Tau Neutrino Physics Introduction Barry Barish 18 September 2000

 – the third neutrino

The Number of Neutrinos big-bang nucleosynthesis D, 3 He, 4 He and 7 Li primordial abundances abundances range over nine orders of magnitude Y < 0.25 from number of neutrons when nucleosynthesis began (Y is the 4 He fraction) Y observed =   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.  Y BBN =  N 1.7  N  4.3

The Number of Neutrinos collider 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 =  (using ratio reduces model dependence) N =  0.008

 properties existence Existence was indirectly established from decay data combined with reaction data (Feldman 81). DIRECT EVIDENCE WAS PRESENTED THIS SUMMER FROM FNAL DONUT EXPERIMENT Observe the  and its decays from  charged current interactions

 properties existence – DONUT concept calculated number of interactions = 1100 (  , e,   ) total protons on target = data taken from April to September 1997

 properties existence – DONUT detectors Spectrometer Emulsion-Vertex Detectors

 properties existence – DONUT detectors triggers yield 203 candidate events

 properties existence – DONUT events/background 4 events observed 4.1  1.4 expected 0.41± 0.15 background

 properties expect    for Majorana or chiral massless Dirac neutrinos extending SU(2)xU(1) for massive neutrinos, where m is in eV and  B  eh/2m e Bohr magnetons. using upper bound m   eV   <   Experimental Bound <   from  e    e  (BEBC) magnetic moment J = ½ J = 3/2 ruled out by establishing that the    is not in a pure H  -1 helicity state in     

 properties < e cm from  (Z  ee) at LEP  charge < from Luminosity of Red Giants (Raffelt) lifetime electric dipole moment > sec/eV Astrophysics (Bludman) for m < 50 eV

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

 properties direct mass measurements method two body decay      p   h   E h  p h     p  tau rest frame – hadronic energy  h   m    m h 2 +m 2 ) / 2m  laboratory frame E h =  (E h * +  p h * cos  ) interval bounded for different m E h max,min =  (E h *   p h * ) two sample events    3   + 2   + (   ) + 

 properties direct mass measurements events & contours 0 MeV/c 2 and 23 MeV/c 2 Log-likelihood fit vs m

 properties direct mass measurements + cosmological bounds bounds on m  from cosmology combined with non observation of lepton number violating decay and direct mass limits Unstable 

 properties lepton sector mixing

 properties oscillation probability

 properties oscillation phenomena

oscillations allowed regions

oscillations atmospheric neutrinos Path length from ~20km to km

atmospheric neutrinos ratio of  events to e events ratio-of-ratios (reduces systematics): R = (   e ) obs / (   e ) pred hint #1 ratio lower than expected

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

atmospheric neutrinos angular distributions with oscillations

atmospheric neutrinos energy dependence - 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

 properties mass difference – neutrino oscillations SuperKamiokande

atmospheric neutrinos high energy events – upward muons MACRO Detector

atmospheric neutrinos MACRO event types Detector mass ~ 5.3 kton Event Rate: (1)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 MACRO at Gran Sasso

atmospheric neutrinos MACRO high energy events MACRO results

atmospheric neutrinos MACRO evidence for oscillations Probabilities of    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 %

atmospheric neutrinos agreement between measurements and experiments

atmospheric neutrinos oscillation to sterile or tau neutrino?? SuperKamiokande

atmospheric neutrinos oscillation to sterile or tau neutrino?? test of oscillations the ratio vertical / horizontal ratio (Lipari- Lusignoli, Phys Rev D ) can be statistically more powerful than a  2 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.     oscillation favoured with large mixing angle:  m 2 ~ 2.5x10 -3 eV 2  sterile disfavoured at ~ 2  level MACRO

atmospheric neutrinos oscillation to sterile or tau neutrino?? excluded regions using combined analysis of low energy and high energy data Sobel 2000 stated …. SuperKamiokande

  future speculations - supernovae SN1987a What can be learned about the  from the next supernovae ….??

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

  future speculations - supernovae  rate in OMNIS, a proposed supernovae detector  tail: 6.1 eV  2.3 events OMNIS delayed counts vs mass 

  the ultra high energy neutrino universe OWL - Airwatch GZK cutoff – neutrinos ??

  the ultra high energy neutrino universe 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 OSCILLATIONS  FLUXES OF  AND  ARE EQUAL

  the ultra high energy neutrino universe

  future speculations – cosmic  ’s high energy ’s E > 10 6 GeV neutrinos from proton acceleration in the cores of active galactic nuclei vacuum flavor neutrino oscillations enhance  /  ratio detectable in under water / under ice detectors (Athar et al hep-ph/ )

  future speculations – cosmic  ’s    identified by characteristic double shower events  charged currect interaction + tau decay into hadrons and   second shower has typically twice as much energy as first  “double bang”

  future speculations – cosmic  ’s shower size vs shower separation identified events will clearly result from vacuum neutrino oscillations, since without enhancement expect  /  <  events can be identified in under water/ice detectors

Accelerators long baseline   –   oscillations K2K MINOS CERN  GS

Accelerators long baseline   –   oscillations  appearance

Accelerators neutrino factory – neutrinos from muon collider muon collider neutrino beams select   ’s or anti  ’s Example 7400 km baseline Fermilab  Gran Sasso “world project”

Accelerators neutrino factory – neutrinos from muon collider accurately determine mixing matrix perhaps even measure CP violation in sector

Conclusions direct observation of the tau neutrino by DONUT is an important milestone properties of tau neutrino like other neutrinos e     neutrino oscillations open up a variety of new future possibilities for  in cosmology, astrophysics and future accelerators