phos4 studies and fit functions for timing

Phos4 Studies and Fit functions for Timing

Michael Henke, Valerie LangKirchhoff-Institute for Physics, University of Heidelberg

L1Calo Joint Meeting, 12.01.2010, Heidelberg

Michael Henke, Valerie Lang 2

Phos4 Scan-Studies

• Run 124774:– 12.08.2009– 2079 Events– 20-40 Events

per Phos4 block– LAr pulsed– TriggerTower

0x00100501(emBarrel)

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Phos4 Scan-Studies

• Run 124774 Trigger Tower 0x00100501(similar to Taylor‘s work)

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Corrected for a shift of the pedestal with respect to the Phos4-Step


Close look at pulse top• Deviations from an ideal

peak form around the maximum

• This complicates the determination of the pulse maximum‘s position.

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Why bother?1. Maximum‘s position from

Phos4 histogram = reference value for quality determination of a certain fit function to Phos4 pulse

2. Calibration precision


Peak tops for other trigger towers

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Trigger tower 0x00100200 fairly ideal pulse

Trigger tower 0x00100901 Trigger tower 0x00100e01

Trigger tower 0x00100301


Number of channels affected• Rough estimate:

– Look at 500 channels for 3 partitions– Count affected channels– No information on Tile Calorimeter as this wasn‘t pulsed

• Results:

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Calorimeter partition

Crate number

Percentage of affected channels

Comments

emBarrel 0 37%

emEndCap 2 16% In general: smaller deformations

forwardCal & hadEndCap

4 13% than in emBarrel

In total: 22%


Causes of peak irregularities?• Data from Phos4-

Scan plotted without mean calculation over the individual Phos4-blocks(pedestal shift correction applied)

• Colour indicates number of times a certain ADC count occured

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Trigger tower 0x00100501:


Causes of peak irregularities?

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Trigger tower 0x00100501:

=> Irregularities don‘t stem from strongly deviating values in the mean calculation


Consider other runs• Run 124777:

– 5 minutes later than run 124774

– 2042 events– LAr pulsed– Unfortunately: many pulses

are saturated, i.e. no information about pulse peak form

– Compare 2 non-saturated channels

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Trigger tower 0x01100a03




– 2042 events– LAr pulsed– Unfortunately: many pulses

are saturated, i.e. no information about pulse peak form

– Compare 2 non-saturated channels

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– 2042 events– LAr pulsed

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Trigger tower 0x00110d03

Strong similarities of pulse forms between runs 124774 and 124777


Preliminary conclusions• Results:

– Pulse peak deformation non-negligible effect

– Causes need to be understood for reasonable testing of the fit functions and precise calibration

• Possible explanation:Addition of single calorimeter cell signals to a trigger tower is not perfectly aligned in time

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Next investigative steps:1. Look at newer runs Have timing updates fixed the problem?2. Take Phos4 runs with only parts of the trigger tower cells

activated see if effects disappear3. Look at Phos4 runs with the Tile Calorimeter pulsed Does

the same effect appear?


Fits to Phos4 pulses: Gauss-Landau fit

• Earlier studies:Simple Gauss-Landau fit works best for:– Tile calorimeter => pulse

doesn‘t drop below pedestal– 5 slice readout => small fitting

range– Sometimes missing Phos4

steps• Now:

– LAr Calorimeter– 15 slice readout– Improved control of Phos4chip

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Plot from Paul‘s diploma thesis


Fits to Phos4 pulses

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Gauss-Landau

Gauss-Landau with undershoot

Landau-Landau with undershoot

Lorentz-Landau with undershoot



Fits to Phos4 pulses• Gauss-Landau

fit with undershoot seems to work best– Largest

applicable range– Best agreement

with histogram, especially around the peak (judged by eye)

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More quantitative approaches in work


Landau-Landau with undershoot


Fits to real pulse simulations• Motivation:

– Look at fits for all possible mistimings

• Procedure:– Read out every 25th value of

the Phos4 scan– Plot in a new histogram

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the Phos4 scan– Plot in a new histogram– Fit with Gauss-Landau and


– Move the readout point by 1ns in Phos4 histogram (Phos4 scan backwards)

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Gauss-Landau fitGauss-Landau fit with undershoot





the Phos4 scan– Plot in a new histogram– Fit with Gauss-Landau and


– Move the readout point by 1ns in Phos4 histogram (Phos4 scan backwards)

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Phos4 maximum‘s position: Determined by Gauss-Landau fit to the highest 10% of values


Fits to real pulse simulations

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Gauss-Landau fitGauss-Landau fit with undershoot

Better fit = Gauss-Landau with undershoot 7-10 slice readout is sufficient


Correlation plots• Definitions:

– mistimings = shift of digitalisation against perfect digitalisation

– fitdigi–fitphos4 = max. position from fit to real pulse – Phos4 reference

• Results:– Simple Gauss-Landau fit shows

some unwanted structure removed in new fit

– Comparable distribution widths in y-direction

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Gaus

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LAr emEndCap A


Conclusions• Pulse peak deformations

– Not a rare phenomenon– To be further investigated (maybe already solved)

• Fit functions for fine timing– The Gauss-Landau function including the undershoot gives the

currently best fit for Phos4 and real pulses– 7-10 slice readout is sufficient for stable and precise fitting

• Outlook– Quantification of agreement of different fit functions with Phos4 scans– More detailed analysis of correlations regarding real pulses

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phos4 studies and fit functions for timing

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