The OPERA nt appearance experiment in the CERN-Gran Sasso neutrino beam

1
The OPERA nt appearance experiment in the
CERN-Gran Sasso neutrino beam

• K.Kodama,
• Aichi University, Aichi, Japan
• M.Guler, E.Pesen, M.Serin-Zeyrek, R.Sever,
  P.Tolun, M.T.Zeyrek
• METU, Ankara, Turkey
• U.Moser, K.Pretzl
• Bern University, Bern, Switzerland
• T.Kawamura, S.Ogawa, H.Shibuya
• Toho University, Funabashi, Japan
• U.Stiegler
• CERN, Geneva, Switzerland
• S.Aoki, T.Hara
• Kobe University, Kobe, Japan
• A.Artamonov, P.Gorbounov, V.Khovansky
• ITEP, Moscow, Russia
• D.Bonekamper, N.Bruski, D.Frekers, D.Rondeshagen,
  T.Wolff
• Muenster University, Muenster, Germany

LNGS-LOI 8/97 and SPSC 97-24/I218, SPSC 98-25/M612
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Physics process neutrino oscillation
nm lt-gt nt t- X

• Posc sin22qmt sin2 (1.27 x Dm2(eV2) x
  L(km)/E(GeV))
• Dm2min (Posc ) x 1/1.27 x E/L

nt appearance esperiment direct
t-decay detection experimental technique
modern nuclear emulsion
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Original OPERA L.o.I
study the atmospheric
neutrino anomaly, as indicated by Kamiokande
large mixing and Dm2 10-2 eV2

• New results from Super Kamiokande and CHOOZ
• importance of nm-nt oscillation
  search

nm-ne
nm-nt
Kamiokande
SuperK.
CHOOZ
4

After the SK result ....

• Explore the possibility of a higher sensitivity
  search,
• exploit high intensity
  of the CERN NGS beam
• increase of detector mass (modularity)
• Perform the exercise with reference options
• optimization will be needed
• detector design, mass
• Assess the feasibility of the experiment tests,
  simulations
• emulsion procurement and handling,
  technical issues

5
Automatic emulsion scanning

• Pioneered by the Nagoya group Track Selector
• speed about x 100 w.r.t. semi-automatic
  systems
• New Track Selector routinely scanning in Japan
  and
  in Napoli (CHORUS analysis)
• speed about x 10 w.r.t. Track Selector
• Other CHORUS laboratories actively scanning
• RD going on at CERN, Germany, Italy and Japan
  needed for a next generation experiment like
  OPERA
• Future prospects Ultra Track Selector and
• Multi Track Systems

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Automatic scanning principle
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Microscope event view
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Track selector
100 mm
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Digitized video-image of a CHORUS neutrino event
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Aim, target mass and
experimental technique

• Atmospheric neutrinos (SK) Dm2
  sensitivity 10-2 -10-3 eV2
• NGS CERN-Gran Sasso beam M O
  (1000) ton
• Impossible with pure emulsion target
• (CHORUS 0.8 ton )
• Different approach required
• iron (lead)-emulsion sandwich
• passive target material, emulsion for
  tracking
• Starting point the Emulsion Cloud Chamber
  (ECC)
• so far used both in accelerator and cosmic
  rays experiments

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The Emulsion Cloud Chamber

• Developed and used for cosmic ray studies
• Recently used in neutrino experiments (
  E872/DONUT)
• n interactions in metal plates
• Rough (1 cm2) event localization by electronic
  det.
• Emulsion tracking
• - 50-100 mm em. layers on both sides of 1
  mm plastic base
• - 2 track segments in space
• t decays identified by impact parameter
• Mult. Scattering measurement Dp/p lt
  20 up to 30 GeV/c

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Using impact parameter as in ECC

• Charm background to t decays in the
  iron
• (shown for muonic decay)
• Similarly background from hadron reinteractions
  in the metal plate
• For a LBL experiment
• background problems

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Rethinking the ECC technique

• Charm decays and hadron reinteractions in the
  passive material backgrounds using impact
  parameter
• The OPERA detector concept
• Use decays in Pb for an independent analysis

- select t-decays in gaps between metal plates -
small plate thickness (et) , 2 emulsion sheets -
measure decay kink in space, by emulsion
tracking
) Oscillation Project with Emulsion tRacking
Apparatus ) A. Ereditato, K. Niwa, P. Strolin,
INFN/AE 97/06
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The OPERA concept

• thin lead plates
• 1 mm lt gct et 0.4
• two emulsion sheets (ES) for tracking, light
  spacer
• each ES
• - 50 mm emulsion layers on both sides of
  100 (200) mm plastic base
• - 2 high quality track segments in space
  (mm granularity)
• retain t decays in the spacer
• decay topology (kink angle) detection in space

low density spacer
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Fraction of ts decaying inL (lead), E
(emulsion layer), B (base), G (gap), L (long
kinks)
For Dm2 2.5 x 10-3 eV2 and 1 mm lead, 3 mm gap
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Event reconstruction

• Study all t decay channels e-, m- , h- ,
  (possibly into 3p)
• Track localization by electronic detectors
• Start scanning from ES upstream of event in
  electronic detector
• General scanning (in the most downstream ES and
  then scan back)
• Find vertex plate (Pb) and neutrino vertex
• Follow down tracks from vertex
• Kink search (in gaps between Pb)
• Kinematics of candidate events
• (few of total)

Start scanning here
n
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The detector

• Lead-emulsion target
• - cell 1 mm Pb, ES, 3 mm gap, ES
• - brick stack of 30 elements ( 13 cm thick,
  15 x 15 cm2 X-sect.)
• - module matrix of bricks ( 5 x 5 m2 )
• - electronic detector planes following each
  module
• - total mass 800 ton, subdivided into
  supermodules
• - maximum detector length 35 m
• - detector mass is scalable (number of
  supermodules)
• Muon detection
• - tracking in the target (electronic
  detectors)
• - magnetised iron m-spectrometer downstream
  sign of charge (momentum)
• Calorimetry
• - in the target Pb (each module 5 X0 )
  electronic det. (Scintillator strips, RPC)
• Momentum measurement from multiple scattering in
  emulsion
• Electron ID from emulsion measurements (EM
  interactions in lead plates)

Present design
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cell brick
3 mm
150 mm
1mm
150 mm
135 mm
19
Example10 supermodules800 ton target(more
compact version under study)
5 m
35 m
3.5m
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A possible shape optimization
... to quasi-circular geometry
from present design....
Optimal use of the emulsion surface
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Brick composition
Metal lead alloy (nickel plated) lead/ino
x sandwich inox .. polyurethane Spacer
polyethylene expanded PVC paper
honeycomb .. Emulsion layers
Low density (lt30 kg/m3)
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Brick materials
Pro's contra
Inox easy to machine light nickel-plated
lead density softness Leadinox
plates densityrigidity - . Polymers density
price viscosity Paper honeycomb very
low total density non uniform
density ..
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Tentative brick assembly
Pressure compression 0.3 mm (spacer elasticity)
Schematic not to scale
Inox C pieces (lt1 mm thickness)
Vacuum packing maybe unnecessary
Gran Sasso Laboratory stable temperature and
humidity
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Brick assembly machine (1)
105 bricks in 1 year (200 days) 500
bricks/day (8 hours) 60 bricks/hour
production lines minutes/brick
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Brick assembly machine (2)
emulsion
spacer
lead
piling position
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Brick positioning
lt 3.5 mm dead space filled with lt 3mm iron
lt 1 mm dead space with air
lt 2.5 mm dead space filled with lt 1mm iron
lt 2.2 mm dead space filled with lt2mm iron
Alternative solution
Accuracy of brick positioning to be defined
Schematic not to scale
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Emulsion

• No target (bulk) emulsion, but still
• 13 m3 of emulsion
  layers
• Diluted emulsion AgBr content 1/2-1/3 w.r.t.
  short baseline experiments cost scales
  down
• (lower grain density allowed by automatic
  scanning and b.g. level)
• Industrial production time schedule, lower cost
• Thin emulsion layers allow special development
  and good sensitivity ( of grains)
• RD on emulsion tests on prototype industrially
  produced ES going on in Japan
• European and American companies could also be
  involved

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Electronic detectors (1)

• OPERA is a large detector 2500 m2 total
  surface needed
• Main task of electronic detectors locate the
  event (shower center)
  moderate position resolution (few b.g.
  tracks) s 5-10 mm
• Need reconstruction behind each emulsion module
• Standard large-surface devices can be used
• Additional tasks event topology (CC/NC),
  calorimetry, timing measurement granularity, low
  noise, analog r/o (?)
• Design/construction schedule use well proven
  techniques

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Electronic detectors (2)
Technologies Scintillator strips with
fiber WLS read-out pros well known technique,
analog information, good timing, no gas,
industrial production, photodetectors, reduced
thickness, cost. cons granularity, attenuation
length. Resistive plate chambers (RPC) pros no
wires, robust construction, streamer/avalanche
mode, non- flammable gas possible, 2-dim
read-out, any shape, timing meas., not sensitive
to g, industrial production. cons limited size,
space resolution, no experience with
calorimetry, HV10 kV. Other possibilities
Monitored Drift Tubes, Honeycomb Chambers, Straw
Tubes, Drift Chambers
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Muon system

• Task identify muons (background reduction),
  charge determination
• Possibly momentum measurement (b.g. reduction,
  En meas., beam monitoring)
• To study kinematical domain, magnets size (match
  module size), required tracker precision,
  combine measurement in the target trackers,
  design/construction issues.
• Design iron toroids 5 cm thick, total 75 cm
  thick, 1.5 T, interspaced by scintillator
  strips, tracking by Mini Drift Tubes, 30
  resolution, calorimetry tail catcher.

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Events

• NGS realistic scheme
  4 x 1019 pot/y, 4 years running
• Data 600 DISQE n
  interactions/kton x 1019 pot (_at_ Gran Sasso)
• 
  7500 CC in 4 years
  (800 ton detector)
• nt interactions 2.84/kton x 1019 pot
• 20 nt interacting in OPERA (Dm2
  2.5 x 10-3 eV2)
• 80 (Dm2 5 x 10-3 eV2)
• 190 (Dm2 8 x 10-3 eV2)

possible improvements by a longer run, dedicated
SPS operation, improved accelerator performance
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t detection efficiency

• Detection efficiency depends on Dm2 below assume
  2.5 x10-3 eV2
• Decays outside Pb (1 mm) egap
  0.42
• (egap depends on beam features)
• 
  0.88 (t m)
• Kink finding efficiency ekink 0.83 (t
  e)
• 0.91 (t h)
• determined by the angular cuts
• (5 mrad resolution) 20 lt qkink lt
  500 mrad (scanning bg rejection)
• BR t m, e, h
  0.174 , 0.178 , 0.5
• Fiducial volume cut
  e 0.90

Total efficiency for the 1-prong channels 0.29
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Background for t- m- , e- , h-
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Charm induced background

• (sign of daughter only measured if muon)

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Charm b.g. to t- h-, m-, e- (before
vertex kinematics of candidate events)

• 0.05
  charm / CC
• x 0.5 D production
  probability
• x 0.22 BR (D h
  neutrals)
• x 0.45 D decay
  outside Pb
• x 0.91 e kink
• x 0.90 fiducial volume cuts
• x 0.04 m- CC not identified
• x 6900 DIS events
  0.55 events (h-)

Nbg(h-)
BR (charged D l neutrals) 0.065 m
charge measured by the downstream spectrometer
(1-e 0.3)
0.05 events (m-)
0.15 events (e-)
Total 0.75 events from single charm (realistic
running scheme)
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Other backgrounds

• Prompt nt in the beam negligible (
  lt0.02 events)
• Reinteractions (spacer) negligible (
  lt0.07 events)
• p , K decays
• (CC and NC) 0.2 events
  (eliminated by momentum cut)
• CCNC associated
• charm production double decay
  topology 0.15 events before
  the vertex kinematics

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Charm b.g. rejection by vertex kinematics

• angles at vertex measured with high accuracy
• momentum measurement by multiple scattering
• electron ID by e.m. interactions
• search for photon conversion
• calorimetric information from electronic detectors

38
B.G. reduction by vertex kinematics

• Before kinematical analysis of candidate events
• Nbg(h-) 0.55 events Nbg(m-)
  Nbg(e-) 0.20 events
• Nbg(associated charm) 0.15 events
  
• Vertex kinematics Nbg Nbg / 2 (could
  be improved)
• 
  Nbg (charm) 0.43 events
• (kinematics also eliminates other
  backgrounds)
  

Important vertex kinematics require track
before decay possible
only with emulsion granularity
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Sensitivity and discovery potential (realistic
running scheme)

• sin2 2qmt ( large Dm2 ) lt 3.8 x 10-3
• Dm2 (full mixing) lt 1.1 x 10-3 eV2
• (90 CL)
• If oscillation occurs _at_
• Dm2 2.5 x 10-3 eV2
  10 detected t events
• Dm2 5 x 10-3 eV2
  40
• Dm2 8 x 10-3 eV2
  90
• 4 s discovery potential 1.8 x 10-3 eV2
  (full mixing)
• (5 detected events)

NO OBSERVED EVENTS (0.43 expected BG)
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Emulsion scanning

• 10000 events nm NCCC to be scanned
• (achievable with fast automatic microscopes)
• rougher event localization w.r.t. short baseline
  exp.
• (allowed by low track density)
• fast general scanning (downstream ES) over few
  cm2
• scan back of all found segments up to the vertex
• scanning more time consuming, specially for
  candidates
• exploit on-going progress and equipment for
  CHORUS

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Feasibility studies, optimization and RD (1)

• Emulsion diluted emulsion quality vs.
  cost
• procurement handling
• ES manufacturing
• dedicated pouring machine (industry), X-ray
  films
• Bricks passive material nickel
  plated lead vs lead/inox
• spacers (plastic, paper honeycomb,
  ....)
• 
  low density, rigid
• vacuum vs. mechanical packing
• optimize dimensions Montecarlo prototype
  tests
• Electronic detectors define requirements space
  time resolution optimize
  performance vs. cost
• industrial production
• tests on prototypes track association to
  emulsion

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Feasibility studies, optimization and RD (2)

• Apparatus design physics goal optimize
  number of supermodules optmize
  bricks/module/supermodule dimensions
• temperature and humidity control
• detector mass and cost
• spectrometer design performance
  requirements
• Tests prototype bricks
  mechanics structure
• install bricks in the Gran Sasso
  Laboratory
• 
  ambient radioactivity,
  alignment by cosmics,
• hit density, optimize layer
  thickness
• beam tests
• kink efficiency, angular
  resolution,
• vertex finding
• RD emulsion collaboration with
  industry
• brick assembly machines
• dedicated scanning systems fast general
  scanning

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at Gran Sasso

• Present design 880 ton , 1.6 x
  1020 pot (4 years)
• 10000 nm CCNC
  events
• Discovery potential small bg, a few events
  are meaningful_at_ Dm2 2.5 x 10-3 eV2
  10 t events (0.4 b.g.)
• Negative search Dm2 10-3 eV2 sin2
  2qmt lt 4 x 10-3
• covers natm (Super Kamiokande)
• Modular structure scalable detector mass
• 
  
• High sensitivity nm-nt search
• explore the atmospheric neutrino signal

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Conclusions

• Emulsion technique to detect nm-nt oscillation
  with an appearance
• Long Baseline Experiment at Gran Sasso in the
  NGS beam
• Further studies, tests and RD will allow to
  optimize the design
• Explore the parameter region with low Dm2
  (indicated by SK)
• to determine the source of the atmospheric
  neutrino signal