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for more than 30 years , solar neutrino experiments  @xcite have been observing fewer neutrinos than what are predicted by the detailed models  @xcite of the sun .
this deficit is known as the solar neutrino problem .
a comparison of the predicted and observed solar neutrino fluxes for these experiments are shown in table  [ tbl : solarnuexp ] .
these experiments probe different parts of the solar neutrino energy spectrum , and show an energy dependence in the observed solar neutrino flux .
these observations can be explained if the solar models are incomplete or neutrinos undergo flavor transformation while in transit to the earth .
the sudbury neutrino observatory@xcite was constructed to resolve this solar neutrino puzzle .
it is capable of making simultaneous measurements of the electron - type neutrino ( @xmath1 ) flux from @xmath3b decay in the sun and the flux of all active neutrino flavors through the following reactions : @xmath14 the charged - current ( cc ) reaction on the deuteron is sensitive exclusively to @xmath1 , and the neutral - current ( nc ) reaction has equal sensitivity to all active neutrino flavors ( @xmath15 ; @xmath16 ) .
elastic scattering ( es ) on electron is also sensitive to all active flavors , but with reduced sensitivity to @xmath17  and @xmath18 .    because of its equal sensitivity to all active neutrinos , the neutral - current measurement can determine the total neutrino flux , hence resolving the solar neutrino problem , _ even if neutrinos oscillate_@xcite .
sno is currently the only experiment that can simultaneously observe the _ disappearance _ of @xmath1  and the _ appearance _ of another active species .
this is illustrated in figure  [ fig : smoking_gun ] .
another feature of the neutral - current interaction is its low kinematic threshold . by efficiently counting the free neutrons in the final state of the neutral - current reaction
, the total active @xmath2b neutrino flux can be inferred for neutrinos with energy above the 2.2-mev kinematic threshold .
recent results  @xcite from the measurements of the solar @xmath3b neutrino flux by the sno detector using the cc , nc and es reactions are presented in this paper .
the results@xcite of a measurement of the day - night asymmetry of the neutrino event rates , which is predicted under certain neutrino oscillation scenarios , are also presented .
finally , the physics implications of these observations will be discussed .
.summary of solar neutrino observations at different solar neutrino detectors .
the measured fluxes at the radiochemical experiments are measured in solar neutrino unit ( snu ) , which is defined as 1 capture per second per 10@xmath19 target atoms .
the kamiokande and super - kamiokande measurements are in units of 10@xmath20  @xmath21  s@xmath22 . [
cols="<,<,<,<",options="header " , ]     [ tbl : dn_chisq ]
the results that are presented in this paper are truly groundbreaking .
the neutral - current measurement is the first direct measurement of the total active @xmath2b neutrino flux .
the neutrino fluxes measured by this channel provide strong evidence for neutrino flavor transformation , thereby solving the long - standing solar neutrino problem .
the significance of @xmath1  transforming into @xmath23 or @xmath24 is at 5.3@xmath25 level .
this neutral - current measurement also verified the standard solar model prediction of the @xmath2b neutrino flux .
the analysis presented in this paper is also the first direct measurement of the day - night asymmetries in the @xmath1  flux and the total neutrino flux .
when combining the day and night energy spectra from sno with results from other solar neutrino experiments in a global 2-@xmath26 flavor analysis of the msw oscillation parameters , the lma solution is strongly favored and the  dark side " ( @xmath271 ) is excluded .    in the coming years
, sno will continue to make significant contributions to solar neutrino physics by refining the neutral - current measurement and the day - night asymmetry with different experimental techniques .
it will also attempt to look for other possible signatures of neutrino oscillation ( e.g. spectral distortion ) and other rare processes ( e.g. nucleon decays , anti-@xmath26 ) in its future physics program .
this research was supported by the natural sciences and engineering research council of canada , industry canada , national research council of canada , northern ontario heritage fund corporation and the province of ontario , the united states department of energy and in the united kingdom by the science and engineering research council and the particle physics and astronomy research council .
further support was provided by inco , ltd . , atomic energy of canada limited ( aecl ) , agra - monenco , canatom , canadian microelectronics corporation , at&t microelectronics , northern telecom and british nuclear fuels , ltd .
the heavy water was loaned by aecl with the cooperation of ontario power generation .
we thank the sno technical staff for their strong contributions .
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the sudbury neutrino observatory ( sno ) is a 1000-tonne heavy water cherenkov detector . 
 its usage of d@xmath0o  as target allows the simultaneous measurements of the @xmath1  flux from @xmath2b decay in the sun and the total flux of all active neutrino species through the charged - current and the neutral - current interactions on the deuterons . assuming the standard @xmath3b shape , the @xmath1  component of the @xmath3b solar neutrino flux is measured to be @xmath4@xmath5 for a kinetic energy threshold of 5  mev . 
 the non-@xmath1component is found to be @xmath6@xmath7 . 
 this @xmath8 difference provides strong evidence for @xmath1 flavor transformation in the solar neutrino sector . 
 the total active neutrino flux is measured with the neutral - current reaction at a neutrino energy threshold of 2.2  mev . 
 this flux is determined to be @xmath9@xmath10 , and is consistent with solar model predictions . 
 assuming an undistorted @xmath2b spectrum , the night minus day rate is 14.0@xmath116.3(stat.)@xmath12(sys.)% of the average rate in the charged - current channel . 
 if the total active neutrino flux is constrained to have no asymmetry , the night - day asymmetry in the @xmath1  flux is found to be 7.0@xmath114.9(stat.)@xmath13(sys.)% . 
 a global analysis of all the available solar neutrino data in terms of matter - enhanced oscillations of two active flavors strongly favors the large mixing angle ( lma ) solution .