# HLT1 KS0KS0 line

The line introduces a new HLT1 line that looks for KS0 pairs. The line occupies minimal bandwidth (adding 8 kHz to the overall rate), but can anyway ensure a minimal efficiency on KS0KS0 decays (as D0->KS0KS0) in case of tightening of selections for general-purpose lines, as TrackMVA and TwoTrackMVA.

Applied selections:

- chi2trk/ndof (pi) < 2.5
- p_t(pi) > 425 MeV/c
- p(pi) > 3000 MeV/c
- IPchi2 (pi) > 15
- chi2_vtx (KS) < 20
- 2 < eta(KS) < 4.2
- |m(pi pi) - m(KS)| < 45 MeV/c2
- p_t(KS) > 1150 MeV/c
- cos(theta_DIRA) > 0.99
- cos(theta(pi pi)) > 0.99
- IP(pi+) x IP(pi-) / IP(KS) > 0.23 mm

Throughput test:

- 103608 evts/s on master branch
- 104326 evts/s on this branch

Exclusive rate: 6 +- 2 kHz

Rate added w.r.t. rate(1-track OR 2-track): +4 kHz (822 kHz -> 826 kHz)

Efficiency computed on D0->KS0KS0 decays through MooreAnalysis (D0_TOS eff.):

- eff(TrackMVA) = (4.4 +- 1.2)%
- eff(TwoTrackMVA) = (10.1 +- 1.8)%
- eff(KS0-Line) = (5.1 +- 1.3)%
- eff(TwoKS0-Line) = (1.4 +- 0.7)%
- eff(TrackMVA | TwoTrackMVA) = (12.8 +- 1.9)%
- eff(TrackMVA | TwoTrackMVA | TwoKS0-Line) = (13.2 +- 2.0)%