Hybrid emulsion detector for the neutrino factory

Giovanni De Lellis

University of Naples“Federico II”

•Recall the physics case•The detector technology•Future prospects

Recalling the physics case

• Study the CP violation in the leptonic sector: e µ the most sensitive (“golden”) channel

• In the (13,) measurement, ambiguities arise– Intrinsic degeneracy [Nucl. Phys. B608 (2001) 301] m2 sign degeneracy [JHEP 0110 (2001) 1]

– [23, /2 -23] symmetry [Phys. Rev. D65 073023 (2002)]

• The “silver” channel (e and µ) is one way of solving the intrinsic degeneracy at the neutrino factory– A. Donini et al., Nucl. Phys. B646 (2002) 321.

• An hybrid emulsion detector is considered– D. Autiero et al., Euro. Phys. J. C33 (2004) 243

Golden and silver channels

truemeas

90,1:parametersInput 13

ambiguities

Solving the ambiguities

A hybrid emulsion detector

8.3kg

10 X0

Pb

Emulsion layers

1 mm

10.2 x 12.7 x 7.5 cm3

• Target based on the Emulsion Cloud Chamber (ECC) concept• Emulsion films (trackers) interleaved by lead plates (passive)• At the same time capable of large mass (kton) and high spatial resolution (<1m) in a modular structure

The basic unit : the « brick »

ECC topological and kinematical measurements• Neutrino interaction vertex and decay topology reconstruction• Measurement of hadron momenta by Multiple scattering• dE/dx for /µ separation at the end of their range• Electron identification and energy measurement• Visual inspection at microscope replaced by kinematical measurements in emulsion

8 GeVECC technique successfully used in cosmic rays (X-particle discovery in 1971) and by

DONUT for the direct observation

Electronic detector task

supermodule

8 m

Target Trackers

Pb/Em. target

ECC emulsion analysis:

Vertex, decay kink e/ ID, multiple scattering, kinematics

Extract selected brick  

Pb/Em. brick

8 cm Pb 1 mm

Basic “cell”

Emulsion

trigger and location of neutrino interactions muon identification and momentum/charge measurement

Electronic detectors:

Brick finding, muon ID, charge and p

Link to muon ID,Candidate event

Spectrometer

p/p < 20%

Topology and kinematics of signal

edunidentifi

C

Muon identification

Punch throughor decaying

NC

iedmisidentif

Charge misidentification: 1-3 x 10-3

from oscillation

Background

Signal and background versus E

732 km

3000 km

signal

charm

decay in flightand

punch-through

+

Emulsion scanning• Real time analysis: several tens of bricks

extracted/day• High speed (20 cm2/h) fully automatic scanning

systems (one order of magnitude faster than previous generation)

• independent R&D in Europe and Japan based on different approaches

• First prototype developed and tuned in Europe• Successfully running since Summer 2004 with

high efficiency (>90%), high purity (~2 tracks/ cm2 /angle) and design speed

• 2 mrad accuracy at small incident angles

Fast CCD camera (3 k frames/sec) Continuous movement of the X-Y stage

Emulsion Scanning load• Boundary conditions:

– detector located 732 km from the beam source– 5 years data taking

• Scan all events with a negative (wrong sign) µ (#evts per kton): – “silver” ~ 30 events and “golden” ~ 310 – Anti-µ with misidentified charge: ~ 2200 – Charm background: ~ 80 events NC with punch-through or decaying h: ~ 4800

• ~ 8 x 103 events in 5 years• 510 kton ECC detector feasible

Combining ECC @ 732km and iron @ 3000km

No clone regions for 13>1°, for 13=1° they show-up in

less than 10% of the experiments

5 kton ECC + 40 kton Iron Allowed regions from the analysis of simulated data for 13 = 1°, = 90°. The best fit

is 13 = 0.9°, = 80°.

Both at 3000 km

•Large reduction of all backgrounds ( 1/L2) except the muonic decay of + events from anti-µ anti- •scanning load reduced by about a factor of 20

Precision measurementsPosition measurement of particle trajectories

0.05 µm 0.06 µm

RMS distribution of fitted angular trajectories

Perpendicular particles Inclined (200 mrad) particles

Median 0.4 mrad Median 0.64 mrad

Nucl. Instr. Meth. A in press

Momentum measurement by Multiple Scattering

Nucl. Instr. Meth. A512 (2003) 539

3 GeV pions 2 GeV pions

30% resolutionwith 3 X0

22% resolutionwith 5 X0

Routine scanning performed

Xav

IN HID OUT

orav

eVolav( )

/µ separation using neural network (multiple scattering and energy deposit)

Dataµ

PRELIMINARY

Exposure at PSI (Zurich) with pure and µ beams (P=202MeV) and (P=120MeV)

follow tracks till they stop and characterize them according to the energy deposition per unit length and the scattering angle

12

2

/

/

2

/

/

/2

N

i

ii

i

ii

e

ey

e

ex

e

2 GeV : data

4 GeV : data

2

0/

2

/ )(

6.132

X

d

zPee

/e separation study:2 = 2e -2

separator

6 GeV : data-MC comparison

Exposure of an ECC to 400 Mev/u C ions at NIRS ECC structure: emulsions and Lexan (C5H8O2) target sheets

( = 1.15 g/cm3) 1 mm thick (73 consecutive “cells”)Cell structure

LE

XA

N

LE

XA

N

LE

XA

N

R0 R1 R2

R0: sheet normally developed after the exposure

R1: sheet refreshed after the exposure (3 days, 300C, 98% R.H.)

R2: sheet refreshed after the exposure (3 days, 380C, 98% R.H.)

12C

Ionization ( only 3 mm chamber– R0 versus R1)

p

Z > 2

R0

R1

Z = 6

Z = 5

Z = 4Z = 3

Z = 2

Ionization (8 cm chamber– R1 versus R2)

Conclusions• A hybrid detector for the study of CP violation in the

leptonic sector by means of the “silver” channel is feasible• The OPERA experiment with the same technology will be

running from next year and demonstrate it• The scanning load is feasible already now • Possible improvements

– dE/dx measurement to reduce the charm background (already shown by test-beam data)

– increase the mass of the detector and/or the exposure– Different strategy: scan > 1 brick per event increase the signal

detection efficiency by about 20% (increase in the brick finding efficiency)

• The emulsion technology is improving in different contexts