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Oscillazioni del mesone D0

Gianluca CavotoINFN Roma La Sapienza

Commissione Scientifica Nazionale IRoma, 3 aprile 2007

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Outline

• Neutral mesons flavor oscillation

• Charm meson mixing

• Evidence from B-factories– D0+

– D0 l l, D0s+-, D0+-+-

• Outlook

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Neutral Mesons systems– Two-level system (M0,M0)

• Weak interactions remove degeneracy, make them unstable

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Neutral mesons oscillations

Time evolution for meson of known flavor at t=0

An opposite flavor component appears after a while!

M0 “oscillates” into M0!(also dubbed “mixing”)

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Some visual examples

Lifetime units

Probability to find a M0(M0) after a given time

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How to generate this ??

No tree level Flavor Changing Neutral Currents (FCNC) in SM

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Can you see New Physics ?

And the top was discovered 8 years after!

B0 mixing was argued by UA1 and directly observed by ARGUS in 1987

Large mixing frequence implied t quark was heavy (mt > 50 GeV/c2)

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Even more ambitious today!Bd,s (K) mixing on the punch line for virtual effects from NP

Not only x and y but also phases in the mixing CP violation

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The missing tile

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Charm Meson Mixing

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Short and Long distance• Prediction x and y

Sum of intermediate REAL states

y

x VIRTUAL states

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SM prediction for charm mixing

Always hard to evaluate SU(3) breaking !!! (HQET, propagation of common hadronic states,…)

SU(3) breaking effect more important for y

bottom quark

ruled out by VCKM Box diagram contribution

Naively

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New Physics in Charm ?

Hard to see a clear cutPushing the limit down

excludes models

Try to separate x and y!Try to separate x and y!

2006 limit

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Experimental Searches

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Charm physics with B-factory

• Run1-5, more than 500M cc events

Run1-5

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The technique

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Flavor tagging

• Same flavour: Wrong-Sign (WS)mixing may have occured

• Opposite flavour: Right-Sign (RS)unmixed events

Flavor at production

Flavor at decay

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Double-Cabibbo Suppressed Decays

V*cd

Vus

Vcs

V*ud

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Time evolution

is the (relative) strong phase

WS (relative to RS) time-dep. rate(small x and small y limit)

RM

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Event Selection

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RS and WS data set

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Decay time analysis

• Resolution function from RS sample

Selectioncriteria

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Background components

Discrimination power from m() and m

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Signal extraction384 fb-1

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RS decay time analysis

D0 lifetime and time resolution function from RS sample

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WS decay time with mixing

384 fb-1

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Evidence for D0 mixing!

3.9

Best fit solution

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Validation: m() and m fit in t bins

Relative rate of WS events clearly increases with time

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Validation: fit RS for mixing

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Systematics uncertainty

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Systematics on Decay time

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Allowing for CP violation

CP asymmetry in DCSD !

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analysis from Belle

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More evidence…!

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Belle evidence on yCP“Apparent” lifetime difference between D0 -+ and +-, +-

D= mixing phase

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Results on yCP

• Plot di combinazioni

Belle hep-ex/0703036

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Separating x and y only cannot separate x and y

Need info on strong phases– Multibody decays:Dalitz models

DCS decays proceed primarily through K*+- while CF through K-+

CF DCS

D0 K-

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D0

Effective phase

Select special region of Dalitz plot

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D0 KS

Both flavor (K*-+/K*+-) final states in the same Dalitz plot!

CP-eigenstate (KS) and flavor states (K*-+) in the same Dalitz plot!

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D0 KS Dalitz model

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Belle D0 KS results

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D-mixing with Semileptonic decay

No DCS sl. !

D0 l l

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Summary and Outlook

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Summary

» BaBar updating multibody decays analysis, yCP measurements

» BaBar KS on-going

y

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Interpreting the results Ciuchini et al. hep-ph/0703294

D0 and D0

95%

68%

HFAGPRELIMINARY

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Measuring To beat down the model systematics measure phases directly

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Double tag at (3770) [CLEO-c]

Need to run

On

threshold

DCP±

neutral D CP eigenstate

(3770) decayconserves CP

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And CP violation?

In general NP weakly constrained if SM not known

Nevertheless SUSY coupling can be constrainedhints on squark and gluino masses!

Neutral meson mixing always a window into unknown (virtual) states!

Ciuchini et al. hep-ph/0703294

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Back up slides

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Fit signal MC events

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Coverage test