Context : The Central Molecular Zone ( CMZ ) is a \sim 200 pc region around the Galactic Center .
The study of star formation in the central part of the Milky Way is of highest interest as it provides a template for the closest galactic nuclei .

Aims : We present a spectroscopic follow-up of photometrically-selected young stellar object ( YSO ) candidates in the CMZ of the Galactic center .
Our goal is to quantify the contamination of this YSO sample by reddened giant stars with circumstellar envelopes and to determine the star formation rate in the CMZ .

Methods : We obtained KMOS low-resolution near-infrared spectra ( R \sim 4000 ) between 2.0 and 2.5 \mu m of sources , many of them previously identified , by mid-infrared photometric criteria , as massive YSOs in the Galactic center .
Our final sample consists of 91 stars with good signal-to-noise ratio .
We separate YSOs from cool late-type stars based on spectral features of CO and Br { \gamma } at 2.3 \mu m and 2.16 \mu m respectively .
We make use of SED model fits to the observed photometric data points from 1.25 to 24 \mu m in order to estimate approximate masses for the YSOs .

Results : Using the spectroscopically identified YSOs in our sample , we confirm that existing colour-colour diagrams and colour-magnitude diagrams are unable to efficiently separate YSOs and cool late-type stars .
In addition , we define a new colour-colour criterion that separates YSOs from cool late-type stars in the H-K _ { S } vs H- [ 8.0 ] diagram .
We use this new criterion to identify YSO candidates in the | l | ¡ 1 \aas@@fstack { \circ } 5 , | b | ¡0 \aas@@fstack { \circ } 5 region and use model SED fits to estimate their approximate masses .
By assuming an appropriate initial mass function ( IMF ) and extrapolating the stellar IMF down to lower masses , we determine a star formation rate ( SFR ) of \sim 0.046 \pm 0.026 M _ { \sun } yr ^ { -1 } assuming an average age of 0.75 \pm 0.25 Myr for the YSOs .
This value is lower than estimates found using the YSO counting method in the literature .

Conclusions : Our SFR estimate in the CMZ agrees with the previous estimates from different methods and reaffirms that star formation in the CMZ is proceeding at a lower rate than predicted by various star forming models .