charged particle tracking for clas12

CLAS12 Detector Review

Charged Particle Tracking for CLAS12

Physics a tracking requirements a detector specifications

Detector Design Barrel Vertex Tracker (BVT)Forward Vertex Tracker (FVT)Drift Chambers (DC)

Optimizing the DesignBVT (mixed Si/MM?)FVT (stereo angle?)

Design optionsSimulation resultsTechnology reviews

December 2, 2009 Mac Mestayer

Maximizing efficiency and resolution at high ratesKey decision points

Basic overview


Tracking: physics a design spec’s

Experiment Characteristics• electron beam• small cross-sections (exclusive reactions,

Q2-dep.)• measure hadronic state

– establish exclusivity (missing mass)– other cuts: co-planarity, etc.

• forward-going particles– small laboratory angles

• broad coverage in center-of-mass December 2, 2009 Mac Mestayer


Goals: Specifications:measure flux-factor accurately

q ~ 1 mraddp/p < 1%

select an exclusive reaction; e.g. only one missing pion

dp < .05 GeV/cdq p < .02 GeV/c sinq df p < .02 GeV/c

small cross-sections

L = 1035/cm2/shigh efficiency

good acceptance Df ~ 50% at 5o

Physics goals a general design spec’s



Tracking Specifications Summary

Fwd. Tracker Central Tracker

Angular coverage 5o – 40o

(50% f-coverage at 5o)

35o – 125o

(> 90% f-coverage)

Momentum resolution

dp/p < 1% dp/p < 5%

q Resolution 1 mrad 5 – 10 mrad

f Resolution 1 mrad/sinq 5 mrad/sinq

Luminosity 1035 cm-2 s-1 1035 cm-2 s-1



CLAS12 tracking: ca. 2008

DC’s

torus

solenoid

May 8, 2008 Mac Mestayer

reg. 1reg. 2

reg. 3

Si tracker


Silicon trackers and drift chambers


Central tracker:

•single-sided Si strips•150 mm pitch•barrel: 4 x 2, graded 3o stereo•fwd: 3 x 2, +/- 12o stereo

DC’s: same concept as present chambers•6 sectors, 3 regions•2 super-layers/region•+/- 6o stereo•regions at ~ 2, 3, 4 m.•112 wires/layer (24192)•250 mm resolution


BST & FVT AssemblySilicon vertex tracker reviewed on April 2:

design meets physics requirements

design is technically feasible

recommend we do the following: • develop alignment specifications• develop an operational plan• develop a grounding scheme

•no further discussion of Si tracker in this review; unless requested



Central vertex tracking

• Central or “barrel” vertex detector (BVT)– mixed: inner - Silicon, outer –

Micromegas– Silicon:

• better position resolution • but, more multiple scattering • and, very small stereo angle

– all-Si design good for dp/p, df; bad for dq, dz


Résultats3 dispositifs ont été étudiés:- 4x2 SI ( = 1.5°, et = 43 mm)- 4x2 MM ( = 0 et 90°)- 2x2 SI+ 3x2 MM

pT/pT SI(+MM)

q MM

Résultats - 2

SI(+MM) z MM


Silicon + Micromegas ?

• simulations show mixed solution best, but– can Micromegas work with a cylindrical

geometry?– can Micromegas work in a high,

transverse B-field ?• Review the technology


Review of Micromegas Tracking Detectors for CLAS12 – May 7, 2009

• Reviewers: Madhu Dixit, Mac Mestayer• Presentations covered the following topics:

– detector overview: layers, strip pitch, segmentation for central & forward regions

– fabrication overview: principles and prototype testing of “bulk” technology– detector simulation: GARFIELD results on drift, diffusion, gain– tracking simulation: particle backgrounds, tracking efficiency and resolution– acceptance and quality assurance: methods to validate component performance– prototype testing: measurements of position resolution, Lorentz angle, gain

times transmission and tracking efficiency for minimum-ionizing tracks; including tests of curved detectors and tests in magnetic fields

– electronics: overview of requirements for charge and time measurements; options for an integrated system: amplification/discrimination/digitization/ readout.

• Impressive new pioneering work on curved Micromegas technology and operation in transverse magnetic fields

Resolution of the charges:

• The simulated performance for resolution, solid angle coverage and efficiency meet or exceed CLAS12 requirements.

• The design is based upon existing technology, simulated at both the signal and track-finding level with key parameters verified by prototype tests. The simulations are consistent with the test results.

• The conceptual plans for detector integration (including safety systems) are consistent with the overall CLAS12 detector layout.

• The schedule and allocated manpower seem reasonable.• The group is competent; recognized world leaders in this

technology.

We are confident that the group can successfully design and build the proposed tracking detectors for CLAS12.


Optimizing the BST design

• what’s best mixture of Si. vs. MM? 2 X 3 ?

• integrated vs. independent mech. structure

• best combination E field/ drift gap?• stereo angle:

– smaller than 90 deg.?• fewer ‘ghost’ hits, worse resolution

– need flex-cable readout for “y” strips• mesh segmentationDecember 2, 2009 Mac Mestayer


Why do we need a forward vertex detector?

• might find ‘stub’ tracks pointing to coils

• might help with track-finding• vastly improves vertex information• improves other track parameters

– better knowledge of Int(B X dl)



How will the FVT be used?

• stand-alone tracker (no)• ‘seed’ for forward track (?)• vernier for dc-only track (yes)

– need good background rejection• Requirements

– Efficiency• prob. of >1 hit in ‘matching circle’ < 20%

– Resolution• ~100 micron spatial resolution


Present forward tracker (DC, FST)

• 3x2 layers• trapezoidal tiles• 12° stereo angle• acceptance: 5°35°

• 6 independent sectors• 3 chambers (‘regions’) per sector• 2 six-layer superlayers (+/- 6 °)• plane tilted by 25° wrt the beam axis• acceptance: 5°40°

DC

FST

Strip layout:

Simulation & Reconstruction 10/30/2008 S.Procureur


Torus magnetic field

•∫B∙dl ~ 3 T-m

•highest field for forward tracks


B (t

esla

)

Scattering angle (degrees)


Match DC track to FST hit


98% of DC tracksextrapolate within+/- 1 cm.

So, how many background hits in the ‘circle of confusion’?

Resolutions with DC+FST(electrons at q = 15°, now from GEMC!):

FST greatly improves the vertex resolution, , q and p

5 times better20 times better

Simulation & Reconstruction 10/30/2008 S.Procureur

DC+FST – resolution with protons

Much better vertex resolution with FST (and resolution at high p)

(protons at q = 15°):

3-4 times better8-10 times better


Change FST to Micromegas?

• Difficulties with FST– massive cooling structure in live area

• no cooling in live area for Micromegas– dead area around each trapezoidal sensor

• very small dead areas for Micromegas– hard to deal with high rate at small radius

• Difficulties with Micromegas– parallel E and B-fields

• very little charge spreading• charged track hits look like x-ray hits



Optimize FST parameters?

• optimum stereo angle? - more choice– large angle gives better theta resolution– but, also gives more fake strip matches

• mixed strip and pixel segmentation– want fewer strip crossings at small

radius– ghost hits will appear at larger radius

• can we cover the full azimuth?• what is the mesh segmentation?

radial?December 2, 2009 Mac Mestayer


Key Decision Points

• BST– how many layers of Si? …MM?

• 2 – 3? 3 – 3?– unified or independent structure ?

• internal accuracy vs. ease of installation/repair

– layout details: stereo angle, mesh segmentation

• study two-layer ‘punch-through’ background– sensor design: drift gap, field strength

• reduce sparking rateDecember 2, 2009 Mac Mestayer


Key Decision Points

• FST– Super-layer structure okay?

• 3 units, each u – v– Background is very radially-dependent

• want radial segmentation?• if so, how do we get signals out?

– What is the optimum stereo angle?• balance dq vs. ghost hits

– Can we cover the full azimuth?



CLAS12 Tracking: Summary

• Si + MM provides excellent resolution in central region: better than Si or MM alone

• FVT: better vertex than DC12 alone– Si disk design works well, but– MM design offers more readout flexibility

• finer segmentation in ‘hot’ region• full azimuthal coverage

• Micromegas has a major role in CLAS12



Backup slides on DC12



measure cross-section accurately

q ~ 1 mraddp/p < 1%

planar chambersidentical cells (easy to calibrate)250 mm accuracy/layer

select an exclusive reaction; e.g. only one missing pion

dp < .05 GeV/cdq p < .02 GeV/c sinq df p < .02 GeV/c

~linear drift velocity+/- 6o stereo angle

small cross-sections

L = 1035/cm2/shigh efficiency

small cellssix 6-layer superlayers30 mm wires

good acceptance Df ~ 50% of 2p at 5o pre-bowed frameslow wire tensionsself-supporting design

Physics goal Physics spec. Design feature



Superlayer Wire LayoutStaggered “Brick-Wall” Hexagonal

colored circles

representdrift

distances

fieldfieldsensefieldfieldsense....

.sensefieldfieldsensefieldfield

6 sense layers, 2 guard layers, 14 field layers: 1 superlayerDecember 2, 2009 Mac Mestayer


Rationale for Design Decisions

6x6 layers robust track-finding+/- 6o stereo better f resolution than CLASplanar; self-supporting identical cells, easy to

calibrate, survey, repair112 wires/layer enough for 1035 operation30 mm sense wire 92/08 Ar:CO2

faster, linear distance-vs-time, strong, more reliable stringing

low wire tension thinner endplateson-chamber amplifiers good signal/noisere-use HV, LV, ADB, TDC

lots of spares; cost savings; better segmentation



Drift Velocity Calculation

20 mm wire 2325 V 88:12 AR:CO2

30 mm wire 2475 V 92:08 AR:CO2

same gain

58% faster

- and more linear ! use 30 mm wire!



Number of Holes4925 feedthrough holes12 survey 3 datum & alignment28 bolt & attachment

1.7 m

Endplates: many precise holes



Endplate Details

0.200 mmtrue positiona “50 mm”



Endplates fit into Frames

Receive endplates- inspect- measure hole positions- cleanReceive frames- inspect and clean- pre-bow endplate and frames- bolt and glue into frames



Box Assembled-endplates attached-attachment brackets affixedNext ---- mount on stringing fixture- insert feedthroughs- install survey points- string wires- attach circuit boards- QA/QC

Chamber Ready to String



CLAS12 Stringing Fixture



Parts: wire a circuit board

conductive rubber

circuit board

crimp pin

feedthrough

endplate

signal routing:wires a pre-amp

wire


circuit board


Stringing wires between “slanted” endplates

endplates

“gravity” stringingwires: 9 cm - 4 m longwires strung individuallywires attached by crimpingwires positioned by “trumpet”



Steps in Stringing



Installing Pre-tensioning Wires

Pre-tensioning- before we start stringing- use springs on guard wires- gradual release of tension



Stringing the Chamber



Installing Pre-amplifier Boards


On-board pre-amplifier boards and high-voltage distribution boards are installed after wires are strung.


1 mA2 - 3 electrons

Pre-amp2 mV/mA

Post-ampx 10 - x 3030 mV disc.

drift chamber

75 ft. cable

TDC’sLecroy 1877

new circuit boardsbased on old SIP’s

Electronics: Chamber a TDC


re-use post-amps, TDC’s


Model of Torus and Chambers


very useful:-installation-cabling-access


Tight-packing of Cables, Connectors


CAD layoutsverified on a model:tight spacing dictated by requirement of50% f-coverage at 5o

multi-layer

composite

endplate !!


Installation and mounting scheme


Linkage system allows quick and accurate installation

Positioning accuracyreproducible to 25 mm


Schedule: Stringing the Chambers

~2 yrs./ 6 chambers

~1/2 time for stringing



Safety and Quality Assurance


Issue Mitigationheavy equipment engineering review; procedures;

training; clasweb.jlab.org/wiki/index.php/Safety

cleanliness Class-10,000 clean-room, cleaning procedures, protective clothing

high-voltage power current-limited to 40 mAlow-voltage power voltage limited to 7.5 Vuse of magnets, motors follow EH&S manual on elec. safetyelectrical connections continuity and isolation checkswire placement accuracy

parts inspections, surveys; tight controls on wire tension and end-plate deflection

wire breakage “stress-tests”, temp., g-force limitspre-installation operability

full commissioning plans (on wiki)

installation accuracy micro-switches, post-installation surveys


Project Overview & Responsibilities

• Oversight: Jefferson Lab• Prototyping

– full-sized Reg. 1 prototype: Jlab, ODU– beam tests: Jlab, ISU

• Design– Region 1 & 2: JLab– Region 3: Idaho State

• Build, String & Commission– Reg. 1 - Idaho State– Reg. 2 - ODU– Reg. 3 - JLab



CLAS Drift Chambers : History

• Operating successfully for ~10 years ….


A photo of the first“Reg. 3” chambermoving into Hall B


Problems in the CLAS Drift Chambers

• We’ve had a couple of problems:• ~60 severe* / year• 16 broken wires• 5 - 10 adb per yr.

• better now?• ~ 10 lv per yr.

• worse now?

* severe problems/ breakthroughs in elog



CLAS Drift Chambers : History

…. with good resolution

mid-cell resolution is 200 - 250 mm

cell average: 310, 315, 380 mm; for R1, R2, R3

…. at the same voltage, with same efficiencya Ar/CO2 shows no conventional

aging


NIM A449 (2000) 81


Conclusions

Large project: 18 chambers, 90K total wires

Reliable design: will achieve resolution and efficiency goals

Low risk cost and schedule: based on detailed knowledge from CLAS

High probability of success: experienced people


charged particle tracking for clas12

Documents

detector overview

4x2 si

discussion of si tracker

mac mestayerpresentations

si mmz

o stereoregions

o stereofwd

o stereo dcs