Frontemare di Trieste
Istituto Nazionale di Fisica Nucleare
Sezione di Trieste

Data Selection Description

See the general description on Analysis Description.

All four Σ (1385) species have been analyzed separately. The main decay channel (branching ratio 88%) Σ→ Λ + π was used. In particular,

  1. Σ+→ Λ + π+
  2. Σ∗−→ Λ + π
  3. Anti-(Σ∗−)→ Anti-Λ + π
  4. Anti-(Σ∗+)→ Anti-Λ + π+

Note that channels 2. and 4. are the same as Ξ→ Λ + π and Ξ+→ Λ + π+. A residual peak at around 1.320 GeV/c2 from the Ξ is indeed present in the invariant mass distributions of Σ∗− and its antiparticle ̅Σ∗+. No topological reconstruction is possible for the Σ (1385) due to its strong decay. The signal peak has to be extracted from the invariant mass distribution of the candidates Λ and π pairs. Accurate candidates selection is mandatory to reduce the combinatorial background under the signal peak. For each particle specie, the analysis has been repeated for 11 bins of the transverse momentum pt: 0.7 − 1.0, 1.0 − 1.2, 1.2 − 1.4, 1.4 − 1.6, 1.6 − 1.8, 1.8 − 2.0, 2.0 − 2.4, 2.4 − 3.0, 3.0 − 4.0, 4.0 − 6.0, 6.0 − 10.0 GeV/c. A window of |y| < 0.8 for the candidates Λ − π pairs has been selected at midrapidity. The procedure for the signal extraction will be discussed for the Σ∗+. The same procedure was used for its antiparticle Anti-(Σ∗-). For Σ∗− and Anti-(Σ∗+), the peak from the Ξ has been fitted with a Gaussian.

Candidates selection

See tables 1 and 2.

pp7TeV_Track_Selection.png

Table 1: Track selection criteria

pp7TeV_Pair_Candidate_Selection.png

Table 2: Selection criteria for the Λ's and π's

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