T2K Near Detector FGD
Initial neutrino beam measurements
Kei Ieki for T2K FGD group
2. Near detector (Off-Axis)

1. T2K experiment

Located 280m downstream from the neutrino production target.
Consists of detectors surrounded by a magnet to measure beam flux and energy
spectrum prior to oscillation.

Tracker295km

ν beam

Optimum detector for CC interaction measurement
FGD: Measure short tracks around ν interaction
vertex ⇒ Identify the interaction type
TPC: Measure the momentum of long tracks⇒ Reconstruct neutrino energy

SuperKamiokande (Kamioka)

J-PARC proton
accelerator (Tokai)High intensity beam & Giant detector

・Discovery of θ13 (νμ → νe )Goal:
・Precise measurement of θ23 (νμ → νx)
Physics run started from 2010.

CCQEμν

W

pCC1πμπνW

Tracker:
FGD*2 & TPC*3

SMRD(in the yoke)pSimulated CC interaction in the Tracker

Short tracks have to bedetected to distinguishinteraction types

3. Fine-Grained Detector
MPPC & fiber readout

AFTER ASIC chip

Wavelength shifting fiber

0.96×0.96 cm2MPPCRaw waveform

Compressed data6mmpedestal

MPPC (Multi Pixel Photon Counter)Compact
Photon counting capability
Works in magnetic field

Readout front end board
MPPC waveform before / after data compression

Special ASIC chip for readout
High noise rate (102~103 kHz)・Waveform digitization (50MHz)
Temperature dependency
・Pulse amplifier & shaper⇒ >20MIP dynamic range
・Light yield ~25p.e. for MIP
Finely segmented scintillator bars
<5ns timing resolution
・>99% hit efficiency
FGD1: Scintillator ~1t
・10μs readout time
FGD2: Scintillator ~0.5t & Water layer ~0.5t ⇒ Capable of reconstructing⇒ Capable of detecting Michel
charged particle tracks with
⇒Measure neutrino interaction rate inelectron to distinguish p/πwater (to compare with Super Kamiokande) good efficiency
Excellent performance for detecting charged particles around ν vertex

1p.e.
2p.e.

MPPC ADC distribution

Light yield vs. Position on bar

4. Initial beam measurements
We accumulated ~3*1019 POT (Proton On Target) data in
the first half of 2010. We analyzed the neutrino event rate in
FGD to confirm the performance of the detector and beam.
Simple neutrino event selection:
1. Noise rejection- Hit time clustering (2.5pe noise threshold, 80ns coincidence)- Beam timing cut (expected timing ±70 ns)

2. Charged Current event selection- Fiducial volume cut (cut if the vertex is in the veto region)- 3 XY layers continuous hits (enhance CC muon track)
FGD1

vertex

Selected event: Charged
Current interaction in FGD FV.
Red band shows the veto region.
Event rate vs. date (after selection)

As a result, we confirmed that the FGD is observings
neutrino events with stable rate. The measured event
rate was 1.5 events / 1015 POT (chi-square / ndf = 0.77).
Systematic error for this number is not calculated yet,but this number roughly agree with the expected event
rate in MC.

FGD2noisehitsmuon
track

FGD Event display before / after noise cut>99.9% of noise
hits can berejected by hit
time clustering.
Background: Muon from the νinteraction at the upstream wall.
Rejected by fiducial volume cut.

Successful operation of detector & beam
⇒ About to present first physics results!

5. Summary
The T2K FGD detector is designed to measure neutrino interactions in the near detector complex. The powerful combination of MPPCand AFTER ASIC chip readout provides excellent performance for detecting charged particle tracks around interaction vertex.
We started physics run in 2010 and accumulated ~3*1019 POT data. Our simple hit level analysis shows that the neutrino events rate isstable and the beam operation is successful. The first result of neutrino oscillation analysis will be presented very soon.