AN EXPERIMENTAL OVERVIEW OF NEUTRINO PHYSICS. Kate Scholberg, Duke University TASI 2008, Boulder, CO

Transcription

1 AN EXPERIMENTAL OVERVIEW OF NEUTRINO PHYSICS Kate Scholberg, Duke University TASI 008, Boulder, CO

2 Alexei Smirnov, Neutrino 008, Christchurch NZ

3 These lectures: experiment How do we know what we know? What's within reach for the future?

4 OUTLINE Lecture 1: Oscillation experiments I Lecture : Oscillation experiments II Lecture 3: Non oscillation experiments

5 Lecture 1 Overview of neutrino sources, detection Neutrino mass and oscillations Current status of oscillation physics, part I: Atmospheric parameter space Super K atmospheric neutrinos KK beam MINOS beam CNGS beam

6 NEUTRINOS ~3 ~ ,000 MeV/c Quarks u d c s t b ~6 ~100 ~400 MeV/c MeV/c Leptons Spin 1/ e νe µ νµ τ ντ In the Standard Model of particle physics, neutral partners to the charged leptons Zero charge 3 flavors (families) Interact only via weak interaction Tiny mass (< 1 ev)

7 Why Do Neutrinos Matter? They are a piece of the puzzle: we must understand their properties if we are to understand fundamental particles and their interactions, as well as gain insight into cosmology What are the masses and mixings? Do neutrinos violate CP? What is the absolute mass scale? Are neutrinos their own antiparticles? Do neutrinos have properties pointing the way beyond the SM? What astrophysical information can we learn from neutrinos?

8 Sources of wild neutrinos The Atmosphere (cosmic rays) The Big Bang Super novae AGN's, GRB's mev ev kev MeV GeV TeV PeV EeV Radioactive decay in the Earth The Sun J. Becker, arxiv:

9 Sources of 'tame' neutrinos Proton accelerators Beta beams Nuclear reactors ev kev MeV GeV TeV Artificial radioactive sources Stopped Muon pion sources storage rings Usually (but not always) better understood

10 Neutrino Interactions with Matter Charged Current (CC) u d Neutral Current (NC) d W+ νl d Z0 l νl + N l± + N' Produces lepton with flavor corresponding to neutrino flavor νx νx Flavor blind (must have enough energy to make lepton) Detect energy loss of final state charged particle

11 Neutrino detectors: in general want to know CC or NC? What flavor? What energy? Features that matter energy resolution and threshold flavor/mode tagging statistics (lots of target mass or neutrinos or both) low background: typically underground to hide from cosmic rays

12 Neutrino Mass and Oscillations How can we learn about neutrino mass? Assume FLAVOR STATES νf > weakly interacting N f >= Ufi i > i=1 unitary mixing matrix are superpositions of MASS STATES νm > If mixing matrix is not diagonal, get flavor oscillations as neutrinos propagate (essentially, interference between mass states)

13 Simple two flavor case f >= cos 1 > sin > g >= sin 1 > cos > Propagate a distance L: iei t i ( t ) >=e i mi L / p i ( 0 ) >~e i ( 0 ) > Probability of detecting flavor g at L: P ( f g )=sin sin 1.7 m L E E in GeV L in km m in ev Parameters of nature to measure: θ, m =m1 m

14 P ( f g )=sin sin 1.7 m L E m =m1 m If flavor oscillations are observed, then there must be at least one non zero mass state * Note: oscillation depends on mass differences, not absolute masses

15 Probability 1.7 m L of changing P ( f g )=sin sin E flavor P ( f f ) Wavelength= πe/(1.7 m) P ( f g ) Amplitude sinθ Distance traveled m, sinθ are the parameters of nature; L, E depend on the experimental setup

16 The Experimental Game Start with some neutrinos (natural or artificial) Measure (or calculate) flavor composition and energy spectrum Let them propagate Measure flavor and energies again Have the flavors and energies changed? If so, does the P ( )=sin sin 1.7 m L f g E change follow? Disappearance: ν's oscillate into 'invisible' flavor e.g. νe νµ at ~MeV energies Appearance: directly see new flavor e.g. νµ ντ at ~GeV energies

17 Oscillation P ( f g )=sin sin Parameter fast wiggle Space Twiddle L/E 1.7 m L E allowed region Frequency ml/e slow wiggle Amplitude sinθ Experimental statistics

18 More generally, for 3 flavors: U e1 U e Ue3 = U 1 U U 3 U U 3 e U 1 Maki Nakagawa Sakata (MNS) matrix m ij L P ( f g )= fg 4 Re( Ufi Ugi U U ) sin E j i * fj * gj.54 m ij L * * ± Im( Ufi Ugi Ufj Ugj )sin E j i Frequently, can use flavor approximation e.g. if mij >> mjk 3 flavors independent m Note: ij

19 The Three Signals SOLAR NEUTRINOS e x Electron neutrinos from the Sun are disappearing Distance ~ 108 km, Energy ~ MeV ATMOSPHERIC NEUTRINOS x Muon neutrinos created in cosmic ray showers are disappearing on their way through the Earth Distance ~ km, Energy ~ GeV ACCELERATOR NEUTRINOS Electron antineutrinos appearing in a beam of muon antineutrinos at LSND Distance ~ 30 m, Energy ~ MeV e

20 The Three Signals in Parameter Space LSND Atmospheric ν's e x Solar (and reactor) ν's e x (Note: can have only independent m, for 3 neutrinos)

21 First, zoom in to atmospheric ν parameter space x

22 Atmospheric Neutrinos cosmic ray (p) π E~ GeV L~ km + µ + νµ e + νµ νe Absolute flux known to ~15%, but flavor ratio known to ~5% By geometry, expect flux with up down symmetry above ~1 GeV (no geomagnetic effects)

23 Detecting Neutrinos with Cherenkov Light Charged particles produced in neutrino interactions emit Cherenkov radiation if β>1/n Thresholds (MeV) E th= m 1 1 /n 1/ e 0.73 µ 150 π 00 p 1350 Angle: cos C= 1 n θc = 40 for relativistic particle in water No. of photons energy loss

24 Water Cherenkov ν Detectors Photons photoelectrons amplified PMT pulses digitize charge, time reconstruct energy, direction, vertex

25 Super Kamiokande Outer detector: 1889 outward looking PMTs Water Cherenkov detector in Mozumi, Japan 3 kton of ultrapure water Inner detector: 11,146 inward looking PMTs 1 km underground to keep away from cosmic rays

26

27 Event display of a high energy neutrino interaction in SK ("snapshot of a ν")

28 Super K Accident November 1, 001 /3 of PMTs destroyed in chain reaction implosion

29 Now have acrylic/ fiberglass shells for shock protection Back online in 003 with 47% of ID PMTs, full OD (SK II) Full reconstruction over winter '05 '06 (SK III) Electronics/DAQ/offline upgrade this year (SK IV)

30 Super K Full Reconstruction Photo Gallery

31 Atmospheric ν's Experimental Strategy: High energy interactions of ν's with nucleons u d νe + n e + p νe + p e + n + W + νl νµ + n µ + p l νµ + p µ+ + n Tag neutrino flavor by flavor of outgoing lepton νl + N l± + N' CC quasi elastic ("single ring"): cleanest sample

32 Get different patterns in Cherenkov light for e and µ (sim. for other detector types) From Cherenkov cone get angle, infer pathlength

33 Zenith angle distribution of 1 ring events 1489 days of SK data (SK I) e like µ like up going down going Deficit of νµ from below (long pathlength)

34 Deficit interpreted as two flavor oscillation SK I+II, preliminary Disappearance consistent with νµ ντ

35 Getting more from the data set: parent ν energies for subsamples Fully contained single ring multi ring e like µ like Partially contained Upward going muons stopping throughgoing

36 SK I+II analysis: Excellent fit to oscillation hypothesis!

37 What flavors are involved in this νµ νx disappearance? Expect about 80 τ's in sample; hard to distinguish from multi π events Pure νµ νe? e like No upgoing e like excess up going down going

38 What flavors are involved in this νµ νx disappearance? Expect about 80 τ's in sample; hard to distinguish from multi π events NOT pure νµ νe: no up going e like excess (some admixture in 3 flavor scenario allowed) Could it be νµ νsterile?

39 For νµ νsterile would expect: Up going NC deficit: ν 's have NC interactions τ νsterile's "really" disappear Angular distortion at high energy (>~ 5 GeV): q q Z ντ q q νs νs vs. 0 ντ "matter effects" in the Earth affect oscillation probability

40 Super K data: select NC multi ring and high energy events SK I data multi ring NC events: no upgoing deficit SK, PRL 85(000) νµ ντ νµ νsterile PC upmu High energy events: (partially contained and upgoing muons) no angular distortion Current preliminary SK I+II νµ νsterile exclusion: 7.3

41 What flavors are involved in this νµ νx disappearance? Expect about 80 τ's in sample; hard to distinguish from multi π events NOT pure νµ νe: no up going e like excess (some admixture in 3 flavor scenario allowed) NOT pure νµ νsterile : would expect not * up going NC deficit seen * angular distortion of high E events }

42 What flavors are involved in this νµ νx disappearance? Expect about 80 τ's in SK I sample; hard to distinguish from multi π events NOT pure νµ νe: no up going e like excess (some admixture in 3 flavor scenario allowed) NOT pure νµ νsterile : would expect * up going NC deficit not * angular distortion of high E events seen Can we check νµ ντ directly? }

43 Tau Appearance in Super K Typical MC τ event Energy Threshold: 3.5 GeV s n o r d a h or or e Hadrons Expect about 80 τ's in SK I sample... but they are hard to distinguish from other multi ring ν interaction events

44 Select τ like events: (energy, shape, rings, decay electrons) analyses (likelihood and neural network) SK, PRL 97(006) yield consistent answers MC expectation: 78.4±7 τ's From fit to τ like sample: (shaded) Neural Network (39% efficiency) 134±48 stat ± τ's Consistent with (expected) slight excess of upgoing τ's

45 What flavors are involved in this νµ νx disappearance? Expect about 80 τ's in sample; hard to distinguish from multi π events NOT pure νµ νe: no up going e like excess (some admixture in 3 flavor scenario allowed) NOT pure νµ νsterile : would expect * up going NC excess not * angular distortion of high E events seen } CONSISTENT WITH νµ ντ : ~.4σ excess of up going "τ like" events

46 Resolving the "wiggle" with SK atm ν's 1.7 m L P ( f g )=sin sin E FC/PC events Poor resolution in L/E (~10's of %) washes it out hard to distinguish oscillation from exotic kinds of disappearance

47 Select events for which resolution in L/E is good: (<70%): exclude horizontal, low E, poorly contained, very high E µ like µ like

48 Similar plot with this selected subset: Decoherence ruled out at 5.0 Decay ruled out at 4.1 "the dip" Seems to be really wiggling!

49 Oscillation fit w/high resolution L/E data sample Standard analysis Improves m resolution a little

50 Next: INDEPENDENT TEST of atmospheric neutrino oscillations using a well understood ν beam Eν~ GeV, L~ 100's of km for same L/E P ( f g )=sin sin 1.7 m L E LONG BASELINE EXPERIMENTS Compare flux, flavor and energy spectrum at near and far detectors

51 KK (KEK to Kamioka) Long Baseline Experiment ~ 1 GeV muon neutrinos 1 GeV protons on Al target + π focusing horn + decay pipe for pions Events matched w/gps

52 The Neutrino Beamline at KEK

53 The Near Detector (300 m away) (scibar) Characterize the ν beam for extrapolation to SK

54 Results from KK: full data sample Total 11 beam events observed; expect 158±9 Single ring µ like events Suppression observed, spectral distortion consistent with oscillations P ( f g )=sin sin 1.7 m L E

55 KK Allowed Oscillation Parameters Consistent with SK atmospheric ν's! SK I No oscillation excluded at >4σ

56 Current state of the art for long baseline disappearance oscillation: MINOS (Main Injector Neutrino Oscillation Search) Fermilab to Minnesota, 735 km baseline muon neutrino beam

57 NuMI Beamline at Fermilab 93% muon neutrino in low energy mode H. Gallagher, Nu008

58 MINOS Detectors: near and far iron plates + planes of scintillating fibers w/ magnetic field Magnetic field allows neutrino vs antineutrino selection νµ + n µ + p νµ + p µ+ + n

59 Event flavors selected based on topology

60 Results of MINOS muon neutrino disappearance analysis H. Gallagher, Nu008 Spectral distortion observed 1.7 m L P ( f g )=sin sin E

61 Allowed oscillation parameters from MINOS Tightest resolution in m

62 CNGS: CERN Neutrinos to Gran Sasso ~0 GeV νµ beam, 73 km baseline

63 The CNGS beamline Designed to search for appearance need high energy beam to make them G. Rosa, Nu008

64 Detectors at LNGS are optimized for τ appearance fine grain imaging detectors to s earch explicitly for τ decays OPERA, ICARUS

65 OPERA lead/emulsion sandwich + active scintillator strip planes + magnetic spectrometer Extract bricks for scanning if electronic detector indicates τ like event 1.35 kton target mass (~90% complete)

66 First long distance data in in target (non tau) events G. Rosa, Nu008

67 Expectations for 5 years of OPERA running G. Rosa, Nu008 total expected signal in target total expected background

68 ICARUS Liquid Argon Time Projection Chamber "Digital Bubble Chamber" Drift ionization charge: space collection of charge gives x,y coordinate drift time gives z coordinate Electronic fine grain imaging

69 600 ton detector at LNGS awaiting fill

70 Summary of atmospheric ν parameter space Super K has clean, high statistics atmospheric disappearance signal; good evidence it's KK confirmed the oscillation hypothesis with disappearance of beam neutrinos MINOS now has highest precision m measurement Soon: CNGS experiments to explicitly see appearance

71 Lecture Current status of oscillation physics, part II: Solar neutrino experiments Reactor neutrino experiments Short baseline experiments What's next for oscillation physics Long baseline experiments Reactor experiments