MONOLITH is a proposed massive (34 kt) magnetized tracking calorimeter at the
Gran Sasso laboratory in Italy, optimized for the detection of atmospheric muon
neutrinos. The main goal is to establish (or reject) the neutrino oscillation
hypothesis through an explicit observation of the full first oscillation swing.
The Delta m^2 sensitivity range for this measurement comfortably covers the
complete Super-Kamiokande allowed region. Other measurements include studies of
matter effects and the NC/CC and anti-nu/nu ratio, the study of cosmic ray
muons in the multi-TeV range, and auxiliary measurements from the CERN to Gran
Sasso neutrino beam. Depending on approval, data taking with part of the
detector could start in 2004. The detector and its performance are described,
and its potential later use as a neutrino factory detector is addressed.Comment: 6 pages. Contribution to NUFACT'00 neutrino factory workshop,
  Monterey, CA, USA, May 22-26, 200

A Geiser

Barger

De Rujula

Fukuda

English

arXiv

MONOLITH is a proposed massive (34 kt) magnetized tracking calorimeter at the Gran Sasso laboratory in Italy, optimized for the detection of atmospheric muon neutrinos. The main goal is to establish (or reject) the neutrino oscillation hypothesis through an explicit observation of the full first oscillation swing. The Delta m^2 sensitivity range for this measurement comfortably covers the complete Super-Kamiokande allowed region. Other measurements include studies of matter effects and the NC/CC and anti-nu/nu ratio, the study of cosmic ray muons in the multi-TeV range, and auxiliary measurements from the CERN to Gran Sasso neutrino beam. Depending on approval, data taking with part of the detector could start in 2004. The detector and its performance are described, and its potential later use as a neutrino factory detector is addressed

Geiser, A

CERN Document Server

August 4, 2000The MONOLITH ProjectA. Geiser, Hamburg Universityfor the MONOLITH Collaboration(Massive Observatory for Neutrino Oscillations or LImits on THeir existence)Bologna, Bonn, CNR Torino, Columbia, LNF Frascati, Hamburg, HumboldtBerlin, INR Moscow, L’Aquila, LNF Frascati, LNGS Gran Sasso, MEPhIMoscow, Milano, Mu¨nster, Napoli, Roma, Torino, TunisAbstractMONOLITH is a proposed massive (34 kt) magnetized tracking calorimeter at theGran Sasso laboratory in Italy, optimized for the detection of atmospheric muon neu-trinos. The main goal is to establish (or reject) the neutrino oscillation hypothesisthrough an explicit observation of the full first oscillation swing. The ∆m2 sensitiv-ity range for this measurement comfortably covers the complete Super-Kamiokandeallowed region. Other measurements include studies of matter effects and the NC/CCand ν¯/ν ratio, the study of cosmic ray muons in the multi-TeV range, and auxiliarymeasurements from the CERN to Gran Sasso neutrino beam. Depending on approval,data taking with part of the detector could start in 2004. The detector and its per-formance are described, and its potential later use as a neutrino factory detector isaddressed.Contribution to the NuFACT’00 neutrino factory workshop, Monterey, California, USA,May 22-26, 200030.0 m13.1 m14.5 m B BFigure 1: Schematic view of the MONOLITH Detector. The arrangement of the magnetic field isalso shown.1 IntroductionWhile the cumulative evidence for neutrino oscillations is very striking, the nal proof thatthe observed anomalies are actually due to neutrino oscillations is still outstanding. In par-ticular, the current observations of atmospheric neutrinos [2, 3] are all consistent with thehypothesis of maximal νµ oscillations, but do not yet exclude some alternative unconven-tional explanations [4, 5]. The main physics goal of the MONOLITH experiment [1] is toestablish the occurrence of neutrino oscillations in atmospheric neutrinos through the ex-plicit observation of the full rst oscillation swing in νµ disappearance [6], and to investigateand presumably exclude alternative explanations. This also yields a signicantly improvedmeasurement of the oscillation parameters with respect to previous measurements.The MONOLITH detector will be located at the Gran Sasso Laboratory in Italy, andthe measurement of the oscillation pattern can be supplemented by measurements in theCERN to Gran Sasso neutrino beam. A proposal is currently in preparation [1]. If approvedpromptly, a rst part of the detector could be operational towards the end of 2004. Thephysics results described in the following sections correspond to an exposure of 4 years withthe full detector.2 The MONOLITH detectorThe goals quoted above can be achieved with a high-mass tracking calorimeter with a coarsestructure and magnetic eld. A large modular structure has been chosen for the detector(gure 1). One module consists in a stack of 120 horizontal 8 cm thick iron planes with asurface area of 15 15 m2, interleaved with 2 cm planes of sensitive elements. The height ofthe detector is thus 12 meters. Thinner plates, 2 and 4 cm thick, were also considered in thepast, however the 8 cm plate thickness resulted to be best compromise between physics resultand detector costs. The magnetic eld conguration is also shown in gure 1; iron platesare magnetized at a magnetic induction of  1.3 T. The detector consists of two modules.Optionally, the downstream module could be complemented by an end cap of vertical planesto improve the performance for non-contained muons from the CNGS beam. The total massof the detector exceeds 34 kt. Glass Spark Counters (resistive plate chambers with glasselectrodes) have been chosen as active detector elements. They provide two coordinates1with a pitch of 3 cm, and a time resolution of 2 ns. Finally, an external veto made ofscintillation counters reduces the background from cosmic ray muons.3 Observation of neutrino oscillation patternIn the two flavour approximation, the survival probability for neutrino oscillations in vacuumcan be expressed by the well known formula P (L/E) = 1 − sin2(2) sin2(1.27 m2 L/E)where L is the distance travelled in km, E is the neutrino energy in GeV,  is the neutrinomixing angle, and m2 is the dierence of the mass square eigenvalues expressed in eV2.00.20.40.60.811.21.410 10 2 10 3 10 4L/E (km/GeV)Data/MCSuper-KamiokandeFigure 2: Left: L/E distribution from Super-Kamiokande [3] compared to the best fit oscillationhypothesis (continous line), and to a parametrization corresponding to the neutrino decay modelof ref. [5] (dashed line). The oscillations are smoothed out by detector resolution. Right: L/Edistribution to be expected from MONOLITH for ∆m2 = 3  10−3 eV2 compared to the bestfit oscillation hypothesis (oscillating line) and to the corresponding best fit of the neutrino decaymodel of ref. [5] (smooth threshold effect).However, none of the experiments which have yielded indications for neutrino oscillationshave so far succeeded to measure an actual sinusoidal oscillation pattern. Figure 2 showsthe L/E distribution of Super-Kamiokande [3] compared to the expectation for neutrinooscillations and to a functional form suggested by a recent neutrino decay model [5]. Once thedetector resolution is taken into account, the two hypotheses are essentially indistinguishable[5]. Even though the current evidence is very suggestive of neutrino oscillations, a moreprecise measurement of the oscillation pattern is the only way to actually prove the oscillationhypothesis for atmospheric neutrinos. The crucial issue here is to prove that muon neutrinosdo not only disappear, but actually reappear at some larger L/E.MONOLITH is explicitly designed to ll this gap. Having a similar mass (26 kt ducial)as Super-Kamiokande, signicantly larger acceptance at high neutrino energies and betterL/E resolution, the experiment is optimized to observe the full rst oscillation swing, in-cluding νµ \reappearance". Therefore, the oscillation hypothesis can be clearly distinguished2from other hypothesis which yield a pure disapperance threshold behaviour (Figure 2).Furthermore, the sensitivity is almost independent of the oscillation parameters (Fig. 3).This is in contrast to MINOS, which can do a similar measurement at the highest allowedm2 if the low energy beam is used [8], but has a hard time to observe a reappearance signalin the lower m2 range. The good L/E resolution can be used to signicantly improve themeasurement of the oscillation parameters over the full allowed range (Fig. 4). The system-atic error can be reduced by comparing the upward neutrino rate with the correspondingdownward rate \mirrored" in L/E (Fig. 3). Finally, if δm2 is high, measurements of νµ dis-appearance in the CERN to Gran Sasso beam could complement the atmospheric neutrinomeasurements (Fig. 4) if the systematic error can be suitably controlled.4 Other physics topicsProvided that the neutrino oscillation hypothesis is conrmed, another goal of the experimentis to further investigate the nature of these oscillations. Depending on the oscillation param-eters, oscillations into active (ντ ) or sterile (νs) neutrinos can be distinguished through theirdierent eects on the up/down ratio of neutral current (NC)-like events, and/or throughthe presence or absence of matter eects yielding a distortion of the observed oscillationpattern as a function of energy and/or muon charge.Even in the absence of sterile neutrinos, matter eects are present in the case of a smallcontribution from νµ − νe oscillations at the \atmospheric" m2. The corresponding MSWresonance might be observable [11] as a localized νµ rate suppression either in νµ or in νµ.Due to its ability of in situ measurement of the energy of every muon in the multi-TeVrange, MONOLITH will also be a unique facility for pioneer investigations of cosmic raymuons in the unexplored 100 TeV energy region. The results of these studies will giveinformation which is relevant for the solution of the problem of the knee in the cosmic rayenergy spectrum.Other potential physics topics include studies of the primary atmospheric neutrino flux,the search for astrophysical point sources, and a search for a neutrino \line" from WIMPannihilation in the center of the earth.5 MONOLITH at a neutrino factoryNeutrino beams from future muon storage rings [13] (neutrino factories) will be essentiallypure beams of either νµ + νe or νµ + νe. The occurence of νe − νµ or νe − ντ oscillationswould therefore manifest itself via the appearance of wrong sign muons. A massive mag-netized iron detector like MONOLITH, with good muon charge separation and momentummeasurement, could therefore be well suited [14] for the observation of such oscillations. Aspointed out in [15, 16] this kind of beam will in particular oer the possibility to measurethe θ13 mixing angle, currently only constrained by the Super-Kamiokande and CHOOZresults, and the sign of m2 through matter eects. Depending on which of the solarneutrino solutions is correct it might also open the way for the study of CP violation inthe neutrino system. Interestingly, the optimization of detectors for the neutrino factory,3focusing on wrong sign muon appearance measurements, has yielded a detector [14] whosebasic parameters are very similar to those of MONOLITH. This is true in particular when thesource is far enough away to impinge at a sizeable angle from below (horizontal geometry ofMONOLITH). For instance, a beam from Fermilab (L=7300 km) would impinge at an angleof 35o, and be almost aligned with the Gran Sasso hall axis, and therefore perpendicular tothe magnetic eld axis. The results obtained in the physics studies of ref. [12] concerningthe measurements of θ13, sign of m2, and CP violation therefore qualitatively apply toMONOLITH used as a neutrino factory detector. Of course the potential timescale of aneutrino factory is quite dierent from the one of the current atmospheric neutrino program.Nevertheless, it might be interesting to consider that such a facility might become realitywithin the lifetime of the MONOLITH project, and that its useful life might be extendedaccordingly.6 ConclusionsMONOLITH is a 34 kt magnetized iron tracking calorimeter proposed for atmospheric neu-trino measurements at the Gran Sasso Laboratory in Italy. Its main goal is the proof of theneutrino oscillation hypothesis through the explicit observation of a sinusoidal oscillationpattern (νµ reappearance). Other goals include auxiliary measurements in the CERN toGran Sasso beam, and the investigation of potential νµ − νe and νµ − νs contributions. Inthe long term, the detector could also be used in a potential neutrino factory beam.References[1] MONOLITH Progress Report, LNGS-LOI 20/99, CERN/SPSC 99-24, August 1999;MONOLITH Proposal, LNGS P26/2000, CERN/SPSC 2000-031, August 2000;M. Ambrosio et al., The MONOLITH Prototype, Proceedings of the Bari RPC work-shop, October 1999, ftp://netview.ba.infn.it/rpc/proceedings/gustavino.ps, submittedto Nucl. Instr. and Meth.[2] Super-Kamiokande Collaboration, Y. Fukuda et al., Phys. Rev. Lett. 81 (1998) 1562;Super-Kamiokande Collaboration, Y. Fukuda et al., Phys. Lett. B 436 (1998) 33;Super-Kamiokande Collaboration, Y. Fukuda et al., Phys. Lett. B 433 (1998) 9.[3] H. Sobel (Super-Kamiokande Collaboration), Proceedings of XIX International Con-ference on Neutrino Physics and Astrophysics (Neutrino 2000), Sudbury, Canada, June16-21, 2000.[4] R. Barbieri et al., P. Creminelli, and A. Strumia, IFUP-TH-2000-00, hep-ph/0002199,February 2000;E. Lisi, A. Marrone, and D. Montanino, hep-ph/0002053, February 2000.[5] V. Barger et al., Phys. Lett. B 462 (1999) 109.[6] G. Mannocchi et al., CERN/OPEN-98-004.4[7] A. Curioni et al., hep-ph/9805249;M. Aglietta et al., LNGS-LOI 15/98, CERN/SPSC 98-28, SPSC/M615, Oct. 1998.[8] S. Wojcicki, Proceedings of Neutrino ’98, Takayama, Japan, June 4-9, 1998.[9] Kamiokande Collaboration, Y. Fukuda et al., Phys. Lett. B 335 (1994) 237.[10] K. Elsener (editor), CERN 98-02 and INFN/AE-98/05, May 1998;R. Bailey et al., CERN-SL-99-034-DI, June 1999.[11] A. Geiser, Future Atmospheric Neutrino Detectors, Proceedings of XIX InternationalConference on Neutrino Physics and Astrophysics (Neutrino 2000), Sudbury, Canada,June 16-21, 2000.[12] C. Albright et al., FERMILAB-FN-692, May 2000.V. Barger et al., hep-ph/0003184, March 2000, hep-ph/0004208, April 2000.A. Cervera et al., hep-ph/0002108, February 2000.A. Bueno, M. Campanelli, and A. Rubbia, hep-ph/0005007, May 2000.M. Freund, P. Huber, and M. Lindner, TUM-HEP-373/00, hep-ph/0004085, April2000.[13] D. Cline and D. Neuer, AIP Conf. Proc. 68 (1980) 846; reproduced in AIP Conf.Proc. 352 (1996) 10;S. Geer, Phys. Rev. D 57 (1998) 6989; Erratum-ibid. D 59 (1999) 039903.[14] J.J. Gomez-Cadenas and A. Cervera-Villanueva, talks given at ν-Fact ’99, Lyon, 5-9July 1999.[15] A. De Rujula, M.B. Gavela and P. Hernandez, Nucl. Phys. B 547 (1999) 21.[16] V. Barger, S. Geer and K. Whisnant, hep-ph/9906487.5Figure 3: Results of the L/E analysis on a simulated sample in the presence of νµ ! νx oscillations,with parameters ∆m2 = 2  10−3 eV2 and sin2(2Θ) = 1.0 (top) and ∆m2 = 5  10−3 eV2 andsin2(2Θ) = 1.0. The figures show from left to right: the L/E spectrum of upward muon neutrinoevents (hatched area) and the L/E “mirrored” spectrum of downward muon neutrino events (openarea); their ratio with the best-fit superimposed and the result of the fit with the correspondingallowed regions for oscillation parameters at 68%, 90% and 99% C.L.; artist’s view of the mirrorneutrino path length: downward going neutrinos (zenith angle θ < pi/2) are assigned the distancethey would have travelled if θ = pi − θ.6Figure 4: Left: Expected allowed regions of νµ − ντ oscillation parameters for MONOLITH afterfour years of atmospheric neutrino exposure. The results of the simulation for ∆m2 = 0.7, 2, 5, 3010−3 eV2 and maximal mixing are shown. Middle: MONOLITH exclusion curves at 90% and 99%C.L. after one or 4 years of data taking assuming no oscillations. The full (dashed) black line showsthe results of the Super-Kamiokande [3] (Kamiokande [9]) experiment. Right: Example for theexpected L/E distribution (νµ survival probability) in MONOLITH with 2 years of data taking ofatmospheric neutrinos and 1 year with the CERN-Gran Sasso neutrino beam for ∆m2 = 5 10−3eV2 (points). Beam neutrinos dominate the L/E region below 102 km/GeV. For L/E > 102 km/GeVonly atmospheric neutrinos contribute. Only statistical errors are shown.7

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