Solenoid Siberian snakes have successfully maintained polarization in particle rings below 1 GeV, but never in multi-GeV rings, because the spin rotation by a solenoid is inversely proportional to ...the beam momentum. High energy rings, such as Brookhaven’s 255 GeV Relativistic Heavy Ion Collider (RHIC), use only odd multiples of pairs of transverse B-field Siberian snakes directly opposite each other. When it became impractical to use a pair of Siberian Snakes in Fermilab’s 120GeV/c Main Injector, we searched for a new type of single Siberian snake that could overcome all depolarizing resonances in the 8.9–120GeV/c range. We found that a snake made of one 4-twist helix and 2 dipoles could maintain the polarization. This snake design could solve the long-standing problem of significant polarization loss during acceleration of polarized protons from a few GeV to tens of GeV, such as in the AGS, before injecting them into multi-hundred GeV rings, such as RHIC.
The CRESST-II cryogenic Dark Matter search, aiming at detection of WIMPs via elastic scattering off nuclei in CaWO
4
crystals, completed 730 kg days of data taking in 2011. We present the data ...collected with eight detector modules, each with a two-channel readout; one for a phonon signal and the other for coincidently produced scintillation light. The former provides a precise measure of the energy deposited by an interaction, and the ratio of scintillation light to deposited energy can be used to discriminate different types of interacting particles and thus to distinguish possible signal events from the dominant backgrounds.
Sixty-seven events are found in the acceptance region where a WIMP signal in the form of low energy nuclear recoils would be expected. We estimate background contributions to this observation from four sources: (1) “leakage” from the
e
/
γ
-band (2) “leakage” from the
α
-particle band (3) neutrons and (4)
206
Pb recoils from
210
Po decay. Using a maximum likelihood analysis, we find, at a statistical significance of more than 4
σ
, that these sources alone are not sufficient to explain the data. The addition of a signal due to scattering of relatively light WIMPs could account for this discrepancy, and we determine the associated WIMP parameters.
We report the first dark matter search results from XENON1T, a ∼2000-kg-target-mass dual-phase (liquid-gas) xenon time projection chamber in operation at the Laboratori Nazionali del Gran Sasso in ...Italy and the first ton-scale detector of this kind. The blinded search used 34.2 live days of data acquired between November 2016 and January 2017. Inside the (1042±12)-kg fiducial mass and in the 5,40 keV_{nr} energy range of interest for weakly interacting massive particle (WIMP) dark matter searches, the electronic recoil background was (1.93±0.25)×10^{-4} events/(kg×day×keV_{ee}), the lowest ever achieved in such a dark matter detector. A profile likelihood analysis shows that the data are consistent with the background-only hypothesis. We derive the most stringent exclusion limits on the spin-independent WIMP-nucleon interaction cross section for WIMP masses above 10 GeV/c^{2}, with a minimum of 7.7×10^{-47} cm^{2} for 35-GeV/c^{2} WIMPs at 90% C.L.
Spin resonances can depolarize or spin flip a polarized beam. We studied 1st and higher order spin resonances with stored 2.1 GeV/c vertically polarized protons. The 1st order vertical (ν(y)) ...resonance caused almost full spin flip, while some higher order ν(y) resonances caused partial depolarization. The 1st order horizontal (ν(x)) resonance caused almost full depolarization, while some higher order ν(x) resonances again caused partial depolarization. Moreover, a 2nd order ν(x) resonance is about as strong as some 3rd order ν(x) resonances, while some 3rd order ν(y) resonances are much stronger than a 2nd order ν(y) resonance. One thought that ν(y) spin resonances are far stronger than ν(x), and that lower order resonances are stronger than higher order; the data do not support this.
The Chao matrix formalism allows analytic calculations of a beam's polarization behavior inside a spin resonance. We recently tested its prediction of polarization oscillations occurring in a stored ...beam of polarized particles near a spin resonance. Using a 1.85 GeV/c polarized deuteron beam stored in the COoler SYnchrotron, we swept a new rf solenoid's frequency rather rapidly through 400 Hz during 100 ms, while varying the distance between the sweep's end frequency and the central frequency of an rf-induced spin resonance. Our measurements of the deuteron's polarization near and inside the resonance agree with the Chao formalism's predicted oscillations.
The CRESST-II cryogenic dark matter search aims for the detection of WIMPs via elastic scattering off nuclei in CaWO
4
crystals. We present results from a low-threshold analysis of a single upgraded ...detector module. This module efficiently vetoes low energy backgrounds induced by
α
-decays on inner surfaces of the detector. With an exposure of 29.35 kg live days collected in 2013 we set a limit on spin-independent WIMP-nucleon scattering which probes a new region of parameter space for WIMP masses below 3 GeV/c
2
, previously not covered in direct detection searches. A possible excess over background discussed for the previous CRESST-II phase 1 (from 2009 to 2011) is not confirmed.
We used an rf solenoid to study the widths of rf spin resonances with both bunched and unbunched beams of 1.85 GeV/c polarized deuterons stored in the COSY synchrotron. With the unbunched beam at ...different fixed rf-solenoid frequencies, we observed only partial depolarization near the resonance. However, the bunched beam's polarization was almost fully flipped; moreover, its resonance was much narrower. We then used Chao's recent equations to explain this behavior and to calculate the polarization's dependence on various rf-solenoid and beam parameters. Our data and calculations indicate that a bunched deuteron beam's polarization can behave as if the beam has zero momentum spread.
The XENON1T dark matter experiment Aalbers, J.; Alfonsi, M.; Amaro, F. D. ...
European physical journal. C, Particles and fields,
12/2017, Letnik:
77, Številka:
12
Journal Article
Recenzirano
Odprti dostop
The XENON1T experiment at the Laboratori Nazionali del Gran Sasso (LNGS) is the first WIMP dark matter detector operating with a liquid xenon target mass above the ton-scale. Out of its 3.2 t liquid ...xenon inventory, 2.0 t constitute the active target of the dual-phase time projection chamber. The scintillation and ionization signals from particle interactions are detected with low-background photomultipliers. This article describes the XENON1T instrument and its subsystems as well as strategies to achieve an unprecedented low background level. First results on the detector response and the performance of the subsystems are also presented.
We recently tested a new spin resonance crossing technique, Kondratenko Crossing (KC), by sweeping an rf-solenoid's frequency through an rf-induced spin resonance with both the KC and traditional ...fast crossing (FC) patterns. Using both rf bunched and unbunched 1.85 GeV/c polarized deuterons stored in COSY, we varied the parameters of both crossing patterns. Compared to FC with the same crossing speed, KC reduced the depolarization by measured factors of 4.7 +/- 0.3 and 19_{-5};{+12} for unbunched and bunched beams, respectively. This clearly showed the large potential benefit of Kondratenko Crossing over fast crossing.
Stored beams of polarized protons, electrons, or deuterons can be spin flipped by sweeping an rf dipole’s or solenoid’s frequency through an rf spin resonance. Fitting such data to the modified ...Froissart-Stora equation’s spin resonance strength E_{FS} gave very large deviations from the ^{*}E_{Bdl} obtained from each rf magnet’s ∫B_{rms}dl. We recently varied an rf dipole’s frequency sweep range Δf, and the momentum spread Δp/p and betatron tune ν_{y} of stored 1.85 GeV/c polarized deuterons. We found a sharp constructive interference when ν_{y} was near an intrinsic spin resonance. Moreover, over large Δf and Δp/p ranges, E_{FS} was about 7 times smaller than the predicted ^{*}E_{Bdl}.
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