andrey korytov, university of florida ieee nuclear science symposium, honolulu, 31 october 2007 1...
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Andrey Korytov, University of Florida IEEE Nuclear Science Symposium, Honolulu, 31 October 2007 1
Performance of CMS Cathode Strip
Chambers
Andrey Korytov
(for CMS Collaboration)
Andrey Korytov, University of Florida IEEE Nuclear Science Symposium, Honolulu, 31 October 2007 2
Compact Muon Solenoidal Detector (CMS)
Endcap Muon Systemis based on CathodeStrip Chambers (CSCs)
4 stations (disks of CSCs) in each endcap
6 sensitive planes per CSC
468 CSCs with totalsensitive area >5000 m2
pseudorapidity coverage0.9<||<2.4
~500K readout channels
Provides:- muon trigger- muon identification and precise measurements
Endcap Muon Systemis based on CathodeStrip Chambers (CSCs)
4 stations (disks of CSCs) in each endcap
6 sensitive planes per CSC
468 CSCs with totalsensitive area >5000 m2
pseudorapidity coverage0.9<||<2.4
~500K readout channels
Provides:- muon trigger- muon identification and precise measurements
Andrey Korytov, University of Florida IEEE Nuclear Science Symposium, Honolulu, 31 October 2007 3
One of 8 endcap stations
Andrey Korytov, University of Florida IEEE Nuclear Science Symposium, Honolulu, 31 October 2007 4
What’s newPerformance of CMS CSCs was extensively studied over the last 10 years during R&D and production:
cosmic ray muons, muon beams, high irradiation rate conditions, etc.BUT one chamber at a time (often a small fraction of a chamber area) in lab conditions
In this talk, we present the first results obtained with: 36 CSCs operated in situ as one system
400 m2 of sensitive planes 8% of the entire CMS CSC system
cosmic ray muons
Presented:Track Segment finding efficiency (Level 1 Trigger)Fast Precision Coordinate reconstruction (High Level Trigger)
Andrey Korytov, University of Florida IEEE Nuclear Science Symposium, Honolulu, 31 October 2007 5
CMS Magnet Test and Cosmic Challenge
ME+4
ME+3
ME+2ME+1
60
Fall 2006
CSC scope• 60-sector of one of the two endcaps• 36 chambers, ~8% of all
Andrey Korytov, University of Florida IEEE Nuclear Science Symposium, Honolulu, 31 October 2007 6
CSC design and readoutLarge chambers Wires groups: 5 cm wide Cathode strips: 8-16 mm wide
3.3
m
wire-group hits every 25 ns same information for trigger/offline
Level-1 Trigger: half-strip hits every 25 nsHLT*/offline: 12-bit digitization every 50 ns
*HLT – High Level Trigger
Andrey Korytov, University of Florida IEEE Nuclear Science Symposium, Honolulu, 31 October 2007 7
Track Segments for L1 Trigger
1D Track Segments(pattern recognition is implemented in firmware)
wire-group hits in six planes half-strip hits in six planes
2D Track Segments are combinatorial combinations of all 1D wire- and strip-
segments
Efficiency requirement >99%
Andrey Korytov, University of Florida IEEE Nuclear Science Symposium, Honolulu, 31 October 2007 8
Digitized strip signals for HLT/offline
Strip signals are sampled and digitized every 50 ns
HLT requirements:• Resolution: <0.5 mm per segment• CPU: ~ ms per segment (time budget for entire HLT is 40 ms)
Offline requirements:• Resolution: 150 m per segment
strip 1 signal
strip 2 signal
strip 3 signal
strip 4 signal
strip 5 signal
strip 6 signal
Andrey Korytov, University of Florida IEEE Nuclear Science Symposium, Honolulu, 31 October 2007 9
Track Segment Efficiency measurement
• Magnetic field 0 T• Trigger is based on ME1 and ME3 stations only• ME2 station is also in readout, but not in the trigger• Only one Track Segment in ME1 and ME3 () • ME1+ME3 provide prediction in ME2 ()• Residual = Segment in ME2 () – Prediction ()
Andrey Korytov, University of Florida IEEE Nuclear Science Symposium, Honolulu, 31 October 2007 10
Predicted Track Segment in ME2/2 CSCs
Coordinates of all predicted hits in ME2/2
Red trapezoid – chamber outlineDashed lines – “semi-dead” areas separating 5 independent plane sections
Predicted hits that were missed in ME2/2
Blue sub-trapezoids – nominal fiducial areaof “guaranteed’ full efficiency
Andrey Korytov, University of Florida IEEE Nuclear Science Symposium, Honolulu, 31 October 2007 11
Track Finding Efficiency of ME2/2 CSCs
NO CUTS
Red points – measurements
Blue line – expectation taking into account“semi-dead” areas separating independentwire plane sections
ONLY FIDUCIAL AREA OF FULL EFFICIENCY
Red points – measurements
Average efficiency 99.93±0.03%
Andrey Korytov, University of Florida IEEE Nuclear Science Symposium, Honolulu, 31 October 2007 12
Sagitta based on found track segments
Scatter plot of sagitta measurements
dY is larger due to courser Y-coordinate measurements (wire groups vs half-strips)
Average offset is due to iron disk misalignmentduring MTCC—confirmed by geodesic survey
Histogram—measured residuals
Line—expected residuals, simple calculations based on cosmic ray muon momentum spectrum
Andrey Korytov, University of Florida IEEE Nuclear Science Symposium, Honolulu, 31 October 2007 13
Fast algorithm for hit/segment reconstruction at HLT
Reuse L1 Track Segments: can be done due to their very high efficiency and good (few mm)
pointing by design, if L1 Track Segment is not found, no data are read out from
that chamber by DAQ
Using digitized strip signals, find x-coordinates drop calibrations (gain, pedestals, x-talks, noise correlation
matrix, plane mis-alignment): can be done due to high uniformity of the system no database access is needed
build x-coordinate as a function of digitized signals no iterative fitting
Using six x-coordinates, find segment coordinates linear procedure (no iterations) prune up to two outliers
CPU time performance: 0.45 ms per segment (Intel 2.8 GHz P4)
Andrey Korytov, University of Florida IEEE Nuclear Science Symposium, Honolulu, 31 October 2007 14
Fast x-coordinate (1)
Use first two time samples to build pedestals dynamically (to reduce noise, average as new events come in)
Add three samples with signal (max ± 1)
Use an old method of ratio of charges to get a first approximation for a local coordinate in strip width units
time
charg
e
pedestal
Q1
Q2
Q3
1 2 3( ) ( ) ( )stripQ Q t Q t Q t Qcenter
Qleft
Qright
1
2 min( , )right left
center left right
Q Qr
Q Q Q
strips
Andrey Korytov, University of Florida IEEE Nuclear Science Symposium, Honolulu, 31 October 2007 15
Fast x-coordinate (2)
Correct for expected non-linearity using the Gatti shape of the induced charge (correction is a simple strip width-dependent function)
Check occupancy for reconstructed coordinate. It is not flat indicating there is a remaining non-linearity.
Fit the occupancy and reconstruct empirical correction (which happens
to be almost strip-width independent)
( , )x r f r w
/dN dx
( )x x g x st1 -order corrected coordinate x
( )g x
True coordinate (strip width units)x
Andrey Korytov, University of Florida IEEE Nuclear Science Symposium, Honolulu, 31 October 2007 16
Residuals in test (3rd) plane
Plane 3 is not used inthe track segment fit
Residual(3) = xmeas(3) – xfit(3)
Plane 3
Plane 4
Plane 5
Plane 6
Plane 2
Plane 1
strip center strip edge
Andrey Korytov, University of Florida IEEE Nuclear Science Symposium, Honolulu, 31 October 2007 17
Extrapolating to the full track segment
There was not a precise reference prediction for a track segment in MTCC. Hence, we just extrapolate single plane resolutions to the overall six-plane resolution
CSC six-plane resolution is ~150 m
by far exceeds the HLT requirement of <0.5 mm
actually, very close to design spec for the ultimate offline resolution
2 2
1 1
( )all sixTOT iplanes
x
HLT requirement
Andrey Korytov, University of Florida IEEE Nuclear Science Symposium, Honolulu, 31 October 2007 18
Summary
Trigger performance of CMS CSCs evaluatedwith cosmic rays using 36 CSCs operated in situ as one system
2d Track Segments for Level-1 trigger: efficiency 99.9% (required 99%)sagitta residuals are consistent with m.s. of cosmic ray muons (~3 mm)decision time 800 ns (firmware, by design)
Track Segments for High Level Trigger localization per chamber ~150 m (required 0.5 mm) robust, no losses in efficiency (by algorithm design)decision time 0.5 ms (software, required ~ ms)
Andrey Korytov, University of Florida IEEE Nuclear Science Symposium, Honolulu, 31 October 2007 19
Backup slides
Andrey Korytov, University of Florida IEEE Nuclear Science Symposium, Honolulu, 31 October 2007 20
CSC Design Parameters
Overall size: 3.3 x 1.5/0.8 m2
(trapezoidal) 7 panels form 6 gas gaps of 9.5 mmAnode-Cathode: h=4.75 mm
Anode wires: d=50 m, gold-plated tungsten Wire spacing: s=3.2 mm pitch Wire tension:T=250 g (60% elastic limit)Readout group: 5 to 16 wires (1.5-5 cm)
Cathode strips:w=8-16 mm wide (one side)
Gas: Ar+CO2+CF4=40+50+10
Nominal HV: 3.6 kV Gas Gain: 105
Andrey Korytov, University of Florida IEEE Nuclear Science Symposium, Honolulu, 31 October 2007 21
Singles Rate Curve
Singles Rate with Cs-137 Source
0
10
20
30
40
50
60
70
80
90
100
3 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4
High Voltage, kV
Rat
e p
er c
ham
ber
, kH
z
4/6-ALCT Rate (cosmic ray muons)
0
0.05
0.1
0.15
0.2
3 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4
High Voltage, kVR
ate
per
ch
amb
er, k
Hz
dark count rate ~ 0.04 Hz/cm2
Andrey Korytov, University of Florida IEEE Nuclear Science Symposium, Honolulu, 31 October 2007 22
CSC aging test results Setup:
Full size production chamberPrototype of closed-loop gas system
nominal gas flow 1 V0/day, 10% refreshedLarge area irradiation
4 layers x 1 m2, or 1000 m of wiresRate = 100 times the LHC rate
1 mo = 10 LHC yrs
Results:
50 LHC years of irradiation (0.3 C/cm)No significant changes in performance:
gas gain remained constant dark current remained < 100 nA (no
radiation induced currents a la Malter effect)
singles rate curve did not change slight decrease of resistance between
stripsOpening of chamber revealed:
no debris on wires thin layer of deposits on cathode (stinky!)
—no effect on performance
Anode wire after aging tests
Andrey Korytov, University of Florida IEEE Nuclear Science Symposium, Honolulu, 31 October 2007 23
CSC Production Sites
CSC Assembly (Fermilab, PNPI-St.Petersburg, IHEP-Beijing, JINR-Dubna) On-CSC electronics (Universities: Ohio State, UCLA, Carnegie-Mellon, Wisconsin) Final Assembly and System Tests (Univ. of Florida, UCLA, PNPI, IHEP, JINR) Pre-installation tests and final commissioning (CERN)