e.kistenev large area electromagnetic calorimeter for alice what emc can bring to alice physics and...
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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
rs
6
mon
ths
Time scale for the project to complete