Machine Learning Classification of Sphalerons and Black Holes at the LHC

In models with large extra dimensions, "miniature" black holes (BHs) might be produced in high-energy proton-proton collisions at the Large Hadron Collider (LHC). In the semi-classical regime, those BHs thermally decay, giving rise to large-multiplicity final states with jets and leptons. On the other hand, similar final states are also expected in the production of electroweak sphaleron/instanton-induced processes. We investigate whether one can discriminate these scenarios when BH or sphaleron-like events are observed in the LHC using Machine Learning (ML) methods. Classification among several BH scenarios with different numbers of extra dimensions and the minimal BH masses is also examined. In this study we consider three ML models: XGBoost algorithms with (1) high- and (2) low-level inputs, and (3) a Residual Convolutional Neural Network. In the latter case, the low-level detector information is converted into an input format of three-layer binned event images, where the value of each bin corresponds to the energy deposited in various detector subsystems. We demonstrate that only a few detected events are sufficient to effectively discriminate between the sphaleron and BH processes. Separation among BH scenarios with different minimal BH masses is also possible with a reasonable number of events, that can be collected in the LHC Run-2, -3 and the high-luminosity LHC (HL-LHC). We find, however, that a large number of events is needed to discriminate between BH hypotheses with the same minimal BH mass, but different numbers of extra dimensions.Comment: 18 pages, 5 figure

Studies of the opto-electronic chain for the LHCb RICH upgrade

The present thesis describes in detail the quality assurance of the photodetectors and related electronics (the so-called Elementary Cells) for the RICH (Ring-Imaging Cherenkov) detectors upgrade of the LHCb experiment, performed on-site at the University of Ferrara. The objective of this thesis is the detailed discussion of the complete quality assurance process, from the development of the experimental test setup together with its software used for acquisition and analysis of measurement data, to the description of actual tests performed on the Elementary Cells and their results

Machine Learning Classification of Sphalerons and Black Holes at the LHC

International audienceIn models with large extra dimensions, "miniature" black holes (BHs) might be produced in high-energy proton-proton collisions at the Large Hadron Collider (LHC). In the semi-classical regime, those BHs thermally decay, giving rise to large-multiplicity final states with jets and leptons. On the other hand, similar final states are also expected in the production of electroweak sphaleron/instanton-induced processes. We investigate whether one can discriminate these scenarios when BH or sphaleron-like events are observed in the LHC using Machine Learning (ML) methods. Classification among several BH scenarios with different numbers of extra dimensions and the minimal BH masses is also examined. In this study we consider three ML models: XGBoost algorithms with (1) high- and (2) low-level inputs, and (3) a Residual Convolutional Neural Network. In the latter case, the low-level detector information is converted into an input format of three-layer binned event images, where the value of each bin corresponds to the energy deposited in various detector subsystems. We demonstrate that only a few detected events are sufficient to effectively discriminate between the sphaleron and BH processes. Separation among BH scenarios with different minimal BH masses is also possible with a reasonable number of events, that can be collected in the LHC Run-2, -3 and the high-luminosity LHC (HL-LHC). We find, however, that a large number of events is needed to discriminate between BH hypotheses with the same minimal BH mass, but different numbers of extra dimensions

Machine Learning Classification of Sphalerons and Black Holes at the LHC

International audienceIn models with large extra dimensions, "miniature" black holes (BHs) might be produced in high-energy proton-proton collisions at the Large Hadron Collider (LHC). In the semi-classical regime, those BHs thermally decay, giving rise to large-multiplicity final states with jets and leptons. On the other hand, similar final states are also expected in the production of electroweak sphaleron/instanton-induced processes. We investigate whether one can discriminate these scenarios when BH or sphaleron-like events are observed in the LHC using Machine Learning (ML) methods. Classification among several BH scenarios with different numbers of extra dimensions and the minimal BH masses is also examined. In this study we consider three ML models: XGBoost algorithms with (1) high- and (2) low-level inputs, and (3) a Residual Convolutional Neural Network. In the latter case, the low-level detector information is converted into an input format of three-layer binned event images, where the value of each bin corresponds to the energy deposited in various detector subsystems. We demonstrate that only a few detected events are sufficient to effectively discriminate between the sphaleron and BH processes. Separation among BH scenarios with different minimal BH masses is also possible with a reasonable number of events, that can be collected in the LHC Run-2, -3 and the high-luminosity LHC (HL-LHC). We find, however, that a large number of events is needed to discriminate between BH hypotheses with the same minimal BH mass, but different numbers of extra dimensions

Measurement of the Z boson production cross-section in proton-lead collisions at sNN \sqrt{s_{\textrm{NN}}} = 8.16 TeV

This article presents the first measurement of the differential $Z$-boson production cross-section in the forward region using proton-lead collisions with the LHCb detector. The dataset was collected at a nucleon-nucleon centre-of-mass energy of $\sqrt{s_\mathrm{NN}}=8.16\,\mathrm{TeV}$ in 2016, corresponding to an integrated luminosity of $30.8\,\mathrm{nb}^{-1}$. The forward-backward ratio and the nuclear modification factors are measured together with the differential cross-section as functions of the $Z$ boson rapidity in the centre-of-mass frame, the transverse momentum of the $Z$ boson and a geometric variable $\phi^{*}$. The results are in good agreement with the predictions from nuclear parton distribution functions, providing strong constraining power at small Bjorken-$x$.This article presents the first measurement of the differential Z-boson production cross-section in the forward region using proton-lead collisions with the LHCb detector. The dataset was collected at a nucleon-nucleon centre-of-mass energy of $\sqrt{s_{\textrm{NN}}}$ = 8.16 TeV in 2016, corresponding to an integrated luminosity of 30.8 nb$^{−1}$. The forward-backward ratio and the nuclear modification factors are measured together with the differential cross-section as functions of the Z boson rapidity in the centre-of-mass frame, the transverse momentum of the Z boson and a geometric variable ϕ$^{*}$. The results are in good agreement with the predictions from nuclear parton distribution functions, providing strong constraining power at small Bjorken-x.[graphic not available: see fulltext]This article presents the first measurement of the differential $Z$-boson production cross-section in the forward region using proton-lead collisions with the LHCb detector. The dataset was collected at a nucleon-nucleon centre-of-mass energy of $\sqrt{s_\mathrm{NN}}=8.16\,\mathrm{TeV}$ in 2016, corresponding to an integrated luminosity of $30.8\,\mathrm{nb}^{-1}$. The forward-backward ratio and the nuclear modification factors are measured together with the differential cross-section as functions of the $Z$ boson rapidity in the centre-of-mass frame, the transverse momentum of the $Z$ boson and a geometric variable $\phi^{*}$. The results are in good agreement with the predictions from nuclear parton distribution functions, providing strong constraining power at small Bjorken-$x$

Study of the doubly charmed tetraquark Tcc+T_{cc}^+

An exotic narrow state in the $D^0D^0\pi^+$ mass spectrum just below the $D^{*+}D^0$ mass threshold is studied using a data set corresponding to an integrated luminosity of 9 fb$^{-1}$ acquired with the LHCb detector in proton-proton collisions at centre-of-mass energies of 7, 8 and 13 TeV. The state is consistent with the ground isoscalar $T^+_{cc}$ tetraquark with a quark content of $cc\bar{u}\bar{d}$ and spin-parity quantum numbers $\mathrm{J}^{\mathrm{P}}=1^+$. Study of the $DD$ mass spectra disfavours interpretation of the resonance as the isovector state. The decay structure via intermediate off-shell $D^{*+}$ mesons is confirmed by the $D^0\pi^+$ mass distribution. The mass of the resonance and its coupling to the $D^{*}D$ system are analysed. Resonance parameters including the pole position, scattering length, effective range and compositeness are measured to reveal important information about the nature of the $T^+_{cc}$ state. In addition, an unexpected dependence of the production rate on track multiplicity is observed

Measurement of the lifetimes of promptly produced Ωc0 and Ξc0 baryons

International audienceA measurement of the lifetimes of the Ωc0 and Ξc0 baryons is reported using proton–proton collision data at a centre-of-mass energy of 13TeV, corresponding to an integrated luminosity of 5.4fb-1 collected by the LHCb experiment. The Ωc0 and Ξc0 baryons are produced directly from proton interactions and reconstructed in the pK-K-π+ final state. The Ωc0 lifetime is measured to be 276.5±13.4±4.4±0.7fs, and the Ξc0 lifetime is measured to be 148.0±2.3±2.2±0.2fs, where the first uncertainty is statistical, the second systematic, and the third due to the uncertainty on the D0 lifetime. These results confirm previous LHCb measurements based on semileptonic beauty-hadron decays, which disagree with earlier results of a four times shorter Ωc0 lifetime, and provide the single most precise measurement of the Ωc0 lifetime

Observation of the suppressed Λb0→DpK- decay with D→K+π- and measurement of its CP asymmetry

International audienceA study of Λb0 baryon decays to the DpK- final state is presented based on a proton-proton collision data sample corresponding to an integrated luminosity of 9  fb-1 collected with the LHCb detector. Two Λb0 decays are considered, Λb0→DpK- with D→K-π+ and D→K+π-, where D represents a superposition of D0 and D¯0 states. The latter process is expected to be suppressed relative to the former, and is observed for the first time. The ratio of branching fractions of the two decays is measured, and the CP asymmetry of the suppressed mode, which is sensitive to the Cabibbo-Kobayashi-Maskawa angle γ, is also reported

Nuclear modification factor of neutral pions in the forward and backward regions in ppPb collisions

The nuclear modification factor of neutral pions is measured in proton-lead collisions collected at a center-of-mass energy per nucleon of $8.16$ TeV with the LHCb detector. The $\pi^0$ production cross section is measured differentially in transverse momentum ($p_{T}$) for 1.5π0 production cross section is measured differentially in transverse momentum (pT) for 1.5<pT<10.0  GeV and in center-of-mass pseudorapidity (ηc.m.) regions 2.5<ηc.m.<3.5 (forward) and -4.0<ηc.m.<-3.0 (backward) defined relative to the proton beam direction. The forward measurement shows a sizable suppression of π0 production, while the backward measurement shows the first evidence of π0 enhancement in proton-lead collisions at the LHC. Together, these measurements provide precise constraints on models of nuclear structure and particle production in high-energy nuclear collisions.The nuclear modification factor of neutral pions is measured in proton-lead collisions collected at a center-of-mass energy per nucleon of 8.16~{\rm TeV}$with the LHCb detector. The$\pi^0$production cross section is measured differentially in transverse momentum ($p_{\rm T}$) for$1.5<p_{\rm T}<10.0~{\rm GeV}$and in center-of-mass pseudorapidity ($\eta_{\rm c.m.}$) regions$2.5<\eta_{\rm c.m.}<3.5$(forward) and$-4.0<\eta_{\rm c.m.}<-3.0$(backward) defined relative to the proton beam direction. The forward measurement shows a sizable suppression of$\pi^0$production, while the backward measurement shows the first evidence of$\pi^0$ enhancement in proton-lead collisions at the LHC. Together, these measurements provide precise constraints on models of nuclear structure and particle production in high-energy nuclear collisions