Leptonic & Semi-Leptonic Charm Decays
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Transcript of Leptonic & Semi-Leptonic Charm Decays
CKM 2006 Workshop, Nagoya, Japan, Dec. 12-16, 2006
Leptonic & Semi-Leptonic Charm Decays
Sheldon Stone,
Syracuse University
S. Stone (Syracuse) CKM 2006 Workshop, Dec. 12-16, 2006 2
What We Hope to Learn Purely Leptonic Charm Decays D→+
Check QCD calculations including Lattice (LQCD) Look for New Physics
Semileptonic decay rates & form-factors QCD checks Use QCD to extract Vcq (See talk of M. Artuso) Use d/dq2 in conjunction with B decay rates to extract Vub.
Use Dto get form-factor for B, at same v•v point using HQET (&
Use BBK*+-, along with DDK*at the appropriate q2
Due to lack of time, many interesting results are omitted
Need fBs/fB from theory.Measure fD+/fDs
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Experimental methodsDD production at threshold: used by Mark III, and more recently by CLEO-c and BES-II.
Unique event propertiesOnly DD not DDx produced
Large cross sections at (3770):
(DoDo) = 3.720.09 nb (D+D-) = 2.820.09 nb
Ease of B measurements using "double tags:“ BA = # of A/# of D's
At (3770) CLEO-c uses beam constrained massAt 4170 MeV, invariant mass with energy cut
Wor
ld
Ave
*
SSD D
* *S SD D
S SD D
•At Y(4S) (charm) ~ 1 nb (DS) ~ 0.15 nb
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Leptonic Decays: D(s) +
Introduction: Pseudoscalar decay constants
c and q can annihilate, probability is to wave function overlap
Example :
_
22+ 2 2 2
221
(P ) 1 | |8 F P P Q
Pq
mG m M Vf
M
In general for all pseudoscalars:
Calculate, or measure if VQq is known
(s)
or cs
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New Physics Possibilities
Another Gauge Boson
could mediate decay Ratio of leptonic decays
could be modified (e.g.)
22 22+2 2
+ 2 2
(P )1 1
(P )/
P P
mmm m
M M
See Hewett [hep-ph/9505246] & Hou, PRD 48, 2342 (1993).
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New Physics Possibilities II
Leptonic decay rate is modified by H+ Can calculate in MSSM. Is mq/mc, so negligible
for D+ but not for DS (mS/mc) Leptonic decay for
DS gets modified by factor of
or
where R=tan/mHSee Akeryod [hep-ph/0308260]
222 2 21 tan / /
qD q cHr m m m m
From Akeroyd
r
22221 /
qD q cRr m m m
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Old CLEO Measurements of fDs
1. Detected & from DS*→ DS → decay
2. Used missing energy & momentum in half of the event, to estimate 4-vector. Event half determined using thrust axis
3. Correct 4-vector to get right DS mass value
4. Measured real background by doing same analysis on DS*→ DS → e
5. Used D*o → Do → K-(+) to measure efficiencies, etc…
6. Used 4.8 fb-1 at or near Y(4S) (M. Chadha et al. Phys. Rev. D58, 32002 (1998))
0.173 0.023 0.035S
S
D
D
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New BABAR Measurements of fDs
Similar analysis to CLEO [1) detect & , 3) correct P4, 4) use e for backgrounds, 5) use D*o → K-
(+)], but much improved because they use only events: e+e-→“D” x DS*-, where the “D” is a fully reconstructed Do, D+ or D*+ (B. Aubert et al [hep-ex/0607094])
This gives much better S/B and also missing energy resolution
Use 230 fb-1
0.143 0.018 0.006
S
S
D
D
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New CLEO-c Measurement of DS+→+
In this analysis CLEO uses DS*DS events where they detect the from the DS*→ DS decay
They see all the particles from e+e- → DS*DS, DS
(tag) + + except for the A kinematic fit is used to (a) improve the resolution
& (b) remove ambiguities Constraints include: total p & E, tag DS mass, m=M(DS)-M(DS) [or m= M()-M()] = 143.6 MeV, E of DS (or DS*) fixed
Lowest 2 solution in each event is kept No2 cut is applied
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Invariant masses
K-K++ KsK+
Inv Mass (GeV)
+
K*K* from KsK-+
Total # of Tags = 19185±325 (stat)
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Tag Sample using First define the tag
sample by computing the MM*2 off of a & DS tag
Total of 11880±399±504
tags, after the selection on MM*2
All 8 Modes Data
s
s
2*2CM D γ
2
CM D γ
MM = E -E -E
- p -p -p
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The MM2 (From Simulation)
To find the signal events, compute
S S
2 2 2CM D γ μ CM D γ μMM =(E -E -E -E ) -(p -p -p -p )
Signal Signal →
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MM2 Results from 200 pb-1
Clear DS
+→+signal for case (i)
Events <0.2 GeV2 are mostly DS→+, →+ in cases (i) & (ii)
No DS→e+ seen, case (iii)
6 DS→+, →+in case (i) + peak Electron Sample
DATA 200/pb<0.3GeV in CC
DATA 200/pb>0.3GeV in CC
64 events
24 events
12 events
Case (i)
Case (ii)
accepts 99% of+, 60% + & K+
accepts 1% of +, 40% + & K+
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Sum of DS+→++, →+
Two sources of background A) Backgrounds under
invariant mass peaks – Use sidebands to estimate
In +signal region 2 background (64 signal)
Sideband bkgrnd 5.5±1.9 B) Backgrounds from real DS
decays, e.g. +oo, or DS→+, →+o< 0.2 GeV2, none in signal region. Total of 1.3 additional events.
B(DS →) < 1.1x10-3 & energy cut yields <0.1 evts Total background < 0.2 GeV2
is 6.8 events, out of the 100
100 events
Sum of case (i) & case (ii)
K0+
signal line shape
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Branching Ratio & Decay Constant
DS+→+
64signal events, 2 background, use SM to calculate yield near 0 MM2 based on known ratio
B(DS+→+(0.657±0.090±0.028)%
DS+→++ →+
Sum case (i) 0.2 > MM2 > 0.05 GeV2 & case (ii) MM2 < 0.2 GeV2. Total of 36 signal and 4.8 bkgrnd
B(DS+→+(7.1±1.4±0.3)%
By summing both cases above, find
Beff(DS+→+(0.664±0.076±0.028)%
fDs=282 ± 16 ± 7 MeV B(DS
+→e+3.1x10-4
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Measuring DS+→++→e+
B(DS+→+B+→e+1.3%is “large”
compared with expected B(DS+→Xe+
Technique is to find events with an e+ opposite DS
- tags & no other tracks, with calorimeter energy < 400 MeV No need to find from DS* B(DS
+→+ (6.29±0.78±0.52)% fDs=278 ± 17 ± 12 MeV
400 MeV
Xe+
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&
Weighted Average: fDs=280.1±11.6±6.0 MeV, the
systematic error is mostly uncorrelated between the measurements (More data is on the way)
Previously CLEO-c measured
M. Artuso et al., Phys .Rev. Lett. 95 (2005) 251801
Thus fDs/fD+=1.26±0.11±0.03
++2.3 †-3.4D
f =(222.6±16.7 ) MeV D+→
K0+
†
sDf +sD Df / f
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Comparisons with Theory We are
consistent with most models, more precision needed
Using Lattice ratio find |Vcd/Vcs|=
0.22±0.03 1993
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Comparison with Previous Experiments
Difficult to average without a clear measurement of B(DS→+). In any case CLEO-c result dominates
?
?
280.1±11.6±6.0
3.6±0.9 248 ± 15 ± 6 ± 31
-2
-2
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Limits on New Physics Lepton Universality
(DS+→+(DS
+→+= 9.9±1.7±0.7 SM = 9.72
(D+→+(D+→+< 4.77 (90% cl) SM = 2.65
Limits on charged Higgs According to Akeryod Unquenched Lattice: fDs=249±3±16 MeV Our result: 280.1±11.6±6.0 MeV Take ms/mc=0.076 (PDG) Then the ratio of our result/SM gives >1, NP<1
222 2 21 tan / /
qD q cHr m m m m
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Limits on Charged Higgs Mass
Can set limits in the tan - mH± plane
Competitive with CDF
But depends on Lattice Model. Don’t take seriously yet
Summary of the 95% CL exclusions obtained by LEP & CDF. The full lines indicate the SM expectation (no H± signal) and the horizontal hatching represents the ±1 bands about the SM expectation.
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Exclusive Semileptonic Decays Best way to determine magnitudes of CKM elements, in principle is to use semileptonic
decays. Decay rate |VQiQf|2
Kinematics: Matrix element in terms of form-factors (for
DPseudoscalar +
For = e, f(q2)0:
22 2 2 2D hadron D P P Dq p p m m E m
2 2( ) ( ) ( )( ) ( )( )P D D P D PP P J D P f q P P f q P P
VQiQf
2 2 3
222 3
( )24
cq F PV G Pd D Pef q
dq
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Form-Factor Parameterizations
In general
Modified Pole
Series Expansion
2
22 2
2 2 2 2( )
(0) 1 1 Im( ( ' ))( ) '
1 1 'DM mpole
f f qf q dq
q m q q
2
2 2 2 2
(0)( )
1 1pole pole
ff q
q m q m
2 20 02 2
00
1( ) ( )[ ( , )]
( ) ( , )k
kk
f q a t z q tP q q t
2
2 02( ) 0 2
0
, ( , )D K
t q t tt M m z q t
t q t t
Hill & Becher, Phys. Lett. B 633, 61 (2006)
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Beam Constrained mass usingEmiss & Pmiss to find
CLEO-c Exclusive Decays (281 pb-1)
Both Tagged results & untagged using reconstruction
reconstruction has larger statistics but larger systematic errors
U = Emiss– |Pmiss| (GeV)
29520
69928
291055
679684 14397132134749
58468845029
Samplesoverlap, so chooseonly oneresult
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Exclusive Branching Ratio Summary
Theory needs to catch up
preliminary
preliminary
preliminary
preliminary
Do → K- e+
νDo → π- e+
ν(2006)(2006)
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CLEO-c Form-Factors Compared to Lattice
Lattice predictions*DKef+(0)=0.73±0.03±0.07 =0.50±0.04±0.07Def+(0)=0.64±0.03±0.06 =0.44±0.04±0.07*C. Aubin et al., PRL 94 011601
(2005)
DATA FIT(tagged)
LQCD
0D e
DATA FIT(tagged)
LQCD
0D K e
Assume Vcd = 0.2238
Assume Vcs = 0.9745
Belle
.
Belle
.
CLEO-c
CLEO-c
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Other Form-Factor Measurements
CLEO-c & Belle somewhat disagree with LQCD, Belle 2 28/18 (K) & 9.8/5 ()
DoKℓ
& FOCUS
LQCD: Aubin et al., PRL94, 011601(2005)
~2.5k signal events
232 signal events
Unquenched LQCDQuenched LQCDSimple pole model
Kℓ
ℓ
Belle
Belle
q2 (GeV2)
(hep-ex/0607077)
BELLE: PRL 97, 061804 (2006) [hep-ex/0604049]
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Pseudoscalar Form Factors
D→K e+ D→ e+
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D Form Factors (CLEO-c)
Can be used to detemine Vub along with BDK*& BK*+- (See Grinstein & Pirjol [hep-ph/0404250]) D+-
Do-
q2
cos
cos e
Line is projection for fitted RV, R2
Rv = 1.40 0.25 0.03,
R2 = 0.57 0.18 0.06B(D0 -e+)=(1.560.160.09)10-3
B(D+ 0e+)= (2.320.200.12)10-3
U = Emiss– |Pmiss| (GeV)
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CLEO-c Discovery of Do→K e+
B(Do→K1(1270)e+)*B(K1(1270) →K-) = consistent with ISGW2 prediction
1.4 41.0(2.2 0.2)x10
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Conclusions not preliminary
fDs=280.1±11.6±6.0 MeV preliminary
fDs/fD+=1.26±0.11±0.03 preliminary
No violation of Lepton Universality observed
Accurate semi-leptonic form-factors confronting LQCD & perhaps indicating deviations
Much much more to do
++2.3-3.4D
f =(222.6±16.7 ) MeV
CKM 2006 Workshop, Nagoya, Japan, Dec. 12-16, 2006
The End
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Simp. Pole
Mod. Pole
Untagged: Form-Factor Results
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D /Ke: Which Form Factor Parameterization?
CLEO preliminary
All these models describe the data pretty well (except when forcing pole mass to nominal value in pole model).
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Compare with Limits from Belle
Belle: assumes fB and |Vub | are known, take the ratio to the SM BF.
rB=1.130.51
22
21 tanB
BH
mr
m
Excluded byCLEO-c95% CL
But taking no theoretical erroris abhorrent
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Goals in Leptonic Decays
fB & fBs/fB needed to
improve constraints from
md & mS/md. Hard to measure directly (i.e. B measures VubfB but we can determine fD+
& fDs using D and use them to test theoretical models (i.e. Lattice QCD)
Constraints from Vub, md,ms & B
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New CLEO-c Measurements of fDs
Two separate techniques (1) Measure DS
+→+ along with DS→+, →+. This requires finding a DS
- tag, a from either Ds*-→Ds
- or Ds*+→+. Then finding the muon or pion using kinematical constraints
(2) Find DS+→+ →e+opposite a Ds
- tag
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Comparisons with Theory
We are consistent with most models, more precision needed
280.1±11.6±6.0 222.6±16.7 +2.8-3.4CLEO-c 1.26±0.11±0.03
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CLEO-c Untagged DK(or ) e
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Define Three Classes Class (i), single track deposits < 300 MeV in
calorimeter (consistent with ) & no other > 300 MeV. (accepts 99% of muons and 60% of kaons & pions)
Class (ii), single track deposits > 300 MeV in calorimeter & no other > 300 MeV (accepts 1% of muons and 40% of kaons & pions)
Class (iii) single track consistent with electron & no other > 300 MeV