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Reply to the initial set of comment and questions

Reply to the initial set of comment and questions. Thanks to all reviewers for your attention and for your thoughtful and penetrating comments and questions. We find them extremely helpful.

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Reply to the initial set of comment and questions

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  1. Reply to the initial set of comment and questions Thanks to all reviewers for your attention and for your thoughtful and penetrating comments and questions. We find them extremely helpful. Some of the questions relate to issues already studied or discussed and we wish to share our thoughts on them, others… Many of the issues raised, as well as lot of others, are addressed in FLARE notes: http://www-off-axis.fnal.gov/notes/notes.html. See in particular materials from the FLARE workshop, November 2004. Adam Para, FLARE Review, round II

  2. Thermodynamics of the large argon tank • Axi-symmetric model using ANSYS (Z. Tang. FLARE note 31) Liquid flow Temperature gradient Note: full scale 0.113oC Adam Para, FLARE Review, round II

  3. Will argon freeze at the bottom of the tank due to 5 atm pressure? • No • "Thermophysical Properties of fluids. Argon, ethylene, parahydrogen, nitrogen, nitrogen trifluoride and oxygen", in the Journal of Physical and Chemical Reference Data, Volume 11, 1982, Supplement No. 1. R. Schmitt: freezing temperature at the pressure at the tank bottom is 83.91oK. Actual temperature is 87.3oK (FLARE note 31). Adam Para, FLARE Review, round II

  4. Argon receiving, quality control, purification systems • Critical set of issues, clearly. More work needed to have them under full control, clearly. Design and specification process has started ( FLARE notes 24,26,27,29) • Experimental effort on proving validity of the underlying assumptions (purification power of commercial filters, effect of impurities on the electron lifetime, composition of impurities, out-gassing rates, time dependence) underway (PAB setup, Lab 3) Adam Para, FLARE Review, round II

  5. Initial purification system • Design throughput: 200 t/day • Oxygen load @1ppm delivered argon purity : 200 g/day. May be more. Probably will be less.. • 24/7 operation for 9 month Adam Para, FLARE Review, round II

  6. Main tank:28 t/hour re-circulation and purification system Phase I: initial purge – 100-200 tons of LAr (~ 2 weeks) (vessel not evacuated) • Very rapid volume exchange (several hours) => rapid purification • Main issue: very large oxygen capacity required Milestone: achieve >10 ms lifetime before continuing the fill process Phase II: filling • Purity level determined by balance of the filtering vs. impurities introduced with the new argon Phase III: operation • Low rate of volume exchange (74 days) • Removal (mainly) of the impurities introduced with argon • Balance between purification and out-gassing • In this phase out-gassing of tank walls, cables and other materials becomes a visible factor, although still very small. Tank walls, materials, cables must not contain quantities of slowly out-gassing contaminants way beyond expectations. Adam Para, FLARE Review, round II

  7. Wasn’t electron lifetime of ICARUS T600 limited by cables outgassing ?? And doesn’t this indicate that cables, walls, etc.. may be a limiting factor for a very large detector ??? Not necessarily. Probably not. Observe: rate of lifetime improvement in ICARUS doubles at 40 days, compared to 20 days (outgassing ~ 1/t) Adam Para, FLARE Review, round II

  8. Signal size vs. drift distance vs. purity • ICARUS: signal = 15,000 el, S/N=6 • FLARE design: signal = 22,500 el, S/N=8. Required purity : 3x10-11 (oxygen equivalent) • Significant margin. 2 m drift distance does not offer major improvement Noise level Adam Para, FLARE Review, round II

  9. Additional tank for ‘repairs’ ? • What if argon in the main tank gets ‘poisoned’? • Install more purification units. Piping must be sized to allow for that Once the tank is filled with Liquid Argon there is no practical possibility of repairs of any failed equipment inside. Frequent suggestion: build another tank to enable transfer of LAr, access and repair. • It is an interesting suggestion requiring detailed risk and cost-benefits analysis. • Design goal: minimize the probability of a requirement for access: • Minimize the number of components inside the tank • Robust, failure proof components and construction techniques • In-situ testing to make failures very improbable • Minimize the impact of an improbable failure(s): a nuisance rather than a disaster (example: broken wire) Likely outcome: all of the above notwithstanding some committee will insist on it. Observation: spare tank must match the size of the main detector tank. Adam Para, FLARE Review, round II

  10. Rightsizing of the tank (experiment?) • ICARUS is building 1200 t detector. A leap to 50,000 tons is too ambitious. • One monolithic (sort of) detector is ‘too risky’. Minimize the risk of unforeseen failures by having several smaller detectors • You have to build prototypes to learn how to build such a detector. They must be relevant to the ultimate detector construction. • How does the detector cost scale with size? What are the cost drivers? Constant costs vs. volume-related. • … … … A lot of wisdom and practical experience speaking.. Adam Para, FLARE Review, round II

  11. Rightsizing of the experiment • Technical solutions and construction techniques are likely to similar for tanks above ~ 10 kton. Linear dimensions scale with cube root of the volume (1.7 for 10/50 kton case). • Most of the site-related, argon receiving and purification costs are almost independent of the size. We are in process of understanding the costs of smaller detectors. • Scenario I: build four tanks (15 kton each), use one as a holding tank. • Scenario II: • Begin with 15 kton tank as a Phase I of an off-axis experiment. • Demonstrate the construction, purification, performance. Determine the running conditions on the surface and measure potential backgrounds for proton decay and supernova detection. • Depending on the experience, proceed with Phase II by building more of 15 kton detectors or jump into 50 kton tank • Reduce the initial risk and provide clear path towards the ultimate program of studies of neutrino oscillations • Physics potential of the Phase I is at least comparable to all other putative experiments Adam Para, FLARE Review, round II

  12. Efficiency/background rejection • What is it? How is it determined? How sure are you? • Why is it so much better than OOPS (Other Options Perceived to be Simpler)? • Are you planning to scan all events in the experiment? • Can you fish out events out of the ocean of cosmic ray-induced ‘stuff’? • When will you have fully automatic reconstruction program ? • … … … Adam Para, FLARE Review, round II

  13. ne Appearance Experiment, A Primer At an off-axis position in the nominal NUMI beam, if no oscillations: • 100 ev/kton/year of nm CC events • 30 ev/kton/year of NC events • 0.5 ev/kton/year of ne CC events All of the above for neutrinos with energy [1.5, 3 GeV] For CC events the observed energy is that of the interacting neutrino (DE/E ~ 10%) . For NC events the observed energy of only ~ 1/6 of events falls into the ’signal’ region. Troublesome sample of NC events is thus 5 ev/kton/year Turn on oscillations: sample of nm CC events is reduced from 100 to ~ 10. The nt resulting from oscillations do not CC interact (below threshold). Some of the nm CC events may show up as ne CC events - signal. Physics potential of an experiment depends on the number of identified signal ne CC events. Adam Para, FLARE Review, round II

  14. Experimental Challenge • Maximize Mxe Where: • M – detector mass • e – efficiency for identification of ne CC events • While maintaining h>20/ e (to ensure NC bckg < 0.5 ne CC bckg) Where h is the rejection factor for NC events with observed energy in the signal region • Why is it hard to achieve high e • Y-distribution – electron energies ranging from 0 to En • Low(er) electron energies emitted at large angles • Why is it hard to achieve high h • p0’s produced in the hadronic shower, early conversions and/or overlap with charged hadrons • Coherent p0 production Adam Para, FLARE Review, round II

  15. Tools • Neutrino event generator: NEUGEN3. Derived from Soudan 2 event generator. Used by MINOS collaboration. Hugh Gallagher (Tufts) is the principal author. • GEANT 3 detector simulation: trace resulting particles through a homogeneous volume of liquid argon. Store energy deposits in thin slices. • LAIR (Liquid Argon Interactive Reconstruction), derived from MAW (Robert Hatcher), derived from PAW. • Project energy depositions onto the wire planes • Bin the collected charge according to the integration time • Ignore (for now) edge effects, assume signals well above the electronics noise • Assume two track resolution (2 ms) • Event display (2D, 3 projections) • Interactive vertex reconstruction • Interactive track/conversions reconstruction • 3D event display (J. Kallenbach). Early stages of development. • Prototypes of automatic event classification software Adam Para, FLARE Review, round II

  16. Early results (MSU, C. Bromberg) • Algorithm for electron ID: • Charged track originating at the vertex and developing into EM shower (at least 3 consecutive hits with more that 1.5 MIP of ionization) • EM shower starting no earlier than 1.5 cm from the vertex • Less than 4 photon conversions in the event Fine longitudinal and transverse granularity of the detector of critical importance. And the answer is: e = 82+-6% (41 events out of 50 events accepted) h > 15 (66% C.L.) (35 events out of 35 rejected) Work in progress. Quite some fun. Come and join, room for major contributions Adam Para, FLARE Review, round II

  17. (Double?) Blind Scan Analysis at Tufts • A random collection of signal and backgrounds events scanned by undergraduate students trained to recognize electron neutrino interactions (assign likelihood from 1 to 5) • Sample of ‘electron candidates) (score > 3) scanned by experts-physicists (still flying blind) • Several examples of events identifiable (according to scanners) thanks to superior granularity and resolution of the detector Adam Para, FLARE Review, round II

  18. It is important to have a good detector • High-y, low energy (170 MeV) electron easily recognized by all scanners  Key to achieving high signal efficiency Adam Para, FLARE Review, round II

  19. It is important to have a good detector • Coherent p0 production • Easily recognized as a conversion • A key to keeping background low Adam Para, FLARE Review, round II

  20. And the bottom line is: • ne identification efficiency, e=76+-11% (13 out of 17) • NC rejection factor, h=53 (3 out of 159) • No nm CC backgruond (0 out od 17) It was the first try. More scanning underway. Improvements expected. Automated analysis software ‘under construction’. WARNING: possibly addictive. Adam Para, FLARE Review, round II

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