Giovanni Petri University of Pisa/INFN Pisa/SLAC

29 August 2005

Study of TEM errors

1.1. Can the LAT produce errors during data Can the LAT produce errors during data acquisition?acquisition?– Choice of Error TypeChoice of Error Type– How often does it happen?How often does it happen?

– Under what condition does it happenUnder what condition does it happen?

2.2. What is the impact of these Errors on-orbit?What is the impact of these Errors on-orbit?

Lost in TranslationLost in TranslationIntroduction

How does it happen???How does it happen???

Tracker

Calorimeter

Tower Electronic Module

Tower Subsystems Tower Subsystems OverviewOverview

Glt Electronics Module

TEM collects them, checks 3-in-a-row and (if TKR triggers) sends it to GEM

GEM opens window on first trigger type and waits for others to arrive (Coincidence Window)

After few ticks CW closes and TAM is sent back to the readout controller to start readout

Readout starts from the

BOTTOM!!!

A particle hits the tower

Trigger Primitives fired by subsystems

TEM CC FIFO ErrorTEM CC FIFO Error– 1 cable stores up to 128 hits

– 8 cables per Tower

– 128 x 8 = 1024 hits per tower

Other Buffer Limits:

– Readout controller: max of 64 hits allowed

– Plane: max of 128 hits allowed (64x2)

– How: Cosmic showers e.g.

– Let’s call an event with FIFO error

“BAD” Cables

Si Planes

Tracker SketchFIFO Definition

How Often?How Often? Statistics Summary

• 6 Towers Runs:• # Runs: 62 (B type)• # Register Config: 3• # Events: 15,346,394• # Bad Events: 1760

• 8 Towers Runs:• # Runs: 81 (B type)• # Register Config: 3 • # Events: 22,391,000• # Bad Events: 2900

• 2 Towers Runs:• # Runs: 48 (all!!)• # Register Config: 19• # Events: 9,564,116• # Bad Events: 915

• 4 Towers Runs:• # Runs: 31 (B type)• # Register Config: 2• # Events: 1,084,655• # Bad Events: 93

• Error Rates for B type Runs:

• 2 Towers: 7.4 · 10-5

» B2: 8.3 · 10-5

» B10: 7.1 · 10-5

» B13: 7.5 · 10-5

• 4 Towers: 8.66 · 10-5

» B10: 8.40 · 10-5

» B13: 8.79 · 10-5

• 6 Towers: 1.13 · 10-4

» B2: 1,15 · 10-4

» B10: 1.09 · 10-4

» B13: 1.20 · 10-4

• Among 2 Towers runs (not B type)

– 135002057-2103– Single RC Right/Left

» ER 2 · 10-4

– 135002166-2168– Single RC R/L + Overlay 10 KHz

» 2,1/2,7 · 10-4

– 135002107– Only Cal Trigger

» 5.9· 10-3

How Often?How Often?Bad Events Rates

What’s that?2 orders of magnitude?

Can we explain this?

B2: Flight Settings

B10: Cal 4 range

B13: Zero Suppression OFF

Cables

Planes

• RC on one side only:• Max hits per plane is 64

• RC try to read its entire plane!– An event that had 70 hits on a

plane now saturates the plane!

– It’s easier to have more hits on the same Cable!!

Single RC ER Anomaly

• The factor 2-3 of difference is not so strange!!

»This can be a first order explanation!!

30 40

70

1. CAL LE has more probability to be triggered by high energy events.

2. Energetic events have more probably high hits occupancy

3. Is it enough to explain the big difference?

• No other runs to compare rates!!

Cal Only Trigger Anomaly

ER = 5.9· 10-3

The run has few events:3000 instead of 300,000!

NOT STRANGE!!

Do you believe me?Do you believe me?

BUT...BUT...We can REPRODUCE that!!!

Cut on CAL LE triggered Events!!

What comes out is ER ~ 3.6 · 10-3!!!

# Events: 3048

# Bad Events:18

You clearly recognize Eduardo when he’s been working late in the night

When do Bad Events happen to good When do Bad Events happen to good people?people?

• Which primitive triggers are there?

» GemConditionsWord

• When do they arrive?» Are there temporal

patterns?

• Is a Bad Event influenced by the previous one?

» GemDeltaEventTime

• How are hits distributed?

• Are there odd configurations?

• You understand “odd” later

» Stay tuned…

Trigger Hits Occupancy

Trigger Topology• GemConditionsWord:– Tells which primitive

triggers arrived in the CW– Possible combinations:

• TKR (2)• CAL LE (4)• CAL HE (8)• TKR + CAL LE (6)• TKR + CAL HE (10)• CAL LE + CAL HE (12)• TKR + both CAL (14)

B10 runs 2 towers B10 runs 2 towers

Trigger Types

GoodBad

•No 8s, 10s, 12s:

•This was expected!!

•Bad Events are “big”!

–High Multiplicity

We expect that the TKR often arrives first!

–TKR is big: high probability to

trigger first

Trigger TopologyTrigger Primitives Arrival Times

Chained B10 runs 2 towers Chained B10 runs 2 towers

TKR arrives soon!!!This is no surprise!

~80%

The number of events goes down very rapidly!!

Ticks

1 tick = 50 ns

Trigger TopologyTrigger Primitives Timing

• CAL LE should open when TKR is not the first:

» CAL LE is faster than CAL HE!

» # Times CAL LE opens CW is consistent!!

This is odd!!

Explanation???Just a case? Remember Log Scale

Ticks

Ticks

3 events

Trigger Topology

Temporal Correlations

The time between a Bad Event and the previous one is long!!

Good Bad

The minimum Delta Time is longer than for Good events

Just low statistics probably

1000 ticks 2000 ticks

Hits OccupancyEvent Display

Cliffhanger

Salt and Pepper

No Cal

Hits only in upper layers

“Recognizable track”

Cal lit up where “track” arrives

Hits everywhere

Drittoni(big straight)

50% 25%

20%

Hits Occupancy

1. Qualitatively: you can distinguish the single layers, one by one, from the other.

2. Hits are only on the borders and are uniformely distributed.

Evt 135002052-268476

CablesRea

dout

Con

trol

lers

Characteristic signature: everything’s FULL

PuffettaePuffettae

Puffettae• There is a Puffetta in 6 Towers

Runs too!!• None found in 4 and 8 towers runs

• It looks exactly the same as the 2 towers one.

135004119-115100

Puffettae Dumps

• Looking at Dumps you find this:

• 0040 (hex) = 64 (dec)

• For every single RC above 1 on every CC.

2

8

1

LDF Dump file

Puffettae Data

EventID CalEneSum (MeV)

Gem

Word

Tkr Cal Le Cal He Delta

Time

Gem

Discarded2 Towers

6 Towers

There is no obvious hint of electronics gone wild!!

Are these energies consistent with showers that big? • Delta Times are long

• GemDiscarded seems reasonable (TOT very long)

115099 117 2 2 31 31 10221 3607

115100 351303 14 3 0 2 47043 3607

115101 26 2 0 31 31 56818 3615

268475 0 2 0 31 31 46600 1367

268476 87766 14 2 0 9 65535 1367

268477 0 2 0 31 31 65535 1367

From Russia with… CAL!

Too good to be true!!!!CAL says:“Everything normal pal!! Just big shower!!”

Layers

Ene

rgy

(GeV

)

Asimmetry

LAT

6 towers

1. At sea level we see 10% of Ep (Tune)

2. From graph 106 e- at sealevel (Tune)

High multiplicity shower of 10 MeV e-

350 GeV measured

All strips hit 10⇒ 4 particles in 6 towers

350GeV/10000 = 35 MeV per particle

10 MeV particles don’t go through the TKR!!

p

For Ep=105 GeV (for consistency with the observed rate)

NO PUFFETTAE!!

What happens on-What happens on-orbit?orbit?

• There will be high-energy photons!!– Will these be high multiplicity events in the TKR?

• Let’s see what MC has to say about this!!• Used photons coming from 45°-60° from the vertical axis

• Energy of 300 GeV

• Searching for behaviours like those observed in FIFO errors

• Backsplash?Total # MC photons 105

# Triggered Events 13006

#1 Towers Saturated: 38

300 GeV

ConclusionsConclusions1. The TKR works (poor me…) too well!!

• FIFO errors are no mistery anymore!!• We know how to characterize AND understand

them!

– Rates are low: • 1 (lonely) bad guy every 100 thousands!!!!

– No influence on other events!!!

2. Bad Events are consistent with showers3. High energy photons MC needs to be

further studied– What about reducing lower layers buffer

bandwidth to improve recon??

TACK Favorite saying:

“I told you NOT my Camaro!! Now I’m angry…”

Anders Borgland

High energy Muon shower

Eduardo do Couto e Silva

Favorite saying: THIS IS TOO COOL!!!!

HIM

…trying to sneak home early… 1 AM…

ME

BACKUP SLIDES…hic sunt leones…

EM Showers

To be in the core area 3.14x4202=5.5x105 m2

Freq = 2 x 10-2/s (~4-8 e/ m2)To be in a 10 times denser area Freq ~ 2 x 10-3/s (~40-80 e/ m2) To be in a 100 times denser area Freq ~ 2 x 10-4/s (~400-800 e/ m2)

To be in the core area 3.14x4202=5.5x105 m2

Freq = 2 x 10-4/s (~40-80 e/ m2)To be in a 10 times denser area Freq ~ 2 x 10-5/s (~400-800 e/ m2) To be in a 100 times denser area Freq ~ 2 x 10-6/s (~4000-8000 e/ m2)

107 Gev

108 Gev• Need ~ 104 particles

• Total Energy ~ 350 GeV

• <Ep> ~ 35 MeV

• Let’s say initial total energy was 105-106 GeV

• We get at sealevel ~ 106 particles

• Assume for such initial energy, Freq ~ 2 x 10-4/s

• The 6 tower data acquisition lasted ~ 1 day

~ 16 Puffettae (or like)

Saturated tower:> 64 hits on each of the 4 bottom planes(both on x and y)

Is this consistent with Is this consistent with Showers?Showers?

# Saturated Towers

1 2 3 4 5 6 7 8

6 Towers Data 78 6 3 1 1 2 / /

8 Towers Data 145 11 3 3 2 1 0 4

91

169

=

V.H.E. Cosmic Rays and Air Shower Profile

Take a proton with Ep=107GeV=1016eV

Flux is 6.8/E1.75 per cm2, second, steradianand bin-width of E where E= 107GeV.We then get, Flux(Ep=107GeV)=3.8x10-12 /cm2/s/sr for a bin-width of 107GeV

Step 1) Read off the flux of 107GeV proton rate

Step 2) Estimate the lateral distr. of particles

Distance from the core is about 14X = 420m

Normalized density of 10-2 /X2 = 10-2 /(30m)2

X=Rad. length of atmosphere=36g/cm2=30m

Observationproton

Electron Component in Hadronic ShowerN

e/E0 [

1/G

eV]

Step 3) Estimate the number of electrons in a 107GeV air shower at sea level.

These are shower measured profiles for 105GeV proton. Since there is no measurement for 107GeV, we assume one sample profile from these.

This gives highest number of electrons at sea level: use as an upper limit.

For a 107GeV proton we get Number of e = 0.2x107 = 2x106

Electrons and Gammas within an EM Shower

Step 4) Calculate electron density per m2

From Step 3) Total number of electrons = 2x106 electronsFrom Step 2) Assume they are distributed uniformly in r=14X=420m of the core. Electron density is then 1.8x10-6 (1/m2) times 2x106 = 3.6/m2

Uncertainty: a) Fluctuation: Trade-off with frequency. Can give a factor of 10-100? b) Low critical energy for LAT? Ec=10MeV > 1.5MeV: a factor of 2? (see Figure)

Step 5) Calculate frequency:

From Step 1) 3.8x10-12 /cm2/s/srFrom Step 2) core radius=14X=420m

To be in the core area 3.14x4202=5.5x105 m2

Freq = 2 x 10-2/s (~4-8 e/ m2)To be in a 10 times denser area Freq ~ 2 x 10-3/s (~40-80 e/ m2) To be in a 100 times denser area Freq ~ 2 x 10-4/s (~400-800 e/ m2)

Horizontal Air Shower? (1/2)Ref: S. Mikamo et al., ICR-Report-100-82-3 (1982) [Spires]; Lett. Nuovo Cimento 34 (1982) 273

Ordinary air shower initiated by protons and nuclei lose ~all energy for zenith ang. >50 deg.

A different population “hirizontal” shower has been detected. If LAT is hit horizontally the electron multiplicity can be much lower.

Step 6) Take horizontal air showers with Ne>104

Intensity = 2 x 10-13 /cm2/s/ster (see the right fig.)Likely zenith angle = 65, 75, 85 deg. (see the fig. in the next slide.)Overburden=1kg/cos(65,75,85deg)=2.4, 3.9, 11.5 kg = 67, 108, 319 X (the shower hist. may be shorter.)Typical lateral size: assume to be half the detector size of the Akeno exp. > radius=20m

Horizontal Air Shower? (2/2)Ref: S. Mikamo et al., ICR-Report-100-82-3 (1982) [Spires]; Lett. Nuovo Cimento 34 (1982) 273

Step 7) Calculate frequency and electron density

Core area = 1250m2

Electron density = >104/1250 = >8/m2

Freq = 2.5x10-6/s/sr

To be in the core area (1250m2)

Freq ~ 2.5 x 10-6/s (>8 e/ m2)To be in a 10 times denser area Freq ~ Prob. of 10 fold fluct. x 2.5 x 10-7/s (>80 e/ m2)

Conclusion1) Frequency of LAT being within the core radius (~420m for 107GeV) is high (~1/min) but average electron density is only ~4-8/m2.2) Electron density probably fluctuate as much as 100 times, but the product of frequency and multiplicity remains constant for a given shower energy. Freq ~ 2 x 10-2/s (~4-8 e/m2) Freq (x 10) ~ prob. of 10 fold fluct. x 2 x 10-3/s (~40-80 e/m2) Freq (x 100) ~ prob. of 100 fold fluct. x 2 x 10-4/s (~400-800 e/m2)3) Guestimate for 108GeV protons: Frequency 1/100, multi. is 10 times. Freq ~ 2 x 10-3/s 2 x 10-4/s (~40-80 e/m2) Freq ~ prob. of 10 fold fluct. x 2 x 10-5/s (~400-800 e/m2) Freq ~ prob. of 100 fold fluct. x 2 x 10-6/s (~4000-8000 e/m2)4) Horizontal showers are likely to produce high multiplicity events than normal showers.