Search for lepton-flavor violation at HERA

has been performed with the ZEUS detector using the entire HERA I data sample, corresponding to an integrated luminosity of 130 pb^{-1}. The data were taken at center-of-mass energies,

\sqrt{s}

, of 300 and 318 GeV. No evidence of lepton-flavor violation was found, and constraints were derived on leptoquarks (LQs) that could mediate such interactions. For LQ masses below

\sqrt{s}

, limits were set on

\lambda_{eq_1} \sqrt{\beta_{\ell q}}

, where

\lambda_{eq_1}

is the coupling of the LQ to an electron and a first-generation quark

q_1

, and

\beta_{\ell q}

is the branching ratio of the LQ to the final-state lepton

\ell

(

\mu

or

\tau

) and a quark

q

. For LQ masses much larger than

\sqrt{s}

, limits were set on the four-fermion interaction term

\lambda_{e q_\alpha} \lambda_{\ell q_\beta} / M_{\mathrm{LQ}}^2

for LQs that couple to an electron and a quark

q_\alpha

and to a lepton

\ell

and a quark

q_\beta

, where

\alpha

and

\beta

are quark generation indices. Some of the limits are also applicable to lepton-flavor-violating processes mediated by squarks in

R

-Parity-violating supersymmetric models. In some cases, especially when a higher-generation quark is involved and for the process

e p\to \tau X

, the ZEUS limits are the most stringent to date.

Note:

37 pages, 10 figures, Accepted by EPJC. References and 1 figure (Fig. 6) added

positron p: colliding beams
electron p: colliding beams
electron p: inclusive reaction
muon: electroproduction
tau: electroproduction
flavor: violation
leptoquark: mass
lower limit
leptoquark: coupling
new interaction: four-fermion interaction

References(70)

Figures(0)

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