Electromagnetic muon-pair contibutions in neutrino trimuon production

Abstract

The electromagnetic production of p+p-pairs in charged-current neutrino scattering is calculated for a scaling parton model. This process gives trimuons at 0.4 X of the single-muon rate at 200 GeV. Energy and invariant-mass distributions for radiative trimuons are presented and characteristic features of azimuthal correlations are discussed.The trimuon events'-3 reported in deep-inelastic neutrino scattering m,ay signal important new physical effects such a s heavy-lepton, heavyquark, o r Higgs-boson p r o d~c t i o n .~ However, t h e r e a r e mechanisms in "old" physics that can produce trimuons, and these must b e evaluated before any new physics can be fully separated. One such mechanism is the associated production of c h a r m plus anticharm in the recoiling hadron jet, with muonic c h a r m decays; quantum-chromodynamic calculations indicate that this gives few trimuons, of o r d e r of the single-muon r a t e a t 200 GeV.' A m o r e direct mechanism i s tKe electromagnetic production of muon p a i r s via virtual photons radiated f r o m the final muon and the interacting parton; in the present paper we calculate and discuss the contributions f r o m this process . 6 We find non-negligible r a t e s f o r the radiative contributions to trimuon production. At E =200 GeV, the r a t e f o r vN-p -p+ p -X is 0.4 x of the single-muon r a t e . Averaged over the F e r m ilab quadrupole triplet spectrum, f o r E > 100 GeV, the predicted r a t e f o r vN including the E, > 4 GeV acceptance cuts i s tributions of the three graphs in F i g . 1 a r e x u (fi,)y,(i -y5)u(lrl) , where E, = i~( k , )~,~~( k , ) /~~ and q = k 3 + k,. The cornplete matrix element f o r distinguishable trileptons is We note that 31130 for E = q , a s required f o r gauge invariance. F o r a r e a l photon with a polarization vector E , Eq. (3) is identical to the bremsstrahlung calculation of Kiskis .7 F o r p-p+ p-production we must antisymmetrize the matrix element, (%??) radiative = 0 . 2 5 x lo-, .(1) %L(P-p + p-1 = W k 2 , kq) -314k4, 4 ) , (4) and divide the phase space by a factor of 2 . This i s a non-negligible background to the r eTo evaluate 1311(2 we have used the computer ported experimental rate2 reduction program REDUCE .8 After calculating experimental the differential c r o s s section d a ( v, d -(3pju) f o r (2) the parton process, we s e t Dl = x P l , iii, = nt, =xrMN, where P, is the target-nucleon momentum, and The quoted r a t e s in Refs. 1 and 3 a r e lower. In 134, is the nucleon m a s s . The observed c r o s s secthis article we present characteristics of radiative tion is then obtained by integrating over x , trimuon production that can be used in identifying weighting with the parton distribution function d(x), events of this origin.O u r calculations a r e based on the scaling parton model with afour-fermion weak-interaction vertex.d o ( v U P -( 3 p ) X ) = do(v,d-(3p)u)d(x)dx, F o r gauge invariance, the virtual photon must b e attached in a l l possible ways to the charged par-ticles in the vd-p-u ...

Neutrino production of same-sign dimuons at the Fermilab Tevatron

“…Radiative trimuon production can be calculated accurately and is limited only by the knowledge of the parton distributions within the target nucleon. We use the parametrization given by Barger et al [47] da…”

Deep Inelastic Lepton-Nucleon Scattering

“…A signal of like-sign dimuons is expected because of associated pro duction and decay of pairs of charmed particles. However, the perturbative QCD prediction, assuming gluon bremsstrahlung as the mechanism, fell short by almost an order of magnitude (93). It was noted (94), however, that the systematic uncertainty in the theoretical prediction could be as large as 60%, in large part because of the uncertainty in the threshold behavior of the process.…”