# Exclusive D02KsHH HLT1 line

An exclusive HLT1 line for selecting D⁰→Kₛ⁰π⁺π⁻ decays.

The line is based on the combination of two `CompositeParticle`

objects (V) and the following requirements are made:

- Each of the CompositeParticle vertex χ² should be 0 < χ² < maxVChi2 (20.)
- The DOCA of the two vertices is DOCA(V₁V₂) < maxDOCA (3 mm)
- The invariant mass of the combination should be |m(V₁V₂)-m(D⁰)| < massWindow (100 MeV)
- The transverse momentum of the combination should be Pₜ(V₁V₂) > minComboPt_D0 (1500 MeV)
- The proper time of the combination should be cτ(V₁V₂) > minCTau_D0 (0.5 * 0.1229 mm)

The V with the largest z is then assumed as the Kₛ⁰ candidate and further requirements are made

- m(Kₛ⁰) mass window [455,545] MeV
- minimum Pₜ (200 MeV) of the Kₛ⁰
- minimum P (1500 MeV), Pₜ (200 MeV) and IP (0.2mm) among the Kₛ⁰ components
- the Kₛ⁰ η in [2,5]

The other V is considered as the hh and provides the D⁰ vertex, therefore

- minP(h₁,h₂) > 1500 MeV;
- 2 < η(V₁V₂) < 5;
- minPₜ(h₁,h₂) > 250 MeV;
- minIP(h₁,h₂) > 0.06 mm

The line also includes a monitoring tuple with the following information:

- m(V₁V₂)
- Pₜ(V₁V₂)
- P(V₁V₂)
- DOCA(V₁V₂)
- cτ(V₁V₂)
- m²(Kₛ⁰h⁺)
- m²(Kₛ⁰h⁻)
- minIPχ²(Kₛ⁰)
- minIPχ²(hh)
- minIP(Kₛ⁰)
- minIP(hh)

**Rate**

Calculated with `$HLTEFFICIENCYCHECKERROOT/scripts/hlt_calculate_rates.py`

`Line: Hlt1D2KshhDecision Incl: 120.6 +/- 26.3 kHz, Excl: 9.2 +/- 6.6 kHz`

**Efficiency**

3.2% (1.0% exclusive)
on a sample of D⁰→Kₛ⁰π⁺π⁻ decays with denominator the events where all the pions are *Long* reconstructable tracks with 2 < η < 5.

**Talks**