Fully leptonic and semileptonic decay

1
Fully leptonic and semileptonic decay
Jim WissUniversity of Illinois

• Acknowledgements and Full Disclosure
• This talk is from the perspective of a brand new
  CLEO-c member
• It borrows very heavily from an excellent longer
  talk of Ian Shipsey
• I have worked on semileptonic decays from the
  Fermilab FOCUS (fixed target) experiment with
  vastly different systematics and very
  complementary techniques.

Allowed transition
2
Hi impact leptonic and semileptonic physics
The most uncertain CKM elements are Vtdand
Vub. Both uncertainties are dominated by
systematics on calculating hadronic effects that
can be significantly reduced by calibrating LQCD
on related charm decays.
D ?mn
D0 ?pln
An impressive check of the unitarity triangle.
3
D meson Decay Constants

In a pseudoscalar D meson decay c and q
annihilate
Helicity suppression
B(D?l?)/ ?D fDVcd B(DS ?l?)/ ?Ds
fDsVcs Charm meson lifetimes known 0.3-2
3 generation unitarity Vcs, (Vcd) known to 0.1
(1.1) ? fD fDs
4
Improving knowledge Vtd using D?mn

1.2
15 (LQCD)
?Lattice predicts fB/fD with small
errors ?precision measurement of fD ?precision
estimates of fB ?precision determination of Vtd

5
D meson Decay Constants Current Status
fDs Values from Ds???

• Common systematic error from B(Ds???)

fD lt 290 MeV _at_ 90 CL (Mark III)

Estimated BR usingfDs260 fD220 fB200 MeV
B(mn) B(tn)
D 4.2?10-4 1.1?10-3
DS 5.7?10-3 5.5?10-2
B 3.2?10-7 7.1?10-5
14 relative error
6
fD from Absolute Br(D ? mn)

• Fully reconstruct one D (tag)
• Require one additional charged track and no
  additional photons

Huge improvement over existing knowledge!
7
Probing the hadronic current
8
Exclusive Charm Semileptonic Signal Yields in 3
fb-1
yellow book
D0 Modes ?() Detection efficiency N Detected Xe? tagging fraction NDetected Xe? Tag CKM
K-e? 3.47 46 559,500 ?14 77,670 Vcs
K-e? 2.02 12 28,200 ?14 3,900 Vcs
?-e? 0.37 63 81,000 ?14 11,190 Vcd
?-e? 0.20 23 15,600 ?14 2,190 Vcd
D Modes D Modes
K0S e? 3.40 37 219,000 ?7.5 16,560 Vcs
K0e? 4.65 19 151,500 ?7.5 11,250 Vcs
?0e? 0.31 44 34,500 ?7.5 2,580 Vcd
?0e? 0.25 38 24,000 ?7.5 1,770 Vcd
yields with 3 fb-1
?Focus Kmn FF sample
The BESIII yields are likely to be 5 to 10 times
larger!
9
Improvements in charm semileptonic branching
ratios from 3 fb-1
List of Modes PDG(2000) ? () PDG(2000) ??/? () (3fb-1) ??/? ()
D0?K-e? 3.47 ? 0.17 4.9 0.36
D0?K-e? 2.02 ? 0.33 16.3 1.60
D0??-e? 0.37 ? 0.06 16.2 0.95
D0??-e? - - 2.14
D?K0e? 6.7 ? 0.9 13.4 0.63
D?K0e? 4.7 ? 0.4 9.4 0.94
D??0e? 0.31 ? 0.15 48.4 1.97
D??0e? 0.22 ? 0.08 36.4 2.38
Threshold running can dramatically improve on
the PDG value of dB/B for every D and D0
semileptonic branching ratio.
10
Importance of absolute charm semileptonic decay
rates.
VCKM2
f(q2)2

I. Absolute magnitude shape of form factors
are a stringent test of theory. II. Absolute
charm semileptonic rate gives direct measurements
of Vcd and Vcs. III Key input to precise Vub
vital CKM cross check of sin2?
?
B
l ?
u
b
?
l ?
D
c
d
1) Measure D?? form factor in D??l?. Calibrate
LQCD uncertainties . 2) Extract Vub at
BaBar/Belle using calibrated LQCD calc. of B??
form factor. 3) But need absolute Br(D ??l?) and
high quality f(q2) data and neither exist
11
f(q2) models of the past
A major disconnect between experiment and theory
afflicts published data
An incisive test of LQCD requires one to measure
f(q2) where there is still rate and compare in a
theoretically controlled q2 region
Previous data had low rates and terrible q2
resolution which required a parametric form for
meaningful measurement

ISGW
12
Measuring q2 evolution
At present, Kln data fits to the pole form
return poles slightly lower than Ds. But past
studies were compromised by poor q2 resolution
and control of backgrounds at low visible mass
and Kln is not an optimal state...
pln probe q2 dependence nearly up to the
spectroscopic pole!
D?Kln
Signals at the y (3770) will be clean , copious,
and well resolved in q2
13
Pole versus ISGW form in D?pen
The lattice can now calculate f as a function of
q2. D?pen provides a powerful test of the
lattice predictions. Once validated, the lattice
can be used with confidence in the extraction of
CKM matrix. for both Bs and Ds
better sys
MC
yellow book1 fb-1
14
D?vector l n decays
A 4-body decay requires 5 kinematic variables
Three angles and two masses.
MKp MW2 ? q2
H0(q2), H(q2), H-(q2) are helicity-basis form
factors computable by LQCDThese evolve according
to vector and axial pole forms
15
Form Factor Ratios
The H , H- , and H0 form factors are various
combinations of vector and axial pole forms which
are parameterized as spectroscopic poles.


Nominal spectroscopic pole masses
The intensity is then described by just 2 numbers

rV
?rv/ rv 4.6 ?r2/ r2 9.2
Focus sysstat
YB 1 fb-1 stat
r2
Although ratios of form factors are known
precisely, A1(0) , A2(0) and V(0) measurement
requires knowledge of (1) absolute BR (2) charm
lifetimes (3) reliance on q2 model
Latest LGT Becirevic (ICHEP02) RV 1.55 ? 0.11
16
Hadronic complications in Kl n
DataMC
Yield 31,254
constant s-wave
The Kpln process consists of both K ln and an
interfering, s-wave component which creates a
forward-backward asymmetry in the K decay angle
with a distinctive mass variation.
17
Both good news and bad news
A very naive calculation
Estimated errors for a 31 000 event sample
amp2
Adds additional complications such as amplitude
and phase variation, an additional helicity form
factor etc. But allows additional handles on the
relevant hadronic physics such as 1. Studies of
the I1/2 s-wave phase variation 2. Detailed
studies of the K line shape
Phase (deg)
18
Great to extend data to D ?rln
Kinematic projections from 1 fb-11 Very
clean2 Great resolution3 Good efficiency
MC
MC
K l n
r l n
It would very interesting to compare form factors
in r l n to K l n and search for s-wave
interference in r l n
MC
MC
BESIII could study S-wave interference in rln
interference with half the (tagged) statistics as
used in the Focus Kmn study
19
Enigma 1 G (D?Kln)
Form factor ratios were well predicted but the
scales were not.
The 2002 CLEO result tended to resolve this
discrepancy.The 2002 FOCUS result tended to
reinstated it.
A1 follows from G (Kmn) measured from Kln/ Kpp
using the Kpp BF and D lifetime. This can then
be compared with LGT prediction
20
Enigma 2 Ds?fln form factors
circa 1999
CL (rV) 44.3 CL(r2) 21.5
It was anticipated that the form factor ratios
for Ds?fln should be within 10 of those for D
?Kln . Until just recently, it looked like rV
values were consistent but r2 for Ds?fln was ? a
factor of two higher than that for D ?Kln . The
new Focus data (hep-ex/0401001) challenges this.
21
Determining Vcs and Vcd
combine semileptonic and leptonic decays
eliminating V CKM
?(D ??ln) / ?(D ?ln) independent of Vcd Test
rate predictions at 4
?(Ds??ln) / ?(Ds?ln) independent of Vcs Test rate
predictions at 4.5
Test amplitudes at 2 Stringent test of theory!
If theory passes the test..
?Vcs /Vcs 1.6 (now
11) ?Vcd /Vcd 1.7
(now 7)
I
Use CLEO-c validated lattice to calc. B
semileptonic form factor, then B factories can
use B?r/p/h/lv for precise Vub
II
22
Improving unconstrained CKM elements
(Snowmass E2 WG)
Without invoking powerful unitarity constraints,
many CKM elements are relatively poorly known.
Vcd Vcs Vcb Vub Vtd Vts
7 11 5 25 36 39
1.7 1.6 3 5 5 5
PDG
PDG
CLEO-c data and LQCD
B Factory/Tevatron Data CLEO-c Lattice
Validation
With lattice validation from threshold ee-
running allows for much better unitarity tests
Vcd2 Vcs2 Vcb2 1 ?? CLEO c test
to 3 (if theory D ?K/?ln good to few )
23
Summary

• Leptonic Decay
• Dramatic improvements in fDs and first
  measurements of fD at 2
• Plays a crucial role in Vtd when combined with
  mixing
• Pseudoscalar semileptonic decay
• Unparalleled cleanliness in f form factor
  measurement in D ?pln
• Remove reliance of f(q2) models to bridge theory
  and experiment
• Pole dominance and ISGW forms can be easily
  distinguished
• Provide clean calibration of f Both value and
  q2 evolution predicted by LQCD
• Provides crucial calibration f to use B ? pln
  to measure Vub
• Vector semileptonic decay
• Improvement in rV and r2 parameters
• Unique advantages in determining A1(q2), A2(q2) ,
  V(q2)
• q2 dependence for the first time
• Hadronic complications / opportunities due to
  s-wave interference
• Settle two long term experimental enigmas
• The Kln/Kln problem
• The Ds ? fln versus D ? Kln r2 inconsistency
• Direct measurements of Vcs , Vcd and incisive
  unitarity tests

24
Interplay between semileptonic , leptonic charm
and improved beauty data and LQCD

• Crucial Validation of Lattice QCD Lattice QCD
  will be able to calculate with accuracies of
  1-2. The CLEO-c decay constant and semileptonic
  data will provide a golden, timely test.

B Factories only 2005


Imagine a world Where we have theoretical master
y of non- perturbative QCD at the 2 level
Theory errors 2
25
Question slides
??
26

Inclusive Semileptonic Decays

• Currently ?SL of all D mesons are consistent with
  being equal
• Threshold the best place to measure inclusive
  semileptonic branching ratios

Mode B PDG2000 B /B PDG2000 B / B() CLEO-c (3fb-1)
D0?eX 6.8?0.3 4.4 0.8
D?eX 17.2?1.9 11.0 0.8
DS?eX 8 ?5 63 1.7
Hadronic tag
Mode ?(10-2ps-1) ??/? () ??/? () CLEO-c (3fb-1)
D0?eX 16.4?0.7 4.4 1.4
D?eX 16.4?1.8 11.0 1.1
DS?eX 16.1?10.1 62.7 2.8

?30 improvement !
HQE predicts the near equality of ?SL for D, D0
and Ds but large 1/mc corrections and duality
violations are a concern. CLEO-c inclusive rate
and spectral shape provide precision test of
1/mc expansion
27
CLEO-c Yellow Book Run Plan
Year 1 y(3770) 3 fb-1 30 million DD
events, 6 million tagged D decays (310
times MARK III)
C L E O - c
Year 2 MeV 3 fb-1
1.5 million DsDs events, 0.3 million tagged
Ds decays (480 times MARK III, 130 times
BES)
Year 3 y(3100), 1 fb-1 1 Billion J/y decays
(170 times MARK III, 20 times BES II)
A 3 year program
and about to begin the year 1 program with 50
pb-1 _at_ y(3770) X5 Mark III with a state of
the art detector that is understood at a
precision level, and has proven itself
with pioneering measurements of Vub, Vcb,
radiative penguins, discovery of the Y D states
and DsJ(2463) and many more.
28
Unique Opportunities at Charm Thresholds
?(3770) ? DD ?s 4140 ? DsDs

• s(DoDo) 5.8 nb
• s(DD-) 4.2 nb
• s(Ds Ds) 0.5 nb

R (units of s(mm-))
s(mm-) 5.4 nb at 4 GeV
29
Decay constants are important in many processes
30
CKM Facts
31

Precision Quark Flavor Physics
Goal for the decade high precision measurements
of Vub, Vcb, Vts, Vtd, Vcs, Vcd, associated
phases. Over-constrain the Unitarity
Triangles - Inconsistencies ? New physics !
CKM Matrix Current Status
?N?c?
W?cs
Many experiments will contribute. Measurement of
absolute charm branching ratios At CLEO-c will
enable precise new measurements at
Bfactories/Tevatron to be translated into
greatly improved CKM precision.
32
Charm Facilities
Future charm data sets
Experiment Current Full K-?
BABAR 91 fb-1 500 fb-1 6.6 x 106
Belle 46.2 fb 1 500 fb-1 6.6 x 106
CDF(Run II-a) 65 pb 1 2 fb-1 14 x 106
CLEO-c - 3 fb-1 5.5 x 105
BESIII - 30 fb-1 5.5 x 106
Super Charm - 500 fb-1 9.2 x 108/ 107s
SuperKEKB - 2 ab-1 2.5 x 107/ 107s
SuperBABAR - 10 ab-1 1.3x 108/ 107s
BTeV - 6 x 108/ 107s