New limit on the strength of mixing betweenνμandνe

Abstract

Measurements have been made of the reactions yen +e p and v, n +p-p in a detector located an effective distance of 96 m from a neutrino source. These measurements yield directly the energydependent ratio of the neutrino fluxes [@( E(v, ) )/@( E ( v,) )labs incident on the detector. When combined with an estimate of the flux ratio emanating from the source [ e( E( ve )/@( E(v,) )Icalc, the measured ratio provides an upper limit on the strength of mixing between v, and v,. We obtain sin22a <3.4X (90% C.L.) in the limit of large mass difference ~m~ ( = m 1 2 -m 2 2 / ) between neutrino mass eigenstates, m and m 2 ; and an upper limit on the product Am sin2a < 0.43 ev2 in the limit of small mass difference.If the masses of neutrinos are nondegenerate, and if separate lepton number is not exactly conserved, neutrinos of a given flavor will oscillate into neutrinos of another flavor.' In this paper we report measurements of events from the reactions ven -+e -p and v,n +p-p induced in a neutrino detector by wide-band neutrino fluxes @( E ( v, ) ) and @( E (v, ) ), respectively. The measurements yield directly the flux ratio incident on the detector. After subtraction of the estimated flux ratio [@(E(ve ))/@(E(Y,))],,,, initially present in the beam, no evidence for the oscillation v,+v, is present. The data exclude a significant region of the Am2-sin22a space,'where Am2 = 1 m 12-m22 1 in ev2, m and m2 are neutrino mass eigenstates, and sln22a is the strength of mixing between Y, and Y,. The neutrino detector consists of 112 planes of liquid scintillator (each plane 4 m~4 m in area x 8 cm thick)and 224 planes of proportional drift cells (4.2 mX4.2 m in area X 3.8 cm thick) uniformally interspersed. The fine segmentation (1792 scintillator cells and 12096 proportional drift cells) and the pulse-height and timing characteristics of the elements provide determination of event topology, identification of electromagnetic showers, and substantial discrimination through dE/dx measurements between electrons and photons as well as pions and protons. Immediately downstream of the detector is a 30-ton shower counter of area 4 m X 4 m with 12 radiation lengths to provide additional containment of showers from events occurring at the downstream end of the detector. Further downstream is a magnet of aperture 1.8 m X 1.8 mX0.46 m for study of the ~e r~-l o w -~~ region of the v,-induced quasielastic reaction and measurement of the antineutrino contamination present in the incident neutrino beam.

Pseudo-Dirac neutrinos as a potential complete solution to the neutrino oscillation puzzle

“…The LSND result [3] is interpreted as direct ν µ − ν e oscillations. The large ∆m 2 region (∆m 2 > 10 eV 2 ) is excluded by NOMAD [17], CCFR [18], BNL 734 [19], and BNL E766 [20]. The latter constrains also the island around ∆m 2 ∼ 6 eV 2 advocated by Caldwell [21].…”

Neutrino mass problem: the state of the art

“…Another record-breaking result for the size of the studied forbidden range of values of Dm 2 (0,5 ± 10 3 eV 2 ) and values of sin 2 2y (3 Â 10 À3 ) was obtained at the Brookhaven National Laboratory (BNL), Upton, New York [178]. A remarkable feature of this experiment, in which 1.5-GeV neutrinos were registered at a distance of 100 m, was the detection of the quasi-elastic processes n m n 3 m À p Y n e n 3 e À p Y 93 which made it possible to study the n m to n e flux ratio, i.e.…”

Hierarchical four-neutrino oscillations with a decay option

“…However, there are two ways that this conclusion may be evaded. (1) Let m 2 4 ∼ 25 eV 2 , then the constraint due to the CDHSW experiment is not a factor, but now there are three other accelerator ν µ → ν e experiments: BNL-E734 [10], BNL-E776 [11], and CCFR [12], which have bounds close to but allowed by the LSND 99% likelihood contour. .…”

“…[The most recent result of the ongoing KARMEN II experiment [18] is P µe < 2.1×10 −3 , which will eventually have the sensitivity to test Eq. (10). ]…”