Thomas Jefferson National Accelerator Facility

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EC / PCAL ENERGY CALIBRATION

Cole SmithUVA

PCALEC

Outline

• Why 2 calorimeters?• Requirements• Using MIP for calibration• Experience with EC• PCAL tests• Summary

Thomas Jefferson National Accelerator Facility

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PCAL + EC = Better resolution at 12 GeV

EC: 100 mm strips uvw: 36 x 36 x 36 16 r.l. PCAL: 45 mm strips uvw: 68 x 62 x 62 5.5 r.l.

(a) Additional thickness improves energy resolution.(b) Finer granularity of PCAL improves pizero efficiency.

Thomas Jefferson National Accelerator Facility

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EC / PCAL Calibration Requirements

Acceptable calibration at startup

• Hit / cluster reconstruction in trigger requires substantial control of both energy and geometry calibration already on Day 1.

• Calibration procedure must provide gain and attenuation constants and relative alignment of EC/PCAL modules.

• Constants must be accessible to trigger firmware.

Calibrations of EC and PCAL must be consistent

• Sum of electron energy from each module must agree with forward tracker momentum (E / p = constant).

• Spatial and energy reconstruction of photons must produce correct invariant mass.

Online monitoring of calibration constants

• Continuous gain monitoring essential to maintain uniform trigger response under changing luminosity and relative backgrounds in PCAL and EC.

Thomas Jefferson National Accelerator Facility

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Components of Energy Calibration

stack of nattenuatio effective

hit tedreconstruc to PMT from distance

pedestal ADC

channel ADC from charge integrated

] channel /MeV 0.1[~ ncalibratio ADC

showers) EM (for fraction sampling

stack orscintillat deposited energy

n

n

pedn

sign

n

s

thn

x

A

nA

g

f

nE

PCAL

EC inner

EC outer

,,,, eee-

π

U

V W1

2

3

Thomas Jefferson National Accelerator Facility

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EC / PCAL Energy Calibration Uses MIP

EM shower: Energy deposition non-uniform function of position and depth. Difficult to define calibration benchmark.

Minimum ionizing muon: Uniform and localizable energy deposition profile (dE/dx ~ 2 MeV / cm in scintillator).

μ

e-

Online Cosmic Calibration

• Provides gain and attenuation constants needed for e- trigger.

• Hardware gain matching of PMTs.

• No sophisticated hit reconstruction – simple Dalitz test.

• Muon tomography can provide relative alignment of modules.

• Requires 12-24 hours to obtain adequate statistics.

Offline Calibration

• Uses physics data: MIP pions (p > 0.6 GeV).

• Run-by-run monitoring of PMT gains using E/P or MIP .

• Cross-check of cosmic muon calibration.

• Extrapolation of MIP calibration to 10+ GeV e-

E / P vs. x,y position

Muon energy vs. x,y position

Thomas Jefferson National Accelerator Facility

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EC Online – Cosmic Event Display

Live monitoring of cosmic muon data permits quick diagnosis of miscalibrated or dead PMTs

Events / pixel

Energy / pixel

Thomas Jefferson National Accelerator Facility

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EC Online - Cosmic Ray Gain Matching

μ

Light Guide

PMT Inner 5 strips

PMT Outer 8 strips

x

Integrated energy deposition

• Linear fit of x-dependence of MIP energy deposition used to obtain attenuation length.

• Fit is extrapolated to x=0 to obtain ADCmax and PMT gain.

• PMT HV adjusted for ADCmax=100 (inner) 160 (outer) → (10 channels / MeV).

Light guide

x-dependence

μ

Thomas Jefferson National Accelerator Facility

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EC Performance using Cosmic Muons

GEANTDATA

Online muon calibration adequate to achieve basic physics analysis.

Refinements possible offline.

Thomas Jefferson National Accelerator Facility

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EC Offline – Calibration Monitoring

Using physics data to determine PMT gains

Using E/P to monitor gain drifts and shifts

Fractional change in E/P vs Run No.

Thomas Jefferson National Accelerator Facility

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PCAL Cosmic Ray Test Runs

• For each PMT, measure light as function of x.

• To determine x, use strips in other views to localize hit.

• Limit multiplicity to 1 for each U,V,W view.

• Use adjacent strips to veto non-vertical hits (pixel cut).

• Fit gaussian to each x slice to determine MIP peak.

Vetoed tracks

μ

x

U66 W59

W35

W15

PCAL Module 2 – EEL Bldg.

Thomas Jefferson National Accelerator Facility

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Selecting Single Pixels - Viviani’s Theorem

real function uvw_dist(is,il)

c Defines normalized u,v,w coordinates for PCALc is=strip number (U=1-68 V,W=1-62)c il=layer number (U,V,W=1,2,3) if (il.eq.1.and.is.le.52) uvw=is/84. if (il.eq.1.and.is.gt.52) uvw=(52+(is-52)*2)/84. if (il.eq.2.and.is.le.15) uvw=2*is/77. if (il.eq.2.and.is.gt.15) uvw=(30+(is-15))/77. if (il.eq.3.and.is.le.15) uvw=2*is/77. if (il.eq.3.and.is.gt.15) uvw=(30+(is-15))/77. uvw_dist = uvw end

u

v

w

PCAL events which pass Level 3 (multiplicity=1 for U,V,W)

Single pixel events require U + V + W = 2

Thomas Jefferson National Accelerator Facility

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Results from PCAL Tests

U PMTs V PMTs W PMTs

Gain matching of PMTs to within 5% possible.

Thomas Jefferson National Accelerator Facility

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Summary of Energy Calibration Software

Legacy code for EC in use since 1996• Stable, platform independent (PAW kumacs, fortran).• Output consists of flat files (HV values, calibration constants)

appropriately formatted for external scripts.• Algorithms tested and upgraded for PCAL with good results.

New Issues for CLAS12 and Suggestions• Combining calibrations of EC and PCAL may be problematic.• Changeover to Flash ADCs (FADC) requires retuning algorithms. • How to extrapolate MIP calibration over larger dynamic range (10 GeV)?

– E.g. - Hardware gain calibration of FADCs needed.

• Cosmic trigger during physics running for continuous calibration.

Future Development• Integration into online services, calibration database and slow controls.• Complete rewrite in JAVA?• Friendly user interfaces.