1,741 research outputs found
A Swarm of Bs
New physics signals containing five or more b-tagged jets, but without MET or
leptons, could realistically be sitting within the current 8 TeV LHC data set
without receiving meaningful constraints from any of the existing LHC searches
at either ATLAS or CMS. This work provides several examples of simple,
motivated models that yield final states containing many b-jets. To study the
potential for uncovering new physics in these high b-jet multiplicity channels,
this paper focuses on a natural supersymmetry scenario where each of the
pair-produced stops decays to an on-shell chargino, which subsequently decays
via an MFV-motivated, R-parity violating coupling. This gives rise to an
eight-jet final state containing six b-quarks. Although no public measurements
exist, estimates indicate that the standard model backgrounds in high b-jet
multiplicity channels should be very small. To circumvent the background
uncertainty, an asymmetric method is presented that utilizes two different
techniques to conservatively exclude or to discover new physics in high b-jet
multiplicity final states.Comment: 14 pages, 4 figures, 2 tables, journal versio
Toward Full LHC Coverage of Natural Supersymmetry
We argue that combining just a handful of searches for new physics at Run I
of the LHC is sufficient to exclude most supersymmetric extensions of the
Standard Model in which the gluino is kinematically accessible and the spectrum
is natural. Such models typically give rise to significant MET, top quarks
and/or high object multiplicity, and we show that having even one of these
signatures generally results in stringent limits. We also identify, among
models that lack these signatures, the few gaps in coverage remaining, and
propose search strategies to close these gaps. Our results are general and
independent of the details of the spectrum, assumptions about minimality,
R-parity, etc. Our analysis strategy should remain applicable when the LHC
moves to higher energy. Central to our argument are ATLAS and CMS searches for
many jets and low MET, a proposed lepton + many jets search, an ATLAS search
for 6-7 high-pT jets, and a reexamination of the control and signal regions of
the CMS black hole search.Comment: 53 pages, 16 figures, journal versio
Long-lived staus and displaced leptons at the LHC
As the majority of LHC searches are focused on prompt signatures, specific
long-lived particles have the potential to be overlooked by the otherwise
systematic new physics programs at ATLAS and CMS. While in many cases
long-lived superparticles are now stringently constrained by existing exotic
searches, we point out that the highly motivated model of gauge mediation with
staus as the next-to-lightest superparticle (NLSP) has received less attention.
We recast LHC searches for heavy stable charged particles, disappearing tracks,
and opposite-flavor leptons with large impact parameters to assess current
constraints on a variety of spectra that contain an NLSP stau, and find that
portions of the parameter space motivated by naturalness are still
experimentally unexplored. We additionally note a gap in the current
experimental search program: same-flavor leptons with large impact parameters
evade the suite of existing searches for long-lived objects. This gap is
especially noteworthy as vetoes on displaced leptons in prompt new physics
searches could be systematically discarding such events. We discuss several
motivated models that can exhibit same-flavor displaced leptons: gauge
mediation with co-NLSP sleptons, extended gauge mediation, R-parity violation,
and lepton-flavored dark matter that freezes in during a matter-dominated era
of the early universe. To address this gap, we propose a straightforward
extension of the CMS search for leptons with large impact parameters, and
project sensitivity to these scenarios at 13 TeV. Throughout this analysis, we
highlight several methods whereby LHC searches for exotic long-lived objects
could potentially improve their sensitivity to the displaced leptons
originating from gauge mediation and beyond.Comment: 48 pages, 6 figures, journal versio
Strong Electroweak Symmetry Breaking and Spin 0 Resonances
We argue that theories of strong electroweak symmetry breaking sector
necessarily contain new spin 0 states at the TeV scale in the tbar-t and
tbar-b/bbar-t channels, even if the third generation quarks are not composite
at the TeV scale. These states couple sufficiently strongly to third generation
quarks to have significant production at LHC via gg \to X or gb \to X. The
existence of narrow resonances in QCD suggests that the strong electroweak
breaking sector contains narrow resonances that decay to tbar-t or
tbar-b/bbar-t, with significant branching fractions to 3 or more longitudinal W
and Z bosons. These may give new "smoking gun" signals of strong electroweak
symmetry breaking.Comment: 4 pages, 1 figur
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