Oscillazioni del mesone D 0 Gianluca Cavoto INFN

Oscillazioni del mesone D 0 Gianluca Cavoto INFN Roma La Sapienza Commissione Scientifica Nazionale I Roma, 3 aprile 2007 Gianluca Cavoto 1

Outline • Neutral mesons flavor oscillation • Charm meson mixing • Evidence from B-factories – D 0 + – D 0 l l, D 0 s + -, D 0 + - • Outlook Gianluca Cavoto 2

Neutral Mesons systems – Two-level system (M 0, M 0) • Weak interactions remove degeneracy, make them unstable Gianluca Cavoto 3

Neutral mesons oscillations Time evolution for meson of known flavor at t=0 M 0 “oscillates” into M 0! (also dubbed “mixing”) Gianluca Cavoto An opposite flavor component appears after a while! 4

Some visual examples Probability to find a M 0(M 0) after a given time Lifetime units Gianluca Cavoto 5

How to generate this ? ? No tree level Flavor Changing Neutral Currents (FCNC) in SM Gianluca Cavoto 6

Can you see New Physics ? B 0 mixing was argued by UA 1 and directly observed by ARGUS in 1987 Large mixing frequence implied t quark was heavy (mt > 50 Ge. V/c 2) Gianluca Cavoto And the top was discovered 8 years after! 7

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 Gianluca Cavoto CP violation 8

The missing tile Gianluca Cavoto 9

Charm Meson Mixing Gianluca Cavoto 10

Short and Long distance • Prediction x and y x VIRTUAL states Sum of intermediate REAL states y Gianluca Cavoto 11

SM prediction for charm mixing bottom quark ruled out by VCKM Box diagram contribution Naively Always hard to evaluate SU(3) breaking !!! (HQET, propagation of common hadronic states, …) SU(3) breaking effect more important for y Gianluca Cavoto 12

New Physics in Charm ? 2006 limit Hard to see a clear cut Pushing the limit down excludes models Try to separate x and y! Gianluca Cavoto 13

Experimental Searches Gianluca Cavoto 14

Charm physics with B-factory Run 1 -5 • Run 1 -5, more than 500 M cc events Gianluca Cavoto 15

The technique Gianluca Cavoto 16

Flavor tagging Flavor at production Flavor at decay • Same flavour: Wrong-Sign (WS) mixing may have occured • Opposite flavour: Right-Sign (RS) unmixed events Gianluca Cavoto 17

Double-Cabibbo Suppressed Decays Vus V*ud V*cd Vcs Gianluca Cavoto 18

Time evolution WS (relative to RS) time-dep. rate (small x and small y limit) RM is the (relative) strong phase Gianluca Cavoto 19

Event Selection Gianluca Cavoto 20

RS and WS data set Gianluca Cavoto 21

Decay time analysis Selection criteria • Resolution function from RS sample Gianluca Cavoto 22

Background components Discrimination power from m( ) and m Gianluca Cavoto 23

Signal extraction 384 fb-1 Gianluca Cavoto 24

RS decay time analysis D 0 lifetime and time resolution function from RS sample Gianluca Cavoto 25

WS decay time with mixing 384 fb-1 Gianluca Cavoto 26

Evidence for D 0 mixing! Best fit solution Gianluca Cavoto 3. 9 27

Validation: m( ) and m fit in t bins Gianluca Cavoto Relative rate of WS events clearly increases with time 28

Validation: fit RS for mixing Gianluca Cavoto 29

Systematics uncertainty Gianluca Cavoto 30

Systematics on Decay time Gianluca Cavoto 31

Allowing for CP violation CP asymmetry in DCSD ! Gianluca Cavoto 32

analysis from Belle Gianluca Cavoto 33

More evidence…! Gianluca Cavoto 34

Belle evidence on y. CP “Apparent” lifetime difference between D 0 - + and + -, + - D= mixing phase Gianluca Cavoto 35

Results on y. CP • Plot di combinazioni Belle hep-ex/0703036 Gianluca Cavoto 36

Separating x and y • only cannot separate x and y Need info on strong phases – Multibody decays: Dalitz models D 0 K- CF DCS decays proceed primarily through K*+ - while CF through K- + Gianluca Cavoto 37

D 0 Select special region of Dalitz plot Effective phase Gianluca Cavoto 38

D 0 KS Both flavor (K*- +/K*+ -) final states in the same Dalitz plot! CP-eigenstate ( KS) and flavor states (K*- +) in the same Dalitz plot! Gianluca Cavoto 39

D 0 KS Dalitz model Gianluca Cavoto 40

Belle D 0 KS results Gianluca Cavoto 41

D-mixing with Semileptonic decay D 0 l l No DCS sl. ! Gianluca Cavoto 42

Summary and Outlook Gianluca Cavoto 43

Summary y » Ba. Bar updating multibody decays analysis, y. CP measurements » Ba. Bar KS on-going Gianluca Cavoto 44

Interpreting the results D 0 and D 0 Ciuchini et al. hep-ph/0703294 68% 95% HFAG PRELIMINARY Gianluca Cavoto 45

Measuring To beat down the model systematics measure phases directly Gianluca Cavoto 46

Double tag at (3770) [CLEO-c] DCP± neutral D CP eigenstate (3770) decay conserves CP Need to run On threshold Gianluca Cavoto 47

And CP violation? Ciuchini et al. hep-ph/0703294 In general NP weakly constrained if SM not known Nevertheless SUSY coupling can be constrained hints on squark and gluino masses! Neutral meson mixing always a window into unknown (virtual) states! Gianluca Cavoto 48

Back up slides Gianluca Cavoto 49

Fit signal MC events Gianluca Cavoto 50

Coverage test Gianluca Cavoto 51