DRS-II results on electron energy scan (Signal integration method)

F.Scuri DRS-II results on electron energy scan

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DRS-II results on electron energy scan(Signal integration method)

F.Bedschi, R. Carosi, M.Incagli, F.Scuri

- A summary of what we learned on features and limits of the DRS chip version II by looking at the Cherenkov and the Scintillation electron signals from the Dream fiber detector during the 1st week of the 2008 test beam.

- A detailed study of the electron energy scan.

- A quick look on single pion events as a function of energy.

Dream Collaboration meeting, Rome, March 16-17, 2009


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Energy scale calibration done on run 592 – 50 GeV electrons

Typical DRS event shape and definition of the integration ranges

Drs cell number Drs cell number

Peak_cell - 15 Peak_cell + 40

Cherenkov signalwindow = 27.5 ns

Peak_cell - 30

Peak_cell - 70} 20 ns wide window for

baseline calculation

mV

x 1

0

mV

x 1

0

Peak_cell - 35

Peak_cell - 75} 20 ns wide window for

baseline calculation

Peak_cell - 20 Peak_cell + 40

Scintillation signalwindow = 30 ns

Peak_cell + 80

(Excluding neutron signal window (20 ns) to be used in hadron analysis)


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Time profile comparison: run 592 – 50 GeV electrons, event 5

10%

-90%

ris

e ti

me:

5 n

s

10%

-90%

ris

e ti

me:

7 n

s

Black: CherenkovRed: Scintillation

Drs cell number

mV

x 1

0


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Cherenkov vs Scintillation: run 592 – 50 GeV electrons

19i

1i _

_1

iTower

Tower

E

Eisolation Cut for energy resolution/linearity measurements

isol_Ch > 0.9 && isol_Sc > 0.9


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run 591/592 (50 GeV e-) to set the energy scale ref. for the DRS int’d charge output

Gaussian fit Gaussian- Landau convolution fit

En

trie

s p

er G

eVE

ntr

ies

per

GeV

En

trie

s p

er G

eVE

ntr

ies

per

GeV

GeV

GeV GeV

GeV


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En

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s p

er G

eVE

ntr

ies

per

GeV

En

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ies

per

GeV

GeV GeV

GeVGeV

run 599 (30 GeV e-): Gaussian+Landau fit has a better 2/ndf at lower energies (S)

Gaussian fit Gaussian- Landau convolution fit


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run 601 (100 GeV e-): Gau+Landau and single Gaussian fit return values within 1%E

ntr

ies

per

GeV

En

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s p

er G

eV

GeV

GeV

Gaussian fit

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eV

GeV

GeV

Gaussian- Landau convolution fit

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eV


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Additional remarks for electron runs:

- Position scan with 50 GeV electrons – run 313 to run 331 – used for equalization of the single tower response (Q and S)

- Electron energy scan with electrons – run 591 to run 623 – used for energy linearity/resolution checks warning ! a) runs at 150 GeV removed because bad beam file was loaded b) runs at 200 GeV removed because of full signal saturation (missing attenuator !)

- Electron runs (50 GeV) 589 to 592 used to measure the attenuation on Q1 and S1 (attenuation factor measured to be exactly the nominal 3 dB value)

…however: 50 GeV e- in runs 589592 gave a 10% less signal (both C and S) w.r.t 50 e- GeV in run 333 (position scan); attenuation box (with cables) left in the line during data taking at 0 nominal attenuation? (see below)


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Linearity plotsCherenkov Scintillation

Blue : Gaussian fitRed : Gaussian + Landau fit

(%) (%)

Ave

rag

e s

ign

al p

er

GeV

Ave

rag

e s

ign

al p

er

GeV

GeV

GeV GeV

GeV


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Linearity results vs Dream published ones

(tilted calorimeter)

10-15% non linearity for Scintillation signal almost compatible with published results

8-10% non linearity for Cherenkov signal NOT compatible with published results

NIM A 536 (2005)


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Q side S side

Blue: Gaussian-Landau fit

Red : Single Gaussian fit

NIM A536(2005) 19-51Table 2

)%5.02.2()%149( )%3.01.6()%233(

)%2.07.6()%3.08.23( )%3.02.2()%6.00.40(

)%5.02.2()%150( )%3.01.6()%235(

Energy resolution plots

Resolution results NOT compatible with DREAM published values

2

E

2

E

1)(

GeVE 1)(

GeVE

100 GeV

50 GeV

30 GeV

20 GeV

100 GeV 50 GeV

30 GeV

20 GeV


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Studies on some “features” of the DRS-II response

Several study were done to understand what can be ascribed to the DRS-II limits/characteristics in order to explain why TB08 electron results do not reproduceDREAM published performances.

Here are listed the main DRS-II bad characteristics we observed, potentially dangerous for good energy measurements:

a) Cherenkov signals always show a decay tail much longer than expected

b) Baseline average value in pedestal events always significantly lower than baseline average value in “physics” events with sizable charge accumulation in the sampling capacitors (even at raw data level)

c) Baseline average value in “physics” events at the spill start always sizably higher w.r.t the spill average


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Explanation: according to the Pisa Magic group, the long decay term contributionshould be due to the non optimal coupling of the DRS-II chip out of the sampling capacitor/switch system to the ADC in the lines of the mezzanine we used at the TB

DRS-II problems analysis (1)

Issue a):

Potential source of limitation in measuring the “slow” neutron contribution

Only possible solution we investigated: use a “time profile template” method to subtract/correct for the effect (see F. Bedeschi talk)

= 5 ns

= 30 ns

mV

x1

0

mV

x1

0

Log scale

DRS cell number DRS cell number

100 cells = 50 ns


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Explanation: “physics” events are taken in “bursts” inside the spill at an instantaneousrate which can be much higher than the typical KHz average trigger rate; in thisconditions, a not complete cell refresh occurs

partial solution: correct of offline by subtracting, event by event, the average baseline value measured in the cells before the signal rise edge (slide 2)

Issue b)

See issue c)

Issue b)

Average event baseline always > 10(1 mV) after subtraction of the averagevalue in the of the pedestal eventbaseline

(baseline spread of ped. events is 5)

Progressive event number in the spill

Av

. b

as

eli

ne

va

lue

b

efo

re s

ign

al

(mV

x1

0)


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Run 599, 20 GeV electrons

Run 599, 20 GeV electrons



Av

. b

as

eli

ne

va

lue

b

efo

re s

ign

al

(mV

x1

0)

Av

. b

as

eli

ne

va

lue

be

fore

sig

na

l (m

Vx

10

)

Events with higher averagebaseline (>60) concentrate at thespill begin (evt. spill num. < 100)

Same behavior in all studied runs(electron and pion energy scan)


Issue c)

Explanation:(given by all experts – Magic,Meg, S. Ritt - separately contacted)When activated at relatively high frequency,chip internal local temperature slowly growsand fluctuates around a dynamic equilibrium

Calibration curve changes with temperature,we did only one calibration at the TB start.

Possible solution, make calibration at dif-ferent temperatures and at each run start(not practical, very long procedure); storeboard temperature during data acquisition (not done during 2008 TB !)


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DAQ input level (mV) (after off-set - 2048 – subtraction)

AD

C c

ou

nts

Pedestal values fall in a non-linear region, difficultto correct for temperature drifts….

DRS-II calibrations curves

T+

T-

Typical shapes: linear region 200 – 700 mV


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GeV GeV

Av

era

ge

sig

na

l p

er

Ge

V

Av

era

ge

sig

na

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Ge

V

Electron energy scan: linearity vs event category

CherenkoV Scintillation

- Just a slight improvement in the scintillation case when selecting events at the spill begin (progressive event number in the spill < 100) - The average signal is almost systematically lower for the first events in the spill, consistent with a shift to higher values of the chip internal temperature after the spill start ….

Red : all events Blue: first events in the spill

A much more sizable effect seen on the energy resolution (next slide…)


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Electron energy scan: resolution vs event category

Q side S side

Blue: all events

Red: only events with ave.baseline value > 60

NIM A536(2005) 19-51Table 2

)%5.02.2()%149( )%3.01.6()%233(

)%2.07.6()%3.08.23( )%3.02.2()%6.00.40(

)%8.01.3()%242( )%7.00.6()%628(

100 GeV 100 GeV

50 GeV

50 GeV

30 GeV

30 GeV

20 GeV

20 GeV

2

E

1)(

GeVE 1)(

GeVE

100 GeV

50 GeV

30 GeV

20 GeV

2

E


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Then I started to look at pions ….

…and I met other problems!

As a first exercise I have analyzed just one run per energy point:

- Run 431 : 20 GeV pi-- Run 406 : 50 GeV pi-- Run 381 : 100 GeV pi-- Run 343 : 200 GeV pi+


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NIM A537

No leakagecorrection

Leakagecorrected

100 GeV

DRS

Q and S measurements…

10% averageS correction

due to leakage

<S>DRS: +10%

<Q>DRS: + 7%

Q/S ratio


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Something is changed just before the electron energy scan!(maybe some attenuation left for the S and Q central towers)

En

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eVE

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per

GeV

GeV

GeV

<Q>333

+4%

<S>333

+9%

Run 591

Run 591

Run 333

Run 333

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GeV

GeV

GeV


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Use 50 GeV electron run 333 (position scan) for Q and S response equalizationin hadron run instead of run 591/592 (50 GeV electrons, energy scan) !!

NIM A537DRS, TB 2008

+2.5%

+4%

Signal (em GeV)

En

trie

s p

er e

m G

eV

100 GeV


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Pion energy resolution before applying any correction

DRS TB 2008

NIM A537

Blue: Cherenkov

Red : Scintillator

10% events saturated DRS

Q Side S Side

DRS TB 2008

(all events)

NIM A537

)%14()%9135(

E

)%5.05.5()%358(

E

%10%86

E

%7%49

E

300 GeV pions, all runs:100% events saturatedNo attenuator !!

Events at the spill begin tendto give better resolutions asIn the electron case. Checkwith the full statistics

bGeVE

a

E)(

E1

E


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S = Q + (-1) E

P0 = ( -1) E, P1 =

Dream published (NIM A537)

= P1 = 0.57

= P0/E – 1 = 0.47

Cherenkov signal (GeV)

<S

co

rr >

(G

eV) 100 GeV

Some check before applying the Q/S method…..


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Leakage correction works,more or less,

as in NIM A537

Which h/e () values should Iuse to compute fe.m. andto apply the Q/S method?

DRS, TB 2008

NIM A537

+10% correction on theaverage in both cases,higher R.M.S for DRS…

En

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s p

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eV


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Moving to the (Q+S)/E method…

NIM A537

Good agreement in this case!

<S

>

E

SQ


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…..I WILL STOP HERE WITH PIONS.TOO MANY THINGS I HAVE NOT YET UNDERSTOOD…..

(see Franco’s talk for pions)


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Conclusions from electron (and pion) energy scan analysis

- DRS version II confirmed many limits, partially already known… Strong non linear response calibration high sensitivity to chip internal temperature drift not complete cell refresh at relatively high (>1 KHz) trigger frequency

- By isolating event categories less sensitive to the temperature drift (spill begin) and by off-line correcting for non linearity and baseline fluctuations: energy linearity and resolution results with electrons approach the Dream published performances

- Analysis of the energy scan with pions shows problems others than DRS limits (see also F. Bedeschi talk)

- The DAQ system used at 2008 TB and based on MAGIC mezzanines hosting the DRS-II chips was operationally reliable, however….

The relatively long tail observed also for the Cherenkov signal decay (not optimi- zed coupling of the DRS capacitor outs to the ADC) required careful treatment in the measure of the scintillation signal (see F. Bedeschi and M.Incagli talks)

- Non-linearity, sensitivity to the temperature drift, and cell incomplete refresh should have been moderated in the version IV of the DRS chip; it should be useful to prove it in a next Dream T.B. (see F. Scuri talk)

Documents

DRS-II results on electron energy scan (Signal integration method)