PROCEEDINGS SUPPLEMENTS

ELSEVIER Nuclear Physics B (Proc. Suppl.) 75B (1999) 20-23

Charmed Baryon and Semileptonic Physics at FOCUS Brian O'Reilly ~*

aDept, of Physics, University of Colorado, Campus Box 390, Boulder CO 80309, U.S.A.

Preliminary analysis indicates that we will exceed our goal of a factor of 10 increase in statistics over Fermilab photoproduction experiment E687. Some preliminary signals are presented.

1. D E S C R I P T I O N O F F O C U S

FOCUS (Photoproduct ion Of C h a r m with an Upgraded Spectrometer) is a Fermilab experi- ment dedicated to producing a high statistics charm sample. During the fixed target run in 1996-1997 the experiment recorded 6 × 109 trig- gers to tape. The goal of the experiment is to accumulate one million fully reconstructed charm decays. A combination of detector upgrades and software improvements were implemented in or- der to achieve this goal. For more details see ref- erence [2].

2. S E M I L E P T O N I C D E C A Y S

The decay rate expression for a pseudoscalar semileptonic decay is (neglecting terms of higher order in the lepton mass);

dF ~ G2F]V~IPa{jf+(q2)I2 + m~lf-(q2)12}, dq2 - 24~r 3

where Vcq is the relevant CKM matr ix element, P is the momen tum of the daughter hadron in the D meson rest f rame and f+ and f_ are the form factors for the decay. Table 1 is a comparison of the predicted yields from FOCUS with those ob- tained in E687. We anticipate measuring f+(0) with a statistical accuracy o f _ ~ 1%. Our semielec- tronic and semimuonic samples are of comparable size. We hope to reduce our systematic errors to the same level of accuracy as the statistical errors. We further expect to test of lepton universality and also measure f_ (0). Using the extra reach in q2 provided by the ~rlu mode, we can make a bet- ter parameter izat ion free measurement of f+ (q2)

* F o r t h e F O C U S C o l l a b o r a t i o n [1].

Table 1 Comparison of Semileptonic yields.

Mode Klu 7flu K*°lu E687 ___ 1250 ~ 78 "~ 875

FOCUS _ 4 0 K "~5K ~ 5 0 K

¢lu ~_ 120

10K

than can be made using the Klu mode alone. The ratio IV~dl/IV~,I will be measured to a statistical accuracy of _~ 2.0%.

Vector semileptonic decays are described by two axial form factors and one vector form fac- tor. Tradit ionally one measures the ratios, Rv =

y~__~ and R2 = ~ Table 2 shows a compar- • ' - 4 1 ( 0 ) "

mon between E687 and the best measurements of these ratios for the modes D + -+ K*°l+u (conjugate modes are implied throughout) and D~ -+ ¢l+u (statistical and systematic errors have been combined in quadrature)•

Prel iminary signals for D O --+ K I u and D + -+ K* l u are shown in Figure 1. With the large increase in statistics we anticipate measuring R2 and R~ to bet ter than 5% for the K* mode, and better than 10% for the ¢ mode. E687 reported the first statistically significant observation of the decay D + --+ p°l+u with a yield of 39 + 9 events [7]. We will measure the branching ratio w.r.t. K*°l+u and the form factors for this decay.

3. C H A R M B A R Y O N S

With a greatly increased sample of charmed baryons FOCUS should be able to build upon the work already reported by E687. E687 is the only experiment tha t measured the lifetimes of all the weakly decaying charmed baryons. Table 3 shows

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B. O'Reilly/Nuclear Physics B (Proc. Suppl.) 75B (1999) 20-23 21

FOCUS SEMILEPTONIC SIGNALS

(c~o !zoo~- ~eld=5532~87 Yield=4170:Jr 79

i i i.'.'." .F;t Histogram ::'[: Fit Histowom I

i~il. ~ r'isigoo, !;.::jsig~o~

~Yield=57~ 1 -i- 119 I |C~

140o~ .... : F;I I~oo F- " "

i...i Signcl ~o=--

.~: 1 F'i ws I

• ,=~ 1.,* )~) tEnu ) ~ q . . . . . .

: iYield=B1~3::E 126

,o ~- .... i nt i o o E . . . . . .

=g

Figure 1. Preliminary signals for the modes D *+ -+ D°rc+ ,D ° ~ K - l + v and D + -+ K * ( K - r c + ) l + u . These plots are from ~ 23% of the FOCUS data. [12]

the results obtained [8]. The current data sup- port v(f2e °) < r(~c °) < r(A +) < v ( : + ) . However, more precision is needed to distinguish between competing theories [10] [11].

Figure 2 shows the A + -+ p K - r r + signal ob- tained from _~ 44% of the FOCUS data set. We anticipate having in excess of 20,000 decays in this mode. The hatched regions in figure 2 indi- cate the signal and sideband events used in figure 3 for the solid(signal) and dotted(sideband) plots.

Figure 3 shows our first signals for the decays Z ++ -+ A%r + , X ° -q, A+~r - and E + --+ A%r °.

These are signals derived from ~_ 44% of the FOCUS data set. This figure also shows our sig- nal for the excited state A~(2625) -+ A%r+Tr - .

For comparison E687 published 68.8 4- 11.0 events in the E ° mode, 55.8 + 10.2 events in the E ++ mode and 24.4 + 6.3 for the A; (2625) [15] .

Table 2 Comparison of R2 and R~ measurements

Mode K*°lv E791 [3] K*Uh, E687 [4]

¢lv CLE2 [53 ¢lu E687 [6]

Exp. R2 R~ 0.72 4- 0.12 1.84 4- 0.14 0.784-0.20

1.04-0.4 1.04-0.5

1.744-0.39 0.94-0.7 1.84-0.8

Table 3 Charmed Baryon lifetimes from E687.

Baryon Lifetime (ps) w+ 0 34 +0.0. -~ • -o.o~ 4- 0.02 A + 0.215 4- 0.016 4- 0.008 =o 0 101 +'U~b ' 0.005 - - c • - 0 . 0 1 7 "+" flo n n ~ a + u . o ~ ' , ~ 0.028 " ' ~ u ' - - 0 . 0 2 0

Figure 4 shows our preliminary signals from the decays -=+ --+ E-~r+lr +, A + --+ E-K+1r +, and ~0 ~ - 7r + '

E687 reported the first conclusive evidence for the f~ and measured its mass [16] and lifetime [9]. We should be able to improve on this result using the FOCUS data.

4. S U M M A R Y

It is clear that we have achieved and indeed ex- ceeded our goal of a factor of 10 increase of statis- tics over E687. Large semileptonic samples will enable us to improve branching ratio and form factor measurements, and to study new modes. In the charmed baryon sector the news is equally good. A significant increase in statistics will al- low us to search for new decay modes and excited states, and perhaps to observe doubly charmed baryon states.

5. A C K N O W L E D G E M E N T S

We wish to acknowledge the assistance of the staffs of Fermi National Accelerator Laboratory, the INFN of Italy and the physics departments of the collaborating institutions. This research was supported in part by the National Science Foundation, the U.S. Department of Energy,

22 B. O'Reilly/Nuclear Physics B (Proc. SuppL) 75B (1999) 20-23

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250

200

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"~eid-3904-41 ~. Yield--321~74 [ ~ ~ -1678:bO3MeY 50 ~" ~ =1677*03MeV /

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i ~ r I , . . I . . , I . , : 0 ~ i . . , I . . . I . . |

~0.16 0.18 0.2 0.16 0.18 0.2 L=~ ++ - - ) /~--*vr* T=° _..> ,%--+~.-

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" , i ~..j ~_,~"~- 20 6~ : 1(19.8d:1,9 MeV i " --221.21

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o o ,½o o:2 ' "o !? ;o ' : ; o )-=+ ~ A~*n- /~° /~con > - -6

Figure 2. Preliminary A + -+ pK-Tr +. This plot represents _ 44% of the FOCUS data [13].

Figure 3. Ec and A* Signals. These plots are from ~_ 44% of the FOCUS data [13].

the Italian Istituto Nazionale di Fisica Nucle- are and Minsitero dell'Universit~ e della Ricerca Scientifica e Tecnologica, the Brazilian Conselho Nacional de Desenvolvimento Cientifico e Tec- noldgico, CONACyT-Mdxico, the Korean Min- istry of Education and the Korean Science and Engineering Foundation.

REFERENCES

1. Focus Collaboration Coauthors:

J.Link, M.Reyes, P.M.Yager (UC Davis); J.C.Anjos, I.Bediaga, C.Gobel, J.Magnin, I.M.Pepe, A.C.Reis, A.S£nchez-Hern~ndez, F.R.A.Sim$o (CBPF, Rio de Janeiro); S.Carrillo, E.Casimiro, H.Mendez, M.Sheaff, C.Uribe, F.Vazquez (CINVESTAV, Mdxico City); L.Cinquini, J.P.Cumalat,

B.O'Reilly, J.E.Ramirez 2, E.Vaandering (CU Boulder); J.N.Butler, H.W.K.Cheung, I.Gaines, P.H.Garbincius, L.A.Garren, S.A.Gourlay, P.H.Kasper, A.E.Kreymer, R.Kutschke (Fermilab); S.Bianco, F.L.Fabbri, S.Sarwar, A.Zallo (INFN Frascati); C.Cawlfield, R.Gardner 3 , E.Gottschalk 4, K.S.Park, A.Rahimi, J.Wiss (UI Champaign); Y.S.Chung, J.S.Kang, B.R.Ko, J.W.Kwak, K.B.Lee, S.S.Myung, H.Park (Korea University, Korea); G.Alimonti, M.Boschini, B.Caccianiga, A.Calandrino, P.D'Angelo, M.DiCorato, P.Dini, M.Giammarchi, P.Inzani, F.Leveraro, S.Malvezzi, D.Menasce, M. Mezzadri, L.Milazzo, L.Moroni, D.Pedrini,

2Present Address: Univ. of Colorado, Boulder 3Present Address: Indiana University, Bloomington 4Present Address: Fermilab

B. O'Reilly/Nuclear Physics B (Proc. Suppl.) 75B (1999) 20-23 23

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- , , . - - ÷ ÷ .== "-).= ~ ~

" f~d - 55:1:10 /t~= 2,4734- 0.002 ~V

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"field= 36+7 hM- 2.283:i: 0.002 Ge~

1=10.4::1:1 .SUeV

2.4 2.6

h~ + -+ --K*C

Figure 4. Preliminary signals involving E-. These plots represent ~ 40% of the FOCUS data set [14].

F.Prelz, A.Sala, S.Sala (INFN and Milano); T.F.Davenport III (UNC Asheville); V.Arena, G.Boca, G.Bonomi, G.Gianini, G.Liguori, M.Merlo, D.Pantea 5, S.P.Ratti, C.Riccardi, L.Viola, P.Vitulo (INFN and Pavia); A.Fernandez (Puebla, M4xico); A.M.Lopez, L.Mendez, A.Mirles, E.Montiel, D.Olaya 6,j.E.Ramirez, C.Rivera, Y.Zhang 7 (Mayaguez, P u e r t o Rico); N.Copty, W.E.Johns s, M.Purohit, J.R.Wilson (USC Columbia); K.Cho, T.Handler (UT Knoxville); D.Engh, M.Hosack, M.Nehring 9, M.Sales,

5Present Address:Nat . Inst . of Phys. and Nucl. Eng., Bucharest , Romania 6present Address: Univ. of Colorado, Boulder 7Present Address: Lucent Technology S Present Address: Univ. of Puer to Rico, Mayaguez 9presen t Address: Adams State College, Alamosa, CO

P.D.Sheldon, M.Webster (Vanderbilt); K.Stenson (Wisconsin, Madison); Y.Kwon (Yonsei University, Korea).

2. D. Pedrini et al., Overview of FOCUS and a report on charmed mesons in FOCUS, In These Proceedings.

3. E.M. Aitala et al., Phys. Rev. Lett. 80 (1998) 1393.

4. P.L. Frabetti et al., Phys. Lett. B307 (1993) 262.

5. P. Avery et al., Phys. Lett. B337 (1994) 405. 6. P.L. Frabetti et al., Phys. Lett. B328 (1994)

187. 7. P.L. Frabetti et al., Phys. Lett. B391 (1997)

235. 8. P.L. Frabetti et al., Phys. Lett. B427 (1998),

211; Phys. Rev. Lett. 70 (1993), 1755; Phys. Rev. Lett. 70 (1993) 2058.

9. P.L. Frabetti et al., Phys. Lett. B357 (1995) 678.

10. M.B. Voloshin and M. A. Shifman, Sov. Phys. JETP 64 (1986) 698; B. Guberina, R. Riickl and J. Trampeti6, Z. Phys. C33 (1986) 297; H. Y. Cheng, Phys. Lett. B289 (1992) 455.

11. B. Blok and M. Shifman, "Lifetimes of Charm Hadrons Revisited. Facts and Fancy", Third Workshop on the Tau-Charm factory, 1-6 June 1993, Marbella, Spain, l~ditions Fronti~res. TPI-MINN-93-55-T, 1991; V. Chernyak, "Calculation of the D and B Me- son Lifetimes and the Unitarity Triangle Pa- rameters", Budker Nuclear Physics Institute preprint, Budker INP 95-18; I. I. Bigi, "Life- times of Heavy-Flavour Hadrons - Whence and Whither?", Sixth International Sympo- sium on Heavy Flavour Physics, 6-10 June 1995, Pisa, Italy. UND-HEP-95-BIG06, 1995.

12. L. Cinquini, Private Communication. 13. E. Vaandering, Private Communication. 14. J. E. Ramirez, Private Communication. 15. P. L. Frabetti et al., Phys. Lett. B365 (1996)

461. 16. P. L. Frabetti et al., Phys. Lett. B338 (1994)

106.