Exclusion limits on the WIMP-nucleon cross section from the Cryogenic Dark Matter Search

Abstract

The Cryogenic Dark Matter Search (CDMS) employs Ge and Si detectors to search for weakly interacting massive particles (WIMPs) via their elastic-scattering interactions with nuclei while discriminating against interactions of background particles. CDMS data, accounting for the neutron background, give limits on the spin-independent WIMP-nucleon elastic-scattering cross section that exclude unexplored parameter space above 10 GeV͞c 2 WIMP mass and, at .75% C.L., the entire 3s allowed region for the WIMP signal reported by the DAMA experiment. Extensive evidence indicates that a large fraction of the matter in the universe is nonluminous, nonbaryonic, and "cold"-nonrelativistic at the time matter began to dominate the energy density of the universe [1][2][3]. Weakly interacting massive particles (WIMPs) are an excellent candidate for nonbaryonic, cold dark matter [2,4]. Minimal supersymmetry provides a natural WIMP candidate in the form of the lightest superpartner, with a typical mass M ϳ 100 GeV͞c 2 [5][6][7][8]. WIMPs are expected to have collapsed into a roughly isothermal, spherical halo within which the visible portion of our galaxy resides. WIMPs scatter off nuclei via the weak interaction, potentially allowing their direct detection [9,10]. The expected spectrum of recoil energies (energy given to the recoiling nucleus during the interaction) is exponential with a characteristic energy of a few to tens of keV [11]. The expected event rate is model dependent, but is generically 1 kg 21 d 21 or lower [10]. This Letter reports new exclusion limits on the spinindependent WIMP-nucleon elastic-scattering cross section by the Cryogenic Dark Matter Search (CDMS). The rate of rare WIMP-nucleon interactions is constrained by extended exposure of detectors that discriminate WIMPinduced nuclear recoils from electron recoils caused by interactions of background particles [12,13].The ionization yield Y (the ratio of ionization production to recoil energy in a semiconductor) of a particle interaction differs greatly for nuclear and electron recoils. CDMS detectors measure phonon and electron-hole pair production to determine recoil energy and ionization yield for each event. The data discussed here were obtained with two types of detectors, Berkeley Large Ionization-and Phonon-mediated (BLIP) and Z-sensitive Ionization-and Phonon-mediated (ZIP) detectors [12][13][14][15][16][17][18]. For both types, the drift field for the ionization measurement is supplied by radially segmented electrodes on the faces of the disk-shaped crystals [19]. In BLIP detectors, phonon production is determined from the detector's calorimetric temperature change. In ZIP detectors, athermal phonons are collected to determine phonon production and xy position. Detector performance is discussed in detail elsewhere [14,[16][17][18][19][20].Photons cause most bulk electron recoils, while lowenergy electrons incident on the detector surfaces cause low-Y electron recoils in a thin surface layer ("surface events"). Neutron, photon, and electron sources a...

Lower limit on the neutralino mass in the general MSSM

“…This is important because not only one would want to know what the impact of the lightest LSP is for cosmology and direct detection but how the collider phenomenology can get affected when one puts aside assumptions related to the LSP mass. For example one might inquire about the sensitivities of the direct search detectors such as CDMS [27], EDELWEISS [28], DAMA [29] and ZEPLIN [30] for neutralino masses below those typical of the LSP of mSUGRA. The LSP, in the R-parity conserving MSSM, being the end product of the decay of any supersymmetric particle, is important for signatures at the colliders since it will always show up in any analysis.…”

Cosmological Reflection of Particle Symmetry

“…In particular, there are no such levels in Xe, which seems to prevent direct comparison with DAMA results in the XENON100 experiment [75]. The existence of such levels in Ge and the comparison with the results of CDMS [72][73][74] and CoGeNT [76] experiments need special study. According to Reference [215], OHe should bind with O and Ca, which is of interest for interpretation of the signal observed in the CRESST-II experiment [241].…”

“…However, direct experimental search for cosmic fluxes of weakly interacting massive particles (WIMPs) may be sensitive to existence of such components (see [68][69][70][71][72][73][74][75][76] and references therein). It was shown in References [77][78][79][80] that annihilation of fourth generation neutrinos and their antineutrinos in the galaxy is severely constrained by the measurements of gamma-background, cosmic positrons, and antiprotons.…”

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