\(B_{(s)}^{0}\rightarrow K_{S}^{0}h^{+}h^{'-}\) BF and

\(B_{s}^{0}\rightarrow K_{S}^{0}\pi^{+}\pi^{-}\) AmAn with Run 1+2 data 

Update 

Sebastian Ordonez-Soto

 

LHCb @ LPCA

 

 

15/12/2025

Context

S. Ordonez-Soto

\(B_{(s)}^{0}\rightarrow K_{S}^{0}h^{+}h^{'-}\) BF and  \(B_{s}^{0}\rightarrow K_{S}^{0}\pi^{+}\pi^{-}\) AmAn

15/12/2025

Figure 1. The oscillation of the \(B_{(s)}^{0}\rightarrow K_{S}^{0}h^{+}h^{'-}\) BF analysis  between 2CWR and different issues (missing veto, L0 eff corr bug, etc)

  • The \(B_{(s)}^{0}\rightarrow K_{S}^{0}h^{+}h^{'-}\) BF analysis has been embroiled between RC+EB and 2CWR due to different issues:
    • v6: It was found a bug in the calculation of the efficiency maps 
    • v7: It was discovered that a relevant veto was missing 
      • ​Likely the paper will be put in 2CWR by the end of the week

 \(\Rightarrow\)

  • Both problems were spotted while I was revisiting inputs for the AmAn
    • Now some unclear structures in the DP disappeared 

Analysis Twiki

\(B_{(s)}^{0}\rightarrow K_{S}^{0}h^{+}h^{'-}\) BF summary

S. Ordonez-Soto

\(B_{(s)}^{0}\rightarrow K_{S}^{0}h^{+}h^{'-}\) BF and  \(B_{s}^{0}\rightarrow K_{S}^{0}\pi^{+}\pi^{-}\) AmAn

15/12/2025

Final combined weighted averages

Comparison of the BR between this analysis and Run I paper

  • The combined yield of \(B_{s}\rightarrow K_{S}^{0}K^{+}K^{-}\) with the tighter selection is \(207\pm 24\) \(\Rightarrow\) Significance ~\(8.6\sigma\) 
  • Results are compatible with the previous LHCb analysis with: improved fit model and bkg. suppression, and reduction of both stats. and syst. uncertainties.

S. Ordonez-Soto

15/12/2025

Selection of the signal
Mass fit on data 
Efficiency evaluation over the DP
Background model
Simultaneous Dalitz plot Fit
  • Selection
    • \(\Lambda\rightarrow p\pi\) veto applied.
    • \(\chi_{c}^{0}\rightarrow \pi^{+}\pi^{-}\) veto removed.
  • Invariant-mass fit
    • MC truth matching not used.
    • Comparison with BF analysis fit OK.

\(B_{s}^{0}\rightarrow K_{S}^{0}\pi^{+}\pi^{-}\) AmAn update

  • Selection
    • \(\Lambda\rightarrow p\pi\) veto applied.
    • \(\chi_{c}^{0}\rightarrow \pi^{+}\pi^{-}\) veto removed.
  • Invariant-mass fit
    • MC truth matching not used.
    • Comparison with BF analysis fit OK.

\(B_{(s)}^{0}\rightarrow K_{S}^{0}h^{+}h^{'-}\) BF and  \(B_{s}^{0}\rightarrow K_{S}^{0}\pi^{+}\pi^{-}\) AmAn

Invariant-mass fit results

S. Ordonez-Soto

Fitted yields in data

Fractions in the \(B_{s}^{0}\) signal window \([\mu-1.4\sigma, \mu+3\sigma]\)

  • Total: ~1.5K signal candidates
  • Run 1: 
    • Total: ~240
    • DD: ~170
    • LL: ~75
  • Run 2: 
    • Total: ~1.25K 
    • DD: ~825
    • LL: ~420

\(B_{(s)}^{0}\rightarrow K_{S}^{0}h^{+}h^{'-}\) BF and  \(B_{s}^{0}\rightarrow K_{S}^{0}\pi^{+}\pi^{-}\) AmAn

15/12/2025

Efficiency maps

S. Ordonez-Soto

Combination of polarities

  • Efficiency maps are obtained from the BF machinery for each polarity for a given binning.
    • They are combined according to the MU-MD fractions available in the RunDB (same as done in the BF analysis) 

\(\Rightarrow\) Quadratically combined

\(B_{(s)}^{0}\rightarrow K_{S}^{0}h^{+}h^{'-}\) BF and  \(B_{s}^{0}\rightarrow K_{S}^{0}\pi^{+}\pi^{-}\) AmAn

15/12/2025

Efficiency maps

S. Ordonez-Soto

Symmetrization and smoothing

\(B_{(s)}^{0}\rightarrow K_{S}^{0}h^{+}h^{'-}\) BF and  \(B_{s}^{0}\rightarrow K_{S}^{0}\pi^{+}\pi^{-}\) AmAn

15/12/2025

Background model

S. Ordonez-Soto

Combinatorial

  • Obtained from the upper mass side-band \(5450~\text{MeV}\leq m_{K_{S}^{0}\pi^{+}\pi^{-}} \leq 5750~\text{MeV}\)
  • Non-DTF variables are employed for Dalitz variables.
  • Veto on \(B^{+}\rightarrow K_{S}^{0}\pi^{+}\) applied: \(|m_{K_{S}^{0}\pi^{\pm}}-m_{B^{+}}|\geq 20~\text{MeV}\)

Combined dataset (all years and both KS)

\(B_{(s)}^{0}\rightarrow K_{S}^{0}h^{+}h^{'-}\) BF and  \(B_{s}^{0}\rightarrow K_{S}^{0}\pi^{+}\pi^{-}\) AmAn

15/12/2025

Background model

S. Ordonez-Soto

Combinatorial

Combined dataset (all years-DD)

Combined dataset (all years-LL)

  • A combined map of all data-taking periods is obtained for each \(K_{S}^{0}\) category
    • The SqDP maps are smoothed and are inputs for the DP fit.

\(B_{(s)}^{0}\rightarrow K_{S}^{0}h^{+}h^{'-}\) BF and  \(B_{s}^{0}\rightarrow K_{S}^{0}\pi^{+}\pi^{-}\) AmAn

15/12/2025

Background model

S. Ordonez-Soto

Combinatorial

  • A combined map of all data-taking periods is obtained for each \(K_{S}^{0}\) category
    • The SqDP maps are smoothed and are inputs for the DP fit.

\(\Rightarrow\)DD

\(\Rightarrow\)LL

\(B_{(s)}^{0}\rightarrow K_{S}^{0}h^{+}h^{'-}\) BF and  \(B_{s}^{0}\rightarrow K_{S}^{0}\pi^{+}\pi^{-}\) AmAn

15/12/2025

Background model

S. Ordonez-Soto

\(B_{d}^{0}\rightarrow K_{S}^{0}\pi^{+}\pi^{-}\) background

Estimated using the model for this decay from Run I:

  • Paper: AmAn of the decay \(B_{d}^{0}\rightarrow K_{S}^{0}\pi^{+}\pi^{-}\) and first observation of the CP asymmetry in \(B_{d}^{0}\rightarrow K^{*}(892)\pi^{+}\).
  • Large  toy  MC generated using CRAFT, weighted by the corresponding efficiency map.

2018-DD

\(B_{(s)}^{0}\rightarrow K_{S}^{0}h^{+}h^{'-}\) BF and  \(B_{s}^{0}\rightarrow K_{S}^{0}\pi^{+}\pi^{-}\) AmAn

15/12/2025

CRAFT v2

S. Ordonez-Soto

\(B_{(s)}^{0}\rightarrow K_{S}^{0}h^{+}h^{'-}\) BF and  \(B_{s}^{0}\rightarrow K_{S}^{0}\pi^{+}\pi^{-}\) AmAn

15/12/2025

A new version of CRAFT is now available at the gitlab repo of LHCb team of Clermont-Ferrand

  • The new version is an entire re-factorization of v1:
    • Classes have been updated with modern C++ and ROOT objects/classes.
    • No changes in the physics or algorithms for the moment
  • Still under tests, but all bugs should come from the use of new constructors
    • Documentation in progress
  • Plan to merge with Eric's framework for handling e.g. syst. studies

Thank you

Backup

\(B_{(s)}^{0}\rightarrow K_{S}^{0}h^{+}h^{'-}\) BF and  \(B_{s}^{0}\rightarrow K_{S}^{0}\pi^{+}\pi^{-}\) AmAn

15/12/2025

S. Ordonez-Soto

Efficiency bug

L0corr typo in the eff. calculation

\(B_{(s)}^{0}\rightarrow K_{S}^{0}h^{+}h^{'-}\) BF and  \(B_{s}^{0}\rightarrow K_{S}^{0}\pi^{+}\pi^{-}\) AmAn

15/12/2025

S. Ordonez-Soto

Efficiency bug

L0corr typo in the eff. calculation

\(B_{(s)}^{0}\rightarrow K_{S}^{0}h^{+}h^{'-}\) BF and  \(B_{s}^{0}\rightarrow K_{S}^{0}\pi^{+}\pi^{-}\) AmAn

15/12/2025

S. Ordonez-Soto

Missing veto

Re-inclusion of the \(\Lambda\rightarrow p\pi\) veto

Invariant-mass fit plots

S. Ordonez-Soto

\(B_{s}^{0}\rightarrow K_{S}^{0}\pi^{+}\pi^{-}\) AmAn

LL

15/12/2025

Invariant-mass fit plots

S. Ordonez-Soto

\(B_{s}^{0}\rightarrow K_{S}^{0}\pi^{+}\pi^{-}\) AmAn

LL

15/12/2025

Invariant-mass fit plots

S. Ordonez-Soto

\(B_{s}^{0}\rightarrow K_{S}^{0}\pi^{+}\pi^{-}\) AmAn

DD

15/12/2025

Invariant-mass fit plots

S. Ordonez-Soto

\(B_{s}^{0}\rightarrow K_{S}^{0}\pi^{+}\pi^{-}\) AmAn

DD

15/12/2025

Dalitz plot fit

S. Ordonez-Soto

Preliminary signal model

  • A preliminary signal model is proposed based on Standard Model expectations. 
    • \(\overline{B}_s \to \rho^0 K^0_S\)
    • \(\overline{B}_s \to K_0^{*+}(1430)\pi^{-}\) 
    • \(\overline{B}_s \to K^0_S \pi^+ \pi^- \text{ (NR)}\)
    • \(\overline{B}_s \to K^{*+}(892) \pi^-\)
  • The model parameterizes the signal amplitude as the isobar sum of three resonances (and conjugates) plus a non-resonant (NR) contribution.

\(B_{(s)}^{0}\rightarrow K_{S}^{0}h^{+}h^{'-}\) BF and  \(B_{s}^{0}\rightarrow K_{S}^{0}\pi^{+}\pi^{-}\) AmAn

15/12/2025

Dalitz plot fit plots

S. Ordonez-Soto

\(B_{s}^{0}\rightarrow K_{S}^{0}\pi^{+}\pi^{-}\) AmAn

Very preliminary plots!!!

Only Run 2

15/12/2025

Dalitz plot fit plots

S. Ordonez-Soto

\(B_{s}^{0}\rightarrow K_{S}^{0}\pi^{+}\pi^{-}\) AmAn

15/12/2025