RECENT RESULTS FROM THE MARK-J EXPERIMENT AT PETRA

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Submitted on 1 Jan 1982

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RECENT RESULTS FROM THE MARK-J EXPERIMENT AT PETRA

J. Burger

To cite this version:

J. Burger. RECENT RESULTS FROM THE MARK-J EXPERIMENT AT PETRA. Journal de

Physique Colloques, 1982, 43 (C3), pp.C3-63-C3-66. �10.1051/jphyscol:1982312�. �jpa-00221865�

JOURNAL DE PHYSIQUE

CoZZoque C3, supple'ment a u n o 12, Tome 43, de'cembre 1982 page C3-63

RECENT

RESULTS

FROM THE MARK-J EXPERIMENT AT PETRA J.D. ~ u r ~ e r "

Deutches EZektronen-Synchrotron, DESY, N o t k e s t r a s s e 85, 2000 Hamburg 52 F.R. G.

The forward-backward charge asymmetry in muon pairs due to interference between the electromagnetic and weak channels in e+e- -t p+p- has been measured using 3209 events obtained in data taking for 63.7pb-I of integrated 1uminosity.After correcting the data for the asymmetry produced by first order radiative effects in the electro- magnetic channel, the value of the asymmetry was calculated

*

On Leave of Absence from Massachusetts Institute of Technology Cambridge/

Massachusetts 02139/USA

are the number of pairs where the .CI- makes an angle 8 less (or greater) than IT with the direction of the incoming electron. For Icosel< 0.8, where the acceptance of the MARK-J detector is uniform, we obtain AW= -8.7%*1.8%, where the error shown is statistical. This may be compared with the prediction of the Glashow-Weinberg-Salam theory for the same region of cos8, which is -7.4%*0.3%, where a correction has been made for photon emission from the inital state going into the weak channel.

Possible sources of systematic error have been studied and found to be small.

The acceptance asymmetry of the detector has been measured with cosmic rays and the result is consistent with zero (the value obtained was -0.7%+1 .4% from % 20x10~ cosmic ray muons which pass through the intersection point with measured momenta above 10 GeV). Any acceptance asymmetry and many other sources of systematic error were removed by switching the magnet polarity regularly during data taking so that acceptance asymmetry reverses sign for positive and negative muons. Since equal amounts of data were taken with both polarities we are confident that systematic errors are less than

1% in our determination of the charge asymmetry. Fig. 1 shows the data as a function of cos8 and symmetric and symmetric-antisymmetric parametrizations of the data.

A similarly defined forward-backward charge asymmetry has also been obtained for -r pairs.

The T pairs were idegtified in the case where one T decays into ~ V V within the detector

acceptance and the other gives an electromagnetic or hadronic shower. For 649 T pairs we obtain A ~ +

-

⁼ -7.4%f4.6% in the detector acceptance.

T T

Assuming the world average branching ratio of 17% for T -+ uvv we obtain cutoff parameters of A-> 120 GeV, A+> 193 GeV with 95% confidence level. Alternatively we can fit for the branching ratio and get BR (T -t ~ V V ) = 16.3%+1.6%.

12

0 9

i $ 0 6 - 0 3

0 0

- 0 8 - 0 L 0 0 OL (18 2

We have made a simultaneous fit for gV and

~ K € I g using: 1) angular distribution of Bhabha

A

Fig. 1 pairs assuming a 3% point to point systematic High energy muon pairs data correct- error on the data shown in ~ i 2, 2) auu and ~ . ed for QED charge asymmetry. The OTT as a function of

6

with 3% and 10% system- solid line is Fl (l+cos2%)+ F2cos8 atic errors. A 3% systematic error on the fit to the data. The broken line is

1 +cos28.

-

l; = 346 GeV

- -

\

,

\ /

,

\

. _-

^{I--- ,}

^,

I

-

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1982312

JOURNAL DE PHYSIQUE

Fig. 2

Difference between high energy Bhabha scattering data and the point-like QED prediction. The solid line is the GWS

prediction for sin28 = 0.23. -

W

Ices e l

luminosity was assumed in 1) and 2). 3) The y pair and T pair forward-backward charge asymmetries with 1% and 2% systematic errors assumed respectively. This gives g2 = -0.02*0.05 and

g4

⁼ +0.28*0.06 or equivalently si1128~0.26+0.09 where the errors sffown are combined systematic and statistical errors. We have also put a limit on the size of a term which could occur in the effective neutral current Hamiltonian

in non standard theories or in the standard theory with more than one Z boson. We find C < 0.021 (95% confidence level. Best fit is C =

-

0.004).

If we combine a fit to the weak neutral current effects on the hadron total cross section with the lepton data fit, using a 3%

point to point systematic error on the data for R shown in Fig. 3 and a 6% overall

L normalization error,we get sin28,= 0.30+0.06.

a

In inclusive muon events we have pre-

QCD . w e a k effects

i

liminary results for the semi leptonic

branching ratios of b and c quarks:

b + pvX and c + pvX as well as for forward- backward charge asymmetries in these decays.

c and b are identified by cuts on the angle

8 12 16 20 21 28 32 36

between the muon and the event thrust axis S (GeV) and on P, and 0,. The table below shows the Fig. 3 number

02

b andUc candidates from the high Experimental values of R used in energy data

(6

% 34.5 GeV) and Monte Carlo

predictions for these decays and background.

combined fit for sin2@,.. Solid line _w is QCD prediction including weak effects.

TABLE I

If we adjust the sernile~tonic branching ratios to fit the data we obtain B(c + pX) = 9.8%f1.1%+2.0% and B(b -t uX) = 9.3%f2.9%f2.0%, where the first errors shown are statistical and the second are estimated systematic errors, coming mostly from an assumed 50% uncertainty in the Monte Carlo results in decay and ~unchthrough-

J.D. Burger C3-65 Preliminary values of forward-backward charge asymmetries for these decays are shown in the next table:

TABLE I1

Data measured

+ 7% ? 5%

-20% +lo%

Charm Sample A(c) Bottom Sample A(b)

The quark direction is estimated to be the event thrust axis on the side containing the muon. The asymmetry values are diluted from the GWS predictions (Acc = +13%, Abb= -23% for g~ = 112 and & = 35 GeV) by the background.

We have made an analysis of jet properties using the variables Xi=Ei/Ebeam

(the energy of the ith jet normalized to the beam energy) to compare our data with models containing scalar and vector gluons.

We use the data to populate a Dalitz plot shown in Fig, 4 where only the shaded area is allowed after the indices are ordered according to jet energy. Cuts are made to separate a region of the plot containing clear three jet events and the distribution of the events in the plot is fit to Monte Carlo predictions for scalar and vector gluon models )

.

TABLE I11

DATA

C U l 02,> 4 5 O x,> 0 2

Fig. 4

Dalitz plot of hadronic data where the three axes are normalized jet energies.

b and c show only the area of the plot We have also analysed the distribution allowed by ordering XI> x2> x3. Two sets of events according to the variable of cuts were made to isolate three jet

events

. _{- s -}

_-

6 . 0 . 2 2

X I + X

I = . 2

*dlO/V) ,

: which is the theoretical ratio of the scalar

-.. scalar differential cross section to the vector.

Monte Carlo expected + 4%

+

^1%

-

^5%

+

^1%

cuts

'23 > 450 X j > 0.2 8 1 2 < 1 6 5 0 5 7

u.0

- v e c t ~ : :

, . . . . - .

:----'

Vector Model

Fig. 5 shows the data and the Monte Carlo pre- dictions for scalar and vector gluons. The

3.0

2.0

1 . 0

0 . o L

X 59

Scalar Model

vector model gives

x2

= 10.5 and the scalar .

-

X2 = 98.1, both for 9 degrees of freedom. Thus

the data strongly favor a vector gluon,

. We have also made an analysis of energy-

: energy correlations in order to make a

. : determination of as. In particular we have fit : the asymmetry in the correlation function

. . . , . . .

.

^.

.

^{1 dC}

degrees of freedom

72 67

X2

110 103

D(x) =

--

^{I dC}

0.0 0.1 0.2 IS,") 0.3 0 . U 0.3 o dcosX

('x) - 3

dcosX

(X)

Fig. 5 which should be proportional to as in first Distribution of hadronic data in order QCD~).

the variable S/V along with Fig. 6 shows the asymmetry times the bin Monte Carlo predictions. width as a function of the cosine of the

degrees of freedom

72 67

C3-66 JOURNAL DE PHYSIQUE

correlation angle for (a) hadron data uncorrected for detector acceptance, (b) Monte Carlo prediction,

(c) a first order analytical prediction (BBEL)~) without detector acceptance corrections.

A preliminary fit in first order gives as = 0.16?0.01 and to second order as = 0.14'0.01

(A

= 200 MeV).

lo-'

Fig. 6

J Asymmetry in the energy correlation

- ₅

function times the bin width for

-

8 hadronic data. The solid line is

a the Monte Carlo prediction. No

Z3

lo-3

corrections were made for detector

n acceptance. The dashed line is the

f

5 BBEL analytic formula.

3 1 0 4

4

1

- 0 9 6 -0.72 -068 -0.2L 0.0

cos

x

References: 1) J. Ellis, M.K. Gaillard and G.G. Ross, Nucl. Phys. Bx,253 (1976);

erratum

m,

516 (1977).

A. deRujula et al., Nucl. Phys. B138, 387 (1978).

2) C. Basham, L. Brown, S. Ellis, S. Love, Phys. Rev. Lett.3, 1585, (1978); Phys. Rev. D B , 2018 (1979), ibid D 2 , 2383 (1981).