1. April 19, 2005Adam Para, FLARE Review, round II1 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.http://www-off-axis.fnal.gov/notes/notes.html

2. April 19, 2005Adam Para, FLARE Review, round II2 Thermodynamics of the large argon tank Axi-symmetric model using ANSYS (Z. Tang. FLARE note 31) Liquid flowTemperature gradient Note: full scale 0.113 o C

3. April 19, 2005Adam Para, FLARE Review, round II3 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 83.91 o K. Actual temperature is 87.3 o K (FLARE note 31).

4. April 19, 2005Adam Para, FLARE Review, round II4 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)

5. April 19, 2005Adam Para, FLARE Review, round II5 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

6. April 19, 2005Adam Para, FLARE Review, round II6 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.

7. April 19, 2005Adam Para, FLARE Review, round II7 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) ICARUSFLARE Input argon purity 10 -6 10 -9 Surface of cables200 m 3 1200 m 3 Mass of argon300 t50000 t Time to purify80 days270 days

8. April 19, 2005Adam Para, FLARE Review, round II8 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

9. April 19, 2005Adam Para, FLARE Review, round II9 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.

10. April 19, 2005Adam Para, FLARE Review, round II10 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..

11. April 19, 2005Adam Para, FLARE Review, round II11 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

12. April 19, 2005Adam Para, FLARE Review, round II12 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 ? … … …

13. April 19, 2005Adam Para, FLARE Review, round II13 e Appearance Experiment, A Primer At an off-axis position in the nominal NUMI beam, if no oscillations: 100 ev/kton/year of  CC events 30 ev/kton/year of NC events 0.5 ev/kton/year of e 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 (  E/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  CC events is reduced from 100 to ~ 10. The  resulting from oscillations do not CC interact (below threshold). Some of the  CC events may show up as e CC events - signal. Physics potential of an experiment depends on the number of identified signal e CC events.

14. April 19, 2005Adam Para, FLARE Review, round II14 Experimental Challenge Maximize Mx  Where: M – detector mass  – efficiency for identification of e CC events While maintaining  >20/  to ensure NC bckg < 0.5 e CC bckg) Where  is the rejection factor for NC events with observed energy in the signal region Why is it hard to achieve high  Y-distribution – electron energies ranging from 0 to E Low(er) electron energies emitted at large angles Why is it hard to achieve high   0 ’s produced in the hadronic shower, early conversions and/or overlap with charged hadrons Coherent  0 production

15. April 19, 2005Adam Para, FLARE Review, round II15 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  s) 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

16. April 19, 2005Adam Para, FLARE Review, round II16 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:  = 82+-6% (41 events out of 50 events accepted)  > 15 (66% C.L.) (35 events out of 35 rejected) Work in progress. Quite some fun. Come and join, room for major contributions

17. April 19, 2005Adam Para, FLARE Review, round II17 (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

18. April 19, 2005Adam Para, FLARE Review, round II18 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

19. April 19, 2005Adam Para, FLARE Review, round II19 It is important to have a good detector Coherent  0 production Easily recognized as a conversion  A key to keeping background low

20. April 19, 2005Adam Para, FLARE Review, round II20 And the bottom line is: e identification efficiency,  =76+- 11% (13 out of 17) NC rejection factor,  =53 (3 out of 159) No  CC backgruond (0 out od 17) It was the first try. More scanning underway. Improvements expected. Automated analysis software ‘under construction’. WARNING: possibly addictive.