SLAC-PUB-7282 August 1996

ctIJ$-9bog,a-- PRELIMINARY MEASUREMENT OF D * / D PRODUCTION AND D* SPIN ALIGNMENT

AT THE Zo RESONANCE*

T.AKAG1 Representing the SLD Collaboration Stanford Linear Accelerator Center

Stanford University, Stanford, CA94309, USA.

Abstract Using hadronic Zo decays recorded by the SLD experiment at SLAC, we have measured the vector/(vector+pseudoscalar) production ratio, V/ (V + P ) , for the prompt charmed mesons, D*+ and D+ . Using the channels D*+ + Doat , Do -+ Ii--a+, and Do + K - a t a - r t , as well as D+ + K-?r+s- , we find V/(V + P ) = 0.61 f O.OS(stat.) f 0.03(BR), which disfavors the expectation of 0.75 from naive spin-counting. We have also measured the degree of D*+ spin alignment along the flight direction and find it to be consistent with zero for D*+ fractional momenta I E D . / E ~ ~ ~ ~ > 0.2. We compare these results with QCD model predictions.

*This work was supported by Department of Energy contract: DE-AC03-76SF00515 (SLAC)

Presented at the annual Divisional Meeting ( D P F 96) of the Division of Particles and Fields of the American Physical Society, 10-15 August 1996, Minneapolis, MN.

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United States Government Neither the United States Government nor any agency thereof, nor any of their employees, make any warranty, express or implied, or assumes any legal liabili- ty or respomibility for the accuracy, completeness, or usefulness of any information, appa- ratus, product, or process disdosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily cons4tute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessar- ily state or reflect those of the United States Government or any agency thereof.

1 Introduction

We present the preliminary results of a study of the production of charmed vector and pseudoscalar mesons in Zo decay events produced by the SLAC Linear Collider (SLC) and recorded by the SLC Large Detector (SLD) exper- iment '. The charmed mesons are tagged via the channels of D*+ + Don$ followed by Do ---i K-n+ ( K n mode) or Do ---i K-n+n-n+ (Knnn mode), and D+ ---i I(-n+n- . By comparing the number of D*+ and D+ mesons found *, we measured PV as a function of X I ) = ED/$, where 4 is the c.m. energy. We also measured the degree of D*+ spin alignment and its de- pendence on X D . This represents the first study of D*+ spin alignment in Zo decays.

2 Measurement of Pv

Tagged D mesons are mixture of cE and bb events. The c? contribution to the D mesons is extracted by subtracting bb contribution which is estimated by a two dimensional impact parameter technique. The measured numbers of D*+ and D+ mesons in e? events 2 , N,,D .+ and N,,D+ respectively, are related to the quantity PV via:

(1) Nc-D*t BY+ - P v B ~ * - -.- N e - ~ + Bro 1 - PvBr , '

where Br, = 68.1 f 1.0 f 1.3%3 is the branching fraction for D*+ ---i Don: , Bro = 3.84 f 0.13%, 7.50 f 0.4% and Br+ = 9.1 f 0.6% are the branching fractions for Do 4 I<-& , Do --f A'-n+n-n+ , and D+ I<-n+n- . We considered separately the number of D*+ formed from each Do decay mode and solved equation (1) in each bin of X D . We obtained results for PV shown in Figure 1. Averaging over the region X D > 0.4, we obtain Pv = 0 .678f0 .095 for the K n mode and PV = 0.519fO.llGfor the Knnn mode, where the errors are the sum in quadrature of the statistical errors and the branching fraction errors. The results are consistcent within the errors so we averaged them to obtain PV = 0.607 f 0.08T(slat.) f 0.029(BR) (PRELIMINARY). This result is not consistent with the naive spin-counting expectation of PV =0.75, but is in agreement with previous measurements from LEP experiments '. These results can also be compared with QCD calculations. PV as a function of X D is shown in Figure 1, together with the predictions of Braaten, Cheung and Yuan

and Suzuki '. The predictions are consistent with the data within errors.

*Charge-conjugate are implied unless stated otherwise.

2

i1.4 $1.2

Figure 1: Pv as a function of XD for (a) KT and (b) Knaa modes. The solid line represents the expectation of naive spin counting, the dotted line is the calculation by Suzuki, and the dashed line is the cal-

culation by Braaten, Cheung and Yuan

a 4

3

2

1

0

-1

-2 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 XU.

Figure 2: Fitted (Y as a function of XD* together with CLEO, HRS, and TPC data from lower c.m. energies. Model calcula-

tions are also shown (see text).

3

We measured the degree of D*+ spin alignment along the flight direction by considering the angle 8* between the momentum direction of the D*+ in the laboratory frame and the Do in the D*+ rest frame. We fitted the function:

Measurement of D*+ spin alignment

[l + acos28*], 3 - - 1 d N

N ~ C O S ~ * (6 + 2a) --

to angular distributions of cos8* for D*+ candidates after statistical subtra.c- tion of random combinatoric background (RCBG). The RCBG contribution was estimated using the Monte Carlo events normalized by the numbers of background events from the data. The fitted a , for each XD- bin are shown in Figure 2. These results are consistent with previous'measurements from CLEO ', HRS lo, and T P C at lower c.m. energies. QCD calculations by Suzuki

and, by Braaten, Cheung and Yuan8 are also shown in Figure 2. Suzuki's ca.lculation is disfavored by the data.

Acknowledgments

We thank the personnel of the SLAG accelerator department and the techni- cal staffs of our collaborating institutions for their outstanding efforts on our

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behalf.

This work was supported by Department of Energy contracts: DEFG02-91ER40676 (BU),

DE-FG02-91ER40672 (Colorado), DE-FG02-91ER40677 (Illinois), DEAC03-76SF00098 (LBL), DE-FG02-92ER40715 (Massachusetts), DE-AC02-76ER03069 (MIT), DE-FG06-85ER40224 (Oregon), DE-AC03-76SF00515 (SLAC), DE-FG05-91ER40627 (Tennessee), DE-FG02-95ER40896 (Wisconsin), DE-FG02-92ER40704 (Yale); National Science Foundation grants: PHY-91- 13428 (UCSC), PHY-89-21320 (Columbia), PHY-92-04239 (Cincinnati), PHY-88-17930 (Rut- gers), PHY-88-19316 (Vanderbilt), PHY-92-03212 (Washington); the UK Science and En- gineering Research Council (Brunel and RAL); the Istituto Nazionale di Fisica Nucleare of Italy (Bologna, Ferrara, Frascati, Pisa, Padova, Perugia); and the Japan-US Cooperative Research Project on High Energy Physics (Nagoya, Tohoku).

DE-FG03-91ER40618 (UCSB), DE-FG03-92ER40689 (UCSC), DEFG03-93ER40788 (CSU),

References

1. SLD Design Report, SLAC Report- 273, 1 (1984). 2. K. Abe et al., Phys. Rev. Lett. 75, 3609 (1995),

3. CLEO Collab., T. Butler et al., Phys. Rev. Lett. 69, 2041 (1992). 4. Particle Data Group, Phys. Rev. D 54, 1 (1996). 5. ALEPH Collab., D. Buskulic et al., 2. Phys. C C62, 1 (1994). 6. DELPHI Collab., P. Abreu et al., 2. Phys. C C59, 533 (1993). 7. M. Suzuki, Phys. Rev. D 33, 676 (1986). 8. E. Braaten et al., Phys. Rev. D 51, 4819 (1995),

K. Cheung and T. C. Yuan, Phys. Rev. D 50, 3181 (1994). 9. CLEO Collab., Y. Kubota et al., Phys. Rev. D 44, 593 (1991).

K. Abe e t al., SLAC-PUB- 7200, (1996).

10. HRS Collab., S. Abachi et al., Phys. Lett. B 199, 585 (1987). 11. TPC Collab., H. Aihara et al., Phys. Reb. D 43, 29 (1991).

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List of Authors

* K. Abe,(lg) K. Abe,(29) I. Abt,(13) T. Akagi,(27) N.J. W.W. A ~ h , ( ’ ~ ) t D. A~ton , ( ’~ ) K.G. Baird,(24) C. B a l t a ~ , ( ~ ~ ) H.R. Band,(32)

M.B. Barakat,(33) G. B a r a n k ~ , ( ~ ) 0. Bardon,(’‘) T. bark lo^,(^^) A.O. Bazarko,(lo) R. B e n - D a ~ i d , ( ~ ~ ) A.C. Benvenuti,(’) G.M. Bilei,(”)

D. BiselIo,(21) G. Blaylock,(‘) J.R. B~gar t , ( ’~ ) B. Bolen,(17) T. Bolton,(lo) G.R. Bower,(27) J.E. Brau,(”) M. Breidenba~h,(’~) W.M. Bugg,(28)

D. Burke,(27) T.H. B ~ r n e t t , ( ~ l ) P.N. Burrows,(15) W. Busza,(15) A. Calcaterra,(”) D.O. Caldwell,(‘) D. C a l l o ~ a y , ( ~ ~ ) B. Carnanzi,(ll)

M. C a r ~ i n e l l i , ( ~ ~ ) R. C a s ~ e l l , ( ~ ~ ) R. Ca~taldi,(’~)(“) A. Castro,(21) M. Cavalli-Sforza,(‘) A. C h o ~ , ( ~ ~ ) E. H.O. Cohn,(’’)

J.A. C ~ l l e r , ( ~ ) V. R. Cotton,(4) R.F. Cowan,(15) D.G. Coyne,(‘) G. Cra~fo rd , ( ’~ ) A. D’OIi~eira,(~) C.J.S. DarnerelI,(25) M. Da~ud i , ( ’~ )

R. De Sangro,(12) R. D e l l ’ O r ~ o , ( ~ ~ ) P.J. D e r ~ a n , ( ~ ) M. Dirna,@) D.N. Dong,(”) P.Y.C. Du,(’~) R. D~bois , ( ’~) B.I. Eisenstein,(13) R. Elia,(27)

E. E t ~ i o n , ( ~ ) D. Falciai,(22) C. Fan,(g) M.J. Fero,(15) R. Rey,(20) K. Furuno,(”) T. G i l l i ~ ~ a n , ( ~ ~ ) G. Gladding,(13) S. Gonzalez,(15) G.D. Halle~ell,(’~) E.L. Hart,(28) J.L. Harton,(’) A. H a ~ a n , ( ~ )

Y. Ha~egawa,(~’) K. Ha~uko,(’~) S. J . Hedges,(3) S.S. Hertzbach,(l‘) M.D. Hildreth,(27) J . Huher,(”) M.E. H~ffer,(’~) E.W. Hughes,(27)

H. Hwang,(”) Y . Iwasaki,(”) D.J. Jackson,(25) P. Jacques,(24) J . A. J a r ~ s , ( ’ ~ ) A S . Johnson,(3) J.R. Johnson,(32) R.A. Johnson,(7) T. Junk,(27) R. Kajikawa,(lg) M. Kalelkar,(24) H. J . I<ang,(26) I. Karliner,(13)

R. King,(27) R.R. Kofler,(’‘) N.M. I < r i ~ h n a , ( ~ ) R.S. Kroeger,(I7) J.F. Labs,(27) M. Langston,(’O) A. Lath,(15) J.A. L a ~ b e r , ( ~ ) D.W.G.S. Leith,(27) V. Lia,(15)

M.X. L ~ u , ( ~ ~ ) X. Liu,(‘) M. Loreti,(’l) A. L u , ( ~ ) H.L. Lynch,(27) J . Ma,(31) G. Mancinelli,(”) S. Manly,(33) G. Mantovani,(”) T.W. M a r k i e w i ~ z , ( ~ ~ ) T. Mar~yarna,(’~) H. M a ~ u d a , ( ~ ~ ) E. Mazzucato,(ll) A.K. M~Kerney,(~) B.T. Meadows,(7) R. Me~sner,(’~) P.M. M ~ c k e t t , ( ~ l ) K.C. M~ffeit,(’~)

T.B. Moore,(33) D. Muller,(27) T. Nagan~ine,(’~) S. Narita,(”) U. N a ~ e n b e r g , ( ~ ) H. M. Nu~sbaurn,(~) Y. Ohnishi,(lg) L.S. 0sborne,(l5) R.S. Pan~ini , (~’) H. Park,(’O) T.J. Pa~e l , ( ’~ )

I. Peruzzi,(’’)(’) M. Piccolo,(12) L. Piernontese,(lI) E. P i e r ~ n i , ( ~ ~ ) K.T. Pitts,(20) R.J. plan^,(^^) R. P r e p ~ s t , ( ~ ~ ) C.Y. P r e ~ c o t t , ( ~ ~ )

G.D. P u ~ i k a r , ( ~ ~ ) J . Quigley,(15) B.N. Rat~liff,(’~) T.W. Reeves,(30) 3. Reidy,(17) P.E. Ren~ing,(’~) L.S. Rochester,(27) P.C. Rowson,(’O) J.J . O.H. sax tor^,(^^) T. Schalk,(‘) R.H. S~hindler,(’~) B.A. Schumm,(14) S. Sen,(33) V.V. S e r b ~ , ( ~ ~ ) M.H. Shaevitz,(lo)

H. K a ~ a h a r a , ( ~ ~ ) H.W. Kendall,(”) Y. D. M.E. King,(27)

5

‘ I

* I

J.T. Shank,(3) G . Shapiro,(14) D.J. Sherder~,(’~) K.D. Shmakov,(”) C . S i m o p o ~ l o s , ( ~ ~ ) N.B. Sinev,(”) S.R. Smith,(27) M.B. Smy,(*)

J.A. Snyder,(33) P. S t a m e ~ - , ( ~ ~ ) H. Steiner,(14) R. Steiner,(l) M.G. Strauss,(l‘) D. SU,( ’~) F. Suekane,(”) A. Sugiyama,(lg) S . Suzuki,(lg) M. swart^,(^^)

A. Szumi10, (~~) T . Takaha~hi,(’~) F.E. Tay1or,(l5) E. Torrence,(15) A.I. Trandafir,(l‘) J.D. Turk,(33) T . Usher,(27) J . V a ’ v ~ a , ( ~ ~ ) C. Vannini,(23)

E. Vella,(27) J.P. Ve~iuti ,(~’) R. Verdier,(15) P.G. Verdini,(23) S.R. Wagner,(27) A. P. Waite,(27) S . J . Watts,(4) A. W . Weidemann ,(28) E.R. W e i ~ s , ( ~ l ) J.S. Whitaker,(3) S.L. White,(”) F.J. wick en^,(^^) D.A. Williams,(‘) D.C. Williams,(15) S.H. Williams,(27) S . Wi l10cq , (~~) R.J. Wilson,(’)

W.J. Wi~niewski,(’~) M. Woods,(27) G.B. Word,(24) J . W ~ S S , ( ~ ~ ) R.K. Yarnamoto,(l5) J.M. Yamartino,(15) X. Yang,(20) S.J. Yellin,(5)

C.C. Young,(27) H. Yuta,(”) G . Zapala~,(~’) R.W. Z d a r k ~ , ( ~ ~ ) C. Zeitlin,(20) and J. Zhou,(20)

(l)Adelphi University, Garden City, New York 11530 (2)INFN Sezione di Bologna, 1-40126 Bologna, Italy (3)Boston University, Boston, Massachusetts 02215

(4)Brunel University, Uxbridge, Middlesex UB8 3PH, United Kingdom ( 5 ) University of California at Santa Barbara, Santa Barbara, California

93106 (‘1 University of California at Santa Cruz, Santa Cruz, California 95064

(7 ) University of Cincinnati, Cincinnati, Ohio 45221 (‘1 Colorado State University, Fort Collins, Colorado 80523

(’1 University of Colorado, Boulder, Colorado 80309 (lO)Columbia University, New York, New Yorlc 10027

(l l)INFN Sezione di Ferrara and Universitli di Ferrara, I-44100 Ferrara, Italy

(“)INFN Lab. Nazionali di Frascati, I-00044 Frascati, Italy ( 1 3 ) University of Illinois, Urbana, Illinois 61801

(14)Lawrence Berkeley Laboratory, University of California, Berkeley, California 94 720

(‘5)Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (l‘) University of Massachusetts, Amherst, Massachusetts 01003

(17) University of Mississippi, University, Mississippi 38677 (lg)Nagoya University, Chikusa-ku, Nagoya 464 Japan

(’’) University of Oregon, Eugene, Oregon, 97403 (21)INFN Sezione di Padova and Universith di Padova, I-35100 Padova, Italy

6

(22)INFN Sezione di Perugia and Universith di Perugia, I-06100 Perugia, Italy

(23)INFN Sezione di Pisa and Universith di Pisa, I-56100 Pisa, Italy (24)Rutger~ University, Piscataway, New Jersey 08855

(25)Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 OQX United Kangdom

(26)Sogang University, Seoul, Korea (27)St an f ord Linear A cce le rat or Center, St an f o rd Universit y , St an f o rd,

California 94309

(29) Tohoku University, Sendai 980 Japan (30) Vanderbilt University, Nashville, Tennessee 37235

(31) University of Washington, Seattle, Washington 98195 (32) University of Wisconsin, Madison, Wisconsin 53706

(33) Yale University, New Haven, Connecticut 06511 t Deceased

(")Also at the Universiti di Genova (')Also at the Universiti di Perugia

University of Tennessee, Knoxville, Tennessee 37996

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Publ. Date (11) &

Sponsor Code (1 8) B ~ - W F X , I xr /R c - 414 1 - , DE I ER UC Category (1 9)

DOE