Physics at a Higgsino factory

Abstract

Naturalness arguments applied to supersymmetric theories imply a spectrum containing four light higgsinos Z 1,2 and W ± 1 with masses ∼ 100 − 300 GeV (the closer to M Z , the more natural). The compressed mass spectrum and associated low energy release from W 1 and Z 2 three-body decay makes higgsinos difficult to detect at LHC14, while the other sparticles might be heavy, and possibly even beyond LHC14 reach. In contrast, the International Linear e + e − Collider (ILC) with √ s > 2m(higgsino) would be a higgsino factory in addition to a Higgs boson factory and would serve as a discovery machine for natural SUSY! In this case, both chargino and neutralino production occur at comparable rates, and lead to observable signals above SM backgrounds. We examine two benchmark cases, one just beyond the LHC8 reach with W 1 ( Z 2 ) − Z 1 mass gap of 15 (21) GeV, and a second more difficult case beyond even the LHC14 reach, where the mass gap is just 10 GeV, close to its minimum in models with no worse than 3% finetuning. The signal is characterized by low visible energy events together with E T in the one or two jets +1ℓ channel from chargino production, and in the opposite sign, sameflavour, acoplanar dilepton channel from Z 1 Z 2 production. For both cases, we find that the signal is observable above backgrounds from the usual 2 → 2 SM events and from γγ collisions with just a few fb −1 of integrated luminosity. We also show that with an integrated luminosity of 100 fb −1 , it should be possible to extract W 1 and Z 1 masses at 2-3% level from chargino events if the mass gap is ≥ 15 GeV, and neutralino masses at the sub-percent level from neutralino events. The latter should also allow a determination of m Z 2 − m Z 1 at the 200 MeV level. These measurements would point to higgsinos as the origin of new physics and strongly suggest a link to a natural origin for W , Z and h masses.

Compressing the inert doublet model

“…This strategy has been applied to nearly-degenerate Higgsinos in the ILC studies of Refs. [114,115,116,117]. Since an ILC-type detector is expected to have a very low lepton p T threshold, perhaps approaching 0.5 GeV [118], it might even be possible to improve the sensitivity for even smaller mass splittings.…”

Supergravity gauge theories strike back: there is no crisis for SUSY but a new collider may be required for discovery

“…13: Sparticle production cross sections vs. √ s for unpolarized beams at the ILC e + e − collider for an RNS benchmark point listed in Ref. [125].…”

Electroweak supersymmetry around the electroweak scale

“…Their combined Higgs boson mass measurements are m h 0 = 125.2±0.3(stat)±0.6(syst) GeV and m h 0 = 125.8 ± 0.4(stat) ± 0.4(syst) GeV, respectively [7,8]. Moreover, the Higgs boson mass around 125.5 GeV gives very strong constraints on the viable supersymmetry parameter space, which have been studied extensively recently [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. Especially, the squark and/or gluino masses will be about a few TeV in general in the Minimal Supersymmetric Standard Model (MSSM) and the Next to the MSSM (NMSSM) with simple supersymmetry mediation mechanisms.…”