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DOE OSTI2016

Observations of Λ b 0 →ΛK +π– and Λ b 0 →ΛK + K – decays and searches for other Λ b 0 and Ξb 0 decays to Λh + h' – final states

A search is performed for the charmless three-body decays of the Λ b 0 and Ξ b 0 baryons to the final states Λh+h' – , where h(') = π or K. The analysis is based on a data sample, corresponding to an integrated luminosity of 3 fb –1 of pp collisions, collected by the LHCb experiment. The Λb 0 → ΛK+π– and Λ b 0 → ΛK+K– decays are observed for the first time and their branching fractions and CP asymmetry parameters are measured. Evidence is seen for the Λ b 0 → Λπ+π– decay and limits are set on the branching fractions of Ξ b 0 baryon decays to the Λh+hh' – final states.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2016

Measurement of forward W and Z boson production in association with jets in proton-proton collisions at $\sqrt{s}=8$ TeV

The production of W and Z bosons in association with jets is studied in the forward region of proton-proton collisions collected at a centre-of-mass energy of 8 TeV by the LHCb experiment, corresponding to an integrated luminosity of 1.98 ± 0.02 fb –1 . The W boson is identified using its decay to a muon and a neutrino, while the Z boson is identified through its decay to a muon pair. Total cross-sections are measured and combined into charge ratios, asymmetries, and ratios of W +jet and Z+jet production cross-sections. Differential measurements are also performed as a function of both boson and jet kinematic variables. All results are in agreement with Standard Model predictions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2016

Observation of Λ$^{0}_{b}$ →ψ(2S)pK– and Λ$^{0}_{b}$ →J/ψπ + π–pK– decays and a measurement of the Λ$^{0}_{b}$ baryon mass

The decays Λ$^{0}_{b}$→ ψ(2S)pK–and Λ$^{0}_{b}$→ J/ψπ+π–pK–are observed in a data sample corresponding to an integrated luminosity of 3 fb –1 , collected in proton-proton collisions at 7 and 8 TeV centre-of-mass energies by the LHCb detector. The ψ(2S) mesons are reconstructed through the decay modes ψ(2S) → μ+μ–and ψ(2S) → J/ψπ+π–. The branching fractions relative to that of Λ$^{0}_{b}$→ J/ψpK–are measured to be $\frac{\mathcal{B}(Λ^{0}_{b}→ψ(2S)pK^{-})}{\mathcal{B}(Λ^{0}_{b}→J/ψpK^{-})}$ = (20.70 ± 0.76 ± 0.46 ± 0.37) x 10 -2 , $\frac{\mathcal{B}(Λ^{0}_{b}→Jψπ+π–pK^{-})}{\mathcal{B}(Λ^{0}_{b}→J/ψpK^{-})}$ = (20.86 ± 0.96 ± 1.34) x 10 -2 , where the first uncertainties are statistical, the second are systematic and the third is related to the knowledge of J/ψ and ψ(2S) branching fractions. The mass of the Λ$^{0}_{b}$ baryon is measured to be M(Λ$^{0}_{b}$)= 5619.65 ± 0.17 ± 0.17 MeV/c 2 , where the uncertainties are statistical and systematic.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Study of the $D^0p$ amplitude in $Λ_b^0$ → $D^0pπ^-$ decays

An amplitude analysis of the decay $Λ_b^0$ → $D^0pπ^-$ is performed in the part of the phase space containing resonances in the $D^0p$ channel. The study is based on a data sample corresponding to an integrated luminosity of 3.0 fb -1 of $pp$ collisions recorded by the LHCb experiment. The spectrum of excited $Λ^+_c$ states that decay into $D^0p$ is studied. The masses, widths and quantum numbers of the $Λ_c$(2880) + and $Λ_c$(2940) + resonances are measured. The constraints on the spin and parity for the $Λ_c$(2940) + state are obtained for the first time. A near-threshold enhancement in the $D^0p$ amplitude is investigated and found to be consistent with a new resonance, denoted the $Λ_c$(2860) + , of spin 3/2 and positive parity.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2019

Detector-size upper bounds on dark hadron lifetime from cosmology

We show that in a confining hidden valley model where the lightest hidden particles are dark hadrons that have mass splittings larger than $ \mathcal{O}(0.1) $ GeV, if the lightest dark hadron is either stable or decays into Standard Model (SM) hadrons/charged leptons during the big-bang nucleosynthesis (BBN), at least one of the heavier dark hadrons needs to decay into SM particles within $ \mathcal{O}(10) $ nanosec. Once being produced at collider experiments, this heavier dark hadron is likely to decay within $ \mathcal{O}(10) $ meter distance, which strengthens the motivation of searching for long-lived particles with sub-meter scale decay lengths at colliders. To illustrate the idea, we study the lifetime constraint in scenarios where the lightest dark particle is a pseudo-scalar meson, and dark hadrons couple to SM particles either through kinetic mixing between the SM and dark photons or by mixing between the SM and dark Higgs. We study the annihilation and decay of dark hadrons in a thermal bath and calculate upper bounds on the lightest vector meson (scalar hadron) lifetime in the kinetic mixing (Higgs portal) scenario. We discuss the application of these lifetime constraints in long-lived particle searches that use the LHCb VELO or the AT-LAS/CMS inner detectors.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2020

Test of lepton universality with $ {\Lambda}_b^0\to {pK}^{-}{\mathrm{\ell}}^{+}{\mathrm{\ell}}^{-}$ decays

The ratio of branching fractions of the decays $ {\Lambda}_b^0 $ → pK - e + e - and $ {\Lambda}_b^0 $ → pK - μ + μ - , $ {R}_{pK}^{-1} $ , is measured for the first time using proton-proton collision data corresponding to an integrated luminosity of 4 . 7 fb - 1 recorded with the LHCb experiment at center-of-mass energies of 7, 8 and 13 TeV. In the dilepton mass-squared range 0 . 1 < q 2 < 6 . 0 GeV 2 /c 4 and the pK - mass range m ( pK - ) < 2600 MeV /c 2 , the ratio of branching fractions is measured to be $ {R}_{pK}^{-1}={1.17}_{-0.16}^{+0.18}\pm 0.07 $ , where the first uncertainty is statistical and the second systematic. This is the first test of lepton universality with b baryons and the first observation of the decay $ {\Lambda}_b^0 $ → pK - e + e - .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2021

Measurement of the D → K - π + π + π- and D → K - π + π 0 coherence factors and average strong-phase differences in quantum-correlated $ D\overline{D} $ decays

The decays D → K - π + π + π - and D → K - π + π 0 are studied in a sample of quantum-correlated $ D\overline{D} $ pairs produced through the process e + e - → ψ (3770) → $ D\overline{D} $ , exploiting a data set collected by the BESIII experiment that corresponds to an integrated luminosity of 2.93 fb - 1 . Here D indicates a quantum superposition of a D 0 and a $ {\overline{D}}^0 $ meson. By reconstructing one neutral charm meson in a signal decay, and the other in the same or a different final state, observables are measured that contain information on the coherence factors and average strong-phase differences of each of the signal modes. These parameters are critical inputs in the measurement of the angle γ of the Unitarity Triangle in B - → DK - decays at the LHCb and Belle II experiments. The coherence factors are determined to be R K 3 π = $ {0.52}_{-0.10}^{+0.12} $ and $ {R}_{K{\pi \pi}^0} $ = 0 . 78 ± 0 . 04, with values for the average strong-phase differences that are $ {\delta}_D^{K3\pi }=\left({167}_{-19}^{+31}\right){}^{\circ} $ and $ {\delta}_D^{K{\pi \pi}^0}=\left({196}_{-15}^{+14}\right){}^{\circ} $ , where the uncertainties include both statistical and systematic contributions. The analysis is re-performed in four bins of the phase-space of the D → K - π + π + π - to yield results that will allow for a more sensitive measurement of γ with this mode, to which the BESIII inputs will contribute an uncertainty of around 6°.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2022

Observation of the doubly charmed baryon decay $Ξ_{cc}^{++}$ →$Ξ_c^{'+}π^+$

The $Ξ_{cc}^{++}$ →$Ξ_c^{'+}π^+$ decay is observed using proton-proton collisions collected by the LHCb experiment at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.4 fb –1 . The $Ξ_{cc}^{++}$ →$Ξ_c^{'+}π^+$ decay is reconstructed partially, where the photon from the $Ξ_c^{'+}$ →$Ξ^+_cγ$ decay is not reconstructed and the $ρK^-π^+$ final state of the $Ξ^+_c$ baryon is employed. The $Ξ_{cc}^{++}$ →$Ξ_c^{'+}π^+$ branching fraction relative to that of the $Ξ_{cc}^{++}$ →$Ξ_c^+π^+$ decay is measured to be 1.41 ± 0.17 ± 0.10, where the first uncertainty is statistical and the second systematic.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2022

Search for the decay $B^0$ → $\phiμ^+μ^–$

A search for the decay $B^0$ → $\phiμ^+μ^–$ is performed using proton-proton collisions at centre-of-mass energies of 7, 8, and 13 TeV collected by the LHCb experiment and corresponding to an integrated luminosity of 9 fb –1 . No evidence for the $B^0$ → $\phiμ^+μ^–$ decay is found and an upper limit on the branching fraction, excluding the $\phi$ and charmonium regions in the dimuon spectrum, of 4.4 × 10 –3 at a 90% credibility level, relative to that of the $B^0_s$ → $\phiμ^+μ^–$ branching fraction and assuming a phase-space model, the absolute branching fraction of the $B^0$ → $\phiμ^+μ^–$ in the full q 2 range is determined to be less than 3.2 x 10 –9 at a 90% credibility level.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2024

Measurements of the branching fraction ratio $$ \mathcal{B}\left(\phi \to {\mu}^{+}{\mu}^{-}\right)/\mathcal{B}\left(\phi \to {\textrm{e}}^{+}{\textrm{e}}^{-}\right) $$ with charm meson decays

Abstract Measurements of the branching fraction ratio$$ \mathcal{B}\left(\phi \to {\mu}^{+}{\mu}^{-}\right)/\mathcal{B}\left(\phi \to {e}^{+}{e}^{-}\right) $$ B ϕ → μ + μ − / B ϕ → e + e − with$$ {D}_s^{+}\to {\pi}^{+}\phi $$ D s + → π + ϕ andD + → π + ϕdecays, denoted$$ {R}_{\phi \pi}^s $$ R ϕπ s and$$ {R}_{\phi \pi}^d $$ R ϕπ d , are presented. The analysis is performed using a dataset corresponding to an integrated luminosity of 5.4 fb −1 ofppcollision data collected with the LHCb experiment. The branching fractions are normalised with respect to theB + →K + J/ψ(→e + e − ) andB + →K + J/ψ(→μ + μ − ) decay modes. The combination of the results yields$$ {R}_{\phi \pi}=1.022\pm 0.012\left(\textrm{stat}\right)\pm 0.048\left(\textrm{syst}\right). $$ R ϕπ = 1.022 ± 0.012 stat ± 0.048 syst . The result is compatible with previous measurements of theϕ→ℓ + ℓ − branching fractions and predictions based on the Standard Model.

Physics↗

DOE OSTI2016

Model-independent measurement of the CKM angle γ using B 0 → DK* 0 decays with D→K S 0 π + π – and K S 0 K + K –

A binned Dalitz plot analysis of the decays B 0 → DK* 0 , with D → K S 0 π + π – and D → K S 0 K + K – , is performed to measure the observables x ± and y ± , which are related to the CKM angle γ and the hadronic parameters of the decays. The D decay strong phase variation over the Dalitz plot is taken from measurements performed at the CLEO-c experiment, making the analysis independent of the D decay model. With a sample of proton-proton collision data, corresponding to an integrated luminosity of 3.0 fb –1 , collected by the LHCb experiment, the values of the CP violation parameters are found to be x + = 0.05 ± 0.35 ± 0.02, x – = –0.31 ± 0.20 ± 0.04, y + = –0.81 ± 0.28 ± 0.06 and y – = 0.31 ± 0.21 ± 0.05, where the first uncertainties are statistical and the second systematic. These observables correspond to values γ = (71 ± 20)°, $r_{B^{0}}$= 0.56 ± 0.17 and δ$_{B^{0}}$ = ($204^{+21}_{–20}$)°. The parameters $r_{B^{0}}$ and δ$_{B^{0}}$ are the magnitude ratio and strong phase difference between the suppressed and favoured B 0 decay amplitudes, and have been measured in a region of ±50 MeV/c 2 around the K*(892) 0 mass and with the magnitude of the cosine of the K*(892) 0 helicity angle larger than 0.4.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Measurement of the $J/ψ$ pair production cross-section in pp collisions at $\sqrt{s}=13$ TeV

The production cross-section of $J/ψ$ pairs is measured using a data sample of pp collisions collected by the LHCb experiment at a centre-of-mass energy of $\sqrt{s}=13$ TeV, corresponding to an integrated luminosity of 279 ±11 pb -1 . The measurement is performed for $J/ψ$ mesons with a transverse momentum of less than 10 GeV/$c$ in the rapidity range 2.0 < $y$ < 4.5. The production cross-section is measured to be 15.2 ± 1.0 ± 0.9 nb. The first uncertainty is statistical, and the second is systematic. The differential cross-sections as functions of several kinematic variables of the $J/ψ$ pair are measured and compared to theoretical predictions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Observation of the decay $Λ^0_b$ → $pK$ - $μ$ + $μ$ - and a search for $CP$ violation

A search for $CP$ violation in the decay $Λ^0_b$ → $pK$ - $μ$ + $μ$ - is presented. This decay is mediated by flavour-changing neutral-current transitions in the Standard Model and is potentially sensitive to new sources of CP violation. The study is based on a data sample of proton-proton collisions recorded with the LHCb experiment, corresponding to an integrated luminosity of 3 fb -1 . The $Λ^0_b$ → $pK$ - $μ$ + $μ$ - decay is observed for the first time, and two observables that are sensitive to different manifestations of $CP$ violation are measured, $ΔΑ$ CP $\equiv$ $ΔΑ$ CP ($Λ^0_b$ → $pK$ - $μ$ + $μ$ - ) - $ΔΑ$ CP ($Λ^0_b$ → $pK$ - $J/Ψ$) and a C P T ^ - o d d , where the latter is based on asymmetries in the angle between the $μ$ + $μ$ - and $pK$ - decay planes. These are measured to be Δ A C P = ( − 3.5 ± 5.0 ( s t a t ) ± 0.2 ( s y s t ) ) × 10 − 2 , a C P T ^ - o d d = ( 1.2 ± 5.0 ( s t a t ) ± 0.7 ( s y s t ) ) × 10 − 2 , and no evidence for $CP$ violation is found

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2018

A light Higgs at the LHC and the B-anomalies

After the Higgs discovery, the LHC has been looking for new resonances, decaying into pairs of Standard Model (SM) particles. Recently, the CMS experimen observed an excess in the di-photon channel, with a di-photon invariant mass of about 96 GeV. This mass range is similar to the one of an excess observed in the search for the associated production of Higgs bosons with the Z neutral gauge boson at LEP, with the Higgs bosons decaying to bottom quark pairs. On the other hand, the LHCb experiment observed a discrepancy with respect to the SM expectations of the ratio of the decay of B -mesons to K -mesons and a pair of leptons, $ {R}_{K^{\left(\ast \right)}}=BR\left(B\to {K}^{\left(\ast \right)}{\mu}^{+}{\mu}^{-}\right)/BR\left(B\to {K}^{\left(\ast \right)}{e}^{+}{e}^{-}\right) $ . This observation provides a hint of the violation of lepton-flavor universality in the charged lepton sector and may be explained by the existence of a vector boson originating form a $ U{(1)_{L_{\mu}}}_{-{L}_{{}_{\tau }}} $ symmetry and heavy quarks that mix with the left-handed down quarks. Since the coupling to heavy quarks could lead to sizable Higgs di-photon rates in the gluon fusion channel, in this article we propose a common origin of these anomalies identifying a Higgs associated with the breakdown of the $ U{(1)_{L_{\mu}}}_{-{L}_{{}_{\tau }}} $ symmetry and at the same time responsible to the quark mixing, with the one observed at the LHC. We also discuss the constraints on the identification of the same Higgs with the one associated with the bottom quark pair excess observed at LEP.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2020

Far-forward neutrinos at the Large Hadron Collider

We present a new calculation of the energy distribution of high-energy neutrinos from the decay of charm and bottom hadrons produced at the Large Hadron Collider (LHC). In the kinematical region of very forward rapidities, heavy-flavor production and decay is a source of tau neutrinos that leads to thousands of charged-current tau neutrino events in a 1 m long, 1 m radius lead neutrino detector at a distance of 480 m from the interaction region. In our computation, next-to-leading order QCD radiative corrections are accounted for in the production cross-sections. Non-perturbative intrinsic-kT effects are approximated by a simple phenomenological model introducing a Gaussian kT-smearing of the parton distribution functions, which might also mimic perturbative effects due to multiple initial-state soft-gluon emissions. The transition from partonic to hadronic states is described by phenomenological fragmentation functions. To study the effect of various input parameters, theoretical predictions for D± s production are compared with LHCb data on double-differential cross-sections in transverse momentum and rapidity. The uncertainties related to the choice of the input parameter values, ultimately affecting the predictions of the tau neutrino event distributions, are discussed. We consider a 3+1 neutrino mixing scenario to illustrate the potential for a neutrino experiment to constrain the 3+1 parameter space using tau neutrinos and antineutrinos. We find large theoretical uncertainties in the predictions of the neutrino fluxes in the far-forward region. Untangling the effects of tau neutrino oscillations into sterile neutrinos and distinguishing a 3+1 scenario from the standard scenario with three active neutrino flavours, will be challenging due to the large theoretical uncertainties from QCD.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2020

Measurement of the ${\Lambda}_b^0$→ J/ψΛ angular distribution and the ${\Lambda}_b^0$ polarisation in pp collisions

This paper presents an analysis of the $ {\Lambda}_b^0 $ → J/ψ Λ angular distribution and the transverse production polarisation of $ {\Lambda}_b^0 $ baryons in proton-proton collisions at centre-of-mass energies of 7, 8 and 13 TeV. The measurements are performed using data corresponding to an integrated luminosity of 4.9 fb – 1 , collected with the LHCb experiment. The polarisation is determined in a fiducial region of $ {\Lambda}_b^0 $ transverse momentum and pseudorapidity of 1 < p T < 20 GeV/ c and 2 < η < 5, respectively. The data are consistent with $ {\Lambda}_b^0 $ baryons being produced unpolarised in this region. The parity-violating asymmetry parameter of the Λ → pπ – decay is also determined from the data and its value is found to be consistent with a recent measurement by the BES III collaboration.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2020

Observation of a new baryon state in the $Λ^0_bπ^+π^-$ mass spectrum

A new baryon state is observed in the $Λ^0_bπ^+π^-$ mass spectrum with high significance using a data sample of pp collisions, collected with the LHCb detector at centre-of-mass energies $\sqrt{s}$ = 7, 8 and 13 TeV, corresponding to an integrated luminosity of 9 fb -1 . The mass and natural width of the new state are measured to be m = 6072.3 ± 2.9 ± 0.6 ± 0.2 MeV , Γ = 72 ± 11 ± 2 MeV , where the first uncertainty is statistical and the second systematic. The third uncertainty for the mass is due to imprecise knowledge of the $Λ^0_b$ baryon mass. The new state is consistent with the first radial excitation of the $Λ^0_b$ baryon, the Λ b (2S) 0 resonance. Updated measurements of the masses and the upper limits on the natural widths of the previously observed Λ b (5912) 0 and Λ b (5920) 0 states are also reported.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2021

Search for CP violation in $D^{+}_{(s)}\to h^{+} \pi^{0}$ and $D^{+}_{(s)}\to h^{+}\eta$ decays

Searches for CP violation in the two-body decays $D^{+}_{(s)}\to h^{+} \pi^{0}$ and $D^{+}_{(s)}\to h^{+}\eta$ (where h + denotes a π + or K + meson) are performed using pp collision data collected by the LHCb experiment corresponding to either 9 fb –1 or 6 fb –1 of integrated luminosity. The π 0 and η mesons are reconstructed using the e + e – γ final state, which can proceed as three-body decays π 0 → e + e – γ and η → e + e – γ, or via the two-body decays π 0 → γγ and η → γγ followed by a photon conversion. The measurements are made relative to the control modes $D^{+}_{(s)}\to K^{0}_{S}h^{+}$ to cancel the production and detection asymmetries. The CP asymmetries are measured to be A CP (D + →π + π 0 )=(–1.3±0.9±0.6)%, A CP (D + →K + π 0 )=(–3.2±4.7±2.1)%, A CP (D + →π + η)=(–0.2±0.8±0.4)%, A CP (D + →K + η)=(–6±10±4)%, A CP (D$^{+}_{s}$→K + π 0 )=(–0.8±3.9±1.2)%, A CP (D$^{+}_{s}$→π + η)=(0.8±0.7±0.5)%, A CP (D$^{+}_{s}$→K + η)=(0.9±3.7±1.1)%, where the first uncertainties are statistical and the second systematic. These results are consistent with no CP violation and mostly constitute the most precise measurements of A CP in these decay modes to date.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗