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Register a new userMeasurement of neutrino flux from the primary proton--proton fusion process in the Sun with Borexino detector
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Neutrino produced in a chain of nuclear reactions in the Sun starting from the fusion of two protons, for the first time has been detected in a real-time detector in spectrometric mode. The unique properties of the Borexino detector provided an oppurtunity to disentangle pp-neutrino spectrum from the background components. A comparison of the total neutrino flux from the Sun with Solar luminosity in photons provides a test of the stability of the Sun on the 10$^{5}$ years time scale, and sets a strong limit on the power production in the unknown energy sources in the Sun of no more than 4% of the total energy production at 90% C.L.
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The Sun is fueled by a series of nuclear reactions that produce the energy that makes it shine. The primary reaction is the fusion of two protons into a deuteron, a positron and a neutrino. These neutrinos constitute the vast majority of neutrinos reaching Earth, providing us with key information about what goes on at the core of our star. Several experiments have now confirmed the observation of neutrino oscillations by detecting neutrinos from secondary nuclear processes in the Sun; this is the first direct spectral measurement of the neutrinos from the keystone proton-proton fusion. This observation is a crucial step towards the completion of the spectroscopy of pp-chain neutrinos, as well as further validation of the LMA-MSW model of neutrino oscillations.
We report on the measurement of the Central Exclusive Production of charged particle pairs $h^{+}h^{-}$ ($h = pi, K, p$) with the STAR detector at RHIC in proton-proton collisions at $sqrt{s} = 200$ GeV. The charged particle pairs produced in the reaction $ppto p^prime+h^{+}h^{-}+p^prime$ are reconstructed from the tracks in the central detector, while the forward-scattered protons are measured in the Roman Pot system. Differential cross sections are measured in the fiducial region, which roughly corresponds to the square of the four-momentum transfers at the proton vertices in the range $0.04~mbox{GeV}^2 < -t_1 , -t_2 < 0.2~mbox{GeV}^2$, invariant masses of the charged particle pairs up to a few GeV and pseudorapidities of the centrally-produced hadrons in the range $|eta|<0.7$. The measured cross sections are compared to phenomenological predictions based on the Double Pomeron Exchange (DPE) model. Structures observed in the mass spectra of $pi^{+}pi^{-}$ and $K^{+}K^{-}$ pairs are consistent with the DPE model, while angular distributions of pions suggest a dominant spin-0 contribution to $pi^{+}pi^{-}$ production. The fiducial $pi^+pi^-$ cross section is extrapolated to the Lorentz-invariant region, which allows decomposition of the invariant mass spectrum into continuum and resonant contributions. The extrapolated cross section is well described by the continuum production and at least three resonances, the $f_0(980)$, $f_2(1270)$ and $f_0(1500)$, with a possible small contribution from the $f_0(1370)$. Fits to the extrapolated differential cross section as a function of $t_1$ and $t_2$ enable extraction of the exponential slope parameters in several bins of the invariant mass of $pi^+pi^-$ pairs. These parameters are sensitive to the size of the interaction region.
We report a new measurement of electron antineutrino disappearance using the fully-constructed Daya Bay Reactor Neutrino Experiment. The final two of eight antineutrino detectors were installed in the summer of 2012. Including the 404 days of data collected from October 2012 to November 2013 resulted in a total exposure of 6.9$times$10$^5$ GW$_{rm th}$-ton-days, a 3.6 times increase over our previous results. Improvements in energy calibration limited variations between detectors to 0.2%. Removal of six $^{241}$Am-$^{13}$C radioactive calibration sources reduced the background by a factor of two for the detectors in the experimental hall furthest from the reactors. Direct prediction of the antineutrino signal in the far detectors based on the measurements in the near detectors explicitly minimized the dependence of the measurement on models of reactor antineutrino emission. The uncertainties in our estimates of $sin^{2}2theta_{13}$ and $|Delta m^2_{ee}|$ were halved as a result of these improvements. Analysis of the relative antineutrino rates and energy spectra between detectors gave $sin^{2}2theta_{13} = 0.084pm0.005$ and $|Delta m^{2}_{ee}|= (2.42pm0.11) times 10^{-3}$ eV$^2$ in the three-neutrino framework.
This Letter reports a measurement of the flux and energy spectrum of electron antineutrinos from six 2.9~GW$_{th}$ nuclear reactors with six detectors deployed in two near (effective baselines 512~m and 561~m) and one far (1,579~m) underground experimental halls in the Daya Bay experiment. Using 217 days of data, 296,721 and 41,589 inverse beta decay (IBD) candidates were detected in the near and far halls, respectively. The measured IBD yield is (1.55 $pm$ 0.04) $times$ 10$^{-18}$~cm$^2$/GW/day or (5.92 $pm$ 0.14) $times$ 10$^{-43}$~cm$^2$/fission. This flux measurement is consistent with previous short-baseline reactor antineutrino experiments and is $0.946pm0.022$ ($0.991pm0.023$) relative to the flux predicted with the Huber+Mueller (ILL+Vogel) fissile antineutrino model. The measured IBD positron energy spectrum deviates from both spectral predictions by more than 2$sigma$ over the full energy range with a local significance of up to $sim$4$sigma$ between 4-6 MeV. A reactor antineutrino spectrum of IBD reactions is extracted from the measured positron energy spectrum for model-independent predictions.
A new measurement of the reactor antineutrino flux and energy spectrum by the Daya Bay reactor neutrino experiment is reported. The antineutrinos were generated by six 2.9~GW$_{mathrm{th}}$ nuclear reactors and detected by eight antineutrino detectors deployed in two near (560~m and 600~m flux-weighted baselines) and one far (1640~m flux-weighted baseline) underground experimental halls. With 621 days of data, more than 1.2 million inverse beta decay (IBD) candidates were detected. The IBD yield in the eight detectors was measured, and the ratio of measured to predicted flux was found to be $0.946pm0.020$ ($0.992pm0.021$) for the Huber+Mueller (ILL+Vogel) model. A 2.9~$sigma$ deviation was found in the measured IBD positron energy spectrum compared to the predictions. In particular, an excess of events in the region of 4-6~MeV was found in the measured spectrum, with a local significance of 4.4~$sigma$. A reactor antineutrino spectrum weighted by the IBD cross section is extracted for model-independent predictions.
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