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We report a measurement of the proton-air cross-section for particle production at the center-ofmass energy per nucleon of 57 TeV. This is derived from the distribution of the depths of shower maxima observed with the Pierre Auger Observatory: systematic uncertainties are studied in detail. Analysing the tail of the distribution of the shower maxima, a proton-air cross-section of 505 ± 22(stat) +28 −36 (sys) mb is found.

The addition of O 2 to gas mixtures in time projection chambers containing CS 2 has recently been shown to produce multiple negative ions that travel at slightly different velocities. This allows a measurement of the absolute position of ionising events in the z (drift) direction. In this work, we apply the z-fiducialisation technique to a directional dark matter search. We present results from a 46.3 live-day source-free exposure of the DRIFT-IId detector run in this new mode. With full-volume fiducialisation, we have achieved the first background-free operation of a directional detector. The resulting exclusion curve for spindependent WIMP-proton interactions reaches 1.1 pb at 100 GeV/c 2 , a factor of 2 better than our previous work. We describe the automated analysis used here, and argue that detector upgrades, implemented after the acquisition of these data, will bring an additional factor of 3 improvement in the near future.arXiv:1410.7821v3 [hep-ex] 23 Jul 2015 DRIFT-IId detector and science runsThe DRIFT experiment is sited at a depth of 1.1 km in the STFC Boulby Underground Science Facility [29], which provides 2805 m.w.e. shielding against cosmic rays. The TPC is housed inside a stainless steel cubic vacuum vessel, surrounded on all sides with 44 g cm −2 of polypropylene pellets to shield against neutrons from the cavern walls. The vessel was filled with a mixture of 30:10:1 Torr CS 2 :CF 4 :O 2 gas, and sealed for the duration of each run. This departure from the normal mode of operation, in which gas is flowed at a constant rate of one complete vacuum vessel change (590 g) /d, was necessary due to safety concerns over sources of ignition in the constant flow system. These concerns have since been addressed with modifications to the gas system.The DRIFT-IId NITPC consists of a thin-film (0.9 µm aluminised Mylar), texturised central cathode [25] at a potential of -31.9 kV faced on either side by two 1 m 2 multi-wire proportional chambers (hereafter, the 'left' and 'right' MWPCs) at a distance of 50 cm. In this way, two 50-cm-long drift regions are defined. A field cage of 31 stainless steel rings on either side steps down the voltage smoothly between the central cathode and the MWPCs to ensure a uniform electric field of 580 V cm −1 throughout the drift regions. The MWPCs are made up of a central grounded anode plane of 20 µm diameter stainless steel wires with 2 mm pitch, sandwiched between two perpendicular grid planes of 100 µm wires at -2884 V, again with 2 mm pitch and separated by 1 cm from the anode plane. A full description of the detector can be found in Ref. [30].Both the inner grid and anode planes have every eighth wire joined together and read out as one, such that a single 'octave' of wires reads out 8 × 2 = 16 mm in x and y: large enough to contain the recoil events of interest. The outermost 52 (41) wires of the 512 total on the inner grid (anode) planes are grouped together into x (y) veto regions, reducing the fiducial volume of the detector to 0.80 m 3 . The anode and grid veto signal...

We present results from a 54.7 live-day shielded run of the DRIFT-IId detector, the world's most sensitive, directional, dark matter detector. Several improvements were made relative to our previous work including a lower threshold for detection, a more robust analysis and a tenfold improvement in our gamma rejection factor. After analysis, no events remain in our fiducial region leading to an exclusion curve for spindependent WIMP-proton interactions which reaches 0.28 pb at 100 GeV/c 2 , a fourfold improvement on our previous work. We also present results from a 45.4 live-day unshielded run of the DRIFT-IId detector during which 14 nuclear recoil-like events were observed. We demonstrate that the observed nuclear recoil rate of 0.31±0.08 events per day is consistent with detection of ambient, fast neutrons emanating from the walls of the Boulby Underground Science Facility.

Now that conventional weakly interacting massive particle (WIMP) dark matter searches are approaching the neutrino floor, there has been a resurgence of interest in detectors with sensitivity to nuclear recoil directions. A large-scale directional detector is attractive in that it would have sensitivity below the neutrino floor, be capable of unambiguously establishing the galactic origin of a purported dark matter signal, and could serve a dual purpose as a neutrino observatory. We present the first detailed analysis of a 1000 m 3 -scale detector capable of measuring a directional nuclear recoil signal at low energies. We propose a modular and multi-site observatory consisting of time projection chambers (TPCs) filled with helium and SF6 at atmospheric pressure. By comparing several available readout technologies, we identify high-resolution strip readout TPCs as the optimal tradeoff between performance and cost. We estimate that suitable angular resolution and head-tail recognition is achievable down to helium recoil energies of ∼6 keVr. Depending on the readout technology, an average of only 4-5 detected 100-GeV c −2 WIMP-fluorine recoils above 50 keVr are sufficient to rule out an isotropic recoil distribution at 90% CL. An average of 10-20 helium recoils above 6 keVr or only 3-4 helium recoils above 20 keVr would suffice to distinguish a 10 GeV c −2 WIMP signal from the solar neutrino background. High-resolution TPC charge readout also enables powerful electron background rejection capabilities well below 10 keV. We detail background and site requirements at the 1000 m 3 -scale, and identify materials that require improved radiopurity. The final experiment, which we name Cygnus-1000, will be able to observe ∼ 10-40 neutrinos from the Sun, depending on the final energy threshold. With the same exposure, the sensitivity to spin independent cross sections will extend into presently unexplored sub-10 GeV c −2 parameter space. For spin dependent interactions, already a 10 m 3 -scale experiment could compete with upcoming generation-two detectors, but Cygnus-1000 would improve upon this considerably. Larger volumes would bring sensitivity to neutrinos from an even wider range of sources, including galactic supernovae, nuclear reactors, and geological processes.