MONOLITH is a proposed massive magnetized tracking calorimeter at the Gran
Sasso laboratory in Italy, optimized for the detection of atmospheric muon
neutrinos. The main goal is to test the neutrino oscillation hypothesis through
an explicit observation of the full first oscillation swing. The sensitivity
range for this measurement comfortably covers the entire Super-Kamiokande
allowed region. Other measurements include studies of matter effects, the NC/CC
and neutrino/anti-neutrino ratio with atmospheric neutrinos and auxiliary
measurements from the CERN to Gran Sasso neutrino beam. Depending on approval,
data taking with part of the detector could start in 2005. The MONOLITH
detector and its performance are described.Comment: 8 pages, contribution to Les rencontres de Physique de la Vallee
  d'Aoste, March 200

de Fatis, Tommaso Tabarelli

English

arXiv

MONOLITH is a proposed massive magnetized tracking calorimeter at the Gran Sasso laboratory in Italy, optimized for the detection of atmospheric muon neutrinos. The main goal is to test the neutrino oscillation hypothesis through an explicit observation of the full first oscillation swing. The sensitivity range for this measurement comfortably covers the entire Super-Kamiokande allowed region. Other measurements include studies of matter effects, the NC/CC and neutrino/anti-neutrino ratio with atmospheric neutrinos and auxiliary measurements from the CERN to Gran Sasso neutrino beam. Depending on approval, data taking with part of the detector could start in 2005. The MONOLITH detector and its performance are described

Tabarelli de Fatis, T

CERN Document Server

MONOLITH: A HIGH RESOLUTIONNEUTRINO OSCILLATION EXPERIMENTTommaso Tabarelli de FatisI.N.F.N. - Sezione di MilanoPiazza della Scienza 3, I-20126 Milano, Italyfor the MONOLITH CollaborationAbstractMONOLITH is a proposed massive magnetized tracking calorimeter at the GranSasso laboratory in Italy, optimized for the detection of atmospheric muon neu-trinos. The main goal is to test the neutrino oscillation hypothesis through anexplicit observation of the full rst oscillation swing. The m2 sensitivity range forthis measurement comfortably covers the entire Super-Kamiokande allowed region.Other measurements include studies of matter eects, the NC/CC and ν/ν ratiowith atmospheric neutrinos and auxiliary measurements from the CERN to GranSasso neutrino beam. Depending on approval, data taking with part of the detectorcould start in 2005. The MONOLITH detector and its performance are described.Talk given at“Les Rencontres de Physique de la Valle´e d’Aoste”,La Thuile (Italy), March 4-10th, 20011 IntroductionThe current observations of atmospheric neutrinos 1, 2) are all consistent with atwo-state neutrino oscillation in the νµ ! ντ channel. However, the experimentalresolution is too poor to clearly resolve the oscillation pattern and models with non-standard νµ disappearance dynamics3, 4, 5) are not ruled out by data. Moreover,scenarios involving admixtures of the electron neutrino (3ν) and of an hypotheticalsterile neutrino (4ν), that would accommodate the current phenomenology, are notfully constrained 6) and even in the simple two-neutrino oscillation picture, a widerange of oscillation parameters is still allowed.MONOLITH 7) is a proposal for a detector explicitly designed to establishthe occurrence of oscillations in atmospheric neutrinos and to discriminate alter-native explanations, through the observation of the full rst oscillation swing inνµ disappearance. This also yields a signicantly improved measurement of theoscillation parameters. The occurrence of matter eects in atmospheric neutrino os-cillations can also be tested with MONOLITH, exploiting its capability to identifythe lepton charge of muon neutrinos. This will constrain 3ν and 4ν scenarios andoer the unique opportunity to test the neutrino mass hierarchy, before the adventof ν-factories.If approved, the detector will be located at the Gran Sasso Laboratoryin Italy, where the measurement of atmospheric neutrinos can be supplemented bymeasurements in the CNGS beam from CERN.2 The MONOLITH detectorMONOLITH is a massive tracking calorimeter with a coarse structure and magneticeld. A large modular structure has been chosen for the detector (gure 1). Onemodule consists in a stack of 120 horizontal 8 cm thick iron planes with a surfacearea of 14.5 15 m2, interleaved with 2 cm planes of sensitive elements. The heightof the detector is about 13 meters. The magnetic eld conguration is also shownin gure 1; iron plates are magnetized at a magnetic induction of  1.3 T. Thedetector consists of two modules and its total mass exceeds 34 kt.Glass Spark Counters (resistive plate chambers with glass electrodes) havebeen chosen as active detector elements. They provide two coordinates with a pitchof 3 cm, and a time resolution of order 1 ns. An external veto made of scintillationcounters is foreseen to reduce the background from cosmic ray muons.30.0 m13.1 m14.5 m B BFigure 1: Schematic view of the MONOLITH detector. The arrangement of the magneticeld is also shown.3 Measurements with atmospheric neutrinos3.1 Test of νµ disappearance dynamicsOscillation studies with atmospheric neutrinos requires that the energy E and thebaseline L of the incoming neutrino be measured in each event. The latter is relatedto the neutrino direction and may be estimated in charged-current (CC) interactionsfrom the direction of the outgoing lepton. MONOLITH, with a mass comparable toSuper-Kamiokande, has a much larger acceptance to muons at high energies, wherethe muon direction gives a better estimate of the neutrino direction. This results ina considerably improved L/E resolution and overcomes the main limitation in thesensitivity to the oscillation pattern of current atmospherics neutrino experiments.High energy atmospheric neutrinos bear another advantage: they representan ideal source for a disappearance experiment, since they naturally comprise thenear (down-going neutrinos) and a far (up-going neutrinos) positions1. Thus adetailed prior knowledge of neutrino fluxes is not required. The atmospheric neutrinobeam is also characterized by a wide range in L/E (from about 1 km/GeV to 105km/GeV), that gives access to a very large range of oscillation parameters and, inparticular, results in a unique sensitivity to oscillations if m2 is low.Figure 2 shows the expected L/E distributions of up-going neutrinos and ofthe reference sample of down-going neutrinos and their ratio, for νµ ! ντ oscillationwith parameters around the current best-t to Super-Kamiokande data. The gurealso shows the allowed regions of the oscillation parameter space of the experiment1MONOLITH has an eective threshold on νµ-CC events around 3 GeV, where the asymmetryof atmospheric neutrino fluxes, mainly due to geomagnetic eects, is below the percent level 8).Figure 2: Results of the L/E analysis on a simulated sample in the presence of νµ ! ντoscillations, with parameters m2 = 2  10−3 eV2 and sin2(2) = 1.0. The gure showsfrom left to right: the L/E spectrum of up-going muon neutrino events (hatched area)and the reference spectrum of down-going muon neutrino events, which are assigned thebaseline L they would have travelled if they were produced with a nadir angle equal to theobserved zenith angle 9) (open area); their ratio with the best-t of νµ ! ντ oscillationsuperimposed; the result of the t with the corresponding allowed regions for oscillationparameters at 68%, 90% and 99% C.L.. The simulated statistics correspond to 25 yearsof exposure, errors and sensitivity contours correspond to four years.after four years of exposure.An oscillation pattern is visible, at clear variance with the unconventionalinterpretations 3, 4, 5) of Super-Kamiokande data, which share the feature of theabsence of a rst clear dip in the L/E distribution. A detailed analysis reveals thatif the true process is oscillations, the alternative hypotheses can be rejected withmore than 99% eciency at 95% C.L., over the entire region of parameters allowedby Super-Kamiokande (see Fig. 3). The clearness of the oscillation pattern alsoresults in a signicantly improved measurement of the oscillation parameters. Aprecision on m2 better than 10% is anticipated (Fig. 3).3.2 Detection of matter induced eectsThe very long baselines available with atmospheric neutrinos oer the possibility tosearch for Earth-induced matter eects. In that endeavour, atmospheric neutrino10-410-310-210-10.6 0.7 0.8 0.9 1sin2(2Θ)∆m2  (eV2 )90% C.L. allowed regionsKamiokandeSuper-KamiokandeMONOLITH00.020.040.060.080.10.120.14precision on ∆m2precision on sin2(2Θ)0.90.920.940.960.9811 10∆m2 (10-3 eV2)efficiency for decay modelrejection at 95% C.L.Figure 3: Left: Expected allowed regions of νµ−ντ oscillation parameters for MONOLITHafter four years of atmospheric neutrino exposure. The results of the simulation for m2 =1, 2, 3, 710−3 eV2 and maximal mixing are shown. The 90% allowed regions for νµ ! ντoscillations of Super-Kamiokande 2) and Kamiokande 10) experiments are also shown.Right: MONOLITH expected precision on oscillation parameters and discrimination poweragainst the decay model of Ref. 3).experiments are not contested by current and planned conventional accelerator beamexperiment, whose baselines are too short for a signicant eect.Matter eects can play an important role if there are signicant contribu-tions of νe or νsterile to atmospheric neutrino oscillations. The non-observation oflarge matter eects has been already exploited by Super-Kamiokande to exclude thepure νµ−νsterile oscillation hypothesis at 99% C.L. 1, 2). For a contribution of non-maximal νµ − νsterile oscillations, matter eects would also manifest themselves indierences in the oscillation patterns for neutrinos and anti-neutrinos. Such dier-ences could be measured with MONOLITH 7), thanks to its capability to identifythe muon charge, and could yield important constraints on hybrid oscillation sce-narios 11, 12).Such eects could be detectable even in standard three flavour oscillationscenarios 13). A subdominant νe mixing could sizeably modify the νµ transitionprobability in particular regions of phase space where the νµ ! νe transition becomes10-410-310-210-210-11sin2(2Θ13)∆m2  (eV2 )CHOOZexcludedSK allowedMONOLITH 200 ktyMONOLITH 400 ktyFigure 4: Region of oscillation parameters in the 3ν scenario over which the sign ofm2 can be determined at 90% C.L. after 200 kty and 400 kty of MONOLITH exposure.The regions excluded by CHOOZ results and allowed by Super-Kamiokande data are alsoshown.resonant in matter. Depending on the sign of m2, such eects occur either forneutrinos or for anti-neutrinos only. By comparing the neutrino and anti-neutrinodistributions in MONOLITH, the sign of m2, and therefore the neutrino masshierarchy, could be determined if a signal would be observed.Figure 4 shows a preliminary estimate of the region of oscillation param-eters over which the sign of m2 can be determined at 90% C.L. after 200 ktyof MONOLITH exposure. The sensitivity achievable in a long-term run (or witha larger detector), corresponding to an exposure of 400 kty, is also shown. Forcomparison, the region excluded by CHOOZ 15) and the region allowed by Super-Kamiokande are displayed. This analysis assumes one mass scale dominance foratmospheric neutrinos (i.e. m2 = m23−m21,2) and maximum mixing in the (2,3) sec-tor, as suggested by Super-Kamiokande data, and no prior knowledge of sin2(213).The latter parameter can also be constrained by MONOLITH over a region that willbe partly accessible to MINOS 16) and fully accessible to long term low-energy beamprojects searching for the subdominant νµ ! νe transition 17). These experiments,however, can not measure the sign of m2.4 Measurements with neutrino beams4.1 Oscillation studies with the CNGS beamThe CNGS beam 14) from CERN to Gran Sasso is optimized for ντ appearanceexperiments and the energy spectrum is somewhat too high to allow the detectionof the rst entire oscillation swing in a disappearance experiment. Nonetheless,MONOLITH can reconstruct with high eciency and good resolution about 40000νµ charged-current interactions per year. The systematic error, mainly related to theknowledge of the beam spectra, need to be suitably controlled for a disappearancemeasurement on the CNGS beam. This is partly achieved in the measurement of theneutral to charged current ratio (NC/CC). In this method looser requirements on themuon reconstruction may be applied and about 100000 events per year (CC+NC)can be reconstructed and classied according their length and shape. Both thesemethod can be used to complement the disappearance measurements with atmo-spheric neutrinos, in particular if m2 is high.4.2 Measurements at a neutrino factoryIn the long term, MONOLITH could be used as a target detector in a potential neu-trino factory beam. Neutrino beams from future muon storage rings 18) (neutrinofactories) will be essentially pure beams of either νµ+νe or νµ+νe. The occurrence ofνe− νµ or νe− ντ oscillations would manifest itself via the appearance of wrong signmuons. It has been checked that MONOLITH, with good muon charge separationand momentum measurement, is well suited for the observation of such oscillations.Neutrino factories will in particular oer the possibility to measure the 13mixing angle, the sign of m2 through matter eects if not observed earlier and,depending on which of the solar neutrino solutions is correct, it might also open theway for the study of CP violation in the neutrino system.5 ConclusionsMONOLITH is a 34 kt magnetized iron tracking calorimeter proposed for atmo-spheric neutrino measurements at the Gran Sasso Laboratory in Italy. Its main goalis the proof of the neutrino oscillation hypothesis through the explicit observationof a sinusoidal oscillation pattern. Other goals include tests of the neutrino masshierarchy in 3ν and 4ν scenarios, trough the investigation of potential matter eects,and auxiliary measurements in the CERN to Gran Sasso beam. In the long term,the detector could also be used in a potential neutrino factory beam.References1. Super-Kamiokande Coll., Y. Fukuda et al., Phys. Rev. Lett. 85 (2000) 3999.2. T. Toshito, (Super-Kamiokande Coll.), hep-ex/0105023, May 2001 (to be pub-lished in the proceedings of XXXVIth Rencontres de Moriond)3. V. Barger et al., Phys. Lett. B 462 (1999) 109.4. E. Lisi, A. Marrone, and D. Montanino, Phys. Rev. Lett. B 85 (2000) 1166.5. R. Barbieri, P. Creminelli, and A. Strumia, Nucl. Phys. B 585 (2000) 28.6. G.L. Fogli, E. Lisi and A. Marrone, hep-ph/0105139, May 2001.7. MONOLITH Proposal, LNGS P26/2000, CERN/SPSC 2000-031, August 2000(available at http://castore.mib.infn.it/monolith/proposal/).8. P. Lipari, T. K. Gaisser and T. Stanev, Phys. Rev. D 58 (1998) 073003;G. Battistoni and P. Lipari, hep-ph/9807475.9. P. Picchi and F. Pietropaolo, ICGF RAP. INT. 344/1997, Torino 1997, (CERNpreprint SCAN{9710037).10. Kamiokande Collaboration, Y. Fukuda et al., Phys. Lett. B 335 (1994) 237.11. E. Lisi, Nucl. Phys. Proc. Suppl. 91 (2001) 167, and hep-ph/0009269.12. O. Yasuda, Proceedings of Neutrino Factory workshop NuFACT’00, Monterey,CA, USA, May 21-26, 2000, and hep-ph/0007076.13. M.C. Ba~nuls, G. Barenboim and J. Bernabeu, CERN-TH/2001-032 and hep-ph/0102184, February 2001.14. K. Elsener (editor), CERN 98-02 and INFN/AE-98/05, May 1998;R. Bailey et al., CERN-SL-99-034-DI, June 1999.15. CHOOZ Collaboration, M. Apollonio et al., Phys. Lett. B 420 (1998) 397;CHOOZ Collaboration, M. Apollonio et al., Phys. Lett. B 466 (1999) 415.16. A. Para, hep-ph/0005012, May 2000.17. T. Kobayashi, These Proceedings.18. A. Blondel, These Proceedings.

MONOLITH: a high resolution neutrino oscillation experiment

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