Noise dependence with pile-up in the ATLAS Tile calorimeter

J. P. Araque !on behalf of the ATLAS Tile Calorimeter System

ANIMMA 2014 Lisbon, 20-24 April 2015

The Tile Calorimeter

• The Tile Calorimeter is the central hadronic calorimeter of the ATLAS detector.

• Composed of iron layers (as passive material) and scintillating plastic layers (as active material).

• Structure: • 4 partitions (LBA,LBC,EBA and EBC). • 4 layers (A,BC,D and special layers). • 16 towers (steps of 0.1 in η). • 64 modules (divisions in the azimuthal

angle φ).

2

Pile-up in the ATLAS detector

• Tens of proton-proton interactions take place in a bunch crossing inside the ATLAS detector.

• Pile-up events also deposit energy in the TileCal cells which is hard to distinguish from the energy deposited by the interesting event.

• This is known as pile-up noise and is a component to the cell noise measured that increases as pile-up increases.

3

-400 -200 0 200 400 600

Nor

mal

ized

ent

ries

-310

-210

-110

ATLAS PreliminaryTile calorimeterEBA Cell A12

=58.6 MeVσ>=20, µMC12 <=89.5 MeVσ>=30, µMC12 <

=80.8 MeVσ>=20, µData 2012 (50 ns) <=97.3 MeVσ>=30, µData 2012 (50 ns) <

Energy [MeV]-400 -200 0 200 400 600

Dat

a/M

C

0.51

1.52

2.5 >=20µ>=20 / MC <µData <>=30µ>=30 / MC <µData <

Mean Number of Interactions per Crossing0 5 10 15 20 25 30 35 40 45

/0.1

]-1

Rec

orde

d Lu

min

osity

[pb

020406080

100120140160180 Online LuminosityATLAS

> = 20.7µ, <-1Ldt = 21.7 fb0 = 8 TeV, s

> = 9.1µ, <-1Ldt = 5.2 fb0 = 7 TeV, s

RMS as the noise estimator

• The RMS of the energy distribution can be used as a noise estimator:

4

phE2i � hEi2

>µ<0 50 100 150 200

Noi

se [M

eV]

0

50

100

150

200

250 ATLAS PreliminaryTile Calorimeter

= 8 TeVs50 ns, Layer A

DataMonte Carlosimulation

• The noise measured increases with the mean number of interactions per bunch-crossing.

• The bunch-spacing also increases the cell noise.

Quantiles of the energy distribution as the noise estimator

• The quantiles of the energy distribution can be used to better characterise its shape.

• The energy ε is the kth quantile of the energy distribution with Q quantiles if:

5

P (E ✏) = k/Q.

>µ<10 15 20 25 30 35

E [M

eV]

-2000

-1000

0

1000

2000

3000

4000

5000

600099.99 % of events99.73 % of events95.45 % of events68.27 % of events

ATLAS PreliminaryTile Calorimeter

= 8 TeVsData 50 ns, | < 0.7ηLayer A, 0.6 < |

• Non-gaussian behaviour with larger positive tails.

>µ<10 15 20 25 30 35

Noi

se [M

eV]

210

310

410

51099.99 % of events

RMS×495.45 % of events

RMS×2

ATLAS PreliminaryTile Calorimeter

= 8 TeVsData 50 ns, | < 0.7ηLayer A, 0.6 < |

>µ<10 15 20 25 30 35

Noi

se [M

eV]

210

310

410

510 99.99 % of eventsRMS×4

95.45 % of eventsRMS×2

ATLAS PreliminaryTile Calorimeter

= 8 TeVsData 50 ns, | < 0.8ηLayer D, 0.6 < |

Conclusions

6J.P. Araque funded by LIP and by the FCT grant SFRH/BD/52002/2012

• The high rate at which the LHC produces proton-proton collisions implies a high amount of pile-up events taking place in the ATLAS detector.

• In the second operation phase of the LHC, with higher energy (13 TeV) and smaller bunch-spacing (25 ns), pile-up is expected to increase.

• To study the TileCal cell noise as a function of pile-up two estimators have been presented:

• The RMS of the energy distribution.

• The quantiles of the energy distribution.

• Using the quantiles estimator the shape of the energy distribution can be better characterised.