513 research outputs found
Study of b- and c-jets identification with quantum machine learning algorithms and application to the Higgs reconstruction
No full textopenIn questa tesi viene presentato un nuovo algoritmo per la classificazione del sapore dei getti adronici ad LHCb, basato su tecniche di calcolo quantistico applicate all’intelligenza artificiale. L’algoritmo è stato sviluppato per distinguere i getti prodotti dai quark bottom e charm, ed è stato applicato alla ricerca del decadimento del bosone di Higgs in due quark charm (H->c c-bar). In questo studio sono stati utilizzati i dati simulati delle collisioni protone-protone ad LHCb, ad un’energia nel centro di massa di 13 TeV. L'accuratezza della classificazione è stata testata in funzione della cinematica dei getti adronici, e le prestazioni dell’algoritmo quantistico sono state confrontate con con quelle di un classico algoritmo di intelligenza artificiale. In particolare i due tipi di algoritmi mostrano prestazioni confrontabili. Successivamente, entrambi i modelli sono stati utilizzati per studiare la sensitività di LHCb nella ricerca dei decadimenti H->bb-bar e H->cc-bar. Entrambi i metodi hanno mostrato un incremento di sensitività rispetto a quello basato sulla ricostruzione dei vertici di decadimento degli aironi b e c, utilizzato nelle precedenti analisi di LHCb. Anche in questo caso sono state ottenute prestazioni confrontabili tra l’algoritmo di intelligenza artificiale quantistico e quello classico. Nonostante lo studio degli algoritmi quantistici sia alle fasi iniziali, i risultati ottenuti sono incoraggianti per continuare la ricerca in questo campo.In this thesis, a new approach for jet flavour classification, between b- versus c-quark jets, based on Quantum Machine Learning techniques for the Higgs to ccbar studies is presented. Besides, the training of the model was carried out by using LHCb proton-proton collision simulated data at the center of mass energy of 13 TeV. The jet flavour classification accuracy was tested as a function of the jet transverse momentum and the jet pseudorapidity between the Quantum Machine Learning model and the classical machine learning model, where the b-quark jet test accuracy shows the most similar classification results between the QML method and the classical ML method. Later, this model was used to study the sensitivity of the Higgs boson decay into a pair of b-quarks and the Higgs boson decay into a pair of c-quarks using samples of LHCb simulated data corresponding to the integrated luminosity of the Run 2. Either the quantum machine learning method or the classical machine learning model gave an improvement in the significance for the Higgs to ccbar observation. At the point of maximum significance improvement, the efficiency and mistagging efficiency were evaluated as functions of the jet transverse momentum, jet pseudorapidity and dijet invariant mass obtaining comparable performances between the quantum machine learning model and the classical machine learning model. In spite of the quantum machine learning is a technique at its early stage, the obtained results are encouraging to continue with the research in this field looking for a better performance
Study of B c + → χ c π + decays
No full textAbstract A study of B c + → χ c π + decays is reported using proton-proton collision data, collected with the LHCb detector at centre-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of 9 fb −1. The decay B c + → χ c 2 π + is observed for the first time, with a significance exceeding seven standard deviations. The relative branching fraction with respect to the B c + → J / ψ π + decay is measured to be B B c + → χ c 2 π + B B c + → J / ψ π + = 0.37 ± 0.06 ± 0.02 ± 0.01 , where the first uncertainty is statistical, the second is systematic, and the third is due to the knowledge of the χ c2 → J/ψγ branching fraction. No significant B c + → χ c 1 π + signal is observed and an upper limit for the relative branching fraction for the B c + → χ c 1 π + and B c + → χ c 2 π + decays of B B c + → χ c 1 π + B B c + → χ c 2 π + = < 0.49 is set at the 90% confidence level
Search for B∗0(s) → μ+μ− in B+c → π+μ+μ− decays
No full textA search for the very rare B∗0 → μ+μ−
and B∗0
s → μ+μ− decays is conducted by analysing the
B+
c → π+μ+μ− process. The analysis uses proton-proton
collision data collected with the LHCb detector between
2011 and 2018, corresponding to an integrated luminosity
of 9 fb−1. The signal signatures correspond to simultaneous
peaks in the μ+μ− and π+μ+μ− invariant masses. No evidence for an excess of events over background is observed
for either signal decay mode. Upper limits at the 90% confidence level are set on the branching fractions relative to that
for B+
c → J/ψπ+ decays,
RB∗0(μ+μ−)π+/J/ψπ+ < 3.8 × 10−5 and
RB∗0
s (μ+μ−)π+/J/ψπ+ < 5.0 × 10−5
Measurement of Λ0b, Λ+c, and Λ Decay Parameters Using Λ0b →Λ+c h- Decays
No full textA comprehensive study of the angular distributions in the bottom-baryon decays Λ_{b}^{0}→Λ_{c}^{+}h^{-}(h=π,K), followed by Λ_{c}^{+}→Λh^{+} with Λ→pπ^{-} or Λ_{c}^{+}→pK_{S}^{0} decays, is performed using a data sample of proton-proton collisions corresponding to an integrated luminosity of 9 fb^{-1} collected by the LHCb experiment at center-of-mass energies of 7, 8, and 13 TeV. The decay parameters and the associated charge-parity (CP) asymmetries are measured, with no significant CP violation observed. For the first time, the Λ_{b}^{0}→Λ_{c}^{+}h^{-} decay parameters are measured. The most precise measurements of the decay parameters α, β, and γ are obtained for Λ_{c}^{+} decays and an independent measurement of the decay parameters for the strange-baryon Λ decay is provided. The results deepen our understanding of weak decay dynamics in baryon decays
Observation of Cabibbo-Suppressed Two-Body Hadronic Decays and Precision Mass Measurement of the Baryon
No full textThe first observation of the singly Cabibbo-suppressed
and decays
is reported, using proton-proton collision data at a center-of-mass energy of
, corresponding to an integrated luminosity of , collected with the LHCb detector between 2016 and 2018. The
branching fraction ratios are measured to be
,
. In addition, using the
decay channel, the baryon
mass is measured to be , improving the
precision of the previous world average by a factor of 4.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2023-011.html (LHCb
public pages
First observation of the B¯s0 → Λc+Λ¯c− decay and evidence for the B¯0 → Λc+Λ¯c− decay
No full textA search is presented for the two-body charmed baryonic decays, B ¯ ( s ) 0 → Λ c + Λ ¯ c − , using a data sample collected by the LHCb experiment during 2011–2012 and 2015–2018, corresponding to an integrated luminosity of 9 fb − 1 . The first observation of the B ¯ s 0 → Λ c + Λ ¯ c − decay is reported with 6.2 σ significance along with 4.3 σ evidence for the B ¯ 0 → Λ c + Λ ¯ c − decay. The branching fractions are measured to be B ( B ¯ 0 → Λ c + Λ ¯ c − ) = ( 1.0 1 − 0.28 + 0.27 ± 0.08 ± 0.15 ) × 10 − 5 and B ( B ¯ s 0 → Λ c + Λ ¯ c − ) = ( 5.0 ± 1.3 ± 0.5 ± 0.8 ) × 10 − 5 , where the first uncertainty is statistical, the second systematic, and the third due to external inputs. These results provide novel experimental inputs for the theoretical framework describing two-body baryonic decays of B mesons via W -emission and W -exchange mechanisms
First observation of the decay and evidence for the decay
No full textInternational audienceA search is presented for the two-body charmed baryonic decays , using a data sample collected by the LHCb experiment during 2011--2012 and 2015--2018 corresponding to an integrated luminosity of . The first observation of the decay is reported with significance, along with evidence for the decay. The branching fractions are measured to be and , where the first uncertainty is statistical, the second systematic, and the third due to external inputs. These results provide novel experimental inputs for the theoretical framework describing two-body baryonic decays of mesons via -emission and -exchange mechanisms
Observation of and decays
No full textThe decays and are observed for the first time, in proton-proton
collision data at TeV corresponding to an integrated luminosity of
5.4 fb collected with the LHCb detector. Their ratios of branching
fractions with respect to the mode
are measured to be
\begin{align*}
\begin{split}
\frac{\mathcal{B}(\Lambda_b^0 \to \Lambda_c^+\bar{D}^0
K^-)}{\mathcal{B}(\Lambda_b^0 \to \Lambda_c^+ D_s^-)} & = 0.1908
{}_{-0.0034}^{+0.0036} {}_{-0.0018}^{+0.0016} \pm 0.0038
\frac{\mathcal{B}(\Lambda_b^0 \to \Lambda_c^+\bar{D}^{*0}
K^-)}{\mathcal{B}(\Lambda_b^0 \to \Lambda_c^+ D_s^-)} & = 0.589
{}_{-0.017}^{+0.018} {}_{-0.018}^{+0.017} \pm 0.012
\frac{\mathcal{B}(\Lambda_b^0 \to \Lambda_c^+
D_s^{*-})}{\mathcal{B}(\Lambda_b^0 \to \Lambda_c^+ D_s^-)} & = 1.668 \pm 0.022
{}_{-0.055}^{+0.061}\ ,
\end{split} \end{align*} where the first uncertainties are statistical, the
second systematic, and the third, for the decays, are due to the uncertainties on the branching
fractions of the and decay
modes. The measured branching fractions probe factorization assumptions in
effective theories and provide the normalization for future pentaquark searches
in decay channels.Comment: All figures and tables, along with machine-readable versions and any
supplementary material and additional information, are available at
https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2023-034.html (LHCb
public pages); v2 after journal revie
Study of states in the mass spectrum
No full textThe study of a wide peaking structure in the Bc+γ mass spectrum is reported using a data sample of proton-proton collisions collected by the LHCb detector at center-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of 9 fb-1. The observed structure is consistent with the lowest excited P-wave Bc+ states and exhibits a statistical significance exceeding 7 standard deviations relative to the background-only hypothesis. A two-peak model serves as an effective description of the data, with various theory-constrained models further explored to provide physical interpretation. Based on the predictions for the Bc(1P)+ spectrum, the relative production cross section of the overall Bc(1P)+ states with respect to the Bc+ ground state with the transverse momentum pT and rapidity y of Bc+ mesons in the regions pT<20 GeV/c and 2.0<y<4.5 at s=13 TeV is measured to be 0.20±0.03±0.02±0.03, where the uncertainty terms represent statistical, systematic, and uncertainties related to the choice of theoretical models, respectively. The results provide a test of theoretical models and deepen our understanding of quantum chromodynamics.The study of a wide peaking structure in the mass spectrum is reported using a data sample of proton-proton collisions collected by the LHCb detector at center-of-mass energies of , , and , corresponding to an integrated luminosity of . The observed structure is consistent with the lowest excited -wave states and exhibits a statistical significance exceeding seven standard deviations relative to the background-only hypothesis. A two-peak model serves as an effective description of the data, with various theory-constrained models further explored to provide physical interpretation. Based on the predictions for the spectrum, the relative production cross-section of the overall states with respect to the ground state with the transverse momentum and rapidity of mesons in the regions and at is measured to be , where the uncertainty terms represent statistical, systematic, and uncertainties related to the choice of theoretical models, respectively. The results provide a test of theoretical models and deepen our understanding of quantum chromodynamics
Summary of the trigger systems of the Large Hadron Collider experiments ALICE, ATLAS, CMS and LHCb
No full textInternational audienceIn modern high energy physics (HEP) experiments, triggers perform the important task of selecting, in real time, the data to be recorded and saved for physics analyses. As a result, trigger strategies play a key role in extracting relevant information from the vast streams of data produced at facilities like the large hadron collider (LHC). As the energy and luminosity of the collisions increase, these strategies must be upgraded and maintained to suit the experimental needs. This whitepaper presents a high-level overview and reviews recent developments of triggering practices employed at the LHC. The general trigger principles applied at modern HEP experiments are highlighted, with specific reference to the current trigger state-of-the-art within the ALICE, ATLAS, CMS and LHCb collaborations. Furthermore, a brief synopsis of the new trigger paradigm required by the upcoming high-luminosity upgrade of the LHC is provided. This whitepaper, compiled by Early Stage Researchers of the SMARTHEP network, is not meant to provide an exhaustive review or substitute documentation and papers from the collaborations themselves, but rather offer general considerations and examples from the literature that are relevant to the SMARTHEP network
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