Search for Microscopic Black Holes in Early Data with the ATLAS Detector at the LHC

With the start of the LHC in 2010 a new era in Particle Physics has begun. In a yet unexplored kinematic regime, the Standard Model can be probed and new physics can be discovered with the ATLAS detector. In this work the search for microscopic black holes at the LHC is presented. Their discovery would unveil the existence of large extra dimensions. Theories of such, establishing low-scale gravity, address problems of the Standard Model like the hierarchy problem. Different search strategies are discussed, which are aimed at an early discovery with the centre-of-mass energies provided by the LHC. They exploit key features of the decay of black holes, namely high mass final states with a large multiplicity of objects with high pT. With the first 297 1/nb of sqrt(s) = 7TeV data, a search for such new physics is conducted. No deviations from Standard Model predictions are found, and consequently a limit on the cross section times acceptance of sigma × A < 0.46 nb at 95% CL is set. Theory predictions for the cross section are of the order O(10 - 100 pb), hence this result has an impact on theories of low-scale gravity

Search for Planckian Black Holes in the Di-Lepton Channel with the ATLAS Detector at the LHC

In some scenarios proposing extra dimensions, the fundamental Planck scale is in the order of a TeV, and the apparent weakness of the gravitational force is a consequence of the large compactified volume of the extra dimensions. These scenarios render possible the non-perturbative process of black hole formation at hadron colliders. It has been argued that black hole signatures based on thermal multi-particle final states are very unlikely. However, strong gravity effects at center of mass energies of the order of the Planck mass are expected to yield an increase in the $2\rightarrow 2$ production cross section. This thesis reviews the signatures and discovery potential of Planckian black holes, by which is meant true or virtual black holes or simply strong gravity effects, decaying to two leptons in the context of the ADD model in $pp$ collisions at $\sqrt{s} = 7$ TeV at the LHC. Based on data recorded by the ATLAS experiment during 2010 which correspond to a total integrated luminosity of $\sim 40$ pb$^{-1}$, no statistically significant excess above the Standard Model expectation is observed. A combined search for high-mass and boosted di-lepton final states results in upper limits at the 95\% confidence level on the production cross section for three Planckian black hole models. Assuming six large extra dimensions and a Planck mass of 2 TeV, the quoted limits are; $8.2 \times 10^{1}$ pb for conservation of B, L and flavours; $6.2 \times 10^{1}$ pb for conservation of B and L; $5.3 \times 10^{1}$ pb for conservation of B-L only

Quantum black holes at the LHC: production and decay mechanisms of non-thermal microscopic black holes in particle collisions

The scale of quantum gravity could be as low as a few TeV in the existence of extra spatial dimensions or if the Planck scale runs fast due to a large number of particles in a hidden sector. One of the most striking features of low-scale quantum gravity models would be the creation of quantum black holes, i.e. non-thermal black holes with masses around a few TeV, in high energy collisions. This thesis deals with the production and decay mechanisms of quantum black holes at current colliders, such as the Large Hadron Collider (LHC). Firstly, a review of models with low-scale gravity is given. We will present an overview of production and decay mechanism of classical and semi-classical black holes, including the Hoop conjecture criterion, closed trapped surfaces and thermal decay via Hawking radiation. We will then introduce a phenomenological approach of black holes, very differently from the (semi-)classical counterparts, which covers a substantially model independent and specifically established field theory, describing the production of quantum black holes. This is done by matching the amplitude of the quantum black hole processes to the extrapolated semi-classical cross section. All possible decay channels and their probabilities are found for quantum black holes with a continuous and discrete mass spectrum, respectively, by considering different symmetry conservation restrictions for a quantum gravitational theory. In conjunction with these branching ratios, we developed a Monte Carlo integration algorithm to determine the cross sections of specific final states. We extended the algorithm to investigate the enhancement of supersymmetric particle production via quantum black hole processes. Studying such objects proves very important, since it provides new possible insights and restrictions on the quantum black hole model and likewise on the low-scale quantum gravity scenarios

Manual of BlackMax. A black-hole event generator with rotation, recoil, split branes, and brane tension. Version 2.02

This is the users manual of the black-hole event generator BlackMax (Dai et al., 2008), which simulates the experimental signatures of microscopic and Planckian black-hole production and evolution at proton–proton, proton–antiproton and electron–positron colliders in the context of brane world models with low-scale quantum gravity. The generator is based on phenomenologically realistic models free of serious problems that plague low-scale gravity. It includes all of the black-hole gray-body factors known to date and incorporates the effects of black-hole rotation, splitting between the fermions, non-zero brane tension and black-hole recoil due to Hawking radiation (although not all simultaneously). The main code can be downloaded from Dai et al. (0000)

Manual of BlackMax. A black-hole event generator with rotation, recoil, split branes, and brane tension. Version 2.02

This is the users manual of the black-hole event generator BlackMax (Dai et al., 2008), which simulates the experimental signatures of microscopic and Planckian black-hole production and evolution at proton–proton, proton–antiproton and electron–positron colliders in the context of brane world models with low-scale quantum gravity. The generator is based on phenomenologically realistic models free of serious problems that plague low-scale gravity. It includes all of the black-hole gray-body factors known to date and incorporates the effects of black-hole rotation, splitting between the fermions, non-zero brane tension and black-hole recoil due to Hawking radiation (although not all simultaneously). The main code can be downloaded from Dai et al. (0000). Program summary Program title: BlackMax Program Files doi: http://dx.doi.org/10.17632/p9jg9dypcg.1 Licensing provisions: GNU General Public License version 3 Programming language: C (with Fortran subroutines) Nature of problem: In the class of models with low scale quantum gravity (known as the “TeV scale gravity models”) collisions of particles at the particle accelerators may lead to novel phenomena, in particular mini black hole production. In order to confirm or exclude this class of models, one needs to calculate the probability of the black hole production in collisions of particles, properties of the formed black holes (mass, spin, charge, momentum), and the signature of the black hole decay (Hawking radiation). Solution method: BlackMax calculates the probability of the black hole production by utilizing the so-called “geometric cross section” for black hole production. From the energy and quantum numbers of the colliding particles BlackMax calculates the mass, spin, charge, and momentum of the formed black holes. In the next step, BlackMax utilizes the greybody factors that characterize Hawking radiation and calculates the final output. The produced particles are then supposed to leave the signature in particle detectors. References: Phys. Rev. D 77, 076007 (2008) Theoretical background summary Models with TeV-scale quantum gravity offer very rich collider phenomenology. Most of them assume the existence of a three-plus-one-dimensional hypersurface, which is referred as “the brane,” where Standard-Model particles are confined, while only gravity and possibly other particles that carry no gauge quantum numbers, such as right handed neutrinos, can propagate in the full space, the so-called “bulk”. Under certain assumptions, this setup allows the fundamental quantum gravity energy scale, to be close to the electroweak scale. The observed weakness of gravity compared to other forces on the brane (i.e. in the laboratory) is a consequence of the large volume of the bulk which dilutes the strength of gravity. In the context of these models of TeV-scale quantum gravity, probably the most exciting new physics is the production of micro-black-holes in near-future accelerators like the Large Hadron Collider (LHC). According to the “hoop conjecture”, if the impact parameter of two colliding particles is less than two times the gravitational radius, rh, corresponding to their center of-mass energy (ECM), a black-hole with a mass of the order of ECM and horizon radius, rh, will form. Typically, this gravitational radius is approximately ECM /M*2. Thus, when particles collide at center-of-mass energies above M*, the probability of black-hole formation is high. Once a black-hole is formed, it is believed to decay via Hawking radiation. This Hawking radiation will consist of two parts: radiation of Standard-Model particles into the brane and radiation of gravitons and any other bulk modes into the bulk. The relative probability for the emission of each particle type is given by the gray-body factor for that mode. This gray-body factor depends on the properties of the particle (charge, spin, mass, momentum), of the black-hole (mass, spin, charge) and, in the context of TeV-scale quantum gravity, on environmental properties such as the number of extra dimensions, the location of the black-hole relative to the brane (or branes), etc. In order to properly describe the experimental signatures of black-hole production and decay one must therefore calculate the gray-body factors for all of the relevant degrees of freedom. Since a black hole can emit particles like quarks and gluons which cannot freely propagate long distance, one has to simulate the process of hadronization. The generator can be interfaced with hadronization generators Herwig and Pythia to obtain the final signature measurable in particle detectors.</p

Manual of BlackMax. A black-hole event generator with rotation, recoil, split branes, and brane tension. Version 2.02

This is the users manual of the black-hole event generator BlackMax (Dai et al., 2008), which simulates the experimental signatures of microscopic and Planckian black-hole production and evolution at proton–proton, proton–antiproton and electron–positron colliders in the context of brane world models with low-scale quantum gravity. The generator is based on phenomenologically realistic models free of serious problems that plague low-scale gravity. It includes all of the black-hole gray-body factors known to date and incorporates the effects of black-hole rotation, splitting between the fermions, non-zero brane tension and black-hole recoil due to Hawking radiation (although not all simultaneously). The main code can be downloaded from Dai et al. (0000). Program summary Program title: BlackMax Program Files doi: http://dx.doi.org/10.17632/p9jg9dypcg.1 Licensing provisions: GNU General Public License version 3 Programming language: C (with Fortran subroutines) Nature of problem: In the class of models with low scale quantum gravity (known as the “TeV scale gravity models”) collisions of particles at the particle accelerators may lead to novel phenomena, in particular mini black hole production. In order to confirm or exclude this class of models, one needs to calculate the probability of the black hole production in collisions of particles, properties of the formed black holes (mass, spin, charge, momentum), and the signature of the black hole decay (Hawking radiation). Solution method: BlackMax calculates the probability of the black hole production by utilizing the so-called “geometric cross section” for black hole production. From the energy and quantum numbers of the colliding particles BlackMax calculates the mass, spin, charge, and momentum of the formed black holes. In the next step, BlackMax utilizes the greybody factors that characterize Hawking radiation and calculates the final output. The produced particles are then supposed to leave the signature in particle detectors. References: Phys. Rev. D 77, 076007 (2008) Theoretical background summary Models with TeV-scale quantum gravity offer very rich collider phenomenology. Most of them assume the existence of a three-plus-one-dimensional hypersurface, which is referred as “the brane,” where Standard-Model particles are confined, while only gravity and possibly other particles that carry no gauge quantum numbers, such as right handed neutrinos, can propagate in the full space, the so-called “bulk”. Under certain assumptions, this setup allows the fundamental quantum gravity energy scale, to be close to the electroweak scale. The observed weakness of gravity compared to other forces on the brane (i.e. in the laboratory) is a consequence of the large volume of the bulk which dilutes the strength of gravity. In the context of these models of TeV-scale quantum gravity, probably the most exciting new physics is the production of micro-black-holes in near-future accelerators like the Large Hadron Collider (LHC). According to the “hoop conjecture”, if the impact parameter of two colliding particles is less than two times the gravitational radius, rh, corresponding to their center of-mass energy (ECM), a black-hole with a mass of the order of ECM and horizon radius, rh, will form. Typically, this gravitational radius is approximately ECM /M*2. Thus, when particles collide at center-of-mass energies above M*, the probability of black-hole formation is high. Once a black-hole is formed, it is believed to decay via Hawking radiation. This Hawking radiation will consist of two parts: radiation of Standard-Model particles into the brane and radiation of gravitons and any other bulk modes into the bulk. The relative probability for the emission of each particle type is given by the gray-body factor for that mode. This gray-body factor depends on the properties of the particle (charge, spin, mass, momentum), of the black-hole (mass, spin, charge) and, in the context of TeV-scale quantum gravity, on environmental properties such as the number of extra dimensions, the location of the black-hole relative to the brane (or branes), etc. In order to properly describe the experimental signatures of black-hole production and decay one must therefore calculate the gray-body factors for all of the relevant degrees of freedom. Since a black hole can emit particles like quarks and gluons which cannot freely propagate long distance, one has to simulate the process of hadronization. The generator can be interfaced with hadronization generators Herwig and Pythia to obtain the final signature measurable in particle detectors.</p