811 research outputs found
LHC discovery potential for supersymmetry with \sqrt{s}=7 TeV and 5-30 fb^{-1}
We extend our earlier results delineating the supersymmetry (SUSY) reach of
the CERN Large Hadron Collider operating at a centre-of-mass energy \sqrt{s}=7
TeV to integrated luminosities in the range 5 - 30 fb^{-1}. Our results are
presented within the paradigm minimal supergravity model (mSUGRA or CMSSM).
Using a 6-dimensional grid of cuts for the optimization of signal to background
ratio -- including missing E_T-- we find for m(gluino) \sim m(squark) an LHC
5\sigma SUSY discovery reach of m(gluino) \sim 1.3,\ 1.4,\ 1.5 and 1.6 TeV for
5, 10, 20 and 30 fb^{-1}, respectively. For m(squark)>> m(gluino), the
corresponding reach is instead m(gluino)\sim 0.8,\ 0.9,\ 1.0 and 1.05 TeV, for
the same integrated luminosities.Comment: 7 pages with 2 .eps figure. In version 2, a new figure has been added
along with associated discussio
Determining the squark mass at the LHC
We propose a new way to determine the squark mass based on the shape of
di-jet invariant mass distribution of supersymmetry (SUSY) di-jet events at the
Large Hadron Collider (LHC). Our algorithm, which is based on event kinematics,
requires that the branching ratio is
substantial for at least some types of squarks, and that
. We select di-jet events with no
isolated leptons, and impose cuts on the total jet transverse energy,
, on , and on the
azimuthal angle between the two jets to reduce SM backgrounds. The shape of the
resulting di-jet mass distribution depends sensitively on the squark mass,
especially if the integrated luminosity is sufficient to allow a hard enough
cut on and yet leave a large enough signal to obtain the
distribution. We simulate the signal and Standard Model (SM) backgrounds for
100 fb integrated luminosity at 14 TeV requiring GeV.
We show that it should be possible to extract to within about
3% at 95% CL --- similar to the precision obtained using --- from the
di-jet mass distribution if GeV, or to within % if TeV.Comment: 20 pages, 9 figures. Footnote added, updated reference
Measurement as a shortcut to long-range entangled quantum matter
The preparation of long-range entangled states using unitary circuits is
limited by Lieb-Robinson bounds, but circuits with projective measurements and
feedback (``adaptive circuits'') can evade such restrictions. We introduce
three classes of local adaptive circuits that enable low-depth preparation of
long-range entangled quantum matter characterized by gapped topological orders
and conformal field theories (CFTs). The three classes are inspired by distinct
physical insights, including tensor-network constructions, multiscale
entanglement renormalization ansatz (MERA), and parton constructions. A large
class of topological orders, including chiral topological order, can be
prepared in constant depth or time, and one-dimensional CFT states and
non-abelian topological orders with both solvable and non-solvable groups can
be prepared in depth scaling logarithmically with system size. We also build on
a recently discovered correspondence between symmetry-protected topological
phases and long-range entanglement to derive efficient protocols for preparing
symmetry-enriched topological order and arbitrary CSS (Calderbank-Shor-Steane)
codes. Our work illustrates the practical and conceptual versatility of
measurement for state preparation.Comment: 22 pages, 9 figures, restructured, relation to Ref. [7, 8] clarifie
Mixed axion/neutralino cold dark matter in supersymmetric models
We consider supersymmetric (SUSY) models wherein the strong CP problem is
solved by the Peccei-Quinn (PQ) mechanism with a concommitant axion/axino
supermultiplet. We examine R-parity conserving models where the neutralino is
the lightest SUSY particle, so that a mixture of neutralinos and axions serve
as cold dark matter. The mixed axion/neutralino CDM scenario can match the
measured dark matter abundance for SUSY models which typically give too low a
value of the usual thermal neutralino abundance, such as models with wino-like
or higgsino-like dark matter. The usual thermal neutralino abundance can be
greatly enhanced by the decay of thermally-produced axinos to neutralinos,
followed by neutralino re-annihilation at temperatures much lower than
freeze-out. In this case, the relic density is usually neutralino dominated,
and goes as \sim (f_a/N)/m_{axino}^{3/2}. If axino decay occurs before
neutralino freeze-out, then instead the neutralino abundance can be augmented
by relic axions to match the measured abundance. Entropy production from
late-time axino decays can diminish the axion abundance, but ultimately not the
neutralino abundance. In mixed axion/neutralino CDM models, it may be possible
to detect both a WIMP and an axion as dark matter relics. We also discuss
possible modifications of our results due to production and decay of saxions.
In the appendices, we present expressions for the Hubble expansion rate and the
axion and neutralino relic densities in radiation, matter and decaying-particle
dominated universes.Comment: 31 pages including 21 figure
Supersymmetry discovery potential of the LHC at 10 and 14 TeV without and with missing
We examine the supersymmetry (SUSY) reach of the CERN LHC operating at
and 14 TeV within the framework of the minimal supergravity
model. We improve upon previous reach projections by incorporating updated
background calculations including a variety of Standard Model (SM)
processes. We show that SUSY discovery is possible even before the detectors
are understood well enough to utilize either or electrons in
the signal. We evaluate the early SUSY reach of the LHC at TeV by
examining multi-muon plus jets and also dijet events with {\it no}
missing cuts and show that the greatest reach in terms of
occurs in the dijet channel. The reach in multi-muons is slightly smaller in
, but extends to higher values of . We find that an observable
multi-muon signal will first appear in the opposite-sign dimuon channel, but as
the integrated luminosity increases the relatively background-free but
rate-limited same-sign dimuon, and ultimately the trimuon channel yield the
highest reach. We show characteristic distributions in these channels that
serve to distinguish the signal from the SM background, and also help to
corroborate its SUSY origin. We then evaluate the LHC reach in various
no-lepton and multi-lepton plus jets channels {\it including} missing
cuts for and 14 TeV, and plot the reach for integrated
luminosities ranging up to 3000 fb at the SLHC. For TeV,
the LHC reach extends to and 2.9 TeV for
and integrated luminosities of 10, 100, 1000 and
3000 fb, respectively. For TeV, the LHC reach for the same
integrated luminosities is to m_{gluino}=2.4,\3.1, 3.7 and 4.0 TeV.Comment: 34 pages, 25 figures. Revised projections for the SUSY reach for
ab^-1 integrated luminosities, with minor corrections of references and text.
2 figures added. To appear in JHE
Fine-tuning implications for complementary dark matter and LHC SUSY searches
The requirement that SUSY should solve the hierarchy problem without undue
fine-tuning imposes severe constraints on the new supersymmetric states. With
the MSSM spectrum and soft SUSY breaking originating from universal scalar and
gaugino masses at the Grand Unification scale, we show that the low-fine-tuned
regions fall into two classes that will require complementary collider and dark
matter searches to explore in the near future. The first class has relatively
light gluinos or squarks which should be found by the LHC in its first run. We
identify the multijet plus E_T^miss signal as the optimal channel and determine
the discovery potential in the first run. The second class has heavier gluinos
and squarks but the LSP has a significant Higgsino component and should be seen
by the next generation of direct dark matter detection experiments. The
combined information from the 7 TeV LHC run and the next generation of direct
detection experiments can test almost all of the CMSSM parameter space
consistent with dark matter and EW constraints, corresponding to a fine-tuning
not worse than 1:100. To cover the complete low-fine-tuned region by SUSY
searches at the LHC will require running at the full 14 TeV CM energy; in
addition it may be tested indirectly by Higgs searches covering the mass range
below 120 GeV.Comment: References added. Version accepted for publication in JHE
Strong disorder fixed points in the two-dimensional random-bond Ising model
The random-bond Ising model on the square lattice has several disordered
critical points, depending on the probability distribution of the bonds. There
are a finite-temperature multicritical point, called Nishimori point, and a
zero-temperature fixed point, for both a binary distribution where the coupling
constants take the values +/- J and a Gaussian disorder distribution. Inclusion
of dilution in the +/- J distribution (J=0 for some bonds) gives rise to
another zero-temperature fixed point which can be identified with percolation
in the non-frustrated case (J >= 0). We study these fixed points using
numerical (transfer matrix) methods. We determine the location, critical
exponents, and central charge of the different fixed points and study the
spin-spin correlation functions. Our main findings are the following: (1) We
confirm that the Nishimori point is universal with respect to the type of
disorder, i.e. we obtain the same central charge and critical exponents for the
+/- J and Gaussian distributions of disorder. (2) The Nishimori point, the
zero-temperature fixed point for the +/- J and Gaussian distributions of
disorder, and the percolation point in the diluted case all belong to mutually
distinct universality classes. (3) The paramagnetic phase is re-entrant below
the Nishimori point, i.e. the zero-temperature fixed points are not located
exactly below the Nishimori point, neither for the +/- J distribution, nor for
the Gaussian distribution.Comment: final version to appear in JSTAT; minor change
Testing Yukawa-unified SUSY during year 1 of LHC: the role of multiple b-jets, dileptons and missing E_T
We examine the prospects for testing SO(10) Yukawa-unified supersymmetric
models during the first year of LHC running at \sqrt{s}= 7 TeV, assuming
integrated luminosity values of 0.1 to 1 fb^-1. We consider two cases: the
Higgs splitting (HS) and the D-term splitting (DR3) models. Each generically
predicts light gluinos and heavy squarks, with an inverted scalar mass
hierarchy. We hence expect large rates for gluino pair production followed by
decays to final states with large b-jet multiplicity. For 0.2 fb^-1 of
integrated luminosity, we find a 5 sigma discovery reach of m(gluino) ~ 400 GeV
even if missing transverse energy, E_T^miss, is not a viable cut variable, by
examining the multi-b-jet final state. A corroborating signal should stand out
in the opposite-sign (OS) dimuon channel in the case of the HS model; the DR3
model will require higher integrated luminosity to yield a signal in the OS
dimuon channel. This region may also be probed by the Tevatron with 5-10 fb^-1
of data, if a corresponding search in the multi-b+ E_T^miss channel is
performed. With higher integrated luminosities of ~1 fb^-1, using E_T^miss plus
a large multiplicity of b-jets, LHC should be able to discover Yukawa-unified
SUSY with m(gluino) up to about 630 GeV. Thus, the year 1 LHC reach for
Yukawa-unified SUSY should be enough to either claim a discovery of the gluino,
or to very nearly rule out this class of models, since higher values of
m(gluino) lead to rather poor Yukawa unification.Comment: 32 pages including 31 EPS figure
Light Sneutrino Dark Matter at the LHC
In supersymmetric (SUSY) models with Dirac neutrino masses, a weak-scale
trilinear A-term that is not proportional to the small neutrino Yukawa
couplings can induce a sizable mixing between left and right-handed sneutrinos.
The lighter sneutrino mass eigenstate can hence become the lightest SUSY
particle (LSP) and a viable dark matter candidate. In particular, it can be an
excellent candidate for light dark matter with mass below ~10 GeV. Such a light
mixed sneutrino LSP has a dramatic effect on SUSY signatures at the LHC, as
charginos decay dominantly into the light sneutrino plus a charged lepton, and
neutralinos decay invisibly to a neutrino plus a sneutrino. We perform a
detailed study of the LHC potential to resolve the light sneutrino dark matter
scenario by means of three representative benchmark points with different
gluino and squark mass hierarchies. We study in particular the determination of
the LSP (sneutrino) mass from cascade decays involving charginos, using the mT2
variable. Moreover, we address measurements of additional invisible sparticles,
in our case the lightest neutralino, and the question of discrimination against
the MSSM.Comment: 25 pages, 16 figure
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