1 The OPERA emulsion detector for a long-baseline neutrino oscillation experiment H.Shibuya Toho Univ., Japan K.Hoshino, M.Komatsu, K.Niwa Nagoya Univ., Japan S.Buontempo, A.Ereditato, G.Fiorillo, P.Migliozzi, P.Strolin Naples Univ. and INFN, Italy G.Romano Salerno 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

2 Physics process: neutrino oscillation  -    h -    n   e -   e  +  -  -   n          - + X CC  appearance esperiment direct  decay detection P osc = sin 2 2   sin 2  ( 1.27 x  m 2 ( eV 2 ) x L( km )/E( GeV ) )  m 2 min = (P osc / 2) x 1/1.27 x E/L

3 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  m 2 ~10 -2 eV 2  amiokande SuperK.  -   - e CHOOZ

4 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 ?

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 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

6 Microscope event view Emulsion to beam Good tracks appear as dots Tracking implies connection of dots in different layers ~100  m

7 Track selector ~ 100  m (emulsion beam) T

8 Aim, target mass and experimental technique  m 2 sensitivity eV 2Atmospheric neutrinos (SK)  m 2 sensitivity eV 2 M = O (1000) tonCERN-Gran Sasso beam M = O (1000) ton Impossible with pure emulsion target (CHORUS ~ 0.8 ton, TOSCA ~ 2.5 ton) New technique required iron (lead)-emulsion sandwich: passive target material, emulsion for tracking passive target material, emulsion for tracking ECCECCStarting point : the Emulsion Cloud Chamber (ECC)

9 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 ** OPERA * ) Oscillation Project with Emulsion tRacking Apparatus ** ) 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

10 Fraction of  ’s decaying in: L (lead), E (emulsion layer), B (base), G (gap), L (long kinks) For  m 2 = 2 x eV 2 and 1 mm lead, 3 mm gap

11 The detector Lead-emulsion target 1 mm Pb, ES, 3 mm gap, ES - element: 1 mm Pb, ES, 3 mm gap, ES stack of 30 elements (~ 13 cm thick, 15 x 15 cm 2 X-sect.) - brick: stack of 30 elements (~ 13 cm thick, 15 x 15 cm 2 X-sect.) 18 x 18 bricks ( ~ 2.8 x 2.8 m 2 ) - module: 18 x 18 bricks ( ~ 2.8 x 2.8 m 2 ) (~ 5 cm thick) - electronic detector planes following each module (~ 5 cm thick) ~ 750 ton, subdivided into 10 identical supermodules modules: ~ 750 ton, subdivided into 10 identical supermodules ~ 3.5 x 3.5 x 40 m 3 (x 2) - overall target dimensions ~ 3.5 x 3.5 x 40 m 3 (x 2) Muon detection - tracking in the target (electronic detectors) - magnetised iron  -spectrometer downstream: sign of charge (momentum) Calorimetry Pb (each module ~ 5 X 0 ) + electronic det. (RPC, straws,...) - in the target: Pb (each module ~ 5 X 0 ) + electronic det. (RPC, straws,...) ~ % at 1-30 GeV/c  p/p ~ % at 1-30 GeV/c from multiple scattering in emulsion Preliminary design

12 element brick 1mm 3 mm 150 mm 135 mm

13 front view 12.5 m 5 m

14 apparatus 5m 3.5m ~ 45 m

15 Emulsion No target (“bulk”) emulsion, but still ~ 13 m 3 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

16 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: ~ 7000 m 2 total detector surface (i.e. using RPC’s) ~ 7000 m 2 total detector surface Similar detectors may be used for the muon spectrometers

17 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

18  interactions 5 x pot/a, 75% efficiency, 220 days runScale reference option: 5 x pot/a, 75% efficiency, 220 days run 2.5 x pot/4 years assume 2.5 x pot/4 years ~ 810 CC interactions/kton x pot (Gran Sasso)Data: ~ 810 CC interactions/kton x pot (Gran Sasso) ~ CC in 4 years (750 ton detector) ~ CC in 4 years (750 ton detector) ~25  interacting in OPERA (  m 2 = 2 x eV 2 ) ~150“ (  m 2 = 5 x eV 2 ) possible improvements by design optimization

19  detection efficiency  gap  ~ 0.50Decays outside Pb (1 mm)  gap  ~ 0.50  gap depends on beam features) 0.87 (     0.87 (    0.84 (   e)Kink finding efficiency   kink  0.84 (   e) 0.89 (   h) determined by the angular cuts: 20 <  kink < 500 mrad (resolution) 20 <  kink < 500 mrad (scanning & bg rejection) 0.174, 0.178, 0.498BR    e, h 0.174, 0.178,  geom  ~ 0.93Fiducial cuts & alignment  geom  ~ 0.93 Total efficiency for the 1-prong channels: 0.36 (3  channel under study)

20 background h-h- signal  --  D+D+ neutrals  - (undetected) h+h+ Charm induced background (sign of daughter only measured if muon)

21 Charm b.g. to  -  h -,  -, e - (before vertex kinematics of candidate events) = charm / CC 0.37 x 0.37 D production probability x BR (D  h + neutrals) 0.47 x 0.47 D decay outside Pb 0.86 x 0.86  kink 0.93 x 0.93 fiducial cuts & alignment 0.05 x 0.05  - CC not identified x CC events ~ 1.8 events (h - ) BR (charged D  l + neutrals) ~  charge measured by the downstream 0.3 spectrometer (1-  ~ 0.3) ~ 0.2 events (  - ) ~ 0.4 events (e - ) Total: 2.4 events from charm N bg (h - )

22 Other backgrounds negligiblePrompt  in the beam: negligible (10 -6 level) rejected by the kink angle cut (20 mrad) and by the detection of heavy fragmentsHadron reinteractions : a few kinks in the spacer are rejected by the kink angle cut (20 mrad) and by the detection of heavy fragments , K decays reduced by possible (CC and NC) :  events (further reduced by possible momentum cut momentum cut) NC associated before the vertex kinematics charm production : double decay topology: 0.4 events before the vertex kinematics

23 B.G. reduction by vertex kinematics Before kinematical analysis of candidate events N bg (h - ) ~ 2 events N bg (  - ) + N bg (e - ) ~ 0.5 events N bg (associated charm) ~ 0.4 events Vertex kinematics: aim  N bg ~ N bg / ~5 (to be studied) N bg (charm) < 1 event Important : vertex kinematics require track before decay possible only with emulsion granularity

24 Sensitivity and discovery potential   CC   /     x BR  vert sin 2 2   ( large  m 2 ) < 2 x 2.3 / (14930 x 0.48 x 0.36 x 0.90) < 2 x  m 2 (full mixing) < eV 2 (90% CL)  f oscillation occurs :  m 2 = 2 x eV 2 ~ 10 detected events  m 2 = 5 x eV 2 ~ 50 detected events NO OBSERVED EVENTS total b.g. : ~ 1 event

25 ~ 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 cm 2 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)

26 Emulsion scanning (2) ~ events/4 years ~ 5000 / bricks removed per year aim: emulsion developed and “quasi on-line” scanning replace bricks (?) fading “regenerates” the emulsion left in place Prompt physics analysis Emulsion experiment with a long-life develop emulsion

27 Feasibility studies, optimization and R&D (1) diluted emulsion: quality vs. costEmulsion diluted emulsion: quality vs. cost procurement & handling procurement & handling ES manufacturing: ES manufacturing: dedicated pouring machine (industry?), X-ray films controlled fading controlled fading passive material: Pb vs. Fe, radioactivityBricks passive material: Pb vs. Fe, radioactivity spacers (plastic, honeycomb,....): spacers (plastic, honeycomb,....): low density, rigid low density, rigid vacuum vs. mechanical packing (both ?) optimize dimensions: Montecarlo + prototype tests define requirements: space & time resolution optimize performance vs. costElectronic trackers define requirements: space & time resolution optimize performance vs. cost industrial production tests on prototypes: track association to emulsion

28 Feasibility studies, optimization and R&D (2) optimize module (supermodule) dimensionsApparatus design optimize module (supermodule) dimensions and layout temperature and humidity control temperature and humidity control detector mass and cost detector mass and cost spectrometer design: performance requirements prototype bricks: mechanics & structureTests prototype bricks: mechanics & structure install bricks in the Gran Sasso Laboratory: install bricks in the Gran Sasso Laboratory: ambient radioactivity, alignment by cosmics, ambient radioactivity, alignment by cosmics, hit density, optimize layer thickness hit density, optimize layer thickness beam tests: kink efficiency, angular resolution, kink efficiency, angular resolution, vertex finding vertex finding emulsion: collaboration with industryR&D emulsion: collaboration with industry pouring machines dedicated scanning systems: fast general scanning optimize beam design: intensity, spectrum, Beam optimize beam design: intensity, spectrum,

29 A possible schedule for OPERA 1997 LoI: studies, conceptual design 1998 Tests, feasibility, design, proposal 1999 Approval, prototypes, tests Construction 2002 Start neutrino data taking 2003 Early physics results

30 at Gran Sasso Possible design: ~ 750 ton, 2.5 x pot (4 years) ~20000  CC+NC events Discovery potential: small bg, a few events are Super K. (  m 2 = 5 x eV 2 )  50 events (~1 b.g.) Negative search:  m 2 < eV 2 ; sin 2 2   < 2 x  covers atm (Super Kamiokande) Modular structure: detector staging is possible High sensitivity  -  search explore the atmospheric neutrino signal

31 Conclusions 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  m 2 > eV 2 to determine the source of the atmospheric neutrino signal