andrey korytov, university of florida ieee nuclear science symposium, honolulu, 31 october 2007 1...

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)


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


One of 8 endcap stations


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)


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


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


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%


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


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 ()


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


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%


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


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)


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


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


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


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


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)


Backup slides


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


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


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


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)

andrey korytov, university of florida ieee nuclear science symposium, honolulu, 31 october 2007 1...

Documents