| s the next generation of reactor neutrino experiment,the medium-baseline reactor neutrino experiment is mainly designed to determine the neutrino mass hierarchy(MH)at a 3-4 ? C.L significance with a running-time of 6 years.However,the recent ab initio calculations predict percent-level fine structure in the ve spectrum that has been an issue of concern for efforts to determine the neutrino MH.On the other hand,as the shape uncertainty is over 2%in the current ve spectrum,it is very difficult to achieve the above 3? significance as expected with a running-time of 6 years.In this work,we estimated fine structure and studied its impact on the determination of neutrino MH together with shape uncertainty.Besides the determination of neutrino MH,the medium-baseline reactor neutrino experiment is also being developed to become a state-of-the-art platform to study new physics and search for astrophysical neutrinos with a spread of physics potentials.In this work,we furthermore studied the decoherence effect with the treatment of neutrino as wave-packet and the neutrinos emitted from the potential gravitational-wave sources.Fine structure is an intrinsic deformation in the small-scale of reactor antineutrino spectrum because it is caused by Coulomb effects in beta decay.However,the energy resolutions of current Daya Bay and other reactor neutrino experiments are not sufficient to measure its size.In view of 8%detector energy resolution at Daya Bay,we managed the ve spectrum from ab initio prediction via a "Smearing" effect.As a result,we refined the scale of fine structure from the ratio of the initial spectrum to the "smeared" spectrum and found its size was do at percent-level.Afterwards,we conservatively treated fine structure as the additional shape uncertainty and studied its impact on the determination of neutrino MH via numerical simulations using the measured ve spectrum from Daya B ay as reference.In numerical simulations,the multiple shape uncertainties were adopted as the input values.The result indicated fine structure won't be like shape uncertainty could lead to signficant impact on the determination of neutrino MH.Furthermore,we produced the ve spectra at a near detector similar with JUNO-TAO according to different setups of energy resolutions and applied them as reference spectra,instead of the measured spectrum from Daya B ay.Using these spectra,we first estimated the scale of fine structure and found fine structure would be measured clearer at a near de-tector with a finer energy resolution.Then,we studied what impacts of shape uncertainty and energy resolution(fine structure)on the determination of neutrino MH again via var-ing shape uncertainties in these reference spectra.A consistent conclusion presented that,compared with energy resolution,(systematic)shape uncertainty would lead to more sig-nificant impact on the determination of neutrino MH.In order to improve the identification sensitivity of neutrino MH,it was a worthwhile approch to add an intermediate-baseline detector at medium-baseline reactor neutrino experiment.Combined with the(main)far detector,such an assistant detector would contribute extra sensitivity on the determination of neutrino MH.On one hand,the contributions were different for two shape uncertainties in two correlations.On the other hand,the contributions were dependent on target mass and baseline of intermediate-baseline detector,the optimal baseline was basically located on 5-25 km.With the treatment of neutrino as wave-packet,the standard plane-wave neutrino oscillation will be corrected via a damping signature,leading to two kinds of decoherence effects:one is resulted from the separasion of wave-packets,corresponding to relatively large wave-packet width(initial energy/momentum uncertainty)?wp;the other is due to the delocalization effect,corresponding to extremely small ?wp.In this work,we studied the decoherence effects at medium-baseline reactor neutrino experiment and attained the lower and upper limits on ?wp at 1,2,3 ? confidence level(C.L):1.13×10-16,7.42×10-17,5.58×10-17;0.0086,0.0127,0.0162.At 95%C.L,7.51×10-17<?wp<0.0125,is far better than the current result from Daya Bay(3.37×10-17<?wp<0.283).Afterwards,we changed statistics,shape uncertainties,detector energy resolutions and evaluated their impacts on the constraints to decoherence effects.Moreover,we discussed the impacts of neutrino wave-packet treatment on the precise measurements of neutrino oscillation parameters.In addition,we also evaluated the impact of an extra detector on the measurement of decoherence effect.After gravitational wave(GW)transients were first observed in 2015,searching for the coincident neutrinos had been performed at the current neutrino experiments and telescopes.Particularly,the coincident searches draw more and more attentions after the GW 170817 event was detected,which was the first sign of a production of a binary neutron star(BNS)merger.However,no candidate neutrinos have been found yet.In this work,we analyzed backgrounds at medium-baseline reactor neutrino experiment and examined the detection sensitivity to the ve signals from GW sources.Based on Monte Carlo simulation,we first studied the temporal correlation between two adjacent backgrounds.To monitor the events at detector,we divided the event bundles according to time intervals.Afterwards,we calculated the detection sensitivity to the ve signals from GW sources at 90%C.L,?90=2.44.Refer to the modeling BNS mergers or BH-NS mergers,?90was converted into the fluence upper limits,FUL 90.For monochromatic energy spectrum or normalized Fermi-Dirac energy spectrum assumptions,FUL 90?O(108)cm-2.Correspondingly,the detectable(luminosity)distance was constrained at the magnitude of O(102)kpc for GW sources.The KamLAND result was also presented as a comparison.Moreover,we studied the improvement of sensitivity from an extra detector.The result suggested that an identical(main)far detector or a RENO-50 detector as the extra one would additionally contribute?38% sensitivity and?27% detectable distance. |
PDF Full Text Request