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Tau Neutrino Physics Introduction

This introduction covers the third neutrino, big-bang nucleosynthesis, collider experiments, tau properties, direct mass measurements, oscillation phenomena, mass difference, and evidence for oscillations in atmospheric neutrinos. It discusses experimental bounds, theoretical predictions, and observational results in the field of neutrino physics and astrophysics.

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Tau Neutrino Physics Introduction

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  1. Tau Neutrino PhysicsIntroduction Barry Barish 18 September 2000

  2. nt – the third neutrino

  3. The Number of Neutrinosbig-bang nucleosynthesis D, 3He, 4He and 7Li primordial abundances • abundances range over nine orders of magnitude • Y < 0.25 from number of neutrons when nucleosynthesis began (Y is the 4He fraction) • Yobserved = 0.2380.0020.005 • presence of additional neutrinos would at the time of nucleosynthesis increases the energy density of the Universe and hence the expansion rate, leading to larger Y. • YBBN= 0.012-0.014 N 1.7  N  4.3

  4. The Number of Neutrinoscollider experiments • most precise measurements come from Z e + e • invisible partial width, inv, determined by subtracting measured visible partial widths (Z decays to quarks and charged leptons) from the Z width • invisible width assumed to be due to N • Standard Model value (  l)SM = 1.991  0.001 (using ratio reduces model dependence) N = 2.984 0.008

  5.  propertiesexistence • Existence was indirectly established from decay data combined with reaction data (Feldman 81). • DIRECT EVIDENCE WAS PRESENTED THIS SUMMER FROM FNAL DONUT EXPERIMENT • Observe thet and its decays from nt charged current interactions

  6.  propertiesexistence – DONUT concept • calculated number of interactions = 1100 ( nm, ne, nt) • total protons on target = 3.6 1017 • data taken from April to September 1997

  7.  propertiesexistence – DONUT detectors Spectrometer Emulsion-Vertex Detectors

  8.  propertiesexistence – DONUT detectors • 6.6 106 triggers yield 203 candidate events

  9.  propertiesexistence – DONUT events/background 4 events observed 4.1  1.4 expected 0.41± 0.15 background

  10.  properties J = ½ • J = 3/2 ruled out by establishing that the is not in a pure H  -1 helicity state in  magnetic moment • expect    for Majorana or chiral massless Dirac neutrinos • extending SU(2)xU(1) for massive neutrinos, • where m is in eV and B  eh/2me Bohr magnetons. • using upper bound mt < 18 MeV   < 0.6 10-11mB • Experimental Bound < 5.4 10-7mB from e  e (BEBC)

  11.  properties electric dipole moment < 5.2 10-17 e cm from (Z  ee) at LEP nt charge < 2 10-14 from Luminosity of Red Giants (Raffelt) lifetime > 2.8 1015 sec/eV Astrophysics (Bludman) for mn < 50 eV

  12. ntpropertiesdirect mass measurements • direct bounds come from reconstruction of  multi-hadronic decays • LEP (Aleph) • from 2939 events   2 +  + < 22.3 MeV/c2 • and 52 events   3 + 2 + () +  < 21.5 MeV/c2 • combined limit < 18.2 MeV/c2

  13. nt propertiesdirect mass measurements • method • two body decay • t(Et,pt)  h (Eh,ph) + nt (En,pn) • tau rest frame – hadronic energy • Eh* = (mt2  mh2 +mn2) / 2mt • laboratory frame • Eh =  (Eh* +  ph* cos) • interval bounded for different mn • Ehmax,min = g (Eh*  b ph*) two sample events   3 + 2 + () + 

  14. nt propertiesdirect mass measurements events & contours 0 MeV/c2 and 23 MeV/c2 Log-likelihood fit vs mn

  15. nt propertiesdirect mass measurements + cosmological bounds Unstable nt • bounds on mnt from cosmology • combined with non observation of lepton number violating decay and direct mass limits

  16. nt propertieslepton sector mixing

  17. nt propertiesoscillation probability

  18. nt propertiesoscillation phenomena

  19. n oscillationsallowed regions

  20. n oscillationsatmospheric neutrinos Path length from ~20km to 12700 km

  21. atmospheric neutrinosratio of nm events to ne events • ratio-of-ratios (reduces systematics): • R = (nm/ne)obs / (nm/ne)pred hint #1 ratio lower than expected

  22. atmospheric neutrinosangular distributions Hint #2 anisotropy up/down and distortion of the angular distribution of the up-going events Superkamiokande

  23. atmospheric neutrinosangular distributions with n oscillations

  24. atmospheric neutrinosenergy dependence - n oscillations Hint #3 anomalies have been found in a consistent way for all energies Detectors can detect internal of external events produced in the rock below the detector – 100 MeV to 1 TeV

  25. nt propertiesmass difference – neutrino oscillations SuperKamiokande

  26. atmospheric neutrinoshigh energy events – upward muons MACRO Detector

  27. atmospheric neutrinosMACRO event types MACRO at Gran Sasso • Detector mass ~ 5.3 kton • Event Rate: • up throughgoing m • (ToF) ~160 /y • (2) internal upgoing m • (ToF) ~ 50/y • (3) internal downgoing m • (no ToF) ~ 35/y • (4) upgoing stopping m • (no ToF) ~ 35/y

  28. atmospheric neutrinosMACRO high energy events MACRO results

  29. atmospheric neutrinosMACRO evidence for oscillations Probabilities of nm nt oscillations (for maximal mixing) • the peak probability from the angular distribution agrees with the peak probability from the total number of events • probability for no-oscillation: ~ 0.4 %

  30. atmospheric neutrinosagreement between measurements and experiments

  31. atmospheric neutrinososcillation to sterile or tau neutrino?? SuperKamiokande

  32. atmospheric neutrinososcillation to sterile or tau neutrino?? MACRO • ratio (Lipari- Lusignoli, Phys Rev D57 1998) can be statistically more powerful than a c2 test: • 1) the ratio is sensitive to the sign of the deviation • 2) there is gain in statistical significance • disadvantage: the structure in the angular distribution of data can be lost. • nm nt oscillation favoured with large mixing angle:m2 ~ 2.5x10-3 eV2 • sterile n disfavoured at ~ 2 slevel test of oscillations the ratio vertical / horizontal

  33. atmospheric neutrinososcillation to sterile or tau neutrino?? SuperKamiokande • excluded regions using combined analysis of low energy and high energy data • Sobel n2000 stated ….

  34. ntfuture speculations - supernovae SN1987a What can be learned about the nt from the next supernovae ….??

  35. ntfuture speculations - supernovae • direct eV scale measurements of m(nm) and m(nt) from Supernovae neutrinos • early black hole formation in collapse will truncate neutrino production giving a sharp cutoff • allows sensitivity to m(ne) ~1.8 eV for SN at 10 kpc in Superkamiokande detector • (Beacom et al hep-ph/0006015) Events in SK Low: 0 < E < 11.3 MeV mid: 11.3 < E < 30 MeV High: 30 < E < 

  36. ntfuture speculations - supernovae • rate in OMNIS, a proposed supernovae detector • tail: 6.1 eV  2.3 events OMNIS delayed counts vs mass nt

  37. ntthe ultra high energy neutrino universe OWL - Airwatch GZK cutoff – neutrinos ??

  38. ntthe ultra high energy neutrino universe OSCILLATIONS  FLUXES OF nt AND nm ARE EQUAL • neutrinos from interactions of ultrahigh energy cosmic rays with 3 K cosmic backgrond radiation • neutrinos from AGNs, GRBs, etc • Zbursts – relic neutrinos from big bang cosmology

  39. ntthe ultra high energy neutrino universe

  40. ntfuture speculations – cosmicnt’s • high energy n’s E > 106 GeV • neutrinos from proton acceleration in the cores of active galactic nuclei • vacuum flavor neutrino oscillationsenhance nt / nm ratio • detectable in under water / under ice detectors • (Athar et al hep-ph/0006123)

  41. ntfuture speculations – cosmicnt’s • ntidentified by characteristic double shower events • charged currect interaction + tau decay into hadrons and nt • second shower has typically twice as much energy as first • “double bang”

  42. ntfuture speculations – cosmicnt’s • shower size vs shower separation • identified events will clearly result from vacuum neutrino oscillations, since without enhancement expect nt / nm < 10-5 • nt events can be identified in under water/ice detectors

  43. Acceleratorslong baselinenm– nt oscillations MINOS K2K CERN  GS

  44. Acceleratorslong baselinenm– nt oscillations nt appearance

  45. Acceleratorsneutrino factory – neutrinos from muon collider muon collider Example 7400 km baseline Fermilab  Gran Sasso “world project” neutrino beams select nm’s or anti nm’s

  46. Acceleratorsneutrino factory – neutrinos from muon collider • accurately determine n mixing matrix • perhaps even measure CP violation in n sector

  47. Conclusions • direct observation of the tau neutrino by DONUT is an important milestone • properties of tau neutrino like other neutrinos ne, nm, nt • neutrino oscillations open up a variety of new future possibilities for nt in cosmology, astrophysics and future accelerators

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