Recent Results on Charm Decays

1
Recent Results on Charm Decays

• Lifetimes
• mesons
• baryons
• Wrong sign D0 decays
• Mixing
• Doubly suppressed cabibbo decays
• CP violation searches
• Semileptonic charm decay
• Summary/Outlook

weak
Results from BABAR BELLE CLEO
FOCUS SELEX
2
Charm Particle Lifetimes

• Lifetime is a defining property of a particle.
• necessary to convert BRs to decay rates Þ
  theoretical comparisons
• Weak interaction lifetime modified by strong
  interaction effects
• Þ non-perturbative QCD

spectator
exchange
annihilation
color suppressed internal spectator
Charmed mesons and baryons provide a rich testing
ground 3 mesons (D, D0, Ds) 4 baryons (Lc,
Xc, Xc0, W0c) doubly charmed baryons
Interference effects are important
Pattern of lifetimes predicted but not exact
lifetime values
3
Colliding Beam vs Fixed Target
Silicon detectors
Beampipe
Silicon detectors
K
g
D0
p
Colliding Beam
Fixed target
Better acceptance for short lifetimes
Better L/s separation
Cleaner environment
Large data samples
Unbinned ML fit
Binned ML fit
1d or 2d vertex
3d vertex
Neither actually see the decay as in emulsion
and/or bubble chamber
4
Charmed meson lifetimes
Fixed target exponential decay
D0Kp- signal
Colliding beam exponential decay smeared by
resolution
D0Kp- sideband
5
Lifetime results for Charmed Mesons
1s PDG2001
lifetime (fs)

D
preliminary
Annihilation and exchange diagrams are important
for mesons. Expect annihilation and exchange. Bigi Uraltsev,
Z.Phys. C.62, 623, 1994
6
Charmed Baryon Lifetimes

• Baryon lifetimes not measured as precisely as
  mesons 5-30 vs 1-2
• Baryon lifetimes shorter than mesons (e.g. tWc
  60 fs vs tD0 410 fs )
• Baryon cross sections are low Þ samples smaller
  than mesons
• Lifetime calculations more complicated than
  mesons
• New results for Lc, Xc, Xc0

not in PDG2001
preliminary
preliminary
1s PDG2001
Lc
7
Recent Xc lifetime Results
t5034718fs
XcX-pp-
25018
not in PDG2001
1s PDG2001
XcX-pp- XcSpK- XcppK- XcLpp- K-
58132
8
Charmed Baryons Lifetimes

• Preliminary Xc0 result from FOCUS
• t10910 fs (PDG2001 t9823 fs)
• Based on a total of 13719 events (Xc0W-K, X-p
  )

-9
-15
Comments Measured lifetime ratio for Xc / Lc
larger than theory
Theory ranges from 1.3 Blok and Shifman,
proceedings of 3rd workshop on physics of a tau
charm factory, (1993) 1.2-1.7 Guberina and
Melic, Eur. Phys. J. C2, 697 (1998)
At some point in the future lifetime analyses may
have to correct for Wc0 Xcp- contamination
of Xc sample Xc0 Lcp- contamination of Lc
in sample Doubly charmed baryons
No Calculations available
Cabibbo suppressed s u instead of c s
9
Why is D0-D0 mixing interesting?
-
Only meson system where mixing has not been
observed Only meson system where mixing is
generated by down quarks Mixing in D sector
expected to be small in Standard Model doubly
Cabibbo Suppressed (DCS) vanishes the limit of
SU(3) flavor symmetry
If D mixing is large DG ³ DM large flavor
SU(3) breaking ? DM DG new physics ?
D mixing only involves the first two
generations CPV 10-3 Þ New Physics
Can make measurements to look for mixing !
10
D mixing Phenomenology


Usual definitions
Phases d is the strong phase between Cabibbo
allowed and doubly Cabibbo suppressed amplitudes
f is the CP violating phase in mixing (very small
in SM)
CP Violation CPV in mixing due to p/q¹1
CPV in interference between decay with and
without mixing µ sinf ¹0 Assume no direct CPV
11
Ways to Observe D mixing

• Measure lifetime difference between CP and/or
  CP- states
• and with flavor specific (CP mixed) states.
• CP D0KK-, pp-
• CP- D0Ks0r0, Ks0w
• Mixed D0K-p
• Gives info on y

ycp y if no CPV
Requires good time (vertex) resolution
Measure Wrong sign Decays. hadronic decays
D0Kp- semi-leptonic decays D0Kl-v
Dont have to measure time dependence
-
12
Wrong sign D0 decays

• These decays can originate from
• Double Cabibbo suppression (DCS) (hadronic decays
  only)
• Mixing

Wrong sign rate (RWS) has interesting time
dependence due to mixingdecay
Usual assumptions CP conserved Þp/q1 x,
y, RDCS
dstrong phase difference between CF and DCS
decays
Convenient to rotate away d xxcosdysind,
yycosd-xsind
NO DCS for semi-leptonic decays
13
Some Recent ycp Lifetime Results
CLEO sub. PRD
Not a full blown lifetime analysis Looking for
lifetime differences
KK ycp -1.9 2.9 1.6 pp ycp 0.5 4.3 1.8
FOCUS PLB485, 62 (2000)
ycp 3.4 1.4 0.7
BABAR preliminary
ycp -1.0 2.2 1.7
14
Recent Mixing Results via ycp
preliminary
0.7 -0.8
15
Mixing Limits using wrong sign and ycp
measurements
CLEOs Time dependence of G(D0Kp- )/
G(D0K-p)
Published Data
E791 Semi-leptonic G(D0Kl-v)/ G(D0K-lv)
limit G(D0Kl-v)/ G(D0K-lv) ycp measurements (FOCUS, E791)
16
Mixing Limits using wrong sign and ycp
measurements

• What will this plot look like in the near future?
• New results expected soon from CLEO, FOCUS,
  BABAR, BELLE

FOCUS, CLEO SL sensitivity
average ycp
FOCUS preliminary Kp
17
Wrong sign D0 Decay rates

• Improved measurements of G(D0Kp- )/ G(D0K-p)

RWSG(D0Kp- )/ G(D0K-p) ()
preliminary 10X data soon
preliminary
Preliminary
D ? D0p
D0 ? Kp-
18
More wrong sign D0 Decay rates
CLEO II.V result for D0 Kp-pp-
9fb-1 of data used in analysis
54 14 WS events from 2D binned ML fit
0.12
(stat) 0.04(sys) (1.070.10)(phase space)()
0.41
-0.11
CLEO II.V result consistent with previous E791
result
0.36
(stat) 0.03 (sys) () (phase space1)
RWS0.25
-0.34
But cannot tell if this result is from DSC or
mixing since
Only other WS D0 result CLEOs
19
D0K0p0 and K0p0
L
S

• Preliminary result from BELLE

-
Interference between the Cabibbo allowed decay
D0K0p0 and the DCS decay D0K0p0 can lead to a
rate difference between D0KLp0 and KSp0.
Expect a 5 (tan2qc) asymmetry in
The magnitude and sign of A provides info the
strong phase difference (d) between D0Kp- and
D0K-p .
Experimentally very challenging ! Difficult to
reconstruct KLs in an ee- experiment
BELLE calibrates KL efficiency using D0K-p ,
with K-KLp- .
20
D0K0p0 and K0p0
L
S
D0KLp0
D0KSp0
Preliminary
First reconstruction of Ds using KLs!
D0K-p KLp-p
D0K-p KSp-p
Using 23 fb-1 of data BELLE measures

21
CP Violation in D0 Decay
CPV expected to be small in the charm sector
SM predictions O(0.1)
CPV 1 evidence for non-SM processes

• Look for particle Û anti-particle rate
  differences

-
Use D tag to distinguish D0 from D0.
Measure
Where f is KK-, pp-, Ksf, Ksp0, p0p0, and KsKs
22
CP Violation in D0 Decay
KK-
p p-
CLEO also has the following results
ACP(Ksf)-2.89.4
ACP(p0p0)0.14.8
ACP(Ksp0)0.11.3
ACP(KsKs)2319
CLEO wrong sign D0Kp- analysis yields
ACP(Kp-)219 1.0
No mixing in fit
-20
No evidence for CP violation in D0 decay
23
CP Violation in D Decay
For charged Ds measure the following

• Look for direct CP violation, no mixing.
• Not much new since 2000
• All results are from fixed target experiments.

K K0
fp
pp-p
KK-p
No evidence for CPV
24
CLEO Measurement of B(DK0lnl)

• This decay is sensitive to P V form factor
• These form factors are related to ffs in bulv
  and bsll.
• Can help reduce uncertainty in extraction of
  Vub

CLEO Method Use D tag, reconstruct n using jet
direction for D direction 2-fold ambiguity,
choose solution closest to dmMD-MD140.6 MeV
fit K mass in bins for dm then fit resulting
dm with Kdata to extract signal
preliminary
Re0.74 0.04 0.06 Rm0.72 0.104
0.06 R0.73 0.04 0.05
PDG B(DK-pp) (9.0 0.6) BRe (6.7 0.4
0.5 0.4) BRm (6.5 0.9 0.5 0.4) BR
(6.6 0.4 0.5 0.4)
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CLEOs form factor ratio measurement in LcLen
Motivation Alternative method for extracting
Vub and Vcb
Same set of form factors in both decays f1(q2),
f2(q2) KornerKramer predict R
f2(q2)/f1(q2)-0.25 (PL B275,495 (1992))
right sign Le, Le-
wrong sign Le-, Le
Extract R using ML fit to 3 variables
t(q/qmax)2 cosqW angle between e and W in cm
of W cosqL angle between p and L in cm of L
Preliminary Result R -0.310.060.06
Improvement over previous CLEO result R
-0.250.140.08, (PRL 75,624 (1995)) Consistent
with KornerKramer
26
Wc0W-en

• Search for Wc0W-en by comparing right (W-e)
  sign and
• wrong sign (W-e-) event yields.

preliminary
(W-e-)
(W-e)
10X smaller than ARGUS result 520230130 fb
Probability of background fluctuation
B(Wc0W-en )s(ee- Wc X)42.214.111.9 fb
First observation of baryon b decay with no u or
d in parent particle
27
Charm Review Summary

• Lifetimes mesons lifetimes measured to 1- 2
• baryons lifetimes measured 2 - 30
• theory may need a tune up tX /tLexp2 vs tX
  /tLth

c
c
c
c
D Mixing Exciting times ahead new results
expected from BELLE BABAR soon
CP Violation Keep looking !
Semileptonic Decays Progress measuring rates and
form factors
The future of charm physics lies ahead of us !
Yogi
Berra? George W.?
b-factories are charm factories too CLEO-c