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The OPERA emulsion detector for a long-baseline neutrino oscillation experiment

H.Shibuya Toho Univ., Japan

K.Hoshino, M.Komatsu, K.NiwaNagoya Univ., Japan

S.Buontempo, A.Ereditato, G.Fiorillo, P.Migliozzi, P.Strolin

Naples Univ. and INFN, Italy

G.RomanoSalerno Univ. and INFN, Italy

Y.Sato Utsunomiya Univ., Japan

LNGS-LOI 8/97 and SPSC 97-24/I218

Presented by: A.Ereditato, INFN Naples M.Komatsu, Nagoya Univ.

Gran Sasso Laboratory, 6/2/1998

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Physics process: neutrino oscillation

-

h-n

e- e+--n

- + X

CC

appearance esperiment direct decay detection

PPosc osc = sin= sin2222 sin sin22((1.27 1.27 xx mm22((eVeV22) ) xx L( L(kmkm)/E()/E(GeVGeV))))

mm22minmin= (P= (Poscosc//2) 2) xx 1/1.27 1/1.27 xx E/L E/L

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New results from Super Kamiokande and CHOOZ: importance of -oscillation search

OPERA L.o.I: study the atmospheric neutrino anomaly, as indicated by

Kamiokande large mixing and m2 ~10-2 eV2

amiokande

SuperK.

--e

CHOOZ

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Explore the possibility of a higher sensitivity search:

exploit high intensity of the beam under study

increase of detector mass (modularity)

Perform the exercise with reference options:

optimization will be needed:

beam, detector design

Assess the feasibility of the experiment: tests

background reduction, emulsion handling, technical issues

s there room for improvements ?

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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 starting-up in

Napoli speed about x 10 w.r.t. Track Selector

• Other CHORUS laboratories actively scanning

• R&D going on at CERN, Nagoya, Napoli and Salerno

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Microscope event view

Emulsion

to beam

Good tracks appear as dots

Tracking implies

connection of dots

in different layers

~100 m

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Track selector ~

10

0

m

(emulsion beam)

T

8 Aim, target mass and experimental technique

• Atmospheric neutrinos (SK) mm22 sensitivity 10 sensitivity 10-2-2 -10 -10-3-3 eV eV22

• CERN-Gran Sasso beam M = M = OO (1000) ton (1000) ton

• Impossible with pure emulsion target (CHORUS ~ 0.8 ton , TOSCA ~ 2.5 ton)

• New technique required iron (lead)-emulsion sandwich: iron (lead)-emulsion sandwich: passive target material, emulsion for trackingpassive target material, emulsion for tracking

• Starting point : the EEmulsion CCloud CChamber (ECCECC)

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Rethinking the ECC technique

• Charm decays and hadron reinteractions in the passive material : unacceptable backgrounds using impact parameter

• Hence, no impact parameter, no decays in Fe (Pb)

• The OPERA* detector concept**

• Charm decays and hadron reinteractions in the passive material : unacceptable backgrounds using impact parameter

• Hence, no impact parameter, no decays in Fe (Pb)

• The OPERA* detector concept**

*) OOscillation PProject with EEmulsion tRRacking AApparatus

**) A. Ereditato, K. Niwa, P. Strolin, INFN/AE 97/06

- select -decays in gaps between metal plates- minimal plate thickness () , 2 emulsion sheets- measure decay “kink” in space, by emulsion tracking

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L E B E G E B E L0

5

10

15

20

25

30

35

40

45

L E B E G E B E L

Decays %

Fraction of ’s decaying in:L (lead), E (emulsion layer), B (base), G (gap), L (long kinks)

For m2 = 2 x 10-3 eV2 and 1 mm lead, 3 mm gap

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The detector

• Lead-emulsion target - element: 1 mm Pb, ES, 3 mm gap, ES1 mm Pb, ES, 3 mm gap, ES - brick: stack of 30 elements (~ 13 cm thick, 15 x 15 cmstack of 30 elements (~ 13 cm thick, 15 x 15 cm22 X-sect.) X-sect.) - module: 18 x 18 bricks ( ~ 2.8 x 2.8 m18 x 18 bricks ( ~ 2.8 x 2.8 m22 ) ) - electronic detector planes following each module (~ 5 cm thick)(~ 5 cm thick) - 300 modules: ~ 750 ton, subdivided into 10 identical supermodules~ 750 ton, subdivided into 10 identical supermodules - overall target dimensions ~ 3.5 x 3.5 x 40 m~ 3.5 x 3.5 x 40 m3 3 (x 2)(x 2)

• Muon detection - tracking in the target (electronic detectors) - magnetised iron -spectrometer downstream: sign of charge (momentum)• Calorimetry - in the target: Pb (each module ~ 5 XPb (each module ~ 5 X0 0 ) + electronic det. (RPC, straws,...)) + electronic det. (RPC, straws,...)

• p/p ~ ~ 10-20 % at 1-30 GeV/c10-20 % at 1-30 GeV/c from multiple scattering in emulsion

Preliminary design

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element brick

1mm

3 mm

150

mm

150 mm

135 mm

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front view

12.5 m

5 m

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apparatus5m

3.5m

~ 45 m

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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

• Alternative: similar emulsion as for X-ray films

• R&D on emulsion: tests on prototype ES and bricks going on in Nagoya and Fuji company

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Electronic detectors

• “Moderate” position resolution (shower center): ~ few mm (low background tracks)

• Standard large-surface trackers can be used:

Resistive Plate Chambers,

Honeycomb chambers,

Streamer tubes.....

• Need reconstruction behind each emulsion module:

(i.e. using RPC’s) ~ 7000 m~ 7000 m2 2 total detector surfacetotal detector surface

• Similar detectors may be used for the muon spectrometers

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Data and event reconstruction

• Study e-, - , h- , (possibly 3• Track localization by electronic detectors

• Start scanning from ES upstream of event in electronic detector

• General scanning and scan back in ES

• 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)

downback

Start scanning here

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interactions

• Scale reference option: 5 x 105 x 1019 19 pot/a , 75% efficiency, 220 days runpot/a , 75% efficiency, 220 days run

assume 2.5 x 102.5 x 1020 20 pot/4 yearspot/4 years

• Data: ~ 810 CC ~ 810 CC interactions/kton x 10 interactions/kton x 101919 pot pot (Gran Sasso)(Gran Sasso) ~ 15000 CC in 4 years ~ 15000 CC in 4 years (750 ton detector)(750 ton detector)

~25~25 interacting in OPERA ( interacting in OPERA (mm22 = 2 x 10 = 2 x 10-3-3 eV eV22))

~150~150 ““ ( (mm22 = 5 x 10 = 5 x 10-3-3 eV eV22))

possible improvements bydesign optimization

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detection efficiency

• Decays outside Pb (1 mm) gapgap~ ~ 0.500.50

gap depends on beam features)0.87 (0.87 ( • Kink finding efficiencykink0.84 (0.84 ( e) e) 0.89 (0.89 ( h) h)

determined by the angular cuts: (resolution) 20 < 20 < kinkkink < 500 mrad < 500 mrad (scanning & bg rejection)

• BR e, h 0.174 , 0.178 , 0.4980.174 , 0.178 , 0.498 • Fiducial cuts & alignment geomgeom~ ~ 0.930.93

Total efficiency for the 1-prong channels: 0.36(3 channel under study)

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background

h-

signal

-

D+

neutrals

- (undetected)

h+

Charm induced background

(sign of daughter only measured if muon)

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Charm b.g. to - h-, -, e-

(before vertex kinematics of candidate events)

= 0.0560.056 charm / CC

x 0.370.37 D production probability

x 0.3060.306 BR (D h + neutrals)

x 0.470.47 D decay outside Pb

x 0.860.86 kink

x 0.930.93 fiducial cuts & alignment

x 0.050.05 - CC not identified x 1490014900 CC events ~ 1.8 events (h-)

BR (charged D l + neutrals) ~ 0.0750.075

charge measured by the downstream

spectrometer (1- ~ 0.30.3)

~ 0.2 events (-)

~ 0.4 events (e-)

Total: 2.4 events from charm

Nbg(h-)

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Other backgrounds

• Prompt in the beam: negligiblenegligible (10-6 level)

• Hadron reinteractions : a few kinks in the spacer are rejected rejected by the kink angle cut (20 mrad) and by by the kink angle cut (20 mrad) and by

the detection of heavy fragmentsthe detection of heavy fragments

• , K decays (CC and NC) : events (further reduced by possiblereduced by possible

momentum cutmomentum cut)

• NC associated charm production : double decay topology: 0.4 events before the vertex kinematicsbefore the vertex kinematics

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B.G. reduction by vertex kinematics

• Before kinematical analysis of candidate events

Nbg(h-) ~ 2 events Nbg(-) + Nbg(e-) ~ 0.5 events

Nbg(associated charm) ~ 0.4 events

• Vertex kinematics: aim Nbg ~ Nbg / ~5 (to be studied)

Nbg (charm) < 1 event

Important : vertex kinematics require track before decay possible only with emulsion granularity

24Sensitivity and discovery potential

CC / x BR vert

sin2 2 ( large m2 ) < 2 x 2.3 / (14930 x 0.48 x 0.36 x 0.90)

< 2 x 10-3

m2 (full mixing) < 10-3 eV2

(90% CL)

f oscillation occurs :m2 = 2 x 10-3 eV2 ~ 10 detected events

m2 = 5 x 10-3 eV2 ~ 50 detected events

NO OBSERVED EVENTS

total b.g. :~ 1 event

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• ~ 20000 events NC+CC 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 ~1 cm2

• scan back of all found segments up to the vertex

• scanning more elaborate, special care for candidates

• exploit on-going progress and equipment for CHORUS

Emulsion scanning (1)

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Emulsion scanning (2)

• ~ 20000 events/4 years ~ 5000 /100000 bricks removed per year• aim: emulsion developed and “quasi on-line” scanning

• replace bricks (?)

• fading “regenerates” the emulsion left in place

Prompt physics analysisEmulsion experiment with a long-life

develop emulsion

27Feasibility studies, optimization and R&D (1)

• Emulsion diluted emulsion: diluted emulsion: quality vs. costquality vs. cost procurement & handling procurement & handling ES manufacturing: ES manufacturing:

dedicated pouring machine (industry?), X-ray dedicated pouring machine (industry?), X-ray filmsfilms

controlled fadingcontrolled fading

• Bricks passive material: passive material: Pb vs. Fe, radioactivityPb vs. Fe, radioactivity spacers (plastic, honeycomb, ....): spacers (plastic, honeycomb, ....):

low density, rigidlow density, rigid vacuum vs. mechanical packing (both ?) vacuum vs. mechanical packing (both ?) optimize dimensions: optimize dimensions: Montecarlo + prototype Montecarlo + prototype

teststests

• Electronic trackers define requirements: define requirements: space & time resolutionspace & time resolution optimize performance vs. cost optimize performance vs. cost

industrial production industrial production tests on prototypes: tests on prototypes: track association to emulsiontrack association to emulsion

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Feasibility studies, optimization and R&D (2)

• Apparatus design optimize module (supermodule) dimensions optimize module (supermodule) dimensions and layoutand layout

temperature and humidity control temperature and humidity control detector mass and cost detector mass and cost

spectrometer design: spectrometer design: performance requirementsperformance requirements

• Tests prototype bricks: prototype bricks: mechanics & structuremechanics & structure install bricks in the Gran Sasso Laboratory: install bricks in the Gran Sasso Laboratory:

ambient radioactivity, alignment by ambient radioactivity, alignment by cosmics, cosmics,

hit density, optimize layer thicknesshit density, optimize layer thickness beam tests: beam tests: kink efficiency, angular resolution, kink efficiency, angular resolution, vertex findingvertex finding

• R&D emulsion: emulsion: collaboration with industrycollaboration with industrypouring machines pouring machines dedicated scanning systems: dedicated scanning systems: fast general fast general

scanningscanning

• Beam optimize beam design: optimize beam design: intensity, spectrum, <E>intensity, spectrum, <E>

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A possible schedule for OPERA

• 1997 LoI: studies, conceptual design• 1998 Tests, feasibility, design,

proposal• 1999 Approval, prototypes, tests• 1999-2002 Construction• 2002 Start neutrino data taking• 2003 Early physics results

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at Gran Sasso

• Possible design: ~750 ton , 2.5 x 1020 pot (4 years)

~20000 CC+NC events

• Discovery potential: small bg, a few events are meaningful:@ Super K. (m2 = 5 x 10-3 eV2) 50 events (~1 b.g.)

• Negative search: m2 < 10-3 eV2 ; sin2 2 < 2 x 10-3 covers atm (Super Kamiokande)

• Modular structure: detector staging is possible

High sensitivity - search

explore the atmospheric neutrino signal

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ConclusionsConclusions

• Promising technique to detect - oscillation with a Long Baseline Experiment at the Gran Sasso

• Further studies, tests and R&D needed to assess the feasibility of the experiment

• Explore the parameter region m2 > 10-3 eV2

to determine the source of the atmospheric neutrino signal