Experiment Proposal - opera - Infn

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the two oscillation parameters sin 2 2θ and ∆m 2 in the two flavour mixing scheme. Given the already known constraint of nearly maximum mixing [30], OPERA can improve the determination of ∆m 2 . Because of its capability of identifying electrons and to the small ν e contamination in the CNGS beam, OPERA is also suited for a ν µ ↔ ν e oscillation search. The sensitivity to oscillations of a NC/CC measurement (where CC and NC represent the rates of events with and without a muon in the final state) is being investigated in view of a three-flavour analysis. 1.2 Oscillation searches with long baseline beams Recently, new neutrino beams and detectors have been designed to provide an E/L spectrum suitable to probe the parameter space region pointed to by atmospheric-neutrino experiments. Compared to natural sources, an accelerator-based neutrino beam offers the advantages of a higher flux and of a good purity in ν µ with known and small contaminations of other flavours. The K2K experiment [34, 35] has been commissioned in 1999. It is searching for ν µ disappearance by using the long baseline neutrino beam from KEK to Super-Kamiokande (250 km away) [36]. Given the low beam energy, which is below the kinematical threshold for τ production, K2K is not able to perform a ν τ appearance search. A significant difference between the ν µ CC rates measured in the Super-Kamiokande detector and the predictions based on extrapolations of near detector rates can be observed provided the effective ∆m 2 value is larger than about 2 × 10 −3 eV 2 . Preliminary results have been recently presented [37], consistent with the oscillation parameters determined by Super-Kamiokande with atmospheric neutrinos. At Fermilab the MINOS experiment [38] will use the NuMI beam [39] from Fermilab to the Soudan Mine, 730 km away. The high repetition rate of the 120 GeV/c Main Injector and the presence of a near detector make it suitable to perform a ν µ disappearance experiment. The granularity of the detector is too coarse to allow the flavour tagging of ν τ CC interactions but the excellent muon identification efficiency will be used to exploit the measurement of the NC/CC ratio as an indirect probe of ν τ appearance. The CNGS facility from the CERN SPS to the Gran Sasso Laboratory is planned to deliver a ν µ beam from 2005 onwards. In its present design, the beam is optimised for a ν τ appearance search, as proposed by both experiments ICANOE [40] and OPERA. The full understanding of neutrino masses and mixings is a long term programme and will certainly require the combination of many experimental efforts, as is still the case for quarks. The difficulty of the experiments require approaches from different points of view, in order to firmly assess the experimental scenario. In a more distant future, the next steps towards the precise determination of all oscillation parameters will require the availability of very intense neutrino beams and of massive detectors placed at even larger distances from the neutrino sources. Along these lines, studies for the use of muon storage rings as powerful and very pure neutrino sources are pursued [41]. 1.3 ν τ detection by the ECC technique So far only the DONUT experiment [42] has succeeded in detecting ν τ interactions, as illustrated in Fig. 2. They are identified in an ECC detector conceptually similar to that planned for OPERA; one 8
difference being the nature of the passive material, iron plates for DONUT and lead plates for OPERA. The DONUT ECC detectors were exposed to a prompt neutrino beam created by 800 GeV/c protons in the beam dump experiment E872 at FNAL. The high position resolution of nuclear emulsions, the existence of automatic readout systems (Track Selector) and the availability of fast data processing (Net Scan) are the essential ingredients of the present ECC detection technique. These advances have largely profited from the experience in the CHORUS and DONUT physics analyses. Beam-view 40 20 µm 50mrad 100mrad τ γ Hadron Unknown 0 1000 2000 150mrad ν EXP.: DONUT 3039/01910 MOD.:ECC1 Em. Fe Em. Em. Base Fe Em. Em. Base Fe Em.Em. Base Em. Base Figure 2: Detected τ event in DONUT [43]. One track, which is isolated and opposite in direction to the other charged particles, shows a kink topology after a short flight of 280 µm. The kink angle is measured to be 90 mrad. The momentum of the kink daughter is 4.6 ± 1.6 0.9 GeV/c (p t = 414 ± 144 81 MeV/c), as evaluated by multiple scattering. Nuclear emulsions are made of micro-crystals of silver halides (AgBr) as sensitive devices dispersed in a thin gelatin layer. The size of the micro crystal is ∼ 0.2 µm and is well controlled by the current industrial technologies developed for photographic films. Emulsion films have nuclear emulsion layers on both sides of a transparent plastic base. In the DONUT ECC, 100 µm thick emulsion layers are coated on both sides of a 200 µm (or 800 µm) thick plastic base. For OPERA we use 50 µm thick emulsion layers on both sides of a 200 µm thick base. This structure of the film allows to connect track segments (micro tracks) on both sides of the base. The positions and angles of the connected tracks (base tracks) are thus free from distortions in the emulsion layers. 9
Page 1 and 2: CERN/SPSC 2000-028 SPSC/P318 LNGS P
Page 3 and 4: N. Bruski, S. Buontempo, F. Carbona
Page 5 and 6: Contents 1 Introduction 5 1.1 Physi
Page 7 and 8: 6.7.1 Multiple scattering analysis
Page 9 and 10: 1 Introduction In this document we
Page 11: eactor experiments (KAMLAND [22], B
Page 15 and 16: The total energy of electrons and
Page 17 and 18: through the decay topology and its
Page 19 and 20: Figure 6: Simulated ν τ event wit
Page 21 and 22: particles above 10 MeV . One can se
Page 23 and 24: vertex position as predicted by the
Page 25 and 26: • stability and maintenance: no p
Page 27 and 28: Figure 11: Illustration of the vari
Page 29 and 30: Table 3: Expected numbers of τ and
Page 31 and 32: 3 The CNGS neutrino beam 3.1 The be
Page 33 and 34: per year of operation because the S
Page 35 and 36: ν µ at GS (p.o.t. GeV m 2 ) -1 10
Page 37 and 38: Figure 19: Generated (continuous li
Page 39 and 40: Emulsion Film + 56 (Lead + Emulsion
Page 41 and 42: The mechanical properties of the fi
Page 43 and 44: Figure 24: Film thickness distribut
Page 45 and 46: contact at different temperature an
Page 47 and 48: Figure 27: Photograph of a minimum
Page 49 and 50: entry : 85 RMS: 0.060 15 10 5 0 0 d
Page 51 and 52: [micron] 2 1 0 -1 -2 [micron] 2 1 0
Page 53 and 54: een searching for old emulsion plat
Page 55 and 56: Figure 33: Thickness distribution f
Page 57 and 58: Figure 35: RMS distribution of 472
Page 59 and 60: Figure 37: Wall support structure.
Page 61 and 62: ensures a well defined brick positi
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Figure 41: Detail of the brick mani
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The strips are 6.7 m long, 2.6 cm w
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the effective maximal length (for p
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Table 7: Characteristics of the 64-
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photomultiplier to be tested diaphr
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modate from 512 up to 5180 fibres.
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The fast shaper has a high gain in
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The Ethernet capable device provide
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R&D already performed by the MINOS
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Figure 54: Isometric view of the di
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Figure 56: Magnetic field distribut
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RPC layout 8.00 m 8.75 m Figure 58:
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formance, it is presently foreseen
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Figure 61: Drift plane arrangement
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Figure 63: Schematic view of a XPC
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Figure 64: Acceleration spectrum fo
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Figure 65: The OPERA detector shown
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Table 9: Number of electronic chann
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Adjustable gain Channel 0 Sample &
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Trigger OUT IN Discri. Time Ref. PP
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Super Module 1 Super Module 2 Super
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5 Analysis of the electronic detect
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Track segments on both the emulsion
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5.5 Brick finding efficiency The se
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Wall finding efficiency 1 0.95 0.9
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The worst case leading to the lowes
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electromagnetic showering events an
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Studies on the strategies have star
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which may enter in such a compariso
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Figure 84: The total brick finding
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Figure 86: Charge determination of
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Figure 89: Muon momentum resolution
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Figure 91: Muon momentum resolution
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Reconstructed Pion Energy N Analog
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Figure 98: The difference between r
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By using the above running modes of
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µm EXP.: DONUT 3039/01910 MOD.:ECC
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emulsion film plastic foils and edg
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200micron base 50micron emulsion la
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Figure 106: Tracking efficiency of
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a base track on film 2 a penetratin
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Long decays, defined as a decay top
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more than 60 views/s recognising al
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Table 12: Basic numbers used to des
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an area that one S-UTS can process
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unit cell L=1300micron Pb plate ( 1
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We recall that the intrinsic positi
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Figure 116: The top histograms show
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The error on θ S due to both the s
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Figure 120: Fraction of pions which
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#1 #2 #3 #4 #5 γ γ ∆θ 4= |θ 5
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Figure 124: Energy resolution for e
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Figure 126: Efficiency for γ’s t
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7 Physics performance 7.1 Electron
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7.2 Muon identification efficiency
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Table 13: Muon identification effic
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Table 14: Brick finding efficiency
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The second result is obtained from
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Figure 134: Brick-to-brick connecti
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Figure 136: Distribution of τ deca
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For long decays the overall efficie
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The φ angle is expected to peak at
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Table 19: Summary of the kinematica
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known. Because of these uncertainti
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Table 21: Expected charm background
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π− e+ γ e- e+ e- γ π− Figur
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Table 24: Estimates of the rate of
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Table 27: Expected numbers of τ an
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Table 28: Sensitivity at the 90% CL
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7.6 Determination of the oscillatio
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measurement of the ratio between ν
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Table 30: Neural network recognitio
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(mrad) 0.04 0.02 0 -0.02 -0.04 10 2
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Table 31: Radioactivity measurement
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ick. There is approximately a facto
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Figure 152: A typical PMT response
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1m π, µ 15 GeV/c mini-walls 1.6 m
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Electrons 1GeV/c 20mm Pb Number of
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tube. An Image Intensifier (II) by
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1 0 0 l = 1 1 .8 m N, p.e. 1 0 1 0
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HPD’s pixels (Fig. 162). The cook
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A complete system has been designed
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The acquisition system (VA-DAQ) use
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The upstream tracker T 1-3 between
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Figure 168: Distributions of the ap
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Figure 169: Example of a large-angl
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multiple scattering, given the smal
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9.1.3 Wall support structures An al
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Nevertheless, the possibility to us
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Figure 174: (a) 3D view of the spec
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9 p.e. and 6.9 p.e. at a distance f
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Figure 176: Neutrino induced charm
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A test programme for emulsion brick
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The space requirements in the exper
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advance. The sets of scintillator s
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Task Name Start Finish Study of mai
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11 Experimental infrastructure 11.1
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After the exposure to cosmic rays,
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on the size of these stations. A co
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Table 38: Expected contributions to
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the developed emulsions and to stan
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As the sensitivity is not limited b
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[26] M. Apollonio et al., Phys. Let
Page 269:
[89] http : //tosca.web.cern.ch/T O
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