infn milano, universita` degli studi milano bicocca siena iprd04 23-26 may 2004 1 testbeam results...

INFN Milano,Universita` degli Studi Milano Bicocca 1

Siena IPRD0423-26 May 2004

Testbeam results of the CMS electromagnetic calorimeter

Alessio Ghezzi

on behalf of CMS ECAL Collaboration



Outline

• Energy reconstruction technique and performances

• Impact point reconstruction

• Intercalibration

• Irradiation monitoring performances

• Cooling system



Experimental setup

SupermoduleMovable Table

Beam

Hodoscopes

Laser monitoring system and HV system(for APDS) : final scheme LV system : prototype cooling system: final prototype

•moving table•plastic scintillator for trigger•Hodoscopes (~145 m)•Laser monitoring system



Test beams data

2002 : 100 channels with “old” electronic (FPPA) detailed study of:• Laser monitoring • intercalibration • cooling system

2003: 2 test periods

Electron energies (GeV) 20, 35, 50, 80, 120, 150, 180, 200 25, 50, 70, 100

SM (# equip. crys.) FPPA (100 chan.) MGPA (50 chan.)

SM0 SM1

# gains 4 3

period long 1.5 months short 10 days



Energy reconstruction

3 pedestal samples and 11 signal samples 40 MHz

Amplitude 1

n

i ii

A S w

Tmax

Tpea

k Time (*25 ns)

SM0/FPPA

0iw Under the constraints

Wi determined minimizing

peak

peak

-T-

T

peak( ) e

T

tt

f t

2 1( ) TS A F P Cov ( S A F P)

1i iw f )( ii tff



Energy resolution

E a bc

E EE

Electrons incident on a 4x4 mm2 central region

Pedestal run

Amplitude (MeV)

: 129 MeVSum over 3x3 matrix

Noise term determined from pedestal runs

E/E

(%

)

Ebeam (GeV)

)%03.04.0() 2129(

/

)%2.09.2(

E

MeV

GeVEEE



Position reconstruction

Deposited energy

Impact point reconstructed by hodoscopes ( ~ 150 m)

Measure impact position from calorimetric information

ii

iii

w

xwx

Xi: position of the i-th crystal

Two methods:

0 log 0 i

i ij

j

Ew w w

E

i iw E

•

•




Y (

reco

.–tr

ue)

m

m

ii Ew S curve is E,dependent

Resolution varies with impact position (better resolution close to crystal edges)

=700m

Y (reco.–true) mm

Y (reco.–true) mm

Logarithmic weights

G. DaskalakisI. Van Vulpen

430/

5040)

GeVEm(Y

1mm



Intercalibration Procedure

selections: e- impacting within a 7 x 7 mm2 central region ( retains ~25% of events )

• Cancel out the dependence of reconstructed energy on impact position by equalizing to the maximum response: IV order

polynomial fit

MRef

ii

M

M Relative calibration:

Channel response:position of peak M, fitted by a Gaussian+ exp left tail



Intercalibration

Comparison of intercalibration from different data set

Same accuracy as 2002 results

Statistical accuracy: comparethe intercalibration obtained using only a reduced sample of data w.r.t. tothe one with the whole statistic

An accuracy of ~ 0.1% can be achievedwith 1000 triggered events

RMS :~0.3%

intercalib.

~1000 triggered events

RMS:~0.09%

intercalib.



Intercalibration from laboratory measurements

Only few modules will be calibrated on a beam

Precalibration starting from Light Yield measurements in laboratory : 60Co source 1.2 MeV

cont beam APD elTestBeam

Signal

E MLY

A

Containment:~0.8 @ 120 GeV

APD Gain

Electronic gain

M

= 4.05%

F. Cavallari



Irradiation Monitoring

Laser signal

Ele

ctro

n s

ign

al

= 1.55

0 0

S

S

R

R

~5%

Irradiation affects only the light transmission

Monitoring and correct for the loss in response by the injection of laser light as reference

A. Van LysebettenP. Verrecchia



Irradiation Monitoring

// = 6.3% = 6.3%// = 6.3% = 6.3%

2002 and 2003 data: it is possible to use the same for all the crystal

After the correction for loss

in transparency

2002A. Van LysebettenP. Verrecchia

Time (hours)

sign

al a

mpl

itud

e (A

DC

cou

nts) PRELIMINARY



Thermal step

0 1 (% / )T

dMC

M dT The APD gain (M) depends on the temperature :

Also the LY depends on the temperature

Average thermistor temperature

T = - 4.1 % / °C

The two effects sum up in the overall response (R): 0 1 (% / )T

dRC

R dT

and measured in a thermal step

Laser runs Electrons runs T = - 2.44 % / °C

1 ºC



Cooling system

1 C

0.1 C

7 days

Cooling system with cooling bar

~1.5 month

Cooling bars

PRELIMINARY

PRELIMINARY



Summary

• The new Very Front End cards equipped with MGPA satisfy the target specifications .

• The impact point reconstruction shows a resolution better than 1mm for Energy > 35 GeV

• A robust intercalibration procedure on e- beam has been developed, and an initial intercalibration at ~4% level is reachable for all the crystals from laboratory measurements of the light yield

• The laser monitoring system and the cooling system satisfy the performances required for

CMS



Back up




peak

peak

-T-

T

peak( ) e

T

tt

f t

i iw f

1

n

i ii

A S w

/)(221 nff

ii

ii

0iw

i

ifn

A

pure signal

f(t)

ii

ii

f

fw

)( 2




(E)/

E

(%)

SM0/FPPA

E resolution VS # of pulse samples

Normalised Tmax

25 ns

Num

ber

of

events

Spread in Time of maximum response

Resolution versus mismatch

Tmax mismatch (ns)

(E)/

E

(%)

SM0/FPPA




=620m

ii Ew Y (

reco

.–tr

ue)

mm uncorrected S-curve

Worst resolution: max. energy fraction in central crystal

Best resolution:

corrected S-curve

Reconstructed (Y) mm

close to crystal edge

Resolution versus impact position Y (reco.–true) mm

E = 120 GeV



Laboratory measurements

Precalibration starting from LY measurements in laboratory : 60Co source 1.2 MeV



Test beam 2002 LY

0.5 %

LY intercalibration coeff.



Test beam 2002 Cooling

average thermistors temperature

2 months

0.06 ºC

2002

Stability over a long period

Uniformity of temperaturewithin a module

6 days

0.04 ºC

infn milano, universita` degli studi milano bicocca siena iprd04 23-26 may 2004 1 testbeam results...

Documents

infn milano

c slide

laser monitoring system

verrecchia slide

days slide

minimizing slide

tail slide

cavallari slide