Complementarity of high energy and high intensity experiments for dark photon benchmarks

Abstract

Physical phenomena that are unexplained by the Standard Model (SM) of particle physics, are the subject of the area of research known as physics Beyond the Standard Model (BSM). BSM physics contains many Dark Matter (DM) theories which have emerged; from particles such as axions, neutrinos, and Weakly Interacting Massive Particles (WIMPs), to primordial black holes and others.

The range of experiments at the frontiers of research are equipped to probe model parameter space with different sensitivites. The energy frontier, exemplified by the Large Hadron Collider (LHC), reaches the TeV energy scale and beyond. The intensity frontier looks for rare processes and precision deviations. The cosmic frontier searches astrophysical data. Some rely on invisble signatures, and some require visible SM decays of DM. There is a great deal of experimental complementarity, and cross-frontier collaboration needs to be prioritized.

Minimal WIMP based models within the reach of current experiments are presented. The model benchmarks allow for the comparison of limits on the ability to constrain model parameters, to be made between experiments.

These limits can be scaled between different couplings within a model, or even between models, provided that only the cross section varies and is known in each case. Limits set for more general vector models could be scaled to dark photon limits, the possibility of which is discussed. The acceptances are confirmed to be the same between the two models considered in this paper.

Thermal relic bounds are also imposed, and comparisons are made for each model in an appropriate plane on the y-axis known as the yield parameter. In addition, a heat map approach to plotting the Dark Matter and mediator masses is presented, with a focus on the minimum coupling limit imposed by the relic density. This approach facilitates visualization on one plot the viable regions of mass-mass parameter space in order not to overproduce DM, for each model considered.

A brief outlook is given on the current state of cross-frontier collaboration, in a number of efforts, all with the aim of exploiting complementarity in DM searches.

Popular Abstract

Particle physics experiments involve accelerating charged particles to high energies, and colliding them against a target or against each other. The energy that is released from collisions causes the production of elementary particles. Measuring these particles opens up a window through which we can examine the matter and forces that make up our universe.

A force can be thought of as a push or a pull. The most familiar force to us is gravity, which is a force between bodies resulting from their mass. Cosmological observations use gravity to measure how matter is distributed. Such observations indicate that more than 80% of matter is invisible. Invisible means it does not interact with Standard Model (SM) matter by any of the known fundamental forces, apart from gravity. It is known as the observed abundance of Dark Matter (DM).

The Standard Model is an extremely successful model which has been validated by all experimental measurements since its inception in the early 20th century. The SM includes all matter particles, but also describes the fundamental forces, or interactions, which are mediated by particles. Each force has certain particles associated with it. The two main frontiers of research which use man made accelerators, are known as the energy frontier and the intensity frontier. The energy frontier refers to colliders like those at the Large Hadron Collider
(LHC) which can reach very high energies. The intensity frontier contains experiments conducted at lower energies, but they are capable of higher precision and are sensitive to rarer processes. These frontiers are inherently complementary, and must work together to uncover the secrets of Dark Matter.

BACKGROUND
DM may be a new particle that interacts with the SM through a new fundamental interaction. Models provide ways to test nature for the presence of new particles and interactions. By hypothesizing that DM has certain properties, or parameters, collision event data is examined for evidence supporting those models. When no
evidence is found, the model parameters are said to be excluded, and the model constrained. One model type adds two new particles to the SM. These are the DM itself, and a dark mediator which carries the force between the DM and the SM. Two examples of such a model are presented in this report. One is mediated by a vector
particle, and the other by a dark photon. These differ in the way the DM is coupled to the SM.

METHOD
If a collision event leads to the appearance of DM, it can be detectable based on what happens to the mediator. If the mediator decays to DM particles, which are invisible, this leads to missing energy in the detector. This
is possible evidence for DM because any SM particles detected from an interaction must have counterparts pointing in the opposite direction, in order to conserve energy. If these counterparts are not visible, it could be because they consist of DM. This report uses data from CMS, an experiment at the LHC, to examine con-
straints on the coupling between DM and the SM for the vector and dark photon models.

RESULTS AND CONSEQUENCES
Constraints for both models are displayed on the same plot in the context of the energy frontier (above 10 GeV mediator mass). High energy experiments like CMS at the LHC are required to constrain models with a heavier mediator, or heavier DM particles themselves. At lower energies (below 10 GeV), intensity frontier
experiments are at their most sensitive. This directly demonstrates the complementarity between high energy and high intensity experiments in the context of dark photon models.

• author: Greaves, Joshua
• supervisor: Caterina Doglioni; Katherine Pachal; Philip Harris
• organization: Particle and nuclear physics; Department of Physics
• course: FYSM30 20221
• year: 2022
• type: H2 - Master's Degree (Two Years)
• subject: Physics and Astronomy
• keywords: Dark matter, LDMX, Dark photon, Complementarity, Snowmass, Relic density, Thermal relic, Relic abundance, Cross section, Constraints, Limits, Minimal models, Energy frontier, Intensity frontier, Madgraph, Madanalysis, Vector mediated
• language: English
• additional info: Katherine Pachal and Philip Harris were co-supervisors; Caterina Doglioni was the primary supervisor.
• id: 9091336
• date added to LUP: 2022-06-22 12:26:13
• date last changed: 2022-06-22 12:26:13