track significance (St) cut
GOAL : following the procedure of previous post, I should start with single track cut to remove background. (for D0 reco. with SVT/SSD)
Daughters of D0 should have longer DCA than background ,then a cut on the track significance St = DCA/σDCA should be useful
Samples used :
- hijing file used for mixing
- single D0 with regular lifetime
- single D0 with 100*ctau (100 * 120μm = 1.2 cm)
As there is 1 D0 per event, reconstructed daughter candidates from 2. and 3. are the real daughters, ie coming from a displaced vertex = larger DCA.
The following plot shows :
- upper left : St for hijing
- upper right : St for single regular ctau
- bottom left : St for single 100*ctau
- bottom right : all
- the cut used is : # of si hits =4 && |ndEdxK|<2
It is hard to really discriminate the background and single D0 (the HFT studies show it clearly) but with the long ctau D0 sample, we see that St is broader.
** July 8th : UPDATE **
Fig. 2 : same cut as Fig. 1 but for DCAXY
Fig. 3 : same cut as Fig. 1 but for DCAZ
Fig. 4 : same cut as Fig. 1 but for the full DCA
The full DCA is calculated as DCA = √(DCAXY2+DCAZ2) [same for the errors]
Comments : for Fig. 4 , it seems the signal curve is slightly above the background for DCA/σDCA > 1
Fig. 5 : same cut as Fig. 4 but with a cut on the # of silicon hits decreased to 2 or more.
Fig. 6 : same cut as Fig. 5 but with a cut on the Pt of daughters more than 1
The cut on Pt of daughters is motivated but the plot below :
Fig. 7 : Pt distribution
** September 10th : UPDATE **
Instead of using dcaXY, I used dca3D (from global) : dcaG[0] = TVector3(mDCAGlobal_mX1Gl[kg],mDCAGlobal_mX2Gl[kg],mDCAGlobal_mX3Gl[kg])
It seems that the significance obtained with this DCA gives a much better discrimination between signal and background.
Results are here
- bouchet's blog
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