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the baikal neutrino telescope is deployed in lake baikal , siberia , from shore at a depth of .
_ nt-200 _ , the medium - term goal of the collaboration @xcite , was put into operation at april 6th , 1998 and consists of 192 optical modules ( oms ) .
an umbrella - like frame carries 8 strings , each with 24 pairwise arranged oms .
three underwater electrical cables and one optical cable connect the detector with the shore station .
the oms are grouped in pairs along the strings .
they contain 37-cm diameter _
quasar _ - photo multipliers ( pms ) which have been developed specially for our project @xcite .
the two pms of a pair are switched in coincidence in order to suppress background from bioluminescence and pm noise .
a pair defines a _
channel_.    a _ muon - trigger _ is formed by the requirement of ( with _ hit _ referring to a channel ) within .
@xmath0 is typically set to for such events , amplitude and time of all fired channels are digitized and sent to shore . a separate _ monopole trigger _ system searches for clusters of sequential hits in individual channels which are characteristic for the passage of slowly moving , bright objects like gut monopoles .    here
we present preliminary results of analysis of data , which were accumulated in the first 234 live days of _
nt-200 _ as well as results obtained from the analysis of data taken with _
nt-96 _ , the 1996 stage of the detector .
the signature of neutrino induced events is a muon crossing the detector from below .
the reconstruction algorithm is based on the assumption that the light radiated by the muons is emitted under the cherenkov angle with respect to the muon path .
we do nt take into account light scattering because the characteristic distances for atmospheric neutrino induced muons detection do not exceed 1@xmath12 scattering lengths of light in baikal water ( mean scattering angle cosine @xmath20.88)@xcite .
the algorithm uses a single muon model to reconstruct events .
we apply procedure rejecting hits , which are very likely due to dark current or water luminosity as well as hits which are due to showers and have large time delays with respect to expected hit times from the single muon cherenkov light .
determination of the muon trajectory is based on the minimization of a @xmath3 function with respect to measured and calculated times of hit channels . as a result of the @xmath3 minimization we obtain the track parameters ( @xmath4 , @xmath5 and spatial coordinates ) .
the reconstruction yields a fraction of about @xmath6 of events which are reconstructed as upward going with respect to whole event sample fulfilling the trigger condition @xmath7 ( at least 6 hits on at list 3 strings ) .
that is still far from a suppression factor 10@xmath8 necessary for the depth of _
nt-200_. to reject most of the wrongly reconstructed events we use the set of quality criteria .
if the event does nt obey any of chosen criteria , it is rejected as wrongly reconstructed .
different to _ nt-96 _
@xcite , the neutrino selection algorithm for _ nt-200 _ operates with trigger @xmath9 .    for _ nt-200 _ neutrino search , the following cuts are most effective : ( 1 ) a traditional @xmath10 cut ; ( 2 ) the minimum track length in the array ; ( 3 ) the probability of non - fired channels not to be hit and fired channels to be hit ; ( 4 ) the correlation of measured amplitudes to the amplitudes expected for reconstructed track ; ( 5 ) an amplitude @xmath11 defined similar to the time @xmath10 ; ( 6 ) the correlation between measured hit times and vertical distances of channels in array ( see eq.1 below ) .
the efficiency of the procedure and correctness of the mc background estimation have been tested with a sample of @xmath12 mc - generated atmospheric muons and with mc - generated upward going muons due to atmospheric neutrinos .
[ cuttable ]    .
the fraction of events passing cuts for experimental and mc background sample . [ cols="^,^,^ " , ]     from 234 days of effective data taking 32957 events survive cut ( 1 ) .    after applying all cuts ,
ten events were selected as neutrino candidates , compared to 8.9 expected from atmospheric neutrinos .
the zenith angular distribution of these ten neutrino candidates is shown in fig.2 .
regarding the ten detected events as being due to atmospheric neutrinos , one can derive an upper limit on the flux of muons from the center of the earth due to annihilation of neutralinos - the favored candidate for cold dark matter .
the combined numbers of observed and expected background events and the 90% c.l .
muon flux limits for six cones around the nadir obtained with the baikal neutrino telescopes
_ nt-96 _ @xcite and _ nt-200 _ ( 1998 ) are shown in table 2 .    the comparison of baikal flux limits with those obtained by baksan @xcite , macro @xcite , kamiokande @xcite and super - kamiokande @xcite is shown in fig.3 .
fast bare monopoles with unit magnetic dirac charge and velocities greater than the cherenkov threshold in water ( @xmath14 ) are promising survey objects for underwater neutrino telescopes . for a given velocity @xmath15
the monopole cherenkov radiation exceeds that of a relativistic muon by a factor @xmath16 ( @xmath17 - index of refraction for water ) @xcite
. therefore fast monopoles with @xmath18 can be detected up to distances @xmath19 m @xmath1
@xmath20 m corresponding to effective areas of ( 1@xmath13)@xmath21 m@xmath22 .    the natural way to search for fast monopoles is based on the selection of events with high multiplicity of hits and high amplitudes . in order to reduce the background from downward atmospheric muons and especially atmospheric muon bundles we restrict ourself to monopoles coming from the lower hemisphere .    in the present analysis of the first 234 live days data of _ nt-200 _ , the following cuts have been applied to the detected events .
* number of hit channels @xmath23 * the value of space - time correlation + @xmath24 + where @xmath25 and @xmath26 are @xmath27-coordinate and time of hit channels , @xmath28 , @xmath29 , @xmath30 and @xmath31 - their average values and standard deviations .
* at least two of all hit channels have the amplitudes more than 400 ph.el . *
the time differences of hit channels @xmath32 fulfill the following condition : + @xmath33 + where @xmath34 and @xmath35 - range between two hit channels and light velocity in the water , respectively .
there are no events which survive all cuts . using the mc calculated acceptance of _
nt-200 _ , a 90% c.l
upper limit on the monopole flux has been obtained .    the combined upper limit for an isotropic flux of bare fast magnetic monopoles obtained with _ nt-36 _ , _ nt-96 _ @xcite and _ nt-200 _ as well as limits from underground experiments macro , soudan2 , kgf , ohya and amanda @xcite are shown in fig.4 .    [ fig4 ]
in this section we present results of a search for neutrinos with @xmath36tev obtained with _ nt-96 _ @xcite .
the used search strategy for high energy neutrinos relies on the detection of the cherenkov light emitted by the electro - magnetic and ( or ) hadronic particle cascades and high energy muons produced at the neutrino interaction vertex in a large volume around the neutrino telescope .    within the 70 days of effective data taking of _ nt-96
_ , @xmath37 events with @xmath38 have been selected .    for this analysis we used events with @xmath394 hits along at least one of all hit strings .
the time difference between any two channels on the same string was required to obey the condition :    @xmath40    the @xmath41 are the arrival times at channels @xmath42 , and @xmath43 is their vertical distance . @xmath44 ns accounts for the timing error and @xmath45 ns / m .
8608 events survive the selection criterion ( 3 ) .
the highest multiplicity of hit channels ( one event ) is @xmath46 .
since no events with @xmath47 are found in our data we can derive an upper limit on the flux of high energy neutrinos which produce events with multiplicity n@xmath4825 .
the shape of the neutrino spectrum was assumed to behave like @xmath49 as typically expected for fermi acceleration . in this case ,
90% of expected events would be produced by neutrinos from the energy range @xmath50gev . comparing the calculated rates with the upper limit to the number of zero events with @xmath47
, we obtain the following 90% c.l .
upper limit to the diffuse neutrino flux :    @xmath51    [ fig5 ]    fig.5 shows the upper limits on the diffuse high energy neutrino fluxes obtained by baikal ( this work ) , sps - dumand @xcite , amanda - a @xcite , eas - top @xcite and frejus @xcite ( triangle ) as well as a model independent upper limit obtained by v.berezinsky @xcite ( curve labeled b ) ( starting from the energy density of the diffuse x- and gamma - radiation @xmath52 ev @xmath53 as follows from egret data @xcite ) and the atmospheric neutrino fluxes @xcite from horizontal and vertical directions ( upper and lower curves , respectively ) .
also shown are predictions from stecker and salamon model @xcite ( curve labeled ss ) and protheroe model @xcite ( curve labeled p ) for diffuse neutrino fluxes from quasar cores and blazar jets .
we expect that the analysis of data taken with _ nt-200 _ ( 1998 ) would allow us to lower this limit down to ( 2@xmath14)@xmath5410@xmath8@xmath55s@xmath56sr@xmath56gev .
since march 1998 we have performed measurements of eas with a cherenkov array deployed on the ice cover just above _ nt-200 _ @xcite .    in march / april 2000 we continue the experiments with the eas array .
it consists of 4 upward facing _ quasar _ pms placed in special containers .
three of them were located at the corners and one in the center of an equilateral triangle .
the distance between the central and each of the outer detectors was 100 m. the array was operating in 2 modes : a cherenkov light detecting mode and a scintillator mode . for the cherenkov mode conic reflectors
were put on the containers to increase the effective area of pms . for the scintillator mode reflectors
were replaced by 0.25 m@xmath22 scintillator plates .    in the cherenkov mode ,
the eas array operated in coincidence with _
nt-200 _ for studying the angular resolution of the latter .
the energy threshold in this case was about 200 tev .
the preliminary analysis of data collected during 1999 shows that the angular resolution of _
applying any cuts , which usually used to reject badly reconstructed tracks ) is better than 5 degrees .    in the scintillator mode
, the eas array has been used as a trigger system in a search for acoustic signals from eas .
the core of eas triggered the scintillater array is expected to lead to an acoustic signal in the ice and in the upper water layer . with 5 pev energy threshold of the eas - array , 2 - 3 events per hour have been observed .
acoustic hydrophone was placed 90 m apart from the center of the eas array at a depth 5 m .
characteristic bipolar acoustic signals with about 150 @xmath57s duration and with a reasonable delay time compared to the eas trigger have been detected .
a preliminary analysis of the data shows that the amplitudes of the acoustic signals are somewhat larger than it would be expected from standard thermoacoustic theory @xcite .
the source of this disagreement may be a rough calibration of hydrophon .
we plan to continue the investigation of acoustic signals from eas in the next year .
the deep underwater neutrino telescope _ nt-200 _ in lake baikal is taking data since april 1998 . using the first 234 live days ,
35 neutrino induced upward muons have been reconstructed .
although in a good agreement with mc expectation this number is on factor 3 lower then predicted for the fully operational _
nt-200_. the reason is that , due to unstable operation of electronics , in average only 50 - 70 channels have taken data during 1998 .
this is in contrast to 1999 and 2000 data taking where stability had improved .
ten events within a 30 degree half angle cone around nadir have been selected and limits on the excess of muon flux due to wimp annihilation in the center of the earth have been derived .
also a new limit on the flux of fast monopoles has been obtained .    in the following years , _
nt-200 _ will be operated as a neutrino telescope with an effective area between 1000 and 5000 m@xmath22 , depending on the energy .
it will investigate atmospheric neutrino spectra above 10 gev ( about 1 atmospheric neutrino per two - three days ) .
due to the high water transparency and low light scattering with effective scattering length greater than 150m@xmath1200 m , the effective volume of _
nt-200 _ for high energy electron and tau neutrinos detection is more than two orders of magnitude larger than its geometrical volume .
this will permit a search for diffuse neutrino fluxes from agn and other extraterrestrial sources on a level of theoretical predictions .    with an effective area two times larger than super - kamiokande , for nearly vertically upward muons ( e@xmath5810 gev ) _
nt-200 _ will be one of the most powerful arrays for indirect search for wimp annihilation in the center of the earth during the next few years .
it will also be a unique environmental laboratory to study water processes in lake baikal .
apart from its own goals , _
nt-200 _ is regarded to be a prototype for the development a telescope of next generation with an effective area of 50,000 to 100,000 m@xmath22 .
the basic design of such a detector is under discussion at present .
_ this work was supported by the russian ministry of research , the german ministry of education and research and the russian fund of fundamental research ( grants _ , ) _ and by the russian federal program `` integration '' ( project no .
we review the present status of the baikal neutrino project and present preliminary results of a search for upward going atmospheric neutrinos , wimps and magnetic monopoles obtained with the detector _ 
 nt-200 _ during 1998 . 
 also the results of a search for very high energy neutrinos with partially completed detector in 1996 are presented .