Long-lived heavy quarks : a review

We review the theoretical and experimental situation for long-lived heavy quarks, or bound states thereof, arising in simple extensions of the Standard Model. If these particles propagate large distances before their decay, they give rise to specific signatures requiring dedicated analysis methods. In particular, vector-like quarks with negligible couplings to the three known families could have eluded the past experimental searches. While most analyses assume prompt decays at the production vertex, novel heavy quarks might lead to signatures involving displaced vertices, new hadronic bound states, or decays happening outside of the detector acceptance. We perform reinterpretations of existing searches for short- and long-lived particles, and give suggestions on how to extend their reach to long-lived heavy quarks.Comment: 17 pages, 9 figures, 8 tables. Version accepted for publication in AHEP on Very Heavy Quarks at the LHC. Version 2: References added and last section update

Closing in on a perturbative fourth generation

A perturbative new family of fermions is now severely constrained, though not excluded yet. We reconsider the current bounds (i.e., direct and from Higgs searches, R_b, oblique parameters) on the fourth generation parameter space assuming the case of a small CKM mixing with the third generation. We identify viable scenarios featuring either a light or a heavy Higgs boson. A set of representative benchmark points targeted for LHC searches is proposed with a normal (inverted) quark mass hierarchy where t' -> b'W (b' -> tW) decays are sizable. In the case where the fourth generation couplings to the lighter quark families are small, we suggest that search strategies at the LHC should include both pair (strong) and single (weak) production with bb+nW (n=2,...,6) final state signatures.Comment: 23 pages, 6 figures, v2: some issues clarified and references added. To appear in JHE

Long-Lived Heavy Quarks: A Review

We review the theoretical and experimental situation for long-lived heavy quarks, or bound states thereof, arising in simple extensions of the Standard Model. If these particles propagate large distances before their decay, they give rise to specific signatures requiring dedicated analysis methods. In particular, vector-like quarks with negligible couplings to the three known families could have eluded the past experimental searches. While most analyses assume prompt decays at the production vertex, novel heavy quarks might lead to signatures involving displaced vertices, new hadronic bound states, or decays happening outside of the detector acceptance. We perform reinterpretations of existing searches for short-and long-lived particles, and give suggestions on how to extend their reach to long-lived heavy quarks

Quarks beyond the top

Since the beginning of its physics programme, the Large Hadron Collider has been delivering high quality results on the Standard Model of particle physics. After the discovery of a new resonance that matches the expectations for a scalar Higgs boson at a mass of 125 GeV, the forthcoming experiments will focus on New Physics searches. In the spotlight of the CMS and ATLAS collaborations, the possibility for new heavy quarks offers interesting clues about the issue of naturalness, and appears as a common feature in many scenarios going beyond the Standard Model. In this thesis, we present the phenomenological implications of tentative new quarks beyond the top, and investigate the processes in which their existence could possibly be unravelled. In synergy with the results of the CMS collaboration, we show that a sequential fourth generation of quarks and leptons can be ruled out with a high degree of confidence level in the context of a single Higgs doublet. Aiming at a systematic analysis, we then introduce a complete and model-independent framework to study the phenomenology of new top partners with general coupling assumptions to the Standard Model quarks. Relying on this parametrisation, we assess the possibility for chiral and vector-like quarks to be singly produced at the LHC, in conjunction with the constraints set from precision physics measurements. Finally, we present a dedicated software recasting the existing limits from the available searches on scenarios with one or multiple heavy quarks. The prospects for the forthcoming search programmes are discussed as a conclusion, stressing their importance to set bounds on extended fermion sectors at the TeV scale and beyond.(SC - Sciences) -- UCL, 201