Higgs Self-Coupling Measurements at a 100 TeV Hadron Collider

An important physics goal of a possible next-generation high-energy hadron collider will be precision characterisation of the Higgs sector and electroweak symmetry breaking. A crucial part of understanding the nature of electroweak symmetry breaking is measuring the Higgs self-interactions. We study dihiggs production in proton-proton collisions at 100 TeV centre of mass energy in order to estimate the sensitivity such a machine would have to variations in the trilinear Higgs coupling around the Standard Model expectation. We focus on the two b-jets plus diphotons final state, including possible enhancements in sensitivity by exploiting dihiggs recoils against a hard jet. We find that it should be possible to measure the trilinear self-coupling with 40% accuracy given 3/ab and 12% with 30/ab of data.

A search for direct heffalon production using the ATLAS and CMS experiments at the Large Hadron Collider

The first search is reported for direct heffalon production, using 23.3/fb per experiment of delivered integrated luminosity of proton-proton collisions at rootS = 8TeV from the Large Hadron Collider. The data were recorded with the ATLAS and the CMS detectors. Each exotic composite is assumed to be stable on the detector lifetime (tau >> ns). A particularly striking signature is expected. No signal events are observed after event selection. The cross section for heffalon production is found to be less than 64ab at the 95% confidence level.

Finding Higgs bosons heavier than 2 m_W in dileptonic W-boson decays

We reconsider observables for discovering a heavy Higgs boson (with m_h > 2m_W) via its di-leptonic decays h -> WW -> l nu l nu. We show that observables generalizing the transverse mass that take into account the fact that both of the intermediate W bosons are likely to be on-shell give a significant improvement over the variables used in existing searches. We also comment on the application of these observables to other decays which proceed via narrow-width intermediates.

A Storm in a T Cup

We revisit the process of transversification and agglomeration of particle momenta that are often performed in analyses at hadron colliders, and show that many of the existing mass-measurement variables proposed for hadron colliders are far more closely related to each other than is widely appreciated, and indeed can all be viewed as a common mass bound specialized for a variety of purposes.

Transverse masses and kinematic constraints: from the boundary to the crease

We re-examine the kinematic variable m_T2 and its relatives in the light of recent work by Cheng and Han. Their proof that m_T2 admits an equivalent, but implicit, definition as the `boundary of the region of parent and daughter masses that is kinematically consistent with the event hypothesis is far-reaching in its consequences. We generalize their result both to simpler cases (m_T, the transverse mass) and to more complex cases (m_TGen). We further note that it is possible to re-cast many existing and unpleasant proofs (e.g. those relating to the existence or properties of kink and crease structures in m_T2) into almost trivial forms by using the alternative definition. Not only does this allow us to gain better understanding of those existing results, but it also allows us to write down new (and more or less explicit) definitions of (a) the variable that naturally generalizes m_T2 to the case in which the parent or daughter particles are not identical, and (b) the inverses of m_T and m_T2 -- which may be useful if daughter masses are known and bounds on parent masses are required. We note the implications that these results may have for future matrix-element likelihood techniques.

Precision Determination of Invisible-Particle Masses at the CERN LHC: II

We further develop the constrained mass variable techniques to determine the mass scale of invisible particles pair-produced at hadron colliders. We introduce the constrained mass variable M_3C which provides an event-by-event lower bound and upper bound to the mass scale given the two mass differences between the lightest three new particle states. This variable is most appropriate for short symmetric cascade decays involving two-body decays and on-shell intermediate states which end in standard-model particles and two dark-matter particles. An important feature of the constrained mass variables is that they do not rely simply on the position of the end point but use the additional information contained in events which lie far from the end point. To demonstrate our method we study the supersymmetric model SPS 1a. We select cuts to study events with two Neutralino_2 each of which decays to Neutralino_1, and two opposite-sign same-flavor (OSSF) charged leptons through an intermediate on-shell slepton. We find that with 300 fb^-1 of integrated luminosity the invisible-particle mass can be measured to M=96.4 +/- 2.4 GeV. Combining fits to the shape of the M_3C constrained mass variable distribution with the max m_ll edge fixes the mass differences to +/- 0.2 GeV.

The Precision Determination of Invisible-Particle Masses at the LHC

We develop techniques to determine the mass scale of invisible particles pair-produced at hadron colliders. We employ the constrained mass variable m_2C, which provides an event-by-event lower-bound to the mass scale given a mass difference. We complement this variable with a new variable m_2C,UB which provides an additional upper bound to the mass scale, and demonstrate its utility with a realistic case study of a supersymmetry model. These variables together effectively quantify the `kink in the function Max m_T2 which has been proposed as a mass-determination technique for collider-produced dark matter. An important advantage of the m_2C method is that it does not rely simply on the position at the endpoint, but it uses the additional information contained in events which lie far from the endpoint. We found the mass by comparing the HERWIG generated m_2C distribution to ideal distributions for different masses. We find that for the case studied, with 100 fb^-1 of integrated luminosity (about 400 signal events), the invisible particles mass can be measured to a precision of 4.1 GeV. We conclude that this techniques precision and accuracy is as good as, if not better than, the best known techniques for invisible-particle mass-determination at hadron colliders.

Weighing Wimps with Kinks at Colliders: Invisible Particle Mass Measurements from Endpoints

We consider the application of endpoint techniques to the problem of mass determination for new particles produced at a hadron collider, where these particles decay to an invisible particle of unknown mass and one or more visible particles of known mass. We also consider decays of these types for pair-produced particles and in each case consider situations both with and without initial state radiation. We prove that, in most (but not all) cases, the endpoint of an appropriate transverse mass observable, considered as a function of the unknown mass of the invisible particle, has a kink at the true value of the invisible particle mass. The co-ordinates of the kink yield the masses of the decaying particle and the invisible particle. We discuss the prospects for implementing this method at the LHC.