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Alexis POMPILI ( University & I.N.F.N. of Bari ) [representing the Collaboration]

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in

Alexis POMPILI

(University &I.N.F.N. of Bari)

[representing the Collaboration]

Les Rencontres de Physique de la Vallee d’Aoste

La Thuile – March 3, 2004

Charm Physics @ BaBar -Outline

Analyses results reviewed here:

D0 mixing with 2-body hadronic decays (wrong sign & CP final states)

states spectroscopy

Other Studies in progress:

D0 mixing with semi-leptonic decays

3-body decays of D0, D+, Ds+( B. R., Light Meson Spectroscopy, CP, mixing )

charmed baryons

ISR processes

2

La Thuile - 2004 Alexis Pompili(U. of Bari & I.N.F.N.)

Charm Physics @ PEP-II B-factory

PEP-II (SLAC):asymmetric e+e- collider @ Y(4S)

Integrated luminosity delivered : ~178fb-1

Effective qq cross sections

at the energy of the Y(4S)

Powerful tool for charm physics

BABAR (90fb-1): ~220K

Focus : 120K

E791 : ~36K

3

La Thuile - 2004 Alexis Pompili(U. of Bari & I.N.F.N.)

Crucial

for

charm

physics

PID

CERENKOV DETECTOR

e+

DRIFT CHAMBER

TRACKING

VERTEXING

SILICON VERTEX

e-

KAON

EFFICIENCY

K-Id

CHERENKOV

PION

CONTAMINATION

Reconstructed K-K+ Mass (GeV/c2)

4

La Thuile - 2004 Alexis Pompili(U. of Bari & I.N.F.N.)

Selecting charm decays from continuum

Kinematical selection: require cut on CMS momentum of charmed meson :

combinatorial background strongly reduced

D(*) from B-decays rejected

D*-TAG withpS

allows flavor-tagging

reduces BKGD through dm = [m(K-p+ps) - m(K-p+)]

D0

Refitting technique with beamspot - constraint

pS

D*

improves dm resolution

Beamspot

5

La Thuile - 2004 Alexis Pompili(U. of Bari & I.N.F.N.)

D-mixing: parameters & search methods

Mass eigenstates:

( flavour eigenstates)

masses: M1 , M2

widths: G1 , G2

MIXING PARAMETERS:

beyond the reach of current experimental sensitivity

SM :

NEW PHYSICSmay enhancex

…but

FSI & SU(3)-breaking can enhance y

Experimental goal : to put limits on the transition D0-D0

1) LIFETIME DIFFERENCE searches

y [if CP conserved]

2) WRONG-SIGNsearches in hadronic decays

x2, y ;d: unknown strong phase difference

NP may not conserve CP

consider CP when measuring mixing

CP in mixing ( sure sign of NP )

CP in interference mixing–decay

6

Mixing would alter the decay-time distributions of D0 and D0 that decay into CP eigenstates.

They can be considered to a good approx. as pure exponential with effective lifetimes:

for CSD of D0 (D0) into CP-even

final states (such as K+K-,p+p-)

for CFD

LIFETIME RATIO

These effective lifetimes

can be combined into:

where

IF NO MIXING:x = y = 0

IF CP-CONSERVATION IN MIXING :rm=1

IFALSO … CP-CONSERVATION IN INTERFERENCE MIXING -DECAY:

Systematics effects on lifetime tend to cancel in the lifetime RATIO

7

La Thuile - 2004Alexis Pompili(U. of Bari & I.N.F.N.)

DATA FIT RESULT

~265K

~26K

SIGNAL (S)

99.4%

97.0%

yield

FROM THE FITS :

BKGD (B)

S/S+B

mass window

~145K

~13K

68.1%

Mass fits determine

event-by-event

signal probability

87.9%

BKGD

constrained

in data

“sidebands”candidates included

as part of proper time fit

8

La Thuile - 2004 Alexis Pompili(U. of Bari & I.N.F.N.)

within mass signal window:

SIGNAL

FROM THE FITS :

BKGD

DATA UNBINNED MAXIMUM

LIKELIHOOD FIT RESULT

9

La Thuile - 2004 Alexis Pompili(U. of Bari & I.N.F.N.)

Summary oflifetime ratio results

[Phys.Rev.Lett.91,12(2003)]

hep-ex/0308034

BaBar has the most

stringent limits on y

BaBar has the firstmeasurement of a CP

parameter with the method of lifetime ratio

10

La Thuile - 2004 Alexis Pompili(U. of Bari & I.N.F.N.)

Wrong-sign searchesin hadronic decays

Study time-evolution of

looking for a signal

dKp: unknown relative strong phase

(not measurable in a mixing analysis):

rotation ofdKp in the x-y plane :

DCSD & CFD may

have different FSI

Assuming and CP conservation :

where

deviation from

pure exponential

DCSD

MIXING

INTERFERENCE

enhances

mixing signal

Integrating :

mixing rate :

Additional CP effects are included by measuring this distribution for D0 and D0 separately:

11

CPin their INTERFERENCE

CPin DCSD

CPin MIXING

Assign each candidate to one of 4 categories: D0(RS,WS),D0(RS,WS)

Unbinned extended max-likelihood fit to RS and WS samples simultaneously in

4D variable space performed in steps :

proper time error

1st step fit

m(Kp)

d m

Number of SIGNAL and BKGD candidates

from a fit to m-dm plane (both RS and WS)

by modelling BKGD categories

Signal

region

Signal

WS

Wrong slow pion

Combinatorial

Sideband

Double mis-id

With 57fb-1: ~120,000 RS

~ 440 WS

12

La Thuile - 2004 Alexis Pompili(U. of Bari & I.N.F.N.)

2nd step fit

Simultaneous fit time-distribution to RS and WS (include mixing parameters).

The larger/clean RS sample fixes D0 lifetime and resolution model parameters for unmixed decays. BKGD time distributions determined from m,dm sidebands in data.

WS

Signal

Wrong slow pion

Combinatorial

Double mis-id

13

La Thuile - 2004 Alexis Pompili(U. of Bari & I.N.F.N.)

[Phys.Rev.Lett.91,17(2003)]

Results presented in 4 cases :

95% C.L. contours by a frequentistic approach

(based on toy Monte Carlo experiments) :

BEST FIT

(x’2 free)

NO CP

BEST FIT

(x’2=0)

(stat.+syst.)

(stat.)

(Prelim.)

CP allowed

14

La Thuile - 2004 Alexis Pompili(U. of Bari & I.N.F.N.)

Two surprising new Charmed Mesons : &

[Phys.Rev.Lett. 90,24(2003)]

BaBar discovered a new narrow state in the Ds+ p0

invariant mass distribution near 2.32GeV/c2

!

!

[Accepted by P.R.L. ; hep/ex-0310050]

BaBar observed a second new narrow state in the

Ds*+ p0 invariant mass distribution near 2.46GeV/c2

sidebands

subtraction

15

La Thuile - 2004 Alexis Pompili(U. of Bari & I.N.F.N.)

To disentangle these 2 possible DsJ(2458) decay modes & extract signal parameters:

unbinned maximum likelihood fit using the channel likelihood method

contribution from DsJ(2458) decays

combinatorial

background

BELLE

CLEO observed them in continuum and…

Belle both in continuum and in B decays []

CLEO

16

Decay to JP=0- mesons only natural spin-parity allowed [0+,1-,2+,…]

JP=0+ suggested by: 1) low mass compared to Ds1(2535) & DsJ*(2573)

2) absence of decay to Ds+g (not allowed if JP=0+)

3) absence of decay to Ds+p+p- (not allowed if JP=0+)

Un-natural spin-parity more likely (lack of decays to DK)

Belle helicity analysis from B-decays favours J=1

Decay to Dsp+p- (by Belle) allowed by JP=1+

Two narrow states observed, in the inclusiveDsp0&Ds*p0

invariant mass distributions, near 2.317GeV/c2& 2.458GeV/c2.

The widths [G<10MeV]are consistent with experimental resolution.

The most likely assignment for their spin-parity is 0+& 1+.

EXPERIMENTAL

SUMMARY

17

La Thuile - 2004 Alexis Pompili(U. of Bari & I.N.F.N.)

Spectroscopy of states (before & after)

Potential models of [heavy-quark | light-quark] mesons: so far

reasonable success for spectroscopy of D, Ds, B, Bs systems

New states do not fit well :

masses below the DK[D*K] threshold.

IF interpreted as ordinary states, they

decay mainly by isospin-violating p-emission thus having widths quite narrow.

?

A possibledecay mechanism is

through a virtual h followed by

h-p0 mixing[Cho-Wise,PRD49].

?

D*K

p

DK

p

g

…as predicted by models based on HQET & chiral symmetry [Bardeen et al.,…] if new states are 0+ & 1+

p

NEW STATES

40(!) papers by theorists:

Exotic (4-quark, molecule, …)

VS

Ordinary explanations (HQET+chiral symmetry, …)

S-wave

P-wave

[j=3/2; NARROW by K-emission]

Crucial to measure radiative decays & di-pion emission

18

Competitive D0 mixing results obtained with 2 different experimental methods

are consistent with no mixing and no CP.

wrong-sign D0 mixing limits

(95% CL,57fb-1;CP-allowed):

D0 lifetime ratio (91fb-1):

Wrong-sign D0 mixing limits from semileptonic decays coming soon

Charmed mesons are a rich laboratory for Heavy Quark studies.

After the discovery of D*sJ(2317) and the observation of DsJ(2458)…

… further Ds mesons (spectroscopic) studies are ongoing.

BaBar is a promising place to study charm physics … studies have just began !

19

La Thuile - 2004 Alexis Pompili(U. of Bari & I.N.F.N.)

likelihood fit

S1

S2

s3

tD

(1-f2)(1-f3)

+ f2(1-f3)

+ f3

Psig(mi)

SIGNAL

proper-time RESOLUTION

tBKG

e

BUT with ...

SBKG S1

+ f0(1-f4)

(1-f0)

SBKG S2

NO-flying BKG

[1-Psig(mi)]

flying BKG

s3

s4 fixed

BKG

f0f4

for tails

BACKUP-1

La Thuile - 2004 A.Pompili(U. of Bari & I.N.F.N.)

Statistical error on lifetime extracted from the fit

BACKUP-2

La Thuile - 2004 A.Pompili(U. of Bari & I.N.F.N.)

Central values for fits of both

separate samples gave x’2<0.

Due to allowing x’2<0 in the fits it is not

clear how to apply a Bayesian ansatz to

derive an error estimate from the 2D

likelihood distributions. Moreover

these ones depend strongly on the

most likely fitted values of x’2 and y.

95% C.L. limits are determined

using toy Monte Carlo samples

at each point on the contour

(frequentistic approach).

(x’2,y) points on separate contours are combined in

pairs to determine (x’2,y) on 95% CP contours.

Systematic uncertainties included by calculating

equivalent statistical deviation for each systematic

check and expanding the 95% C.L. contour appropriately.

BACKUP-3

La Thuile - 2004 A.Pompili(U. of Bari & I.N.F.N.)

La Thuile - 2004 A.Pompili(U. of Bari & I.N.F.N.)

Unbinned maximum likelihood fit

Assign likelihood to each event for:

- DsJ(2458)+ Ds*(2112)+ 0
- DsJ(2458)+ DsJ*(2317)+
- Combinatorial Ds+ 0 bkgd
- Ds*(2112)++ random 0
- DsJ*(2317)++ random
- DsJ(2458)+ Ds*(2112)+ 0

… using wrong

The DsJ(2458) signal for a particular decay mode can be isolated by calculating a weight for each

Dsp0g combination proportional to the relative likelihood contributed by the decay mode of interest

BACKUP-5

La Thuile - 2004 A.Pompili(U. of Bari & I.N.F.N.)

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