BTeV Level-1 Trigger Segment Finding Algorithm Internships for Physics Majors, August 8 th, 2002...

BTeV Level-1 TriggerSegment Finding Algorithm

Internships for Physics Majors, August 8th, 2002

Jennifer Seiler, Fermilab

(supervised by Jin-Yuan Wu)

Jennifer SeilerBTeV L1 Tracking & Vertexing Trigger Algorithm

BTeV detector

Silicon pixel vertex detector provides:•Pattern recognition power•Very good position resolution (~7•Radiation hardness


Si- pixel Detector

• 50 m x 400 m pixels bump-bonded to readout chips – 22 million total

• Two pixel planes per station (supported on a single substrate), with 30 planes (a station is 10 cm tall and they are 4.42 cm apart)

• Beam hole ~ 12 mm x 12 mm

• Detectors in vacuum

• Half planes move together when Tevatron beams are stable.

7.2 mm

8 mm

A pixel


BTeV trigger block diagram

1.5 TB/s7.6 MHz

L1 rate reduction: ~100x

L2/3 rate reduction: ~20x

4 KHz

B TeV d etecto r

L 1 m u on

L 1 v ertex

G lo b a lL ev el-1

L evel-1

L ev el 2 /3 C ro ssin g S w itch

D a ta L o gg in g

F ro n t-en d e lec tro n ics

L ev e l-1 B u ffe rs

L ev e l-2 /3 B u ffe rs

In fo rm a tio n Tra n sfer C o n tro l H a rd w a re

IT C H

L evel-2 /3 P rocessor F arm

# 1

# 2

# m -1

# m

RDY

Crossing #N

Req. data for crossing #N

L evel-3 accep t

G L 1 accep t

P IX

> 3 x 1 0 ch an n e ls7


L1 vertex trigger block diagram

3 0 P ix e l S ta tio n s

P ix e l P ro ce sso rs

F P G A S e g m e n t F in d e rs

~ 2 ,5 0 0 -n o d e D S P tra c k /v e rte x fa rm

S w itch (so rt b y cro ssin g n u m b er)

M E R G E

To G lo b a l L e v e l-1 (G L 1 )


Triplet to Track Finding (T2T)

10 cm


L1 vertex trigger algorithm

• Find beginning and ending segments of tracks from hit clusters in 3 adjacent stations (triplets):– beginning segments: required to originate from beam region– ending segments: required to project out of pixel detector

volume

FPGA Segment Finder (Pattern Recognition)

• Match beginning and ending segments found by FPGA segment finder to form complete tracks

• Reconstruct primary interaction vertices using complete tracks• Find tracks that are “detached” from reconstructed primaries

DSP Tracking and Vertexing


L1 vertex trigger algorithm

• Generate Level-1 accept if “detached” tracks in the same arm of the BTeV detector with:

2

2.0

6

25.02

b

b

pT

(GeV/c)2

cm

Execute Trigger

b

p p

B-meson


L1 trigger efficiencies

Process Eff. (%) Monte Carlo

Minimum bias 1 BTeVGeant

Bs D+sK- 74 BTeVGeant

B0 D*+- 64 BTeVGeant

B0 00 56 BTeVGeant

B0 J/s 50 BTeVGeant

Bs J/*0 68 MCFast

B- D0- 70 MCFast

B- Ks- 27 MCFast

B0 2-body modes 63 MCFast

()


Summary: Problems & Options

• False track / Good Track Found ratio = .1502 on average

– In false tracks the false hit is most often the first station hit

– Many of the false tracks we are seeing are too close to be resolved, other false tracks intersect at small angles with real tracks

• 85% as many external tracks found as internal found

– Internal are closer together and harder to resolve

– External track finding is very complete and accurate

Problems Seen

• One fix I did was to change to equation for finding matching precision-x hits in the non-bend view, so that precision-x hits for a give station would be found using only the other two stations

• Another possibility is to find tracks by finding short precision doublets 1st

• And a third is to find secondary interior triplets and see how they overlap onto the primary interior triplets, as a quadruplet finding algorithm

• All these options have potential problems

Options


• 85% as many external as internal tracks:– Means extra data flow and

more trouble matching triplets to tracks

– Also means lower triggering rate

– Options:• Tighter requirements for

interior matches than for exterior

• Quadruplet finding by overlapping triplets for interior

Proximity Issues

Too Many Internal Tracks


• Few real tracks are missed, but they exist among the extra tracks that are found

• Internal tracks find more extra tracks, but all of the tracks it finds are basically reasonable to consider as valid tracks

Found versus Real Tracks

Found Tracks


What BB33 is Finding

Dir Sta x1 y1 z1 x2 y2 z2 x3 y3 z3 track #1 #2 #3 All-1 5 0.08191 -0.60437 -46.92006 0.06346 -0.65716 -51.17007 0.08923 -0.71165 -55.42007 67 67 67 67 0 5 0.00000 0.00000 0.000000 0.07918 -0.65196 -50.77007 0.08437 -0.70800 -55.02007 -99999 67 67-1 6 0.17461 0.74860 -42.67004 0.31188 0.93675 -46.92005 0.51947 1.17190 -51.17004 766 484 934 0 0 6 0.16701 0.74222 -42.27004 0.31291 0.93336 -46.52005 0.00000 0.00000 0.00000 766 484 -99999-1 7 0.15769 0.63582 -38.42004 0.17461 0.74860 -42.67004 0.17878 0.86394 -46.92005 766 766 766 766 0 7 0.14627 0.64118 -38.02003 0.16701 0.74222 -42.27004 0.18857 0.86125 -46.52005 766 766 766-1 7 0.25261 0.71937 -38.42004 0.28862 0.82680 -42.67004 0.31188 0.93675 -46.92005 484 484 484 484 0 7 0.25893 0.72209 -38.02004 0.28442 0.81960 -42.27004 0.31291 0.93336 -46.52005 484 484 484-1 11 0.76146 -0.31655 -21.42002 1.04804 -0.38669 -25.67002 1.32104 -0.43427 -29.92003 716 716 716 716 0 11 0.73228 -0.32195 -21.02003 1.00861 -0.38545 -25.27003 1.28699 -0.42141 -29.52003 716 716 716-1 11 0.79615 -0.36298 -21.42002 1.04804 -0.38669 -25.67002 1.32104 -0.43427 -29.92003 502 716 716 0 0 11 0.79318 -0.34968 -21.02002 1.00861 -0.38545 -25.27003 1.28699 -0.42141 -29.52003 502 716 716-1 11 0.76146 -0.31655 -21.42002 0.95540 -0.51116 -25.67003 1.11232 -0.68513 -29.92003 716 502 502 0 0 11 0.73228 -0.32195 -21.02003 0.94011 -0.51084 -25.27002 1.08892 -0.67355 -29.52002 716 502 502-1 11 0.79615 -0.36298 -21.42002 0.95540 -0.51116 -25.67003 1.11232 -0.68513 -29.92003 502 502 502 502 0 11 0.79318 -0.34968 -21.02002 0.94011 -0.51084 -25.27002 1.08892 -0.67355 -29.52002 502 502 502-1 14 -0.18752 -0.70090 -8.67001 -0.24316 -0.96602 -12.92001 -0.35650 -1.20455 -17.17002 525 525 525 525 0 14 -0.18019 -0.67240 -8.27002 -0.25718 -0.95745 -12.52002 -0.33892 -1.20030 -16.77003 525 525 525-1 14 -0.06413 -0.74273 -8.67002 -0.24316 -0.96602 -12.92001 -0.35650 -1.20455 -17.17002 78 525 525 0 0 14 -0.03917 -0.72432 -8.27002 -0.25718 -0.95745 -12.52002 -0.33892 -1.20030 -16.77003 78 525 525-1 14 -0.06413 -0.74273 -8.67002 -0.05126 -0.92096 -12.92003 -0.04046 -1.11612 -17.17003 78 78 78 78 0 14 -0.03917 -0.72432 -8.27002 -0.04237 -0.91233 -12.54720 -0.04744 -1.11445 -16.77003 78 868 78-1 16 -0.52026 -0.60268 -0.17000 -0.67110 -0.84793 -4.42002 -0.84493 -1.05162 -8.67002 841 247 247 0 0 16 0.00000 0.00000 0.00000 -0.67105 -0.80221 -4.02002 -0.81364 -1.02810 -8.27002 -99999 247 247-1 16 -0.54949 -0.61751 -0.22999 -0.67110 -0.84793 -4.42002 -0.84493 -1.05162 -8.67002 736 247 247 0 0 16 -0.52883 -0.62656 0.22999 -0.67105 -0.80221 -4.02002 -0.81364 -1.02810 -8.27002 247 247 247-1 16 -0.53961 -0.65092 -0.17002 -0.67110 -0.84793 -4.42002 -0.84493 -1.05162 -8.67002 247 247 247 247 0 16 -0.52883 -0.62656 0.22999 -0.67105 -0.80221 -4.02002 -0.81364 -1.02810 -8.27002 247 247 247


What’s Happening Here?

• Tracks crossing at small angles

• Tracks too close• Tracks options with

different curvatures in the bend view

• Third hit issues occur with from issue like the one illustrated in the second image (middle hit confusion occurs most rarely)


• A good portion of the good tracks have missing precision-x matches

• A small percentage of false tracks can be eliminated with missing or bad short doublet hits and a significant portion are falsely confirmed

• Lower resolution in either dimension

• Finding tracks by first looking at the short doublets and projecting forward can be done one many ways:

– Projecting to other doublets and comparing slopes to make a long doublet, then projecting forward again

– Projecting the short doublet to the next plane and then the next plane

Beyond: Track Finding Options

Short Doublet Finding BB33

New

Short Doublet Finding Issues


• Significantly higher data flow (>20%)• The secondary triplets will only have as many false tracks• Trade-off: slightly higher computation time on finding more

triplets and matching them, but cuts computation for matching false interior tracks to exterior tracks

Beyond: Track-Finding Issues

Secondary Triplets Issues

• Quadruplets can be found without new hardware by finding secondary triplets and seeing how they overlap onto the primary interior triplets:– Allows for another confirming hit– Allows for better delta dy and delta

dx checks

Secondary Triplets (Quadruplets)


• The BB33 algorithm finds the short doublet match at a station by looking between that station and the next

– This finds the doublets for real and false tracks alike

• My algorithm projects the other two stations onto the station in question (only in the non-bend view), then looks at the slope of that short doublet

The False Precision Hit Problem

False Precision Hits

BB33

New

Problem: Only Works in non-bend view

Solution:


Quick note

• Good to Bad doublet ratio 1:3 (reasonable, maybe? But could be lower?)

• Short doublet finding might give fewer false doublets, but a number of good tracks with missing false doublets would be lost, and most false tracks (though a lower percentage than real tracks) find precision hits

• Any suggestions?

Doublet Finding


Bad versus Good TripletsB

B33

All

Trip

lets

My

All

Trip

lets

False Tracks & Hits


Which Hits Are BadB

B33

My


Missing Precision-x MatchesB

B33

Trip

lets

My

Trip

lets


What’s to be done?

• Conclusions:– A short doublet algorithm wouldn’t be very helpful,

because good tracks would be lost and it would give an almost equal ratio of bad:good tracks

– Using the other two stations to find the precision hits on for a station in a triplet lowers the frequency of false tracks

– A quadruplet algorithm while costly in time and bandwidth, could improve track finding efficiency

– We need more ideas• Further Study:

– I have yet to finish my quadruplet finding algorithm.– If I have the time this summer I will attempt a short

doublet algorithm, if no other ideas are available


QOTDs May-Aug 2002

• "Turns out that this algorithm doesn't work, but it has a worse problem....it's very slow"- Myers (CS312 professor)

• “Then I stared blankly at the dashboard of the car with a look on my face which suggested I was trying to calculate in my head the square root of oatmeal.” ~Dave Schoonover

• In the hall at Fermilab: “Yeah, I’m taking a vacation in August with the family. I think I’ll head out to SLAC.”

• “Does anyone else want to smell the projector?” –Nathan

• “These observations are actually correlated and connected!” (Symmetries in K-Physics, 7/9/02)

• In the Cornell Graphics lab: “ ‘what are you doing? Are you playing Quake Battlefield?’ ‘Uh…um…no…I’m ….uh…doing graphics research…yeah…. the physics engine…”

• “My emacs says, "TeX-shell" and I saw that and thought of tacos” ~Jerry, 7/11/02

• “You have a beam of electrons going around the accelerator. And then they get to the wiggler and the wiggler shakes them like this. <shakes hands> And this pisses the electrons off, so they radiate more.” ~Jerry, 7/16/02

• “The NSA has a website. And it has a "Kid's Page." I sense fundamental wrongness.” ~ Chase, 7/8/02


More QOTD 5/02-8/02

• “A Friday field trip to explore the possible combinations and interactions of Subway food-multiplets with the 19-dim summer-student-group people…Due to z´the hogh calculation efforts one should consider a pretest with a smaller low-dimensional subgroup… That’s not silly!!!… It is supposed to find the underlying field structure of the student-student interactions transmitted via the food-force. A very serious research topic!!” ~Andreas

• “The velocity selector is like having a bunch of little elves inside the box looking at all the particles, and if it's not exactly the right speed, they molest it.” ~ Dr. Dell

• “Einstein always asked the right questions -- the ones that had answers. Except for that unified field theory thing, but, oh well, he was old.” ~Dr. Dell

• “Imagine I'm this massless thing with two balls.” ~Dr. Dell

• "If you're out in space and have no environment to interact with, you can always rip off your arm and throw it out. And, because the center of mass of the system remains constant, you'll just be this bloody mass accelerating backwards. Of course, when you got to your spaceship, you'd immediately cauterize the wound with some bizarre laser device." ~Dr. Dell

• “Q: How is a chain saw like a Hilbert space? A: Both comprise an infinite number of infinitesimal axes.” ~Eric 7/29/02


Acknowledgements

• I would like to thank my family for allowing me to leave home for the 6th summer in a row, and for supporting, though discouraging, my love of physics.

• I would like to thank my friends for making physics that much more fun, geeks that they all are.

• Thanks to Michael Wang for arranging the code for me, and answering many of my questions.

• Most of all, I would like to thank Eric, Roger, Max, and my supervisor, Jin-yuan Wu, for making all of this possible.

• And Thanks too all of the Fermilab Interns for making this such a fun and wonderful experience.

BTeV Level-1 Trigger Segment Finding Algorithm Internships for Physics Majors, August 8 th, 2002...

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