ELSEVIER Nuclear Physics B (Proc. Suppl.) 59 (1997) 17-26

PROCEEDINGS SUPPLEMENTS

CLEO: Recent Results and Future Prospects Giancarlo Moneti a Representing the CLEO Collaboration.

a201 Physics Bldg., Syracuse University, Syracuse, NY, 13244-1130, USA

After summarizing the present goals and current activities of the CLEO collaboration, I report on: (i) new measurements of the CKM matrix elements Vcb and V~b; (ii) a new measurement of B(B--+K*(892)V) and upper limits on B(B°--+p°'y), B(B°---~wv), 13(B----rp-7); (iii) the observation of the B+--+w(Tr + or K +) rare decays modes. I conclude outlining the current activities for the upgrade of CESR and the CLEO detector.

1. T h e s c o p e o f t h e C L E O c o l l a b o r a t i o n

The central goal of the the CLEO Collabora- tion is extracting fundamental physics quantities from the study of B decays with additional great interest in charm and tau decays.

1.1. B physics The study of B decays in CLEO allows us: • To improve the measurement of the CKM ma-

trix element accessible from the study B decays:

Vub, Vcb, Vtd. • To measure, or set bet ter limits to, the rates

of the rare B decays that may: - eventually lead to evidence of CP violation in

B decay or - probe the validity of the Standard Model. • To tests the Heavy Quark Effective Theory

(HQET), to probe its validity and its limits. • To test the validity of nonperturbative QCD

calculations in heavy quark weak decays. • To measure or constrain those parameters

that are needed to extract fundamental physical quantities from the experimental measurements (e.g. form factors for B semileptonic decays, QCD correction parameters, strong phases of weak de- cays final states, fB).

• To measure more accurately the charm parti- cle decay rates and other properties that are tools in the analysis of B decay physics.

1.2. T h e C L E O I I d e t e c t o r CLEO at the Cornell Electron-positron Stor-

age Ring (CESR) uses the reaction e + e---+T (4S),

0920-5632/97/$17.00 © Elsevier Science B.V. All rights reserved. PII S0920-5632(97)00424-6

D

T ( 4 S ) ~ B B , to obtain a large and relatively pure sample of Bu and Bd'S nearly at rest. The CLEO II detector (1989) [1] is the successor of the initial CLEO detector (1979). It has excellent charged track a n d photon detection and energy measure- ment and it is fairly hermetic. The use of the " b e a m c o n s t r a i n e d m a s s " (see later) greatly suppresses the background to the B sample.

Presently, our data set contains about 6.4 mil- lion B and B. As a byproduct, we have a very large sample of charm hadrons and of T'S.

1.3. Charm, tau, a n d 27 phys i c s CLEO has also produced a large number of im-

pressive results: • on ~- physics, • on charm meson decay, • on charm baryon spectroscopy and decay, • on 7-7 interactions and gluon and quark frag-

mentation. You can easily browse through all these

results, as presented at the recent Interna- tional Conference on High Energy Physics in Warsaw, as well as all other CLEO papers and preprints, visiting the CESR-CLEO web site http:/ /w4.1ns.cornell .edu/public/CONF and . . /CLNS/CLEO.html.

1.4. C E S R u p g r a d e a n d C L E O I I I But the project that currently absorbs a large

fraction of the collaboration resources is the con- struction effort to upgrade the CLEO detector

(i) to allow it to operate in the much increased

18 G. Moneti/Nuclear Physics B (Proc. Suppl.) 59 (1997) 17-26

luminosity expected from CESR (phase III up- grade) and

(ii) to strongly improve the vertex detector and particle identification capabilities,

to pursue the goal of detecting CP violation in the bottom sector.

In this talk, because of lack of time, I shall report only on a few results on B physics and give a few more details of the CESR-CLEOIII upgrade program.

2. A n e w d e t e r m i n a t i o n o f Vcb

The importance of precise and reliable mea- surements of the heavy flavor related CKM ma- trix elements has already been stressed by J. Ros- ner in the preceding talk. CLEO has recently produced new measurements of Vcb and Vub and, through radiative penguin analyses, provided new information about Vtd and Vts.

Vcb has been determined from the lepton spec- tra in inclusive B semileptonic decays and in the exclusive B°-~D*-g+ut decay. There is a trade off between statistical error (smallest in the for- mer) and errors due to the model dependence of the extraction of Vcb from the data (smallest in the latter). This is shown clearly below where world averages of the two methods are compared [2].

B(B°-~D*-g+ue) = 0.0392 4- 0.0027 4- 0.0013

13(B-~xgu) = 0.0393 4- 0.0009 4- 0.0039.

Our most recent effort has been to measure VCb from the exclusive decay B°-+D-g+u~ [3].

The problem here as well in the case of the B°-~D*-g+vt decay, is to catch the unseen neu- trino. Two methods have been used, both of them in six separate bins in q2, the mass squared of the virtual W:

1. The missing mass squared (MM 2) in the decay of an individual B is calculated from the lepton and the opposite sign D ob- served in its decay D+-+KTTr+rr +, consid- ering the B at rest. The B motion, in an unknown direction, causes a smearing of MM 2 of 0.2 GeV 2 r.m.s.. The background from B°---~D*-g+ul is separately studied

and subtracted. The resulting distributions are fitted to the Gaussian signal plus a back- ground from B°--+D-Xg+ut with a Monte Carlo simulated shape.

. The neutrino energy and momentum are calculated as missing energy and momen- tum from the whole event, after discarding events with magnitude of the total charge greater than 1 and those with two charged leptons. Furthermore it was required that -450 < MM~y/2Emiss < 300 MeV. The neutrino candidate thus reconstructed is then used in the standard fashion, together with the D ± decay and the charged lepton to reconstruct the candidate B using the "beam constrained mass" Mu and the "en- ergy difference" AE defined below.

[ 1 , n x~ 2

Mg = t ~ i ~ i ) --(Ebeam) 2' (1)

1,n

A E = E Ei - Ebe,~m (2) i

where Ei and ~ i are the energies and momenta of the n B decay products.

The signals and backgrounds obtained by the two methods, and integrated over the virtual W squared mass q2, are displayed in Fig.s 1 and 2.

In order to extract Vcb we need a model for the q2 dependence of decay rate, i.e. the form factor. Using the HQET form factors functions of the velocity transfer variable w -= v - v ' = (M 2 + m 2 - q2)/2Mm [4] we have:

dF

dw G~lVcb[2 (M + m ) 2 ( m v / ~ - 1)3 JY'(w)l 2

487r 3

where M, m and q2 are, respectively the mass of the initial heavy quark, the mass of the fi- nal heavy quark and the square of the four- momentum transfer between them. ~'(w) is re- lated to the HQET universal form factor ~(w) by correction terms that go to zero for very heavy quarks [h+ (w)-+~(w), h_ (w)--+0]:

G. Moneti/Nuclear Physics B (Proc. Suppl.) 59 (1997) 17-26 19

%

"" 4 0 0

o

g

10 - 5 - 2 . 5 MM ~' (GeV ~)

. . . . 1 , r " , , l c ' , , , I . . . . i , , , - r - T - , , , - r -

- 7 . 5 0 2 . 5

Figure 1. The M M 2 distribution summed over q2 for all g+D- events in data. The dashed line is the sum of the contributions from uncorrelated background and fake leptons, the dotted line in- cludes the D-Xg+ve background, the dot-dash line includes the D*-Xg+ve, and the solid line includes the result of the fit for the signal yield. The contribution from the continuum has been subtracted.

M - m h _ ( w ) - h+(w) M + rn

= be(l)(1 - p2(w - 1))

The two analysis methods are in excel- lent agreement. The differential distribution Ibr(~)V~b] is shown in Fig. 3. ~ is the observed value of w taking into account the smearing due to the detector resolution.

Combining the fits of the differential distribu- tions from the two analysis methods, we extract:

f(1)lVcbl = (3.46 4- 0.42 4- 0.46) x 10 -2

p2 = 0.64 + 0.18 4- 0.10

Using .T(1) = 0.98 + 0.07 [6] one then gets:

IVcb[ = (3.53 + 0.46 4- 0.44 4- 0.25) x 10 - :

that agrees very well with value extracted from B°---+D*-g+~ [5]:

iVcbl = (3.88 4- 0.20(exp.) =t: 0.12(theory)) x 10 -2

> ~bu

150

50

~3

;i

512 514 5.16 51B 52 5.22 5.24 5.26 52B 53 Beor~ constcained ~ss ((~ev)

Figure 2. Beam constrained mass spectrum for all the events passing the cuts described in the text (points). The white area represents the sig- nal events, the hatched area represents the com- binatorial background, the crosshatched area rep- resents the B ° ~ D * - g + v t background, and the shaded area represents the all the remaining back-

grounds.

We also obtained the branching ratio (prelimi- nary):

13(B°--+D-g%,) = 0.0178 4- 0.0020 4- 0.0024.

An alternative parameterization of the form factor is in terms of a vector meson pole:

dF 2 2 3 2 GFIV~b I K M s if+~q2~12,, ,, dq 2 24rr 2

where K is the momentum of D + in the B rest mass frame and:

f+(o) f + (q2) _ 1 ----qq-~M 2 "

This parameterization, extrapolated to q2 = 0 and averaged over the two analyses, gives IVebf+(O)l = (2.57 + 0.14 4- 0.17) x 10 -2

We can use the experimental values of ]Y(1)Vcbl and [Vcbf+(O)[ and the combined value of iVcbl measured in different experiments, to ob- tain: 5r(1) = 0.89 4- 0.16 + 0.05 and f+(0) = 0.66 ± 0.06 4- 0.04, where the second error comes from the error on IVcb[.

20 G. Moneti /Nuclear Physics B (Proc. Suppl.) 59 (1997) 17-26

u uy

o o~

0 0 7

0 0 6

0 0 5

0 0 4

~ 0 3

0;02

o o 1

o

: - ~ ' ' T ' ' ' I ' ' ' I ' ' ' I ~ - T - ~ - ~

I 1 12 13 I 4 t .5 1 6

Figure 3. Measured values of 19v(~)Vcbl with the results of the neutrino reconstruction analysis (solid dots) and the missing mass analysis (aster- isks) with the combined results shown as the solid line. Note that the curve shown is not a fit to the points shown. The dashed line denotes Jr(w) as measured in B ° ~ D * - t + ~ e decay [5].

3. A n e w m e a s u r e m e n t o f IVubl

The magnitude of the small CKM matrix ele- ment {V=bl has been extracted by ARGUS [7] and CLEO [8] from the excess of events close to or be- yond the kinematic limit for b~c~v in the inclu- sive lepton energy spectrum from the T(4S) BB resonance. This way of measuring IV~bl (or more accurately the ratio IV~,b/Vcbl) depends strongly on the theoretical model for the expected lepton energy spectra for the b--+cg~ and, especially, the one for the b--+u~, transitions. This model de- pendence is considerably reduced when extract- ing IVubl from the lepton energy spectra of the exclusive decays B--+~+~ and B---+p(oJ)g+~ '.

We have recently analyzed these decays [9] us- ing the technique of "neutrino reconstruction" briefly described in the previous section, i.e. in- ferring the neutrino four-momentum from the measurements of the missing energy and miss- ing momentum of the entire event. In this case the stronger requirement was used that the total charge of the event be zero. The resulting neu- trino energy resolution is about 110 MeV.

We have analyzed the decays B ~ r ~ and B--+p(w)~ for all three charge states of the ~r and the p. Fig. 4 shows the distribution of the

"beam constrained mass" (eq. 1), Mca,~d, of the B candidate for the sum of the. scalar ~r+£u and :r°gu(top) and the vector modes (p and w) (bot- tom). The selection -0.15 < AE < 0.25 GeV (eq. 2) has been applied.

The points are the data after continuum and fake background subtractions. The unshaded his- togram is the signal, while the dark shaded one shows the b ~ c X background estimate, the cross hatched the estimated b--+u~u feed-down. For the ~(vector) modes, the light-shaded and hatched histograms are ~-~Tr (vector ~ vector) and vec- tor --+~ (~--+ vector) cross feed, respectively. The insets show the lepton momentum spectra for the events in the B mass peak (the arrows indicate the momentum cuts).

1 L ~ I I N - I ~ I

3 5 P - ' l ' ' ' l ' ' ' ; ' ' ' i ' ' ' t ' ' ' t ' ' ' t ' ' ' t ' ' ' l ' ' ' +

[ [ _ , , - , .~.,, . . . . , . . . . ~40.~ I > • ..~ . ~[- ~ . , , , -m ,m,~ , , , , j o .<1~-

20

_.¢ 15 e-

~ lO

6

:>

30

® 20

10

5.12 5.14 5.16 5.18 5.20 8.22 5.24 5.26 8.28 5.30

Mc~nd (GeV)

Figure 4. The B candidate mass distribution. See text

Fig. 5 shows the distributions of m(~r+Tr - ) (left), rn(lr°:r °) (upper right) and m(lr+~r-~ °)

G. Moneti/Nuclear Physics B (Proc. Suppl.) 59 (1997) 17-26 21

(lower right) for the channels with a vector me- son in the final state. The events are candidates B--+xtv decays which satisfy all the other B can- didates selections, including a cut on the B mass. The shading is the same as in the previous fig- ure. The arrows indicate the mass range used in the analysis. The r%r ° plot shows that the ~rTr channel is dominated by the p resonance. The 7r+Tr-Tr ° plot shows that the w~, rate is consis- tent both with zero and the same rate as that of p&,.

5 0

40

30

e ,

10

O.S 1.0 1.5 ~';r Mass (GeV)

m

Q 0 ~ 1

Ill

1 0 ~

5 Q

0 .§ 1 . 0 1 .5

~ o ~ o Mass (GeV)

Figure 5. m(~r+~r-), m0r%r °) and m(zr%r-Tr °) distributions. See text

We use the Isospin relations

r ( B ° ~ T r - f + u ) = 2r(B+--+Tr°f+u)

F(B°--+p-e+u) = 2F(B+ ~p°f+u)

r(B+~e+u)] to combine the distributions from the six ob- served final states into just two, one for the 7r channel and the other for the vector meson chan- nel. The two- (three-)dimentional distributions in AE, MB (and m(~rzr(~r°)) for the p(w) case) of these two channels are then fit to Monte Carlo simulated shapes of signal and of backgrounds from b--4c, cross feed between modes and feed down from other B--+X~,~v decays. The Monte Carlo simulations are also used to determine the detection efficiency that is also model dependent.

Five different theoretical models are used to generate the Monte Carlo events. All five models give consistent results. The average of the five fits gives:

13(B°~zc-f+~,) = (1.8 + 0.4 ± 0.3 ± 0.2) x 10 -4

I3(B°--+p-~+~,) = (2.5 + 0 4 +0.5 4- 0.5) x 10 -4 • - 0 . 7

where the third error is the spread over the five models used.

Using TB ---- 1.65 4- 0.05 ps and 7(B°)/'r(B +) = 1.02 ± 0.04, we can then calculate IVub[ from each model, for the 7r and p channels. Again, we get consistent results. We average them and add a third error from the spread of values obtained, finding:

]Vub[ = (3.3 ± a 0 +0.3 ± 0.7) X 10 -3. v - , - _ 0 . 4

4. Radiative Penguin Decays

CLE0 saw the first evidence of one-loop ra- diative (penguin) decays in the exclusive process B ~ K * ( 8 9 2 ) 7 and measured its branching frac- tion [10]. We then succeeded in measuring also the branching fraction for the inclusive process b--+s7 [11].

4.1. B-~K*(892)7 We have now produced a more precise re-

measurement of B(B-~K*(892)V ) [12] using higher statistics and more K* decay modes, K*°~K+Tr - , K°zc °, and K*--+K°Tr - , K-zr °, thus approximately halving the errors in our pre- vious measurement•

The main problem in this analysis is obviously background suppression• Backgrounds originate mostly from e+e - --+ q~ (not bb) annihilation and consist of 7 from 7r ° and 7/and from Initial State Radiation (ISR). In order to suppress these back- grounds we applied the following selections:

1. We veto 7 from 7r ° and r 1 candidates• 2. Jet-like events are suppressed by cuts on

R2, the second Fox-Wolfram moment, and on cos Othrust, the angle between the photon and the thrust axis of the rest of the event, i.e. excluding the K, 7r and 7 that constitute the B candidate•

3. 11 more event shape quantities are then combined linearly in a Fisher discriminant [13]•

'22 G. Moneti /Nuclear Physics B (Proc. Suppl.) 59 (1997) 17-26

They are: (i) the angle between the thrust axis of the whole event and the beam axis; (ii) the angle between the momentum of the candidate B and the beam axis; (iii) the flows of the magnitude of momentum of all other particles in the event in a succession of nine 10 ° cones around the K*7 axis (Fig. 6).

15

S Z

, , ~na l , ' - '" : QQ : '"'"": ISR ' ' ' I . . . . I ' ' ' ' I ' ' '

i • , L .

0.00 1.00

.:',,

i , J " ~ - : ',

0,25 0.50 0.75 Fisher Discfiminant Output

Figure 6. The distribution of the Fisher dis- criminant output for Monte Carlo sample of B°--+K*°7 (K*°-~K+1r - ) signal, q~ISR. The his- tograms have equal area and and the x axis has been rescaled to to make the Fisher discriminant output lie between 0 and 1.

The validity of the Fisher discriminant was tested separately, comparing data and Monte Carlo distributions for events with a B--+DTr can- didate, as shown in Fig. 7

The scatter plots A E vs M s for the candidates that pass all these selections are shown in Fig. 8. We used the variables AE, MB, M g n and the Fisher discriminant, and a maximum likelihood method to fit signal and background yields over these plots.

We thus obtain the individual branching frac- tions shown in Table 1.

,MonteCadoB~D~ • Data

3 0 . . . . I . . . . 1 1 . . . . I ' ' ' '

10

h

o . 1 . 1 ,lL,,.l.~.l.; 0 . ~ 0.25 0.50 0.75 1 . ~

Fisher Dlscrlmlnan! Otdput

Figure 7. Comparison between Fisher discrim- inant distributions for Monte Carlo and data B~DTr signal events.

Table 1 Individual B--+K*'7 branching Fractions

Decay Mode

K * o --+ K %r - K*O~KOTr o

K *---+ KO Tc -

K *-_-+ K-Tro

Signal Branching Ratio Events (in 10 -5 ) 24.2 : + 0.4 2.81 : 0 61]:] ± 0.8 63 I 4.31.7 4- 0.5 4.6~:~ 2.6~: 5 -t- 0.3

Combining the results for the two K* decay modes and than those for B ° and B- , we obtain the branching fraction:

B(B--+K*(892)"/) = (4.2 4- 0.8 4- 0.6) x 10 -5

and combining this with our previous measure- ments [11] of b--+s'),, we find:

F(B--+K*(S92)7)/P(b--+ST) = 0.181 + 0.068

We have reduced the statistical error to a half of that of our 1993 result and the systematic error is also reduced by 2/3.

G, Moneti/Nuclear Physics B (Proc. Suppl.) 59 (1997) 17-26 23

K ~ _ 4 ~ K+ ~" ° ' '

0.1o

++I0

K~_ ,K°~ °

$ . ~ $.ZSO S + ~ S ~ o S2So S.XO

o~ K" "* K° x" K'" -* K" *°

o,o ° ." I "~" ,~ :" m I , " • . r - I ~k r " . " m . |

m N

• m . • •

-O.aO • a " - 0 3 e t Y t . , . x . ~ ~ . . Ic ~ . . , i f _

S ~ O 62S0 S300 5.200 S2SO S 30o

MB

Figure 8. Distribution of the B~K*v events in the AE, Ms plane. The box indicates the signal region.

, , B-~F'r ; ° ' " : B "*K° 7 ' ' ' ' I . . . . I ' ' ' ' I ' ' ' '

(a)

i'i.

-1.0 -0.5 0,0 0.5 1.0 N e u r a l N e t w o r k Output

Figure 9. Distribution of the output of the neural network for Monte Carlo samples of (a) B°--+p° 7 and B°-+K*°7(K*°--+K+~r- ) and (b) B--+p-Tand B--+ K*-7( K*--+ K-Tr° ).

4.2. B-~p(w)7 Isgur and Wise and Burdman and Donoghue

[16], in the framework of HQ approximations (hence an SU(2) symmetry for the (c,b) doublet) have shown that the B semileptonic decay form factors are related to those of B--+p(w)e+e - and also to the matrix element of B--+p(w)7. It is thus possible to use the measurement of B-+K* 7 to constrain the nonperturbative QCD calcula- tion of the B--+p~u and extract Vub more reliably from it.

However the process B-~p(w)7 is much rare and more difficult to detect than B-~K*7. In ad- dition to the backgrounds already discussed for the latter, we have now the additional problem of the background generated by just B~K* 7. To suppress this background we have used a neu- ral network that uses the kinematic variables A E ~ , M,,~, MK,r and cos0p (the p decay angle in its rest frame). Fig. 9 shows that discrimina- tion provided by the neural network.

Our presently available data allow us only to set upper limits to their rates. Fig. 10 shows the AE vs MB scatter plot of the candidate

events for the three channels considered. We observed 4 candidate events for B°-+p°7, most likely feed-down from B--+K±TrT,'/, and 0 candi- dates for B----+p- 7 and B°~w7. After subtract- ing several estimated backgrounds, we obtained the following 90% C.L. upper limits:

B(B°~p°7) < 3.9 x 10 -5

B(B°--+w7) < 1.3 x 10 -5

B ( B - ~ p - 7 ) < 1.1 x 10 -5

If we compare them with theoretical predictions for B(B--~p-7): (0.04 to 0.07)×10 -5 [14] or (0.12 to 0.30)x10 -5 [15], we see that our upper limits are still about an order of magnitude larger than the expected values.

4.3. A measu remen t of I V t d / V t s l

The matrix elements for B-+p(w)7 decays are related to those for B--oK* 7 by flavor SU(3) at the quark level. Neglecting long distance and other effects in the actual hadronic transitions, one ob-

~24 G. Moneti/Nuclear Physics B (Proc. Suppl.) 59 (1997) 17-26

OJO -

O . tO

-0.1C

B°~p°. r . . . . , • " "K -

-O.3O . . . . * . . . .

I~ o . ~ B" ~ p"f N

• s K •

0 . t 0

~ . tO

B°-~ w¥

S 2 S 0 S 3 0 0

- 0 . 3 0 . . . . | . . . .

MB

Figure 10. Distribution of the B--~(p,ca)~/events in the A E , MB plane. The box indicates the signal region.

tains the approximate relationship:

B ( B - ~ p - 7 ) = ~fl td

B ( B - - + K * - 7 )

where ~(,~ 0.5 to 0.9) accounts for SU(3) sym- metry breaking and fl = 1.02 4- 0.02 is the phase space ratio. The measurement of B(B---+p-'~) then provides a determination of [Vtd/Vts] and possibly a better way than B°-B ° mixing to get the upper right side length of the unitarity trian- gle (because only ratios of calculated quantities enter the calculation of ~). With the present data we can only get an upper limit for IVtd/VtsI. Us- ing the measurements described in the previous sections and the isospin relation F(B---+p-')') = 2F(B°-+p°-y) = 2F(B°-+ca'y) we get:

V 2 v td < 0.19 Vts

Considering the uncertainty in xi and other sys- tematic errors, we can set the upper limit to IVtd/Vtsl in the 0.45 to 0.56 range. ALEPH [17] has recently fond a similar upper limit range (0.37

to 0.42) from the study of Bs oscillation. The two methods are thus competitive.

5. Other rare B decay modes

Direct CP violation effects in B decays are due to interference of two different processes. In ex- clusive charmless hadronic decays of Bu, the in- terfering processes can be the tree-level spectator diagram and the one loop hadronic "penguin" di- agram. It is important to understand the rela- tive contributions of these diagrams and to col- lect information that may help refining the phe- nomenological description of these decay mech- anisms. CLEO has been conducting a search of exclusive, charmless B decays and found evidence for the sum of the two decays B°~Ir+Tr - and B°~K+Tr - [18]. This result was recently con- firmed by DELPHI [19]. CLEO has recently es- tablished a number of upper limits for charm- less B decay branching ratios. Here I have time to discuss only the recent search that resulted in the actual observation of the charmless decay B+~ca(rr + or K +) [20]. Theoretical predictions for the branching fractions for these decays, and for the decays where an r/is produced instead of an w, vary from 3 x 10 -7 to 1.1 x 10 -5.

In this search we detect the ca (or the ~) through its ~r+rr-~r ° decay. The selections de- scribed in Sect. 4 were used to suppress con- tinuum and other backgrounds. Fig. 11 shows the AE, MB scatter plot of the candidates for B+~c~(~ + or K+). 10 events are seen in the signal region, with an expected background of 2.0 + 0.3. The probability that the 10 events are all background is estimated to be 1.2 x 10 -4. Hav- ing estimated a detection eficiency of 8.5-t- 1.5, we find the branching fraction:

B(B+-4ca(Tr + or K+)) = (2.8+ 1.04-0.5) x 10 -5.

Fig. 12 shows the AE, Ms scatterplot of the candidates for B+--+u(Tr + or K+). No events are found in the signal region, where a background of 0.7 4- 0.2 is expected. Having estimated a detec- tion eficiency of 2.8 -t- 0.5, we obtain the 90% C.L. upper limit:

B(B+--+rl(~r + or K+)) < 3.0 x 10 .5

G. Moneti/Nuclear Physics B (Proc. Suppl.) 59 (1997) 17-26 25

0.20 • " ' ' | " " " " I ' ' " ' I . . . . $

4. 4" 4,

4. 41" ÷ ÷ ~4" 4" 4. ÷

0.10 4" 4. 4. 4.

÷ 4. 4. ÷

A ' . 4"

0.00

÷ 4"

- 0 . I 0 4" + + 4. ÷ 4"

4 . 4" 4- 4-

÷ ÷ 4"

4- ÷ 4.

- 0 . 2 C ] . . . . I . 4 . . • , + 1 . . . . I • . a . . ,

5.200 5.225 5.250 5.275 5.300 M, (~Vlc')

Figure 11. AE vs MB distribution for B->wh + after all selections. The box indicates the signal region.

0.20

0.10

> o 0.00 v

-0 .10

' ' ' ' 1 ' ' ' ' 1 ' ' ' ' 1 ' ' '

4" ÷

4- 4. 4.

4-

4.

4"

.D - 0 . 2 0 . . . . I , . . , I . . . . I • • o ,

5.200 5.225 5.250 5.275 5.300 u. ( ~ v / c ' )

Figure 12. AE vs MB distribution for B--->~h + after all selections. The box indicates the signal region.

6. T h e fu ture o f C E S R and CLEO

CESR is a symmetric electron-positron collider and, as such, it is not best suited to detect CP vi- olation effects induced by B ° - B ° mixing. That is because of the very short average decay path of the B coming from the decay of the T(4S) res- onance where the cross section for B production is about 1.1 nb. The present plan is to attain a luminosity large enough to detect direct CP vi- olation effects in charged Bu decays. There are hopes to see such CP violation effects starting at an integrated luminosity of 30 fb - l a t the T(4S). This could be possible, very optimistically, using current expectations according to the standard model for the B+--+r±Tr ° decay [21]. Otherwise we may have to collect data for a considerably longer time.

The present CESR luminosity record (this is a world record) is ~ = 0.35 nb-% -1 with 9 trains of 2 bunches each, a current of 1.4 × 10 l° elec- trons/bunch, /3* = 1.8 cm, and a crossing angle of 2 mrad. The limiting beam-beam tune shift is

= 0.039. In these conditions CESR can provide an integrated luminosity of about 3 fb -1/y.

The effort now under way, is:

• to work with 9 trains of 5 bunches; • to switch to superconducting RF cavities that

currently being built; • to change focusing in the Intersection Region

(IR) with quadrupoles (some of them supercon- ducting) much closer to the intersection point to get a bunch length of 1.0 cm.

The projected result of this program is to reach a peak luminosity of i: > 1.0 to 1.8 nb-% -1, i.e. between 10 and 18 fb -1 /y , by the year 1999.

Luminosity improvements beyond this goal are also under study. They contemplate colliding round beams, increased tune-shift limit and in- creasing the number of circulating bunches by a further factor of 2 or even 4. These changes could boost beyond 30 f b -1 /y the luminosity delivered per year.

Presently, CLEO 2.5 has very good charge particle tracking and and a CsI electromagnetic shower detector that provides excellent energy and space resolution and granularity. The detec- tor is fairly hermitic, the tracking devices covering over 90% of 4r and the shower detector 97%.

A three-layer Silicon Vertex Detector was added in Fall 1995. It will increase tracking effi-

26 G. Moneti /Nuclear Physics B (Proc. Suppl.) 59 (1997) 17-26

ciency, especially for low momentum tracks, and sharply reduce the combinatorial background in charm particle detection. No analysis project us- ing this new facility has been completed yet.

The gas in the main drift chamber has been changed from Argon-propane to Helium-propane (60/40) with the effect of considerably reducing multiple scattering. The effect of this change has been to reduce the r.m.s, spread in m(Ir+~ -) from K~--+r+7~ - from 11 MeV to 8 MeV.

The goal for the CLEO III detector now under construction is:

• To add excellent charged hadron ID by a Ring Imaging Cherenkov detector (RICH) designed to separate ~r + from K + at the 3.5a level up to 2.8 GeV, over 82% of the 41r solid angle.

• To further improve vertex detection with a four-layer, double-sided Silicon Vertex Detector, capable of independent tracking.

• To allow a much faster, pipelined data tak- ing, to take advantage of the higher luminiosity projected for CESR. This requires a complete re- building of the data acquisition system.

The main drift chamber is being rebuilt in or- der to make room for the RICH detector and to replace the current inner tracking detector that is incompatible with the future focusing quadrupoles of CESR. It will have an outer ra- dius 20 cm smaller that the present one but also a smaller inner radius by 7 cm. The loss in path length with respect to the CLEO II chamber will be compensated by the decreased multiple scat- tering due to the use of the He-propane gas mix- ture.

The new vertex detector and new drift chamber will be partners in tracking, with the vertex detec- tor providing precise initial position and direction of the tracks, and the drift chamber providing the measurement of the transverse momentum.

The current, excellent CsI electromagnetic shower detector, the magnet, and the muon iden- tification system will remain unchanged.

The most recent projection is to install CLEO III in the second half of 1988.

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