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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

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).
  • DIRECT EVIDENCE WAS PRESENTED THIS SUMMER FROM FNAL DONUT EXPERIMENT
  • 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

Spectrometer

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
 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)
properties1
 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

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 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

Superkamiokande

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

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 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 oscillation to sterile or tau neutrino1
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

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

SuperKamiokande

  • excluded regions using combined analysis of low energy and high energy data
  • Sobel n2000 stated ….
n t future speculations supernovae
ntfuture speculations - supernovae

SN1987a

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

OMNIS

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

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
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 neutrino factory neutrinos from muon collider
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

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
conclusions
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
ad