Transcript Hybrid emulsion detector for the neutrino factory

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

Input parameters: 13  1 ,   90
  meas  true
ambiguities
Solving the ambiguities
A hybrid emulsion detector
1 mm


• 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 (<1mm) in a modular structure
Pb
The basic unit : the « brick »
Emulsion layers
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
ECC technique successfully used in cosmic
rays (X-particle discovery in 1971) and by
DONUT for the  direct observation
10 X0
8.3kg
10.2 x 12.7 x 7.5 cm3
8 GeV
Electronic detector task
 trigger and location of neutrino interactions
 muon identification and momentum/charge measurement
ECC emulsion analysis:
Electronic detectors:
Target
Trackers
Pb/Em.
target
Vertex, decay kink e/g ID, multiple
scattering, kinematics
Spectrometer
Link to muon ID,
Candidate event
Pb/Em. brick
8m
Basic “cell”
Extract selected
brick
Brick finding, muon ID, charge and p
8 cm
Pb Emulsion
p/p < 20%
1 mm
Topology and kinematics of signal
Muon identification


m
Background
m  unidentified
m
m
C
 NC

Charge misidentification: 1-3 x 10-3


Punch through
or decaying



m  misidentified
from oscillation
Signal and background versus E
charm
decay in flight
and
punch-through
732 km
+
signal
3000 km
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
• 510 kton ECC detector feasible
Combining ECC @ 732km and iron @ 3000km
Allowed regions from the
analysis of simulated data for
13 = 1°,  = 90°. The best fit
is 13 = 0.9°,  = 80°.
5 kton ECC + 40 kton Iron
No clone regions for 13>1°,
for 13=1° they show-up in
less than 10% of the experiments
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 measurements
Position measurement of particle trajectories
0.05 µm
0.06 µm
Nucl. Instr. Meth. A in press
RMS distribution of fitted angular trajectories
Median 0.4 mrad
Perpendicular particles
Median 0.64 mrad
Inclined (200 mrad) particles
Momentum measurement by Multiple Scattering
Routine scanning performed
3 GeV pions
30% resolution
with 3 X0
Nucl. Instr. Meth. A512 (2003) 539
2 GeV pions
22% resolution
with 5 X0
 /µ separation using neural network
(multiple scattering and energy deposit)
Exposure at PSI (Zurich) with pure  and µ beams
 (P=202MeV) and m (Pm=120MeV)
follow tracks till they stop and characterize them according to the
energy deposition per unit length and the scattering angle
av
Xav
IN
HID
OUT
 or m
( eVolav
)
Data
µ

/e separation study:2 = 2e -2 separator
 x i   e /  i     y i   e /  i  

  

e /  i 
e /  i 
 

 
2N  1
2

2
e /
e /  


 13.6
2  
 Pe /  ( z)
2
d
X0




2
4 GeV : data
2
6 GeV : data-MC comparison
2 GeV : data
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
LEXAN
R2
LEXAN
12C
R1
LEXAN
R0
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.)
Ionization ( only 3 mm chamber– R0 versus R1)

R0
Z>2
p
Ionization (8 cm chamber– R1 versus R2)
Z=6
Z=5
Z=3
Z=4
Z=2
R1
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