Search for new physics in e ± q contact interactions at HERA

Deep-inelastic e(+/-) p scattering at high squared momentum transfer Q(2) up to 30 000 GeV2 is used to search for eq contact interactions associated to scales far beyond the HERAcentre of mass energy. The neutral currentcross section measurements dsigma / dQ(2), corresponding to integrated luminosities of 16.4 pb(-1) of e(-) p data and 100.8 pb(-1) of e(+) p data, are well described by the Standard Model and are analysed to set constraintson new phenomena. For conventional contact interactions lower limits are set on compositeness scales A ranging between 1.6-5.5 TeV. Couplings and masses of leptoquarksand squarks in R-parityviolating supersymmetry are constrained to M / lambda > 0.3-1.4 TeV. A search for low scale quantum gravityeffects in models with large extra dimensionsprovides limits on the effective Planck scaleof MS > 0.8 TeV. A form factor analysis yields a bound on the radius of light quarks of R-q < 1.0 10(-18) m. (C) 2003 Published by Elsevier B.V.