1. (University & I.N.F.N. of Bari) [representing the Collaboration]
CHARM PHYSICS 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

2. 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 Alexis Pompili (U. of Bari & I.N.F.N.)

3. 3 Charm Physics @ PEP-II B-factory
PEP-II (SLAC) : asymmetric e+e- 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
E : ~36K 3
La Thuile Alexis Pompili (U. of Bari & I.N.F.N.)

4. 4 The detector K-Id Crucial for charm physics PID e+ e-
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 Alexis Pompili (U. of Bari & I.N.F.N.)

5. 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 with pS
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 Alexis Pompili (U. of Bari & I.N.F.N.)

6. 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 PHYSICS may enhance x
…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-SIGN searches 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

7. Lifetime difference searches
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
IF ALSO … CP-CONSERVATION IN INTERFERENCE MIXING -DECAY :
Systematics effects on lifetime tend to cancel in the lifetime RATIO 7
La Thuile Alexis Pompili (U. of Bari & I.N.F.N.)

8. Mass fits 8 La Thuile - 2004 Alexis 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 Alexis Pompili (U. of Bari & I.N.F.N.)

9. Decay-time distributions fit
within mass signal window:
SIGNAL
FROM THE FITS :
BKGD
DATA UNBINNED MAXIMUM
LIKELIHOOD FIT RESULT
D0 SAMPLES
MEASURED QUANTITY
MEASURED PARAMETER
K-K+ , p-p+ [CSD – CP-even]
K-p [CF – CP-mixed] -
D*-untagged K-K+ 9
La Thuile Alexis Pompili (U. of Bari & I.N.F.N.)

10. Summary of lifetime ratio results
[Phys.Rev.Lett.91,12(2003)]
CS Sample
Y(%)
DY(%)
K-K+
p-p+
D*-untagged K-K+ -
Combined
hep-ex/
BaBar has the most
stringent limits on y
BaBar has the first measurement of a CP
parameter with the method of lifetime ratio 10
La Thuile Alexis Pompili (U. of Bari & I.N.F.N.)

11. Wrong-sign searches in hadronic decays
Study time-evolution of
looking for a signal
dKp : unknown relative strong phase
(not measurable in a mixing analysis):
rotation of dKp 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
CP in DCSD
CP in MIXING
CP in their INTERFERENCE

12. Mass-mass difference Fit
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
~ WS 12
La Thuile Alexis Pompili (U. of Bari & I.N.F.N.)

13. Decay time Fit 13 2nd step fit WS
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 Alexis Pompili (U. of Bari & I.N.F.N.)

14. Summary of wrong-sign results
[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 Alexis Pompili (U. of Bari & I.N.F.N.)

15. ! ! 15 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 ]
BaBar observed a second new narrow state in the
Ds*+ p0 invariant mass distribution near 2.46GeV/c2
sidebands
subtraction 15
La Thuile Alexis Pompili (U. of Bari & I.N.F.N.)

16. Channel Likelihood Fit
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

17. SPIN-PARITY 17 La Thuile - 2004 Alexis Pompili (U. of Bari & I.N.F.N.)
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+
EXPERIMENTAL
SUMMARY
Two narrow states observed, in the inclusive Dsp0 & 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+. 17
La Thuile Alexis Pompili (U. of Bari & I.N.F.N.)

18. 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 possible decay 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

19. 19 SUMMARY La Thuile - 2004 Alexis Pompili (U. of Bari & I.N.F.N.)
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 Alexis Pompili (U. of Bari & I.N.F.N.)

20. Backup Slides

21. tD tBKG BACKUP-1 s3 Psig(mi) [1-Psig(mi)] s3 s4 fixed Unbinned maximum
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
(1-f0)
+ f0(1-f4)
SBKG S2
NO-flying BKG
[1-Psig(mi)]
flying BKG s3
s4 fixed
BKG
f0f4
for tails
BACKUP-1
La Thuile A.Pompili (U. of Bari & I.N.F.N.)

22. BACKUP-2 La Thuile - 2004 A.Pompili (U. of Bari & I.N.F.N.)
Statistical error on lifetime extracted from the fit
BACKUP-2
La Thuile A.Pompili (U. of Bari & I.N.F.N.)

23. BACKUP-3 La Thuile - 2004 A.Pompili (U. of Bari & I.N.F.N.)
Fit allowed x’2<0.
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 A.Pompili (U. of Bari & I.N.F.N.)

24. BACKUP-4
La Thuile A.Pompili (U. of Bari & I.N.F.N.)

25. BACKUP-5 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 
… 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 A.Pompili (U. of Bari & I.N.F.N.)