Production and decay of heavy flavors

Nuclear Physics B ( ",oc. Suppl .) 16 (1990) 108-123 North-Holland

108

P ODUCTION AND DECAY OF HEAVY FLAVORS Rollin J. MORRISON Univ. of California, Santa Barbara, CA 93106 1. INTR01UCTION Although top has not yet been directly observed, and there is no evidence for b~, there have been many beautiful and important results on the production and spectroscopy of heavy flavors and their hadronic and the semileptonic decays . The semileptonic decays, including first evidence for b -i- u transitions, are particularly important. In Table I are listed the types of experiments which have been, or will soon be, important in the study of heavy flavors. Interestingly, for charm there are now three very productive approaches. Both fixed target experiments using vertex detectors, and CLEO and GUS working with e+e' continuum events in the 10.5 GeV region, are free of the constraints of the r/r" and can study charmed meson resonances and charmed baryons. In the last year ARGUUI and CLE02 have both done impressive work in charm physics as seen in Fig. 1 and Fig. 2.

MASS (D*+ KS) , xp > O6 [GeV/c2 Fig. 1. ARGUS data showing the D**(2536) in D*+gs0 mass combinations .

Table I Experinnental Methods for Studying eavy Quarks Charm * e+e- 011(3770) Mark III * photo- and hadroproduction with E691, NA32, precision vertex NA27/E743, WA82 * e+c 10.5 GeV continuum CLEO, ARGUS B decays CLEO, ARGUS v production CDHS Z decays SLC, LEP Bottom * e+e- T(4s) CLEO, ARGUS hadroproduction UAI, WA75, WA78 e+c continuum JADE, CELLO, Mark II, MAC Z decays SLC, LEP 0920-5632/90/$3 .50 Q Elsevier Science Publishers B.V. North-Holland

R.J. Morrison/Production and decay of heavy pavots ble II Ch 3p ave c (6 of ~~ st~g ®

tr~c ed)

Ig =

Jp M~as

~P 2+ Zl59 Ees1, ARGUS, CLEO

~P

ARGUS

moi, ARGUS

1+ 2920 ARGUS, E691, CLEO i+ OT

ARGLS,CLE4

~+ Ch ed ary®ns ( : Of g states observed)

cuc~ Iseen

cuu

cud

EO

MT rC

MO yC

w .1 ,~.T

cdd

cus

cds

cra ~ cds cu

I seen I ®_ ~seen~s~n es~n

yL

_

~ .~ .LV .~.C

_ i _ r

A major recent advance in the i:~nderstanding of photo- and hadroproduct:on of heavy flavors has Mass (~

- n + )GeV

Fig. 2 . CLEO data showing the Sd in ?-x+ mass combinations.

The first indications of B mixing came from UA1, 3 and evidence for mixing was presented at this conference from JADE,4 CELL0,5 and Mask Its (and pre viously from MAC) at PEP and PETRA . Even so, B physics is now strongly dominated by ARGUS? and CLEOB . The Z will be a very nice source of moving

B's if we can learn to cleanly detect 4ilenï . 2 . PRODUCTION

come through the higher order f~CD calculations of R .I{ . Ellis, S . Dawson, and P. I~ason .10,11 ~ discussed by G . Schulerll at this conference, the eff~t of hi~,her order is to Eignifica"~itly change the sire of the cross section but to Nave very little effect vn the shape of the distributions . There is a pattern in which the calculations see more reliable for photoproduction than for hadroproduction, and are more reliable a~ the quark mass gets heavier . A brief summary of the situation with photoproduction is that the experiments agree with each other (in particular E691 13 and NA1~ 14 ) and that the four

There have been important advances in charm

measurable quantities, Qcc, ~,

F(pT), and F(z~)

spectroscopy, due to E691, ARGUE and CLEO . Five

can be consistently fit by a reasonable value of the

of the 12 expected P-wave D** states of the cq' sys

charm quark mass and by a reasonable gluon distri-

tem have now been observed, as sYiown in Table Ii. A

bution, G(a) _ (1-z)"* . The results of this fit should

beautiful example is the D8*(2536) shown in Fig . 1 .

be available soon .

After the initial difficulties in studying the DS it is impressive that the first p-wave state has already been seen. Five of the nine expected ~+ single charm baryons have now been convincingly observed, as seen in Table II . The OLEO data for the 8~ is shown in Fig. 2. Beautiful data on bottomonium spectroscopy from CUSB was presented by Mike Tuts

9

Hadroproduction is more difficult theoretically and experimentally. The K factor, K -

° o(a~~

is arge, N 3 . The measurements are more difficult because-~ â .001 and because the charged multiplicity is large, as compared with photoproduction. Many measurements of charm hadroproduction were made before the proper tools were available . Much

,

R.J. Morrison/Production and decay of heavy flavors of the more recent work has been devoted to sorting out the confusion caused by the earlier results. An example is the work presented to this conference from Serpukov.15 Measurement of prompt neutrinos and muons set upper limits on the charm cross section at Vs- l,s 12 GeV of 4.5 and 2pb, respectively, which are well below earlier measurements and which are consistent with expectations from QCD. Results presented by Dr. O. Botnerl6 from Uppsala using the UA2 apparatus indicate that at f -:- 630 GeV the charm cross section is less than 1.9 millibarn . This bound is again very consistent with QCD expectations. These limits, taken with the measurements of NA27/E743,17 clearly indicate that the magnitude of charm hadroproduction cross sections is as expected from QCD (within the admittedly large uncertainties of the calculations) and that the energy dependw .ce is reasonable. To make sense of the hadroproduction data I have considered just those experiments which have very strong signals in numerous channels. NA27/E743 has, in addition to the energy dependence, comparisons between xp and pp production and has detected D's and Ac's of all possible charges. NA3218 has data with 7r- on Cu with some incident K- . They observe DO, TO, D+, D- , D.+, D8-, A+, AC- 9 SC+9 -=C- . The new experiment, WA82,19 with the D+ peak shown in Fig . 3 represents a major breakthrough in experimental technsque . For the first time an experiment has successfully implemented a precision vertex trigger . The picture which emerges is that none of the funny effects observed earlier are reproduced by these experiments . In particular there is no large leading partiçle effect and also no extreme energy dependence; the production is central with F(-TF) = (1 xF) n and n > 3; the production is approximately independent of incident particle type; and particles and anti-particles are produced roughly equally. WA82 finds the A dependence A0 .89f.05f .05 which is what one gets by comparing NA27 with NA32. NA32 finds

100 N/4MeV

90 80 70 60

40 30 20 10 01

1 .75

1.85

1.95

2.05

2] mass combinations

M (Kt Tr* 7r*) [GeV/c

in

Fig . 3. WA82

7r+A collisions.

K*r'FirT-

o.B(gé .~ g- x+x+) = 0.04 f .02 f .0214b/nucleon . This is roughly 20% of the Ac+ production, which is about what is expected as the cost of the s quark. It should be noted that the results are completely inconsistent with the results of WA6220 on 8+ production by incident E' . If the WA62 results are con firmed by the new data, expected with the omega spectrometer this winter, our picture of charm hadroproduction will again be in a state of confusion . The hadroproduction of bottom has been observed in trimuon events at fixed target energy by WA7821 and at pp by UA122 as shown in Fig. 4. These measurements are in agreement with higher order QCD, but there was discussion during the talk by G. Schuler 12 in the parallel session about wh-ther the very high pT point should be explained by the existing theory. This issue has not been resolved. It should be pointed out that the mean pT of B production is expected to be about 5 GeV/c and that the

R.J. Morrison/Production and decay of heavy flavors Table III Ratio of Decays

100

pp collisions. dS = .63 TeV. lyl< 1 .5. kT>k 0 :.date points UAI - m .-4.75 GeV, A.-260 MeV.

B D°-"K-K+ B D -A-A+

DFL1i. /b - d(m;+k'@) . ---- 4 .5
~ rO

k

3.7f1.4

2.5 i .7 2.2t .5

lots of ai production, B(DO--# K-ai) -- 0.080 ± .008 f .019, and B(D+--+ K0_ai) = .081 i .020 f .02?.

Ia

a b

Mark III ARGUS CLEO

.001

.0001

0

10

kmte

20 [GeV]

30

40

Fig. 4. UA1 data on B productions integrated over PT for values of PT > Kmin . The circular data point for the lowest Km1n is for the detection of muon pairs from J/1jr from B decays . The next circular data point is for high mass dimuons. The triangle is for low mass dimuons and the squares are for single muons. UAI observations are made only in the high pT part of the distribution . The conclusion which I reach is that, at the cur-

The vector-vector branching ratio, B(D®-+ Kip°) = .023 f .003 f .007, is about the value predicted Bauer, Stech, and Wirbel (BSW)26 The state of D8 decays has p

rapidly

in the last three years. The measured branching rar tios are given in Table IV,27 shown as ratios to D,+,--,

Oir+ . These decays are expected to take place via the spectator diagram of Fig. 5a . This me hansm leads

to a9 final states. If decays should take place via the annihilation diagram of Fig. 5b the final states will be irim, pr, wir, etc. A look at Table IV indicates

that the decays are dominated by 85 final states in-

rent level of experimental and theoretical precision,

dicating,that the annihilation contribution is small.

duction of bottom are in excellent agreement with

decays where early measurements of large branching

photo- and hadroproduction of charm and hadroproQCD predictions .

3. HADRONIC DECAYS OF C AND B At the present time something like 25,000-30,000

clean, fully reconstructed charm decays have been observed by Mark III, E691, CLEO, ARGUE, NA32, NA14, etc. Due to obvious limitations I can just

touch on a few highlights from this extremely rich data. One of the most significant problems in DO de-

cays is the ratio of Cabibbo suppressed branching K ratios, BDOfi) . The predictions for this ratio are about one and have been pushed up to 2.7 in 11123 result attempts to explain the very large Mark 1,24 and given in Table III. New results from ARGUS CLEO,8 also given in Table III, reduce the problem

somewhat. Mark 11125 has performed a resonance analysis of

D®-+ K-it+ir+ir- and D+--, K0ir+ir+ir -. They find

There is some controversy with respect to

qA

and q ir

ratios are contradicted by upper limits from Mark III and E691 .

The smallness of the annihilation contribution

(Fig . 5b) to DS decays indicates that the associated W exchange process in DO decays is also small. The conclusion then is that W annihilation/ W exchange processes are not the primary cause of the large DiRr lifetime ratio. (0) SPECTATOR

fib) ANNIHILATION

s

Fig. 5. Quark level diagrams for D8 decays indicating (a) spectator and (b) annihilation processes.

R.J. Morrison/Production and decay of heavy flavors

Ds

s

Table ranching Ratio/Branching Ratio DS --~ 15x

branching ratios compared with the branching ratio DS --> fix . Those decays with ss final states are given above the break in the table. Mode

CLEO

TO-K+ TO-K+' KO. K+

1.2±0.21± .07

KO°K+' (K+K rT )NR +~ ~+ 4*+Ir0 (K + K

Ir _ Ir0 )NR

.NR

f0(975)W+ nW+

4f ir+ p0W+ (lr+

WW +

lr-A+)NR (ir+ x- w+ir- A+)NR KO,r +

E691

Mark III

.99± .l7± .06

.92± .32± .20

1.05 ±17 ±- .06 .87±13 ± .05

.84± .30± .22

.25± .07± .05

ARGUS

Other

1.44± .37

2.3 ± 1.2 NA32 .96 ± .32 NA32

1.11±.37f.28 .41± .13±.11

.42 ± .13 ± .07 2.4 ±1 .0± .S

.39 ± .17 NA32 < 2.6 90% C.L. NA14

< 2.4 90% C .L . < .32 90% C.L . .28± .10± .03

0.11 ± 0.07 NA32

.58± .21± .28

< 1.5 90% C.L . < 2.5 90% C.L.

3.0 ± 1.3 Mark II

< 1.7 90% C.L . < 1.9 90°% C.L. < .08 90% C.L.

< .22 90°% C.L .

< .5 90% C.L. < .29 ± .09 ± .03 < .29 90% C.L.

I comment on absolute branching ratios for the

A+ and the Ds . At the Cornell Heavy Quark Sym-

posium both ARGUE and CLEO presented determi nations of the A+ -~ PK7r branching ratio using B decays . The technique involves the measurement of

-~ Ac x) - B(A+ ~ pKx) and of B --~ A+ $ where

final state baryons are assumed to come predominately from Ac . The average result was presented by K. Schubert28 and is 4.2 f 1.5%, significantly larger than the Particle Data Group value, 2.6 f 0.9%.

The situation with the DS absolute branching ra

do is not so good . Mark 111129 has looked for D8 Ds

double tag events . They do not find any events pro viding a branching ratio upper limit, DS-+ 07r < 4.1% at °% confidence level. CLEO uses a subtrac-

tion technique to get the DScross section in the e+econtinuum. They assume, BD® -- a charm - Or D° o~ + - aAc - a"c - o°C, with the charm contri-

4.8f3 .4 Mark-II 6-9J2.4±1 .4 NA14

< .2190% C.L .

â, from theory. They find30

bution taken as .37oh

D,+--> jhr = (1 .5 f .8)% . This is clearly a difficult

technique. A value this low lmplaer. that the fraction

of two-body decays for DS would be smaller than the 40-45% observed for DO and D+ . I think that the result will turn out to be larger than the CLEO determination . All of these charm numbers are important when we come to bottom.

From our knowledge of charm decays what do we expect for bottom? First consider charm. The spectator quark diagram without QCD correction is shown by the diagram in Fig. 6,a . Here we see that the ud and sg systems are automatically color sin-

glets. The ud has a net positive charge . Perturbative QCD can change the color singlet structure as seen

in Fig. 6b . Here the effective neutral current is color singlet. Perturbative QCD gives two amplitudes cl

R.J. Morrison/Production and decay of heavy flavors and e2(b) (Fig. 6a and Fig. 6b) calculated to be 1 .3 and

(a)

-.6 respectively for the case of charm . These ampli-

CI

c2 }a

tudes lead to final states which can be identified by the charges in many cases . For the Cabibbo favored

b

C NLW-

-.1 }D

D+, I is d and the two amplitudes interfere. This destructive interference is the main part of the explanation of the long D+ lifetime . (a)

c i = 1 .3

(C)

(b)

ci

(d)

c2

a el -06

C

/} SHAGGED d

CHARGED

C

S

lCOLOR ISINGGET

Fig. 6. Quark level diagrams for hadronic charm decays. Fig. 6a is the uncorrected spectator diagram. After perturbative QCD corrections it corresponds to the amplitude cl . Perturbative QCD correction generates the diagram of Fig . 6b with the amplitude c2 . Unfortunately it is not clear how to go from quarks to hadrons . Bauer, Stech and Wirbel26 use factorization, decay constants and form factors to express all two-body decays in terms of two constants al and a2 . Experimentally, it is observed that al - 1.2 and a2 - - .5 . These are close to the values of c1 and c2 . The BSW model has been under attack by theo-

q Fig. 7 . Quark level diagrams for B decays indicating how the c1 and c2 type diagrams similar to those of Fig. 6 lead to particular final states. Due to the very large B maw the W can couple to as giving final states containing eff as shown in (c) and (d) . fraction of the decays for the case of bottom. Final state interactions should play a smaller role since we are well above the resonance region. The net effect is that the ratio of lifetimes should be 1 < - < 1 .2. 'Ne might also expect BSW to work better . ARGUS31 and CLEO 8 together now have some-

rists, because the assumptions are hard to justify, and

thing like 200 exclusive hadronic bottom decays.

by experimentalists, because the predictions are only

As presented at the Cornell Heavy Quark Sympo-

roughly borne out by experiment . Branching ratios

sium both CLEO and ARGUE now measure the maw

that are predicted to be very small are often filled

difference between the B- and BO to be essentially

in, presumably by rescattering and final state effects .

zero . OLEO finds$ OM =

Nonetheless, the general pattern of decay is about

MeV/c2 and ARGUE has? ®M = 0.0 f 1 .3 f 1 .0

right . What do we expect for bottom?

MeV/c 2 . This is important because the unmeasured B r 4s -" B°B involved in most B measureratio B T° 4s -"B+B-)

For bottom we again expect the two-quark level diagrams corresponding to c1 and c2 of Fig . 7a and 7b . Due to the high B mass the W- also couples to sc leading to diagrams 7c and 7d . Here we get DD states proportional to cl and OK states proportional to c2. Perturbative QCD predicts that 1 51 1 at the b mass is about 71 the value at the c mass. Only the diagrams of Fig. 7a and 7b interfere, for the case of B - . We also expect two-body states to be a smaller

Bo -

MB- = 0.6 f .5

ments at the T(4s), and this ratio depends upon the

phase space available in the decay. Both CLEO and ARGUE now take this ratio to be 1 .0 (many old numbers must now be corrected by about 10°X) . The exclusive hadronic branching ratio_4 nose sured by CLEO and ARGUS are g ;ven in Table V. (Note that old results have been corrected for the effect discussed above .) In general the CLEO and

R.J. Morrison/Production and decay ofheavy fiavors Table V ranching Ratios

ja2l = .20 ± .03. The 2 B- decays, DOp and D0 7r -

involve both al and a2 but the a2 contribution is small. For these we take a2 = -0.2. Its mentioned,

the D8 absolute branching ratio is quite uncertain, so these decays are not included in the fit. The value of al found is 0.88 ± .06 and we can see that the data from all of the decays are in reasonable agreement with the values found. This is true for the D8 decays only if higher values of the DS --i~ ¢hr branching ratios are used. For comparison we show the data in Fig . 8 assuming 4.1% for B(D s -i~ 4x) . ~`+Ds D+Ds OP Ds

D°P

CLEO

® ARGUS

1

D*+âi

D+p _F-_I-®----I

1 I i

jK_ o IK*_o

l

i

D*+P

CM+

1

4K*ir-

D+W0

A GUS numbers are in excellent agreement . The DD8 decays are new, indicating decays of the type

shown in Fig . 7c for the first time. In evaluating the B branching ratios CLEO has used the value of D+-o- 0x = 1.5%. As we have seen, values for this as large as 4.1% are also quite reasonable, leading to smaller B -+ DD8 branching ratios. Also shown in Table V are the predictions of BS W for the two-body decays. The comparison with BSW can be seen from Fig . 8 where the value of al and a2 from the branching ratios of Table V are given. First we use the 0 data to find a2 with the value

1! 1

2

3

0

0.1

02

0 03

0.4

Fig . 8. Comparison of hadronic B decay branching ratios with the model of Bauer, Stech, and Wirbel. The fit is described in the text. The modes with D8 in the final state were not included in the fit, but are shown assuming a DS -+ Or branching ratio of 4.1%. The ratio of coefficients, ja2/al I is found to be 0 .23 f .04. This is about half the value found for charm and is consistent with expectations if (al /a21 is approximately the same as I sI. At the level of - 200 events there appears to be no problem with BSW. Obviously this is not a very stringent test due to the very poor statistics of the data.

R.J. Morrison/Production and decay of heavy flavors A lot of effort has gone into searches for exclusive b --+ u decays8,28 and for evidence of penguin diagrams?+ 32 No events in either class have been found. 4. SEMILEPTONIC DECAYS This is a big year for semileptonic decays. Semileptonic decays are theoretically the simplest, and therefore provide the method for determining CKM matrix

First we consider the pseudoscaiar decays, D -* UP and B -+ Dfv. These are just like Kl3

except the 92 range is larger. For massless leptons the matrix element depends upon a single form factor F(q2 ) . In the models of er, S d Wirbe1,33 the form factors are assumed to be pole dominated, F(q;) _ '-, where the pole mass 1-~ m* is the mass of the lowest v~tAr meson with the

decays are large, compared with individual exclusive

appropriate quantum numbers. For the favored decays these are D8 and B~, for charm and bcAom,

tics in the measurements .

measured . To determine the K-

elements . The semileptonic branching ratios for B

hadronic modes, and consequently have better statisThe diagrams for semileptonic decays are shown in Fig. 9a for Cabibbo favored charm decays, and

in Fig. 9b for b --+ c decays . From these diagrams we measure IVcs l and JVbJ. Note that there are just two valence quarks in the final state. The matrix el-

respectively. The 92 dependence can in principle be matrix elements

Fp must be calculated from theory.t It is clear that, at least in principle, the pseudoscalar semileptonic decays are the best way to measure the

M matrix.

The pseudoscalar measurements from charm are

in relatively good shape. Assuming that JVc.) is given

ement for forming the final K, K*, D, or D* particles is governed by form factors which depend upon 92,

by cos ®c, both E69134 and Mark 11113,5 measure Fp to

represent 85 f 12% of the Cabibbo-favored charm

value is also reproduced in lattice calculations . The

the mass squared of the virtual W. The K and K*

decays while the D and D+ are 63 f 16°rß of b --> c B decays . Note that in charm decays the lepton, de-

fined from the helicity point of view, is the neutrino . For the case of bottom decays the lepton is charged. This difference between charm and bottom has fairly dramatic experimental consequences, as we shall see. The elements Vcd, and Vyu are determined from the suppressed decays leading to 7r, p, etc. for both the charm and bottom cases. (a) D DECAYS

be about 0.75. This is the value predicted by BS

and we have seen in the talk by Mart'melli36 that this lattice calculation also predicts a 42 dependence ris-

ing with 92 in a pole dominated way. The E691 data

is fit to a pole dominated form with the mass m* as a free parameter and the value of the D8 mass is found. Mark 11135 measures the decay D -+ arIr and finds

Vc

= 0'23Ô38, with very limited statistical precision. This measurement is not yet at the level o

precision obtained with the inverse process observed by CDHS,37 but should be significantly improved in the near future .

(b)

B DECAYS

In contrast with the charm case, the pseudoscalar decays for bottom are hard to measure. This is due

c

Fig. 9. Quark diagrams for semileptonic decays of D and B mesons. The inclusive final states are dominated by K,K*, and D,D*, re spectively, as described in the text .

to the dominance of the vector decay B -+ D*w, and the impossibility of detecting B decays with a vertex detector in CLEO or ARGLi$. As a consequence we must come to terms with the more complicated vector decays.

t In the model of ISGW44 the form factor intercept is evaluated at g2maz rather than at 42 = 0.

R.J. Morrison/Production and decay of heavy flavors In the parallel session Prof.

6rner38 discussed

the most general case of massive leptons, appropriate

charged lepton from the dominant transverse component is energetic and is easy to observe experimen-

for the case of r's . This involves five form factors. I

tally. For charm decays the lepton is a neutrino . The

consider the massless lepton case,39 appropriate for

charged anti-lepton is soft and the dominant trans-

electrons and muons, involving two axial vector and

verse component is hard to observe in the case of

one vector form factor. The angular dependences are

charm.

given in terms of two transverse helicity amplitudes, :k (92), which corresponds to quark spin flip, and one longitudinal non-flip amplitude, HO (q2) . These amplitudes are lines- combinations of the three form factors . Due to parity nonconservation, H- (92)

> H+(q2 ).

This can be seen in a simple way by reference to

For charm the vector case has been studied by E691 40 via the mode D+ --~ K*Oe+ve . The ratio of D+--o.K .o v branching ratios, rr D -+K - e+v , is observed to be .45 ± .09 ± .07 . The ratio of longitudinal to transverse components, rT

_

Ho I2dg 2

f (IH+I

+IH-I

)dg21

Fig. 10, illustrated here for B decays in the b quark frame where the c quark recoils against a virtual W- .

obtained from the K* decay angular distribution of

The dominate spin flip amplitude corresponds to a left handed c quark . Since the quark spin has flipped,

measurements have been corrected for the poor ef-

the

- has negative helicity and both lepton and

anti-lepton spins are oriented in the direction opposite to that of the virtual WV - momentum . The lepton is left handed so it tends to recoil against the c quark and has a large momentum . For the case of B decays the lepton is charged . For B decays the

Fig. 11, is found to be 2 .4± 97 f .2 . Both of these

ficiently for observing the H - component discussed above . The small branching ratio, and particularly the large longitudinal polarization, are hard to explain theoretically. The proper analysis, as pointed out by Prof. K5rner, 38 separately determines the three form factors . This can be done by fitting the data as a function of

O

the four quantities, ® ,

ENTA

®e,

X, and

q2,

where ® is the

decay angle of the vector particle in the vector frame, fe is the charged lepton decay angle in the W frame, and X is the angle between these two decay planes . E691 is in the middle of this analysis and the results

SPINS C W_

LEPTON ANTILEPTON

Fig . 10 . Heuristic picture indicating why H - > H+ in semileptonic D or B decays to a vector (K* or D*, respectively) . Shown is the case for B in the b quark frame . H- dominates since the c quark is dominantly left-handed . For this case of quark spin flip the W has a helicity of -1 . The left-handed lepton then predominantly recoils against the c quark, leading to energetic charged and neutral leptons in B and C decays, respectively.

should shed some light on the unexpected results . Great progress has been made recently in the study of B semileptonic decays . These include exclusive measurements of B -+ D*lv and the polarization of the D*, measurements of B -> Dlv, measurements of the lifetime ratio for the charged and neutral B's, and the first evidence for 6 -+ u transitions. These results and inclusive results are given in Table VI41 The technique used by CLE08,42 and ARGUS7,43 to observe exclusive semileptonic decays is to select candidate decays with identified leptons of momen-

R.J. Morrison/Production and decay of heavy flavors Uble Seulileptonic

aft CLEO

eluâve B(B

-+ xf-v)

(10.6f2.8t1 .1)%

ived ExclusiveVector

-046+-005

B(B0 -' D*+` a)

I (4.6 f .s f .z)%

rL/rT Ivebl = .20%1'9 BKS B(B- - D*01r-0)

.043 :k M4 (3.9 t .S+ gt)%

1

1

Exclusive Pseudowcalar

1

_~

Rd AiT BO -+ D*+1-9/00 --* D+1-D B- -è- D*01-0/B- --* D01,r-/r4

.36 .83f

(2 .4 f .8±:ß)96 .14 .67t 20f 1 . 2

1

Q46±

1 (5 .9*1.3) .4t

I

As * .46 A46±ß .4110

1 (1 .7 d: .5 1: .S)%

1

.69+17 3.2* 1 .6

0.85f0.20+:, 1 10 0 f23f14 0.14 :E .05

COs

ARGUS

(10.1t .3t .7)% !(10.3t .?t .2)%

B(BJ --+ xt-a)

B( BO -"- D+f-y) B( B -" DOt-0)

1

1

11 :L .05

D* . Examples of these missing mass distributions are given in F:g. 12, the D*+f- distribution from AR Fig. 11 . Data from E691 indicat ing a large longitudinal polarization in D+ --* K*oe+v . The angle 8 is the angle between the 'r and D directions in the K* frame. After correcting for experimental smearing and acceptance a value, rL/rT = 2 .4+09 17 f 0 .2 is obtained. tum between 1-1 .5 GeV/c and 2 .5 GeV/c. Using the tracks from the candidate D or D* and the lepton, the missing 4 momenta, PM = Pg - PpD* - Pl, is

1-

defined and the missing mass squared MM = EM M

I2

computed . The beam energy constraint is im-

posed by assuming that the energy of the B is the beam energy. The momentum of the B is about 300 MeV/c but the direction is unknown so this momentum is set equal to zero, introducing a substantial smearing in the missing mass distribution. The missing mass should equal the neutrino mass squared for true exclusive semileptonic decays to just the D or

GUS, and Fig. 13, the continuum subtracted DOI distri'bution from CLEO . The D- --* D0 9- P distribution of Fig. 13 illustrates why the pseudoscalar measurements are hard for the case of bottom . The branching ratio to D stars is about three times larger, and the D stars decay to DO, giving a large background to the scalar case. Figure 12b gives the ARGUE decay angular distribution, for the D* case, from which the ratio of longitudinal to transverse polarization is determined . Figure 12c gives the momentum transfer squared distribution . The interpretation of the exclusive results is strongly dependent on models of the form factors, for both the magnitude and q2 dependence . It should be noted that less than half of the available phase space is observable with reasonable signal-to-background . For the pseudoscalar case JVc6J is determined from the

R.J. Morrison/Production and decay of heavy flavors 50

80

ARGUS 0

z

30

60

20

40

10 0 -15 .0

-10 .0

-5 .0

0 .0

5.0

rroe(G"* I-)

10 .0

20

[GeV 2 /t 4 )

0 -10 0 .8

a Z

,_-

0.0 -1 .0

5

Fig. 13 . Continuum subtracted CLEO D01 missing mass spectrum used to find B(B- -i DOl-G) . Contributions from the various fit components are indicated.

Z

0.4

-5 0 MISSING MASS SQUARED (GeV/c2 )2

and KS45 models, respectively. The values derived -0 .5

0.0

0 .5

1 .0

from the ARGUE B- -+ D0L -D and the CLEO BO -+ D+l- G measurements using the WSB/KS models,

COSW .

and ,r = 1.13 ps, are given in Tables VI and VII.

--0.2

The interpretation of the vector cases involves more model dependence since three form factors are involved . The model dependence can be partially

removed by measuring the ratio of longitudinal to

transverse polarization, from the decay distribution of the D*+, as seen in Fig. 12b for example, and includ-

0 .0

0 .0

4.0

q2

8 .0

12 .0

ing this in the formula for IV~bl,

[GeV 2 /c 2 j

Fig. 12. ARGUS data on BO -* D*+l-p. (a) Missing mass squared distribution corresponding to the neutrino mass squared. The dotted curve is the sum of the backgrounds. (b) Angular distribution of the D*+ decay pion in the D* frame. The value of rL/rT derived from this plot is 0.85 f 0.45. (c) The q2 distribution comp with the model prediction of K6rner and Schuler. expression,

Table VU Value of IVebl Experiment

ivcbi

ARGUS

.046± .005

Inclusive

CLEO

.046 ± .005

n

CUSB

.047 ± .004

ARGUS

.046+*00Ô

B -. D*lv

B -o

ratio I+ = branching r - KPeIVcbI2 1012s-1,

CLEO

.043 ± .004

ARGUS

with Kpa =11.0, 8.0, and 8.3 in the GISW,44 BSW,33

CLEO

.043+*008 010

.051± .009

N

Dim

R.J. Morrison/Production and decay ofheavy Savors r = KvIV,

\1 + TT l

1012s-1~

where models give K  in the range 10-14 . Both AR GUS and CLEO measure rLlrT

Fs

.84 but with

large errors . This is the value predicted by either the K6rner-Schuler (KS) or Bauer, Stech, Wirbel (BSW) models . We take the value K = 12 and obtain the values for IVA given in Tables VI and VII. The vector cases are more precise because the branching ratios are larger and because the D* trick is used to suppress backgrounds . All of the results of Table VII for the value of

This result is somewhat sensitive to con ' the D*91-9 signal from D** events. ARGUS

' the

fact that B- decays to D or D* always lead to a DO in the final state since D*O decays to a DO 1~ the time. BO days on the other hand always give a D+ or a D*+ but the D*+ decays to a DO about of the time. ARGUS uses an approacL indicated by the equation, r-ra

- B B -+B*+1- v +B

-

where the correction is for the D*+ decays which re-

sult in a DO .

r

IVcbI are model dependent . It is encouraging that the exclusive measurements are in good agreement with

/ra =1.W f 0.23 f 0.14, a remit not sensitive to D** contamination if r /ra is c

the inclusive results, for which the free quark model

to 1.0. We see that both ARGUS and CLEO find the

of ACCMM46 is used to interpret the data.

lifetime ratio to be about 1.0 as expected.

ARGUS fnds,

A crucial measurement which is very important

The results for the lifetime ratio and the fraction

in itself, and is also important in that it is involved

of decays of the T(4s) to BOBO and B- B+ affect the

in determining other important quantities, is the life-

experimentally determined values of the mixing par

time ratio,

= 'rh_ g0

This has not yet been directly determined from decay length distributions but has just recently been determined from semileptonic branching ratios. From ' isospin conservation we have

B

s'-"x+l-l -

r(Bô --

x+`- r ,) =

r(B-

--,

x91-9),

where Xa and X+ are isospin partners . This implies that,

r_ =

B(B_ -Xo1-v) B(Bu-.X+l_

v)

for any pair of isospin doublets (XO, X+), or for the inclusive decays. ARGUS and CLEO take different approaches to this problem. Both ARGUE and CLEO find that the D and D* decays are about 68 f 16% of the inclu sive semileptonic decays. CLEO finds some evidence that the remaining decays are through D**'s. CLEO

measures r- /rO directly from the ratio, r = B(_B_-iD*o1 -v) = .85 ± .2+ .22 * r B(B°~D *+I-v)

rameter, r = B0B °~x . These values are given in Table VI. New mixing results from UAI, the first experiment to claim B mixing, were presented by P. Sphicas3 in the parallel session . Combining the

old and new data they find X = --"T = 0.1? f 0.05, where X is a combination of both Bd and Bs The most exciting new development in heavy quark physics involves the search for b --o- u transitions, and the first real progress in measuring Vbu " This is the most important unknown in the CKM matrix, with the exception of the CIA violating phase. The experimental sensitivities for CL-110 or AR GUS for exclusive b -+ u modes, such as DO -+ x+w-, are still a factor of or more from that needed to see these decays . Evidence was presented by CLE047

at the Cornell symposium in July of a 2.29 effect in

the endpoint region of the inclusive lepton spectrum. This was followed by results presented by ARGUU48 at the Stanford Lepton-Photon Symposium in August of a 3 .39 effect.

R.J. Morrison/Production and decay of heavy flavors

120

A Dalitz plot of the phase space available for b -~ c, and b --+ u decays is shown in Fig. 14, in the rest frame of the B. Since the B has a momentum of 300 MeV/c the kinematics in the lab are smeared a bit . There is a region above 2.3 GeV/c where the contribution to the lepton spectrum from b --+ c decays is very small and above 2.4 GeV/c it is zero . There is a big contribution from continuum background . After event shape cuts and the continuum subtraction, using data from below the T(4s) resonance, the sum of the electron and muon spectra from CLEO is as shown in Fig . 15 . The numbers of events are listed in Table VIII. After background subtraction the result is a partial cross section, v(2.3 --+ 2 .6) = 0 .33 ± .15 pb for the endpoint region . It is a bit uncomfortable that the excess should be larger in the low energy bin but just the opposite is observed in the experiment. Presumably this is just a quirk of the statistics. The ARGUE experiment takes o$ resonant background less frequently and has a less reliable background subtraction. They take advantage of their more hermetic detector to make tighter cuts and therefore have less background to subtract . In particular they require 1 GeV/c < Pn,i,, < 3.5 GeV, where Pmiae is the missing momentum associated with the neutrino, and the cosine of the angle between PI and Pn,iw to be < -0.5 . Also Pmiss may not be in a kinematic region common for two photon collisions. They have a second sample requiring an additional lepton. The results from ARGUS, all in

the region 2.3 GeV/c < Pl < 2 .6 GeV/c, are given in Table IX. The ARGUS result is expressed as the ratio of number of corrected b --> u events in the region PI > 2.3 GeV/c divided by the number of corrected b --+ c events in region 2 GeV/c < PI < 2.3 GeV/c . This ratio is (4 .5 f 1 .4 t 1)% .

The most important issue at this point is whether CLEO and/or ARGUS have seen a real signal. If the

standard model explanation of CP violation in K decays is correct, V6,ß must be non-zero and we expect 0 .04

<

I

f611:1

I

< 0.14. The endpoint region of the

LEPTON ENERGY (GeV) Fig. 14 . B semileptonic decay Dalitz plot. The kinematic boundaries of the decays B -+ Dtv, B -+ pfv, and B -+ 7rty are shown in the space of q2 versus charged lepton energy, in the B rest frame. The acceptance regions for AR vUS and CLEO shown are only approximate since the requirement, 2.3 GeV < El < 2 .6 GeV, is imposed in the lab where the B has about 300 MeV/c of momentum. Note that the allowed phase space for B -+ atv approaches the B* pole. Since B -+ rip is a longitudinal transition the center of the allowed lepton energy region is more strongly populated . The dominant transverse component of B -> ptv tends to populate the large lepton energy region. The missing momentum cut of ARGUS eliminates the low q2 region.

spectrum is very difficult from the theoretical point of view, due to the very large mass difference between the b and u quarks . A glance at the Dalitz plot of Fig . 14 where the kinematical boundaries for some of the many possible states are shown illustrates some of the problems. We note that the pion region extends very close to the B* pole and that the transversely polarized p's play an important ode . We also note that the P,d,, cuts of ARGUE limit the accepted phase space to a very small portion of the Dalitz plot . The values of

I~ I

which are allowed by the data,

using various models, are given in Table X. One can see that there is a substantial variation between the

R.J. Morrison f Production and decay ofheavy flavors

300

0141189-014

2400

5. SUMMARY

M 2000

250

There has recently been great p

quark physics, particularly with B decays.

in

and photoproduction of heavy quarks seem to S

1600

â 1200 s

f

c

-1200

f

-4150

0

ô 800

z

-1 100

400

50

' 1 -; I -; _1_ 01 1 1 2.4 2.6 2.0 2.2 2.8 P,j IGeV/c)

'-91

3.0

0

very consistent with perturbat-ve QCD. In addi-

tion to the B physics that gets our attention we note that ARGUS and CLEO are doing impressive charm has physics. The absolute branching ratio A, --,-~ PKx been determined but the D8 absolute branching ra-

tios are a serious problem. The ratio of Cabibbo sup. pressed decays of the D® to K+K- and r+r

found to be closer to theory. The decays B -+ DDS have been seen for the first time. Within cie very

poor current level of statistics hadronic B decays appear to be consistent with the Bauer, Ste h,

Fig. 15. Sum of the CLEO electron and muon momentum spectra for on resonance (filled squares), and scaled off resonance data (open circles), and fit to the off resonance data (dashed line), and the fit to the off resonance data plus the b -+ cev yield (solid line) . Note that the vertical scale for the inset (b) is different than for (a).

is now

irlu'l

prediction . No penguin diagrams have been seen .

The current sensitivity is too low*to observe exclusive b -+ u transitions . In the very important semileptonic decays there is

a problem with the large longitudinal polarization in

D+ - K*5e+v. There is now beautiful data on exclusive B semileptonic dec
models and it may even be that the models are all

and the ratio of

like b --* u transitions have been observed and at

charged and neutral B lifetimes is now measured to be close to 1.0. Finally, it appears that b --+ u tran-

ter data in the next few years. It will be well worth

level .

wrong in the same direction. Nevertheless, it looks about the right rate. We can expect significantly bet-

sitions have been observed and at about the expected

the effort to make comparable progress with the theory.

Table

CLEO Events in the Lepton Endpoint Region

12.3 GeV/c < Cont. Subtr. Yield

electrons

muons

37±11±3

26±12±2 11±4

Fakes b --* ctv Net Yield

Pg < 2.4 GeV/c ~.4 GeV/c < Pl < 2.6 GeV/c

4.0±1 .4

4.0± 1.4

16±4

20±4 -9±13±5

38±14±5 1.2 ±0.7 3.5 ± 1

muons 36±15±2 8.0±3 .8 3.5 ± 1

32±14±5

24±15±2

electrons

R.J. Morrison/Production and decay of heavy flavors

122

-ARGUS Events in the Lepton Endpoint Region 2.3 GeV/c < Pg < 2.6 GeV/c Sample 2 has two leptons in the event Sample

1

2

Sample

electrons

muons

electrons

muons

Yield

24

16

7

8

Continuum

4.2

2.6

0.7

0.7

Fakes

0.7

1.4

0.5

1.1

T, T'

0.5

0.3

0.2

0.1

b -+ clv

4.1

4.6

1.2

1.3

Net Yield is +e

14.5 ± 6.6 7.1 ± 6.2 4.4 ± 2.8 3.2 ± 0.9 21 .6

± 9.1

9.2

± 4.2

Table X-Values of I Vbn Model

lY I

be

CLEO ISGW 0.12± .03 WSB .08 ± .02 ACCMM .07± .02 KS -06± .02 WSB ACCMM

ARGUS -09± .02 -10± .03

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4. E. Elsen, "B-Asymmetry, Weak Couplings, and B-B Mixing from JADE," session on Flavor Physics, this conference . 5. H. Kvoha, "Results on B Physics from CELLO," session on Flavor Physics, this conference . 6. F. Porter, "Results on B-B Mixing from Mark U," session on Flavor Physics, this conference. 7. M. Reidenbach, "B-Physics Results from ARGUS," session on Flavor Physics, this conference; Yu . Zaitsev, "Evidence for b --+ u transitions from ARGUS," session on Flavor Physics, this conference . 8. D. Miller, "Results from CLEO," session on Flavor Physics, this conference .

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10 . Predictions for photoproduction are from R.K . Ellis and P. Nason, Fermilab-Pub-88/54-T (1988) .

11 . Predictions for hadroproduction are from P. Nason, S. Dawson, and R.K. Ellis, Nucl. Phys . B303, 607 (1988) ; P. Nason, S. Dawson, and R.K . Ellis,, Particle Physics 303, 607 (1988) . Also see Reference 22 . 12. Gerhard A. Schuler, "Theory of Heavy Flavor Production in PP Collisions," session on Flavor Physics, this conference. 13 . J.C . Anjos et al . (E691), Phys . Rev. Lett . 62, 513 (l989) . 14 . R.W. Forty (NA14), Proceedings of the XXIV Int'1. Conf. on High Energy Physics, Munich 1988, Springer-Verlag (Berlin, 1989), p. 668. 15 . A.K . Likhoded, session on Flavor Physics, this conference . Results were presented from the Serpakov experiment on prompt neutrino production by V.V. Ammosov et al., and from the experiment on prompt muon production by S.V . Belikov et al. 16. O. Botner, "Production of prompt electrons in the charm Pt region at E(CM)=GeV," session on Flavor Physics, this conference .

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R.J. Morrison/Production and decay of heavy flavors 19 . R. Hurst, "Results on Charm Hadroproduction with an Impact Parameter Trigger,"session on Heavy Flavors, this conference .

Phys. C28, 175 (1985) . 21 . M.G . Catanesi et al., Phys. Lett . B187,431 20. S.F. Biazi et al., Z. (1987) .

22. I.R. Kenyon et al., Proc. of the XXIV Int. Conf. on High Energy Physics, ed. R. Kotthaus and J. Kiihn, Springer-Verlag, 1989, p. 981. Also see Reference 23 . 23 . R.M. Baltrusaitis et 150 (l985) . 24 . H. Albrecht et (1989) .

at., Phys. Rev. Lett . 55,

al., DESY Preprint DESY 89-102

25 . F. DeJongh, Symposium on Heavy Quark Physics, Cornell (June 1989) . 26. M. Bauer, B. Stech, M. Wirbel, Z. Phys. C34, 103 (1987) . 27. References for Table IV. CLEO, Reference 8; E691, J.C . Anjos et al., Phys. Rev. Lett . 60, 897 (1988) ; J.C. Anjos et al ., Phys. Rev. Lett . 62, 125 (1989) ; J.C . Anjos et al., Phys. Lett . 228, -d 267 (1989) ; P. Karchin, "Weak Decays r" Particles," Symposium on Lepton and Interactions, Stanford (Aug. 1989); Mark III, J. Adler et at., SLAC-Pub-4952 (1989) ; S.R . Wasserbaech, SLAC-345 (1989) ; J. Adler et at., Phys. Rev. Lett . 65,1211 (1989) ; ARGUS, H. Albrecht et al., B153, 343, 1985 ; H. Albrecht et al., Phys. Lett. B195, 102 (1987) ; NA32, S. Barlag et at., CERNEP188-103 (1988) ; Mark II, G. Wormser et at., Phys. Rev. Lett. 61, 1057 (1988) ; NA14, G. Wormser, XXIVth Rencontres de :~i3riuad, Les Arcs (1989) . 28. K. Schubert, Symposium on Heavy Quark Physics, Cornell (June 1989). 29. S.R . Wasserbaech, SLAC-385 (1989) .

30 . S. Stone, "Session Summary-Heavy Quark Decay," Cornell Preprint CLNS 89/925 (1989) .

31 . H. Albrecht et al., Phys . Lett . 185B, 218 (1987) ; H. Albrecht et at., DESY 88-131 (1988) ; K. Schubert Symposium on Heavy Quark Physics, Cornell (June 1989). 32 . P. Avery et

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33 . M. Wirbel, B. Stech, and M. Bauer, Z. Phys. C29637(1985).

34 . J.C . Anjos et (1989) .

al., Phys . Rev. Lett. 62,1587

35 . J. Adler et al., Phys. Rev. Igitt. 62,1821 (1989) . 36. G. Martinelli, "Field Theory on the Lattice," Plenary talk at this conference. 37. K. Kleinknecht and B. Renk, Z. Phys. (1987) .

,

38 . J. Körner, "Angular Distributions in Exclusive Semileptonic B-Decays," scion in Flavor Physics, this conference ; J. Körner and G.A . Schuler, DES 89-123 (1989) .

Y

39 . J.G. Körner and G.A . Schuler, Z. Phys. , 511 (1988), and Erratum J.G. Körner, Mains Preprint MZ-TH/88-12 (1988) . M. Bauer and M. Wird, Heidelberg Preprint HD-THEP-88-21(1 ). F.J . Gilman and R.L . Singleton, SLAC Preprint SLAC-Pub-5065 (1989) .

40. J.C. Anjos et at., Phys. Rev. Lett. 62, 722 (1989) 41 . References for Table VI. ARGUS, Reference 7; H. Albrecht et at., DESY 89-082 (1989) ; H. Albrecht et al., Phys. Lett . 219B,121 (1989) ; Reference 29; M.V . Danilov, "B Physics from ARGUS; Symposium on Lepton and Photon Interactions, Stanford (Aug. 1989); CLEÔ, Reference 8; D.L . Kreinick, "B Physics from CLEO ; Symposium on Lepton and Photon Interactions, Stanford (Aug . 1989); N. Katayama, "Semileptonic Decays of B Mesons into Charmed Mesons, Symposium on Heavy Quark Physics, Cornell (June 1989); D. Bartoletto et al., Phys. Rev. Lett. , 1667 (1989) . 42 . D. Bartoletto et al., CLNS 89/92 (1989) .

43 . H. Albrecht et al., Phys. Lett. 219B, 121 (1989) ; H. Albrecht et at., DESY 89-082 (l989) .

44 . B. Grinstein et al., Phys. Rev. D 39, 794 (1989) . 45. J.G . Körner and G.A. Schuler, Z. Phys . C38, 511 (1988) . 46. G. Altarelli et al., Nucl. Phys. 208B, 365 (1982) . 47 . M. Procario, "Charmless B Decays at CLEO," Symposium on Heavy Quark Physics, Cornell (June 1989). Also see R. Fulton et at., CLNS 89/95, and Reference 8.

48 . M.V. Danilov, "B-Physics From ARGUS," Symposium on Lepton and Photon Interaction, Stanford (Aug . 1989). Also see Yu . Zaitsev, "Evidence for b ---+ u Transitions from ARGUS," session on Flavor Physics, this conference.