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EMCal design

MICE collaboration meetingFermilab

2006-06-08Rikard Sandström

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Outline

• Improved analysis• Design principles• Longitudinally

– Size– Segmentation

• Transversally– Size– Segmentation

• Summary

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Improved analysis

• At last collaboration meeting 87.6% of background was rejected for 200±20 MeV/c beam at 99.9% signal efficiency.

• Since then, hard work has gone into improving fits and analysis.– Also some changes to geometrical setup.

• EMCal closer to TOF2. • Both detectors wide enough to catch all muons.• TOF2 4 cm thick.

• Now: Diffused Aug’05 beam gives 99.0% background rejection at 99.9% signal efficiency.

• I.e ~12 times as low miss identified background!– 40-50 times more powerful than basic requirement. – More on this during analysis session.

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Purpose of the calorimeter

• The EMCal is not necessarily used to measure energy!

• Main objective:– Provide separation capability between muons and

decay positrons.

• Secondary objectives:– Separate muons from other form of background.

• Pions• X-rays• Electrons

– Give independent information on particle momentum.• Through range, barycenter, energy etc.

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Design principles

• Relative energy resolution gets worse with lower energy.

• For high energy, resolution is lost by energy leakage.– Longitudinal leakage is

worse than transversal.

• -> Increase dE/dx by inhomogeneous designs. (sampling calorimeters)

ATLAS

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Sampling calorimeters

• Sampling fluctuations dominate energy resolution!

• For best energy resolution, the passive material should1. be as thin as possible 2. be made of as high Z

material as possible• U excellent, Pb more

practical.

• Problem with channeling.

H1 SPACAL

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Sampling vs non-sampling

• If energy is low:– More sensitive to

sampling fluctuations.– Range is shorter.

• If the shorter range allows leakage prevention with a homogeneous (non-sampling) calorimeter, it will give better energy resolution.

• MICE is not a HEP experiment!

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EMCal

• Back end, layer 1-10, of EMCal Sandwich design is non sampling, fully active.

• Front end, layer 0, is sampling (lead & SciFi) to induce EM showers for electrons.– Low energy muons get stuck in layer 0, and if pure

lead we would not have any information on their energy.

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Few words on EMCal analysis

• More than only energy reconstruction.

• For example:– Looks for Bragg peak,

compare with track parameters.

– Looks for how continous the signal is to the Bragg peak.

– Barycenter.– Two TDC peaks means

muon decay @ t<t_gate.

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Longitudinal size

• Layer 0 – 4cm thick which is

appropriate for showering electrons without losing too much energy of muons.

• Layers 1-10 – In total 70 cm thick,

which makes longitudinal leakage small.

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Longitudinal segmentation• Normally muons are

stopped in EMCal.– No energy leakage gives

good energy resolution.– Range and barycenter

become powerful tools for PID.

• Range resolution is dominated by thickness of layer at stopping position / track length.– Use thinner layers in the

front.• Rates are higher in the

front.– Again, use thinner layers

in the front.

0

0,5

1

1,5

2

2,5

1 2 3 4 5 6 7 8 9 10

thickness/z middle

Series1

With layer thicknesses1,2,3,4,6,8,10,12,12,12 cm

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Transversal size

• Calorimeter should capture any muons which1. Are contained within tracker active volume.2. Are hitting TOF2.3. Are within momentum region of interest.– (= good muons)

• In addition, question have been raised about muons hitting cryostat after tracker.

End Coil 2 Estimated positions

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Transversal size

• Not meaningful to define calorimeter transversal size before size of TOF2 is defined.– However results already existing give a good

notion.

• TOF2 PMTs need shielding from magnetic fields.– So could also be the case for calorimeter.– Double shields help for TOF2, and this option has

also been examined for calorimeter.– As next slides show, a split design (to allow for 3rd

shield) would require a larger calorimeter.

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Full phase space beam

51 k events

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Full phase space beam, non split

63 k events

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Transversal segmentation

• I have kept the number of channels fixed to the KLOE light design proposal (240 channels).

• With 10 plastic layers, that gave 9 cells per layer.

• Studies suggest full width of calorimeter should be ~1 m. – Each cell is ~1 dm high.

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Summary

• Refined analysis shows dramatically improved performance.

• Calorimeter design has been tailored for special MICE conditions.

• Longitudinal size and segmentation chosen with muon range and momentum in mind.

• Transversal size needs decision on TOF2 size to be finalized.