Juan Sebastián Ordoñez Soto
Supervised by D. Milanés and C. Sandoval
Master thesis defense
Grupo de Partículas FENYX-UN
Departamento de Física, Universidad Nacional de Colombia
Bogotá, Colombia
January 24th, 2025
-
Sebastian Ordoñez-Soto
January 24th, 2025
Scientific context
Sebastian Ordoñez-Soto
January 24th, 2025
https://cds.cern.ch/record/1473657
The strong sector of the SM is not perturbative at low-energy scales!
Scientific context
Sebastian Ordoñez-Soto
January 24th, 2025
Multi-body decays of \(D\) mesons have been used for light-meson spectroscopy in recent decades.
The \(D^{+}\rightarrow K^{-}K^{+}K^{+}\) decay is an excellent lab for the measurement of the \(K\bar{K}\) amplitude in \(\mathcal{S}\)-wave.
Scientific context
Sebastian Ordoñez-Soto
January 24th, 2025
Isobar parameters
Notation:
Experimental Setup
Sebastian Ordoñez-Soto
January 24th, 2025
27 km circumference collider at CERN, near Geneva.
The main objective of the LHC is to explore physics beyond the SM.
Experimental Setup
Sebastian Ordoñez-Soto
January 24th, 2025
Single-arm forward detector
These components altogether allow to identify and measure –with high precision– the physical properties of particles produced after the \(pp\) collisions
Stable particles in LHCb terminology: \(\pi^{\pm}\), \(K^{\pm}\), \(p\), \(e^{\pm}\), \(\mu^{\pm}\), \(\gamma\).
Experimental Setup
Sebastian Ordoñez-Soto
January 24th, 2025
Sebastian Ordoñez-Soto
January 24th, 2025
Experimental Setup
The LHC can provide a bunch crossing every 25ns \(\Rightarrow\) How is decided what to save?
Experimental Setup
Sebastian Ordoñez-Soto
January 24th, 2025
The LHCb detector measures physical properties of particles -variables- resulting from \(pp\) collisions.
Experimental Setup
Sebastian Ordoñez-Soto
January 24th, 2025
Key points for the \(D^{+}\rightarrow 3K\) analysis:
Dalitz plot folded
Invariant mass of the three kaons and Dalitz plot
Main variables used:
Sebastian Ordoñez-Soto
January 24th, 2025
Amplitude Analysis of the \(D^{+}\rightarrow K^{-}K^{+}K^{+}\) decay
Selection of the signal |
Efficiency evaluation over the DP |
Background model |
Dalitz plot Fit |
Mass fit on data |
The analysis consists of mainly five stages, from the signal selection to the final Dalitz plot fit.
Sebastian Ordoñez-Soto
January 24th, 2025
Amplitude Analysis of the \(D^{+}\rightarrow K^{-}K^{+}K^{+}\) decay
Sebastian Ordoñez-Soto
January 24th, 2025
Amplitude Analysis of the \(D^{+}\rightarrow K^{-}K^{+}K^{+}\) decay
After the trigger selection, the background levels in the data samples are still elevated.
Invariant mass before and after pre-selection
DP before and after pre-selection
Sebastian Ordoñez-Soto
January 24th, 2025
Amplitude Analysis of the \(D^{+}\rightarrow K^{-}K^{+}K^{+}\) decay
Use of machine learning techniques to reduce the amount of the remaining background.
A cut at valBDTG> 0.575 achieves a purity of 92.5% within the signal region with a signal efficiency of ~54%.
Sebastian Ordoñez-Soto
January 24th, 2025
Amplitude Analysis of the \(D^{+}\rightarrow K^{-}K^{+}K^{+}\) decay
Sebastian Ordoñez-Soto
January 24th, 2025
Amplitude Analysis of the \(D^{+}\rightarrow K^{-}K^{+}K^{+}\) decay
The \(K^{-}K^{+}K^{+}\) mass spectrum is fitted to determine:
The number of signal and bkg. events within the signal region yields \(512202\pm 745\) and \(42383\pm 225\), resp.
Dalitz plot distribution of selected data.
\([1861.94,1878.3]\) MeV
Sebastian Ordoñez-Soto
January 24th, 2025
Amplitude Analysis of the \(D^{+}\rightarrow K^{-}K^{+}K^{+}\) decay
Sebastian Ordoñez-Soto
January 24th, 2025
Amplitude Analysis of the \(D^{+}\rightarrow K^{-}K^{+}K^{+}\) decay
The efficiency impacts 3 regions at the DP boundary \(\Rightarrow\) Does not compromise significantly the region near threshold.
The binning is a source of systematic uncertainty
\(\epsilon(s_{12},s_{13})\)
It is necessary to account for the variation of the detection efficiency across the phase space.
Sebastian Ordoñez-Soto
January 24th, 2025
Amplitude Analysis of the \(D^{+}\rightarrow K^{-}K^{+}K^{+}\) decay
\(\mathcal{B}_{PDF}(s_{12},s_{13})\)
The contribution of background needs to be accounted for in the DP fit.
The model is a source of systematic uncertainty
Sebastian Ordoñez-Soto
January 24th, 2025
Amplitude Analysis of the \(D^{+}\rightarrow K^{-}K^{+}K^{+}\) decay
Sebastian Ordoñez-Soto
January 24th, 2025
Amplitude Analysis of the \(D^{+}\rightarrow K^{-}K^{+}K^{+}\) decay
The isobar parameters (\(a_{k}\), \(\delta_{k}\)) for each channel are floated in the fit as well as the fit fractions \(FF_{k}\).
An unbinned maximum-likelihood fit is applied to the final Dalitz plot distribution.
Interference fit fractions
Sebastian Ordoñez-Soto
January 24th, 2025
Amplitude Analysis of the \(D^{+}\rightarrow K^{-}K^{+}K^{+}\) decay
Four models are considered, all containing \(\mathcal{S}\)-wave components:
\(\phi K^{+}\) mode is chosen as reference \(\Rightarrow\) Fixed: \(a_{\phi} = 1\) and \(\delta_{\phi} = 0°\)
Sebastian Ordoñez-Soto
January 24th, 2025
Amplitude Analysis of the \(D^{+}\rightarrow K^{-}K^{+}K^{+}\) decay
Results for the baseline model
Comparison between data DP and a baseline model simulation
Data
Simulation
Sebastian Ordoñez-Soto
January 24th, 2025
Amplitude Analysis of the \(D^{+}\rightarrow K^{-}K^{+}K^{+}\) decay
https://arxiv.org/pdf/1902.05884
Previous LHCb results
Sebastian Ordoñez-Soto
January 24th, 2025
Amplitude Analysis of the \(D^{+}\rightarrow K^{-}K^{+}K^{+}\) decay
The main sources of syst. uncertainties are the background model and the binning scheme of the efficiency map.
Total systematic uncertainties (%)
Conclusion
Sebastian Ordoñez-Soto
January 24th, 2025
A Dalitz plot analysis of the doubly Cabibbo-suppressed \(D^{+}\rightarrow K^{-}K^{+}K^{+}\) decay was performed, using the largest dataset collected to date.
The decay is largely dominated by S-wave components, with an additional contribution from the \(\phi(1020)\) (~5.5%) and significant interference among the different components.
Difficulty in disentangling individual S-wave components due to the limited phase space, lack of structures beyond \(\phi(1020)\), and the \(f_{0}(980)\) lying below the \(K^{+}K^{-}K^{-}\) threshold.
The findings align with other three-body decays of \(D^{+}\) and \(D_{s}^{+}\), while exploring alternative approaches for describing the S-wave within the LHCb collaboration.
Scientific context
Sebastian Ordoñez-Soto
January 24th, 2025
Mesons are classified according to their quark content, total angular momentum, parity and various other properties
Because mesons are made of one quark and one antiquark, they are found in triplet and singlet spin states
The \(D\) mesons are the lightest particle containing charm quarks.
\(D^{+}\) mass: 1869.62\(\pm\)0.20 MeV
Scientific context
Sebastian Ordoñez-Soto
January 24th, 2025
Scientific context
Sebastian Ordoñez-Soto
January 24th, 2025
Scientific context
Sebastian Ordoñez-Soto
January 24th, 2025
Given an initial set of well defined states |i⟩ that are allowed to interact under fundamental interactions, which are going to be the observable results, i.e. the final states |f ⟩
Sebastian Ordoñez-Soto
January 24th, 2025
Scientific context
Sebastian Ordoñez-Soto
January 24th, 2025
Scientific context
Sebastian Ordoñez-Soto
January 24th, 2025
Scientific context
Experimental Setup
Sebastian Ordoñez-Soto
January 24th, 2025
Experimental Setup
Sebastian Ordoñez-Soto
January 24th, 2025
Experimental Setup
Sebastian Ordoñez-Soto
January 24th, 2025
Sebastian Ordoñez-Soto
January 24th, 2025
Amplitude Analysis of the \(D^{+}\rightarrow K^{-}K^{+}K^{+}\) decay
Hardware Trigger
Software trigger (I)
Sebastian Ordoñez-Soto
January 24th, 2025
Amplitude Analysis of the \(D^{+}\rightarrow K^{-}K^{+}K^{+}\) decay
Selection criteria corresponding to the trigger systmem which selects the \(D\rightarrow 3K\) candidates.
Sebastian Ordoñez-Soto
January 24th, 2025
Amplitude Analysis of the \(D^{+}\rightarrow K^{-}K^{+}K^{+}\) decay
Sebastian Ordoñez-Soto
January 24th, 2025
Amplitude Analysis of the \(D^{+}\rightarrow K^{-}K^{+}K^{+}\) decay
Sebastian Ordoñez-Soto
January 24th, 2025
Amplitude Analysis of the \(D^{+}\rightarrow K^{-}K^{+}K^{+}\) decay
Sebastian Ordoñez-Soto
January 24th, 2025
Amplitude Analysis of the \(D^{+}\rightarrow K^{-}K^{+}K^{+}\) decay
Sebastian Ordoñez-Soto
January 24th, 2025
Amplitude Analysis of the \(D^{+}\rightarrow K^{-}K^{+}K^{+}\) decay
Data
Simulation
Sebastian Ordoñez-Soto
January 24th, 2025
Amplitude Analysis of the \(D^{+}\rightarrow K^{-}K^{+}K^{+}\) decay
The goal of MC data is to replicate the observed signal, though discrepancies may require additional corrections \(\Rightarrow\) Incorporation of weights (\(\omega\)):
Data ready for Multivariate Analysis selection to fight against the remaining combinatorial background!
Sebastian Ordoñez-Soto
January 24th, 2025
Amplitude Analysis of the \(D^{+}\rightarrow K^{-}K^{+}K^{+}\) decay
Sebastian Ordoñez-Soto
January 24th, 2025
Amplitude Analysis of the \(D^{+}\rightarrow K^{-}K^{+}K^{+}\) decay
Before GB reweight
After GB reweight
Sebastian Ordoñez-Soto
January 24th, 2025
Amplitude Analysis of the \(D^{+}\rightarrow K^{-}K^{+}K^{+}\) decay
Sebastian Ordoñez-Soto
January 24th, 2025
Amplitude Analysis of the \(D^{+}\rightarrow K^{-}K^{+}K^{+}\) decay
The gradient descent optimization.
An example of a Decision Tree
Sebastian Ordoñez-Soto
January 24th, 2025
Amplitude Analysis of the \(D^{+}\rightarrow K^{-}K^{+}K^{+}\) decay
Discriminant input variables for training of the BDTG classifier
Sebastian Ordoñez-Soto
January 24th, 2025
Amplitude Analysis of the \(D^{+}\rightarrow K^{-}K^{+}K^{+}\) decay
Linear correlation matrices
Sebastian Ordoñez-Soto
January 24th, 2025
Amplitude Analysis of the \(D^{+}\rightarrow K^{-}K^{+}K^{+}\) decay
Over-training check
Sebastian Ordoñez-Soto
January 24th, 2025
Amplitude Analysis of the \(D^{+}\rightarrow K^{-}K^{+}K^{+}\) decay
Evaluation of the performance of the BDTG classifier
Sebastian Ordoñez-Soto
January 24th, 2025
Amplitude Analysis of the \(D^{+}\rightarrow K^{-}K^{+}K^{+}\) decay
Distributions of the predicted BDTG decision variable for both data and
simulated samples
Sebastian Ordoñez-Soto
January 24th, 2025
Amplitude Analysis of the \(D^{+}\rightarrow K^{-}K^{+}K^{+}\) decay
Signal PDF, Background PDF and Total PDF
Sebastian Ordoñez-Soto
January 24th, 2025
Amplitude Analysis of the \(D^{+}\rightarrow K^{-}K^{+}K^{+}\) decay
The main sources come from the background model and the binning scheme of the efficiency map.
Systematic uncertainties (%) due to the bkg. modeling.
Systematic uncertainties (%) due to the binning scheme.
Total systematic uncertainties (%)