T2K neutrino experiment at JPARC

Approved since 2003, first beam in April 2009. Priorities:

1. search for, and measurement of, e appearance sin2213

2. precise measurement of disappearance sin2223 and m223

3. (Longer term) precise measurement of e , e Matter effects and CP violation

T2K Scheme:Neutrino oscillations:

measured neutrino events in SK prediction without oscillations (flux. )

-- there exist no measurement of particle production off carbon with 30 GeV protons-- the near detector neutrino flux is not identical to far detector neutrino flux (geometry) resulting uncertainties in the near/far ratio are thus not well known (up to 20%)-- there is no absolute secondary hadron flux measurement available on the T2K beam line cross-sections cannot be measured

30 (->50) GeV protons on90 cm carbon target

(disappearan

ce) CC

near/far ratiois *not* flat

,Kp

near/far ratio for backgrounds (esp. e) are not constant either

plots from Max Fechner’s thesis

CCe

e flux important for e appearance search:

signal cross-section, backgrounds

requires measurement of

Systematic uncertainties due to the hadron production model

F/N ratio difference among hadron production models: ~ 20% @E1GeV

Syst. error due to F/N

bg( ) 10%N

Goal of T2K

Impossible to achieve T2K GOAL!

It is difficult to evaluate the validity of the hadron production model !! The uncertainty is probably not less than the difference among several models inspired by similar data sets

momentum flux

G-FLUKA vs. MARS vs. FLUKA up to ~20% difference!

bg( ) ~ 15%Ne appearance

disappearance

e appearance

disappearance

Ratios of F/N ratios

(sin2223)~ 0.01,(m23

2)<~ 3 105eV2

(sin2223)~ 0.015 -0.03,(m23

2)<~ 5-10 105eV2

MARS/G-FLUKA FLUKA/G-FLUKA

T2K with and without NA49:

I. 13 discovery:

GOAL: search down to sin213 ~0.008 (90%CL) (signal ~ 10 / 20 bkg, ~20% stat. error)

NC 0 and CC e backgrounds will be predicted from the near detector Achieving the above goal requires N/F (all sources of errors) < 10% ==> requirement on N/F from hadro-production: <2-3%

This can be achieved in NA49 with 10% precision on pion rates and K0K / ratio. NA49 has achieved 3% on both in the past.

present status: -- no 30 GeV p-Carbon data -- interpolation between 12 GeV p-C (HARP, no K yet, no K0) and 158 GeV (NA49!) required-- anomalous behaviour of K/pi ratio (3 to 7%) observed in nearby nuclei ==> errors on hadro-production are at least 20- 30% level and uncertain

Without NA49, uncertainties in the particle production would yield the largest error on the background estimate to e search and preclude to achieve the aspired systematics. The sensitivity would be worsened by ~10-20%.

This is as much an issue of reliability than of precision.

T2K with and without NA49:

II. Atmospheric oscillation parameters sin2 223, m223

Statistical accuracy: sin2 223 ~0.01, (m223 ) = 3 10-5 eV2 (1%) (5yrs @0.75MW)

statistics

nonQE/QE (20%)

Energy scale (4%)

10% on flux

10% on flux width

flux slope (20%)

In the presently favored region of m223 the flux related errors are important wrt statistical accuracy.

The 20-30% uncertainties on particle production would lead to up-to-20% errors on N/F ratio and would spoil

the measurements, with syst. errors as large as sin2 223 ~0.015-0.03, (m223 ) = 5-10 10-5 eV2

An NA49 measured precision of 10% per bin would lead to a N/F ratio error of 2-3% and render these small.

Without NA49-T2K, ill-defined flux-errors would be worse than the statistical precision, and spoil the atmospheric parameters measts

CONCLUSIONS

For the first phase of T2K (5 yrs @0.75 MW on target):

10% measurements of hadron production ( K K0 ) with NA49 ensure flux-related errors small wrt statistical errors:T2K stat: sin2 223 ~0.01 , (m2

23 ) = 3 10-5 eV2 , sin2213 ~0.008 (90%CL)

present: ( sin2 223 ~0.04 , (m223 ) = 2 10-4 eV2 , sin2213 ~0.1 (90%CL) )

They are crucial to achieve the goals of the experiment with reliable systematic error estimates.

Absolute neutrino cross section measurements with errors of 10%or better become possible.

For the longer time scale (Hyper-KamiokaNDE or higher power) 3% measurements in NA49 should be achievable and will be important for precision meaasurements of

transitions, ==> matter effects and CP violation

ee vs