Low Recoil Research Articles

Dark Matter implications of DAMA/LIBRA-phase2 results

Recently, the DAMA/LIBRA collaboration released updated results from their search for the annual modulation signal from Dark Matter (DM) scattering in the detector. Besides approximately doubling the exposure of the DAMA/LIBRA data set, the updated photomultiplier tubes of the experiment allow a lower recoil energy threshold of 1keV electron equivalent compared to the previous threshold of 2keV electron equivalent. We study the compatibility of the observed modulation signal with DM scattering. Due to a conspiracy of multiple effects, the new data at low recoil energies is very powerful for testing the DM hypothesis. We find that canonical (isospin conserving) spin-independent DM-nucleon interactions are no longer a good fit to the observed modulation signal in the standard halo model. The canonical spin-independent case is disfavored by the new data, with best fit points of a DM mass of ∼8GeV, disfavored by 5.2σ, or a mass of ∼54GeV, disfavored by 2.5σ. Allowing for isospin violating spin independent interactions, we find a region with a good fit to the data with suppressed effective couplings to iodine for DM masses of ∼10GeV. We also consider spin-dependent DM-nucleon interactions, which yield good fits for similar DM masses of ∼10GeV or ∼45GeV.

Physics and technology of time projection chambers as active targets

Many nuclear structure studies are presently performed with secondary radioactive beams to explore the nuclear chart far from stability. This entails a large decrease of available intensities, as compared to stable beam experiments, even with the highest power primary beam accelerators. To compensate for this intensity loss, thick targets and high detection efficiency are needed. Using secondary beams implies a change from direct kinematics to inverse kinematics: the target becomes the light reaction partner and the beam the heavy reaction partner. In quasi-elastic processes, the light reaction partner carrying most of the information emerges with very low recoil energy. In these conditions Time Projections Chambers (TPCs) filled with a gas that serves as both target and tracking medium (Active Target) have very unique properties that mitigate these difficulties. By construction, a TPC has a solid angle coverage of $ 4\pi$ , and even short tracks of low energy particles can be precisely measured if the readout has a high enough granularity. Due to the reaction characteristics large dynamics of the electronics and gas multipliers are needed, and specific data analysis methods of the 3-dimensional tracks have to be developed.

Sensitivity of the PICO-500 bubble chamber to supernova neutrinos through coherent nuclear elastic scattering

Ton-scale direct dark matter search experiments should be sensitive to neutrino-induced recoil events from either 8B solar neutrinos or the brief but intense flux from a core collapse supernova in the Milky Way. These low-threshold detectors are sensitive to the very low recoil energies, of order 10 keV, deposited via coherent elastic scatters between supernova neutrinos and target nuclei. Large superheated fluid detectors like PICO-500, a bubble chamber to be initially filled with an active target of 1 t of C3F8, should see multiple-bubble events from CEνNS if the detector is live during a neutrino burst from a supernova at a distance up to 10 kpc. This paper discusses conditions under which bubble chambers could be used as an independent measurement in the event of a supernova similar to SN 1987A, with particular sensitivity to the currently less-constrained heavy-lepton νx channel.

Angular moments of the decay \u039bb0\u2009\u2192\u2009\u039b\u03bc+\u03bc\u2212 at low hadronic recoil

An analysis of the angular distribution of the decay Λb0 → Λμ+μ− is presented, using data collected with the LHCb detector between 2011 and 2016 and corresponding to an integrated luminosity of approximately 5 fb−1. Angular observables are determined using a moment analysis of the angular distribution at low hadronic recoil, corresponding to the dimuon invariant mass squared range 15 < q2 < 20 GeV2/c4. The full basis of observables is measured for the first time. The lepton-side, hadron-side and combined forward-backward asymmetries of the decay are determined to beAFBℓ=−0.39±0.04stat±0.01syst,AFBh=−0.30±0.05stat±0.02syst,AFBℓh=+0.25±0.04stat±0.01syst.\\documentclass[12pt]{minimal}\t\t\t\t\\usepackage{amsmath}\t\t\t\t\\usepackage{wasysym}\t\t\t\t\\usepackage{amsfonts}\t\t\t\t\\usepackage{amssymb}\t\t\t\t\\usepackage{amsbsy}\t\t\t\t\\usepackage{mathrsfs}\t\t\t\t\\usepackage{upgreek}\t\t\t\t\\setlength{\\oddsidemargin}{-69pt}\t\t\t\t\\begin{document}$$ \\begin{array}{l}{A}_{\\mathrm{FB}}^{\\ell }=-0.39\\pm 0.04\\left(\\mathrm{stat}\\right)\\pm 0.01\\left(\\mathrm{syst}\\right),\\hfill \\\\ {}{A}_{\\mathrm{FB}}^h=-0.30\\pm 0.05\\left(\\mathrm{stat}\\right)\\pm 0.02\\left(\\mathrm{syst}\\right),\\hfill \\\\ {}{A}_{\\mathrm{FB}}^{\\ell h}=+0.25\\pm 0.04\\left(\\mathrm{stat}\\right)\\pm 0.01\\left(\\mathrm{syst}\\right).\\hfill \\end{array} $$\\end{document}The measurements are consistent with Standard Model predictions.

Particle detection at cryogenic temperatures with undoped CsI

Scintillators are widely used as particle detectors in particle physics. Scintillation at cryogenic temperatures can give rise to detectors with particle discrimination for rare-event searches such as dark matter detection. We present time-resolved scintillation studies of Cesium Iodide (CsI) under excitation of both α and γ particles over a long acquisition window of 1 ms to fully capture the scintillation decay between room temperature and 4 K. This allows a measurement of the light yield independent of any shaping time of the pulse. We find the light yield of CsI to increase up to two orders of magnitude from that of room temperature at cryogenic temperatures, and the ratio of α to γ excitation to vary significantly, exceeding 1 over a range of temperatures between 10 and 100 K. This property could be useful in separating α backgrounds from the low energy nuclear recoil signal region. We also find the time structure of the emitted light to follow similar exponential decay time constants between α and γ excitation, with the temperature behavior consistent with a model of self-trapped exciton de-excitation. Based on these properties, undoped CsI is an interesting candidate for use in cryogenic particle detectors.

Saturation of tungsten surfaces with hydrogen: A density functional theory study complemented by low energy ion scattering and direct recoil spectroscopy data

Herein, we investigate the saturation limits of hydrogen on the (110) and (100) surfaces of tungsten via Density Functional Theory (DFT) and complement our findings with experimental measurements. We present a detailed study of the various stable configurations that hydrogen can adopt upon the surfaces at coverage ratios starting below 1.0, up to the point of their experimental coverage ratios, and beyond. We provide the many low-energy configurations that exist at all coverages along with the energy landscape they form. Our findings allow us to estimate that the saturation limit on each surface exists with one monolayer of hydrogen atoms adsorbed. In the case of (110) this corresponds to a coverage ratio of one hydrogen atom per tungsten atom, while in the case of (100) a full monolayer is present at a coverage ratio of 2.0 hydrogen atoms per tungsten atoms. Preliminary Low Energy Ion Scattering (LEIS) and Direct Recoil Spectroscopy (DRS) measurements complement this work on the W(110) surface. These results and some previously published measurements obtained on the W(100) surface confirm the findings obtained by DFT. In particular, the saturation limits on each surface, the preferred adsorption sites on both surfaces up to saturation, and the reconstruction of the bare and unsaturated (100) surface.

Low-energy electronic recoil in xenon detectors by solar neutrinos

Low-energy electronic recoil caused by solar neutrinos in multi-ton xenon detectors is an important subject not only because it is a source of the irreducible background for direct searches of weakly-interacting massive particles (WIMPs), but also because it provides a viable way to measure the solar pp and 7Be neutrinos at the precision level of current standard solar model predictions. In this work we perform ab initio many-body calculations for the structure, photoionization, and neutrino-ionization of xenon. It is found that the atomic binding effect yields a sizable suppression to the neutrino-electron scattering cross section at low recoil energies. Compared with the previous calculation based on the free electron picture, our calculated event rate of electronic recoil in the same detector configuration is reduced by about 23%. We present in this paper the electronic recoil rate spectrum in the energy window of 100 eV to 30 keV with the standard per ton per year normalization for xenon detectors, and discuss its implication for low energy solar neutrino detection as the signal and WIMP search as a source of background.

The COSINUS project - a NaI-based cryogenic calorimeter for direct dark matter detection

At present the results in the field of direct dark matter search are in tension: the positive claim of DAMA/LIBRA versus null results from other experiments. However, the comparison of the results of different experiments involves model dependencies, in particular because of the different target materials in use. The COSINUS R&D project aims to operate NaI as a cryogenic calorimeter. Such a detector would not only allow for a direct comparison to DAMA/LIBRA, but would also provide a low(er) nuclear recoil threshold and particle discrimination.

Revisiting B→K*(→Kπ)νν¯ decays

The rare decay $B\to K^\ast( \to K\pi) \nu\bar{\nu}$ is expected to play an important role in searches for physics beyond the Standard Model at the near future $B$-physics experiments. We investigate resonant and non-resonant backgrounds that arise beyond the narrow-width approximation for the $K^\ast$. Non-resonant $B\to K\pi \nu\bar{\nu}$ decays are analyzed in the region of low hadronic recoil, where $B \to K \pi$ form factors from Heavy-Hadron-Chiral-Perturbation Theory are available. In a Breit-Wigner-type model interference-induced effects in the $K^*$ signal region are found to be sizable, as large as $20\%$ in the branching ratio. Corresponding effects in the longitudinal polarization fraction $F_L$ are smaller, at most around few \%. Effects of the broad scalar states $K_0^\ast$ and $\kappa$ are at the level of percent in the branching fraction in the $K^\ast$ signal region and negligible in $F_L$. Since the backgrounds to $F_L$ are small this observable constitutes a useful probe of form factors calculations, or alternatively, of right-handed currents in the entire $q^2$-region. The forward-backward asymmetry in the $K \pi$-system, $A_{\rm FB \, L}^K$, with normalization to the longitudinal decay rate probes predominantly S,P-wave interference free of short-distance coefficients and can therefore be used to control the resonant and non-resonant backgrounds.

Measuring the breaking of lepton flavor universality in B→K*ℓ+ℓ−

We propose measurements of weighted differences of the angular observables in the rare decays $B \to K^*\ell^+\ell^-$. The proposed observables are very sensitive to the difference between the Wilson coefficients $\mathcal{C}_9^{(e)}$ and $\mathcal{C}_9^{(\mu)}$ for decays into electrons and muons, respectively. At the same time, the charm-induced hadronic contributions are kinematically suppressed to $\lesssim 7\% (4\%)$ in the region $1\,$GeV$^2 \leq q^2 \leq 6\,$GeV$^2$, as long as LFU breaking occurs only in $\mathcal{C}^{(\ell)}_{9}$. This suppression becomes stronger for the region of low hadronic recoil, $q^2 \geq 15\,$GeV$^2$.

Zooming in on Brightarrow K^*ell ell decays at low recoil

We analyse Brightarrow K^*ell ell decays in the region of low hadronic recoil, where an operator product expansion (OPE) in 1/m_b applies. Using a local model for charm contributions based on e^+ e^- rightarrow mathrm{hadrons} against the OPE provides a data-driven method to access the limitations to the OPE’s accuracy related to binnings in the dilepton mass. Model-independent fits to Brightarrow K^*mu mu low recoil angular observables exhibit presently only small sensitivity to different charm models. They give similar results to the fits based on the OPE and are in agreement with the standard model, but leave also room for new physics. Measurements with resolution small enough to probe charm resonances would be desirable.

Dynamical response of dark matter to galaxy evolution affects direct-detection experiments

Over a handful of rotation periods, dynamical processes in barred galaxies induce non-axisymmetric structure in dark matter halos. Using n-body simulations of a Milky Way-like barred galaxy, we identify both a trapped dark-matter component, a shadow bar, and a strong response wake in the dark-matter distribution that affects the predicted dark-matter detection rates for current experiments. The presence of a baryonic disk together with well-known dynamical processes (e.g. spiral structure and bar instabilities) increase the dark matter density in the disk plane. We find that the magnitude of the combined stellar and shadow bar evolution, when isolated from the effect of the axisymmetric gravitational potential of the disk, accounts for >30% of this overall increase in disk-plane density. This is significantly larger that of previously claimed deviations from the standard halo model. The dark-matter density and kinematic wakes driven by the Milky Way bar increase the detectability of dark matter overall, especially for the experiments with higher $v_{min}$. These astrophysical features increase the detection rate by more than a factor of two when compared to the standard halo model and by a factor of ten for experiments with high minimum recoil energy thresholds. These same features increase (decrease) the annual modulation for low (high) minimum recoil energy experiments. We present physical arguments for why these dynamics are generic for barred galaxies such as the Milky Way rather than contingent on a specific galaxy model.

Measurements of the inclusive neutrino and antineutrino charged current cross sections in MINERvA using the low- ν flux method

The total cross sections are important ingredients for the current and future neutrino oscillation experiments. We present measurements of the total charged-current neutrino and antineutrino cross sections on scintillator (CH) in the NuMI low-energy beamline using an {\em in situ} prediction of the shape of the flux as a function of neutrino energy from 2--50 GeV. This flux prediction takes advantage of the fact that neutrino and antineutrino interactions with low nuclear recoil energy ($\nu$) have a nearly constant cross section as a function of incident neutrino energy. This measurement is the lowest energy application of the low-$\nu$ flux technique, the first time it has been used in the NuMI antineutrino beam configuration, and demonstrates that the technique is applicable to future neutrino beams operating at multi-GeV energies. The cross section measurements presented are the most precise measurements to date below 5 GeV.

Predictors of acute scaffold recoil after implantation of the everolimus-eluting bioresorbable scaffold: an optical coherence tomography assessment in native coronary arteries.

This study investigated the predictors of acute recoil after implantation of everolimus-eluting BRS based on optical coherence tomography (OCT). Thirty-nine patients (56 scaffolds) were enrolled. Acute absolute recoil by quantitative coronary angiography was defined as the difference between the mean diameter of the last inflated balloon (X) and the mean lumen diameter of BRS immediately after balloon deflation (Y). Acute percent recoil was defined as (X - Y) × 100/X. Plaque eccentricity (PE) and plaque composition (PC) were assessed by OCT. PC was classified into two different types: calcific (score = 1), fibrous and lipid (score = 0). Based on the mean acute scaffold recoil value of the present study, scaffolds were divided into two groups: the low acute recoil group (LAR, n = 34) and the high acute recoil group (HAR, n = 22). Acute percent and absolute recoil were 6.4 ± 3.0 % and 0.19 ± 0.11mm. PE, PC score and scaffold/artery ratio were significantly higher in HAR than in LAR. In multivariate logistic regression analysis, PE > 1.49, PC score (score 1) and scaffold/artery ratio >1.07 were significant positive predictors for the occurrence of acute scaffold recoil (OR 10.7, 95 % CI 2.2-51.4, p < 0.01; OR 5.6, 95 % CI 1.9-22.0, p = 0.04; OR 12.4, 95 % CI 2.6-65.4, p < 0.01, respectively). Acute recoil of BRS is influenced by BRS sizing as well as OCT-derived plaque characteristics.

Multiple scattering mechanisms causing interference effects in the differential cross sections of H + D2 → HD(v' = 4, j') + D at 3.26 eV collision energy.

Differential cross sections (DCSs) for the H + D2 → HD(v' = 4, j') + D reaction at 3.26 eV collision energy have been measured using the photoloc technique, and the results have been compared with those from quantum and quasiclassical scattering calculations. The quantum mechanical DCSs are in good overall agreement with the experimental measurements. In common with previous results at 1.97 eV, clear interference patterns which appear as fingerlike structures have been found at 3.26 eV but in this case for vibrational states as high as v' = 4. The oscillatory structure is prominent for low rotational states and progressively disappears as j' increases. A detailed analysis, similar to that carried out at 1.97 eV, shows that the origin of these structures could be traced to interferences between well defined classical mechanisms. In addition, at this energy, we do not observe the anomalous positive j'-θ trend found for the v' = 4 manifold at lower collision energies, thus reinforcing our explanation that the anomalous distribution for HD(v' = 4, j') at 1.97 eV only takes place for those states associated with low product recoil energies.

WIMP detection and slow ion dynamics in carbon nanotube arrays.

Large arrays of aligned carbon nanotubes (CNTs), open at one end, could be used as target material for the directional detection of weakly interacting dark matter particles (WIMPs). As a result of a WIMP elastic scattering on a CNT, a carbon ion might be injected in the body of the array and propagate through multiple collisions within the lattice. The ion may eventually emerge from the surface with open end CNTs, provided that its longitudinal momentum is large enough to compensate energy losses and its transverse momentum approaches the channeling conditions in a single CNT. Therefore, the angle formed between the WIMP wind apparent orientation and the direction of parallel carbon nanotube axes must be properly chosen. We focus on very low ion recoil kinetic energies, related to low mass WIMPs (approx 11 GeV) where most of the existing experiments have low sensitivity. Relying on some exact results on two-dimensional lattices of circular obstacles, we study the low energy ion motion in the transverse plane with respect to CNT directions. New constraints are obtained on how to devise the CNT arrays to maximize the target channeling efficiency.

Atomic ionization by neutrinos at low energies

It is well-known that neutrino-electron scattering at low recoil energies provides sensitivity gain in constraining neutrinos’ magnetic moments and their possible milli-charges. However, in detectors with sub-keV thresholds, the binding effects of electrons become significant. In this talk, we present our recent works of applying ab initio calculations to germanium ionization by neutrinos at low energies. Compared with the conventional differential cross section formulae that were used to derive current experimental bounds, our results with less theoretical uncertainties set a more reliable bound on the neutrino magnetic moment and a more stringent bound on the neutrino milli-charge with current reactor antineutrino data taken from germanium detectors.

Leptoquark effects on and decay processes

We study the rare semileptonic decays of B mesons induced by as well as transitions in the scalar leptoquark (LQ) model, where the LQs have the representation (3, 2, 7/6) and (3, 2, 1/6) under the standard model gauge group. The LQ parameter space is constrained using the most recent experimental results on and processes. Considering only the baryon number conserving LQ interactions, we estimate the branching ratios for the exclusive and inclusive decay processes by using the constraint parameters. We also obtain the low recoil (large lepton invariant mass, i.e., ) predictions for the angular distribution of process and several other observables including the flat term and lepton flavour non-universality factor in this model.

Angular analysis of the decay Λ b → Λ(→ Nπ)ℓ + ℓ −

We study the differential decay rate for the rare Λ b → Λ(→ Nπ)ℓ + ℓ − transition, including a determination of the complete angular distribution, assuming unpolarized Λ b baryons. On the basis of a properly chosen parametrization of the various helicity amplitudes, we provide expressions for the angular observables within the Standard Model and a subset of new physics models with chirality-flipped operators. Hadronic effects at low recoil are estimated by combining information from lattice QCD with (improved) form-factor relations in Heavy Quark Effective Theory. Our estimates for large hadronic recoil — at this stage — are still rather uncertain because the baryonic input functions are not so well known, and non-factorizable spectator effects have not been worked out systematically so far. Still, our phenomenological analysis of decay asymmetries and angular observables for Λ b → Λ(→ Nπ)ℓ + ℓ − reveals that this decay mode can provide new and complementary constraints on the Wilson coefficients in radiative and semileptonic b → s transitions compared to the corresponding mesonic modes.

The B ¯ → K ¯ πℓℓ $$ \overline{B}\to \overline{K}\pi \ell \ell $$ and B ¯ s → K ¯ Kℓℓ $$ {\overline{B}}_s\ \to \overline{K}K\ell \ell $$ distributions at low hadronic recoil

The rare multi-body decays $$ \overline{B}\to \overline{K}\pi \ell \ell $$ and $$ {\overline{B}}_s \to \overline{K}K\ell \ell $$ are both important as backgrounds to precision analyses in the benchmark modes $$ \overline{B}\to {\overline{K}}^{*}\ell \ell $$ and $$ {\overline{B}}_s\to \phi \ell \ell $$ as well as sensitive probes of flavor physics in and beyond the standard model. We work out non-resonant contributions to $$ \overline{B}\to \overline{K}\pi \ell \ell $$ and $$ {\overline{B}}_s \to \overline{K}K\ell \ell $$ amplitudes, where l = e,μ, at low hadronic recoil in a model-independent way. Using the operator product expansion in 1/m b , we present expressions for the full angular distribution. The latter allows to probe new combinations of |ΔB| = |ΔS| = 1 couplings and gives access to strong phases between non-resonant and resonant contributions. Exact endpoint relations between transversity amplitudes based on Lorentz invariance are obtained. Several phenomenological distri- butions including those from the angular projections to the S-, P-, D-waves are given. Standard model branching ratios for non-resonant $$ \overline{B}\to \overline{K}\pi \ell \ell $$ and $$ {\overline{B}}_s \to \overline{K}K\ell \ell $$ decays are found to be in the few 10−8 region, but drop significantly if cuts around the K * or ϕ mass are employed. Nevertheless, the non-resonant contributions to $$ \overline{B}\to \overline{K}\pi \ell \ell $$ provide the dominant background in the $$ \overline{B}\to {\overline{K}}^{*}\ell \ell $$ signal region with respect to the low mass scalars. In $$ {\overline{B}}_s \to \overline{K}K\ell \ell $$ , the narrowness of the ϕ allows for more efficient background control. We briefly discuss lepton-flavor non-universal effects, also in view of the recent data on R K .