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The MINOS Far Detector

The MINOS Far Detector. Cosmic Rays and their neutrinos are being collected now. How does this work, and of what use is this data?. Alec Habig, Univ. of Minnesota Duluth, for the MINOS collaboration. The MINOS Experiment. 735 km. Main Injector Neutrino Oscillation Search

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The MINOS Far Detector

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  1. The MINOS Far Detector Cosmic Rays and their neutrinos are being collected now. How does this work, and of what use is this data? Alec Habig, Univ. of Minnesota Duluth, for the MINOS collaboration

  2. The MINOS Experiment 735 km • Main Injector Neutrino Oscillation Search • Will utilize NuMI beam from Fermilab • Front-to-back nm oscillation study • Produce well-studied nm beam • Measure nm spectrum just after production with “Near Detector” • Measure again 735 km later with “Far Detector” • Beam goes from Fermilab to the Soudan Mine Underground Lab Alec Habig

  3. The Far Detector To Fe rmi l ab 8m 15m ½ of the Far Detector • Steel/Scintillator sampling calorimeter • 5.4 kt, 8m diameter, 31m long • 486 layers, each made of: • 1” steel • 1 cm plastic scintillator • Magnetized to ~1.5 T • Design goals • ne/nm/p discrimination • Good energy resolution • For both m and showers • Good timing, both hit-to-hit and absolute • For particle direction and synching with Fermilab beam Alec Habig

  4. Far Detector Progress • Construction began August 2001 • Now up to about plane #225 • Almost halfway done! • First half complete in July when it will be magnetized • Taking Cosmic Ray data as it is built • Each plane independently instrumented Plane #200, May 3, 2002 Alec Habig

  5. Particle Detection 28 28 20 20 20 20 28 From FNAL 28 • 4.1 cm x 8m scint strips bundled into “modules” • Light channeled out via 2-ended fiber • Each plane’s strips are 90o from the last • “U” and “V” views • 17 GeV MC m shown below from side, in U,V Alec Habig

  6. Multiplexing Fiber Layout 16 mm M16 PMT • Light detected by 16 pixel PMTs • 8 fibers per pixel, ganged together with: • Maximal physical strip separation • Minimal in-PMT cross-talk One of 3 Ham. M16 PMTs in this “Mux Box” Alec Habig

  7. Front End Electronics • Fibers from each strip end are multiplexed onto PMT pixels • Signals amplified, shaped, and tracked+held by “VA” chips • Calibration charge can also be injected in the same place as PMT charge for functionality check and calibration of full electronics path • Timing information sent upstream from this “Front End” rack Alec Habig

  8. Data Gathering • VME “Master” crate • VA Readout Controllers “VARC”s • Charge from PMTs digitized by 14-bit ADCs • Time stamped to 1.6ns by internal clock • 2/6 or 2/36 pre-trigger applied • Hits given absolute GPS time • Data read out over PVIC bus to computer room • 4/5 plane software trigger applied, hits time ordered • Data formatted in ROOT 1 of 16 VME crates Digitizes 72 mux boxes Each w/3 16-pixel PMTs Alec Habig

  9. De-multiplexing • Scintillator strip ends are multiplexed 8-1 per electronics channel • How to figure out which strip a particle really went through? • Matching hits on both ends of a strip helps in the simplest track case • For multiple hits on a plane and showers: • All the different possible “hypotheses” of which strip was really hit tested against the possible real physics • Best fitting hypotheses saved • Reconstructing close multiple muons very difficult! Alec Habig

  10. A Cosmic Ray De-multiplexed • Success rate for Cosmic Rays: • 94% of hits correctly associated with their strips • 97% of CR events successfully sorted out CR m after De-multiplexing CR m before De-multiplexing Alec Habig

  11. Light Injection • Calibration using controlled light: • LEDs illuminate 8-10 calibration fiber ends each • Fibers carry light from LED to shine on ends of scint strip fibers • Varying light levels used to map out detector and phototube response • Regular pulsing at a constant light level during normal operations • Tracks changing detector response • Flags problems with optical path Light from calibration fibers illuminating ends of fibers from the scintillator where they are bundled Alec Habig

  12. Cosmic Rays • As planes are added to the detector, they contribute to the data acquisition • Currently taking Cosmic Ray data • CR rate: 1000 m/strip/month, 2% stop in detector • Excellent “beam” for detector commissioning • Real particle data provide end-to-end test of all hardware, software systems • Good calibration source • Geometry, gain, timing, reconstruction software CR-m light output with expectations ~10 pe at mid-strip (sum of both ends) Alec Habig

  13. CR Calibrations • Physical plane locations are surveyed as the planes are raised • CR m draw nice straight lines • Residuals to the m fits are not bad with nominal plane geometry, excellent with survey-corrected data • Timing calibrations • CR m are nice straight lines moving at b=1 • Use this physics to find and fit absolute timing offsets Timing offsets (ns) vs. channel. Different delays in different electronics paths are clearly seen, as is the few (2.6) nanosecond resolution Need t0 fit plot Alec Habig

  14. Initial n Searches • Atmospheric n are present in the data • Contained vertex search being refined • Up-going m search underway as part of CR timing calibrations • Reconstruct timing of m tracks • Down-going CR’s have b=1 • Up-going n-induced m have b=-1 An up-m! Alec Habig

  15. Summary • The MINOS Far Detector construction is nearing the ½ way point • Data being taken as the detector grows is used to validate and calibrate both hardware and software • Will be ready for beam • Plus atmospheric n work can be done with magnetic field! • n/n separation First n! An up-going m seen on the evening of March 22, 2002 – MINOS works! The presenter gratefully acknowledges support for this poster from the National Science Foundation via its RUI grant #0098579 Alec Habig

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