Uni-Geneva in the T2K experiment

Alain Blondel CHIPP Neutrino meeting NEUCHATEL 21-22 June 2004

Uni-Geneva in the T2K experiment

Aim: following involvement in HARP / K2K, take part in the concept/construction of the T2K experiment as part of the T2K-Europe team and be there for the first data taking and results of the experiment in 2009.

This will be scientifically exciting.




The T2K experimental programme

Disappearance1. improve measurement of m2

13 (after MINOS, CNGS)

2. improve measurement of sin22

These require good knowledge of -- flux shape -- absolute energy scale, -- experimental energy resolution. Here the fact that the 2km flux is much similar to the SK flux than at 280 m is clearly an argument in favor of 2km detector location.

3. Appearance search for e oscillation 13

This is probably the highest priority measurement Appearance experiment. The main problem here is the understanding of the backgrounds from anything that produces or mimics an electromagnetic shower. - beam e from K and mu decay

- 0

- pions and secondary interactions etc…


disappearance: ratio of events seen/expected

appearance events seen over background


Off Axis Beam (another NBB option)

WBB w/ intentionally misaligned beam line from det. axis

(ref.: BNL-E889 Proposal)

Target Horns Decay Pipe

Far Det.

Decay Kinematics

Quasi Monochromatic Beamx2~3 intense than NBB




p

140 m0 m 280 m 2 km 295 km

Problem with water Cerenkov:not very sensitive to details of interactions. Either 280 m or 2 km would be good locations for a very fine grained neutrino detectorPlanned: a scintillating fiber/water calorimeter.

Liquid argon TPC would be a very good (better) candidate! Event numbers: near/SK = m(near[tons]) / 22500 . (300/2)2 = m(near[tons])

=> Need 10-50 tons fiducial or so at 2km 200-500 kg fid @ 280m

The (J-PARC-T2KBeamline

1.5km

295km

Neutrino spectra at diff. dist

280m


1. Flux

target

Decay tunnel 280m

2.5 deg=42mrad

130m

12m

1. Detector at 280 m in 42 mrad position sees angles from 42 to 80 mrad! (target to end of DK tunnel) 2. This spread is 2X larger than detector size, +- 2m at 200 m is +-10 mrad.

detector is able to tell the position (yes) but not the angle of theNeutrinos Fermi motion gives +- 200 MeV/c Pt… vs 600MeV/c neutrino mom.

84m@2km

42 to 45 mrad at 2km

1X at 2km+-3m at 2km is +-1.5 mrad



Some coments about the off-axis beam

The off-axis technique is, really, a way to tune the pion-neutrino beam energy.

The fact that the e component is 0.2-0.3% under the pion neutrino energy peak is true more or less in any wide-band beam.

There is a loss of neutrino events wrt on axis wide-band beam due to the fact that the neutrino cross-section is proportional to E.

In addition, the beam systematics are very different from those we are used to.In first order the flux is now insensitive to the secondary particles energy but is is now sensitive directly to angular variables in the beam (alignment, pion production angular distribution etc….

A NEW GAME!

Finally the oscillation experiment is performed for neutrino energies of 500-800 MeVfor which very little is known. (e.g. in GGM, a cut was placed at 1 GeV for neutrino energy)Precise measurement of the properties of these events (and of neutral currents with this visible energy) is crucial for the experiment.


Flux: Pions, muons and kaons.

The dominant source of electron neutrinos at the off axis peak is from muons. How do we know muons -- and their polarization ? (pion decay -- but the muons go in the walls.)

This is not true of the high energy tail,which can feed into the peak

Kaons give a secondary off axis peak at high energy (from K->Which is never seen in the pictures.MRD should monitor this quite well.


What we know and dont know2. Cross-sections

Well known: how to simulate Cherenkov light emission and detection

in a water detector. This should take care of the acceptance calculations IFF we knew the production cross-sections and topologies.

Not well known: how to simulate emission of secondary 0 & photons from

neutrino, nuclear or secondary interactions in water. (let alone carbon or argon)There are some interesting models but no certainty. We do not know inclusive or exclusive cross-sections on water target. We do not know the difference between electron- and muon-neutrino cross-sections at 300-600 MeV.

=> These measurements must be made.Detector needs to have at least 10-20 times rate of far detector That is 200-400 kilos at 280 meters (10 to 20 tons at 2km)and to be able to measure the detail of interactions,

Including low energy photon detection. This is the crux.


idea; loverre


loverreloverre, sanchez, radicioni


The present detector concept

empty targets

water targets

suggested detectors:

loverre, sanchez, radicioni


charge ID of pions is relevant since pi+, mu+ and pi-, mu- have different stopping properties in water.

sanchez


I think I have some good news for you. After discussion with the DG, I can say that CERN would be in favour of making the ex UA1 magnet available to the T2K experiment. We have to see what would be the best procedure (loan or donation). I let you know more details soon which we could also discuss next time you are coming to CERN.

Best regards

Dieter Schlatter


One of the important design constraints is the rate: 0.2 event per ton per spill at 280 m. Each spill contains 11 bunches in 2 microseconds about. The 1 kton water cerenkov would be swamped and there will be many interaction in the iron joke and calorimeter.

to be able to associate photons seen in the calorimeter to the interactio vertex one must be able to have their time preciselyand possibly a pointing.

=> Lead glass blocks, (There exist many 'mines' of lead glass blocks, Tristan, Opal, thatcould be used for the purpose … under investigation (OPAL's is at CERN)but also active converters inside the tracker.


At Uni-Geneva:

Our participation in the 280 m detector is very natural in the framework of the T2K-Europe group. We would like to contribute to the tracker, and preferably with thesame technology as will be used for MICE.

TPC (we have some 2000 channels available from HARP) or scintillating fibers… see MICE talk tomorrow. The forces liberated at the end of HARP/K2k constitute a bare minimum, further evidently welcome.


CONCLUSION:

The T2K experiment will bring considerable improvements in neutrino mixing parameters with emphasis on 13 from appearance search for e oscillation

In line with the involvement in HARP K2K Gva will get involved in T2K. This will of course be more direct than for K2K and we are foreseing to contribute directly to the hardware (tracker of the fine-grained detector)

The concept of a magnetic detector is specially appealing since it allows adetailed measurement of the properties of the final state of neutrino events, the understanding of which will be crucial for the background estimates for the e search.

This should take place within the European effort in T2K.

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Uni-Geneva in the T2K experiment

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