Towards τ reconstruction at the High Luminosity LHC with a High Granularity Endcap Calorimeter for CMS

Ali Izadi RadSharif University of Technology, Tehran, IRAN

Supervisors: M. Mannelli , P.Silva (CERN-CMG)

CERN Summer Student Lectures14 August 2014

Outline

What is HL-LHC

What is High Granularity Endcap Calorimeter of CMS

Why τ reconstruction ?

How τ reconstruction?

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Future of LHC

I will

be

30 y

ears

ol

d!Yo

u Ar

e H

ere

!!Good News!

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The High Granularity CalorimeterSub-

Detector

Active

Medium

Passive

Medium

#Layers

# Channe

ls

Thickness

Electromagne

tic

Si Pb+W 30 6M 25 X0 / 1λ

Front Hadro

nic

Si Brass 12 2.7 M 3.5λ

Back Hadro

nic

Plastic

Scintillator

Brass 10 ~1M 5.5λ

Refer to yesterday talk of Alena

Good News!

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Why ??• In the HL-LHC we expect to have an average pileup of 140

while so far we had ~20 pileup.This means that the energy flow and the occupancy of the detector willincrease drastically. The endcap detectors must be upgradedotherwise they won't be able to: - sustain the radiation damage - distinguish a hard collision from the superposition of pileup eventsIn this context a high granularity calorimeter can help has the

• occupancy is reduced because the energy flow is divided by • more cells, one is able to distinguish single particles.

Given the calorimeter architecture is new, reconstruction • algorithms must be adapted,

For the first time a calorimeter is able to behave as a "tracker".

Higgs physics prospects at the HL-LHC• In July 2012, ATLAS and CMS discovered a SM Higgs-like particle using ~25 fb -1 of 7+8 TeV pp data• The nature of this particle not yet fully established : spin, CP, couplings will benefit from high luminosity

The measurement of the Higgs self coupling will become feasible at higher energy and integrated luminosity

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Main branches of Higgs decays

Channel BR(%)

Cross section x BR (fb)

Events expected @ 14 TeV

(L=3000 fb-1)

bb+bb 33.41

11.33 34 k

bb+WW 24.97

8.36 26 k

bb+ττ 7.36

2.50 7.5 k

WW+WW 4.67

1.58 4.7 k

ZZ+bb (ZZ+bb 4l+bb)

3.09

1.03 3.1 k (13.9)

ZZ+WW 1.15

0.39 1.2 k

gg+bb 0.27

0.09 270

bb+μμ 0.013

0.004 12.8

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Towards reconstructionτThe most abundant particles found after a τ lepton decay are π±, π0, K± and K0. To reconstruct a τ lepton we naturally start by studying how pions are reconstructed.

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π0 reconstruction• Neutral pions decay mostly to two photons. As the decay

products interact electromagnetically it is detected in the electromagnetic calorimeter. Due to interaction

• with the tracker material we may observe several electromagnetic showers developing in parallel.

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Exploring the shower structure

By looking at the structure of energy deposit in the Calorimeter we can study- how collimated is the shower- How many particles it containsAn Hough transform can be used for this purpose.

The total accumulated in the maximum of the Hough transform can help us to distinguish between single and multiparticle showers.As shown in the Figures single photons are expected to produce collimated, high energy showers while neutral pions tend to produce multiple-core showers of lower energy.We are exploring these properties for particle identification.

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π± reconstruction• π± are charged hadrons which interact

mostly in the hadronic calorimeter. In the electromagnetic calorimeter they are expected to leave low energy ionization deposits.

• Showers are expected to be wider with respect to π0.

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Thank you

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