watch out, experiments in progress! - Lunds · PDF fileAccording to the Standard Solar Model...

Christina Zacharatou Jarlskog

Neutrino oscillations...

... watch out, experiments in progress!

Is there something new?

• Standard Model neutrinos:

– massless

– spin 1/2

– three flavours ( , , )

– lepton number

• Direct mass measurements:

– tritium beta decay:

– pion decay:

– tau decay:

• Indirect mass measurements:

– oscillation experiments

νe νµ ντ

mνe2.8 eV<

mνµ0.17 MeV<

mντ18.2 MeV<

2 Christina Zacharatou Jarlskog

Mixing and Oscillations

... what do we expect?

... what do we see?

... what does ‘mixing’ mean?

... what does ‘oscillation’ mean?

source detector

source detector

flavour states mass states

νe, νµ, ντ ν1, ν2, ν3

= ν1

= ν2νe

νµ


The two-neutrino case

If the neutrinos have non-zero masses, at ,

we have pure flavour states:

where v1,2 have masses m1,2. α=mixing angle.

• How does that lead to oscillation (=change

of flavour)?

v1,2 evolve in time, so at time :

we can write this as a function of the flavour

states:

The probability for oscillation is:

No oscillation if α=0 or if m1=m2.

t 0=

νe αν1cos ανsin 2+=

νµ ανsin 1– ανcos 2+=

t 0≠

νe t( ) αeiE1t–

cos ν1 αeiE2t–

ν2sin+=

νe t( ) A t( )νe B t( )νµ+=

P νe νµ→( ) B t( )22αsin( )2

E2 E1–( ) t2---sin

2= =


Solar neutrinos

According to the Standard Solar Model (SSM),

the energy of the Sun comes from fusion:

• pp, Be and B neutrinos:

4p α 2e+

2νe+ +→

p p+ d e+ νe (1)+ +→

d p+ He γ+3→

He4

He3

+ Be7 γ+→

Be7

e-

+ Li7 νe (2)+→

Be7

p+ B8 γ+→

(3) B8

Be8

e+ νe+ +→

Li7

p+ 2α→

Be8

2α→


• hep neutrinos:

• also pep neutrinos from:

• Experiments that measured the νe flux:

– chlorine in target: Homestake

– gallium in target: SAGE, GALLEX

– water in target: Kamiokande,

Super-Kamiokande

He3

p+ α e+ νe (4)+ +→

p e-

p+ + d νe (5)+→

2

2

1

3

4

5


Homestake

The tank contains about 615 tons of C2Cl4.

Under neutrino interaction, 37Cl becomes 37Ar

( ), which is radioactive with a

half-life of 35 days. 37Ar is isolated and its

radioactivity is measured. The number of 37Ar

atoms detected gives the number of neutrino

interactions in the chlorine tank, thus the solar

neutrino flux. Result for the flux:

νe n+ p e-

+→

observed:Rν 2.55 0.17 0.18± SNU±=

expected:Rν 7.3 2.3 SNU±=


GALLEX

The detector is a container with 12.2 tons of

watered 71Ga, which, after an interaction with a

solar neutrino, becomes 71Ge (half-life of 11.43

days.) The 71Ge atoms are counted and the flux

is calculated.

GALLEX: Rν 79 10 6± SNU±=

SAGE: Rν 69 11 9± SNU±=

expected:Rν 132 9 SNU±=


Super-Kamiokande

• inner detector (ID): 32000 tons

• outer detector (OD): 18000 tons

• 1200 m of rock overburden

• 11460 PMTs (50 cm diameter) in ID

• 1885 PMTs (25 cm diameter) in OD


Super-Kamiokande

• observed reaction: (elastic

scattering in water)

• detection method: the recoiling electron

produces Cherenkov light, which is seen by

the PMTs.

νe e-

+ νe e-

+→

θcos1

ηβ-------, β v

c-- η, 1.33= = =

pointentrance

PMT

hitno hit

42


Super-K: solar neutrinos

• B neutrinos:

• recoiling electron energies above 5.5 MeV

1. B neutrino flux is calculated (1996-1999 data):

2. Recoil electron energy spectrum:

Indication for vacuum oscillations but modeldependent. Maybe there are matter effects (MSW)?

3. Day-night and seasonal variation of flux: model

independent but need few more years of data taking.

B8

Be8

e+ νe+ +→

dataSSM----------- 0.471 0.008 0.013±±=

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

5 7.5 10 12.5 15

Energy(MeV)

Dat

a/S

SM

BP

98 SK SLE 419day + LE 708day 22.5kt ALL

5.5-20MeV (Preliminary)

LESLE

stat. error

stat.2+syst.2

sin22θ=0.87

∆m2=m22-m1

2=4.3 10-10 eV2

νe νx→


Atmospheric neutrinos in SK

• They are produced by cosmic rays:

so 1. the ratio is expected to be 2.

• The neutrinos in SK travel different distances:

but that should not affect their number as a

function of zenith angle: 2.up-down symmetry.

Oscillations would imply deviations from 1 and 2.

π+ µ+ νµ , µ+e

+ νe νµ+ +→+→

π- µ- νµ , µ-e

- νe νµ+ +→+→

r=νµ νµ+

νe νe+------------------

zenithangleΘ

Detector

cosΘ

= 0

.8

cosΘ = 0

cosΘ = -0.8

L =

20 k

m

L = 500 km

L = 10000 km

Earth

mantle

outer core

inner

core

atmosphere


Detection of atmospheric ν’s in SKEν: 0.1 GeV - 100 GeV. ν’s are detected by lepton

production:

N, N’ are nucleon and l=e,µ. The lepton emits

Cherenkov light.

νl N+ l N '+→

NUM 112RUN 3021SUBRUN 112EVENT 653785DATE 96-Oct-29TIME 16:45: 5TOT PE: 5852.6MAX PE: 27.3NMHIT : 3120ANT-PE: 47.3ANT-MX: 14.2NMHITA: 35

NUM 2RUN 2534SUBRUN 2EVENT 9440DATE 96-Aug-15TIME 0: 7:59TOT PE: 4489.7MAX PE: 25.8NMHIT : 1927ANT-PE: 25.6ANT-MX: 2.3NMHITA: 34

muon

electron


SK atmospheric v’s - Results

• Flavour ratio:

should be unity if no oscillations. But:

• Up-down asymmetry:

U=number of neutrinos below the horizon,

D=number of neutrinos above the horizon

A should be zero if no oscillations. But:

More than 7 σ away from zero!

What is the explanation for all that??

RNµ Ne⁄( )data

Nµ Ne⁄( )theory

-----------------------------------=

E<1.33 GeV: R 0.680 0.023 0.053 0.005th±±±=

E>1.33 GeV: R 0.678 0.042 0.009 0.080th±±±=

AU D–U D+---------------=

A 0.32– 0.04 0.01±±=


SK atmo - The oscillation

We measure the number of νe’s and νµ’s as a function of

their zenith angle Θ (which tells us what distance they

have travelled). Some of them must have changed

flavour - most probably those that travelled a long way

(transition probability depends on distance).

dots = data, blue bars=theory (no oscillation), red line = best fit

for oscillation:

with parameters: ∆m2=3.05x10-3 eV2, sin22θ=0.995.

0

150

300

450

600

750

-0.8 -0.4 0 0.4 0.80

200

-0.8 -0.4 0 0.4 0.8

sub-GeV e-like sub-GeV µ-like

multi-GeV e-like

cosΘ

multi-GeV µ-like + PC

cosΘ

Eν < 1.33 GeV

Eν > 1.33 GeV

νe

νe

νµ

νµ

νµ ντ→


Atmospheric ν’s in MACRO

The MACRO experiment detects muons which are produced by

muon neutrinos interacting in the rock below the detector. The

average neutrino energy for through-going muons is 100 GeV.

The muon energies are above 1 GeV. The muon flux is measured

and compared with theory (no oscillations).

0

1

2

3

4

5

6

7

8

9

10

-1 -0.9 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1 0

cos θ

Up

wa

rd t

hro

ug

hg

oin

g µ flu

x (1

0-13 c

m-2

s-1

sr-1

)

νµ −−> ντ


Other sources of neutrinos?

The neutrino sources we saw so far are:

• the Sun, where νe’s are produced by fusion

(solar neutrinos, )

• the atmosphere, where νe’s, νe’s, νµ’s and

νµ’s are produced in cosmic shower pion

decays (atmospheric neutrinos, )

There is another natural source: supernovae.

There are also ‘man-made’ sources of neutrinos:

• accelerators

• reactors

There are experiments observing such neutrinos

and looking for oscillations. Depending on the

distance source-detector they are subdivided to:

– short-baseline experiments (SBL)

– long-baseline experiments (LBL)

These experiments have seen no evidence for

oscillations, with the exception of LSND

(short-baseline accelerator experiment).

νe νx→

νµ ντ→


LSND: SBL accelerator experimentDetector:

- cylindrical tank 8.3 m long by

5.7 m in diameter.

- 1220 20-cm phototubes.

- 167 tons of liquid scintillator

(mineral oil).

- Cherenkov light and

scintillation light are detected.

Oscillation:

Source of νµ’s: µ+ decays at rest. The muons come from pion decays.

Pions are produced by a 800 MeV proton beam. The protons are

accelerated in the LANSCE accelerator. Lsource-detector=30 m.

Signature of νe’s:

the positron and photon

are correlated in position

and time.

KARMEN is a similar

experiment (1990-2001)

that has tried to rule out

the LSND result. It is not

expected to cover the

entire LSND allowed

region (blue and yellow

areas in the plot). A new

experiment is needed to

give a definite answer:

MiniBooNE.

νµ νe→

νe p+ e+

n+→ n p+ d γ (2.2 MeV)+→

99 % CL90 % CL


The future in accelerator SBL: MiniBooNE

Detector:

- spherical tank 6.1 m in radius.

- 1280 20-cm phototubes.

- 807 tons of mineral oil.

- operation similar to LSND,

much higher statistics.

Oscillation:

Neutrino source: from the 8

GeV proton booster of FNAL.

The detector will be 500 m away

from pion decay region.

Detection method:

quasi-elastic events

electrons and muons

will be identified from

their Cherenkov rings.

If oscillations occur,

MiniBooNE will collect

1000 events in 1 year (at

least 9σ signal). If not,

the sensitivity is enough

to refute LSND (plot).

Data taking will start at

the end of 2001.

νµ νe→

νµ C+ µ-X+→

νe C+ e-

X+→


LBL accelerator experiments

The CNGS project

Approved 17/12/99 - Data in 2005

Boosted by the Super-Kamiokande result on

oscillations, the project will use a

beam for appearance. The beam will be

produced by protons from CERN’s SPS and will

be directed to Gran Sasso laboratory, 732 km

away. It comprises the experiments:

• ICANOE

• ICARUS

• NOE

• Aqua-RICH

• OPERA

νµ ντ→ νµντ


OPERA: a LBL accelerator experimentThe experiment will search for oscillations.

Detection method: direct observation of τ lepton produced in the

interaction of with the target.

Detector: made of metal (=target) and emulsion (=tracking device)

alternated layers. Gaps between emulsion sheets allow for direct

observation of the τ decay kink. The kink is reconstructed by the four

track segments in the emulsion sheets ES1 and ES2:

νµ ντ→

ντ

µ ,h e,τ

ντ

Pb ES1 ES2

100 5050

3 mm

( )µm

µm2001 mm


Can OPERA explore the SuperK region?

sin22Θµτ

∆m2 /e

V2

10-4

10-3

10-2

10-1

1

10-3

10-2

10-1

1


Neutrino telescopes

• They study high energy neutrinos of cosmic

origin:

- from galactic sources, like remnants from

supernovae explosion and binary systems

(pulsar or black hole and companion star)

- from extragalactic sources, like active

galactic nuclei

- from more exotic sources (WIMPs,...)

• Why study such neutrinos?

- they are insensitive to magnetic fields and

interact very weakly, so one can use them to:

-- probe the universe

-- study acceleration mechanisms

- they have very high energies, not available

at accelerators, which can be used to:

-- test models

-- look for new processes

-- understand better the beginning of

the universe


Neutrino astronomy in 11 steps

1 - to be seen, ν’s must interact with nucleons

2 - we need a target with many nucleons

3 - a νµ with produce a muon and a hadronic shower

4 - Eνµ > 1 TeV, so angle between νµ and µ is less than 1o

5 - the muon points to the ν origin : ν astronomy

6 - given the ν energy, the µ will be relativistic

7- relativistic muons in water emit Cherenkov light in acone of about 42o opening angle and can travel manykilometers before they slow down and decay

so here comes the recipie:

νµ

µ

shower


...

8 - use the Earth as a target, it has enough nucleons ;-)

9 - use the Earth as a filter to block other particles

10 - use the sea as a detection medium (Cherenkov)

11 - use the sea as a filter to reduce cosmic ray muons ordo energy cut on detected muons


ANTARESDetector: a 3d matrix of PMTs covering 1 km3.


ANTARES - detection


Summary

• Solar neutrinos:

– Super-Kamiokande : indication

– are there any matter effects?

– maybe 10 more years of data needed

• Atmospheric neutrinos:

– Super-Kamiokande : signal

– MACRO : signal

• SBL accelerator experiments:

– LSND : signal

– KARMEN : no evidence

– MiniBooNE : will answer about

• LBL accelerator experiments:

– OPERA : as in SuperK (2005)

• Reactor experiments:

– no evidence for oscillations

• Neutrino telescopes:

– ANTARES : astronomy

νe νx→

νµ ντ→νµ ντ→

νµ νe→νµ νe→

νµ νe→

νµ ντ→


Web sites for experiments• The neutrino oscillation industry (reference page):

http://hepunx.rl.ac.uk/neutrino-industry/

• GALLEX, Homestake:

http://wwwlapp.in2p3.fr/neutrinos/anexp.html

• SAGE:

http://www.npl.washington.edu/npl/ar96/ch2_9.html

• Super-Kamiokande:

http://www-sk.icrr.u-tokyo.ac.jp/doc/sk/index.html

• MACRO:

http://infn-bo-macro1.bo.infn.it:8080/

• LSND:

http://www.neutrino.lanl.gov/LSND/

• KARMEN:

http://www-ik1.fzk.de/www/karmen/karmen_e.html

• MiniBooNE:

http://www.neutrino.lanl.gov/BooNE/

• CNGS:

http://www.cern.ch/NGS/

• OPERA:

http://opera.web.cern.ch/opera/

• ANTARES:

http://antares2.in2p3.fr/

• more links at:

http://www.quark.lu.se/~christin/neutrinolinks.html


watch out, experiments in progress! - Lunds · PDF fileAccording to the Standard Solar Model...

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