Neutrino oscillation experiments at accelerators and reactors

ELSEVIER

Nuclear Physics B (Proc. Suppl.) 81 (2000) 143-152

PROCEEDINGS SUPPLEMENTS www.elsevler.n]/locate/npe

Neutrino oscillation experiments at accelerators and reactors J. Brunner a aCentre de Physique des Particules de Marseille, 163, Avenue de Luminy, Case 907, 13288 Marseille Cedex 09 A whole generation of neutrino experiments at artificial neutrino sources has recently finished data taking. CHORUS and NOMAD took their last data in 1997 and 1998 respectively. LSND and Choos stopped running in 1998 and Palo Verde will switch off in 1999. Only Karmen will continue to take data until 2001. Final or preliminary results of all these experiments will be reviewed. Two future short baseline accelerator projects - Boone and I216 - will be presented which address the verification of the LSND result. The Kandand project - a very long baseline reactor experiment - will be described as well.

1. u~ a p p e a r a n c e

search

1.1. N e u t r i n o b e a m The experiments described below used the neutrino facility of the C E R N SPS. It supplied 450 GeV protons with a cycle of 14.4 s. Per double extraction, 2 × 10 x8 protons were directed on a Be target. A two-stage magnetic focus system followed the target to enhance the flux of positive mesons in the decay pipe. The detectors were located a b o u t 900 meters downstream of the proton target. The mean flight length for neutnnos was a b o u t 600 meters taken from the middle of the decay pipe. The relative abundance of the neutrino fiavours in the b e a m and the mean neutrino energies are summarised in table 1.

Table 1 Mean energy and composition of the neutrino b e a m at the CERN-SPS wide-band v facility mean Energy relative rate v~ 26.9 GeV 100% P~ 21.7 GeV S.6% ve 4'/'.9 GeV 0.7% Pe 35.3 GeV 0.2% 3 • 10 - e 43.0 OeV

The small fraction of vT can be understood

from the following arguments: The v~ can only be produced by heavy mesons, containing the charm or b o t t o m quark, but the production cross section for these particles is much smaller than for kaons and pions. The heavy mesons which could produce vr are too short-lived to reach the b e a m focusing. Therefore the v~ component of the beam has typically a much largerdivergence, which further reduces the flux at the detector location. The branching ratio of the decay of these particles into vX is small. The combination of such a small ~,~ contamination in the beam and an average v~, energy well above the kinematic threshold for chargedcurrent vT interactions (3.5 GeV) opens the unique possibility to search for v~, - vr oscillations in appearance mode with very high sensitivity towards small mixing angles. The accessible p a r a m e t e r range is sin 2 20 > 10 -4 A m 2 > 1 eV ~.

(I)

Two experiments have been performed on the C E R N SPS neutrino beam to search for ~,~ interactions in the v~, b e a m : CHORUS and NOMAD. 1.2. N O M A D The lay-out of the NOMAD [1] detector is shown in figure 1. The target volume consists of 45 drift chambers with a total mass of 2.7 tons. These drift chambers achieve a position resolution of~y : 200/~m and ~rffi = 2ram and a m o m e n t u m

0920-5632/00/$ - see front matter © 2000 ElsevierScience B.V. All rights reserved. PIl S0920-5632(99)00869-5

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J.. Brunner/Nuclear Physics B (Proc. Suppl.) 81 (2000) 143-152

resolution of 3.5% for p < 10 GeV. Each chamber is equivalent to 0.02 radiation length which minimizes photon conversion close to the interaction vertex. This is important to distinguish electrons from photon conversion and electrons from the neutrino vertex. The drift chambers are followed by 5 modules of a transition radiation detector (TRD) to separate electrons from hadrons. The electron identification by the T R D is based on the difference of energy deposited in the straw tubes by particles of different Lorenz factors ( E l m ) . The TRD provides a 103 pion rejection factor and 90% electron identification efficiency for isolated tracks below 50 GeV. After the T R D there is a preshower detector followed by a calorimeter for energy measurement of electro-magnetic showers. All the above mentioned detector parts are located inside a dipole magnet which supplies a field of 0.4 Tesla perpendicular to the beam axis. The NOMAD detector is completed by trigger planes, muon chambers and front and back calorimeters which are the only components outside the magnet coils.

recorded on tape. Oscillation limits have been derived from the analysis of the 940,000 events taken in the first three years [1]. The analysis of the 1998 data is in progress. T-decay searches in several exclusive channels have been performed: channel r - --. e-Peur v - --~ h - ( n l r ° ) u r r - --*p-l/r r - - - * 7r 7r lr+(nlr°)u~

Data taking with detector started in in September 1998. 106 charged-current

the completely assembled August 1995 and finished During this period 1.3 x v~ interactions have been

ezpec~ed 6.8 5.1 5.0 6.9

(2)

For every channel a set of kinematic selection criteria has been established. Angular cuts in the transverse plane with respect to the beam direction have been used and lepton identification criteria for the electron decay channel. For the hadronic decay channels additionally the transverse mass, composed of missing m o m e n t u m and m o m e n t u m of the leading negative particle(s), and an isolation criteria for the leading hadrons with respect to the residual hadronic jet play an important role. Behind the reaction channels in Eq. 2 the number of observed events aRer all cuts and the expected number of background events are indicated. In total 21 candidate events have been observed where 24.1 :l:3.3 background events had been expected. For neutrino oscillations with maximal mixing and large A m 2 8370 r events would have been seen[l]. The non-observation of excess events can be transformed into an exclusion of u~ - Pr oscillations: sin220 > 1.2. I0 -s

Figure 1. Elevation view of the NOMAD detector.

observed 5 6 5 5

for

A m 2 --* oo

(3)

Recently [2] preliminary results based on the analysis of the full data sample have been presented. No tau candidate events above background have been found. The sensitivity could be extended down to sin2 20 > 8.4.10 -4 for large Am ~. The full excluded area is indicated in figure 8. This result can bc considered as almost final as only marginal improvements are expected from further analyses. Based on the powerful electron identification, limits for the channel u~ - Pe have been derived as well [3]. The event sample of u~ charged current events has a contamination of only 3% from

J. Brunner/Nuclear Physics B (Proc. Suppl.) 81 (2000) 143-152

145

short life time of the r lepton. Nuclear emulsion supplies a three-dimensional resolution of 1 tzm and it integrates the properties of an active detector and a heavy target which is best suited for neutrino experiments. The disadvantage of the long procedure of the emulsion analysis after exposure has been overcome by using fully automatic scanning. In the CHORUS experiment an emulsion target of 800 kg is used.

re oo

0

1 !BNL7 7 6 ~ ~ , ~

~HULSIOH T ~ G E T S AND FmRE TRACKERS

HIGH R~JOLUTION

lo~o-4

io=3

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sin22~

Figure 2. Excluded region due to the NOMAD v~, - ~e study compared with other results. The shaded area indicates the preferred region of the LSND antineutrino result.

muonless events with an early photon conversion resembling a primary electron track. The ~,~ contamination in the beam is 0.7% (see table 1) which would be modified by about 10% if ~ u - v ~ oscillations occurred on the 10 -8 level. The main problem is the correct estimation of the ~e contamination in the beam. Two methods have been tried: The direct simulation of the beam line using dedicated simulation packages and the measurement of the beam composition using the detected vj,, Pl,, P~ events in the detector. Both methods yield comparable results. No excess of ~e events could be observed, which leads to the following limit on ~ , - r e oscillations: sin s 28 > 2 . 1 0

-3

for

Am ~ ---, oo

(4)

with 90% C.L.. This excludes the LSND results [4] for A m 2 > 100 e V ~ as indicated in figure 2. Unfortunately NOMAD cannot test lower A m ~ values due to an average t'e energy of 48 GeV and a neutrino flight path of less than 1 kin. 1.3. C H O R U S The concept of the CHORUS experiment is based on the detection of the 7" decay vertex. This requires a high tracking resolution due to the

i:i!: Figure 3. Elevation view of the CHORUS detector.

Scintillating fibre trackers give precise tracking close to the emulsion target and define the entry point of the tracks in the emulsion with a spatial resolution of 200 # m and an angular resolution of 3 m r a d . A hexagonal air-core magnet determines the momenta of hadronic tracks. All above mentioned parts of the detector are contained in a cool-box (5°C) which supplies a stable environment to slow down fading of the emulsion and aging of the fibres. The tracker region is followed by a high-resolution calorimeter, built from scintillation fibres embedded in lead, for energy measurement of hadronic and electro-magnetic showers. It provides an energy resolution of 13%/v/-E for electrons and 3 0 % / v / E for hadrons. A muon spectrometer determines charge and m o m e n t a of muons. The detector is completed by several veto and trigger hodoseope planes. A view of the detector is shown in figure 3. A detailed description of the detector and its performance can be found in [5].

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J. Brunner /Nuclear Physics B (Proc. Suppl.) 81 (2000) 143-152

CHORUS took data from May 1994 until November 1997. After 2 years of exposure the emulsion target had been replaced by a fresh target of the same weight. About 840,000 charged current ~,~ interactions in the emulsion were recorded during the 4-years running time. The current analysis concentrates on the muonic and single-prong hadronic r decay modes: r - ---, IJ-P~,~'~. r - ~ h-(n~°)~,~-

B r = 17.4% B r : 49.8%

(5)

For the muon decay channel, 66% of the data have been analysed. Events with a vertex reconstructed in the emulsion target and an identified muon with p~, < 30 GeV have been selected for scanning leading to about 125,000 located interaction vertices in the emulsion [6] The muon tracks in these events have been followed into the emulsion using fully automatic scanning which allows the validation of a given track at a given position (±100pm) within 1 second. The condition for a r decay signal is the observation of a kink with a transverse momentum ("daughter" track with respect to "parent" track) of at least 250 MeV with a maximal distance of 4 mm from the primary vertex. Main background source is the muonic decay of a D - meson which can be produced in antineutrino charged current reaction with an unidentified primary lepton (/~+, e+). For the presently analysed data sample less than 0.1 background events are expected. No r-candidate events have been found. Acceptances and kink-finding efficiency have been calculated using Monte Carlo methods. The kink finding efficiency has been verified by analysing semi-leptonic charm decays resulting in events with/~-/~+ pairs. This event sample is relatively small and has been scanned parallel to the oscillation analysis. So far 25 semi-leptonic oneprong charm decays have been found where 24 ± 4 had been expected. For the hadronic decay sample muon-less events have been selected with a negative hadron of 1 GeV < p < 20 GeV. Only the data from 1994-1995 have been used so far in the oscillation analysis. They represent about 20% of the total data sample. After following the selected hadron track into the emulsion target 7500 vertices could

be located. The condition for a r decay signal is similar to the analysis of the muonic events, however the maximal distance between primary and decay vertex is restricted to 2.5 mm. This is due to the larger background from "white" hadronic interactions, where no recoil or nuclear breakup is visible. For the present sample 0.5 such events are expected. No r-candidate events have been found. The combination of both analyses allows to exclude v l, - u ~ oscillations for sin z28 > 8.0.10 -4

for

A m 2 --, oo

(6)

The corresponding exclusion area is given in figure 8. Extrapolating the present result to the analysis of the full data sample assuming an increased efficiency by a factor 1.7 as well as the inclusion of the hadronic decay channel r - --* h - h - h + (nlr°)L,r a sensitivity of sin 2 2 8 > 2 . 1 0 -4 Am ~ > 0.4 eV 2

for for

Am ~--,oo sin: 20 -- 1

(7)

can be reached as indicated in figure 9. The present analysis can be easily applied to ve - ~,~. One has to replace the v~-spectrum by the re-spectrum and fold it with the energy dependent acceptances. This leads to an exclusion of ve - v~ oscillations for sin ~ 20 > 0.06 at large A m : as indicated in figure 8. 1.4. F u t u r e p r o j e c t s The negative results of CHORUS and NOMAD as well as the increasing evidence of SuperKamiokande for t,~ - ~ oscillations disfavour ~r appearance searches with Am 2 > 1 e V : . Therefore all such projects (TOSCA, COSMOS) have been cancelled. 2. Pe a p p e a r a n c e s e a r c h 2.1. N e u t r i n o s f r o m P i o n d e c a y a t r e s t Sending pulses of protons with momentum 800 MeV onto a massive target will mainly produce pions (apart from nuclear break up). These pions are stopped inside the target. The lr- are captured by nuclei. Only a fraction o f 10 -4 of the produced lr- decay before they are captured.

J Brunner/Nuclear Physics B (Proc. Suppl.) 81 (2000) 143-152

In contrast, the a"+ decay at rest. The muons which are produced come to rest and decay on a different time scale defined by their lifetime. ~r+ --+ ~+ -k u~ #+ --+ e+ + ue + P~

7" : 26 n s r - - 2.2 ~zs

(8)

Using this production mechanism one gets a neutrino flux pattern which is completely defined by the two- and three-body decay kinematics of the pion and muon decay as it is shown in figure 4. An oscillation search can be performed in appear4

~)

7 / z+ . e+v¢~

N I

I-'/e / I" /~//t///s

1

//1"1

0 0

10

I 20

....

30

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50

V - Energy (MeV)

Figure 4. Neutrino flux pattern from pion decay at rest.

ance mode for the channel ~, ~ ~e because no ~e are produced in the above described scheme. The only source of~e is lr- decay in flight (followed by a ~ - decay) which is suppressed by several orders of magnitude. The detection principle is quite similar to the detection of reactor p~. One uses the inverse beta decay as given in Eq. 9. The positron is measured, followed by a space and time correlated neutron capture reaction. The photons released in the neutron capture process are measured. Different materials can be used for the neutron capture. The main difference with respect to reactor neutrino detection is the higher energy of the neutrinos from muon decay. The signal is a positron of about 30 to 50 MeV energy which corresponds to the main part of the P~, spectrum which would signal P~, - ~,~ oscillations (see figure 4).

147

2.2. L S N D The experiment LSND [4] consisted of a 167 t mineral oil tank viewed by 1220 photomultipliers. A small amount of scintillator had been added to the oil which allows to see scintillator fight as well as Cerenkov fight. This allows particle identification, especially the distinction between neutrons and electrons. LSND has been operated at the LAMPF facility (800 MeV protons) from 1993 until 1998. During this time an integrated charge of 28,700 C could be accumulated. The target configuration of the beam dump had been changed in 1996, which led to a more complete absorption of the pions reducing therefore the signals from decay in flight. The oscillation signature of Pe consists of a positron signal with an energy between 20 and 60 MeV (an alternative analysis uses a lower threshold of 36 MeV) followed by a correlated neutron capture signal of 2.2 MeV. The correlation is tested by a Likelihood function which takes into account time, space and energy information. Before and after the neutrino trigger a veto time is requested to avoid signals correlated with cosmic ray activity. The background contribution which is not correlated to the neutrino beam could be directly measured during beam-off periods. 70 candidate events have been measured with an expected beam-off background of 17.7 i 1.0 events and 12.8 4- 1.7 background events related to the neutrino beam. This leaves an excess of 39.5 -6 8.8 events [7]. The positron energy distribution for the two running period is shown in figure 5. In both periods a clear access of events is visible. The more recent data show a higher excess at lower energies which favours low A m 2 when fitted with oscillation hypotheses. Interpreting the excess as oscillation signal gives an oscillation probability of P : (3.14-0.9 40.5)" 10 -3. An analysis of the 2 run periods (9395 and 96-98) independently supplies consistent values for P. The favoured region (90% C.L.) for the oscillation parameters based on the analysis of the 93-98 data is shown in figure 8.

148

J. Brunner /Nuclear Physics B (Proc. Suppl.) 81 (2000) 143-152 ~to s ~' 6 2 o o ~-2

'1 positron energy

to

8

96-97 data

4 c~

2

E o Q

~-2

positron er, ergy (MeV) Figure 5. The energy distribution of the LSND beam-off subtracted Pe signal events (data points) compared with the estimated neutrino background (dashed line) and the expected distribution for neutrino oscillations at the best-fit points for ( A m ~, ,in~20) (fun line) [4,7].

2.B. K A R M E N Karmen is a 56 ton segmented liquid scintillator detector at the ISIS facility at Rutherford lab. The segmentation of the detector allows a better energy and spatial resolution than LSND, but the absence of Cerenkov light disables particle identification. The segment walls contain Gd-paper to enhance the neutron capture. A detailed comparison of the properties and performances of the LSND and Karmen detectors can be found in [8]. Karmen-I took data from 1991 until 1995. Cosmic ray induced background events caused serious problems for the oscillation analysis. In 1996 a veto shielding has been installed around the detector which reduces the cosmic ray related background by more than a factor 50. In February 1997 Karmen-II started data taking and until February 1999 4670 Coulombs have been accumulated [9]. The selection of delayed coincidences between a positron signal and a neutron capture is similar to LSND. A positron energy range of 16-50 MeV has been accepted and the delayed

event should occur within 300 ps and 80 cm from the primary event. There should be no activity in the veto shield. The total expected background rate has been 7.8 + 0.7 events and 8 candidate events have been observed. This allows to exclude for large A m 2 neutrino oscillation transition probabilities of P > 1.05 • 10 -3 with 90% C.L. as shown in figure 8. This excludes savely the LSND favoured region of oscillation parameters for Am 2 > lOeV 2 but it cannot cover completely the region A m ~ < l e V 2. The higher sensitivity for small A m 2 for LSND is due to its longer neutrino flight lengths (LSND 30m, Karmen 17m) and due to the enhancement of the event excess in lower energy bins (see figure 5). Karmen will continue data taking until 2001 and its final sensitivity will be P ,-~ 7.10 -4 in case of non-observation of excess events (see figure 9). However the low A m 2 region of the LSND signal will remain partly uncovered by Karmen. 2.4. F u t u r e p r o j e c t s The LSND oscillation signal calls for new independent checks. The sensitivity of a new experiment should be at least a factor ten better than the assumed LSND signal to allow a robust decision whether the signal is real or not. It is desirable to design the new experiment for a different energy regime and with a different detection signature. Two such experiments have been proposed: 1-216 [10] The aim of the experiment is to test ve - v~ oscillations for Am 2 < 3eV 2, which covers the full band of the LSND favoured region which cannot be excluded by Karmen. The experiment will reuse the neutrino beamline at the CERN-PS. The average neutrino energy would be 1.5 GeV and 2.5.102° protons could be delivered in 2 years. The ue contamination of the v~, beam is about 0.3%. Two detectors are planned with distances of 130 m and 885 m from the neutrino target. This helps to eliminate uncertainties in the beam composition. The detectors are modular with total fiducial masses of 128 t and 256 t. To ensure a good elec-

J. Brunner /Nuclear Physics B (Proc. Suppl.) 81 (2000) 143-152 tron identification and ~-°/e separation detector modules should have a sampling of 10-20% radiation length. No final decision on the detector material has been made, plastic and liquid scintillator are under discussion. After two years of data taking 130,000 1.,t, charged current interactions are expected in the far detector. About 300 ~,e events will be recorded. If the LSND claim is correct this number should double to 600 and the difference of the ratios between v~, and v~ events at the two detector locations would deviate by 10 standard deviation from zero, because the oscillations affect just N t , / N , for the far detector but not for the near detector. The sensitivity curve after two years of data taking is indicated in figure 9. The collaboration plans to submit a full proposal in 1999. If the experiment is approved construction can start in 2000 and data taking in 2002. B o o n e [II] This experiment will use the 8 GeV booster of the Fermilab. A neutrino energy range between 0.1 and 1 GeV will be explored for the experiment. As a first step (MiniBoone) there will be one detector at a distance of 500 m from the beam dump. The detector will be an unsegmented 445 t liquid scintillator tank viewed by about 1000 photomultipliers very similar to the LSND design. The beam composition can be varied by changing the free decay path of the pions after the proton beam dump between 25 and 50 m. Within one year of data taking 1,000,000 vg charged current interactions and 1700 v~ events are expected. Additionally 1000 r,~ events would be seen in case of oscillations. The sensitivity for neutrino oscillations after one year of data taking is shown in figure 9. The first step of the experiments (MiniBoone) has been approved and the experiments is under construction. Data taking will start late in 2001. If the LSND signal can be confirmed by MiniBoone a second detector will be constructed at 1 km distance from the neutrino source. The aim of the two detector experiment Boone would then

149

be to determine precisely the oscillation parameters. 3. R e a c t o r n e u t r i n o s

Nuclear reactors are an intense source of PcRecall that the discovery of neutrinos was performed at a nuclear reactor [12]. The source of neutrinos are beta-decays related to the fission of heavy nuclei (mainly 23sU, 2~gPu). Nuclear reactors produce exclusively 0,, related to the net reaction n ~ p + e - + P~. For nuclear fusion, as in the core of the Sun, the opposite reaction takes place leading to a flux of exclusively v~. A precise flux monitoring can be achieved by performing a determination of the thermal output of the reactor, a neutron flux measurement at the reactor and reference measurements of the neutrino flux. A group working on the reactor at Rovno [13] has published an uncertainty for the total neutrino rate of 2.8%. The produced neutrinos have an energy of less than 8 MeV. The inverse beta decay is used to detect them: Oe+p---,n+e +

E ~ > 1.8MeV.

(9)

The scintillation light of the positron or its annihilation photons is detected, followed by a signal from the neutron capture. For the neutron capture Gd is used. Due to the low neutrino energy, reactor neutrino oscillation searches are pure disappearance experiments. The results could be interpreted equally well as Oe ~ tg~, or tge ---, ~ oscillations. The sensitivity for the mixing angle is limited to values sin 2 2t~ > 0.1 due to the limited knowledge of the neutrino flux, whereas the sensitivity for Am ~ varies considerably according to the experimental setup. 3.1. C h o o z The detector is located at a distance of 1 km of a nuclear power station in a mine with a rock overburden of 300 m water-equivalent. This reduces cosmic ray related background to about 1 event per day. The detector is a homogeneous liquid scintillator tank of 5 t as shown in figure 6. At full reactor power 25 events per day have

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Physics B (Proc. Suppl.) 81 (2000) 143-152

Data taking started in 1998. Preliminary results from 3 months of data taking have been presented [17]. 237 events had been accumulated which is compatible with the Monte Carlo expectation as well as with the Chooz result. For 1999 further runs are planned. About 2000 events should be accumulated at the end of the experiment .

l

Data

o Background -

Figure 6. The Chooz detector

Expected

[14].

been recorded. Data have been taken from April 1997 until July 1998. Results of the first 4 months of data taking can be found here [14]. 1320 neutrino events had been recorded during this peThe positron energy spectrum of these riod. data together with Monte Carlo expectation is shown in figure 7. The measured spectrum follows the expected curve. Also the absolute rate is within expectation. This allows to exclude ye - fiZ for sin228 > 0.18 at large Am2 and Am2 > 9. 10-4eV2 for maximal mixing. Recently final results from the full running period have been published [15]. The amount of data has been almost doubled and the sensitivity for oscillations has been significantly increased. Without any deviation from the expected number of neutrino events oscillations can now be excluded for sin228 > 0.1 at large Am2 and Am” > 7 - 10b4eV2 for maximal mixing as indicated in figure 8. 3.2. Palo Verde The detector has a distance of 750 m from a nuclear power plant and has a shielding of 25 m water equivalent. Contrary to Chooz the detector is segmented. The segmentation is used to define signals as four-fold coincidences which reduces the cosmic ray background considerably [16].

.s d

0

2

I... OO

2

4

6

8

4

6

a

MeSO

2 1.75

Figure 7. The positron energy spectrum after 4 months of data taking [14].

Medo

of Chooz

3.3. Future projects The sensitivity in sin’2t3 in oscillation searches at reactors is limited to about 0.1 due to the systematic uncertainties about the neutrino flux. Also the energy spectrum cannot be varied. The only open parameter is therefore L - the distance between source and detector. Naturally new reactor projects aim for larger distances to increase the sensitivity towards lower Am’.

J Brunner/Nuclear Physics B (Proc. Suppl.) 81 (2000) 143-152 Kamland [18] is under construction at the former Kamiokande location. The central detector is a 1,200 m s scintillator balloon, viewed by 1,280 photomultipliers. The fiducial mass will be about 600 t. 7 nuclear power plants are distributed around the detector at distances between 80 and 250 kin. 450 events per year are expected with a background of about 30 events. The expected sensitivity after one year of data taking is shown in figure 9. Kamland will be the first experiment operating at an artificial neutrino source which will test the parameter space interesting for the solar neutrino puzzle. It will cover the complete parameter region o.f the large-mixing-angle solution of the MSW oscillation. Kamland has been approved in 1996 and is under construction. Data taking will start in 2001. 4. C o n c l u s i o n CHORUS, NOMAD Chooz and PaloVerde found no evidence for neutrino oscillations after analysing a large fraction of their data. This is consistent with the SuperKamiokande result, which indicates •t, - ~ oscillation. LSND confirms the oscillation hypothesis on the basis of its last two years of data taking whereas Karmen continues to get negative results. However Karmen will not be able the check the entire LSND region. Two new experiments have been proposed the check LSND. MiniBoone is under construction and 1-216 is at the proposal stage. Kamland, a new reactor neutrino experiment, will test solar neutrino oscillations from 2001 on. REFERENCES 1. P. Astier et al. NOMAD coll., Phys. Lett. B453 (1999) 169. 2. P. Astier et al. NOMAD coll., Proc. of EPS-HEP'P9 (Tampere, 1999). 3. E. Pennacchio et al. NOMAD coll., Nucl. Phys. Proc. Suppl. 65 (1998) 177. 4. C. Athanassopoulos et aL, LSND coll., Phys. Rev. C54 (1996) 2685. 5. E. Eskut et al., CHORUS coll., Nucl. Instr. Meth. A401 (1997) 7.

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6. P. Zucchelli et al., CHORUS coll., hep-ex/9907015. 7. M. Mezzetto, Proc. to 8th International Workshop on Neutrino Telescopes (Venice, 1999); http://axpd24.pd.infn.it/conference/indexof-proceed ings.html. 8. S.Y. Yellin, hep-ex/9902012. 9. M. Steidl et at., KARMEN coll., Proc. to Les Rencontres de Physique de la Vallee Aoste (La Thuile, 1999); http://wwwikl.fzk.de/www/karmen/karmen_e.html. 10. N. Armenise et al., I216 coll., CERN-SPSC-97-21. 11. E. Church et al., Boone coll., FERMILAB-P-0898. 12. F.Reines and C.L.Cowan, Phys. Rev. 92 (1953) 830. 13. A.A.Kuvshinnikov et al., Rovno coll., Yad. FIS. 52 (1990) 300. 14. M. Apollonio et al., Chooz coll. Phys. Left. B420 (1998) 397. 15. M. Apollonio et al., Chooz coll., hep-ex/9907037. 16. F. Boehm et at., Palo Verde coll., Prog. Part. Nucl. Phys. 40 (1998) 253; 17. http://citnp.caltech.edu/PV/PaloVerde.html. 18. A. Suzuki et at., Kamland coll., Proc. to 8~h International Workshop on Neutrino Telescopes (Venice, 1999); http: / /www.awa.tohoku.ac.jp / h t m l / K a m LAND/presentation/index.html.

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Figure 8. Comparison of results from oscillation searches for all three channels. The shaded areas are positive results as reported from LSND, SuperKamiokande and solar neutrino experiments. All other experiments obtain negative results and exclude the regions to the right of their sensitivity borders. No distinction has been made between v and ~. 10 3

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or near future experiments. Shaded areas: existing negative final results of running experiments; dashed lines: proposed which have been discussed in this paper, sensitivities of var(Minos, NGS, K2K) which are described elsewhere in these