Tau Neutrino PhysicsIntroduction

Barry Barish

18 September 2000

– the third neutrino

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 = 0.2380.0020.005

• 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 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)

SM

l

l

invN

N = 2.984 0.008

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 the and its decays from charged current interactions

propertiesexistence – DONUT concept

•calculated number of interactions = 1100 ( , e , )

• total protons on target = 3.6 1017

• data taken from April to September 1997

propertiesexistence – DONUT detectors

Spectrometer

Emulsion-Vertex Detectors

propertiesexistence – DONUT detectors

• 6.6 106 triggers yield 203 candidate events

propertiesexistence – DONUT events/background

4 events observed4.1 1.4 expected0.41± 0.15 background

properties

• expect for Majorana or chiral massless Dirac neutrinos

• extending SU(2)xU(1) for massive neutrinos,B Fm m eG 19 2

10 20 . 3 2 8/ 3

where m is in eV and B eh/2me Bohr magnetons.

• using upper bound meV < 0.6 10-11

• Experimental Bound < 5.4 10-7 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

< 5.2 10-17 e cm from (Z ee) at LEP

charge

< 2 10-14 from Luminosity of Red Giants (Raffelt)

lifetime

electric dipole moment

> 2.8 1015 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/c2 and 52 events 3 + 2 + () + < 21.5 MeV/c2

combined limit < 18.2 MeV/c2

propertiesdirect mass measurements

• method

two body decayph Ehphp

tau rest frame – hadronic energyh

mmh

2 +m2) / 2m

laboratory frameEh = (Eh

* + ph* cos)

interval bounded for different m

Ehmax,min = (Eh

* ph*)

two sample events 3 + 2 + () +

propertiesdirect mass measurements

events & contours 0 MeV/c2 and 23 MeV/c2

Log-likelihood fit vs m

propertiesdirect mass measurements + cosmological bounds

• bounds on m from cosmology

• combined with non observation of lepton number violating decay and direct mass limits

Unstable

propertieslepton sector mixing

propertiesoscillation probability

propertiesoscillation phenomena

oscillationsallowed regions

oscillationsatmospheric neutrinos

Path length from ~20km to 12700 km

atmospheric neutrinosratio of events to e events

ratio-of-ratios (reduces systematics): • R = (e)obs / (e)pred

hint #1 ratio lower than expected

atmospheric neutrinosangular distributions

Superkamiokande

Hint #2 anisotropy up/down and distortion

of the angular distribution of the up-going events

atmospheric neutrinosangular distributions with oscillations

atmospheric neutrinosenergy 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

propertiesmass difference – neutrino oscillations

SuperKamiokande

atmospheric neutrinoshigh energy events – upward muons

MACRO Detector

atmospheric neutrinosMACRO 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 neutrinosMACRO high energy events

MACRO results

atmospheric neutrinosMACRO 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 neutrinosagreement between measurements and experiments

atmospheric neutrinososcillation to sterile or tau neutrino??

SuperKamiokande

atmospheric neutrinososcillation to sterile or tau neutrino??

test of oscillations the ratio vertical / horizontal

• ratio (Lipari- Lusignoli, Phys Rev D57 1998) 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:m2 ~ 2.5x10-3 eV2

sterile disfavoured at ~ 2 level

MACRO

atmospheric neutrinososcillation 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/0006015)

Events in SKLow: 0 < E < 11.3 MeVmid: 11.3 < E < 30 MeVHigh: 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• Zbursts – 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 > 106 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/0006123)

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 / < 10-5

• events can be identified in under water/ice detectors

Acceleratorslong baseline – oscillations

K2K

MINOS

CERN GS

Acceleratorslong baseline – oscillations

appearance

Acceleratorsneutrino factory – neutrinos from muon collider

muon collider

neutrino beamsselect’s or anti ’s

Example7400 km baseline

Fermilab Gran Sasso“world project”

Acceleratorsneutrino 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