Reply to the initial set of comment and questions

April 19, 2005 Adam Para, FLARE Review, round II 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.

http://www-off-axis.fnal.gov/notes/notes.html


Thermodynamics of the large argon tank

Axi-symmetric model using ANSYS (Z. Tang. FLARE note 31)

Liquid flow Temperature gradientNote: 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 processPhase II: filling Purity level determined by balance of the filtering

vs. impurities introduced with the new argonPhase 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 FLAREInput argon purity 10-6 10-9

Surface of cables 200 m3 1200 m3

Mass of argon 300 t 50000 tTime to purify 80 days 270 days


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 eventsAll 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 MxWhere:

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 eventFine 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.

Reply to the initial set of comment and questions

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