Bounds on large extra dimensions from the simulation of black hole events at the Large Hadron Collider

Abstract

Large extra dimensions were originally proposed to solve the hierarchy problem of the Standard Model (SM) of elementary particle physics. The presence of large extra dimensions dilutes gravity, lowering the Planck scale, while SM particles are required to propagate only in the usual 4 dimensional spacetime, leaving the electroweak scale unchanged. If large extra dimensions exist and they are large enough, the Planck scale may be as low as a few TeV’s, so that the hierarchy problem is solved. A smaller Planck scale will bring about numerous phenomenological consequences; in particular, microscopic black holes may be produced in high-energy particle collisions at this energy scale. The decay of black holes, via the Hawking effect, into elementary particles enables the detection of the black hole events, which can be used to infer the existence of large extra dimensions. In this work, we simulate microscopic black hole formation at the Large Hadron Collider with the black hole event generator CATFISH, and compare the simulation results with the experimental data published by the Compact Muon Solenoid collaboration in 2013 at a center of mass energy $\sqrt{s}= 8$ TeV, corresponding to an integrated luminosity of 12.1 fb$^{-1}$. The goal of this work is to test the large extra dimension model and to determine the value of the Planck scale if large extra dimensions exist. The absence of observed black hole events in the experimental data allows us to set lower bounds on the Planck scale and various parameters related to microscopic black hole formation for a number (3 - 6) of large extra dimensions. Assuming no energy loss during high-energy particle collisions, our analysis sets lower bounds on the fundamental Planck scale ranging from 0.8 TeV to 4.9 TeV for black holes fully decaying into SM particles and 0.5 TeV to 3.0 TeV for black holes settling down to a charge neutral, invisible remnant, depending on the minimum allowed black hole mass at formation. Formation of black holes with mass less than 5.2 TeV to 6.5 TeV (SM decay) and 2.2 TeV to 4.0 TeV (remnant) is excluded at 95\% C.L. Further investigation takes into account the effects of the Generalized Uncertainty Principle (GUP), which is expected to play an important role because the mass of a microscopic black hole is only a few fundamental Planck masses. An analysis similar to the one carried out without including GUP effects reveals smaller lower bounds on the fundamental Planck scale ranging from 0.8 TeV to 1.4 TeV for black holes fully decaying into SM particles, only when $\alpha\ge0.9$, depending on the minimum allowed black hole mass at formation. Therefore, this work constrains not only the sizes of the large extra dimensions and the masses of the microscopic black holes, but also sets the lower limits on the energy scale where the effects of quantum gravity start to become significant.