# Presentation: 102176

## 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](http://www-off-axis.fnal.gov/notes/notes.html)__. See in particular materials from the FLARE workshop, November 2004. _

## 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

## 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).

## 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)

- 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

## 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.

## 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)

|  | ICARUS | FLARE |
| --- | --- | --- |
| Input argon purity | 10-6 | 10-9 |
| Surface of cables | 200 m3 | 1200 m3 |
| Mass of argon | 300 t | 50000 t |
| Time to purify | 80 days | 270 days |

## Signal size vs. drift distance vs. purity 

- 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

## 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.

## 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..

## 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

## 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 ?
- ... ... ...

## 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.

## 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

## 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

## 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

## (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

## 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

## It is important to have a good detector

- Coherent 0 production
- Easily recognized as a conversion
- A key to keeping background low

## 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.