Quark and Gluon Contents of a Lepton at High Energies

Abstract

In high-energy leptonic collisions, such as at a multi-TeV muon collider, the collinear splittings of the electroweak (EW) gauge bosons and leptons are the dominant phenomena, and the scattering processes should thus be formulated in terms of the EW parton distribution functions (EW PDFs). We complete this formalism in the Standard Model to include the QCD sector and evaluate the quark and gluon PDFs inside a lepton at the double-log accuracy. The splittings of the photon and subsequently the quarks and gluons control the quark/gluon PDFs below the EW scale. The massive gauge bosons lead to substantial contributions at high scales. The jet production cross section can reach the order of a few nb (50 pb) in e + e − (µ + µ − ) collisions, at the TeV c.m. energies with a moderate acceptance cut, that governs the overall event shape up to about p j T ∼ 60 GeV.

Searching for Leptoquarks at Future Muon Colliders

“…In scenarios 1 and 2, the most identifiable final state will be U 1 → bμ, and we will always focus on this decay channel unless otherwise noted. In flavor scenarios 3 and 4, however, the large β 33 L coupling means that the U 1 → bτ decay mode always has an appreciable branching ratio, while BR(U 1 → bμ) 1% already for β 32 L < 0.1. We will therefore consider only τ final states for scenarios 3 and 4, though a more detailed analysis could in principle include additional information from other final states as well.…”

“…1. These structures are somewhat motivated by a U (2) 5 symmetry breaking pattern, which allows for a potentially large β 33 L coupling and treats the off-diagonal β 32 L as a spurion [71]. The four scenarios are primarily chosen, though, to give a representative picture of the phenomenology at a muon collider in different flavor structures.…”

“…In light of these experimental advances, there has been a proliferation of interest from theoretical physics in muon colliders [31]. These studies include both detailed studies of the PDFs that are relevant in muon collisions [32,33] and estimates of the rates of SM processes and projections for measuring Higgs couplings [34][35][36]. There have also been numerous studies of the reach for high energy muon colliders to probe various BSM possibilities, including new scalars [37][38][39][40][41][42], minimal dark matter [43][44][45], explanations for discrepancies in the muon (g − 2) µ [46][47][48][49][50] or the neutral current B-meson anomalies [51,52], and for new physics encoded in higher-dimensional operators [53,54].…”

Probing New Gauge Forces with a High-Energy Muon Beam Dump

“…The number of muons available at a beam dump experiment associated with a high-energy collider depends significantly on the beam design, for which at this time there are only rough proposals. Parametrically, the number of muons in a collider beam, per unit time, is given by Ṅµ = f 0 × n b × N µ/bunch (14) where f 0 is the muon source repetition rate (i.e., the rate at which the muons are generated by the source, which could be either a proton or a positron beam), n b is the number of colliding bunches in each beam, and N µ/bunch is the number of muons per bunch. Assuming the MAP design parameters [6,78] (f 0 = 5 Hz, N µ/bunch = 2×10 12 , n b = 1), this translates to Ṅµ ∼ 10 20 /year generated for collisions.…”

“…Such a muon collider (µC) is a particularly compelling option as it affords a complementary physics program to that of a high-energy hadron collider like the LHC. For example, with a µC we gain access to direct couplings of both electroweak-mediated and secondgeneration processes [7][8][9][10][11][12][13][14][15][16][17]. Additionally, with increased available center-of-mass energy, we can expand our discovery prospects for massive new physics.…”