Measurement of the branching fractions and forward - backward asymmetries of the Z0 into light quarks

Using approximately 4.3 million hadronic Z^0 decays collected with the OPAL detector at LEP between 1990 and 1995, we measure the branching fractions of the Z^0 into up-type and down-type light quarks, R_q, and the forward-backward asymmetries, A_FB(q), using high-momentum stable particles as a tag. Adopting a method that employs double tagged events to determine the flavour tagging efficiencies, and assuming the flavour independence of strong interactions and SU(2) isospin symmetry, we measure: R_{d,s}/(R_d + R_u + R_s) = 0.371 +/- 0.016(stat.) +/- 0.016(syst.) and A_FB(d,s) = 0.068 +/- 0.035(stat.) +/- 0.011(syst.), assuming the branching fractions and forward-backward asymmetries of down and strange quarks to be equal. The results are essentially free of assumptions based on hadronisation models. These results are in agreement with the Standard Model expectations and are used to infer the left and right handed couplings of strange/down quarks to the Z^0, yielding g_L^{d,s} = -0.44^{+0.13}_{-0.09} and g_R^{d,s} = +0.13^{+0.15}_{-0.17}. The results for the up quark, R_u/(R_d + R_u + R_s) = 0.258 +/- 0.031(stat.) +/- 0.032(syst.) and A_FB(u)= 0.040 +/- 0.067(stat.) +/- 0.028(syst.), are fully negatively correlated and almost completely positively correlated, respectively, with the corresponding down-type results.

Note:

33 pages, LaTeX, 7 eps figures included, uses a4p.sty, submitted to Zeit. f. Physik C Report-no: CERN-PPE/97-063

electron positron: colliding beams
electron positron: annihilation
Z0: hadroproduction
Z0: hadronic decay
quark: pair production
angular distribution: asymmetry
particle identification: flavor
symmetry: SU(2)
Z0: branching ratio
coupling: (Z0 quark)

References(46)

Figures(0)

Weak Interactions with Lepton-Hadron Symmetry

- Phys.Rev.D 2 (1970) 1285-1292,
- Also in *Lai, C. H. (ed.): Gauge Theory Of Weak and Electromagnetic Interactions*, 203-210,
- In *Rosner, J.L. (ed.): New Particles*, 18-25,
- In *Lichtenberg, D. B. (Ed.), Rosen, S. P. (Ed.): Developments In The Quark Theory Of Hadrons, Vol. 1*, 193-200.,
- In *Bologna 1984, Proceedings, Fifty Years of Weak-Interaction Physics* 687-694
•
DOI:
- 10.1103/PhysRevD.2.1285

A Model of Leptons

Steven Weinberg
(
- MIT, LNS
)

- Phys.Rev.Lett. 19 (1967) 1264-1266,
- Also in *Lichtenberg, D. B. (ed.), Rosen, S. P. (ed.): Developments In The Quark Theory Of Hadrons, Vol. 1*, 157-159,
- In *Lai, C. H. (ed.): Gauge Theory Of Weak and Electromagnetic Interactions*, 185-187,
- In *Rosner, J. L. (ed.): New Particles*, 26-28
•
DOI:
- 10.1103/PhysRevLett.19.1264

Weak and Electromagnetic Interactions

Abdus Salam
(
- Imperial Coll., London and
- ICTP, Trieste
)

- Conf.Proc.C 680519 (1968) 367-377,
- Reprinted in *Lichtenberg, D. B. (ed.), Rosen, S. P. (ed.): Developments In The Quark Theory Of Hadrons, Vol. 1*, 160-170, and in *Lai, C. H. (ed.): Gauge Theory Of Weak and Electromagnetic Interactions*, 188-198,
- Also in *Rosner, J.L. (ed.): New particles* 29-39,
- Also in *Ali, A. (ed.) et al.: Selected papers of Abdus Salam* 244-254
•
DOI:
- 10.1142/9789812795915_0034

Review of particle physics. Particle Data Group

et al.

- Phys.Rev.D 54 (1996) 1, 1-720
•
DOI:
- 10.1103/PhysRevD.54.1

Final state photon bremsstrahlung in e+ e- ---> Z0 ---> hadrons as a tool for a precise measurement of the weak quark couplings

Peter Mattig
(
- Bonn U.
)
,
W. Zeuner
(
- CERN
)

- Z.Phys.C 52 (1991) 31-42
•
DOI:
- 10.1007/BF01412324

Studies of strong and electroweak interactions using final state photon emission in hadronic Z0 decays

OPAL

Collaboration

•

P.D. Acton

et al.

- Z.Phys.C 58 (1993) 405-418
•
DOI:
- 10.1007/BF01557697

Determination of quark electroweak couplings from direct photon production in hadronic Z decays

L3

Collaboration

•

O. Adriani

et al.

- Phys.Lett.B 301 (1993) 136-144,
- Phys. Lett. B301 (1993) 136-144 and CERN Geneva - CERN-PPE-92-209 (92/12,rec.Feb.93) 15 p
•
DOI:
- 10.1016/0370-2693(93)90735-Z

Study of prompt photon production in hadronic Z0 decays

DELPHI

Collaboration

•

P. Abreu

et al.

- Z.Phys.C 69 (1995) 1-14
•
DOI:
- 10.1007/s002880050001

First measurement of the strange quark asymmetry at the Z0 peak

DELPHI

Collaboration

•

P. Abreu

et al.

- Z.Phys.C 67 (1995) 1-14

A New method to determine the electroweak couplings of individual light flavors at LEP

J. Letts
(
- Bologna U. and
- INFN, Bologna
)
,
P. Maettig
(
- Dortmund U.
)

- Z.Phys.C 73 (1997) 217-228
•
DOI:
- 10.1007/s002880050311

The Structure of Jets in $e^+ e^-$ Collisions

Peter Mattig
(
- IPP, Canada and
- Carleton U.
)

- Phys.Rept. 177 (1989) 141
•
DOI:
- 10.1016/0370-1573(89)90057-4

An Improved measurement of R( $b$ ) using a double tagging method

OPAL

Collaboration

•

K. Ackerstaff

et al.

- Z.Phys.C 74 (1997) 1-17
•
DOI:
- 10.1007/s002880050366

The Lund Monte Carlo for Jet Fragmentation and e+ e- Physics: Jetset Version 6.2

Torbjorn Sjostrand
(
- Lund U., Dept. Theor. Phys.
)

- Comput.Phys.Commun. 39 (1986) 347-407
•
DOI:
- 10.1016/0010-4655(86)90096-2

The Lund Monte Carlo for Jet Fragmentation and e+ e- Physics. Jetset Version 6.3: An Update

- Comput.Phys.Commun. 43 (1987) 367
•
DOI:
- 10.1016/0010-4655(87)90054-3

High-energy physics event generation with PYTHIA 5.7 and JETSET 7.4

Torbjorn Sjostrand
(
- CERN
)

- Comput.Phys.Commun. 82 (1994) 74-90,
- CERN Geneva - TH. 7111 (93/12,rec.Jan.94) 17 p. and e: CERN th-7111-93
•
DOI:
- 10.1016/0010-4655(94)90132-5