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All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Transverse polarization measurement of Λ hyperons in pNe collisions at $\sqrt{{\textrm{s}}_{\textrm{NN}}}$ = 68.4 GeV with the LHCb detector

A measurement of the transverse polarization of the Λ and $\bar{Λ}$ hyperons in p Ne fixed-target collisions at $\sqrt{{\textrm{s}}_{\textrm{NN}}}$ = 68.4 GeV is presented using data collected by the LHCb detector. The polarization is studied using the decay Λ → p $π$ − together with its charge conjugated process, the integrated values measured are $P_Λ = 0.029 ± 0.019$ (stat) $±$ $0.012$ (syst), $P_{\bar{Λ}} = 0.003 ± 0.023$ (stat) $±$ $0.014$ (syst). Furthermore, the results are shown as a function of the Feynman x variable, transverse momentum, pseudorapidity and rapidity of the hyperons, and are compared with previous measurements.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Measurement of the CKM angle γ from a combination of LHCb results

A combination of measurements sensitive to the CKM angle γ from LHCb is performed. The inputs are from analyses of time-integrated B+ → DK+, B0 → DK*0, B0 → DK+π- and B+ → DK+π+π- tree-level decays. In addition, results from a time-dependent analysis of Bs0 → Ds∓K± decays are included. The combination yields γ = (72. 2- 7.3+ 6.8)°, where the uncertainty includes systematic effects. The 95.5% confidence level interval is determined to be γ ϵ [55.9, 85.2]°. A second combination is investigated, also including measurements from B+ → Dπ+ and B+ → Dπ+π-π+ decays, which yields compatible results.

Aaij, R↗
DOE OSTI2023

The LHCb state $P^{Λ}_{ψs}$(4338) as a triangle singularity

We present a model for the J/ψ Λ spectrum in B – → J/ψ Λ $\bar{p}$ decays, including the $P^{Λ}_{ψs}$(4338) baryon recently observed by the LHCb collaboration. We assume production via triangle diagrams which couple to the final state via non-perturbative interactions which are constrained by heavy- quark and SU 3 -flavor symmetry. The bulk of the distribution is described by a triangle diagram with a color-favored electroweak vertex, while the sharp $P^{Λ}_{ψs}$(4338) enhancement is due to the ψs triangle singularity in another diagram featuring a 1/2 – baryon consistent with Σ c (2800). We predict a comparable $P^{Λ}_{ψs}$(4338) signal in η c Λ, and anticipate possible large isospin mixing effects ψs through decays to J/ψ Σ 0 and η c Σ 0 .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Observation of the rare $B^0_s\to\mu^+\mu^-$ decay from the combined analysis of CMS and LHCb data

A joint measurement is presented of the branching fractions $B^0_s\to\mu^+\mu^-$ and $B^0\to\mu^+\mu^-$ in proton-proton collisions at the LHC by the CMS and LHCb experiments. The data samples were collected in 2011 at a centre-of-mass energy of 7 TeV, and in 2012 at 8 TeV. The combined analysis produces the first observation of the $B^0_s\to\mu^+\mu^-$ decay, with a statistical significance exceeding six standard deviations, and the best measurement of its branching fraction so far. Furthermore, evidence for the $B^0\to\mu^+\mu^-$ decay is obtained with a statistical significance of three standard deviations. The branching fraction measurements are statistically compatible with SM predictions and impose stringent constraints on several theories beyond the SM.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Bulk flow and correlation measurements at LHCb

Particle correlations are a powerful tool to study the properties of the bulk nuclear matter produced in relativistic heavy ion collisions. The momentum correlations between identical particles originating from the same particle-emitting source, referred to as the Bose-Einstein correlations, measure scales that are related to the geometrical size of the source. The two-particle azimuthal angular correlations measure the spatial anisotropy of produced particles, providing information on collective phenomena arising in the dense nuclear medium. This contribution will discuss new LHCb measurements of Bose- Einstein correlations and, for the first time, the collective flow coefficients in the far forward rapidity region.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Search for the rare decays $W^+ → D^+_s \gamma$ and $Z → D^0 \gamma$ at LHCb

A search for the rare decays $W^+ → D^+_s \gamma$ and $Z → D^0 \gamma$ is performed using proton-proton collision data collected by the LHCb experiment at a centre-of-mass energy of 13TeV, corresponding to an integrated luminosity of 2.0fb -1 . No significant signal is observed for either decay mode and upper limits on their branching fractions are set using W⁺ → μ⁺v and Z → μ⁺μ⁻ decays as normalization channels. The upper limits are 6.5 x 10 -4 and 2.1 x 10 -3 at 95% confidence level for the $W^+ → D^+_s \gamma$ and $Z → D^0 \gamma$ decay modes, respectively. This is the first reported search for the $Z → D^0 \gamma$ decay, while the upper limit on the branching fraction $W^+ → D^+_s \gamma$ improves upon the previous best limit.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Centrality determination in heavy-ion collisions with the LHCb detector

The centrality of heavy-ion collisions is directly related to the created medium in these interactions. A procedure to determine the centrality of collisions with the LHCb detector is implemented for lead-lead collisions at √ s NN = 5 TeV and lead-neon fixed-target collisions at √ s NN = 69 GeV. The energy deposits in the electromagnetic calorimeter are used to determine and define the centrality classes. The correspondence between the number of participants and the centrality for the lead-lead collisions is in good agreement with the correspondence found in other experiments, and the centrality measurements for the lead-neon collisions presented here are performed for the first time in fixed-target collisions at the LHC.

47 OTHER INSTRUMENTATION↗
DOE OSTI2015

Calibration of the LHCb electromagnetic calorimeter via reconstructing the neutral-pion invariant mass

The calibration of the LHCb electromagnetic calorimeter is a multistep procedure aimed at reconstructing photon and electron energies to a precision not poorer than 2%. A method based on measuring the neutral-pion invariantmass is applied at the last step of this procedure. A regular application of this method makes it possible to improve substantially the resolution for particles that decay through channels featuring electrons and photons in the final state.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Hint of a new scalar interaction in LHCb data?

Abstract We explain recent LHCb measurements of the lepton universality ratios, $$R_{D^{(*)}}^{\tau /\ell }\equiv \frac{\mathcal {B}(\bar{B} \rightarrow D^{(*)+} \tau ^- \bar{\nu }_\tau )}{\mathcal {B}(\bar{B} \rightarrow D^{(*)+}\ell ^- \bar{\nu }_\ell )}$$ R D ( ∗ ) τ / ℓ ≡ B ( B ¯ → D ( ∗ ) + τ - ν ¯ τ ) B ( B ¯ → D ( ∗ ) + ℓ - ν ¯ ℓ ) and $${R(\Lambda _c^+)}^{\tau /\ell } \equiv \frac{\mathcal {B}(\Lambda _b \rightarrow \Lambda _c^+ \tau ^- \bar{\nu }_{\tau })}{\mathcal {B}(\Lambda _b \rightarrow \Lambda _c^+ \ell ^- \bar{\nu }_{\ell })}$$ R ( Λ c + ) τ / ℓ ≡ B ( Λ b → Λ c + τ - ν ¯ τ ) B ( Λ b → Λ c + ℓ - ν ¯ ℓ ) with $$\ell =\mu $$ ℓ = μ , via new physics that affects $$R_D^{\tau /\ell }$$ R D τ / ℓ and $$R(\Lambda _c^+)^{\tau /\ell }$$ R ( Λ c + ) τ / ℓ but not $$R_{D^*}^{\tau /\ell }$$ R D ∗ τ / ℓ . The scalar operator in the effective theory for new physics is indicated. We find that the forward-backward asymmetry and $$\tau $$ τ polarization in $$\bar{B} \rightarrow D^+ \tau ^{-} \bar{\nu }_{\tau }$$ B ¯ → D + τ - ν ¯ τ and $$\Lambda _b \rightarrow \Lambda _c^+ \tau ^- \bar{\nu }_{\tau }$$ Λ b → Λ c + τ - ν ¯ τ decays are significantly affected by the scalar interaction. We construct a simple two Higgs doublet model as a realization of our scenario and consider lepton universality in semileptonic charm and top decays, radiative B decay, B -mixing, and $$Z \rightarrow b \bar{b}$$ Z → b b ¯ .

Physics↗
DOE OSTI2018

Search for resonances in $b$-jets final states with the CDF II and the LHCb experiments

This thesis describes the search for resonances decaying into a pair of b-jets performed with the datasets collected by the CDF II experiment at the Tevatron and the LHCb at the LHC. The unique characteristics of these particle detectors, which are highlighted through the thesis with a constant comparison between the two experiments, give the opportunity to search also in the low dijet invariant mass region, unaccessible to the other general purpose detectors at the LHC. A dataset corresponding to 5:4 fb

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Implications from ${B\to K^*\ell^+\ell^-}$ observables using $3 \text{fb}^{-1}$ of LHCb data

The decay mode${B\to K^*\ell^+\ell^-}$ is regarded as one of the attractive mode to look for physics beyond standard model (SM) due to the measurement of large number of observables in experiments. Starting with the most general parametric form of the decay amplitude within SM, two differ- ent analyses have been carried out. First we show how recent LHCb data can be used without any approximations to extract theoretical parameters describing the decay. We find significant discrepancies in the form factor values obtained from experimental data when compared with theoretical expectations in several dilepton invariant mass squared (q 2 ) bins. We emphasize that the discrepancy observed in certain variables cannot arise due to resonances and non-factorizable contributions from charm loops. Secondly, the same model independent framework has been implemented in the maximum q 2 limit to highlight strong evidence of right-handed currents, which are absent in the SM. The conclusions derived are free from hadronic corrections. Our approach differs from other approaches that probe new physics at low q 2 as it does not require estimates of hadronic parameters but relies instead on heavy quark symmetries that are reliable at the maximum q 2 kinematic endpoint.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Development of an MCP-Based Timing Layer for the LHCb ECAL Upgrade-2

The increase in instantaneous luminosity during the high-luminosity phase of the LHC represents a significant challenge for future detectors. A strategy to cope with high-pileup conditions is to add a fourth dimension to the measurements of the hits, by exploiting the time separation of the various proton–proton primary collisions. According to LHCb simulation studies, resolutions of about 10–20 picoseconds, at least an order of magnitude shorter than the average time span between primary interactions, would be greatly beneficial for the physics reach of the experiment. Microchannel plate (MCP) photomultipliers are compact devices capable of measuring the arrival time of charged particles with the required resolution. The technology of large-area picosecond photodetectors (LAPPDs) is under investigation to implement a timing layer that can be placed within a sampling calorimeter module with the purpose of measuring the arrival time of electromagnetic showers. LAPPD performances, using a Gen-I tile with a delay-line anode and a Gen-II with a capacitively coupled anode, have been measured thoroughly both with laser (wavelength of 405 nm and pulse width of 27.5 ps FWHM) and high-energy electron (1–5.8 GeV) beams. Time resolutions of the order of 30 ps for single photoelectrons and 15 ps for electromagnetic showers initiated by 5-GeV electrons, as measured at the shower maximum, are obtained.

47 OTHER INSTRUMENTATION↗
DOE OSTI2017

Resolving the SELEX--LHCb Double-Charm Baryon Conflict: The Impact of Intrinsic Heavy-Quark Hadroproduction and Supersymmetric Light-Front Holographic QCD

In this paper we show that the intrinsic heavy-quark QCD mechanism for the hadroproduction of heavy hadrons at large $x_F$ can resolve the apparent conflict between measurements of double-charm baryons by the SELEX fixed-target experiment and the LHCb experiment at the LHC collider. We show that both experiments are compatible, and that both results can be correct. The observed spectroscopy of double-charm hadrons is in agreement with the predictions of supersymmetric light front holographic QCD.

Brodsky, Stanley↗