${Q^p_{\rm W}}$ , with a 4% combined statistical and systematic error. This measurement will be used to determine the weak mixing angle, ${\sin^2\theta_{\rm W}}$ , that is predicted by the Standard Model from the Z ⁰ pole down to lower energies. Qweak will determine ${\sin^2\theta_{\rm W}}$ to a 0.3% relative precision, providing a competitive measurement of the running of this quantity. Moreover, if there is a significant deviation of the weak mixing angle from the Standard Model prediction, then the Qweak experiment will give a glimpse of possible extensions of the Standard Model.     

Neutrinos in a spherical box

The purpose of the present paper is to study the neutrino properties as they may appear in the low-energy neutrinos emitted in the triton decay \(_1^3 H \to _2^3 He + e^ - + \bar \nu _e \) with maximum neutrino energy of 18.6 keV. The technical challenges to this end can be summarized as building a very large TPC capable of detecting low-energy recoils, down to a few 100 eV, within the required low-background constraints. More specifically, we propose the development of a spherical gaseous TPC of about 10 m in radius and a 200-MCi triton source in the center of curvature. One can list a number of exciting studies concerning fundamental physics issues that could be made using a large volume TPC and low-energy antineutrinos: (i) The oscillation length involving the small angle δ = sinθ₁₃, directly measured in our ν_e disappearance experiment, is fully contained inside the detector. Measuring the counting rate of neutrino-electron elastic scattering as a function of the distance of the source will give a precise and unambiguous measurement of the oscillation parameters free of systematic errors. In fact, first estimates show that, even with a year's data taking, a sensitivity of a few percent for the measurement of the above angle will be achieved. (ii) The low-energy detection threshold offers a unique sensitivity for the neutrino magnetic moment which is about two orders of magnitude beyond the current experimental limit of 10^?10μ_B. (iii) Scattering at such low neutrino energies has never been studied and any departure from the expected behavior may be an indication of new physics beyond the Standard Model. We present a summary of various theoretical studies and possible measurements, including a precise measurement of the Weinberg angle at very low momentum transfer.