annabelle chuinard mcgill university wipc 2013 measurement of cp violation with the lhcb experiment...

Annabelle Chuinard

McGill University

WIPC 2013

Measurement of CP violation with the LHCb experiment at

CERN

WIPC 2013

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Key facts

b-physics: study of particles containing a (anti-)beauty quark! Branching fraction of B

meson decay Feynman diagram

CP asymmetry CKM matrix terms

Physics beyond the SM

The LHC experiment

WIPC 2013

b

Physics goals

b

760 people, 14 countries 4500 t. apparatus, 100 m

underground single arm forward (≠

ATLAS)

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The LHCb detector

pp collisio

n

VErtex LOcator

RICH 1

Magnets

TrackersRICH 2

ElectronicCALorimeter

HadronicCALorimeter

Muons detector (MWPC)

-25°C

-5 to 5°C

-271.3°C

Proton beam

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My job: measure CP asymmetry for

WIPC 2013

There are 2 main Feynman contributions to this decay.

Tree

Penguin (loop)

Radiative B decay :

A1

A2

Amplitudes

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CKM terms and couplings

WIPC 2013

Cabbibo-Kobayashi-Maskawa CKM) matrix describes quark mixing in weak interactions.

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Asymmetry

Conjugate process (CP)

WIPC 2013

Charge asymmetry

Measured valuefrom experimental rates

Corrections

Detection asymmetry between K+ et K-

(found compatible with 0)

Asymmetry due to production rate of B+ et B-

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How to determine raw asymmetry?Distribution of the invariant mass η’K+

Blue line: Multiparameter fit to maximize the

extended likelihood function Distribution of the

invariant mass η’K-

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Detection asymmetry

Detection efficiency is a function of the cross-section of with matter.

At high energy, K+ and K- indistinguishable = same cross section

Use this as a boundary

condition to fit ρ as of function of pK+.

Map ρ and use MINUIT tool to minimize χ2

Test sample: (no production asymmetry)

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Detection asymmetry computation

Distribution ofas a functionof the momentum

Distribution of thenumber of eventsas a function of

Distribution of thenumber of eventsas a function of

Integrate over the distribution to have number of events

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SUMMARY

Calculated using new

method based on kaons cross-

sections

Calculated using rates from mass

distributions

Compatible with PDG world average :

Improvements :Increase luminosity = more statistics

Appendix 1: 2D Likelihood fit

Poisson’s distr.

mB and mη’ are uncorrelated

Unbinned limit (either 0 or 1 event per bin)

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Appendix 2: Detection asymmetry – Mapping

process

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