Transcript Charm Physics in BaBar - Istituto Nazionale di Fisica Nucleare

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
Charm Physics @ BaBar - Outline
Analyses results reviewed here:
D0 mixing with 2-body hadronic decays (wrong sign & CP final states)
cs
states spectroscopy
[DsJ* (2317), DsJ (2458)]
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
La Thuile - 2004
2
Alexis Pompili (U. of Bari & I.N.F.N.)
Charm Physics @ PEP-II B-factory
1
Ldt
[
fb
]

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)
e+e- 
bb
cc
ss
uu
dd
 (nb)
1.05
1.30
0.35
1.39
0.35
++e+e-
0.94
1.16
 40
La Thuile - 2004
Powerful tool for
charm physics
D *  D0  , D0
3
BABAR (90fb-1): ~220K
: 120K
 K   Focus
E791
: ~36K
Alexis Pompili (U. of Bari & I.N.F.N.)
The
Crucial
for
charm
physics
PID
detector
CERENKOV DETECTOR
TRACKING
VERTEXING
e+
DRIFT CHAMBER
SILICON VERTEX
e-
D0  K  K 
KAON
EFFICIENCY
K-Id
CHERENKOV
Reconstructed K-K+ Mass (GeV/c2)
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PION
CONTAMINATION
plab[GeV c]
Alexis Pompili (U. of Bari & I.N.F.N.)
Selecting charm decays from continuum
Kinematical selection: require cut on CMS
momentum of charmed meson :
pD* (* )  2.5GeV c
combinatorial background strongly reduced
D(*) from B-decays rejected
D*-TAG with S


ee- cc  D* X ; D*  D0 πs ; D0 K -π 
allows flavor-tagging
reduces BKGD through dm = [m(K-+s) - m(K-+)]
 140μm
D0
 70μm
Refitting technique with beamspot - constraint
D*
 10μm
improves dm resolution
Beamspot
 120μm
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S
Alexis Pompili (U. of Bari & I.N.F.N.)
D-mixing: parameters & search methods
Mass eigenstates: | D10, 2   p | D 0  q | D 0  , | p |2  | q |2  1 ( | D 0  , | D 0  flavour eigenstates)
G G1  G2
G  ( G1  G2 ) / 2
M  M 1  M 2
G
M
x
,y
2G
G
MIXING PARAMETERS:
SM : | x |, | y |  103
beyond the reach of current
experimental sensitivity
…but
masses: M1 , M2
widths: G1 , G2
NEW PHYSICS may enhance x
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
NP may not conserve CP
rm  q p  0
6
x2 , y ; d: unknown strong phase difference
consider CP when measuring mixing
Af  f | H D | D0 
  arg (q p)  ( Af Af )   

2,  2
rm  1
CP in mixing ( sure sign of NP )
0
CP in interference mixing–decay
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:

    0  1  rm1 ( y cos   x sin 

1
for CSD of D0 (D0) into CP-even
final states (such as K+K-,+-)
for CFD D0  K   ( D 0  K   )
These effective lifetimes
0

can be combined into: Y 
0
 1 , Y 
 A
 
 
IF NO MIXING : x = y = 0
 
LIFETIME RATIO
   0
IF CP-CONSERVATION IN MIXING : rm=1
where
Y , Y  0
1
2
(

  )
   
A   
 
Y  y cos
Y  x sin 
IF ALSO … CP-CONSERVATION IN INTERFERENCE MIXING -DECAY :
sin   0
Systematics effects on lifetime tend to cancel in the lifetime RATIO
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Alexis Pompili (U. of Bari & I.N.F.N.)
Yy
Y  0
Mass fits
DATA
~265K
~26K
99.4%
97.0%
FIT RESULT
SIGNAL (S)
FROM THE FITS :
yield
BKGD (B)
S/S+B
 15MeV c 2
mass window
~145K
~13K
68.1%
87.9%
Mass fits determine
event-by-event
signal probability
91 fb1
“sidebands”candidates included
as part of proper time fit
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BKGD
constrained
in data
Alexis Pompili (U. of Bari & I.N.F.N.)
Decay-time distributions fit
within mass signal window:  15MeV
SIGNAL
FROM THE FITS :
DATA
c2
BKGD
UNBINNED MAXIMUM
LIKELIHOOD FIT RESULT
 0 , 
D0 SAMPLES
K-K+ , -+ [CSD – CP-even]
K-+
[CF – CP-mixed]
D*-untagged K-K+
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MEASURED QUANTITY
MEASURED PARAMETER
   , A
Y , Y
0
 
-
Alexis Pompili
Y
(U. of Bari & I.N.F.N.)
Summary of lifetime ratio results
CS Sample
K-K+
Y(%)
Y(%)
1.5  0.8  0.5  1.3  0.8  0.2
-+
1.7 1.210..26
D*-untagged K-K+
0.2  0.500..54
0.8  0.400..54  0.8  0.6  0.2
Combined
[Phys.Rev.Lett.91,12(2003)]
0.3  1.1  0.2
hep-ex/0308034
BaBar has the most
stringent limits on y
BaBar has the first measurement of a CP
parameter with the method of lifetime ratio
91 fb1
La Thuile - 2004
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Alexis Pompili (U. of Bari & I.N.F.N.)
Wrong-sign searches in hadronic decays
Study time-evolution of D0  K π looking for a signal D 0  D 0  K  π 
Assuming
x  x cosd K  y sin d K
y   x sin d K  y cosd K
dK : unknown relative strong phase
DCSD & CFD may
have different FSI
(not measurable in a mixing analysis):
rotation of dK in the x-y plane :
x, y  1 and CP conservation (rm  1,  0) :


GWS (t )  G D  K  (t )  e
0


Gt
G( D0 DCS

 K   )
RD 
CF
G( D 0 
K   )
Integrating :
where
1 2

2
2 2
 RD  y RD Gt  4 x  y G t  G  1  D0

DCSD

INTERFERENCE

MIXING
enhances
mixing signal

RWS  RD  y RD  x2  y2 2
mixing rate :
RM
Additional CP effects are included by measuring this distribution for D0 and D0 separately:
RD  RD
RM  RM
AD  
; AM  
,  ( rotationof x, y)
RD  RD
RM  RM
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CP in DCSD
CP in MIXING
CP in their INTERFERENCE
deviation from
pure exponential
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 m( K ) , dm  [m( K S )  m( K )], t ,  t performed in steps :
proper time error
1st step fit
m(K)
dm
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
Double mis-id
Sideband
With 57fb-1: ~120,000 RS
~
440 WS
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Alexis Pompili
(U. of Bari & I.N.F.N.)
Decay time Fit
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
Combinatorial
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Wrong slow pion
Double mis-id
Alexis Pompili
(U. of Bari & I.N.F.N.)
Summary of wrong-sign results
95% C.L. contours by a frequentistic approach
(based on toy Monte Carlo experiments) :
[Phys.Rev.Lett.91,17(2003)]
Results presented in 4 cases :
RD  RWS
RWS
BEST FIT
(x’2 free)
NO CP
BEST FIT
(x’2=0)
(stat.+syst.)
(stat.)
(Prelim.)
E791:
CLEO II:
FOCUS:
PDG:
Belle:
CP allowed
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Aitala et al., PRD 57, 13 (1998)
Godang et al., PRL 84, 5038 (2000)
Link et al., PRL 86, 2955 (2001)
2002
hep-ex/0208051
Alexis Pompili (U. of Bari & I.N.F.N.)
Two surprising new Charmed Mesons : DsJ* (2317) & DsJ (2458)
m( KK )
m( )
[Phys.Rev.Lett. 90,24(2003)]
0
Ds
D
BaBar discovered a new narrow state in the Ds+ 0
invariant mass distribution near 2.32GeV/c2
Ds* (2112)   Ds 0
G  8.5MeV
!
!
91 fb1
m( Ds ) [GeV / c2 ]
[Accepted by P.R.L. ; hep/ex-0310050]
BaBar observed a second new narrow state in the
Ds*+ 0 invariant mass distribution near 2.46GeV/c2
m( 0 )  m(Ds 0 ) m(Ds )
T hisstatemay decay toDs 0
throughDs* 0 or DsJ* (2317) 
La Thuile - 2004
m( Ds 0 ) [GeV c 2 ]
 0 sidebands
Ds sidebands
m( KK 0 ) [GeV c 2 ]
p* (Ds 0 )  3.5GeV c
15
p* (Ds 0 )  3.5GeV c
91 fb1
sidebands
subtraction
Ds* sidebands
m( 0 ) [GeV c 2 ]
m( 0 ) [GeV c 2 ]
Alexis Pompili (U. of Bari & I.N.F.N.)
Channel Likelihood Fit
To disentangle these 2 possible DsJ(2458) decay modes & extract signal parameters:
unbinned maximum likelihood fit using the channel likelihood method
1022  50
DsJ (2458)
DsJ* (2317)
 m   2317.3  0.4 (stat.)  0.8(syst.) MeV c 2
 m   2458.0  1.0 (stat.)  1.0(syst.) MeV c 2
G  8.5  1.0 (stat.)MeV
G  7.3  0.2 (stat.) MeV
195  26
contribution from DsJ(2458) decays
0  23
R[ DsJ (2458)]
 0.25  0.03( stat.)  0.03( syst.)
R[ DsJ* (2317)]
BELLE
CLEO
m( Ds 0 ) [GeV c 2 ]
combinatorial
background
m( Ds 0 ) [GeV c 2 ]
CLEO observed them in continuum and…
*
Belle both in continuum and in B decays [ B  D DsJ
]
Re lativeproductionratein cc ( p*  3.5GeV/c2 )
16
SPIN-PARITY
DsJ* (2317)
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+ (not allowed if JP=0+)
3) absence of decay to Ds++- (not allowed if JP=0+)
DsJ (2458)
Un-natural spin-parity more likely (lack of decays to DK)
DsJ (2458)  Ds [by Belle] J  0
Belle helicity analysis from B-decays favours J=1
Decay to Ds+- (by Belle) allowed by JP=1+
EXPERIMENTAL
SUMMARY
Two narrow states observed, in the inclusive Ds0 & Ds*0
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+.
La Thuile - 2004
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Alexis Pompili (U. of Bari & I.N.F.N.)
Spectroscopy of
cs states (before & after)
Potential models of [heavy-quark | light-quark] mesons: so far
reasonable success for spectroscopy of D, Ds, B, Bs systems
1 1P1 (2.53)
D*K
1 3P0 (2.48)

DK

?
?
IF interpreted as ordinary cs states, they
decay mainly by isospin-violating -emission
thus having widths quite narrow.
1 3P2
1 3P1
DsJ (2458)
*
DsJ
(2317)
1 3S1
11S0  
New states do not fit well :
masses below the DK[D*K] threshold.
A possible decay mechanism is
through a virtual h followed by
h-0 mixing [Cho-Wise,PRD49].
m[ DsJ* (2317)]  m[ Ds (1969)] 
 m[ DsJ (2458)]  m[ Ds* (2112)]
NEW STATES
…as predicted by models based on HQET & chiral
symmetry [Bardeen et al.,…] if new states are 0+ & 1+
40(!) papers by theorists:
Exotic (4-quark, molecule, …)
S-wave
Ds (1969)
Ds* (2112) 
P-wave
Ds1 (2535)

VS
*
DsJ
(2573) 
[j=3/2; NARROW by K-emission]
  
  
J  j  Sheavy , j  L  Slight
Ordinary explanations (HQET+chiral symmetry, …)
Crucial to measure radiative decays & di-pion emission
18
SUMMARY
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):
x2  0.0022,0.056  y  0.039, RM  0.0016
Y  [0.8  0.4(stat.)00..54 (syst.)]%  y (if CP conserved)
Y  [0.8  0.6(stat.)  0.2(syst.)]% (CP parameter)
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 !
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Alexis Pompili (U. of Bari & I.N.F.N.)
Backup Slides
Unbinned maximum
likelihood fit
L   i Pi where Pi (mi , t , δt; 11 parameters) 
S1
D
(1-f2)(1-f3)
Psig(mi)
SIGNAL
3
S2
+ f2(1-f3)
+ f3
proper-time RESOLUTION
BKG
+ f0(1-f4)
(1-f0)
[1Psig(mi)]
BKG
La Thuile - 2004
e
flying BKG
NO-flying BKG
BUT with ...
SBKG S1
SBKG S2
3
4 fixed
f0f4
BACKUP-1
for tails
A.Pompili (U. of Bari & I.N.F.N.)
Statistical error on lifetime extracted from the fit
La Thuile - 2004
BACKUP-2
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.
La Thuile - 2004
BACKUP-3
A.Pompili (U. of Bari & I.N.F.N.)
La Thuile - 2004
BACKUP-4
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
Ds0 combination proportional to the relative likelihood contributed by the decay mode of interest
La Thuile - 2004
BACKUP-5
A.Pompili (U. of Bari & I.N.F.N.)