Leptoquarks and compositeness scales from a contact interaction analysis of deep inelastic e±p scattering at HERA

Abstract

Abstract.A contact interaction analysis is presented to search for new phenomena beyond the Standard Model in deep inelastic e ± p → e ± hadrons scattering. The data are collected with the H1 detector at HERA and correspond to integrated luminosities of 0.909 pb −1 and 2.947 pb −1 for electron and positron beams, respectively. The differential cross sections dσ/dQ 2 are measured in the Q 2 range between 160 GeV 2 and 20, 000 GeV 2 . The absence of any significant deviation from the Standard Model prediction is used to constrain the couplings and masses of new leptoquarks and to set limits on electron-quark compositeness scales and on the radius of light quarks.

Hunting for contact interactions at HERA with polarized lepton and proton beams

“…For instance, we have chosen the systematic errors on the unpolarized cross sections to be ∆σ unpol syst /σ unpol = 3%, for the entire Q 2 domain. With this choice we recover to a good accuracy the limits on Λ presented in [28]. However, this difference in the analysis strategy in comparison to [40], gives some discrepancies on the Λ bounds for destructive interferences (ǫ = −1), obtained from the analysis of the unpolarized cross sections.…”

“…The main uncertainties come from luminosities measurements which produce an unknown normalization factor f [9,28]. In the present analysis we do not take 4 There are some larger values in the low Q 2 region due to energy calibration [28], but we are not concerned with this domain of Q 2 .…”

Leptoquark signals via ν interactions at neutrino factories

“…It is clear that with the increase in baseline length, the LQ event rate falls off and neutrino oscillations are the main source events examined here. At near-site experiments, on the other hand, the events mainly arise from new interactions and can thus be used to constrain the theory (figures [3][4][5][6][7][8]. In particular one can obtain constraints on LFV couplings between the first and third generation, the bounds on which are generally not available.…”

“…There have been numerous phenomenological studies to put constraints on LQ from low energy flavour changing neutral current (FCNC) processes which are generated by both the scalar and vector LQ interactions, since there is no reason why the quark-lepton couplings with LQ have to be simultaneously diagonal in quark and lepton mass matrices. Direct experimental searches for leptoquarks have also been carried out at the e p collider and bounds obtained [7,8]. In this letter, we compute and analyse the contribution of mediating LFV LQ in ν(ν)-N charged current (CC) interactions, including constraints obtained from low energy phenomenology.…”

Heavy quark production via leptoquarks at a neutrino factory

“…Direct experimental searches for leptoquarks have also been carried out at the e-p collider and bounds obtained [11,12] and in particular bounds obtained from B meson decays (B −→ l + l − X, where l + l − = µ + µ − , e + e − ) and also bounds derived from meson-antimeson (BB) mixing would have direct bearing on the processes considered here. This is because low energy limit puts stringent bound on effective four-fermion interactions involving two leptons and two quarks and since at the NF the centre of mass energy in collision is low enough, we can consider the neutrino-quark interaction as an effective four-fermion interaction.…”