Cid Vidal, XabierVázquez Sierra, CarlosLópez Soliño, Saúl2025-01-222025-01-222024https://hdl.handle.net/10347/38874This work presents studies in Beyond Standard Model Physics, using two different experiments, LHCb and future CODEX-b. Asearch for Dark Matter fromΛ𝑏 decays is performed within theLHCbexperiment during the LHC Run II at a center of mass energy of √ 𝑠 = 13 TeV. Two dark matter operators are studied, 𝒪𝑐𝑑( ¯ 𝑏 → 𝜓DM𝑐𝑑) and 𝒪𝑐𝑠( ¯ 𝑏 → 𝜓DM𝑐𝑠) with 0.940 GeV/c2 < 𝑚(𝜓DM) < 4.430 GeV/c2, respectively. The Λ𝑏 baryons originate in Σ(∗) 𝑏 decays. Λ𝑏 → 𝜓DM𝐾(𝐷 → 𝜋𝜋𝐾) and Λ𝑏 → 𝜓DM𝐾(𝐷 → 𝜋𝜋𝐾) are the final observed states. No signal is observed in any of the studied decay modes and the following upper limits are set for the first time: ℬ(𝒪𝑐𝑠( ¯ 𝑏 → 𝜓DM𝑐𝑠)) < 8.96 × 10−5 − 6.23 × 10−4 for 0.940 GeV/c2 < 𝑚(𝜓DM) < 3.0 GeV/c2 and ℬ(𝒪𝑐𝑑( ¯ 𝑏 → 𝜓DM𝑐𝑑)) < 2.45 × 10−4 − 8.25 × 10−5 for 0.940 GeV/c2 < 𝑚(𝜓DM) < 3.5 GeV/c2 at 95% CL. Within the CODEX-b, some studies for potential long lived particles searches are performed. A generator level efficiency for three different production modes (inclusive, Higgs-strahlung and weak-boson fusion) is computed in the framework of the CODEX-b experiment assuming a minimal Higgs portal model. These Higgs production modes are the dominant ones, while the Higgs portal decay models show a minimal decay model that would allow for future searches within the CODEX framework. This two experiments could also work together for collaborative searches, as showcased in this work.engAttribution-NonCommercial-NoDerivatives 4.0 Internationalhttp://creativecommons.org/licenses/by-nc-nd/4.0/Dark MatterLHCbCodex221202 Partículas elementalesdoctoral thesisopen access