T2K
Tokai to Kamioka A Long­baseline Neutrino Experiment SuperKamiokande
295 km
J­PARC
(Tokai)
KEK
Laura Kormos
LANCASTER
UNIVERSITY
DEPARTMENT
OF PHYSICS

 

The MNSP Mixing Matrix
(Maki­Nakagawa­Sakata­Pontecorvo)
e U e1 U e2 U e3 1
 = U  1 U  2 U  3  2
mass  U  1 U  2 U  3 3 eigenstates
weak eigenstates
cij = cos ij and sij = sin ij

c13
0 s13 e−i 
0
1
0
0 −s23 c23 −s13 e−i  0
c13
1
U= 0
0
c23
0
s23
sin2 223

c12
s12 0
−s12 c12 0
0
0
1

The J­PARC Facility (Japan Proton Accelerator Research Complex)
First
Beam:
April
2009
Linac
(350 m)
3 GeV Synchrotron
1 MW
Near Detector
50 GeV Synchrotron
0.75 MW
Neutrinos to
Kamioka
The Near Detector is 280 m downstream from the  production, in order to characterise the beam before the neutrinos oscillate, including studying the e appearance background. The  flux can be compared with that at the Far Detector 295 km away.
2 Types of measurements at T2K
 Disappearance:
Look for a deficit of  events
in the far detector.
Sensitive to sin2 223 and m232 .
CHALLENGES
Measuring energy spectrum well.
Near/far corrections:
­ Spectrum isn't the same at
the far detector as the near
detector.  can mimic  .
  e Appearance:
Look for an excess of e events
in the far detector.
Sensitive to sin2 213 .
Potentially sensitive to .
CHALLENGES
0 backgrounds:
- 0  , photons can mimic e
in SuperKamiokande.
Beam e backgrounds:
­ Difficult to differentiate from oscillated e .
l
CCQE
l + n  l­ + p
l­
Consider as a 2­body interaction
Find l Energy
l­
l
n
W
u
d
u
d
d
u
l + n  l + p +  ­
l
p
­ignore binding energy.
­ignore Fermi motion.
­measure l­ momentum and direction.
­measure the p recoil.
­assume l direction is beam direction.
 + p  + p + 0 

0
l­
0 Production
W
d
d
u
u
d
u
u
_
u
Z
u
u
d
u
_
u u
u
d
flux × CC Cross section
Off­axis beam  smaller energy range, lower energy 
can tune E to oscillation max.
Osc. Prob.=
sin2(1.27∆m2L/Eν)
OA2o
OA2.5o
OA3o
The ND280
Near Detector at 280 m
p
π
OA0o
off­axis
 energy
ν
on­axis
0m
140m
280m
2 km
295 km
Super Kamiokande
The far detector
 On­axis detector
● Determines precise beam direction
relative to the far detectors. ● Iron­scintillator tracking detectors
● Tracks muons from CCQE events.
ND280 Off­axis detector 
● Study exact composition of the beam.
● Study neutrino interaction cross­sections
and properties required to extract the oscillation parameters from SK data.
● Measures  flux, energy.
● Measures 0 production.
The Electromagnetic Calorimeter ECal modules: Will be assembled at Daresbury Lab, UK.
The Silicon Photo Multiplier chip is a new device which is currently being tested by the manufacturer. It serves the same purpose as a PMT, but is TINY, robust, and not sensitive to magnetic fields.
Charged particles and 's cause electromagnetic showers
in the calorimeter, which produce light.
Layers of lead alternating with plastic scintillator bars.
Each bar has a WLS fibre to
collect and transport the light
to the photosensor.
 Disappearance: E() spectra at Super­K
Depth of the dip  value of sin2 223 .
2
● Position of dip  m
.
23
Expected ND280 errors: 5% on normalisation + bkgds, 1% on energy scale, 20% on spectral shape, 5% on spectral width.
●
e Appearance: E(e) spectra at Super­K
 interactions producing 0 s. (poorly known)
Beam e Super­K e selection(5  1021 POT)  CC Bg  NC Bg Beam e Bg e CC sig.
Fully contained Evis  100 MeV 1 ring e­like 0.35 ≤ E(reconst) ≤0.85 GeV
e/0 separation
2215 847
12 156
1.8 47
0.7
9
184
243
71 187
21
146 13
103
Disappearance:
Measure  energy and flux,
and non­QE bkds in ND280 using FGD, TPC & ECal.
Energy spectrum at SK differs
from spectrum at ND280 ⇒ Work out near/far correction.
We expect systematic uncertainties
in the flux, backgrounds, energy, spectral shape, spectral width will
lead to a measurement accuracy of:
(sin2 223 )  0.01,
(m232 ) < 1  10­4 eV2 .
(1 order of magnitude better than
any existing measurement.)
Appearance:
Measure beam e background flux and energy: FGD, TPC &ECal.
Measure 0 production cross­
sections in plastic, and plastic+water (in POD and FGDs).
Subtract former from latter to get cross­sections in water (c/wSK).
Predict backgrounds in SK.
We hope to observe   e
appearance.
If not, we expect to improve
constraints by more than an order
of magnitude.
●
If   e is observed, it could be large 13 and small , or vice­versa.
● If    is not observed, the  e sensitivity to sin2 213 depends on CP phase .
Why T2K?
100 times higher intensity than K2K.
Already has Super K – 10 years of detection experience.
High stats, good systs can look for  e appearance.
Good sensitivity for sin2 213 . Phase II: Increase beam power from 0.75 MW to 4 MW, Hyper Kamiokande, 24 times the size of Super Kamiokande, and add a 2 km detector: ­ water Cerenkov detector, like Super K.
­ sees essentially the same  energy spectrum as Super K.

much higher statistics and better systematics .
Conclusions
Our understanding of neutrinos has changed dramatically
in the past 8 years.
T2K is an exciting new experiment with the potential to measure oscillation parameters and neutrino properties which are not yet known. The ND280 is an essential component of the experiment. All subdetector groups have now submitted proposals.
Commissioning data starts: early 2010.
Conclusions
Our understanding of neutrinos has changed dramatically
in the past 8 years.
T2K is an exciting new experiment with the potential to measure oscillation parameters and neutrino properties which are not yet known. The ND280 is an essential component of the experiment. All subdetector groups have now submitted proposals.
Commissioning data starts: early 2010.