Search for lepton-flavor violation ine+pcollisions at DESY HERA

Abstract

A search has been made for lepton-flavor-violating interactions of the type e ϩ p→lX, where l denotes a or with high transverse momentum, at a center-of-mass energy ͱs of 300 GeV with an integrated luminosity of 47.7 pb Ϫ1 using the ZEUS detector at HERA. No evidence was found for lepton-flavor violation and constraints were derived on leptoquarks ͑LQs͒ that could mediate such interactions. For LQ masses below ͱs, limits are set on eq 1 ͱ␤ lq , where eq 1 is the coupling of the LQ to an electron and a first-generation quark q 1 and ␤ lq is the branching ratio of the LQ to l and a quark. For LQ masses exceeding ͱs, limits are set on the four-fermion contact-interaction term eq ␣ lq ␤ /M LQ 2 for leptoquarks that couple to an electron and a quark q ␣ and also to l and a quark q ␤ . Some of the limits are also applicable to lepton-flavor-violating processes mediated by squarks in R-parity-violating supersymmetric models. In some cases involving heavy quarks and especially for lϭ, the ZEUS limits are the most stringent published to date.

The color dipole picture and the ratio ofR(W2,Q2)=σL/σTKuroda1, Schildknecht2 2008Physics Letters B140110View full textAdd to dashboardCite

“…The upper bound on the actively contributing dipole states must coincide with the upper end of the mass spectrum for copious diffractive production in γ * -proton scattering at any given energy. Indeed, the upper end of the diffractive mass spectrum at W = 225GeV at HERA [4] roughly coincides with the simple estimate based on the crude limit adopted in (4). In most applications [5] of the CDP, the upper bound on the qq mass is ignored.…”

“…The value of 1/ρ from (16) suppresses "small-size" longitudinal versus "largesize" transverse hadronic qq cross sections. Note that σ (qq) J =1 (16), is identical to helicity independence for (qq) vector-state scattering 4…”

“…Relation (16) follows immediately. 4 In the talk at DIS2008 given by one of us (D.S. ), helicity independence was erroneously presented as necessary.…”

Collider physics at HERA

“…The DIS inclusive and photoproduction dijet measurements discussed in some detail above are two of the most basic jet measurements at HERA. The follow-up measurements to these can be found in [122,116,123,124]. An example of a more complex measurement is that of multijet in DIS which is shown in Figure 15 [125,126].…”

Study of taupair production at HERA

“…The jet shape was characterised by six variables. Five of these variables were the same as those used in previous analyses [7,32]: the first and the second moment of the radial extension of the jet-energy deposition (R mean and R rms , respectively); the first moment of the energy deposition in the direction along the jet axis (L mean ); the number of subjets within the jet resolved with JHEP02(2011)117 a resolution criterion y cut [33] of 5 · 10 −4 (N subj ); and the mass of the jet calculated from the CAL cells associated with the jet (M jet ). The sixth variable, which was used for this analysis, was the sum of the distances in the η-φ plane between the jet axis and the tracks associated with the jet, R trk = N trk i (∆η 2 i + ∆φ 2 i ).…”