1,720,998 research outputs found
A new strategy to discover heavy colored vectors at the early LHC
Full text linkWe perform a study of the LHC discovery reach on a heavy gluon (G∗) and heavy fermions (top and bottom excitations), coming from a new composite sector. We find that heavy fermion resonances have a great impact on the composite gluon phenomenology. If the composite gluon is heavier than composite fermions, as flavor observables seem to suggest, the search in the channel where G∗ decays into a heavy fermion plus its Standard Model partner is very promising, with the possibility for both the G∗ and heavy fermions to be discovered at the early stage of the LHC. The channel offers also the possibility to extract important information on model parameters, such as the top degree of compositeness
Δf=1 constraints on composite Higgs models with left-right parity
No full textWe analyze the bounds on the spectrum of composite Higgs models that come from flavor observables, by means of simple two-site effective Lagrangians, which incorporate a custodial symmetry and a left-right parity, and which could also be adopted in further phenomenological studies on composite Higgs models. We derive, in particular, an important constraint on the masses of the (t L,bL) partners, which does not depend on the flavor structure of the sector beyond the Standard Model. This bound is obtained from the "infrared" contribution to b→sγ induced by the flavor-conserving effective vertex WtRbR. We find that the presence of a custodial symmetry can play a role in protecting this effective coupling and, as a consequence, in attenuating the constraint, which, however, remains of the order of 1 TeV. In addition to this bound, we calculate the constraints from the "ultraviolet" contribution to b→sγ, induced by loops of heavy fermions, and to μ′/μ K
New W′ signals at the LHC
No full textWe study the W′ phenomenology in composite Higgs/Warped extra-dimensional models focusing on the effect of fermionic resonances at ∼1TeV. After deriving the existing bounds from the current LHC-8 analyses, we highlight the most promising signatures for W′ discovery at the 14 TeV LHC. We find in particular very promising the study of W′ decay modes into vectorlike top partners, specifically the decay into a doublet of custodian heavy fermions, T5/3T2/3, and the decay into a heavy fermion plus a Standard Model quark. We perform a detailed parton-level analysis of the channel W′→T5/3T2/3 in the same-sign dilepton final state, finding that it is a very promising signature to test the region at high W′ mass, mW′ 2TeV, and of the W′→Tb mode, which is one of the best channels to test the intermediate W′ mass region and that, already with the LHC-8 data, could extend the present exclusion bounds
Early discovery of top partners and test of the Higgs nature
No full textTop partners from a new strong sector can be discovered soon, at the 8 TeV LHC, by analyzing their single production, which exhibits a large enhancement in the cross section compared to the analogous productions of bottom partners and exotic quarks. We analyze the subsequent decay of the top partners into a 125 GeV Higgs. This channel proves to be very promising for both the discovery of top partners and a test of the Higgs sector. For a reference value λ T∼=3 of the Higgs coupling to the top partner, we could have a discovery (observation) at the 8 TeV LHC, with 30fb -1, for top partner masses up to 760 (890) GeV. If the LHC and Tevatron excesses near 125 GeV are really due to a composite Higgs, naturalness arguments demand top partners below ∼1TeV. Our results highlight thus that the 8 TeV LHC already has a large sensitivity on probing the composite Higgs hypothesis. The LHC reach is even wider at √s=14TeV. With λ T∼=3 the LHC with 100fb -1 can observe (at 5σ) a Higgs from a top partner decay for masses of this latter up to ≃1450GeV. In the case that the top partner is as light as ≃500GeV, the 14 TeV LHC would be sensitive to the measure of the λ T∼ coupling in basically the full range λ T∼>1 predicted by the theory
Z -peaked excess from heavy gluon decays to vectorlike quarks
No full textA 3 sigma excess has been recently announced by ATLAS in events with Z-peaked dilepton pairs, jets, and large transverse missing energy. We interpret this finding in the context of composite Higgs/Randall-Sundrum theories. We find that composite Higgs theories with custodial symmetry protection to the Zbb ̄ coupling predict a significant contribution to ZZbb (and to hhbb) final states coming from heavy gluon decays to pairs of bottom partner vectorlike quarks. The heavy gluon to vectorlike quark signal is largely accepted by the ATLAS selection if one of the Z bosons in the ZZbb final state decays leptonically and the other to neutrinos. For a bottom partner of ∼900GeV, we find that the ATLAS excess can be reproduced by composite Higgs models, in an experimentally allowed parameter space, for heavy gluon masses roughly in a range 1.87-2.15 TeV and for heavy gluon couplings to light quarks within ∼(0.3-0.65)gS. We briefly discuss the implication of this result for future experimental tests
Seeking leptoquarks in the t t ̄ plus missing energy channel at the high-luminosity LHC
Full text linkThe tt̄ plus missing energy channel is one of the most efficient to detect third-generation leptoquarks (LQs). It offers an important test to models which explain flavor anomalies in B meson decays. We outline a search strategy in the channel, relying on tagging the tops and on observables constructed out of the tops, and we assess the reach on LQs of the future high-luminosity LHC program. We find that with 3 ab-1 a vector (scalar) LQ decaying 50% (100%) to top and neutrino can be excluded up to masses of 1.96 TeV (1.54 TeV). We also indicate several observables that, in case of a future discovery in the channel, can be used to distinguish a scalar LQ from a vector LQ. The implications of our findings to models addressing the recent flavor anomalies are finally discussed
Discovering the composite Higgs through the decay of a heavy fermion
No full textA possible composite nature of the Higgs could be revealed at the early stage of the LHC, by analyzing the channels where the Higgs is produced from the decay of a heavy fermion. The Higgs production from a singly-produced heavy bottom, in particular, proves to be a promising channel. For a value λ = 3 of the Higgs coupling to a heavy bottom, for example, we find that, considering a 125 GeV Higgs which decays into a pair of b-quarks, a discovery is possible at the 8 TeV LHC with 30 fb−1 if the heavy bottom is lighter than roughly 530 GeV (while an observation is possible for heavy bottom masses up to ' 650 GeV). Such a relatively light heavy bottom is realistic in composite Higgs models of the type considered and, up to now, experimentally allowed. At s = 14 TeV the LHC sensitivity on the channel increases significantly. With λ = 3 a discovery can occur, with 100 fb−1, for heavy bottom masses up to ' 1040 GeV. In the case the heavy bottom was as light as ' 500 GeV, the 14 TeV LHC would be sensitive to the measure of the λ coupling in basically the full range λ> 1 predicted by the theory. ar X i
Heavy-light decay topologies as a new strategy to discover a heavy gluon
No full textWe study the collider phenomenology of the lightest Kaluza-Klein excitation of the gluon, G*, in theories with a warped extra dimension. We do so by means of a two-site effective lagrangian which includes only the lowest-lying spin-1 and spin-1/2 resonances. We point out the importance of the decays of G* to one SM plus one heavy fermion, that were overlooked in the previous literature. It turns out that, when kinematically allowed, such heavy-light decays are powerful channels for discovering the G*. In particular, we present a parton-level Montecarlo analysis of the final state Wtb that follows from the decay of G* to one SM top or bottom quark plus its heavy partner. We find that at √s = 7 TeV and with 10fb -1 of integrated luminosity, the LHC can discover a KK gluon with mass in the range MG* = (1.8 - 2.2) TeV if its coupling to a pair of light quarks is gG*qq - = (0.2 - 0.5)g3. The same process is also competitive for the discovery of the top and bottom partners as well. We find, for example, that the LHC at √s = 7 TeV can discover a 1TeV KK bottom quark with an integrated luminosity of (5.3 - 0.61) fb -1 for gG*qq - = (0.2 - 0.5)53. © SISSA 2012
Minimal Dark Matter bound states at future colliders
No full textThe hypothesis that Dark Matter is one electroweak multiplet leads to predictive candidates with multi-TeV masses that can form electroweak bound states. Bound states with the same quantum numbers as electroweak vectors are found to be especially interesting, as they can be produced resonantly with large cross sections at lepton colliders. Such bound states exist e.g. if DM is an automatically stable fermionic weak 5-plet with mass M ≈ 14 TeV such that the DM abundance is reproduced thermally. In this model, a muon collider could resolve three such bound states. Production rates are so large that details of DM spectroscopy can be probed with larger statistics: we compute the characteristic pattern of single and multiple γ lines
An accurate evaluation of electron (anti-)neutrino scattering on nucleons
No full textWe discuss as accurately as possible the cross section of quasi-elastic scattering of electron (anti-)neutrinos on nucleons, also known as inverse beta decay in the case of antineutrinos. We focus on the moderate energy range from a few MeV up to hundreds of MeV, which includes neutrinos from reactors and supernovae. We assess the uncertainty on the cross section, which is relevant to experimental advances and increasingly large statistical samples. We estimate the effects of second-class currents, showing that they are small and negligible for current applications
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