The count rate of Weakly Interacting Massive Particle ( WIMP ) dark matter candidates in direct detection experiments experiences an annual modulation due to the Earth ’ s motion around the Sun .
In the standard isothermal halo model , the signal peaks near June 2nd at high recoil energies ; however , the signal experiences a phase reversal and peaks in December at low energy recoils .
We show that this phase reversal may be used to determine the WIMP mass .
If an annual modulation were observed with the usual phase ( i.e . , peaking on June 2nd ) in the lowest accessible energy recoil bins of the DAMA , CDMS-II , CRESST-II , EDELWEISS-II , GENIUS-TF , ZEPLIN-II , XENON , or ZEPLIN-IV detectors , one could immediately place upper bounds on the WIMP mass of [ 103 , 48 , 6 , 97 , 10 , 52 , 29 , 29 ] GeV , respectively .
In addition , detectors with adequate energy resolution and sufficiently low recoil energy thresholds may determine the crossover recoil energy at which the phase reverses , thereby obtaining an independent measurement of the WIMP mass .
We study the capabilities of various detectors , and find that CRESST-II , ZEPLIN-II , and GENIUS-TF should be able to observe the phase reversal in a few years of runtime , and can thus determine the mass of the WIMP if it is \mathcal { O } ( 100 GeV ) .
Xenon based detectors with 1000 kg ( XENON and ZEPLIN-IV ) and with energy recoil thresholds of a few keV require 25 kg-yr exposure , which will be readily attained in upcoming experiments .