Commissioning of the ATLAS Tile Hadronic Calorimeter with ... · João Gentil Saraiva LIP & FCUL On...

João Gentil SaraivaLIP & FCUL

On behalf of the ATLAS Tile Calorimeter group

Commissioning of the ATLAS Tile Hadronic Calorimeter with Single

Beam and First Collisions

12th Topical Seminar on Innovative Particle and Radiation Detectors

Siena, Italy 7 – 20 June 2010

J G Saraiva ([email protected]) IPRD10 7 - 10 June 2010 Siena, Italy 2

Outline

1) The Tile Calorimeter :

● Detector description

● Operational status

● Calibration tools

● Signal reconstruction

2) Readiness for collisions:

● Energy and timing response with cosmic ray muons

● Timing with Single beam

3) First collisions

4) Summary and conclusions

EXTRA*EXTRA*EXTRA*EXTRA

Poster by Renato

Febbraro on signal

reconstruction and

calibration tools for the

tile calorimeter


ATLAS detector


Tile Calorimeter (I)

● ~ 10000 channels

● Each collecting the signal from a group of tiles -> cell

● Double read-out of a cell

● Uniformity + redundancy

EBCLBC

LBA

EBA

ro = 4230 mm

ri = 2280 mm

~ 12 meters● Hadronic barrel calorimeter of ATLAS

● Sampling calorimeter :

● Iron matrix with scintillating tiles

● Light transported through wavelength shifting optical fibers to the photomultipliers

● Coverage in | η | < 1.7


Tile Calorimeter (II)

● 3 radial layers A, B/C, D divided in cells

● Δη x Δφ :

● 0.1 x 0.1 for A and B/C

● 0.2 x 0.1 for D

● Performance from testbeam with high energy pions gave a good energy resolution (close to design!)

● Within the ATLAS physics program it will be important for:

● Top mass measurements require a 1 % precision in jet energy scale

● Physics beyond the standard model such as SuSy models require a good missing transverse energy measurement

● Quark compositness

● Still important :

● Assistance in muon measurements

● In lepton isolation e.g. H->ZZ*->4l (4μ,2e2μ)

Segmentation

Energy resolution for standalone testbeam

with pions

Performance and physics goalsNIM A 606 (2009) 362-394

● Data□ MC


Tile Calorimeter (III)Calorimeter status

● Tile calorimeter has a total of 5182 cells

● 97.1 % of cells used in physics

● Masking (not used for physics)

– 2.9 % of masked cells

– 2.6 % of which are OFF

– Most due to LVPS failures

Noise description● Tile electronic noise has non-gaussian tails

● Important in clustering algorithms

● Double gaussian description fits well with noise and is used to separate signal from noise

Preliminary


TileCal calibration tools

● Calibration tools of the tile calorimeter

● Charge injection system (CIS) : ADC -> pC

● Integrator : used by cesium system, dedicated monitoring during several bunch crossings (time constant of 13.9 ms)

● Laser : photomultipliers (PMT) gain stability and readout electronics linearity

● Cesium : equalize cell response to set electromagnetic (EM) scale

In testbeam 12% of the modules

calibrated with beams of high

energy particles set EM energy scale to

1.05 pC/GeV Integrator time constant 13.9 ms

A amplitude in ADC countsE

channel in GeV


Calibration (I) ● A known charge is injected into each channel

simulating the PMT response:

● Two readout: High Gain and Low Gain

● ADC to pC conversion factors

● Time stability below 0.1 %0.7 % systematic per channel

due to injected charge uncertainty

Charge Injection System

Laser System● A calibrated light signal is injected in each PMT that

mimics the light signal produced by scintillating tiles

● Gain stability of the photomultipliers during detectors operation

● Measure the non-linearity of PMTs and front-end electronics

● 0.28 % (high gain) variations for measurements made during 50 days

● Time synchronization of Tile Calorimeter channels with a precision better than 1 ns

● Gain variation during 22 months period below 0.01 %

● Individual channel stability is better that 0.05 %

Preliminary

Preliminary Preliminary

Integrator


Calibration (II)

● A movable 137Cs radioactive source

● Travels across each cell of the calorimeter

● Check quality and uniformity of optical response

● Adjust photomultipliers HV to set the same energy scale in all cells

● After equalization a dispersion of 0.3 %

● Cosmic ray muons, single beam used for certification.

● Stability with time

● Following approximately the decay curve of cesium sources

– The increasing trend is under investigation

Cesium System

Preliminary


Signal reconstruction● Reconstruction performed in Read Out Driver

(ROD) boards [with Digital signal processors (DSPs)]

● After level 1 trigger accept digitized signal send from drawers to RODs

● Fast reconstruction < 10 μs

● Optimal filter algorithm

● Algorithm coefficients are time (phase) dependent:

– Several iterations for asynchronous signals (cosmics) only one during LHC

– Prior knowledge of channel time

1 2

3

4 5

6

7

After phase correctionOnline reconstruction precision

below 1% for a | τ | < 10ns

Limited Numerical resolution in DSP reconstruction

Offline vs Online reconstruction


Commissioning with cosmic muons (I)

● Cosmic ray muons with 10 GeV/c < p < 30 GeV/c crossing the inner detector

● Tracks extrapolated to tile calorimeter radial layers to obtain crossed path length

● dE/dx (MeV/mm) is the mean after 1% high tail truncation

Energy scale check using cosmic muons

● Results per radial layer

● Systematic uncertainties on data depending on the layer and partition

– 3-4 % for LB and 5-6 % for EB

● Layer non-uniformity of 4 % at most is under investigation

● Good agreement between data and MC

● Energy scale in cavern compatible within 3% with testbeam results:

Ecosmics

Etestbeam÷MC cosmics

MC testbeam=0.99±0.03

Preliminary


Commissioning with cosmic muons (II) : φ and η

● Good uniformity in η and φ within each radial layer

● η : within window of ± 2 % for LB and ± 3 % for EB

● φ : within window of ± 3 %



Time Synchronization (I)● Pre-LHC timing set with laser system

● Channel synchronization required for good energy precision

● Validated with cosmic muons (2008) and single beam (2008-2010)

● Using single beam in 2010 to set time to ± 1 nsResults from 2008 Cosmics

● Method uses the time of flight between cells to verify the offset

● Combines all measurements in a matrix

● Extracts the solution based on a least square minimization

● Offsets between partitions expected due to lack of partitions inter-calibration

● 2008 Single beam also saw these offsets (see next slide)

Cosmic Muons (2008) Preliminary


Larger precision -> Combined in 2008 with laser for time synchronization

● In 2008 dependency also on partition as observed with cosmic ray muons

● The comparison of time of tile calorimeter cells from 2008 single beam and cosmic ray muons

● A agreement better than 2 ns

Time Synchronization (II)

2008 single beam

Results from 2008

Results from 2008

Single beam (2008)

Single beam vs Cosmic muons (2008)



single beam 2009-2010

● In 2010 the time synchronization is achieved successfully

● Time synchronization using 2009 single beam data

● Precision better than 1 ns

Average time in cells within ± 1 ns

+ 1 ns

- 1 ns

97% of cells used

Results from 2009

Results from 2010

Time Synchronization (III)

ATLAS Preliminary

ATLAS Preliminary


First Collisions (I)

● After LHC repairs the start-up in October 2009

● Minimum bias trigger

● Coincidence between MB scintillators located ~3 m from interaction point

● Since then gradual increase in center of mass energy

● 900 GeV, 2.36 TeV and 7 TeV

● General agreement between data and MC for the Tile Calorimeter cell energy


First Collisions (II) : φ and η response

φ : ● Uniformity better than 10 %

● Good agreement with MC

+10 %

-10 %

Results

for

Ecm =

7 T

eV

LB EBAEBC η :● Distinction between EB from LB

● Both regions show good agreement with MC


Summary & Conclusions● 97.1 % of the calorimeter operational

● Accurate noise description reviewed as a double gaussian model

● Signal reconstruction algorithm set to 1 % precision

● Calibration tools operational and being used as expected

● Long commissioning with cosmic muons + single beam:

● Energy scale from cosmic muons reproduced within 3 %

● Uniformity better than 3 % for both η and φ

● Synchronizing the calorimeter and reaching an agreement better than 2ns between single beam and cosmics

● First collisions showed good response in preliminary analysis both for η and φ

TileCal is eagerly awaiting more physics challenges from LHC collisions!

Commissioning of the ATLAS Tile Hadronic Calorimeter with ... · João Gentil Saraiva LIP & FCUL On...

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