7 research outputs found

    A scheme to fix multiple solutions in amplitude analyses

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    Decays of unstable heavy particles usually involve the coherent sum of several amplitudes, like in a multiple slit experiment. Dedicated amplitude analysis techniques have been widely used to resolve these amplitudes for better understanding of the underlying dynamics. For special cases, where two spin-1/2 particles and two (pseudo-)scalar particles are present in the process, multiple equivalent solutions are found due to intrinsic symmetries in the summed probability density function. In this paper, the problem of multiple solutions is discussed and a scheme to overcome this problem is proposed by fixing some free parameters. Toys are generated to validate the strategy. A new approach to align helicities of initial- and final-state particles in different decay chains is also introduced.Comment: 17 pages, 2 figure

    Orthogonal Subspace Learning for Language Model Continual Learning

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    Benefiting from massive corpora and advanced hardware, large language models (LLMs) exhibit remarkable capabilities in language understanding and generation. However, their performance degrades in scenarios where multiple tasks are encountered sequentially, also known as catastrophic forgetting. In this paper, we propose orthogonal low-rank adaptation (O-LoRA), a simple and efficient approach for continual learning in language models, effectively mitigating catastrophic forgetting while learning new tasks. Specifically, O-LoRA learns tasks in different (low-rank) vector subspaces that are kept orthogonal to each other in order to minimize interference. Our method induces only marginal additional parameter costs and requires no user data storage for replay. Experimental results on continual learning benchmarks show that our method outperforms state-of-the-art methods. Furthermore, compared to previous approaches, our method excels in preserving the generalization ability of LLMs on unseen tasks.Comment: EMNLP 2023 finding

    Student Sessions 2023

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    Measurement of Λ EMD/MDM using LHCb data I am Tianze Rong (荣天泽) from Beijing, China. I just got my bachelor's degree in astronomy from School of Physics, Peking University, before I came to CERN. During the summer student programme, I have been working on measurement of Λ! EDM/MDM at LHCb. Though I had some experience in LHCb experiment before, this project indeed broadens my horizons, and shows me the possibility and opportunity of LHCb. After the programme, I will start my PhD in experimental high energy physics at Peking University. The experience at CERN is a treasure for me and a good start of my future study

    Heteroplasmy Detection of Mitochondrial DNA A3243G Mutation Using Quantitative Real-Time PCR Assay Based on TaqMan-MGB Probes

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    A point mutation of mitochondrial DNA (mtDNA) at nucleotide position 3243 A to G (mt.3243A>G) is involved in many common diseases, including maternally inherited diabetes and deafness (MIDD) and mitochondrial encephalomyopathy, lactic acidosis with stroke-like episodes (MELAS). However, the mutant level of mt.3243A>G varies both among individuals and in different organs, tissues, and even cells of single individuals. For detection of this mutation, current methods have limited universality and sensitivity and may be not adequate for a routine clinical test. Here, we develop and evaluate a rapid TaqMan-MGB quantitative real-time PCR (qPCR) method for detecting and quantifying the heteroplasmy level of mt.3243A>G in single-tube analysis. With our method, the sensitivity of detection was as low as 0.1%, but the accuracy of quantification was reliable, down to 4%. All positives could be correctly identified, and the heteroplasmy levels determined by qPCR correlated well with the results from restriction fragment length polymorphism (RFLP) and pyrosequencing assays (r = 0.921~0.973 and 0.972~0.984). In addition, we demonstrated that the urinary sediments, leukocytes, or hair follicles might be ideal templates to detect and quantify the heteroplasmy of mt.3243A>G mutation; however, they should be optimized or retreated for further accurate quantification. Our study should allow rapid and high throughput diagnostic testing and can potentially be used to clarify the association between clinical phenotype and pathogenic mitochondrial mutations derived from various tissues

    Comprehensive analysis of local and nonlocal amplitudes in the B0K0μ+μB^0 \to K^{*0} \mu^+\mu^- decay

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    A comprehensive study of the local and nonlocal amplitudes contributing to the decay B0K0(K+π)μ+μB^0\rightarrow K^{*0}(\to K^+\pi^-) \mu^+\mu^- is performed by analysing the phase-space distribution of the decay products. The analysis is based on pppp collision data corresponding to an integrated luminosity of 8.4fb1^{-1} collected by the LHCb experiment. This measurement employs for the first time a model of both one-particle and two-particle nonlocal amplitudes, and utilises the complete dimuon mass spectrum without any veto regions around the narrow charmonium resonances. In this way it is possible to explicitly isolate the local and nonlocal contributions and capture the interference between them. The results show that interference with nonlocal contributions, although larger than predicted, only has a minor impact on the Wilson Coefficients determined from the fit to the data. For the local contributions, the Wilson Coefficient C9C_9, responsible for vector dimuon currents, exhibits a 2.1σ2.1\sigma deviation from the Standard Model expectation. The Wilson Coefficients C10C_{10}, C9C_{9}' and C10C_{10}' are all in better agreement than C9C_{9} with the Standard Model and the global significance is at the level of 1.5σ1.5\sigma. The model used also accounts for nonlocal contributions from B0K0[τ+τμ+μ]B^{0}\to K^{*0}\left[\tau^+\tau^-\to \mu^+\mu^-\right] rescattering, resulting in the first direct measurement of the bsττb s\tau\tau vector effective-coupling C9τC_{9\tau}.A comprehensive study of the local and nonlocal amplitudes contributing to the decay B0K0(K+π)μ+μB^0\rightarrow K^{*0}(\to K^+\pi^-) \mu^+\mu^- is performed by analysing the phase-space distribution of the decay products. The analysis is based on \proton\proton collision data corresponding to an integrated luminosity of 8.4fb1^{-1} collected by the LHCb experiment. This measurement employs for the first time a model of both one-particle and two-particle nonlocal amplitudes, and utilises the complete dimuon mass spectrum without any veto regions around the narrow charmonium resonances. In this way it is possible to explicitly isolate the local and nonlocal contributions and capture the interference between them. The results show that interference with nonlocal contributions, although larger than predicted, only has a minor impact on the Wilson Coefficients determined from the fit to the data. For the local contributions, the Wilson Coefficient C9C_9, responsible for vector dimuon currents, exhibits a 2.1σ2.1\sigma deviation from the Standard Model expectation. The Wilson Coefficients C10C_{10}, C9C_{9}' and C10C_{10}' are all in better agreement than C9C_{9} with the Standard Model and the global significance is at the level of 1.5σ1.5\sigma. The model used also accounts for nonlocal contributions from B0K0[τ+τμ+μ]B^{0}\to K^{*0}\left[\tau^+\tau^-\to \mu^+\mu^-\right] rescattering, resulting in the first direct measurement of the bsττb s\tau\tau vector effective-coupling C9τC_{9\tau}

    Study of bb-hadron decays to Λc+hh\Lambda_c^+h^-h^{\prime -} final states

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    Decays of Ξb\Xi_{b}^{-} and Ωb\Omega_{b}^{-} baryons to Λc+hh\Lambda_{c}^{+} h^- h^{\prime -} final states, with hhh^- h^{\prime -} being ππ\pi^{-}\pi^{-}, KπK^{-}\pi^{-} and KKK^{-}K^{-} meson pairs, are searched for using data collected with the LHCb detector. The data sample studied corresponds to an integrated luminosity of 8.7fb18.7 \rm fb^{-1} of pppp collisions collected at centre-of-mass energies s=7\sqrt{s} = 7, 88 and 13TeV13 \rm TeV. The products of the relative branching fractions and fragmentation fractions for each signal mode, relative to the BΛc+pˉπB^{-} \rightarrow \Lambda_{c}^{+} \bar{p} \pi^{-} mode, are measured, with ΞbΛc+Kπ\Xi_{b}^{-} \rightarrow\Lambda_{c}^{+} K^{-} \pi^{-}, ΞbΛc+KK\Xi_{b}^{-} \rightarrow\Lambda_{c}^{+} K^{-} K^{-} and ΩbΛc+KK\Omega_{b}^{-} \rightarrow\Lambda_{c}^{+} K^{-} K^{-} decays being observed at over 5σ5\,\sigma significance. The ΞbΛc+Kπ\Xi_{b}^{-} \rightarrow\Lambda_{c}^{+} K^{-} \pi^{-} mode is also used to measure the Ξb\Xi_{b}^{-} production asymmetry, which is found to be consistent with zero. In addition, the BΛc+pˉKB^{-} \rightarrow \Lambda_{c}^{+} \bar{p} K^{-} decay is observed for the first time, and its branching fraction is measured relative to that of the BΛc+pˉπB^{-} \rightarrow \Lambda_{c}^{+} \bar{p} \pi^{-} mode.Decays of Ξb\Xi_b^- and Ωb\Omega_b^- baryons to Λc+hh\Lambda_c^+ h^- h^{\prime -} final states, with hhh^- h^{\prime -} being ππ\pi^-\pi^-, KπK^-\pi^- and KKK^-K^- meson pairs, are searched for using data collected with the LHCb detector. The data sample studied corresponds to an integrated luminosity of 8.7fb18.7\,\mathrm{fb}^{-1} of pppp collisions collected at centre-of-mass energies s=7\sqrt{s} = 7, 88 and 13TeV13\,\mathrm{Te\kern -0.1em V}. The products of the relative branching fractions and fragmentation fractions for each signal mode, relative to the BΛc+pπB^- \to \Lambda_c^+ \overline{p} \pi^- mode, are measured, with ΞbΛc+Kπ\Xi_{b}^- \to\Lambda_{c}^+ K^- \pi^-, ΞbΛc+KK\Xi_{b}^- \to\Lambda_{c}^+ K^- K^- and ΩbΛc+KK\Omega_{b}^- \to\Lambda_{c}^+ K^- K^- decays being observed at over 5σ5\,\sigma significance. The ΞbΛc+Kπ\Xi_{b}^- \to\Lambda_{c}^+ K^- \pi^- mode is also used to measure the Ξb\Xi_{b}^- production asymmetry, which is found to be consistent with zero. In addition, the BΛc+pKB^- \to \Lambda_{c}^+ \overline{p} K^- decay is observed for the first time, and its branching fraction is measured relative to that of the BΛc+pπB^- \to \Lambda_{c}^+ \overline{p} \pi^- mode

    Transverse polarisation measurement of Λ\Lambda hyperons in ppNe collisions at sNN\sqrt{s_{NN}}=68.4 GeV with the LHCb detector

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    A measurement of the transverse polarization of the Λ\Lambda and Λˉ\bar{\Lambda}hyperons in ppNe fixed-target collisions at sNN\sqrt{s_{NN}}=68.4 GeV is presented using data collected by the LHCb detector. The polarization is studied using the decay Λpπ\Lambda \rightarrow p \pi^- together with its charge conjugated process, the integrated values measured are PΛ=0.029±0.019(stat)±0.012(syst), P_{\Lambda} = 0.029 \pm 0.019 \, (\rm{stat}) \pm 0.012 \, (\rm{syst}) \, , PΛˉ=0.003±0.023(stat)±0.014(syst) P_{\bar{\Lambda}} = 0.003 \pm 0.023 \, (\rm{stat}) \pm 0.014 \,(\rm{syst}) \, Furthermore, the results are shown as a function of the Feynman xx variable, transverse momentum, pseudorapidity and rapidity of the hyperons, and are compared with previous measurements.A measurement of the transverse polarization of the Λ\Lambda and Λˉ\bar{\Lambda} hyperons in ppNe fixed-target collisions at sNN\sqrt{s_{NN}} = 68.4 GeV is presented using data collected by the LHCb detector. The polarization is studied using the decay Λpπ\Lambda \rightarrow p \pi^- together with its charge conjugated process, the integrated values measured are PΛ=0.029±0.019(stat)±0.012(syst), P_{\Lambda} = 0.029 \pm 0.019 \, (\rm{stat}) \pm 0.012 \, (\rm{syst}) \, , PΛˉ=0.003±0.023(stat)±0.014(syst). P_{\bar{\Lambda}} = 0.003 \pm 0.023 \, (\rm{stat}) \pm 0.014 \,(\rm{syst}) \,. Furthermore, the results are shown as a function of the Feynman~xx~variable, transverse momentum, pseudorapidity and rapidity of the hyperons, and are compared with previous measurements
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