Measurement of the branching fraction and C P asymmetry for B → D ¯ 0 π decays
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72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
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Strange hadron production in Au + Au collisions at s N N = 7.7 , 11.5, 19.6, 27, and 39 GeV
In this paper, we present STAR measurements of strange hadron (K$0\atop{s}$, Λ, $\bar{Λ}$, $Ξ$ - , $\bar{Ξ}$ + , Ω - , $\bar{Ω}$ + , and Φ ) production at mid-rapidity (|y|<0.5) in Au+Au collisions at √s NN = 7.7 – 39 GeV from the Beam Energy Scan Program at the Relativistic Heavy Ion Collider (RHIC). Transverse momentum spectra, averaged transverse mass, and the overall integrated yields of these strange hadrons are presented versus the centrality and collision energy. Antibaryon-to-baryon ratios(Λ/$\bar{Λ}$, $Ξ$ - / $\bar{Ξ}$ + , Ω - / $\bar{Ω}$ + ) are presented as well, and used to test a thermal statistical model and to extract the temperature normalized strangeness and baryon chemical potentials at hadronic freeze-out (μ B / T ch μ S / T ch ) in central collisions. Strange baryon-to-pion ratios are compared to various model predictions in central collisions for all energies. The nuclear modification factors (R CP ) and antibaryon-to-meson ratios as a function of transverse momentum are presented for all collision energies. The K$0\atop{s}$ R CP shows no suppression for p T up to 3.5 GeV/c at energies of 7.7 and 11.5 GeV. The $\bar{Λ}$/ K$0\atop{s}$ ratio also shows baryon-to-meson enhancement at intermediate p T (~2.5 GeV/c) in central collisions at energies above 19.6 GeV. In conclusion, both observations suggest that there is likely a change of the underlying strange quark dynamics at collision energies below 19.6 GeV.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Semitauonic b-hadron decays: A lepton flavor universality laboratory
The study of lepton flavor universality violation (LFUV) in semitauonic b-hadron decays has become increasingly important in light of long-standing anomalies in their measured branching fractions, and the large datasets anticipated from the LHC experiments and Belle II. Here, in this review, a comprehensive survey of the experimental environments and methodologies for semitauonic LFUV measurements at the B factories and LHCb is undertaken, along with an overview of the theoretical foundations and predictions for a wide range of semileptonic decay observables. The future prospects of controlling systematic uncertainties down to the percent level, matching the precision of standard model (SM) predictions, are examined. Furthermore, new perspectives and caveats on combinations of the LFUV data are discussed and the world averages for the R(D(*)) ratios are revisited. Here it is demonstrated that different treatments for the correlations of uncertainties from D** excited states can vary the current 3σ tension with the SM within a 1σ range. Prior experimental overestimates of D**τν contributions may further exacerbate this. The precision of future measurements is also estimated; their power to exploit full differential information, and solutions to the inherent difficulties in self-consistent new physics interpretations of LFUV observables, are explored.
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Color transparency and the proton form factor: Evidence for the Feynman mechanism
A recent experiment by D. Bhetuwal et al. [Phys. Rev. Lett. 126, 082301 (2021)] used the (e,e'p) reaction on 12 C to search for the effects of color transparency (the absence of final-state interactions). Color transparency was said to be ruled out. Observing the effects of color transparency depends on the ability of a putative point-like-configuration (PLC), formed in a high-momentum transfer coherent reaction, to escape the nucleus without expanding its size. Here, we study the expansion aspect of color transparency using superconformal baryon-meson symmetry and light-front holographic QCD. A new formalism is obtained and used to analyze the recent experiment. The resulting conclusion is that effects of expansion would not be sufficiently significant in causing final-state interactions to occur. Therefore, we conclude that a PLC was not formed. In conclusion, this means that the Feynman mechanism involving virtual photon absorption on a single high-momentum quark is responsible for the high-momentum electromagnetic form factor of the proton.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Measurements of dielectron production in Au + Au collisions at s N N = 27 , 39, and 62.4 GeV from the STAR experiment
We report systematic measurements of dielectron (e + e – ) invariant-mass M ee spectra at midrapidity in Au + Au collisions at s N N = 27 = 27, 39, and 62.4 GeV taken with the STAR detector at the Relativistic Heavy Ion Collider. For all energies studied, a significant excess yield of dielectrons is observed in the low-mass region ( 0.40 < M ee < 0.75 MeV / c 2 ) compared to hadronic cocktail simulations at freeze-out. Models that include an in-medium broadening of the ρ -meson spectral function consistently describe the observed excess. In addition, we report acceptance-corrected dielectron-excess spectra for Au + Au collisions at midrapidity ( |y ee | < 1) in the 0–80% centrality bin for each collision energy. The integrated excess yields for 0.4 < M ee < 0.75 GeV / c 2 , normalized by the charged particle multiplicity at midrapidity, are compared with previously published measurements for Au + Au at s N N = 27 = 19.6 and 200 GeV. Models that include an in-medium broadening of the ρ -meson spectral function consistently describe the observed excess. Furthermore, the normalized excess yields in the low-mass region show no significant collision energy dependence. The data, however, are consistent with model calculations that demonstrate a modest energy dependence.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Observation of the ϒ ( 3 S ) Meson and Suppression of ϒ States in Pb-Pb Collisions at s N N = 5.02 TeV
The production of ϒ ( 2 S ) and ϒ ( 3 S ) mesons in lead-lead (Pb-Pb) and proton-proton ( p p ) collisions is studied in their dimuon decay channel using the CMS detector at the LHC. The ϒ ( 3 S ) meson is observed for the first time in Pb-Pb collisions, with a significance above 5 standard deviations. The ratios of yields measured in Pb-Pb and p p collisions are reported for both the ϒ ( 2 S ) and ϒ ( 3 S ) mesons, as functions of transverse momentum and Pb-Pb collision centrality. These ratios, when appropriately scaled, are significantly less than unity, indicating a suppression of ϒ yields in Pb-Pb collisions. This suppression increases from peripheral to central Pb-Pb collisions. Furthermore, the suppression is stronger for ϒ ( 3 S ) mesons compared to ϒ ( 2 S ) mesons, extending the pattern of sequential suppression of quarkonium states in nuclear collisions previously seen for the J / ψ , ψ ( 2 S ) , ϒ ( 1 S ) , and ϒ ( 2 S ) mesons. © 2024 CERN, for the CMS Collaboration 2024 CERN
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First measurement of coherent ρ 0 photoproduction in ultra-peripheral Xe–Xe collisions at s NN = 5.44 TeV
The first measurement of the coherent photoproduction of ρ 0 vector mesons in ultra-peripheral Xe–Xe collisions at s NN = 5.44 TeV is presented. This result, together with previous HERA γ p data and γ –Pb measurements from ALICE, describes the atomic number ( A ) dependence of this process, which is particularly sensitive to nuclear shadowing effects and to the approach to the black-disc limit of QCD at a semi-hard scale. The cross section of the Xe + Xe → ρ 0 + Xe + Xe process, measured at midrapidity through the decay channel ρ 0 → π + π – , is found to be d σ / d y = 131.5 ± 5.6 ( stat . ) – 16.9 + 17.5 ( syst . ) mb. The ratio of the continuum to resonant contributions for the production of pion pairs is also measured. In addition, the fraction of events accompanied by electromagnetic dissociation of either one or both colliding nuclei is reported. The dependence on A of cross section for the coherent ρ 0 photoproduction at a centre-of-mass energy per nucleon of the γA system of W γ A , n = 65 GeV is found to be consistent with a power-law behaviour σ ( γ A → ρ 0 A ) ∝ A α with a slope α = 0.96 ± 0.02 ( syst . ) . This slope signals important shadowing effects, but it is still far from the behaviour expected in the black-disc limit.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Chiral anomaly: From vacuum to Columbia plot
Here, we use a low-energy effective approach, the extended linear sigma model, to study realizations of the U(1) A anomaly with different operators, linear and quadratic in the ’t Hooft determinant. After discussing the parameterization in agreement with vacuum’s phenomenology, we investigate the influence of these different anomaly terms on the Columbia plot: the square of the ’t Hooft determinant favors a cross-over for small quark masses. Finally, we also discuss the extension of the ’t Hooft determinant to cases in which different mesonic multiplets interact with each other. Novel chiral anomalous interaction terms involving excited (pseudo)scalar states, pseudovector, and pseudotensor mesons are expressed via a mathematical extension of the determinant, denoted as a polydeterminant.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Exclusive photoproduction of excited ρ mesons decaying to four pions in ultraperipheral Pb–Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV
The intense photon fluxes from relativistic nuclei provide an opportunity to study photonuclear interactions in ultraperipheral collisions. In particular, it allows for the investigations of excited, light-flavour vector mesons. The measurement of coherently photoproduced 𝜋⁺𝜋 − 𝜋⁺𝜋 − final states in ultraperipheral Pb–Pb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV is presented for the first time. The cross section, d𝜎/d𝑦, times the branching ratio (𝜌 → 𝜋⁺𝜋⁺𝜋 − 𝜋 − ) is found to be 47.8 ± 2.3 (stat.) ± 7.7 (syst.) mb in the rapidity interval |𝑦| < 0.5. The invariant mass distribution is not well described with a single Breit-Wigner resonance without an interference term. Including in- terference with a non-resonant contribution results in the mass and width values being too far from those reported in PDG, while the production of two interfering resonances, 𝜌(1450) and 𝜌(1700), also provides a good description of the data. The values of the masses (𝑚) and widths (Γ) of the resonances extracted from the fit assuming two interfering resonances are 𝑚₁ = 1385 ± 14 (stat.) ± 3 (syst.) MeV/𝑐², Γ₁ = 431 ± 36 (stat.) ± 82 (syst.) MeV/𝑐², 𝑚₂ = 1663 ± 13 (stat.) ± 22 (syst.) MeV/𝑐² and Γ₂ = 357 ± 31 (stat.) ± 49 (syst.) MeV/𝑐², respectively. The measured cross sections times the branching ratios are compared to recent theoretical predictions.
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Transverse single-spin asymmetry of forward 𝜂 mesons in 𝑝 ↑ +𝑝 collisions at √𝑠 =200 GeV
Utilizing the 2012 transversely polarized proton data from the Relativistic Heavy Ion Collider at Brookhaven National Laboratory, the forward 𝜂-meson transverse single-spin asymmetry (𝐴 𝑁 ) was measured for 𝑝 ↑ +𝑝 collisions at √𝑠 =200 GeV as a function of Feynman-x (𝑥 𝐹 ) for 0.2 <|𝑥 𝐹 | <0.8 and transverse momentum (𝑝 𝑇 ) for 1.0 <𝑝 𝑇 <5.0 GeV/𝑐. Large asymmetries at positive 𝑥 𝐹 are observed (⟨𝐴 𝑁 ⟩=0.086±0.019), agreeing well with previous measurements of 𝜋 0 and 𝜂𝐴 𝑁 , but with reach to higher 𝑥 𝐹 and 𝑝 𝑇 . The contribution of initial-state spin-momentum correlations to the asymmetry, as calculated in the collinear twist-3 framework, appears insufficient to describe the data.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
First measurement of the $Λ–Ξ$ interaction in proton–proton collisions at the LHC
The first experimental information on the strong interaction between $Λ$ and $Ξ$ - strange baryons is presented in this Letter. The correlation function of $Λ–Ξ$ - and $\overline{Λ}$ –$\overline{Ξ}$ + pairs produced in high-multiplicity proton–proton (pp) collisions at $\sqrt{s}$=13 TeV at the LHC is measured as a function of the relative momentum of the pair. The femtoscopy method is used to calculate the correlation function, which is then compared with theoretical expectations obtained using a meson exchange model, chiral effective field theory, and Lattice QCD calculations close to the physical point. Data support predictions of small scattering parameters while discarding versions with large ones, thus suggesting a weak $Λ–Ξ$ - interaction. The limited statistical significance of the data does not yet allow one to constrain the effects of coupled channels like $Σ–Ξ$ and $N–Ω$.
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Charmonium production in $p$Ne collisions at $\sqrt{s_{\scriptscriptstyle \text {NN}}} =68.5$ GeV
The measurement of charmonium states produced in proton-neon (pNe) collisions by the LHCb experiment in its fixed-target configuration is presented. The pro duction of J/ψ and ψ(2S) mesons is studied with a beam of 2.5 TeV protons colliding on gaseous neon targets at rest, corresponding to a nucleon-nucleon centre-of-mass energy $\sqrt{s_{NN}}$ = 68.5 GeV. The data sample corresponds to an integrated luminosity of 21.7 ± 1.4 nb -1 . The J/ψ and ψ(2S) hadrons are reconstructed in μ + μ - final states. The J/ψ production cross-section per target nucleon in the centre-of mass rapidity range y* ϵ [-2.29, 0] is found to be 506 ± 8 ± 46 nb/nucleon. The ratio of J/ψ and D 0 cross-sections is evaluated to (1.06 ± 0.02 ± 0.09)%. The ψ(2S) to J/ψ relative production rate is found to be (1.67 ± 0.27 ± 0.10)% in good agreement with other measurements involving beam and target nuclei of similar sizes.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Measurement of C P Violation in the Decay B + → K + π 0
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73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Branching Fraction Measurements of the Rare B s 0 → ϕ μ + μ − and B s 0 → f 2 ′ ( 1525 ) μ + μ − Decays
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72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Measurement of Differential Branching Fractions of Inclusive B → X u ℓ + ν ℓ Decays
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46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
Neutron detection and application with a novel 3D-projection scintillator tracker in the future long-baseline neutrino oscillation experiments
Neutrino oscillation experiments require a precise measurement of the neutrino energy. However, the kinematic detection of the final-state neutron in the neutrino interaction is missing in current neutrino oscillation experiments. The missing neutron kinematic detection results in a smaller detected neutrino energy than the true neutrino energy. A novel 3D-projection scintillator tracker, which consists of roughly ten million active cubes covered with an optical reflector, is capable of measuring the neutron kinetic energy and direction on an event-by-event basis using the time-of-flight technique thanks to the fast timing, fine granularity, and high light yield. The $\overline{v}$ μ interactions tend to produce neutrons in the final state. By measuring the neutron kinetic energy, the $\overline{v}$ μ energy can be reconstructed better, allowing a tighter incoming neutrino flux constraint. This article shows the detector's ability to reconstruct neutron kinetic energy and the $\overline{v}$ μ flux constraint achieved by selecting the charged-current interactions without mesons or protons in the final state.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Probing lepton flavor violation in meson decays with LHC data
Abstract In this letter, we use LHC data from the Drell–Yan processes $$pp\rightarrow \ell _i\ell _j$$ p p → ℓ i ℓ j (with $$i\ne j$$ i ≠ j ) to derive model-independent upper limits on lepton-flavor-violating meson decays. Our analysis is based on an Effective Field Theory (EFT) approach and it does not require a specific assumption regarding the basis of effective operators. We find that current LHC data (140 $$\textrm{fb}^{-1}$$ fb - 1 ) already provides competitive limits on $${\mathcal {B}}(B\rightarrow \pi e \tau )$$ B ( B → π e τ ) and $${\mathcal {B}}(B\rightarrow \pi \mu \tau )$$ B ( B → π μ τ ) with respect to the ones obtained through experimental searches at the B -factories. Moreover, we derive upper limits on several decays that have not been searched for experimentally yet, such as $$D^0\rightarrow e\tau $$ D 0 → e τ in the charm sector, and various semileptonic decays such as $$B\rightarrow \rho \mu \tau $$ B → ρ μ τ , $$B_s\rightarrow K \mu \tau $$ B s → K μ τ and $$B_s\rightarrow \phi \mu \tau $$ B s → ϕ μ τ . Lastly, we discuss the validity of the EFT description of LHC data and the impact of loop corrections in our analysis.
Descotes-Genon, S.↗
Measurements of the azimuthal anisotropy of prompt and nonprompt charmonia in PbPb collisions at $\sqrt{s_{\textrm{NN}}} $= 5.02 TeV
The second-order (v 2 ) and third-order (v 3 ) Fourier coefficients describing the azimuthal anisotropy of prompt and nonprompt (from b-hadron decays) J/ψ, as well as prompt ψ(2S) mesons are measured in lead-lead collisions at a center-of-mass energy per nucleon pair of $\sqrt {^{S}NN}$ = 5.02 TeV. The analysis uses a data set corresponding to an integrated luminosity of 1.61 nb –1 recorded with the CMS detector. The J/ψ and ψ(2S) mesons are reconstructed using their dimuon decay channel. The v 2 and v 3 coefficients are extracted using the scalar product method and studied as functions of meson transverse momentum and collision centrality. The measured v 2 values for prompt J/ψ mesons are found to be larger than those for nonprompt J/ψ mesons. The prompt J/ψ v 2 values at high p T are found to be underpredicted by a model incorporating only parton energy loss effects in a quark-gluon plasma medium. Prompt and nonprompt J/ψ meson v 3 and prompt ψ(2S) v 2 and v 3 values are also reported for the first time, providing new information about heavy quark interactions in the hot and dense medium created in heavy ion collisions.
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