double sum() {

for ( Int_t itrk = 0; itrk < NtpSR.evthdr.ntrack; itrk++ )

    {
       int match=0;

       if(NtpSR.trk.momentum.qp[itrk]==0) trk_momentum_fit=0;
       else {trk_momentum_fit = 1/NtpSR.trk.momentum.qp[itrk];}

        if(NtpSR.trk.fit.ndof[itrk] ==0) trk_reduced_chi2=0;
        else {trk_reduced_chi2 = NtpSR.trk.time.chi2[itrk] / 
NtpSR.trk.fit.ndof[itrk] ;}

      // reconstruction cuts

        if(trk_reduced_chi2 > 20 )  continue;

        if(NtpSR.trk.fit.pass[itrk] == 0 ) continue;

        if(TMath::Abs(NtpSR.trk.plane.begu[itrk] - 
NtpSR.trk.plane.begv[itrk] )> 6 ) continue;


//cuts for ensuring that tracks begin in the instrumented region

        if(NtpSR.trk.vtx.z[itrk] < 0.6 || NtpSR.trk.vtx.z[itrk]> 3.56 ) 
continue;

        if(NtpSR.trk.vtx.u[itrk] < 0.3 || NtpSR.trk.vtx.u[itrk]> 1.8 ) 
continue;

        if(NtpSR.trk.vtx.v[itrk] < -1.8 || NtpSR.trk.vtx.v[itrk]> -0.3 ) 
continue;

        if(NtpSR.trk.vtx.x[itrk] > 2.4) continue;

        
if(TMath::Sqrt((NtpSR.trk.vtx.x[itrk]*NtpSR.trk.vtx.x[itrk])+(NtpSR.trk.vtx.y[itrk]*NtpSR.trk.vtx.y[itrk]))<0.8) 
continue;
 }


}