We present R -band photometry of the X-ray transient and candidate black hole binary XTE J1650-500 obtained between 2003 May and August with the 6.5m Clay Telescope .
A timing analysis of these data reveals a photometric period of 0.3205 \pm 0.0007 days ( i.e .
7.63 hr ) with a possible alias at 0.3785 days ( 9.12 hr ) .
Our photometry completely rules out the previously published spectroscopic period of 0.212 days ( 5.09 hr ) .
Consequently , we reanalyzed the 15 archival ESO/VLT spectra ( obtained 2002 June by Sanchez-Fernandez et al . )
that were the basis of the previously published spectroscopic period .
We used a “ restframe search ” technique that is well suited for cases when the signal-to-noise ratio of individual spectra is low .
For each of roughly 1.1 million binary ephemerides , we summed all of the spectra in a trial restframe of the secondary star , and each restframe spectrum was cross-correlated against a template spectrum .
We then searched for the set of orbital parameters that produced the strongest cross-correlation value .
The results confirmed the photometric period of 0.3205 days , and rule out the alias period near 0.38 days .
The best value for the velocity semiamplitude of the companion star is K _ { 2 } = 435 \pm 30 
km s ^ { -1 } , and the corresponding optical mass function is f ( M ) = 2.73 \pm 0.56 M _ { \odot } .
The spectral type of the companion star is not well constrained because we only have six template spectra available to us .
The K4V template provides the best match ; next best matches are provided by the G5V and K2III templates .
We also find that the accretion disk dominates the light in the R -band where the disk fraction is 80 % or higher , although this value should be treated with caution owing to the poor signal-noise-ratio and the limited number of templates .
The amplitude of the phased R -band light curve is 0.2 magnitudes , which gives a lower limit to the inclination of 50 \pm 3 ^ { \circ } 
in the limiting case of no contribution to the R -band light curve from the accretion disk .
If the mass ratio of XTE J1650-500 is similar to the mass ratios of other black hole binaries like A0620-00 or GRS 1124-683 ( e.g . Q \gtrsim 10 ) , then our lower limit to the inclination gives an upper limit to the mass of the black hole in XTE J1650-500 of M _ { 1 } \lesssim 7.3 M _ { \odot } .
However , the mass can be considerably lower if the R -band flux is dominated by the accretion disk .
For example , if the accretion disk does contribute 80 % of the flux , as our preliminary results suggest , then the black hole mass would be only about 4 M _ { \odot } .