candidate events are selected by reconstructing a d, called a tag, in several hadronic modes then...
TRANSCRIPT
Candidate events are selected by reconstructing a D, called a tag, in several hadronic modes
Then we reconstruct the semileptonic decay in the system recoiling from the tag.
Two key variables in the reconstruction of a tag
cut onand fit to
For semileptonic D U peaks at zero for real semileptonic decays
Tagging creates a single D beam of known 4-momentum
0
0
0
0
(3770)
,
D
D
D
D K eK
|| missmiss PEU
22 4 2
D beam
bc beam D
E E E
M E / c p / c
##############
818 pb-1 @3770
Pure DD, zero additional particles, ~5-6 charged particles per event
~4.8 x 105 D+ tags reconstructed from ~2.4 x 106 D+D- events
Introduction
CLEO’s measurements most precise for ALL modes; 4
modes observed for the first time
Normalized to PDG
*
0 0
branching fractions are for 56/pb
/ / / branching fractions are for 818/pb
D K e
D K K e
Precision Measurements:
The Global Global Branching Fractions
D Tagging at 3770 MeV
Summary
Measurement of the Dηe Form factor
Study of dΓ/dq2 in D→ηeν
Bo Xin, Ian Shipsey, Purdue University, CLEO Collaboration
Observation of D+’ e and study of D+e
Upper limit for D e
D→K/π eν are the gold-plated modes to measure |Vcs| and |Vcd| and to test LQCD
Observations and form factor studies of new modes are desired to gain a complete picture of charm semileptonic decaysNine exclusive D semileptonic BF’s (56pb-1) + DK/π e
(281pb-1)
Inclusive semileptonic branching fractions (281/pb):
There is room left for new semileptonic modes with small branching fractions. Two of these modes have been found using 281 pb-1 of data
Study of D→η/η’ eν may shed light on the contents of the η/η’ mesons.
0( ) (6.2 0.2 0.2)%
( ) (15.0 0.5 0.5)%
excl semil
excl semil
B D
B D
0( ) (6.46 0.17 0.13)%
( ) (16.13 0.20 0.33)%
incl semil
incl semil
B D
B D
0 1.3 41 1 1.0
4
4
1 146 events (281 pb ), fo
( (1270) ) ( (1270) ) (2.5 0.2) 10
( ) (13.3 2.0 0.6) 10
( ' ) 3.5 10
rm factor study doable with 8
c
18pb
B D K e B K K
B D e
B D e
1
4( ) 1.6 10
lose to theoretical pre
diction, possible observation with 818pb
is not expected in the absence of mixing betwee n the and B D e
First observation
of D→ηeνPRL.102:
081801(2009)
PRL.99:191801(20
07)
The branching fraction of the semileptonic decay
The branching fraction determined by tagging is an absolute measurement, independent of the integrated luminosity and number of D mesons in the data sample
, ,,
,
/, where /tag SL tag tag SL
SL tag SL tagtag tag SL tag
N NB
N N
from fits to U
from fits to Mbc
In this analysis, using this global method, we will present Improved branching fraction
measurement for D→ηeν Observation of D→η’eν and
measurement of its branching fraction
Improved upper limit for D→Φeν
D+ e branching fraction
Observation of D+’ e
: 84.9 11.6Yield events
eventsYield 3.51.28:
Without applying MC/data correction factors and systematic uncertainties
Consistent
Signal (2-tail CB) and background shapes (2nd order polynomial) are taken from signal MC and generic MC.
Each fit has two floating parameters: signal yield and background yield.
One event observed in the signal region (-60, 60) MeV.
And one in the background region.
90% C.L. interval: (0.00,3.58),
corresponds to a 90% C.L. upper limit of 0.8x10-4
(without MC/data corrections)
First Form Factor Measurement for D→ηeν
The total estimated number of background events for two η decay modes, with statistical uncertainties only, is 0.0425±0.0257
After including the systematic uncertainties, the total number of background events is 0.0425±0.0284
According to Poisson statistics, with the uncertainty on the background accounted for with a toy MC experiment, the probability for this background to fluctuate into 5 events is 9.7 x 10-9 ,
which corresponds to 5.6 standard deviations. The branching fractions, with asymmetric Poisson errors
First observation of D’e
Without applying MC/data correction factors and systematic uncertainties
Background level is high Main background: D+→ e+FSR or unassociated
noise photons B(D→η’eν)<3.9x10-4
• When statistics allow (D→ηeν in our case),The method described above can also be used to obtain partial branching fractions, or equivalently, partial rates in q2 bins.
• The theoretically predicted partial rates (P→P transition)2 2
' 2 2 3 2'3
| || ( ) |
24F Qqpredicted
i P
i i
G Vd f q p dq
1,
1j
ij tag SLjmeasured
i i DD tag
N
BN
from fits to U
from fits to Mbc
Inverse of the efficiency matrix
2 1
,
( )[cov( , )] ( )measured predicted measured predictedi i i j j j
i j
• Use the least squares method to fit to the partial rates
• Make fits to the partial rates using several form factor parameterizations to extract form factor parameters and branching fraction (First form factor study for D→ηeν)
• B(D→ηeν) using this derived method supersedes the global B(D→ηeν), which serves as a cross-check.
Each η decay mode is divided into 3 q2 bins; each plot is for all tag modes combined, due to limited statistics.
Signal (2-tail CB) and background shapes (2nd order polynomial) are taken from signal MC and generic MC.
Each fit has two floating parameters: signal yield and background yield.
Total yield: 110.2±12.7
(All tag modes/q2 combined fit: 113.0±12.8)
Distributions of kinematic
variables in D+ e
Br(De):
consistent with but more precise than our previous result
First observation of D’e. 5 events consistent with signal, significance: 5.6 sigma
Improved upper limit for D e
First form factor measurement of D+ e
MC/data correction factors applied