:

Chris Parkes

Part VCP violation and D Physics

Chris Parkes 2

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

Nucl.Phys. B871 (2013) 1-20

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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 mesonsBaBar 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

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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 even more difficult to calculate

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reminder x<<1Only small fraction of an oscillation before decay

suppressed

suppressed

suppressedsuppressed

DCS mixinginterference

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1. Flavour at productionKey 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 signKey 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 signKey points on D mixing

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

See just first part of oscillation curve

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yCP

Another way to measure D mixing

Measure lifetime of decays into CP eigenstates→ here CP even, e.g. K+K-

Assume D2 ≡ p|D0 - q|D̅⟩ 0 is CP even ⟩→ then this measures τCP+ = 1 / Г2

Compare to decay into flavour-specific final state, e.g. K-π+

→ this measures τ = 2 / (Г1+Г2) ≡ 1 / Г̅

Therefore τ / τCP+ - 1 = Г2 – Г1 / (Г1 + Г2) = ΔГ / (2Г) ≡ y

For non-zero CP violation D2 is not the physical state DH

→ measure yCP ≡ τ(Kπ) / τ(KK) – 1 = (1 – AM

2/8) y cos ϕ – AM/2 x sin ϕ

CP Violation Am Weak Phase ϕOur groupUpdate imminentwith ~100x more data

Indirect CPV

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AΓ : indirect CP violation *

* Actually it has a direct CP violation contribution if direct CPV is large→ see M. Gersabeck, C. Parkes et al., J.Phys. G39 (2012) 045005

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….Phys.Rev.Lett. 112 (2014) 041801 (our group)

Direct CPV

ΔACP: 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

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ΔACP: Direct CP violation in two-body charm

Measure difference of raw asymmetries for KK and ππ final states

Leads to difference of CP asymmetries (at first order)

Araw(KK) - Araw(ππ) ≈ ACP(KK) - ACP(ππ)

Expect similar magnitude and opposite sign for ACP(KK) and ACP(ππ)

→ ACP(KK) - ACP(ππ) ≈ 2 |ACP(KK)| ≈ 2 |ACP(ππ)|

Enhanced sensitivity in difference measurement!

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 statesno D detection asymmetry

• Difference of final statescancel 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 recorded during LHC run 1! 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