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Tau Neutrino Physics Introduction. Barry Barish 18 September 2000. n t – 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

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Tau neutrino physics introduction

Tau Neutrino PhysicsIntroduction

Barry Barish

18 September 2000

N t the third neutrino
nt – the third neutrino

The number of neutrinos big bang nucleosynthesis
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

The number of neutrinos collider experiments
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

Properties existence
 propertiesexistence

  • Existence was indirectly established from decay data combined with reaction data (Feldman 81).


  • Observe thet and its decays from nt charged current interactions

Properties existence donut concept
 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

Properties existence donut detectors
 propertiesexistence – DONUT detectors


Emulsion-Vertex Detectors

Properties existence donut detectors1
 propertiesexistence – DONUT detectors

  • 6.6 106 triggers yield 203 candidate events

Properties existence donut events background
 propertiesexistence – DONUT events/background

4 events observed

4.1  1.4 expected

0.41± 0.15 background

 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)

 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)


> 2.8 1015 sec/eV Astrophysics (Bludman) for mn < 50 eV

N t properties direct mass measurements
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

N t properties direct mass measurements1
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 + () + 

N t properties direct mass measurements2
nt propertiesdirect mass measurements

events & contours

0 MeV/c2 and 23 MeV/c2

Log-likelihood fit vs mn

N t properties direct mass measurements cosmological bounds
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

N t properties lepton sector mixing
nt propertieslepton sector mixing

N t properties oscillation probability
nt propertiesoscillation probability

N t properties oscillation phenomena
nt propertiesoscillation phenomena

N oscillations allowed regions
n oscillationsallowed regions

N oscillations atmospheric neutrinos
n oscillationsatmospheric neutrinos

Path length from ~20km to 12700 km

Atmospheric neutrinos ratio of n m events to n e events
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

Atmospheric neutrinos angular distributions
atmospheric neutrinosangular distributions

Hint #2

anisotropy up/down and distortion of the angular distribution of the up-going events


Atmospheric neutrinos angular distributions with n oscillations
atmospheric neutrinosangular distributions with n oscillations

Atmospheric neutrinos energy dependence n oscillations
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

N t properties mass difference neutrino oscillations
nt propertiesmass difference – neutrino oscillations


Atmospheric neutrinos high energy events upward muons
atmospheric neutrinoshigh energy events – upward muons

MACRO Detector

Atmospheric neutrinos macro event types
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

Atmospheric neutrinos macro high energy events
atmospheric neutrinosMACRO high energy events

MACRO results

Atmospheric neutrinos macro evidence for oscillations
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 %

Atmospheric neutrinos agreement between measurements and experiments
atmospheric neutrinosagreement between measurements and experiments

Atmospheric neutrinos oscillation to sterile or tau neutrino
atmospheric neutrinososcillation to sterile or tau neutrino??


Atmospheric neutrinos oscillation to sterile or tau neutrino1
atmospheric neutrinososcillation to sterile or tau neutrino??


  • 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

Atmospheric neutrinos oscillation to sterile or tau neutrino2
atmospheric neutrinososcillation to sterile or tau neutrino??


  • excluded regions using combined analysis of low energy and high energy data

  • Sobel n2000 stated ….

N t future speculations supernovae
ntfuture speculations - supernovae


What can be learned about the nt from the next supernovae ….??

N t future speculations supernovae1
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 < 

N t future speculations supernovae2
ntfuture speculations - supernovae

  • rate in OMNIS, a proposed supernovae detector

  • tail: 6.1 eV  2.3 events


delayed counts vs mass nt

N t the ultra high energy neutrino universe
ntthe ultra high energy neutrino universe

OWL - Airwatch

GZK cutoff – neutrinos ??

N t the ultra high energy neutrino universe1
ntthe 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

N t the ultra high energy neutrino universe2
ntthe ultra high energy neutrino universe

N t future speculations cosmic n t s
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)

N t future speculations cosmic n t s1
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”

N t future speculations cosmic n t s2
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

Accelerators long baseline n m n t oscillations
Acceleratorslong baselinenm– nt oscillations




Accelerators long baseline n m n t oscillations1
Acceleratorslong baselinenm– nt oscillations

nt appearance

Accelerators neutrino factory neutrinos from muon collider
Acceleratorsneutrino factory – neutrinos from muon collider

muon collider


7400 km baseline

Fermilab  Gran Sasso

“world project”

neutrino beams

select nm’s or anti nm’s

Accelerators neutrino factory neutrinos from muon collider1
Acceleratorsneutrino factory – neutrinos from muon collider

  • accurately determine n mixing matrix

  • perhaps even measure CP violation in n sector


  • 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