e.kistenev large area electromagnetic calorimeter for alice what emc can bring to alice physics and...

E.Kistenev

Large area

Electromagnetic Calorimeter for ALICE

•What EMC can bring to ALICE•Physics and engineering constrains•One particular implementation•How much it will cost•Schedule

Large area calorimeter will:

•deliver the rate for high Pt photons;

•make possible the low level triggering on electrons and photons(*);

•allow precision jet measurements;

•allow triggering on jets (e/m component is good enough);

•allow for correlated photon-jets physics;

•allow for parton dE/dx measurement via leading particle spectra in tagged jets (direct access to measuring modifications to fragmentation function);

(*) Neither TRD nor EMCal can do this job alone, pion decays in flight will become a main source for TRD triggers, large energy deposits from hadrons will dominate the EMCal trigger.

STARDesign

Problems&Solutions

Too High Occupancy.

Relevant parameters are: • Elow pt in the angular cone in which the shower is measured;• overlap probability (two hits in the same calorimeter cell).

Handles:

calorimeter density and/or granularity;

calorimeter depth and longitudinal segmentation: very high energy shower has much of its energy at depths where the low pt showers have died away.

PS. Overlaps are irrelevant to the high Pt showers.

Problems&Solutions

Energy measurements:

Photons and electronsIn the central AuAu event at LHC the average “foreign”

energy per tower is ~ 25 MeV - use “essential contributors” only.

Pile-up does limit the precision of the energy measurements for the lower end of the shower energy range, but not in the “natural range for High Density QCD at LHC ” around ~ few GeV;

Problems&Solutions

Energy measurements:

Jets

In the most of LHC experiments it is the uncertainties of jet definition what limits the resolution not the shower-type dependence

Ejet = (EEMCal(depth > 1Labs) ~ 0.75 Eimpigent ) + corrections from tracking;

If functionality (energy and position) is not separated reaching few mm goal within the framework of traditional design requires matching cell size to radiation length (one needs a reasonable amount of energy to leak out of the hit cell to measure impact position) -> cost prohibitive for large area devices.

Problems&Solutions

Position measurements:

• Have no effect on Pt measuremnts;• Only secondary to effective mass measurements;• Constrains are set by track-to-shower matching: few mm resolution is certainly sufficient.

Problems&Solutions

Angular measurements:

very useful to reject non-vertex background;

nearly a must if diamond is large and more then one event per crossing is possible;

costly - but desirable

Particle Id: primarily e/h separation but can do better

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Particle Id: primarily e/h separation but can do better

Energy measurements (E - P matching) x 100 (*)

Lateral shower shape x 50 (*)

Longitudinal shower shape x 2 (*)

Signal timing structure ?

(*) Unfortunately - calorimeter based criteria are correlated: practical limit to hadron rejection in a stand-alone calorimeter is ~200 for a few GeV/c hadrons.

ANTIBARYON SHOWERS

Late arrivals in EMCal( -flash corrected > 2.5 ns)

Shoulder consistent with

antibaryon contribution

EMCal ToF effective at low energies,

works nicely for antyneutrons

Something about time segm.

ALICE EM calorimeter

(1) full coverage (rate&jets) but hermeticity is not a must;

(2) energy resolution of (15-20)% at 1 GeV-> comparable tracking and calorimeter resolution at a lower limit of the “natural range for High Density QCD at LHC ”

(3) deps of ~ 25 Lrad / 1 Labs (em resolution + jets);

(4) high density to limit shower size (it also helps to limit the cost);

(5) relatively coarse granularity - two high Pt showers are unlikely to overlap, limit is set by 0 background to prompt photons;

(6) some degree of a pointing capability;

(7) high light yield to retain ToF capability;

(8) upgradability -> to offset initial cost.

May EMC be designed and built along these lines and still be reasonably costed:

The answer would be YES if design allows to resolve internal contradictions between density, granularity and ability to point.

B.Aubert et al, NIM, A309, 438 (1991)

Sampling fraction = 10.5%

Energy resolution = 15% (3mm plates)

Why Accordion…

•very uniform;

•no dead areas;

•very linear - autocompensation for light attenuation in the fibers;

•best possible position resolution for a given cell size;

•shower shape is very sensitive to impact angle - built-in pointing;

•multiple options for longitudinal segmentation,

•relatively easy industrialization.

Energy resolution ~ 15%

Pb thickness 3 mmSc thickness 3 mmFibers (diameter) 0.6 – 1 mmFiber length ~50 cmFiber spacing 1 cmFibers/cell 5Cells per tower 4 - 5Tower size x = 0.01 x 0.01Fibers per tower 24-30Light yield ~6000 /GeVPhotodetector APD (3 mm)Longitudinalsegments

2 (?)

Basics of costing:

PHENIX EMCal Design -> 0.5 106 $US

PHENIX EMCal Mechanics -> 1.3 106 $US (*)

Fibers -> 0.2 106 $US

Assembly&testing -> 0.2 106 $US

PHENIX EMCal Readout

PMT’s -> 0.5 106 $US

HV -> 0.3 106 $US

LV -> 0.05 106 $US

FEM -> 0.8 106 $US (4k/FEM - production cost only)

Total -> ~ 4 106 $US + FEM development costs (~ 1 106 $US)

(*) Cost per kg of active media $15

ALICE large area EMCal (mechanics)

Cost/kg (active media) 20 $US

Contingency 50%

Cost (active media - mechanics) ~ 12 106 $US

Industrial comp. (fibers etc) ~ 1.0 106 $US

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Development costs (incl. R&D) ~ 1 106 $US

Support structures (10%) ~ 1.2 106 $US

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Total ~ 16 106 $US

W [tonn] Quantity Total weightFront/Rear Segments 12.67 16 202Lateral FaceSegments

46.56 4 186

All Detector 390

ALICE large area EMCal (readout)

Cost per channel:

APD’s (=5 mm) $ 50 (*)

readout $ 20

power $ 5

Total per channel $75

Channel count: 5x5 cm2 60k -> 5 106 $US

7x7 cm2 30 k -> 2.5 106 $US

10x10 cm2 (staged) 15k -> 1.2 106 $US

(*) Smaller size APD’s are the option - we may use smaller diameter fibers and loose some light but regain the timing - all this is the subject for optimization

Fine tuning the specifications

Baseline simulation of the EMCal performance & optimization

Decision on longitudinal segmentation

Prototype design:multiple options

Readout evaluation

Prototype construction

Envelope studies

Infrastructure design

Test beam

Prototype readout

Detector Design

Construction

2 Y

ears

1.5

Yea

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6

mon

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Time scale for the project to complete