28 research outputs found
Background determination for the LUX-ZEPLIN dark matter experiment
The LUX-ZEPLIN experiment recently reported limits on WIMP-nucleus interactions from its initial science run, down to 9.2×10-48 cm2 for the spin-independent interaction of a 36 GeV/c2 WIMP at 90% confidence level. In this paper, we present a comprehensive analysis of the backgrounds important for this result and for other upcoming physics analyses, including neutrinoless double-beta decay searches and effective field theory interpretations of LUX-ZEPLIN data. We confirm that the in-situ determinations of bulk and fixed radioactive backgrounds are consistent with expectations from the ex-situ assays. The observed background rate after WIMP search criteria were applied was (6.3±0.5)×10-5 events/keVee/kg/day in the low-energy region, approximately 60 times lower than the equivalent rate reported by the LUX experiment
Theoretical predictions for the direct detection of neutralino dark matter in the NMSSM
We analyse the direct detection of neutralino dark matter in the framework of
the Next-to-Minimal Supersymmetric Standard Model. After performing a detailed
analysis of the parameter space, taking into account all the available
constraints from LEPII, we compute the neutralino-nucleon cross section, and
compare the results with the sensitivity of detectors. We find that sizable
values for the detection cross section, within the reach of dark matter
detectors, are attainable in this framework. For example, neutralino-proton
cross sections compatible with the sensitivity of present experiments can be
obtained due to the exchange of very light Higgses with m_{h_1^0}\lsim 70
GeV. Such Higgses have a significant singlet composition, thus escaping
detection and being in agreement with accelerator data. The lightest neutralino
in these cases exhibits a large singlino-Higgsino composition, and a mass in
the range 50\lsim m_{\tilde\chi_1^0}\lsim 100 GeV.Comment: Final version to appear in JHEP. References added. LaTeX, 53 pages,
23 figure
PAMELA, DAMA, INTEGRAL and Signatures of Metastable Excited WIMPs
Models of dark matter with ~ GeV scale force mediators provide attractive
explanations of many high energy anomalies, including PAMELA, ATIC, and the
WMAP haze. At the same time, by exploiting the ~ MeV scale excited states that
are automatically present in such theories, these models naturally explain the
DAMA/LIBRA and INTEGRAL signals through the inelastic dark matter (iDM) and
exciting dark matter (XDM) scenarios, respectively. Interestingly, with only
weak kinetic mixing to hypercharge to mediate decays, the lifetime of excited
states with delta < 2 m_e is longer than the age of the universe. The
fractional relic abundance of these excited states depends on the temperature
of kinetic decoupling, but can be appreciable. There could easily be other
mechanisms for rapid decay, but the consequences of such long-lived states are
intriguing. We find that CDMS constrains the fractional relic population of
~100 keV states to be <~ 10^-2, for a 1 TeV WIMP with sigma_n = 10^-40 cm^2.
Upcoming searches at CDMS, as well as xenon, silicon, and argon targets, can
push this limit significantly lower. We also consider the possibility that the
DAMA excitation occurs from a metastable state into the XDM state, which decays
via e+e- emission, which allows lighter states to explain the INTEGRAL signal
due to the small kinetic energies required. Such models yield dramatic signals
from down-scattering, with spectra peaking at high energies, sometimes as high
as ~1 MeV, well outside the usual search windows. Such signals would be visible
at future Ar and Si experiments, and may be visible at Ge and Xe experiments.
We also consider other XDM models involving ~ 500 keV metastable states, and
find they can allow lighter WIMPs to explain INTEGRAL as well.Comment: 22 pages, 7 figure
Direct detection of neutralino dark matter in supergravity
The direct detection of neutralino dark matter is analysed in general
supergravity scenarios, where non-universal soft scalar and gaugino masses can
be present. In particular, the theoretical predictions for the
neutralino-nucleon cross section are studied and compared with the sensitivity
of dark matter detectors. We take into account the most recent astrophysical
and experimental constraints on the parameter space, including the current
limit on B(Bs-> mu+ mu-). The latter puts severe limitations on the dark matter
scattering cross section, ruling out most of the regions that would be within
the reach of present experiments. We show how this constraint can be softened
with the help of appropriate choices of non-universal parameters which increase
the Higgsino composition of the lightest neutralino and minimise the chargino
contribution to the b->s transition.Comment: 27 pages, 22 figure
Baryogenesis, Electric Dipole Moments and Dark Matter in the MSSM
We study the implications for electroweak baryogenesis (EWB) within the
minimal supersymmetric Standard Model (MSSM) of present and future searches for
the permanent electric dipole moment (EDM) of the electron, for neutralino dark
matter, and for supersymmetric particles at high energy colliders. We show that
there exist regions of the MSSM parameter space that are consistent with both
present two-loop EDM limits and the relic density and that allow for successful
EWB through resonant chargino and neutralino processes at the electroweak phase
transition. We also show that under certain conditions the lightest neutralino
may be simultaneously responsible for both the baryon asymmetry and relic
density. We give present constraints on chargino/neutralino-induced EWB implied
by the flux of energetic neutrinos from the Sun, the prospective constraints
from future neutrino telescopes and ton-sized direct detection experiments, and
the possible signatures at the Large Hadron Collider and International Linear
Collider.Comment: 32 pages, 10 figures; version to appear on JHE
Model Independent Approach to Focus Point Supersymmetry: from Dark Matter to Collider Searches
The focus point region of supersymmetric models is compelling in that it
simultaneously features low fine-tuning, provides a decoupling solution to the
SUSY flavor and CP problems, suppresses proton decay rates and can accommodate
the WMAP measured cold dark matter (DM) relic density through a mixed
bino-higgsino dark matter particle. We present the focus point region in terms
of a weak scale parameterization, which allows for a relatively model
independent compilation of phenomenological constraints and prospects. We
present direct and indirect neutralino dark matter detection rates for two
different halo density profiles, and show that prospects for direct DM
detection and indirect detection via neutrino telescopes such as IceCube and
anti-deuteron searches by GAPS are especially promising. We also present LHC
reach prospects via gluino and squark cascade decay searches, and also via
clean trilepton signatures arising from chargino-neutralino production. Both
methods provide a reach out to m_{\tg}\sim 1.7 TeV. At a TeV-scale linear
e^+e^- collider (LC), the maximal reach is attained in the \tz_1\tz_2 or
\tz_1\tz_3 channels. In the DM allowed region of parameter space, a
\sqrt{s}=0.5 TeV LC has a reach which is comparable to that of the LHC.
However, the reach of a 1 TeV LC extends out to m_{\tg}\sim 3.5 TeV.Comment: 34 pages plus 36 eps figure
Mixed Higgsino Dark Matter from a Large SU(2) Gaugino Mass
We observe that in SUSY models with non-universal GUT scale gaugino mass
parameters, raising the GUT scale SU(2) gaugino mass |M_2| from its unified
value results in a smaller value of -m_{H_u}^2 at the weak scale. By the
electroweak symmetry breaking conditions, this implies a reduced value of \mu^2
{\it vis \`a vis} models with gaugino mass unification. The lightest neutralino
can then be mixed Higgsino dark matter with a relic density in agreement with
the measured abundance of cold dark matter (DM). We explore the phenomenology
of this high |M_2| DM model. The spectrum is characterized by a very large wino
mass and a concomitantly large splitting between left- and right- sfermion
masses. In addition, the lighter chargino and three light neutralinos are
relatively light with substantial higgsino components. The higgsino content of
the LSP implies large rates for direct detection of neutralino dark matter, and
enhanced rates for its indirect detection relative to mSUGRA. We find that
experiments at the LHC should be able to discover SUSY over the portion of
parameter space where m_{\tg} \alt 2350-2750 ~GeV, depending on the squark
mass, while a 1 TeV electron-positron collider has a reach comparable to that
of the LHC. The dilepton mass spectrum in multi-jet + \ell^+\ell^- + \eslt
events at the LHC will likely show more than one mass edge, while its shape
should provide indirect evidence for the large higgsino content of the decaying
neutralinos.Comment: 36 pages with 26 eps figure
Mixed Wino Dark Matter: Consequences for Direct, Indirect and Collider Detection
In supersymmetric models with gravity-mediated SUSY breaking and gaugino mass
unification, the predicted relic abundance of neutralinos usually exceeds the
strict limits imposed by the WMAP collaboration. One way to obtain the correct
relic abundance is to abandon gaugino mass universality and allow a mixed
wino-bino lightest SUSY particle (LSP). The enhanced annihilation and
scattering cross sections of mixed wino dark matter (MWDM) compared to bino
dark matter lead to enhanced rates for direct dark matter detection, as well as
for indirect detection at neutrino telescopes and for detection of dark matter
annihilation products in the galactic halo. For collider experiments, MWDM
leads to a reduced but significant mass gap between the lightest neutralinos so
that chi_2^0 two-body decay modes are usually closed. This means that dilepton
mass edges-- the starting point for cascade decay reconstruction at the CERN
LHC-- should be accessible over almost all of parameter space. Measurement of
the m_{\tz_2}-m_{\tz_1} mass gap at LHC plus various sparticle masses and cross
sections as a function of beam polarization at the International Linear
Collider (ILC) would pinpoint MWDM as the dominant component of dark matter in
the universe.Comment: 29 pages including 19 eps figure
Mixed Higgsino Dark Matter from a Reduced SU(3) Gaugino Mass: Consequences for Dark Matter and Collider Searches
In gravity-mediated SUSY breaking models with non-universal gaugino masses,
lowering the SU(3) gaugino mass |M_3| leads to a reduction in the squark and
gluino masses. Lower third generation squark masses, in turn, diminish the
effect of a large top quark Yukawa coupling in the running of the higgs mass
parameter m_{H_u}^2, leading to a reduction in the magnitude of the
superpotential mu parameter (relative to M_1 and M_2). A low | mu | parameter
gives rise to mixed higgsino dark matter (MHDM), which can efficiently
annihilate in the early universe to give a dark matter relic density in accord
with WMAP measurements. We explore the phenomenology of the low |M_3| scenario,
and find for the case of MHDM increased rates for direct and indirect detection
of neutralino dark matter relative to the mSUGRA model. The sparticle mass
spectrum is characterized by relatively light gluinos, frequently with
m(gl)<<m(sq). If scalar masses are large, then gluinos can be very light, with
gl->Z_i+g loop decays dominating the gluino branching fraction. Top squarks can
be much lighter than sbottom and first/second generation squarks. The presence
of low mass higgsino-like charginos and neutralinos is expected at the CERN
LHC. The small m(Z2)-m(Z1) mass gap should give rise to a visible
opposite-sign/same flavor dilepton mass edge. At a TeV scale linear e^+e^-
collider, the region of MHDM will mean that the entire spectrum of charginos
and neutralinos are amongst the lightest sparticles, and are most likely to be
produced at observable rates, allowing for a complete reconstruction of the
gaugino-higgsino sector.Comment: 35 pages, including 26 EPS figure
Exploring the BWCA (Bino-Wino Co-Annihilation) Scenario for Neutralino Dark Matter
In supersymmetric models with non-universal gaugino masses, it is possible to
have opposite-sign SU(2) and U(1) gaugino mass terms. In these models, the
gaugino eigenstates experience little mixing so that the lightest SUSY particle
remains either pure bino or pure wino. The neutralino relic density can only be
brought into accord with the WMAP measured value when bino-wino co-annihilation
(BWCA) acts to enhance the dark matter annihilation rate. We map out parameter
space regions and mass spectra which are characteristic of the BWCA scenario.
Direct and indirect dark matter detection rates are shown to be typically very
low. At collider experiments, the BWCA scenario is typified by a small mass gap
m_{\tilde Z_2}-m_{\tilde Z_1} ~ 20-80 GeV, so that tree level two body decays
of \tilde Z_2 are not allowed. However, in this case the second lightest
neutralino has an enhanced loop decay branching fraction to photons. While the
photonic neutralino decay signature looks difficult to extract at the Fermilab
Tevatron, it should lead to distinctive events at the CERN LHC and at a linear
e^+e^- collider.Comment: 44 pages, 21 figure