121 Search Results

Chirality is a distinct signature that characterizes triaxial shapes in nuclei. We report the first observation of chirality in the nucleus ¹³⁵Pr using a high-statistics Gammasphere experiment with the ¹²³Sb(¹⁶O, 4n) ¹³⁵Pr reaction. Two chiral-partner bands with the configuration π(1h11/2 )1 ⊗ ν(1h_11/2)⁻² have been identified in this nucleus. Angular distribution analyses of the ΔI = 1 transitions connecting the two bands reveal a dominant dipole character, and quasiparticle triaxial rotor model calculations show good agreement with the data. Since the simultaneous observation of chirality and transverse wobbling in ¹³⁵Pr relies critically on these angular distribution results, we also addressmore » and refute the experimental and theoretical criticisms raised in a recent work by Lv et al., presenting additional evidence that further strengthens our interpretation. Furthermore, this marks the first observation of both hallmarks of triaxiality—chirality and wobbling—in the same nucleus.« less

The transverse momentum spectra and integrated yields of anti-$$Σ$$ hyperons ($$\overline{\Sigma}^{\pm}$$) have been measured in and collisions at $$\sqrt{s_{\textrm{NN}}} = 5.02$$ TeV with the ALICE experiment. Measurements are performed via the newly accessed decay channel $$\overline{\Sigma}^{\pm}$$ → $$\bar{\textrm{n}}π^±$$. A new method of antineutron reconstruction with the PHOS electromagnetic spectrometer is developed and applied to this analysis. The p_T spectra of $$\overline{\Sigma}^{\pm}$$ are measured in the range 0.5 < p_T < 3 GeV/c and compared to predictions of the PYTHIA 8, DPMJET, PHOJET, EPOS LHC and EPOS4 models. The EPOS LHC and EPOS4 models provide the best descriptions of the measuredmore » spectra both in pp and p-Pb collisions, while models which do not account for multiparton interactions provide a considerably worse description at high p_T. The total yields of $$\overline{\Sigma }^{\pm }$$ in both pp and p-Pb collisions are compared to predictions of the Thermal-FIST model and dynamical models PYTHIA 8, DPMJET, PHOJET, EPOS LHC and EPOS4. All models reproduce the total yields in both colliding systems within uncertainties. The nuclear modification factors R_pPb for both $$\overline{\Sigma}^{+}$$ and $$\overline{\Sigma}^{-}$$ are evaluated and compared to those of protons, $$Λ$$ and $$Ξ$$ hyperons, and predictions of EPOS LHC and EPOS4 models. No deviations of R_pPb for $$\overline{\Sigma}^{\pm}$$ from the model predictions or measurements for other hadrons are found within uncertainties.« less

The first results of K*(892)^± production at midrapidity (|y| < 0.5) in pp collisions at $$\sqrt{s}$$= 13 TeV as a function of the event multiplicity are presented. The K*(892)^± has been reconstructed via its hadronic decay channel K*(892)^± → π^± + K$$^0_{\textrm{S}}$$ using the ALICE detector at the LHC. For each multiplicity class, the differential transverse momentum (p_T) spectrum, the mean transverse momentum ⟨p_T⟩, the p_T-integrated yield (dN/dy), and the ratio of the K*(892)^± to K$$^0_{\textrm{S}}$$ yields are reported. These are consistent with previous K*(892)⁰ resonance results with a higher level of precision. Comparisons with phenomenological models such as PYTHIA6,more » PYTHIA8, EPOS-LHC, and DIPSY are also discussed. For the first time, a significant K*(892)^±/K$$^0_{\textrm{S}}$$ suppression in pp collisions is observed at a 7σ level passing from low to high multiplicity events. The ratios of the p_T-differential yields of K*(892)^± and K$$^0_{\textrm{S}}$$ in high and low multiplicity events are also presented along with their double ratio. For p_T ≲ 2 GeV/c this double ratio persists below unity by more than 3σ suggesting that the suppression affects mainly low p_T resonances. The measured decreasing trend of the K*(892)^±/K$$^0_{\textrm{S}}$$ ratio with increasing multiplicity, which in heavy-ion collisions is typically attributed to the rescattering of decay particles of the short-lived resonances, is reproduced by the EPOS-LHC model without the use of hadronic afterburners.« less

In this letter, the first measurement of the femtoscopic correlation of protons and $Σ^+$ hyperons is presented and used to study the p–$Σ^+$ interaction. The measurement is performed with the ALICE detector in high-multiplicity triggered pp collisions at $$\sqrt{s}$$ = 13 TeV. The $Σ^+$ hyperons are reconstructed using a missing-mass approach in the decay channel to p + π⁰ with π⁰ → $γγ$, while both $Σ^+$ and protons are identified using a machine learning approach. These techniques result in a high reconstruction efficiency and purity, which allows the measurement of the p–$Σ^+$ correlation function for the first time. Thanks tomore » the high significance achieved in the p–$Σ^+$ correlation signal, it is possible to discriminate between the predictions of different models of the N–$$Σ$$ interaction and to accomplish a first determination of the p–$Σ^+$ scattering parameters.« less

Meson-baryon systems with strangeness content provide a unique laboratory for investigating the strong interaction and testing theoretical models of hadron structure and dynamics. In this work, the measured correlation functions for oppositely charged $$Ξ$$-K and $$Ξ$$ − 𝜋 pairs obtained in high-multiplicity pp collisions at $$\sqrt{𝑠}$$ = 13 TeV at the LHC are presented. For the first time, high-precision data on the $$Ξ$$-K interaction are delivered at small relative momenta. The scattering lengths, extracted via the Lednický–Lyuboshits expression of the pair wavefunction, indicate a repulsive and a shallow attractive strong interaction for the $$Ξ$$-K and $$Ξ$$ − 𝜋 systems, respectively.more » The $$Ξ$$(1620) and $$Ξ$$(1690) states are observed in the $$Ξ$$ − 𝜋 correlation function and their properties, mass and width, are determined. These measurements are in agreement with other available results. Such high-precision data can help refine the understanding of these resonant states, provide stronger constraints for chirally motivated potentials, and address the key challenge of describing the coupled-channel dynamics that may give rise to molecular configurations .« less

The dependence of f₀ (980) production on the final-state charged-particle multiplicity is reported for proton–proton (pp) collisions at the centre-of-mass energy, $$\mathbf{\sqrt{s}}$$ = 13 TeV. The production of (980) is measured with the ALICE detector via the decay channel in a midrapidity region of |y| < 0.5. The evolution of the integrated yields and mean transverse momentum of f₀ (980) as a function of charged-particle multiplicity measured in pp at $$\mathbf{\sqrt{s}}$$ = 13 TeV follows the trends observed in pp at $$\mathbf{\sqrt{s}}$$ = 5.02 TeV and in proton–lead (p–Pb) collisions at$$\mathbf{\sqrt{s_{NN}}}$$ = 5.02 TeV. Particle yield ratios of f₀ (980)more » to π^± and K* (892) are found to decrease with increasing charged-particle multiplicity. These particle ratios are compared with calculations from the canonical statistical thermal model as a function of charged-particle multiplicity. The thermal model calculations provide a better description of the decreasing trend of particle ratios when no strange or antistrange quark composition for f₀ (980) is assumed, which suggests that the data do not support significant hidden strangeness in the f₀ (980).« less

This Letter presents measurements of long-range transverse-momentum correlations using a new observable, 𝑣_0⁡(𝑝_T), serving as a probe of event-by-event radial-flow fluctuations, the underlying radial expansion, and the medium’s properties in heavy-ion collisions. Results are reported for inclusive charged particles, pions, kaons, and protons across various centrality intervals in Pb-Pb collisions at $$\sqrt{𝑠_{\textrm{NN}}}$$ = 5.02 TeV, recorded by the ALICE detector. A pseudorapidity-gap technique, similar to that used in anisotropic-flow studies, is employed to suppress short-range correlations. At low 𝑝_T, a characteristic mass ordering consistent with hydrodynamic collective flow is observed. At higher 𝑝_T (>3 GeV/𝑐), protons exhibit larger 𝑣₀⁡(𝑝_T) thanmore » pions and kaons, in agreement with expectations from quark-recombination models. Comparisons to viscous hydrodynamic calculations with varying bulk viscosity and equation of state demonstrate the sensitivity of the 𝑣₀⁡(𝑝_T) observable to these key medium properties. The findings establish 𝑣₀⁡(𝑝_T) as a valuable addition to the set of observables used in Bayesian analyses for extracting the transport properties and constraining the equation of state of strongly interacting matter, while also helping to systematically explore its sensitivity and impact within such global studies.« less

Femtoscopy of nonidentical particle pairs has been instrumental for precision measurements of both two-particle sources and the final-state interactions in high-energy elementary and heavy-ion collisions. The majority of measurements assessing the source properties are based on identical particle pairs, providing direct access to the characteristics of the single-particle source. The work in this paper demonstrates, via femtoscopy measurements of charged pion-deuteron pairs in Pb-Pb collisions at $$\sqrt{s_{NN}}$$ = 5.02 TeV, the feasibility of accessing the characteristics of the single-particle femtoscopic source by using particle pairs with large mass differences such as pions and deuterons. The first experimental results of themore » measurement of deuteron source sizes in ultrarelativistic heavy-ion collisions are presented. The results show good agreement with the trend derived from other charged hadrons such as pions, kaons, and protons as a function of transverse mass, indicating similar source properties.« less

This paper presents the measurement of the isolated prompt photon inclusive production cross section in pp and p–Pb collisions by the ALICE Collaboration at the LHC. The measurement is performed in p–Pb collisions at centre-of-mass energies per nucleon pair of $$\sqrt{s_{NN}}$$ = 5.02 Te and 8.16 TeV, as well as in pp collisions at $$\sqrt{s}$$ = 5.02 TeV and 8 TeV. The cross section is obtained at midrapidity (|γ| < 0.7) using a charged-track based isolation momentum p$$^{iso,~ch}_{T}$$ < 1.5 GeV/c in a cone with radius R = 0.4. The data for both collision systems are well reproduced by perturbativemore » QCD (pQCD) calculations at next-to-leading order (NLO) using recent parton distribution functions for free (PDF) and bound (nPDF) nucleons. Furthermore, the nuclear modification factor R_pA for both collision energies is consistent with unity for p_T > 20 GeV/c. However, deviations from unity (R_pA < 1) of up to 20% are observed for p_T < 20 GeV/c with limited significance, indicating the possible presence of nuclear effects in the initial state of the collision.« less

High-energy hadronic collisions generate environments characterized by temperatures above 100 MeV (refs.), about 100,000 times hotter than the centre of the Sun. At present, it is therefore unclear how light (anti)nuclei with mass number A of a few units, such as the deuteron, ³He or ⁴He, each bound by only a few MeV, can emerge from these collisions. Here, the ALICE Collaboration reports that deuteron–pion momentum correlations in proton–proton (pp) collisions provide model-independent evidence that about 90% of the observed (anti)deuterons are produced in nuclear reactions following the decay of short-lived resonances, such as the Δ(1232). These findings, obtained by themore » ALICE Collaboration at the Large Hadron Collider, resolve a gap in our understanding of nucleosynthesis in ultrarelativistic hadronic collisions. Apart from offering insights on how (anti)nuclei are formed in hadronic collisions, the results can be used in the modelling of the production of light and heavy nuclei in cosmic rays and dark-matter decays.« less