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Introduction to B Physics in ATLAS Detector at LHC

Ahmet BİNGÜL

Department of Engineering Physics

University of Gaziantep

Feb 2010

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Outline

Introduction

Physics in ATLAS Experiment

ATLAS B-Physics Programme

Trigger

Simulation of the Events

Example Reconstruction

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Introduction

This is a short introduction to some current topics in B-Physics in ATLAS Detector at LHC.

We will look at briefly

the LHC the ATLAS detector

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LHC: Large Hadron Collider

Circumference 27 km ~100 m underground Protons ve Pb nuclei will collideCost: 3 billions €

PHYSICS Higgs Boson(s) Supersymmetric particles furher quarks and/or hadronsBig-Bang and mini-black holes

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LHCAbout p-p collisions

Max proton energy: E = 7 TeV

Velocity: v = 0.999999991 c ~ 300,000 km/s

2808 x 2808 bunches of protons

# of p / bunch = 1011

Bunch diameter = 16 μm (hair 50 μm)

Max Luminosity: L = 1034 cm‒2s‒1

Collision frequency f = 1/25 ns = 40,000,000 Hz = 40 MHzDebris

of a collis

ion

E = m c2

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LHC Detectors

CMS

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Sayfa 816/11/2007 YFD

22 m

44 m

ATLAS Detector (http://atlas.ch)

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Physics Groups in ATLAS

https://twiki.cern.ch/twiki/bin/view/Atlas/AtlasResults

Standard Model (SM) QCD W/Z and jets Electroweak measurements

Higgs Discovery of SM Higgs Boson (for several decay channels) Charged Higgs Boson searces

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Physics in ATLAS

B-Physics Heavy quarkonium physics with early ATLAS data Production cross-sections measurements Study of B-hadrons Rare B-dacays

Top Physics t-tbar pair cross-section Top mass, charge, spin measurements Rare top decays

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Physics in ATLAS

SUSY Discovery of SUSY particles Test of SUSY models

Exotics Black hole Production New quarks and leptons

Heavy Ion Results of Pb-Pb collisions Heavy quark production Jet studies Quarkonia Reconstruction

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ATLAS B-Physics Programme

B-Physics programme covers many aspects of

beauty flavour physics.

by measuring production cross-sections of beauty and charm hadrons and of heavy-flavour quarkonia (J/ψ and Y (upsilon)),ATLAS will provide sensitive tests of QCD predictions.

ATLAS will study the properties of entire family of B-mesons (B+, Bd, Bs, Bc) and B-baryons (Y, Λb )

Precise measurements of weak B-hadrons decays

Rare decays of B-hadrons

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The rate of B-hadron production at the LHC is enormous thanks to the large hadronic cross-section for b-quark production and the high luminosity of the machine (L = 1033 / s.cm2)

About one collision in every hundred will produce a b-quark pair. (better S:N ratio wrt Tevatron)

At the LHC, ATLAS and CMS will face stiff competition from LHCb, which is a dedicated B-physics experiment.ATLAS and CMS will improve the combined precision of B-physics measurements from the LHC.

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In ATLAS, B-Physics potential begins during early data taking at low luminosity (L = 1031/ s.cm2)

Main B-Physics measurements will be made at the luminosity of L = 1033/ s.cm2.

With the integrate luminosity of Lint = 10 pb-1 ATLAS will be able to register about 1.3x105 events containing

either directly produced from p-p collisions or indirectly from decays of B-hadrons.

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During the period of Lint = 10 – 100 pb-1 B-physics and heavy quarkiona signatures will help

understand the detector performance and muon trigger promt J/ψ and Y events and

B-hadron decays to muon pairs via J/ψ will be analysed followind exclusive decays will be stuied

During the period of Lint = 200 pb-1 – 1 fb-1 Statistics will be simalar to Tevatron SM rare decays will be studied (e.g. )

During the period of Lint = 10 – 30 fb-1 (around 3 years) Luminosity will mostly be L = 1033/ s.cm2

Measuremnts of Λb and osciallation pghenomena of Bs – Bs_bar

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Trigger

All B-Physics studies include trigger reconstruction

ATLAS have three levels of trigger L1 – Hardware trigger L2 - L3 – Software trigger

B-Physics events is initiated by a L1 di-muon trigger by a L1 single-muon trigger L2 is used to combine ID tracks with L1 muon each muon has to have pT > 4 GeV (later rising to 6-8 GeV)

After getting L1 muon(s), cuts on invariant mass and secondary vertex reconstruction of B decay products are used.

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Simulation of Events

Some 1 million B-hadron events, along with 4x105 prompt J/ψ and Y as well as c-cbar events were produced using PYHTIA 6.4.

The events were passed trough detector simulation based on GEANT4.

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Example Reconstruction