Search for sphalerons in proton-proton collisions

John Ellis,Kazuki Sakurai

doi:10.1007/jhep04(2016)086

Abstract

In a recent paper, Tye and Wong (TW) have argued that sphaleron-induced transitions in high-energy proton-proton collisions should be enhanced compared to previous calculations, based on a construction of a Bloch wave function in the periodic sphaleron potential and the corresponding pass band structure. Here we convolute the calculations of TW with parton distribution functions and simulations of final states to explore the signatures of sphaleron transitions at the LHC and possible future colliders. We calculate the increase of sphaleron transition rates in proton-proton collisions at centre-of-mass energies of 13/14/33/100 TeV for different sphaleron barrier heights, while recognising that the rates have large overall uncertainties. We use a simulation to show that LHC searches for microscopic black holes should have good efficiency for detecting sphaleron-induced final states, and discuss their experimental signatures and observability in Run 2 of the LHC and beyond. We recast the early ATLAS Run-2 search for microscopic black holes to constrain the rate of sphaleron transitions at 13 TeV, deriving a significant limit on the sphaleron transition rate for the nominal sphaleron barrier height of 9 TeV.

Highlights

JHEP04(2016)086 transitions would be a beautiful confirmation of profound theoretical insights, but would have important cosmological implications, since sphalerons are thought to have played an essential role in generating the baryon asymmetry of the Universe [11, 15,16,17,18,19,20]
In a recent paper, Tye and Wong (TW) have argued that sphaleron-induced transitions in high-energy proton-proton collisions should be enhanced compared to previous calculations, based on a construction of a Bloch wave function in the periodic sphaleron potential and the corresponding pass band structure
We convolute the calculations of TW with parton distribution functions and simulations of final states to explore the signatures of sphaleron transitions at the LHC and possible future colliders

Summary

Theoretical background

It is argued in [14] that sphaleron transitions can be modelled by a one-dimensional Schrodinger equation of the form 1 ∂2. Averaging over the energies E1,2 of the colliding quark partons yields a strong suppression at E1 + E2 ESph, which corresponds to the exponential suppression found in a conventional tunnelling calculation This suppression decreases as E1 + E2 → ESph, and there is no suppression for E1 + E2 ≥ ESph. The result of the analysis in [14] can be summarized in the partonic cross-section. Where E is the centre-of-mass energy of the parton-parton collision, c ∼ 2 and the suppression factor S(E) is shown in figure 8 of [14] As seen there, it rises from the value S(E) = −1 in the low-energy limit (E ESph) to S(E) = 0 for energies E ≥ ESph, with very similar results being found in [14] for calculations based on the work of [2] and [23].

Cross-section calculations

Simulations of sphaleron-induced processes

Analysis of ATLAS 2015 data

Findings

Future prospects