MARK II RESULTS AT PEPSLAC-LBL-Harvard Collaboration

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Submitted on 1 Jan 1982

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MARK II RESULTS AT PEPSLAC-LBL-Harvard Collaboration

G. Trilling

To cite this version:

G. Trilling. MARK II RESULTS AT PEPSLAC-LBL-Harvard Collaboration. Journal de Physique

Colloques, 1982, 43 (C3), pp.C3-57-C3-58. �10.1051/jphyscol:1982310�. �jpa-00221863�

JOURNAL DE PHYSIQUE

CoZZoque C3, suppl6ment au n o 1 2 , Tome 43, de'cembre 1982 page C3-57

MARK

I 1

RESULTS AT PEP

SLAC-LBL-Harvard Collaboration Presented by G.H. Trilling

Department of Physics, U n i v e r s i t y o f C a l i f o r n i a , Berke Zey, California 94720, U.S.A.

1. Properties of T Decays

The addition of a high precision vertex drift chamber has permitted a highly improved T lifetime measurement, namely T~ = (

3.3

f

0.57

t

0.60)

x 10-l3 s

,

to be com- pared with the standard expectation of (2.8 rt 0.2) x s

.

^{The T} decay charged multiplicity distribution has been measured from a sample corresponding to 20 pb-l.

The results are Bl = 1

-

^{B3 =}

(86 + ³

^{f 1)%, B?}

< 0.7% (95%

C. L. ). It follows that most of the unmeasured, uncalculated T decay modes produce one charged prong.

2. Measurements of R and s(da/dx)

R has been measured in large statistics samples at E c m = 5.2,

6.5

and 29 GeV, the lower two energies from Mark I1 operation at SPEAR. The results at the three energies are

3.90

% 0.02 f 0.25, 3.95

+ 0.05

f 0.25, and

3.90

f

0.05

f 0.25 respectively.

These numbers agree with PETRA results, with QCD expectations, and show no evidence for the t quark at 29 GeV. Measurements of s(da/dx) at the three energies exhibit substantial scaling violation with the 29 GeV data falling significantly below the low energy data for X

>

0.2.

3.

^D* Production and Charm Fragmentation

- + +

The sequence D*+ + DOO+ -, K n n (and charge conjugate) has been used in a 31 pb-' data sample at

29

GeV to study the fragmentation of the charm quark into a charmed meson (the D*). Clear evidence for D*+ production (25 events) in the region

0.4 <

Z

<

1.0 (2 s

~E~*/Js)

has been observed, but there appears to be no signal for

Z

< 0.4.

The inclusive cross section a(D*+)

+

^{a(~*) is 0.3 f 0.13 nb,} and implies

that c-quark fragmentation into D* is dominant at

29

GeV. The fragmentation func- tion s(du/dz) appears to peak at Z --

0.5 (0.6

pb GeV ) 2 and drop off at higher values of Z. A Do lifetime measurement based on 7 particularly well-measured Do gives

4.

Inclusive Electrons From Hadronic Events

Inclusive electron production in hadronic events has been studied in a data sample corresponding to integrated luminosity of

35

pb-l. From 1013 candidate tracks with p

>

1 G~V/C, a signal of

388 * ⁹⁵

electrons is extracted after subtrac- tion of various backgrounds. For each candidate event containing an electron, a thrust axis is constructed and the electron transverse momentum pT relative to that

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1982310

C3-58 JOURNAL DE PHYSIQUE

a x i s determined. I n c l u s i v e e l e c t r o n r a t e s p e r hadronic event f o r various lower l i m i t s on momentum and t r a n s v e r s e momentum (p, pT) a r e a s follows: 0.09+-0.01+-0.02

(1, O ) , o.035+0.004+0.006 (1, o.5), o.041+0.004+0.006 (2, 0 ) . we have made a

f i t t o t h e observed j o i n t p,pT d i s t r i b u t i o n of t h e e l e c t r o n s i n terms of t h e follow- ing f r e e parameters: B(C + e ) ( t h e average charm semileptonic branching r a t i o ) ,

~ ( b -, e ) and a parameter eb defining t h e shape of t h e b fragmentation function from t h e formula

The charm fragmentation parameter E i s taken t o be 0.3 t o agree with t h e previously discussed D* data. The f i t leads t o e l e c t r o n populations i n various p,pT bins i n e x c e l l e n t agreement w i t h t h e data, and g i v e s f o r t h e parameters,

The branching r a t i o values a r e i n good agreement with o t h e r measurements, and t h e small value of cb implies a highly forward peaked b-quark fragmentation function.

5. Search f o r Point-Like Charged Spin-Zero P a r t i c e

We have searched f o r p o i n t - l i k e charged s p i n l e s s p a r t i c l e s H' produced v i a t h e

+ -

r e a c t i o n e e + H+K i n a sample corresponding t o an i n t e g r a t e d luminosity of 14 pb-l. TWO s e t s of f i n a l s t a t e s were considered, namely (1) H+ T+V, H- + as -+ hadrons and ( 2 ) H' + T'V. Results of t h i s search i n d i c a t e t h a t H' of masses between about 2 and 10 GeV/c2 a r e excluded a s long a s they have s i z a b l e branching r a t i o s t o -rv ( a t l e a s t 5 - 10% f o r most of t h e above mass range).