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## PACE3 Pulse Height Parametrization

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### PACE3 Pulse Height Parametrization

Hellenic Society for the Study of High Energy Physics

2006 Workshop on Recent Advances in Particle Physics and Cosmology

Dr Ioannis Papadopoulos

HEP Laboratory

Physics Department

University of Ioannina

GR-45110 Ioannina, Greece

pyannis@uoi.gr

Ioannina, 14/4/2006

Summary

- CMS Preshower
- The PACE3 ASIC
- PACE3 characterization
- Pulse shape data
- Pulse parametrization
- Pulse height parametrization
- Start of pulse estimation
- Conclusions – Outlook

Ioannina, 14/4/2006

The CMS detector

Ioannina, 14/4/2006

CMS Preshower

absorber

absorber

γ

γ

γ

- absorber – Si strip sensors – absorber – Si strip sensors sandwich.
- provides the “foot” of showers developed in the ECAL
- rejects closely spaced γ’s coming from π0 decays
- very important for the Zγγ decays

Ioannina, 14/4/2006

The PACE3 ASIC

- PACE3 is composed of two separate ASICs:
- Delta
- performs amplification and shaping
- operates in two gain modes:
- High gain (HG)for calibration purposes usingsingle minimum ionizing particles (MIPs)
- Low gain (LG)for normal physics runningwith a wide dynamic range (1 – 400 MIPs)
- incorporates an internal calibration circuit
- PACE-AM (Analogue Memory)

Ioannina, 14/4/2006

PACE3 characterization

Ioannina, 14/4/2006

PACE3 characterization

- PACE3 chips undergo various tests:
- power
- digital functionality

Ioannina, 14/4/2006

PACE3 characterization

- PACE3 chips undergo various tests:
- power
- digital functionality
- linearity

Ioannina, 14/4/2006

PACE3 characterization

- PACE3 chips undergo various tests:
- power
- digital functionality
- linearity
- noise (High gain)

Ioannina, 14/4/2006

PACE3 characterization

- PACE3 chips undergo various tests:
- power
- digital functionality
- linearity
- noise (High gain)
- noise (Low gain)

Ioannina, 14/4/2006

PACE3 characterization

- PACE3 chips undergo various tests:
- power
- digital functionality
- linearity
- noise (High gain)
- noise (Low gain)
- memory uniformity

Ioannina, 14/4/2006

PACE3 characterization

- PACE3 chips undergo various tests:
- power
- digital functionality
- linearity
- noise (High gain)
- noise (Low gain)
- memory uniformity
- timing scan data used in this work

Ioannina, 14/4/2006

PACE3 characterization

- PACE3 chips undergo various tests:
- power
- digital functionality
- linearity
- noise (High gain)
- noise (Low gain)
- memory uniformity
- timing scan data used in this work

Ioannina, 14/4/2006

PACE3 pulse parametrization

Ioannina, 14/4/2006

PACE3 pulse parametrization

Ioannina, 14/4/2006

PACE3 pulse parametrization

Ioannina, 14/4/2006

PACE3 pulse parametrization

- Assuming for a specific gain thatt0 ,n and ωc are the same for any pulse i

- Summing up all pulsesand averaging:

- has the same shape as a single pulse
- fitting the averaged pulse, we can obtain t0 ,n and ωcwith better statistical errors

Ioannina, 14/4/2006

PACE3 pulse height parametrization

- In CMS: taking three time samples per pulse
- Why not take only one sample at the peaking time?
- reduce noise (electronic noise, time jitter)
- ParametrizationSmax = a S1 + b S2 + c S3
- a, b and c have to be determined
- they depend on the times the sampling is done(and of course on the gain mode…)

Ioannina, 14/4/2006

PACE3 pulse height parametrization

fts=10ns

t0=15ns

Δt=-5ns

25ns

25ns

- PACE3 provides three samples in steps of 25ns
- time samples at fts, fts+25ns and fts+50ns
- Δt = fts - t0 : time(first sample) – time(start of the pulse, t0)
- parameters a, b and c depend on Δt and the gain mode.

Ioannina, 14/4/2006

Pulse height parametrization

- Estimation method of the a, b and c parameters:
- construction of a χ2function, fcn
- fcn minimization using the CERNLIB MINUIT package

where, for each pulse i,S1i, S2i and S3i : measured signals at times fts, fts+25ns and fts+50ns respectively,Smaxi : measured maximum signaland σSmaxi is 7 (3) ADC counts for High (Low) gain.

Ioannina, 14/4/2006

Pulse height parametrization

- fit results for fts=8ns (all High gain data)
- Pulse height difference between measured and calculated values

Ioannina, 14/4/2006

Pulse height parametrization

- fit results for fts=8ns (all Low gain data)
- Pulse height difference between measured and calculated values

Ioannina, 14/4/2006

Pulse height parametrization

- a, b and c fit results as a function of fts
- all parameters exhibit a linear dependence with fts
- they behave the same for both High and Low gain

High gain

Low gain

Ioannina, 14/4/2006

Start of pulse estimation

- n and ωc :
- gain specific
- estimated fitting the averaged summed pulses
- Intensity and pedestal :
- selecting pulses of similar height, e.g. with S2(S2-ΔS, S2+ΔS),can be considered as constant for all these pulses
- signal : using 3 time samples, setting the fts parameter
- t0 : can be estimated constructing a χ2 function, fcn, and minimizing it

Ioannina, 14/4/2006

Start of pulse estimation

- fit results for High gain data with fts=8ns
- selection: S2(3000, 3100)

Ioannina, 14/4/2006

Start of pulse estimation

- fit results for Low gain data with fts=8ns
- selection: S2(3400, 3500)

Ioannina, 14/4/2006

Start of pulse estimation

- application of the method for data from 150GeV μ-taken during the Preshower beam test at CERN H4 (sep. 2004)

Ioannina, 14/4/2006

Conclusions – Outlook

- PACE3 pulse height estimation is very important
- it is translated to energy deposition affects the energy resolution of the Preshower
- The methods described allow
- the estimation of the pulse shape parameters for High/Low gain
- the estimation of the pulse height parameters for High/Low gainas a function of the sampling synchronization
- the determination of the absolute starting time, t0, of the PACE3 pulses, from real datacorrect selection of the pulse height parameters
- To do:
- acquire more statistics,as PACE3 characterization tests continue at UOI HPLAB
- study of systematic errors / sensitivity studiesusing also the data from the Preshower 2004 beam test at CERN
- publish …

Ioannina, 14/4/2006

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