:

Chris Parkes

Part V

CP violation and D Physics

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Outline

PHENOMENOLOGY AND EXPERIMENTS

III. CP violation and Kaon physicsMixing in the neutral kaon system

Neutral kaon decays

Rare kaon decays

IV. CP violation and B physicsB factories, old and future experiments

Mixing in neutral B mesons

Benchmark B decays

Rare B decays

V. CP Violation and D physicsMixing in neutral D mesons

Direct and Indirect CP Violation Searches

Future prospects

VI. Concluding remarks

D mesons

c

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Mixing:

D0 mixing slightly different from K0 and B0(s) mixing

only ‘up’ type quark system that can mix

D0 mixing only recently observed experimentally (2007 onwards)

Beyond Standard Model (BSM) effects may enhance mixing

(Accurate) SM and BSM theoretical calculations/predictions are difficult and show a broad range of estimates

why?: D-mesons are too light to be treated as heavy … and too

heavy to be treated as light!

CP violation:

Predicted to be negligible in the SM

large effects would be evidence for New Physics …

Experimental evidence for CP violation with D mesons not yet clear

(CPV in Kaons got a Nobel prize, CPV in B got a Nobel prize….)

Why study mixing and CP violation in the D sector?

Mixing in neutral D mesons

BaBar and Belle find first evidence for D0 mixingWell established by combining multiple channels

Announcement at the Rencontres de Moriond Conference in March 2007

BaBar and Belle find first evidence for D0 mixingWell established by combining multiple channels

Announcement at the Rencontres de Moriond Conference in March 2007

First single channel 5σ measurment D0 mixing

LHCb, November 2012

First single channel 5σ measurment D0 mixing

LHCb, November 2012

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Mixing in the neutral D0 – D0 system

c

ud, s, b W+

W-_

u

c_d, s, b

c

u d, s, bW- W+

_

u

c_

d, s, b___

D0D0 -

Feynman (box) diagrams for D0 mixing: down type quarks in loops

D0 D0-

_ _ _

b loop CKM suppressed from Wolfenstein parametrisation is order (λ3λ2)2

and s,d loops GIM suppressed

Long distance effects important

– but difficult to calculate

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reminder x<<1

Only small fraction of an oscillation before decay

suppressed

suppressed

suppressedsuppressed

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1. Flavour at production

Key points on D mixing

Hence, don’t need to use the flavour tagging procedures we discussed for B,

mistag rate will be low

2. Decay DiagramsRight sign – Cabibbo Favoured Wrong sign – Double Cabibbo Suppressed

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1. Wrong sign / right sign

Key points on D mixing

Consider events that are either wrong sign (rare and time independent)

or mixed (rare and number will increase with time).

to cancel systematics take ratio to right sign events

Flat with time? no mixing, increases with time ? mixing

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1. Wrong sign / right sign

Key points on D mixing

Flat with time? no mixing, increases with time ? mixing

See just first part of oscillation curve

Indirect CPV

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AΓ : indirect CP violation *

* Actually it has a direct CP violation contribution if direct CPV is large, see arXiv:1111.6515v2 (our group)

Same concept as B or K measurements we saw before

But experimentally different since don’t see oscillations as x is so small

Measure from lifetimes of decay to CP eigenstate

Oscillation & Decay

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t=0 t

D0

D0

D0

D0

D0

D0

CP Violation Am Ad

Weak Phase ϕ

Prompt/Secondary Separation

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Experimental Complication

D come from both production in proton-proton (prompt)

And from decay of B to D (secondary)

Separate out to get prompt D for time dependent measurement

Use impact parameter that is the distance of flight vector of reconstructed D from the primary vertex (proton-proton interaction point)

World’s best measurement

– No sign of CP Violation yet….ArXiv:1310.7201 (2013) (our group)

Direct CPV

Direct CP violation in two-body charm Search for CP asymmetry

Use decays

where slow pion charge determines the D flavour at production

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What we

measure

What we

want

What we

don’t want (1)

What we

don’t want (2)

Note time-integrated not time dependent

Production Asymmetry of D*+

Technical Scale Drawing of LHC Collision

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Proton (Matter) Proton (Matter)

• Cancel by measuring difference of KK and ππ final states

+ve charge

-ve charge

Detection Asymmetry of D and of π+s

• Symmetric final states

no D detection asymmetry• Difference of final states

cancel slow π+ detection asym.

• Periodic reversal of magnetic field

Phys. Rev. Lett. 108, 111602 (2012)

World Average Results

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ΔA

CP

: di

rect

CP

vio

latio

n

AΓ : indirect CP violation

(some tension more results needed )

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Mixing

Fully established - 5σ single channel measurement

CP violation:

So far there is no clear evidence for CP violation with D mesons – some discrepancy in direct, none in indirect

Large CP Violation would be evidence for New Physics, as SM prediction is small

Prospects:

Enormous samples at LHCb under analysis ~ 10 billion charm events taken in last year !

Picture changing very quickly

In addition to two-body decays discussed here, there is active work on 3-body (and 4-body) final state analyses using Dalitz plots

Status / Future prospects

(and a number of good LHCb PhD thesis topics…)

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Key Points – D section

• Neutral meson mixing

• only ‘up’ type system

• x<<1, very slow oscillations

• Long distance effects important, not only box diagrams

• D0 -> K+π-, Wrong sign / right sign event ratio with time

• 5σ single channel discovery LHCb

• No CP Violation observed (yet)

• Small in SM, could be larger due to new physics

• Search for indirect CP Violation

• Search for direct CP Violation