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.
We investigated mu(+) decays at rest produced at the ISIS beam stop target. Lepton flavor (LF) conservation has been tested by searching for nu(e) via the detection reaction p(nu(e),e(+))n. No nu(e) ...signal from LF violating mu(+) decays was identified. We extract upper limits of the branching ratio (BR) for the LF violating decay mu(+)-->e(+)+nu(e)+nu(-) compared to the standard model (SM) mu(+)-->e(+)+nu(e)+nu(mu) decay: BR<0.9(1.7) x 10(-3) (90% C.L.) depending on the spectral distribution of nu(e) characterized by the Michel parameter rho=0.75(0.0). These results improve earlier limits by one order of magnitude and restrict extensions of the SM in which nu(e) emission from mu(+) decay is allowed with considerable strength. The decay mu(+)-->e(+)+nu(e)+nu(mu) often proposed as a potential source for the nu(e) signal observed in the LSND experiment can be excluded.
A \(\theta_{13}\) 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 \(\theta_{13}\) 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 \nue 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\(^2(2\theta_{13})=0.094\pm0.017\), 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 \(\theta_{13}\) 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.
The temperature of the upper atmosphere affects the height of primary cosmic ray interactions and the production of high-energy cosmic ray muons which can be detected deep underground. The MINOS far ...detector at Soudan, MN, has collected over 67×106 cosmic ray induced muons. The underground muon rate measured over a period of five years exhibits a 4% peak-to-peak seasonal variation which is highly correlated with the temperature in the upper atmosphere. The coefficient, αT, relating changes in the muon rate to changes in atmospheric temperature was found to be αT=0.873±0.009(stat)±0.010(syst). Pions and kaons in the primary hadronic interactions of cosmic rays in the atmosphere contribute differently to αT due to the different masses and lifetimes. This allows the measured value of αT to be interpreted as a measurement of the K/π ratio for Ep≳7TeV of 0.12-0.05+0.07, consistent with the expectation from collider experiments.
The velocity of a ˜3GeV neutrino beam is measured by comparing detection times at the near and far detectors of the MINOS experiment, separated by 734 km. A total of 473 far detector neutrino events ...was used to measure (v-c)/c=5.1±2.9×10-5 (at 68% C.L.). By correlating the measured energies of 258 charged-current neutrino events to their arrival times at the far detector, a limit is imposed on the neutrino mass of mν<50MeV/c2 (99% C.L.).
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 they are subject to different muon
spectra. The near (far) detector has an overburden of $\sim$120 m.w.e.
($\sim$300 m.w.e.) corresponding to a mean muon energy of
$32.1\pm2.0\,\mathrm{GeV}$ ($63.7\pm5.5\,\mathrm{GeV}$). 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 $5.51\pm0.51$ and
$7.90\pm0.51$, respectively, in units of $10^{-8}\mu ^{-1} \mathrm{g^{-1}
cm^{2} }$. 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 $Y = Y_0( <E_{\mu} >/
1\,\mathrm{GeV})^{\overline{\alpha}}$, giving $\overline{\alpha}=0.72\pm0.06$
and $Y_0=(0.43\pm0.11)\times 10^{-8}\mu ^{-1} \mathrm{g^{-1} cm^{2}}$. This
relationship gives future liquid scintillator based experiments the ability to
predict their cosmogenic $^9$Li background rates.
KARMEN upgrade and prospects at ESS Drexlin, G.; Armbruster, B.; Eberhard, V. ...
Progress in particle and nuclear physics,
1998, 1998-1-00, Letnik:
40
Journal Article
Recenzirano
The KARMEN experiment at the ISIS spallation source has enhanced its sensitivity for
ν
μ
→
ν
e
oscillations in 1996 by the installation of an additional large area veto counter system. Consisting of ...136 highly transparent plastic scintillator modules, the new veto is completely embedded inside the experiment's 7000 tonne steel blockhouse. It allows to eliminate the main background component in the search for
ν
μ
→
ν
e
appearance originating from high energy neutrons induced by deep inelastic scattering of cosmic ray muons in the massive shielding. First measurements after the detector upgrade show a substantial reduction of this background meeting the expected factor of 40. If no oscillation signal is seen after 3 years of measuring (1997–1999) KARMEN will be able to exclude mixing amplitudes of sin
22
Θ≃1
x10
-3. The ongoing KARMEN2 measurements will thus allow a decisive and reliable test of the entire parameter space favoured by the positive result of LSND.
An even higher oscillation sensitivity can be achieved by experiments at future high intensity short spill proton accelerators such as the planned European Spallation Source ESS.
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