I will present the status of the long baseline neutrino oscillation
experiment MINOS at Fermi National Accelerator Laboratory (Fermilab). I will
summarize the status of the detector and beam construction, the expected event
rates and sensitivity to physics. I will also comment on possible future plans
to improve the performance of the experiment.Comment: Invited talk at the Seventh International Workshop on Tau Lepton
  Physics (TAU02), Santa Cruz, Ca, USA, Sept 2002, 7 pages, 6 figures, LaTeX
  Higher res figures at http://minos.phy.bnl.gov/~diwan/tau02_th08.p

Adamson

Ahmad

Apollonio

Athanassopoulos

Ayres

Beavis

Diwan

Fukuda

Hylen

Kajita

Lang

Marciano

Mcdonald

Milind V. Diwan

English

arXiv

Crossref

Status of the MINOS experiment

We report on the status of the MINOS long baseline neutrino experiment presently under construction at the Fermi National Accelerator Laboratory and the Soudan mine. There is growing evidence that the solar neutrino and atmospheric neutrino anomalies [1] are the result of neutrino oscillations. The MINOS experiment is a long baseline neutrino oscillation experiment designed to study the region of parameter space indicated by the SuperKamiokande atmospheric neutrino results [2]. The experiment consists of two detectors, one with a mass of 980 tons located at Fermilab (the near detector) and the other of mass 5400 tons located 731 km away in the Soudan mine in northern Minnesota (the far detector). The third component is the neutrino beam which is currently under construction at Fermilab

Buckley-Geer, Elizabeth

UNT (University of North Texas) Digital Library

Fermilab FERMILAB-Conf-01/451-E  March 2003Status of the MINOS ExperimentElizabeth Buckley-Geer 1Fermi National Accelerator Laboratory, P.O. Box 500, Batavia, Il 60510, USAAbstractWe report on the status of the MINOS long baseline neutrino experiment presentlyunder construction at the Fermi National Accelerator Laboratory and the Soudanmine.Key words: Neutrino oscillationsPACS: 14.60.Pq1 IntroductionThere is growing evidence that the solar neutrino and atmospheric neutrinoanomalies [1] are the result of neutrino oscillations. The MINOS experimentis a long baseline neutrino oscillation experiment designed to study the regionof parameter space indicated by the SuperKamiokande atmospheric neutrinoresults [2]. The experiment consists of two detectors, one with a mass of 980tons located at Fermilab (the near detector) and the other of mass 5400 tonslocated 731 km away in the Soudan mine in northern Minnesota (the fardetector). The third component is the neutrino beam which is currently underconstruction at Fermilab.2 The Neutrino beamA 120 GeV proton beam from the Fermilab Main Injector strikes a carbontarget. The pions are focussed by two magnetic horns and allowed to decay ina 670 m evacuated pipe. A prototype of the rst horn has been built and its1 Presented on behalf of the MINOS Collaboration at the NUFACT01 Workshop,Tsukuba, Japan, 24-30 May 2001.Preprint submitted to Elsevier Science 11 September 2001measured magnetic properties agree very well with calculations. The targetand second horn are moveable enabling three dierent neutrino beam spectrato be produced. The best t from the SuperKamiokande data [2] for m2 is2:510 3eV 2 which means that with a baseline of 731 km the rst oscillationmaximum occurs at about 2 GeV. This corresponds well to the low energybeam spectrum which has its maximum at about this energy. This option hasbeen chosen for the startup of the experiment.3 The far detectorThe far detector is an 8 m diameter octagonal tracking calorimeter constructedof 486 layers of 2.54 cm steel with plastic scintillator planes sandwiched inbetween. There are 2 supermodules each 16m long. The scintillator planes aremade from 4 cm wide solid scintillator strips with WLS ber readout. Theyare readout by multichannel Hammamastu PMTs (16 channels per tube). Thedetector occupies a new cavern in the Soudan mine. Civil construction andouttting is complete and the detector construction has begun. Figure 1 showsthe rst far dectector plane mounted on the steel support frame. Planes will beinstalled at the rate of  5 per day and cosmic ray muon tracks have alreadybeen observed in the rst few planes.Fig. 1. The rst steel plane of the MINOS far detector at Soudan.4 The near detectorThe near detector is designed to be as similar as possible to the far detector.It uses the same steel and scintillator and consists of 282 \squashed octagon"planes of steel. The scintillator is read out using multichannel HammamatsuPMTs (64 channels per tube).25 Physics GoalsMINOS has the following physics goals: Obtain rm evidence for neutrino oscillations by measuring the chargedcurrent interaction rate and energy distribution as well as the ratio of neutralcurrent interaction rate to the total rate (neutral + charged current). Measure the oscillation parameters to better than 10%. Figure 2 shows theexpected 68% C.L. errors for m2 and sin2 2 assuming a 10 kton-yearexposure with the low energy beam option. Either observe  ! e or improve the limit [3] to Ue3 < 0:013 assuming a10 kton-year exposure.Fig. 2. Expected m2 and sin2 2 sensitivity for a 10 kton-year exposure with thelow energy beam.References[1] Y. Fukuda et al., Phys. Rev. Lett. 81 1562 (1998).S. Fukuda et al., Phys. Rev. Lett. 86 5656 (2001).Q. R. Ahmad et al., Phys. Rev. Lett 87 071301 (2001).[2] T. Toshito for the Super-K Collaboration, hep-ex/0103033.[3] M. Apollonio et al., Phys. Lett. B466 415 (1999).3

Status of the MINOS Experiment

The author presents the status of the long baseline neutrino oscillation experiment MINOS at Fermi National Accelerator Laboratory (Fermilab). He also summarizes the status of the detector and beam construction, the expected event rates and sensitivity to physics. He also comments on possible future plans to improve the performance of the experiment

DIWAN,M.

I BNL- 69 45 4 1 Status of the MINOS experiment Milind V. Diwan" * "Brookhaven National Laboratory, Upton, NY, 11973 I will present the status of the long baseline neutrino oscillation experiment MINOS at Fermi National Accel- erator Laboratory (Fermilab). I will summarize the status of the detector and beam construction, the expected event rates and sensitivity to physics. I will also comment on possible future phns  to improve the performance of the experiment. 1. Introduction The strongest evidence for neutrino oscillations comes from astrophysical observations of atmo- spheric neutrinos with Am:,, = (1.6 - 4.0) x eV2 and maximal mixing [1,2], and from so- lar neutrinos with Am:ola,. = (3 - lo)  x eV2 assuming the LMA solution [3-51. The observa- tion by the LSND experiment [6] will soon be re-tested at Fermilab by the mini-Boone [7] ex- periment. Therefore we will not discuss it further in this document. There is now a consensus that there are four main goals in the field of neutrino oscillations that should be addressed soon with accelerator neutrino b eams : 1. Precise determination of Am& = AmZt, and sin2 2823 and definitive observation of oscillatory behavior. 2. Detection of up -+ u, in the appearance mode. If the measured Am2 for this mea- surement is near Am& then this appear- ance signal will show that IUe3I2 (= sin2 813) from the neutrino mixing matrix in the standard parameterization is non-zero. 3. Detection of the matter enhancement effect in up -+ u, in the appearance mode. This effect will also allow us to measure the sign of Ami,, i.e. which neutrino is heavier. *Representing the MINOS collaboration which has N 200 collaborators from 30 institutions. 4. Detection of CP violation in neutrino physics. The neutrino CP-violation in the standard neutrino mixing model comes from the phase of Ue3 in the mixing matrix. This phase causes an asymmetry in the os- cillation rates vp -+ u, versus Vp + P,.  In this paper I will describe how the MINOS ex- periment [8-121 will make the first important con- tributions to  this program of physics. 1.1. The neutrino beam A new neutrino beamline, called NuMI, has been constructed at  Fermilab [ll]. High energy, 120 GeV, protons from the main injector with in- tensity of 4 x l O I 3  every 1.9 sec in 8.1,~-long pulse will strike a 1 m-long segmented graphite target. The secondary mesons are collected by a two-horn focusing system and directed towards the Soudan Iron Mine in Minnesota, 735 km away, at an angle of 58 mrad into the ground. The mesons, most of which are charged pions, are sign selected to  be positive by the horn system and allowed to  decay in a 675 m long and 2 m diameter evacuated decay tunnel. The two-horn wide band system allows us to  tune the mean energy of the up from about 3 to  18 GeV. Since the latest oscillation param- eters from the Super Kamiolande atmospheric neutrino data are in the range of N 3 x 10-3eV2, the first run of MINOS will most likely be with the lowest energy beam to get as large an oscil- lation effect as possible for the 735 km baseline. The expected up flux from the NuMI beamline is shown in Figure 1. The contamination from v, flux scaled to 1 km Figure 1. The muon neutrino flux expected from the NuMI beam. The flux is normalized for 0.4 MW of 120 GeV proton for lo7 sec of running time. The flux is scaled to  be at 1 km distance from the NuMI target, but the spectrum shape was calculated for 735 km. The spectrum ex- pected at several angles to  the 0' axis is also shown. electron neutrinos will be less than 1% with ap- proximately the same spectrum. 1.2. The MINOS detector The MINOS experiment has two detectors, the near detector and the far detector, to  determine the neutrino flux close to  the source as well as 735 km away. The near detector, with a mass of - 1 kTon, will be placed 1040 m downstream of the target, or a.bout 300 m beyond the end of the decay tunnel, and about 100 m underground. It is designed to  precisely measure neutrino bea.m characteristics such as the energy spectrum and the v, contamination. The near detector is con- structed to  be nearly identical to  the far detector in terms of segmentation so that the event recon- struction, background levels, and energy resolu- Figure 2. Schematic of the MINOS far detector. The octagonal area is the mainly iron detector mass; the central hole accomodates a coil to  gen- erate the toroidal magnetic field. The racks on both sides of the detector house the multi-anode photomultipliers and the front end electronics. tion can be studied with the unoscillated neutrino flux with high statistics. The neutrino interaction rate in the near detector is sufficient to  provide nearly continuous beam monitoring. For the final analysis we expect that interations in the central region of 25 cm radius will be used. Beam mon- itoring will also be provided by a set of ceramic pad ionization chambers placed in 3 caves after the end of the decay tunnel. These chambers were designed to  provide stable, precise monitoring of the secondary muon flux as a function of time as well as azimuthal position [lZ]. The far detector has a total mass of 5.4 kT. It is placed in a new cavern dug 713 m underground in the Soudan mine in northern Minnesota, about 735 km away from the primary target at Fermi- lab. The far detector is made out of two super- modules, each an 8m-diameter octagonal toroid composed of 243 layers. Each layer is made of a 2.54 cm-thick steel plane and 1 cm-thick and 4.1 cm-wide scintillator strips grouped in 20- or 28-strip wide light-tight modules. The scintil- lator strips are made in an industrial extrusion process using Styron 663W polystryrene, manu- factured by the DOW chemical company, doped with 1% PPO and 0.03% POPOP. A 0.25 mm- thick reflective layer, made by adding 12.5% Ti02 to polystyrene, is co-extruded with the scintilla- tor strips. A 1.4 mm-wide and 2 mm-deep groove in the center of the 4.1 cm-side is also made dur- ing the extrusion process. A 1.2 mm diameter wave length shifting (WLS) fiber is embedded in the groove during the assembly of the scintillator modules. The J-type Y11 multiclad PMMA, non- S WLS fiber made by Kuraray and doped with the K27 dye at 175 ppm (with maximum intensity emission at 520 nm) is used. The fibers are opti- cally coupled to the scintillator strips with epoxy. The WLS fibers are read out from both ends. They are grouped (multiplexed) inside a light- tight box into sets of 8 fibers from strips spaced more than 1 m apart in each plane. Each 8-fiber bundle is coupled, using a “cookie”, to a single pixel of a 16-pixel R5900-M16 Hamamatsu photo- multiplier (PMT). Thus each PMT reads out 128 fibers; one end of each scintillator plane needs 24 pixels. This arrangement allows us to  read out the entire MINOS far detector using only 1452 PMTs. Since the event rate is small, unambigu- ous event recontruction can be achieved in soft- ware despite the multiplexing. An important de- tector parameter is the photo-electron yield for a minimum ionizing particle (MIP) incident at right angle to  the scintillator strip: the average yield, measured using a radioactive source for each strip during assembly, is about 6 photo-electrons per MIP summed from both sides. The attenuation over the 8 meter length of the strip is about a factor of 3. The near detector is a 3.8 m by 4.8 m “squeezed” octagonal toroid made of solid 2.54 cm iron plates with scintillator strips of similar design as the far detector between the iron plates. The near detector has two longitudinal sections: The first 96 planes are called the target or the hadron/shower calorimeter. In these planes the 3 area that will be exposed to  the central part of the beam (about half of the tranverse area) has scin- tillator modules in every plane. Every 4th plane in the hadron/shower calorimeter has full area scintillator coverage. The second, muon tracking, section has 164 planes with every 5th gap instru- mented with full area scintillator coverage. The fibers are read out individually (no multiplexing) from one end only by 215 64-anode Hamamatsu PMTs. The opposite ends of the fibers are reflec- tively coated to  increase the average light yield to similar level as the far detector. Both detectors are magnetized using a coil through a hole in the center of the planes to  an average field of about 1.5 T (2 m away from the coil). The front end electronics is different for the two detectors because the event rate in the 8.1 ysec  neutrino pulse in the near detector is far higher than the far detector. In the far detec- tor the read out electronics is based on a VA chip from IDE and in the near detector it is based on the QIE chip designed at Fermilab. Simula- tions show that these detectors have a resolution of 60%/- for hadronic showers and 25%/@ for electromagnetic showers. Both detectors are being calibrated by cosmic rays and a light in- jection system. A test beam calibration module is being used to  perform relative calibration be- tween the near and far detectors of about 2% and absolute calibration of about 5%. The MINOS experiment is currently under con- struction. Approximately 2/3 of the detector has been assembled in the Soudan mine and is tak- ing cosmic ray data. The civil construction for the NuMI beam line is finished and the technical items are now being assembled. Data with the neutrino beam is expected in December 2004. 2. The physics sensitivity A summary of the important parameters of the MINOS experiment is shown in Table 1. 2.1. Muon neutrino disappearance MINOS plans to  detect oscillations by observ- ing the absolute event rate as well as the energy distribution for charged current muon neutrino events. We will also obtain a confirming oscil- 4 Table 1 Para.meters of the MINOS experiment Proton Energy 120 GeV Time Structure Intensity 4 x protons/spill Exposure 3.8 x lo2' protons/yea.r 8.1 p s every 1.9 sec Beam Ba,seline 1 m graphite target 2-horn pion focusing LE 1-6 GeV up with tail to  50 GeV 735.340 km Detector Resolution hadronic 6 0 % / a  Event rate 2.54 cm Iron, 1 cm scint. Magnetized Average field 1.5 T electromagnetic 25%0/@ Nea.r det. 3 events/spill in ta.rget region Far det. 300 up CC events/kT/yr (no osc) lation signature in the ratio of the number of charged and neutral current events. The total neutrino energy will be measured by measuring the muon momentum and range as well as the to- tal energy of the hadron shower. The resulting distribution of reconstructed neutrino energy is shown in Figures 3 and 4, for Am2 = 0.002 eV2 and Am2 = 0.0035 eV2, respectively; sin228 = 0.9 for these plots. To extract oscillation param- eters it will be necessary to  precisely predict the spectrum without oscillations at the far detector using the near detector data. Using known toler- ances on the target/horn geometry as well as the differences in the near and far reconstrution e%- ciencies we expect to  reduce the systematic error on the far spectrum to about 2% in normalization and 2% in bin-to-bin fluctuations. Using these systematic uncertainties we predict that MINOS will be able to  measure the oscillation parameter Am2 to f10% at the best fit point of the Super- Kamiokande allowed region. This is shown in Fig- ure 5. The Super-Kamiokande best fit point is now at 0.0025 eV2 [13]. For this value, the mini- mum in the oscillation probability for MINOS will be at 1.5 GeV which is on the lower rising edge of the charged current spectrum (See the unoscil- Iated histogram in Figure 3). Therefore, one pos- sibility under study for improved performance is to  increa.se the flux below 2 GeV by appropriate modifications to  the ta.rget/horn geometry. 2.2. Electron neutrino appearance The main oscillation channel in the case of atmospheric oscillations is now thought to  be vp + v,[2]. Nevertheless, in the 3 neutrino for- mulation of oscillations it is natural to expect a small component of the disappearing vp to  con- vert to  v, with the same oscillation length as the atmospheric one. This will occur if the presently unknown neutrino mixing matrix element Ue3 is nonzero. The best limit on Ue3 currently comes from the reactor experiment Chooz[l4] in which a search was made for disappearance of 9,. At the Super Kamiokande best fit Am2 = 0.0025 eV2 the Chooz limit implies IUe3I2 < 0.03 at 90% con- fidence level. The expected sensitivity of MINOS for up + u, appearance is shown in Figure 6. With 10 kT-year of exposure we expect to  im- prove the Chooz limit by about a factor of 2. At Am2 = 0.0025 eV2 and lUe3I2 = 0.03 we expect an excess of 24 electron event over a background of 40 events. For Figure 6 we assumed that the background will be known to about 10% by using the near detector data. The sensitivity is limited by the neutral current background (28 events) out of which approximately half will be from high en- 5 Figure 3. Expected spectrum of reconstructed muon neutrino energy for Am2 = 0.002 eV2 and sin2 20 = 0.9. We assume l0kT-year of exposure in the low energy beam for this result. ergy (> 10 GeV) neutrinos. We are examining the possibility of reducing the background and improving the signal by 1) eliminating the high energy tail of the beam by using a "beamplug", 2) improving the flux at low energies. A more sensitive approach to  vk + v, has been proposed to use the off-axis narrow band NuMI beam (See Figure 1)[15] and a new detector placed on the Earth's surface near Soudan[l6]. With an up- graded more intense main injector such an exper- iment could also be sensitive to  CP violation. U1- timately, for the best sensitivity to  matter effects and CP violation using a conventional neutrino beam one may have to  go to  much longer base- lines [17,18]. 3. Conclusion The NuMI neutrino beamline and the MINOS near and far detectors are being constructed. Ap- Figure 4. Expected spectrum of reconstructed muon neutrino energy for Am2 = 0.0035 eV2 and sin2 20 = 0.9. We assume l0lrT-year of exposure in the low energy beam for this result. proximately 2/3 of the 5.4 kT MINOS detector has been assembled in the Soudan mine; it is now gathering cosmic ray data. The NuMI beamline will be finished in 2004 and data gathering with the neutrino beam will commence in December of 2004. With 10 kT-year of data with 3.8 x lo2' protons per year we expect to  confirm the oscil- latory behaviour of muon neutrinos and measure Am2 with 10% error. We will also improve the limit on vk + v, beyond the limit of Chooz or discover this appearance channel if the parame- ter IU,3I2 is sufficiently large. The sensitivity to  the appearance channel is limited by the neutral current background, and we are examining vari- ous possibilities to  reduce this background. This work was supported by U.S. Department of Energy, Contract No. DE-AC02-98CH10886. 6 t “E a 0.005 0.004 - 0.003 - 0.002 - L j Super-K, 1144 days 0.001 ‘0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 sin22fi Figure 5. Expected resolution from MINOS from the disappea.rance signature for selected pa.rame- ters (the stars). The favored region from Super Ka.miokande data is also indicated. REFERENCES 1. Y. Fukuda et al., Phys. Rev. Lett. 81, 1562 2. S. Fukuda et al., Phys. Rev. Lett. 85, 3999 3. Q. R. Ahma.d et al., Phys. Rev. Lett. 87, 071301 (2001) 4. Q. R. Ahmad et al., Phys. Rev. Lett. 89, 011301 (2002). 5. Q. R. Ahmad et al., Phys. Rev. Lett. 89, 011302 (2002). 6. C. Athanassopoulos et al., Phys. Rev. Lett. 77 3082 (1996); C. Atha.nassopoulos et al., Phys. Rev. Lett. 81 1774 (1998) 7. Booster Neutrino Experiment, Fermi Na- tional Laboratory, (1998) (2000) I MINOS v +v,sensitivity 1 10-’t EXCLUDED (90% C.L.) E a Figure 6. Expected 90% confidence level limit for vp + v, appearance if MINOS sees no excess of electron neutrino events with 10 kT-year of expo- sure. http:/www-boone.fnal.gov/ 8. Fermilab Proposal P875, February, 1995. The MINOS technical design report, Fermilab, NuMI-L-337, October, 1998. 9. P. Adamson et al., Nucl. Instrum. Meth. 10. K. Lang et aI., Nucl. Instrum. Meth. A461 571 (2001) 11. J. Hylen et al., FERMILAB-TM-2018, Sep 1997. 12. J. Mcdona.ld et al., Archive:physics/0205042, May 2002, To be published in Nucl. Instrm. Meth. 13. T. Kajita and Y. Totsuka, Rev. Mod. Phys. 73, 85 (2001). 14. M. Apollonio et al., Phys. Lett., B466, 415 15. Long Baseline Neutrino Oscillation Experi- ment, D. Beavis et al., Physics Design Report, BNL-52459. April 1995. A492 325-343 (2002) (1999). L L 7 16. Letter of Intent to  build an Off-axis Detec- tor to  study vp -+ v, oscillations with the NuMI Neutrino Beam, D. Ayres et.al, hep- ex/02 10005 17. William J. Marciano, arXiv: hep- phy/O108181,22 Aug 2001. 18. Report of the BNL Neutrino Working Group: Very Long Baseline Neutrino Oscillation Ex- periment for Precise Determination of Oscil- lation Parameters and Search for vp + v, Ap- pearance and CP Violation, M. diwan, et al., BNL-69395, Oct 28, 2002. hep-ex/0211001. 4 

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Status of the MINOS experiment

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