an experimental overview of neutrino physics - University of ...
an experimental overview of neutrino physics - University of ...
an experimental overview of neutrino physics - University of ...
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AN EXPERIMENTAL OVERVIEWOF NEUTRINO PHYSICSKate Scholberg, Duke <strong>University</strong>TASI 2008, Boulder, CO
Alexei Smirnov, Neutrino 2008, Christchurch NZ
These lectures:experimentHow do we know what we know?What's within reach for the future?
OUTLINELecture 1: Oscillation experiments ILecture 2: Oscillation experiments IILecture 3: Nonoscillation experiments
Lecture 1Overview <strong>of</strong> <strong>neutrino</strong> sources, detectionNeutrino mass <strong>an</strong>d oscillationsCurrent status <strong>of</strong> oscillation <strong>physics</strong>, part I:Atmospheric parameter spaceSuperK atmospheric <strong>neutrino</strong>sK2K beamMINOS beamCNGS beam
NEUTRINOS~3 ~1200 174,000 MeV/c 2QuarksuctdsbLeptons~6 ~100 ~4200 MeV/c 20.511 105.6 1778 MeV/c 2eµτν ν νe µ τ●Spin 1/2●Zero charge●3 flavors (families)●Interact only via weak interaction●Tiny mass (< 1 eV)In the St<strong>an</strong>dardModel <strong>of</strong> particle<strong>physics</strong>, neutralpartners to thecharged leptons
Why Do Neutrinos Matter?They are a piece <strong>of</strong> the puzzle: we must underst<strong>an</strong>d theirproperties if we are to underst<strong>an</strong>d fundamental particles <strong>an</strong>dtheir interactions, as well as gain insight into cosmologyWhat are the masses <strong>an</strong>d mixings? Do <strong>neutrino</strong>s violate CP?What is the absolute mass scale?Are <strong>neutrino</strong>s their own <strong>an</strong>tiparticles? Do <strong>neutrino</strong>s haveproperties pointing the way beyond the SM?What astrophysical information c<strong>an</strong> welearn from <strong>neutrino</strong>s?
The Big B<strong>an</strong>gSources <strong>of</strong> wild <strong>neutrino</strong>sThe Atmosphere(cosmic rays)SupernovaeAGN's, GRB'smeV eV keV MeV GeV TeV PeV EeVRadioactivedecay in theEarthThe SunJ. Becker,arXiv:0810.1557
Sources <strong>of</strong> 'tame' <strong>neutrino</strong>sNuclearreactorsProton acceleratorsBeta beamseV keV MeV GeV TeVArtificialradioactivesourcesStoppedpionsourcesMuonstorageringsUsually (but not always) better understood
Neutrino Interactions with MatterCharged Current (CC) Neutral Current (NC)d ud dW +ν ll Z 0ν l+ N → l ± + N'Produces leptonwith flavor correspondingto <strong>neutrino</strong> flavor(must have enough energyto make lepton)ν xν xFlavorblindDetect energy loss <strong>of</strong> final state charged particle
Neutrino detectors: in general w<strong>an</strong>t to knowCC or NC?What flavor?What energy?Features that matter energy resolution<strong>an</strong>d threshold flavor/mode tagging statistics (lots <strong>of</strong> target massor <strong>neutrino</strong>s or both) low background: typicallyunderground to hide fromcosmic rays
AssumeNeutrino Mass <strong>an</strong>d OscillationsHow c<strong>an</strong> we learn about <strong>neutrino</strong> mass?FLAVOR STATES| ν f>weaklyinteractingaresuperpositions<strong>of</strong>MASS STATES| ν m>N| f>=∑i=1U fi| i>unitary mixing matrixIf mixing matrix isnot diagonal,get flavor oscillationsas <strong>neutrino</strong>s propagate(essentially, interference between mass states)
Simple twoflavor case| f>= cos| 1>sin| 2>| g>=−sin| 1>cos| 2>Propagate a dist<strong>an</strong>ce L:| i( t )>=e −iE t i| i( 0 )>~e −im 2 L/2pi|i ( 0 )>Probability <strong>of</strong> detecting flavor g at L:P( f g)=sin 2 2sin 2 1.27m2 LEE in GeVL in km∆m 2 in eV 2Parameters <strong>of</strong> nature to measure: θ, ∆m 2 =m 12m 22
P( f g)=sin 2 2sin 2 1.27 m2 LE∆m 2 =m 12m 22If flavor oscillations are observed,then there must be at least onenonzero mass state* Note: oscillation depends on mass differences,not absolute masses
Probability<strong>of</strong> ch<strong>an</strong>gingflavorP( f f)P ( f g)=sin 2 2sin 2 1.27 m2 LEWavelength=πE/(1.27∆m 2 )P( f g)Amplitude∝ sin 2 2θDist<strong>an</strong>ce traveled∆m 2 , sin 2 2θ are the parameters <strong>of</strong> nature;L, E depend on the <strong>experimental</strong> setup
The Experimental Game●Start with some <strong>neutrino</strong>s (natural or artificial)●Measure (or calculate) flavor composition<strong>an</strong>d energy spectrum●Let them propagate●Measure flavor <strong>an</strong>d energies againHave the flavors <strong>an</strong>d energies ch<strong>an</strong>ged?If so, does thech<strong>an</strong>ge followP ( f g)=sin 2 2sin 2 1.27 m2 LDisappear<strong>an</strong>ce: ν's oscillate into 'invisible' flavore.g. ν e→ ν µat ~MeV energiesAppear<strong>an</strong>ce: directly see new flavore.g. ν µ→ ν τat ~GeV energiesE?
Experimental statisticsOscillationParameterSpaceTwiddleL/EFrequency∝ ∆m 2 L/Efastwiggle2 P ( f g)=sin 2 2sin 1.27 Lm2 Eallowed regionslowwiggleAmplitude∝ sin 2 2θ
More generally, for 3 flavors: e e1U e2U e3 1 U 1U 2U 3 2 U =U 1U 2U 3 3MakiNakagawaSakata (MNS)matrixP( f g)= fg−4∑ji±2∑ji2 Re(U fiU giU * fjU * gj)sin 1.27m 2ijEIm(U fiU giU * fjU * gj)sin 2.54 m 2ijEFrequently, c<strong>an</strong> use 2flavor approximatione.g. if ∆m ij 2 >> ∆m jk2LLNote:3 flavors ⇒ 2 independent ∆m ij2
The Three SignalsSOLAR NEUTRINOS e xElectron <strong>neutrino</strong>s from the Sun aredisappearingDist<strong>an</strong>ce ~ 10 8 km, Energy ~ 0.115 MeVATMOSPHERIC NEUTRINOS xMuon <strong>neutrino</strong>s created in cosmic ray showersare disappearing on their way through the EarthDist<strong>an</strong>ce ~ 1013000 km, Energy ~ 0.1100 GeVACCELERATOR NEUTRINOSElectron <strong>an</strong>ti<strong>neutrino</strong>s appearing in a beam<strong>of</strong> muon <strong>an</strong>ti<strong>neutrino</strong>s at LSNDDist<strong>an</strong>ce ~ 30 m, Energy ~ 3050 MeV e
The Three Signals in Parameter SpaceLSND eAtmosphericν's xSolar(<strong>an</strong>dreactor)ν's e x(Note: c<strong>an</strong> have only 2 independent ∆m 2 , for 3 <strong>neutrino</strong>s)
First, zoom in to atmospheric ν parameter space x
Atmospheric Neutrinoscosmic ray (p)E~ 0.1100 GeVL~1013000 kmπ + µ + e +ν µν µν eAbsolute flux knownto ~15%, but flavor ratioknown to ~5%By geometry, expect flux withupdown symmetry above ~1 GeV(no geomagnetic effects)
Detecting Neutrinos with Cherenkov LightCharged particles produced in <strong>neutrino</strong>interactions emit Cherenkov radiation if β>1/nThresholds (MeV)mE th=e 0.731−1/n 2 1/2µ 150π 200p 1350Angle: cos C= 1θ C= 42 0No. <strong>of</strong> photons ∝ energy lossnfor relativisticparticle in water
Water Cherenkov ν DetectorsPhotons → photoelectrons→ amplified PMT pulses→ digitize charge, time→ reconstruct energy,direction, vertex
SuperKamiok<strong>an</strong>deOuterdetector:1889outwardlookingPMTsWater Cherenkov detectorin Mozumi, Jap<strong>an</strong>32 kton <strong>of</strong>ultrapure waterInner detector:11,146inwardlookingPMTs1 km underground to keep away from cosmic rays
Event display <strong>of</strong> ahigh energy <strong>neutrino</strong>interaction in SK("snapshot <strong>of</strong> a ν")
SuperK Accident November 12, 20012/3 <strong>of</strong> PMTsdestroyedin chain reactionimplosion
Now haveacrylic/fiberglassshellsfor shockprotectionBack online in 2003 with 47% <strong>of</strong> ID PMTs, full OD (SK II)Full reconstruction over winter '05'06 (SK III)Electronics/DAQ/<strong>of</strong>fline upgrade this year (SK IV)
SuperK Full Reconstruction Photo Gallery
Atmospheric ν's Experimental Strategy:High energy interactions <strong>of</strong> ν's with nucleonsd uW +ν l l ν e+ n → e − + pν e+ p → e + + nν µ+ n → µ − + pν µ+ p → µ + + nTag neutrin<strong>of</strong>lavorby flavor <strong>of</strong>outgoingleptonν l+ N → l ± + N'CC quasielastic ("single ring"): cle<strong>an</strong>est sample
Get differentpatternsin Cherenkovlight fore <strong>an</strong>d µ(sim. for otherdetector types)From Cherenkov cone get <strong>an</strong>gle, infer pathlength
Deficit interpreted as twoflavor oscillationSK I+II, preliminaryDisappear<strong>an</strong>ceconsistentwith ν µ→ν τ
Getting more from the data set:parent ν energies for subsamplesFullycontainedsingle ring multi ringelikeµlikePartiallycontainedUpwardgoing muonsstopping throughgoing
SK I+II <strong>an</strong>alysis:Excellent fit tooscillation hypothesis!
What flavors are involved in thisν µ→ ν xdisappear<strong>an</strong>ce?Expect about 80 τ's in sample;hard to distinguish from multiπ events●Pure ν µ→ ν e?No upgoingelike excesselikeupgoingdowngoing
What flavors are involved in thisν µ→ ν xdisappear<strong>an</strong>ce?Expect about 80 τ's in sample;hard to distinguish from multiπ events●NOT pure ν µ→ ν e: no upgoing elike excess(some admixture in 3flavor scenario allowed)●Could it be ν µ→ ν sterile?
For ν µ→ ν sterilewould expect:Upgoing NC deficit:●ν τ's have NC interactions●ν sterile's "really" disappearAngular distortion at high energy (>~ 5 GeV):qν τZ 0qν τvs.qν sqν s"mattereffects"in theEarthaffectoscillationprobability
SuperK data: select NC multiring<strong>an</strong>d highenergy eventsSK I dataSK, PRL 85(2000) 39994003ν µ→ ν τν µ→ ν sterilemultiringPCupmuNC events:no upgoingHigh energy events:(partially contained<strong>an</strong>d upgoing muons)deficit no <strong>an</strong>gular distortionCurrent preliminary SK I+II ν µ→ ν sterileexclusion: 7.3
What flavors are involved in thisν µ→ ν xdisappear<strong>an</strong>ce?Expect about 80 τ's in sample;hard to distinguish from multiπ events●NOT pure ν µ→ ν e: no upgoing elike excess(some admixture in 3flavor scenario allowed)●NOT pure ν → µν sterile: would expect* upgoing NC deficit* <strong>an</strong>gular distortion <strong>of</strong> high E events} notseen
What flavors are involved in thisν µ→ ν xdisappear<strong>an</strong>ce?Expect about 80 τ's in SK I sample;hard to distinguish from multiπ events●NOT pure ν µ→ ν e: no upgoing elike excess(some admixture in 3flavor scenario allowed)●NOT pure ν → µν sterile: would expect* upgoing NC deficit} not* <strong>an</strong>gular distortion <strong>of</strong> high E events seen●C<strong>an</strong> we check ν µ→ ν τdirectly ?
Tau Appear<strong>an</strong>cein SuperKTypical MC τ event Energy Threshold:3.5 GeVe or or hadronsHadronsExpect about 80 τ'sin SK I sample... but they arehard to distinguishfrom other multiringν interaction events
Select τlike events: (energy, shape, rings, decay electrons)2 <strong>an</strong>alyses (likelihood <strong>an</strong>d neural network)yield consistent <strong>an</strong>swersSK, PRL 97(2006) 171801MC expectation:78.4±27 τ'sNeural Network(39% efficiency)From fit toτlike sample:(shaded)16.0134±48 stat ± 27.2τ'sConsistent with (expected) slight excess <strong>of</strong> upgoing τ's
What flavors are involved in thisν µ→ ν xdisappear<strong>an</strong>ce?Expect about 80 τ's in sample;hard to distinguish from multiπ events●NOT pure ν µ→ ν e: no upgoing elike excess(some admixture in 3flavor scenario allowed)●NOT pure ν → µν sterile: would expect* upgoing NC excess* <strong>an</strong>gular distortion <strong>of</strong> high E events●CONSISTENT WITH ν µ→ ν τ:~2.4σ excess <strong>of</strong> upgoing "τlike" events} notseen
Resolving the "wiggle" with SK atm ν'sP( f g)=sin 2 2sin 2 1.27m2 LEFC/PC eventsPoor resolution in L/E (~10's <strong>of</strong> %) washes it out⇒ hard to distinguish oscillationfrom exotic kinds <strong>of</strong> disappear<strong>an</strong>ce
Select events for which resolution in L/E is good: (
Similar plot with this selected subset:Decoherence ruled out at 5.0Decay ruled out at 4.1"the dip"Seems tobe reallywiggling!
Improves ∆m 2 resolution a littleOscillation fit w/highresolution L/E data sampleSt<strong>an</strong>dard <strong>an</strong>alysis
Next: INDEPENDENT TEST <strong>of</strong>atmospheric <strong>neutrino</strong> oscillationsusing a wellunderstood ν beamE ν~ GeV, L~ 100's <strong>of</strong> km for same L/E2LP( f g)=sin 2 2sin 1.27m2 ELONG BASELINE EXPERIMENTSCompare flux, flavor <strong>an</strong>denergy spectrum atnear <strong>an</strong>d far detectors
K2K (KEK to Kamioka)Long BaselineExperiment~ 1 GeV muon <strong>neutrino</strong>s12 GeV protons on Al target+ π focusing horn+ decay pipe for pionsEvents matched w/GPS
The Neutrino Beamline at KEK
The Near Detector (300 m away)(scibar)Characterize the ν beam for extrapolation to SK
Results from K2K: full data sampleSingleringµlikeeventsTotal 112beam eventsobserved;expect 158±9Suppression observed,spectral distortionconsistent withoscillations2 P ( f g)=sin 2 2sin 1.27 Lm2 E
K2K Allowed Oscillation ParametersConsistentwith SKatmosphericν's !SK INooscillationexcluded at>4σ
Current state<strong>of</strong> the art forlong baselinedisappear<strong>an</strong>ceoscillation:MINOS(Main InjectorNeutrino OscillationSearch)Fermilab to Minnesota,735 km baselinemuon <strong>neutrino</strong> beam
NuMI Beamline at FermilabH. Gallagher, Nu200893% muon <strong>neutrino</strong>in low energy mode
MINOS Detectors:near <strong>an</strong>d fariron plates+ pl<strong>an</strong>es <strong>of</strong>scintillating fibersw/ magnetic fieldMagnetic fieldallows <strong>neutrino</strong> vs<strong>an</strong>ti<strong>neutrino</strong> selectionν µ+ n → µ − + pν µ+ p → µ + + n
Event flavors selected based on topology
Results <strong>of</strong> MINOS muon <strong>neutrino</strong> disappear<strong>an</strong>ce <strong>an</strong>alysisH. Gallagher, Nu2008SpectraldistortionobservedP( f g)=sin 2 2 sin 2 1.27 m2 LE
Allowed oscillation parameters from MINOSTightestresolutionin m 2
CNGS: CERN Neutrinos to Gr<strong>an</strong> Sasso~20 GeV ν µbeam, 732 km baseline
The CNGS beamlineDesignedto searchfor appear<strong>an</strong>ceneed highenergy beam tomakethemG. Rosa, Nu2008
Detectors at LNGS are optimizedfor τ appear<strong>an</strong>cefinegrain imaging detectors tos earch explicitly for τ decaysOPERA, ICARUS
OPERAlead/emulsion s<strong>an</strong>dwich +active scintillator strip pl<strong>an</strong>es +magnetic spectrometerExtract bricks forsc<strong>an</strong>ning ifelectronic detectorindicates τlike event1.35 kton target mass(~90% complete)
First long dist<strong>an</strong>ce data in 2007G. Rosa, Nu200838 intarget(nontau)events
Expectations for 5 years <strong>of</strong> OPERA runningG. Rosa, Nu2008totalexpectedsignal in targettotalexpectedbackground
ICARUSLiquid Argon Time ProjectionChamberElectronic finegrain imaging"Digital BubbleChamber"Drift ionizationcharge: space collection<strong>of</strong> charge givesx,y coordinate drift time givesz coordinate
600 ton detector at LNGS awaiting fill
Summary <strong>of</strong> atmospheric ν parameter space SuperK has cle<strong>an</strong>,high statistics atmospheric disappear<strong>an</strong>ce signal;good evidence it's K2K confirmed the oscillationhypothesis with disappear<strong>an</strong>ce<strong>of</strong> beam <strong>neutrino</strong>s MINOS now has highestprecision m 2 measurement Soon: CNGS experimentsto explicitly see appear<strong>an</strong>ce
Lecture 2Current status <strong>of</strong> oscillation <strong>physics</strong>, part II:Solar <strong>neutrino</strong> experimentsReactor <strong>neutrino</strong> experimentsShort baseline experimentsWhat's next for oscillation <strong>physics</strong>Long baseline experimentsReactor experiments