Some Recent Results from Cleo Ii

SOME RECENT RESULTS FROM CLEO I I

Richard Kass

DepartmentofPhysics

The Ohio State University, Columbus Ohio 43210

Representing the CLEO Collab orati on

ABSTRACT

The CLEO exp eriment has b een op erating for several years now

collecting e e annihilatio n data at and near the 4S resonance

E 10:6 GeV. The accumulated event sample contains several

million B B and pairs. This data is used to explore rare b; c and

decays. In this rep ort several recent CLEO results in the area of

B -meson and decay are presented. The topics covered include: p en-

guin decays of B -mesons, measurement of exclusive b ! u semileptonic

transitions, decays with an in the nal state, precision measure-

ment of the Michel parameters in leptonic decay, and a search for

lepton numb er violation using 's.

Supp orted by DOE grant DE-FG02-91ER40690.

1 Intro duction

In this rep ort B -meson and lepton physics results from the CLEO collab oration

will b e discussed. The CLEO exp eriment o ccupies the sole interaction region at

the Cornell Electron-Positron Storage Ring CESR. To date, CLEO has collected

a total integrated luminosity in excess of 5 fb , with two thirds of the data

s =10.58 GeV, and the rest at energies slightly b elow collected at the 4S

the 4S. This luminosity corresp onds to the pro duction of 310 B B and

510 -pairs.

The CLEO-I I detector, shown in Fig. 1, emphasizes precision charged particle

tracking, high resolution electromagnetic calorimetry, and go o d lepton identi ca-

tion. The various subsystems that make up the detector are describ ed in Table 1.

All detector subsystems, with the exception of the muon chamb ers reside in a 1.5

T solenoidal magnetic eld. The momentum of a charged particle is measured

by reconstructing its tra jectory as it traverses the three drift chamb er systems

PTL,VD, DR. The energy and angle of electrons and photons is measured using

a calorimeter BCC, ECC that consists of 8000 CsI crystals.

The identi cation of electrons is primarily accomplished by comparing the

momentum measured by the drift chamb er with the energy measured in the CsI

calorimeter. Muons are identi ed by their ability to p enetrate a signi cant amount

of iron without undergoing an inelastic collision. Thus charged particles which

traverse the drift chamb ers, calorimeter, magnet iron, and match up with hits

in the muon chamb ers are lab eled muons. The lepton identi cation eciencies

and fake rates are summarized in Table 2. Finally,charged hadrons ; K; p are

identi ed over a limited momentum region using an array of scintillation counters

to measure their time of ight and the main drift chamb er to measure their average

ionization energy loss dE =dx.

2 B -meson Physics

The pro duction and subsequent decay of the 4S provides the B -mesons for the

CLEO exp eriment. This source of B -mesons has several attractive features for

the exp erimentalist including:

The 4S decays exclusively into a pair of B -mesons, no extra particles are pro duced.

Table 1: The detector subsystems of the CLEO detector.

Device Rcm jz jcm jcos j Resolution

PTL 6 4.7-7.2 25 0.96 50m DME @ 6 mm H O

Inner VD Cath 1 7.6 19 0.92 1.3 mm 5.85 mm strips

VD 10 8.5-16 35 0.91 90m Ar/Et @ 6 PSIG

Outer VD Cath 1 17.1 33 0.90 1.3 mm 6.85 mm strips

Inner DR Cath 1 18.6 48 0.92 1.3 mm 1cm strips

DR 1 19.9-90.1 97 0.71 120m Ar/Et @6 mm H O

Outer DR Cath 1 96.1 91 0.71 1.3 mm 1cm strips

2 2

Combined CD 67/4 47-90.1 - 0.92 =p = 0:15p +0:5

e=6:3 @ 5 GeV

dE =dx

TF-Barrel 64 96-101 140 0.77 =154 ps

2K for p <1.1 GeV/c

TF-Endcap 2x28 31-89 120-125 0.81-0.96 =240 ps

0:35

CC-Barrel 6144 102-132 167 0.82 = +1:90:1E

0:75

E E

mrad=2.8/ E +1.9

CC-Endcap 2x828 33-91 125-155 0.81-0.98 =E =0:26=E +2:5

Mu-Barrel 3 210,246,282 240 0.71 4 cm @ 5GeV

Mu-Endcap 2x1 160-310 280 0.67-0.85 5 cm @ 5GeV

Table 2: Lepton identi cation eciencies and fake rates.

Lepton p GeV Fake rate/track

electron 0.4-5.3 95 0.3

muon 1.5-2.1 70-93 0.7 /1.0K

2.1-5.3 93 1.2 /1.7K

Figure 1: Quarter section of the CLEO I I detector.

o o +

To the accuracy that it can b e measured B B and B B pairs are pro duced

in equal numb ers.

The energy of a B -meson is given by the CESR b eam energy and hence is

determined to a higher accuracy than if it were to b e measured by CLEO.

The mass resolution of a B meson is improved by using the b eam energy in

place of the measured energy of a B candidate, i.e. M = E p , with

beam

p the measured momentum of the B decay pro ducts.

A B -meson free sample of data can b e obtained by running CESR at a center

of mass energy b elow the mass of the 4S.

The cross section for pro ducing B -mesons from the decay of the 4S is

ab out 1/3 the continuum hadronic cross section e e ! q q.

The fact that m 2m is a mixed blessing. Since the B 's are practically

at rest 0:06 when they decay the particles pro duced in these events tend to

p opulate the detector in an isotropic fashion. This is in contrast to the `jet-like'

e ! q q. This di erence in event shap e can structure of events pro duced via e

b e exploited when a B -meson richevent sample is desired.

There are however two drawbacks to having the B 's decay at rest. First, since

the particles tend to b e pro duced isotopicall y, itisvery dicult to asso ciate a given

particle with its parent B . This is in contrast to the situation at LEP and/or SLC

where the B decay pro ducts tend to follow the direction of the parent B . Second,

the mean decay length of a B is 30m, to o short for silicon vertex detectors

to separate the primary and secondary vertices. Again, this is in contrast to the

situation at LEP/SLC where the mean decay length is several mm.

o +

2.1 B ! D D

o +

Two b o dy decays of the form B ! D D are thought to b e go o d mo des for

the observation of CP violation with sensitivityinsin2 comparable to the decay

o 3

B ! K . The branching fractions for these decay mo des can b e estimated

using the measured rates for the analog reactions where the D is replaced with a

Cabibb o favored D . Making the appropriate substitutions wehave:

1 B!D D

2 2 2

f =f tan 0:9

D B!D

s s

o +

Table 3 gives the exp ected B ! D D branching fractions where the CLEO

measurements for the D mo des have b een used.

o +

Table 3: B ! D D branching ratio estimates.

Mo de BR of D mo de Estimated BR

o +

B ! D D 2.4 0.097

o + +

B ! D D + D D 2.0 0.081

o +

B ! D D 1.1 0.045

1 6

An integrated luminosity of 3.09 fb 3:3 10 B B pairs taken at the 4S

was used for this analysis. Charged tracks were required to b e consistent with

originating from a primary vertex in b oth the r and r z planes. Photon

candidates were required to have energies greater than 30 MeV if jcos j < 0:71

=p olar angle and greater than 50 MeV for other regions of the CsI calorimeter.

Pairs of photons with invariant mass within 2:5 of the nominal mass were

kept for further consideration. Both dE =dx and time of ight information were

used to distinguish charged kaons from pions.

+ + + o o

Candidate D 's were reconstructed using the D ! D mo de while D 's

o + + o + +

were reconstructed using the mo des D ! K ;K , and K .

+ + + +

Only the mo de D ! K was used for D candidates. The D D mass

resolution for mo des containing a D decayinto all charged tracks was improved

by p erforming a vertex constrained t.

Backgrounds from non-B sources were minimized using the b eam constrained

mass and energy di erence E = E E . Since the decays under study here

B beam

are all of the form P seudoscal ar ! V ector + P seudoscal ar a cut of jcos j >

helicity

0:5was used in the analysis. Background events are exp ected to have a at

jcos j distribution.

helicity

The results of this analysis are displayed in Fig. 2 where E vs. m is plotted

for the three decay mo des. In each case the signal region is given by the b ox

and the sideband regions lie ab ove and b elow the dotted lines. Table 4 gives

a summary of the event yields and 90 con dence level upp er limits for each

mo de. The probability that the exp ected background of 0.0220.011 events in

o +

the B ! D D channel uctuates up to or exceeds the observed one event

is 2.2. If weinterpret this one event to b e a signal then the corresp onding

branching fraction is:

o + +8:1 4

B B ! D D = [6:0 stat 10 ] [1 0:18sy st]

4:2

where the systematic error is largely due to uncertainties in the D and D branch-

ing fractions, and tracking eciencies. No signi cant excess of events is found in

the other two mo des.

o +

Table 4: Summary of B ! D D analysis.

Mo de Evts. in E Pred. Bkgd. Evts. in Upp er Limit

sidebands in signal region signal region 90 CL

+ 3

D D 4 0.0220.11 1 2.510

+ + 3

D D + D D 117 0.640.10 2 2.010

+ 3

D D 539 2.640.34 3 1.310 0.4 0.4

0.3 0.3 E (GeV) E (GeV) ∆ ∆

0.2 0.2

0.1 0.1

0 0

-0.1 -0.1

-0.2 -0.2

-0.3 -0.3

-0.4 -0.4 5.2 5.22 5.24 5.26 5.28 5.3 5.2 5.22 5.24 5.26 5.28 5.3 mB (GeV) mB (GeV) 0.4

0.3 E (GeV) ∆

0.2

0.1

-0.1

-0.2

-0.3

-0.4 5.2 5.22 5.24 5.26 5.28 5.3

mB (GeV)

Figure 2: E v s: m for data. The signal region is indicated by the b ox. The

sideband region lies ab ove and b elow the dotted lines.

2.2 Non-resonant Three Bo dy Hadronic B -meson Decays

Decays of charged B mesons to three charged hadrons are of interest as they

+ + +

may exhibit CP violation. In particular, decays of the form B ! h h h

where h can b e a ;K ;p orp mayhaveCP asymmetries as large as 10

+ 5

when the h h invariant mass is close to the or mass. The non-resonant

c co

+ + + 6

decay B ! is predicted to have a branching fraction in the range 1.5-

8.410 . Here the authors p oint out that interference b etween the non-resonant

+ +

amplitude with m 3:4GeV and B ! ; ! could lead to

co co

a CP asymmetry of 0.4-0.8sin , with =argV . If this is so, then can b e

measured at an e e facility op erating at the 4S.

of data The CLEO collab orati on has searched for these decays using 3.2 fb

taken at the 4S and 1.1 fb of data taken at energies ab out 60 MeV b elow

the 4S. The continuum event background non-B B events is greatly reduced

using a combination of event shap e cuts and kinematic based criteria optimized for

three b o dy B decay. Charged tracks in hadronic events are identi ed as ;K ;p

orp using dE =dx information from the central drift chamb er system. B -meson

related backgrounds e.g. B ! K are suppressed byvetoing anyevent where a

charged track is identi ed as either an electron or muon or the invariant mass of

opp ositely charged tracks is within 60 40 MeV of the D mass. The detection

eciency of each mo de listed in Table 5 is determined using a GEANT based

Monte Carlo simulation. In all cases the energy of the B -meson is constrained to

b e the same as the b eam energy.

The mass distributions for the various decay mo des are shown in Fig. 3. The

signal region for eachmodeisshown b etween the arrows. Unfortunately, there

is no signal in any of the mass plots. The details of the analysis are summarized

in Table 5 and 90 con dence level upp er limits are given in Table 6. While

this analysis do es not nd any evidence for these decay mo des it do es rule out

+ + +

a substantial range of the predicted branching fraction for B ! and

provides improved limits in all other cases.

2.3 Electromagnetic Penguin Decays of the B -meson

The rst direct observation of p enguin mediated B -meson decaywas by CLEO in

with the observation of B ! K . Precision measurements of this decay 1993

rate as well as other other p enguin decays give a new windowinto and p erhaps

+ + +

Figure 3: Mass distributions for the various B ! h h h mo des. In all cases

the signal region is b etween the arrows

+ + +

Table 5: Summary of B ! h h h analysis.

Mo de Signal Est. Bkgd. Eciency 90 CL Upp er Limit

yield No. Events

+ + +

B ! 2 1.21.2 4.50.66 5.3

+ + +

B ! K 5 3.91.8 4.50.66 7.2

+ + +

B ! K 8 13.04.0 7.11.1 5.6

+ + +

B ! K K 14 8.83.0 6.70.98 14.3

+ + +

B ! K K K 2 3.92.0 3.60.54 3.9

+ +

B ! pp 8 8.62.4 4.80.7 7.2

+ +

B ! ppK 9 4.31.5 4.50.66 11.4

beyond the standard mo del as they involveinternal lo ops with heavy mass quarks

and vector b osons Fig. 4. In addition, the mo de B ! K is imp ortantasit

can b e used to constrain the mo dels used to estimate form factors in semi-leptonic

b ! u decay, e.g. B ! l . The decay B ! is similar to B ! K but has

a decay rate that is dep endent on the CKM matrix element jV j rather than

jV j. Given the diculty with measuring direct t-quark decays, the simultaneous

measurementof B ! and B ! K o ers the b est opp ortunity to determine

jV j=jV j for the near term future.

td td

Vts γ Vtd γ t t b s b d

W W

Figure 4: Electromagnetic p enguin decay.

The CLEO collab oratio n has up dated its electromagnetic p enguin decay anal-

ysis by using a larger data set than used in the 1993 analysis. This new analysis

1 1

uses 2.4 fb of data taken at the 4S and 1.1 fb of data taken at energies

ab out 60 MeV b elow the 4S. Candidate B -mesons are formed by combining a

vector meson ; ! ,or K with a high energy photon. The mass resolution of a

Table 6: Comparison of branching fractions with previous results and theoretical

predictions.

Mo de 90 CL Upp er Limit Previous b est limit Prediction

5 5 5

10 10 10

+ + + 8 6

B ! 4.1 5.0 1.5-8.4

+ + +

B ! K 5.6 - -

+ + + 9

B ! K 2.8 19 -

+ + +

B ! K K 7.5 - -

+ + + 10

B ! K K K 3.8 20 -

+ + 8

B ! pp 5.3 8.4 -

+ +

B ! ppK 8.9 - -

candidate B is improved using the b eam energy in place of the measured energies.

In Fig. 5 the invariant mass of B ! K candidates for the various K mo des is

shown. Backgrounds to this analysis arise from pro cesses that pro duce either high

energy photons or high energy 's and 's that are reconstructed as single showers

in the calorimeter. High energy photons are pro duced by initial state radiation

o +

ISR while high energy 's and 's can b e present in non-resonant e e annihi-

lation events QQ. Extreme care is taken in this analysis to suppress backgrounds

from these sources. A combination of event shap e cuts Fox-Wolfram moment R ,

thrust axis and a Fisher discriminant Fig. 6 e ectively remove contamination

from ISR and QQ events.

The B ! K analysis is also sub ject to contamination from B ! events

where a charged pion is misidenti ed as a kaon. In order to distinguish b etween

these twotyp es of B decay a neural network is employed. The neural network

uses the following inputs: E ;M ;M ; and cos . Here is the angle

found by transforming the momentum vector of the 's daughter with the larger

momentum into the 's rest frame and measuring the angle b etween this trans-

formed momentum vector and the ight direction of the in the lab frame. In

Fig. 7 the output from the neural network for B ! K p eak at -1 and B !

p eak at +1 Monte Carlo events is shown.

In Fig. 8 the data is shown for the various K decay mo des. The b oxineach

gure represents the signal region in the E , M plane. A maximum likeliho o d B B0 → K*0 γ : K*0 → K0 π0 B0 → K*0 γ : K*0 → K- π+ B- → K*- γ : K*- → K- π0 B- → K*- γ : K*- → K0 π-

Events/(2.5 MeV)

Mass (GeV)

Figure 5: Mass plot for B ! K candidates.

Signal QQ ISR Number of Scaled Events/bin

0.00 0.25 0.50 0.75 1.00

Fisher Discriminant Output

Figure 6: The distribution of the Fisher discriminant output for a Monte Carlo

o o o +

sample of B ! K K ! K signal, QQ, and initial state radiation

ISRevents. The histograms all have equal area. B→ργ B→K* γ

(a)

(b)

-1.0 -0.5 0.0 0.5 1.0

Neural Network Output

Figure 7: Distribution of the output of the neural network for Monte Carlo samples

o o o o o +

of a B ! and B ! K K ! K and b B ! and

B ! k K ! K .

t using M ;M ; E , and the Fisher discriminant is used to determine the

B K

signal and background for each K mo de. Table 7 gives the numb er of signal

events, eciency, and branching fraction for each K mo de. The rst error on the

branching fraction is from the maximum likeliho o d t and includes statistical and

systematic errors. The second error is due to the uncertainty in the eciency.In

Table 8 the combined B ! K branching fraction is given for b oth the old and

new analysis. The new results are in go o d agreement with the previous CLEO

results.

Table 7: Individual B ! K branching ratios.

K Mo de Signal Evts. Signal E . Branching Ratio

+6:1 +1:1

K 24.2 22.32.0 4.2 0:4

5:6 1:0

+2:0 +4:2

o o

K 2.8 1.80.2 6.1 0:8

1:5 3:3

+3:0 +2:1

K 6.3 5.70.6 4.3 0:5

2:5 1:7

+4:4 +2:5

K 4.6 6.90.7 2.6 0:3

3:0 1:7

Table 8: Comparison of old and new B ! K branching ratios.

Mo de New Branching Ratio Old Branching Ratio

5 5

10 10

o o

B ! K 4.41:0 0:6 4.01:7 0:8

+2:0

B ! K 3.8 0:5 5.73:1 1:1

1:7

B ! K 4.20:8 0:6 4.51:5 0:9

There are many predictions for the ratio B B ! K =B B ! s as shown

in Fig. 9. By combining CLEO's previous measurement of

B B ! s =2:32 0:57 0:35 10

with these new results we obtain:

B B ! K

=0:181 0:068:

B B ! s

This result is shown in Fig. 9 along with a numb er of theoretical predictions for

this ratio. Clearly, more precise measurements and calculations are needed to

discriminate b etween the mo dels.

The B ! ! analysis su ers from a lack of statistics in comparison to the

B ! K analysis. Since the candidate sample is so small, signals or limits are

extracted by cutting on variables rather than p erforming a maximum likeliho o d

analysis. In Fig. 10 events which pass all cuts are plotted in the M ; E plane.

The events within the signal region rectangle in Fig. 10 as well the various

background estimates are given in Table 9. There is no signal apparentinthe

B! and B ! ! channels. While there are four events in the signal region

for B ! these events all havelowvalues of E and neural net output values

marginally consistent with that exp ected from true B ! events. Hence these

four events are not to b e taken as evidence for B ! . The 90 upp er limit

con dence levels for these decay mo des are given in Table 10. The upp er limit for

B ! is still ab out an order of magnitude higher than the theoretical estimates

14 5 15 5

from Soares 0.04-0.0710 and Greub et al. 0.12-0.3010 .

The ratio of rates for B ! K and B ! ! can b e related to the CKM

matrix elements jV j and jV j through:

ts td K*0 → K+ π- K*0 → K0 π0 0.30

0.10

-0.10

-0.30 -0.30 5.200 5.250 5.300 5.200 5.250 5.300

*- 0 - *- - 0

E K → K π K → K π

∆ 0.30 0.30

0.10 0.10

-0.10 -0.10

-0.30 -0.30 5.200 5.250 5.300 5.200 5.250 5.300

Figure 8: Distribution of B ! K events in the M and E plane. B

CLEO

Tang et al. 1995 Ciuchini et al. Bowler et al. Narison Holdom & Sutherland Bernard,Hsieh & Soni Ali,Braun & Simma 1994 Ball Ali & Greub O'Donnell & Tung Colangelo et al. El hassan & Riazuddin Ali, Ohl & Mannel 1993 Faustov & Galkin 1992 Ali & Mannel 1991 Aliev et al. 1990 Deshpande & Trampetic 1989 Dominguez et al. Deshpande et al. Altomari 1988

0 5 10 15 20 25 30 35 40

B(B->K*γ) / B(B->sγ) %

B B !K

Figure 9: Summary of predictions and the CLEO result.

B B !s B0 → ρo γ B0 → ω γ 0.30 0.30

0.10 0.10

-0.10 -0.10

-0.30 -0.30 5.200 5.250 5.300 5.200 5.250 5.300

- -

E B → ρ γ

∆ 0.30

0.10

-0.10

-0.30 5.200 5.250 5.300

Figure 10: Distribution of B ! ! events in the M and E plane.

o o o

B B ! B B ! +BB ! ! V

= = j j :

o o

B B ! K BB ! K V

Here we neglect contributions from long distance e ects. In the ab ove equation

accounts for SU 3 symmetry breaking and accounts for the di erence in phase

space. An upp er limit combining all the mo des can b e calculated if one assumes

that B B ! K =BB !K . Doing so we obtain:

Table 9: Events and background estimates.

B ! B ! ! B !

Events 4 0 0

QQ 0.230:08 0.560.18 0.400:11

ISR 0.180:12 0.140:10 0.120:09

B ! K 0.450:11 0.0 0.270:06

SUM 0.850:17 0.700:14 0.790:14

Table 10: Branching fraction upp er limits @ 90 C.L.

Mo de Signal events E . Branching Fraction 10

B ! 47.99 9.21.3 < 3:9

B ! ! 02.30 8.91.2 < 1:3

B ! 02.30 9.21.3 < 1:1

B B ! !

< 0:19:

B B ! K

The phase space factor can b e estimated using :

2 2 3

2 2

m +m

b d

: =

2 2 2

2 3

m +m m +m

b s B K

Assuming m =5 GeV, m =300 MeV, m =100 MeV and the nominal masses

b s d

for m ;m , and m we obtain = 1:02 0:02. The SU3 term has b een

B K

evaluated by several groups. In Table 11 estimates of as well as the upp er limits

on the ratio jV j=jV j are given. These limits are comparable to recent ALEPH

td ts

18 o

results which rely on B oscillatio ns.

Table 11: Upp er limits for jV j=jV j.

td ts

Group Mo del Upp er Limit

Ali,et al. QC D Sum Rule 0.58 < 0:56

Soares BSW Formalism 0.72-0.90 < 0:45 50

Narison Hybrid QC D Sum Rule 0.77 < 0:49

2.4 Search for b ! s Gluonic Penguins using inclusive

and K Decays

To date there is no exp erimental evidence for gluonic p enguin decay in the b-quark

sector. Unlike the photon radiated in an electromagnetic p enguin decay the gluon

is not directly observable in the CLEO detector. This greatly complicates the

search strategy for these decays. One way to lo ok for gluonic p enguin decay

is to take advantage of the kinematics of the underlying b ! sg reaction and

search for events in a phase space region forbidden to b ! c decays. For example

b ! sg ! sss can hadronize into B ! 0X X a meson system containing a

s s

strange quark and pro duce an 0 with momentum larger than that p ossible from

the analog charm reaction B ! 0X . Another such example is b ! sg ! sdd

which can hadronize to B ! K X X a meson containing no strange quarks, the

K pro duced with momentum greater than that p ossible from B ! K X .

s s c

s s η' t b s

W X

u u

Figure 11: Penguin decayof b! 0X.

Inclusive searches for b ! sg havetwo p ossible advantages over exclusive

searches. First, the rate for inclusive b ! sg can b e reliably calculated and is not

sub ject to the same uncertainties as the exclusive calculations. Second, the rate

19,20

for inclusive b ! sg ! sq q with q = u; d; s is exp ected to b e of order 1

with b ! sss exp ected to b e 0:2. This is in contrast to two b o dy exclusive

o o +

mo des suchas B !K or B ! K whichhave rates estimated to b e in

the 10 range.

The signature for a B ! 0X gluonic p enguin decayisan 0 with 2.0

s 0

2:7 GeV/c. This kinematic region eliminates most of the 0's pro duced by b ! c

transitions. Backgrounds from b ! c transitions e.g. B ! D 0 can only

contribute to the region 2.0

There are many sources of K 's in B decay including B ! D X; B !

s s

o +

D X; B ! D X; and B ! X . However, these sources pro duce K 's with

c s

p < 2 GeV/c. Thus a signature for b ! sg is an excess of K 's pro duced in B

K s

decay with p > 2 GeV/c. The most imp ortant background in this momentum

region is from the Cabibb o suppressed internal sp ectator decay B ! K D .

1 6

The data sample used in this analysis consists of 3.1 fb 3.310 B B pairs of

of data taken at energies b elow the 4S. data taken at the 4S and 1.6 fb

Hadronic continuum events are suppressed using a combination of event shap e

cuts and a Fisher discriminant. To reconstruct an 0 rst the is reconstructed

through the ! mo de and then the is combined with pairs of opp ositely

charged pions. The K decays are reconstructed through the K ! mo de.

s s

For convenience the analysis is done using the scaled momentum of the meson

0;K :

meson

x =

E m

meson

beam

to aid in the continuum subtraction. In terms of x the region 0.45

is heavily p opulated by b ! sg ! 0X while for b ! sg ! K X the interesting

s s

region is 0.46

In Fig. 12 the inclusive continuum subtracted x sp ectrum of K 's and 0's

from B -meson decay is shown. There is no apparent b ! sg signal in the K x

sp ectrum. The data can b e used to calculate 90 upp er limit con dence levels

of:

B B ! K X < 7:5 10

for 0.40

B B ! K X < 2:1 10

for 0.46

For B ! 0X there is a mo dest excess 2 of 0's in the region of interest.

However, this is not comp elling evidence for b ! sg at this time, so we quote 90

upp er limit con dence levels of:

B B ! 0X < 7:4 10

for 0.45

B B ! 0X < 17 10

for 0.39

+ + + +

2.5 Search for B ! !h and B ! h

Two b o dy decays of B -mesons into nal states containing either an ! or and a

charged pion or kaon are sensitive prob es of the standard mo del as they can b e

describ ed by either hadronic p enguin or sp ectator b ! u graphs. For example, 40000

20000 dN/dX

0.30 0.40 0.50 0.60 0.70 0.80 0.90

X(η/)

Figure 12: The continuum subtracted yield of K 's and 0's as a function of the

scaled momentum x.

+ +

as shown in Fig. 13 B ! ! can o ccur as the result of a sp ectator b ! u

+ +

decay while B ! !K can result from gluonic p enguin decay. Theoretical

21 7 5

predictions for these decays range from 3 10 to 1.110 while previous

4 1

exp erimental upp er limits are in the 10 range. u πK u ω d,s u W t b u b s

ω W K

u u u u

Figure 13: B ! !h via sp ectator and p enguin graphs.

1 6

The data used in this analysis consist of 3.1 fb 3.310 B B pairs taken at

the 4S and 1.6 fb of data taken at energies slightly b elow the 4S. As in

many other CLEO analyses, continuum suppression is achieved by a combination

of event shap e cuts and use of a Fisher discriminant. Both the 's and ! 's were

+ o

reconstructed using the decay mo de. Charged pion candidates were re-

quired to have drift chamber dE =dx within 3 of their exp ected value. However,

no particle identi cation cuts were applied to the h in these decays. Candidates

+ + + +

for B ! !h and B ! h were formed by combining reconstructed 's and

! 's with a charged track. Here the b eam energy and known B mass was substi-

tuted for the measured quantities. The events passing all selection criteria are

shown in Fig. 14. In these gures the signal region is the area inside the b ox.

The results of this analysis are presented in Table 12. There are no B ! h

candidates which leads to a 90 con dence level upp er limit on the branching

5 +

fraction of < 3:0 10 . There are ten events in the signal region for B ! !h

with a predicted background of only 2 events. Assuming binomial statistics, the

probability of the observed signal to b e a background uctuation is only 1:2 10 .

This observed excess over the background corresp onds to a branching fraction of

2.81:0 0:5 10 where the rst error is due to statistics and the second is due

to systematics. A more detailed analysis using particle identi cation to extract

+ + + +

the individual branching fractions for B ! !K and B ! ! is currently in

progress.

+ + +

Table 12: Results for B ! !h and B ! h .

Mo de Background E . Events Branching Ratio10

!h 2.00:3 8.51.6 10 2.81:0 0:5

h 0.70:2 2.80.5 0 <3.090 C.L.

+ + + +

Figure 14: Candidate events for B ! !h left and B ! h right. The

boxes indicate the signal regions.

2.6 Measurementof jV j using exclusive B -meson Decays

In order to determine the origin of CP violation it is imp ortant to measure as

precisely as p ossible the elements of the CKM matrix. The matrix element jV j

plays in imp ortant role in the search for CP violation in the b-quark sector. That

jV j is not zero was demonstrated rst by CLEO and shortly thereafter by

ARGUS. Both exp eriments found evidence for b ! u transitions by studying

the lepton momentum sp ectrum ab ove the b ! c kinematic endp oint. While this

metho d is ne for demonstrating a non-zero value for jV j theoretical uncertainties

in the lepton momentum sp ectrum prevent a precise determination of jV j with

this technique. CLEO has recently side stepp ed this problem by explicitly recon-

structing several semileptonic b ! u decay mo des including B ! l ; B ! l ,

and B ! !l .

1 6

The data used in this analysis consist of 2.66 fb 2.8410 B B pairs taken

at the 4S. The hermiticity of CLEO is exploited to select 4S decays where

only a single neutrino go es undetected. Here the neutrino energy and momentum

P P

is given by E =2E E and ~p = ~p resp ectively. B -mesons decaying

beam i i

via the mo des listed ab ove should also satisfy the following constraints, E

2 2 1=2

E + E + E E = 0 and M =[E ~p + ~p + p~ ] = M

l m beam ml l m B

beam

where m = ; ; ! .From Monte Carlo studies Fig. 15 the resolution in p~ is

determined to b e 110 MeV/c.

Electrons are identi ed by combining drift chamber dE =dx, time of ight, and

calorimeter information. Muons are identi ed by their ability to p enetrate the

magnet iron. Pairs of photons whichhaveinvariant masses within 2 of the

mass are kept for further study and are used in decay mo des with 's and ! 's in

the nal state.

Care must b e taken to reduce background without losing to o much of the

signal. A ten-fold reduction in continuum related backgrounds is achieved using

the thrust axis of the ml pair. Additional background reduction is achieved by

using only high momentum leptons p > 1:5 GeV for mo des and p > 2 GeV

l l

for ; ! mo des to discriminate against b ! c ! sl decays and to some extent

b ! cl decays. Finally, non-B B contributions were determined using data taken

at energies b elow the 4S.

In order to extract the decay rate for each mo de the data was binned into 11

regions in the M ; E 5.1075 M < 5:2875 GeV, jE j < 75 MeV plane.

ml ml 400 300 350 250 300 Events / 50 MeV Events / 100 MeV 200 250

200 150 150 100 100 50 50

0 0 -2 0 2 4 -1 0 1 2

Emiss - Egen |pmiss| - |pgen|

900 600 800 500 700 Events / 0.002

Events / 100 MeV 600 400 500 300 400

200 300 200 100 100 0 0 01230.94 0.96 0.98 1 θ

|pmiss - pgen| cos mr

Figure 15: The resolution of neutrino energy, momentum, and angle from B !

+ o

l Monte Carlo events. The solid histograms are distributions when no K

and/or extra neutrinos are present in the event. The dashed histograms had at

least one K and/or extra neutrinos in the event. L

For the l !l mo des the yield was further sub divided into 4 5 bins over the

2 3 mass range. For all decay mo des Monte Carlo simulations were used to

provide signal, b ! c backgrounds, cross feed and feed down from higher mass

o +

B ! ul states. The isospin and quark symmetry relations B ! l =

+ o + o + + o + + +

2B ! l and B ! l = 2B ! l 2B ! !l

+ o

are used to constrain the B rates relativetoB. Prior to tting, the data

was corrected for backgrounds due to residual continuum and sources of fake

leptons. In Fig. 16 the data along with the various background estimates is shown

separately for the B ! l and B ! ; ! l mo des. Here the ISGWI I mo del is

used for the normalization. A clear signal over the background is present in b oth

plots. A summary of the data yields for the ISGWI I t is given in Table 13. There

Table 13: Summary of event yields using the ISGWI I mo del.

o o

Yield !

Raw 46 19 47 73 7

Corrected 26.6 8.6 19.5 15.1 3.5

E .10 2.3 1.5 1.5 2.4 0.6

24{28

are many mo dels of semi-leptonic b ! u decay. For each of these mo dels a

simultaneous t for the number of B ! l events N and B ! l events

N is p erformed. In Fig. 17 the results of such ts are shown. The KS mo del

gives a p o or t to the data con dence level < 0:5 while the other mo dels

give acceptable ts. Results from these ts are used to calculate the branching

fractions shown in Fig. 18. Values for jV j are calculated for each mo del assuming

o o

=1:56 0:05 ps and = =1:02 0:04. Averaging over the mo dels a

B B

+0:3

value of jV j =3:30:2 0:7 10 is obtained where the uncertainties

0:4

are statistical, systematic, and mo del dep endence. This value of jV j is in go o d

agreement with the previous results using the endp oint of the lepton sp ectrum.

3 Lepton Physics

The CLEO detector is also well suited for the study of decay. Its ne grained

electromagnetic calorimeter reconstructs 's and 's with high eciency and low

background. This combined with excellentcharged particle tracking and particle 35 ± ± π lν, π0lν ρ lν, ρ0lν, ωlν π→π feed across 50 ρ→ρ feed across 30 ρ→π feed across π→ρ feed across b→ulν feeddown b→ulν feeddown 25 40 b→c b→c

20 30 / 7.5 MeV / 7.5 MeV > 15 > 20

Events 10 Events < <

10 5

0 0 5.15 5.2 5.25 5.3 5.15 5.2 5.25 5.3

Mcand (GeV) Mcand (GeV)

Figure 16: The M mass distribution in the E signal band for the combined

cand

and vector meson mo des. The data p oints have b een corrected for continuum

and background fakes. The ISGWI I mo del is used for normalization. 1500

1000

500

1500

1000

500

1500

1000

500

0 1000 2000 0 1000 2000 0 1000 2000

Figure 17: The half sigma contours in the t parameters N vs. N for the various

mo dels. The lines are the = rates predicted by each mo del. ISGW II 2.0±0.5±0.3

WSB 1.8±0.5±0.3

Melikhov 1.8±0.4±0.3±0.2

Burdman-Kambor 1.7±0.4±0.3±0.2

Average 1.8±0.4±0.3±0.2

1234 Br(B0→π+l-ν) / 10-4

± ±0.4 ISGW II 2.2 0.4 0.6

± ±0.5 WSB 2.8 0.5 0.8

± ±0.5± Melikhov 2.8 0.5 0.8 0.4

± ±0.4± UKQCD/Stech 2.1 0.4 0.6 0.4

± ±0.5± Average 2.5 0.4 0.7 0.5 1234

Br(B0→ρ+l-ν) / 10-4

Figure 18: The results for the branching ratios for several mo dels. The central

vertical line is the average of the mo dels. -3 |Vub| / 10 ± ±0.3 ISGW II 3.4 0.2 0.4 WSB 2.9±0.2±0.3

± ±0.4± Melikhov 4.0 0.2 0.5 0.5 ± ±0.3± Burdman-Kambor/UKQCD 3.1 0.2 0.4 0.5 ± ±0.3± Average 3.3 0.2 0.4 0.7 Ball et al.

Khodjamirian-Rückl

Narison

APE

ELC

Demchuk et al.

Faustov et al.

Grach et al.

Lellouch

Endpoint Method 3.1±0.8

Figure 19: The values of jV j from several mo dels of B ! l and B ! l

decay. Also included is the value of jV j from the lepton endp oint technique. The

vertical line is the average of the top four mo dels.

+ o

identi cation e; ; ; K ;K ;pover a large momentum range allows for many

detailed studies of nal states.

At the center of mass energies available to CLEO leptons are pro duced

+ +

through the reaction e e ! . The cross section for this reaction is \large",

approximately 1 nb.To date CLEO has accumulated 10 decays, by far the

world's largest data sample. If we neglect intial and nal state radiation then each

is pro duced with energy equal to the b eam energy.Thus like the situation with

B -mesons the 's energy and momentum is a priori accurately known.

Even at CLEO's center of mass energy the event top ology is jet-like. In

addition, a event has four or fewer charged tracks 98 of the time. These

twocharacteristics make it easy to separate events from B B events. A

more serious background comes from lowmultiplicity hadronic events pro duced

via e e ! q q continuum events. However, with a judicious choice of total en-

ergy and momentum cuts and particle identi cation even the continuum hadronic

background can b e kept b elow 1. The CLEO exp eriment is therefore in the

enviable p osition of having a high statistics low background sample of 's to work

with. This has allowed CLEO to b ecome the rst exp eriment to p erform detailed

4 5

studies of decays with branching fractions in the 10 10 range and search

for decay mo des with branching fractions O 10 .

3.1 Decays with an in the Final State

Decays of the with an in the nal state are of interest as they provide b oth

valuable information concerning the b ehavior and violation of several hadronic

symmetries and a new system for the study of the weak hadronic current. There

is very little information available on these nal states due to their small branching

fractions. In fact, the Particle Data Group only lists exclusive branching fractions

o 29

for B ! 0.170:2 0:2 and B ! K 0.0260:02

0:02 . Other ! mo des are exp ected to b e severely suppressed by the

chiral anomaly term and phase space.

The CLEO exp eriment has recently measured the branching fraction of the

+ 31

decay ! h h h at a rate two orders of magnitude larger than predicted.

1 6

The analysis uses 4.86fb 4.2710 pairs of data collected at energies at and

slightly b elow the 4S. Events that are consistent with the 1 vs. 3 top ology are

searched for 's decaying via ! and ! 3 . In Fig. 20 there are clear

Table 14: CLEO results for ! h h h

mo de tags events backgd. BR10

! e; ; h= 65.112.9 5.01.1 3.80.8

! 3 e; 11.23.7 - 5.11.7

signals in b oth decay mo des.

Care must b e taken to insure that these events with 's are from 's and

not hadronic in origin. Therefore the signal is studied as a function of the

1-prong tag as shown in Table 14. Backgrounds from events feeding into this

decay mo de are estimated using Monte Carlo simulations based on the KORALB

and TAUOLA computer routines. The CLEO exp eriment is mo deled using the

GEANT package. The contribution to the sample from hadronic and 2-photon

events is estimated using data rather than Monte Carlo. As listed in Table 14

there is small contamination in the ! sample from hadronic events and

negligible background in the 3 sample. The detection eciencies are calculated

separately for each 1-prong tag and branching mo de. The branching fractions for

the two decay mo des are listed in Table 14. Since these results are statistically

indep endentwe can average them and nd:

+ 4

B ! h h h =4:10:70:7 10 :

The second error ab ove is the systematic uncertainty in the branching fraction.

It includes contributions from background mo deling, and reconstruction,

sp ectral functions, tracking, luminosity, and cross sections. It is interesting to

note that this measurementis 100 larger than the prediction from Pich !

An e ort is underway to lo ok for resonant substructure in these ! h h h

events. In Fig 21 left the mass is plotted twoentries p er event for the

! events. There is an enhancement at the mass of the f 1285. In the lower

part of Fig 21 left a scatterplot of m vs. m is presented four entries

per event. This plot suggests that the is pro duced through an intermediate

state, a 980, and the overall decaychain is: ! f 1285 ; f 1285 !

o 1 1

+ + +

a ;a . A t to the data yields 30.48.8 events. To convert 980 980 !

o o

these events into a branching fraction we use B f 1285 ! =0:54 0:15 1

Figure 20: The signals in the ! left and ! 3 right mo des. For

b oth plots the solid line is a t including signal and random photon background

dashed line. The arrows indicate the range used for sideband subtraction. The

contamination from e e ! q q events is given by the hatched area.

and the isospin prediction that is 2/3 of the state. We nd:

B ! f 1285 =6:01:72:1 10 :

The second error quoted ab ove is the systematic and it has comp onents similar

to the 3 analysis.

The decay ! f 1285 can also b e present in 1-prong decays through

o o

! . A sample of events consistent with this top ology was isolated

using similar and criteria as in the 3-prong case. In Fig 21 top, right the

o o

invariant mass of the system is plotted 1 entry p er event. There is a clear

enhancement at the f 1285 mass. The scatterplot Fig 21, b ottom, right of m

o o

vs. m also resembles the 3-prong case as there app ears to an enhancement

at the a 980 mass. The branching fraction extracted from this analysis is:

B ! f 1285 =8:12:62:6 10 :

This result is in go o d agreement with and indep endent of the 3-prong result. The

two results can b e combined to give:

B ! f 1285 =6:71:42:2 10 :

Using this result we nd that a large comp onentof ! h h h contains an

f 1285, i.e.

B ! f 1285

=0:59 0:17:

B ! h h h

These results have implications for CVC predictions for ! 6 using e e !

o o

6 data. The ab ove results imply that ! 3 3 and ! 5 have

signi cant contributions from the ! 3 mo de. Since this mo de has G parity

opp osite to that of direct 6 decays and pro ceeds through the axial-vector current

it must b e subtracted b efore applying isospin or CVC to compare with e e

annihilati on data.

+ o o

Figure 21: Mass of a, left and a, right system. Lower plots b

are M vs. M . The dotted lines show the exp ected p ositions of the f 1285

and a 980 resonances.

3.2 Measurement of the Michel Parameters in Leptonic

Decay

The leptonic decays of the , ! e and ! , can provide detailed

information on the W vertex. Since these decays are not clouded by the

strong interaction they are ideal lab oratories to explore the Lorentz structure of

the W current. Neglecting radiative corrections the distribution of the scaled

energy x = E =E of the charged lepton in the rest frame can b e written as:

l max

8x 6+24 m 121 x+

1 d

3 x

= x

dx 1+4 m

In the ab ove equation and are the sp ectral shap e Michel Parameters and m is

the scaled lepton mass m = m =m . In the standard mo del =3=4 and =0.At

CLEO center of mass energies pairs are pro duced with no net p olarization, hence

the scaled energy sp ectrum is insensitive to the two other Michel Parameters,

and . It is imp ortant to measure and as accurately as p ossible, since non-

standard electro-weak mo dels predict values other than =3=4; =0. For

example, 6= 0 suggests the presence of a scalar b oson that couples a right

handed to a left handed l . Another example is the Two Higgs Doublet Mo del

with a charged Higgs. Here measured using ! is related to the ratio

of vacuum exp ectation values of the neutral comp onents of the Higgs doublet

and the mass of the Higgs m by

2 2

=m m tan =2m :

1 6

The sample of 's used in this analysis were taken from 3.5fb 3.210

pairs of data collected at E 10.6 GeV. The decaymode ! h

h = ;K was used as a tag in order to obtain a clean, high statistics

sample of events.

Pairs of photons with p olar angles satisfying jcos j < 0:71 are used to form

o o

's if their invariant mass is within 3 of the nominal mass. Electrons with mo-

mentum ab ove 0.5 GeV/c are identi ed using a combination of dE =dx and tracking

information from the drift chamb er and energy measurements from the calorime-

ter. The background in this electron sample is estimated to b e 0:178 0:026.

Muons with momentum ab ove 1.5 GeV/c are identi ed as charged particles which

are tracked through the inner and outer detector and pass through at least three

absorbtion lengths of material. The background in this muon sample is estimated

as 1:08 0:16. Muons with momentum 0.5-1.5 GeV/c are identi ed by kine-

matically eliminating all other decayhyp otheses ; K ; ev ; hn . This

muon sample contains a small amountofbackground from =K; h , and e

events 4 total.

The rest frame is the ideal Lorentz frame for simultaneously measuring

and . CLEO, however, measures the momentum of the electrons and muons

in the LAB frame. Unfortunately there is no unambiguous way to transform

from the LAB frame to the rest frame due to the unmeasured neutrinos in the

event. This lack of information can in part b e comp ensated for using information

from the \tag" . In the absence of initial or nal state radiation the two 's

in an event are pro duced back-to-back each with the energy of the b eam. In a

o o

! h decay the angle between hadronic system H h and the

can b e calculated using:

2 2 2

m + m 2E E +2p p cos = m :

H H

In the ab ove equation E ;p , and m are calculated quantities while we assume

H H H

m = 0 and E = E .Ascos ! 1 the ambiguityindisapp ears and the

beam

momentum vector of the h system gives a go o d estimate of the ! l direc-

tion. Thus events with cos > 0:970 are used to transform the lepton momentum

sp ectra to a pseudo rest frame PRF. After the cos cut there are 18587 elec-

trons and 12580 2931 high momentum low, p<1:5 GeV/c muons left in the

sample. The x sp ectrum for electrons and muons passing all cuts is shown in

Fig. 22. In order to extract and values from the data a t is p erformed

3101296-003 3101296-004 1200 1000 ( a ) Pseudo Rest Frame ( b ) Pseudo Rest Frame e 1000

750

800

600 500 Events / 0.05 Events / 0.05

400

250

200

0 0.5 1.0 1.5 2.0 0 0.5 1.0 1.5 2.0 X X

Figure 22: Scaled energy sp ectrum x for electrons a and muons b in the

pseudo rest frame of the . The dotted line in a is a V + A Monte Carlo cal-

culation, while the dotted line in b is a Monte Carlo calculation of the muon

sp ectrum assuming =1.Events with x>1 are the result of imp erfect recon-

struction of the direction. The discontinuity in b at x =0:6 is due to low

momentum muons.

using three binned Monte Carlo x sp ectrums. The three individual x sp ectrums

are generated with ; values: 3/4,0, 0,0, and 3/4,1. The data sp ectrum

is then represented by:

dN dN dN dN

; =N 3=4; 0 + N 0; 0 + N 3=4; 1 N

VA 0;0 V +A =1

3=4;0 3=4;1

dx dx dx dx

Table 15: CLEO results along with the corresp onding previous world average

results.

Parameter CLEO I I World Average

0.7320:014 0:009 0.7360:028

0.7470:048 0:044 0.740:04

0.0100:149 0:171 -0.240:29

0.7350:013 0:008 0.7420:027

-0.0150:061 0:062 -0.010:14

with:

1 4=3 1+4m 4=3

+ + : N = N + N + N =

3=4;0 0;0 3=4;1

1+4 m 1+4 m 1+4 m

The 's are eciency corrections for each Monte Carlo x sp ectrum. The

Monte Carlo sp ectrums are generated using the simulation packages KORALB,

33 36 7

TAUOLA, and PHOTOS. The CLEO I I detector is simulated using GEANT.

All e ects due to radiation, resolution, and eciency are included in these sp ec-

tra. The events which passed the cos cut are analyzed in the PRF frame. An

additional 12981 9186 electron muon events which do not satisfy the cos cut

are analyzed in the LAB frame.

The results from tting the sp ectra are given in Table 15. A detailed study

of systematic errors leads to the uncertainties quoted in this Table. Using lepton

universality a simultaneous t to the electron and muon data is p erformed result-

ing in the values of and given in Table 15. In Fig. 23 the results from the

e e

individual and combined mo des are displayed as well as the prediction from the

standard mo del. All measurements are consistent with a V A Lorentz structure

for the currentin decay. In Fig. 24 the CLEO results along with other measure-

ments of and are presented. The CLEO results are consistent with, but more

precise than previous measurements. Finally, the measurementof leads to the

mo del dep endent limit on the charged Higgs mass of M > 0:97 tan GeV

at the 90 con dence level. 3101296-005 0.250

zy 0.125

z|y{

e Mode I 0.125 Mode e + Modes

I 0.250

z|0.65 0.70 y{|0.75 0.80 0.85

Figure 23: v s: for electron, muon and combined mo des. The standard mo del

prediction is given by the cross.

Figure 24: Results for the Michel parameters and .

e e

3.3 Search for ! e and !

The standard mo del do es not contain a symmetry asso ciated with lepton numb er.

Therefore one exp ects that lepton numb er violating decays should b e presentin

nature. Clearly the rate of these decays is small as shown by the exp erimental

upp er limits for lepton numb er violation in muon decayB ! e < 4:9

11 12

10 ; B ! eee < 1 10 . Although it is not p ossible to collect data

samples comparable to those used to obtain the limits from muon decay there

are reasons to use 's as a prob e of lepton numb er violation. For example, there

are mo dels which relate lepton numb er violation to mass dep endent couplings.

One such mo del favors decay and predicts an enhancementof B ! =

B ! e . 210

Lepton numb er violation in decay has b een studied extensively for close to

two decades now. The 1996 version of the Review of Particle Prop erties gives

limits on 37 di erent lepton numb er violating decay mo des. The most stringent

38 6

limit in the list is a result from CLEO, B ! < 4:2 10 . Here we up date

this CLEO result and present a new upp er limit for B ! e .

1 6 +

The data in this analysis consists of 4.68 fb 4:24 10 pairs of

data taken at energies at and slightly b elow the mass of the 4S. Events that

are consistent with the 1 vs. 1 top ology i.e. opp ositely charged tracks in di erent

hemispheres are kept for further consideration. Requirements on the tag hemi-

sphere are minimal and all standard 1-prong decays are used. Event selection

criteria were develop ed from a study of Monte Carlo events incorp orating b oth

32 7

KORALB and GEANT.

This analysis relies heavily on lepton electron and muon identi cation b oth

for isolating a signal and rejecting background. The standard CLEO lepton identi-

cation software package is used here. Electrons are identi ed with a combination

of calorimeter, drift chamb er tracking and dE =dx, and time of ight information.

Identi ed muons are charged tracks that are tracked from the inner drift cham-

b ers all the way through the magnet iron. Since radiative bhabhas and -pairs

are backgrounds to this analysis events can have only one identi ed electron or

one identi ed muon.

Additional background suppression is achieved by examining b oth the missing

momentum and transverse momentum in the event. Since there must b e at least

one undetected neutrino on the tag side of the event the missing momentum in

Table 16: Eciencies, observed events n , background events , calculated

o B

numberofevents including systematic error for 90 con dence level upp er limits

, and the 90 con dence level upp er limits for ! e and ! .

Channel MC eciency n Upp er limit at 90 CL

o B

! e 10.1 0 2.0 2.3 2.710

! 14.4 3 5.5 3.7 3.010

a event should lie in the tag hemisphere. However, the missing momentum in

QE D background pro cesses will b e randomly oriented with resp ect to the \tag"

track. Thus only events where the cosine of the angle b etween the tag track's

momentum vector and the missing momentum vector is greater than 0.4 are kept

for further study. A cut on transverse momentum p > 0:3GeV/c is made to

tr ans

eliminate backgrounds from the 2-photon pro cess.

The events that pass all selection criteria are shown in Fig. 25. The signature

for ! e or ! is an l combination with measured energy and invariant

mass consistent with the b eam energy and mass resp ectively.For convenience

the variables E = E E and m m are used in this analysis. The central

l beam l

box in b oth plots of Fig. 25 shows the signal region in the E; m plane. The

b oundaries of the signal region were determined using a Monte Carlo simulation

two b o dy phase space of the decays ! e ; ! op en circles in Fig. 25.

There are no candidate events for the e channel and three candidates for the

channel. From a study of the sideband regions in Fig. 25 2 5.5 background

events are predicted for the e channel. A Monte Carlo study suggests that

the background events originate from generic decays. The results of the

analysis are summarized in Table 16. The upp er limits presented here include

systematic uncertainties calculated according to the prescription of Cousins and

Highland. Thus the strictest limit on lepton numb er violation in decaynow

b elongs to the e mo de.

4 Future Plans, CLEO I I I

The CLEO exp eriment is currently taking data at the 4S with a recently

summer 1995 installed three layer silicon vertex detector. Data taking with this v o and yin ts. en b; c; Cerenk terest for . The solid violation in er CLEO I I v y p eople who CP ! uon detector are also taneous luminosit and Installed in place of the ation of te Carlo signal ev e tum region of in ! til early 1998 when the exp eri- ation. v b er, and a ring imaging tage of CLEO I I I o able exp erience. y y colleagues in the CLEO collab o- an ue un ham tire momen ord of thanks to the man The RICH detector should b e able to tin w for the rst observ ts er the en distributions for v er an order of magnitude in the areas of bination of detector and accelerator will increase v ti cation. m wn for ma jor reno t calorimeter, magnet, and m en allo yo l yev ut do wledge the e orts of m m . This com ers, a new main drift c 1 kno separation o vs. y s 2 E wledgemen . Upgrades to CESR should put the instan h of CLEO b y C Summer Institute a most enjo ersion of CLEO. The main adv cm =K 33 3 kno quark sector. ysics reac t detector will b e CLEO I I I Fig. 26. This detector features a new silicon Ac ysics. In fact, it ma t and CESR will sh b meson deca vide ph ertex detector 4 la squares are the data while the op en circles aredetector the con guration Mon is exp ectedmen to con presen v used in this v is in the areapro of particle iden Figure 25: The detector RICH. The presen B excess of 10 the ph the 5 It is a pleasure toration ac and the sta ofmade CESR. the A SLA sp ecial w

E (GeV) I I

0.6 I 0.4 0.4 0.2 0.2 0.6 0.24 I 0 Data MC

0.16 I

0.08 I (GeV/c m m e

I 0 0.08 2 ) 0.16 3350996-002 e 0.24

E (GeV) I 0.25 I 0.50 0.50 0.25 0

.5 0.125 0.250 I Data MC

I (GeV/c m m

I 0 2 ) 0.125 3350996-005 0.250

Figure 26: Quarter section of the CLEO I I I detector.

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