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We present a polarisation-maintaining all-normal dispersion photonic crystal fibre designed for 1030 nm femtosecond pumping, enabling ultra-stable and coherent supercontinuum (SC) generation spanning 650–1300 nm. The fibre’s polarisation-maintaining properties are achieved through two larger central holes in the structure, which is an alternative approach to using conventional stress rods. The fibre is specifically engineered to achieve minimum dispersion near 1030 nm, making it ideal for ultrafast comb-based metrology, and widely tunable optical parametric amplifier (OPA) systems. We further investigate the influence of input pulse contrast on supercontinuum generation through both numerical simulations and experiments. Relative intensity noise (RIN) and phase noise (PN) are characterized using three complementary techniques: dispersive Fourier transform (DFT), the Bellini–Hänsch interferometric method, and the dual-reference oscillator cross-correlation technique. The results demonstrate excellent stability, with pulse-to-pulse RIN below 0.5%, an optical phase deviation under 15 mrad, and phase noise levels down to − 150 dBc/Hz at 10 kHz from the carrier, confirming the fibre’s suitability for demanding ultrafast applications.

We report on a measurement of Spin Density Matrix Elements (SDMEs) in hard exclusive [Formula omitted] meson muoproduction at COMPASS using 160 GeV/c polarised [Formula omitted] and [Formula omitted] beams impinging on a liquid hydrogen target. The measurement covers the kinematic range 5.0 GeV/ [Formula omitted] [Formula omitted] 17.0 GeV/ [Formula omitted], 1.0 (GeV/c) [Formula omitted] [Formula omitted] 10.0 (GeV/c) [Formula omitted] and 0.01 (GeV/c) [Formula omitted] [Formula omitted] 0.5 (GeV/c) [Formula omitted]. Here, W denotes the mass of the final hadronic system, [Formula omitted] the virtuality of the exchanged photon, and [Formula omitted] the transverse momentum of the [Formula omitted] meson with respect to the virtual-photon direction. The measured non-zero SDMEs for the transitions of transversely polarised virtual photons to longitudinally polarised vector mesons ( [Formula omitted]) indicate a violation of s-channel helicity conservation. Additionally, we observe a dominant contribution of natural-parity-exchange transitions and a very small contribution of unnatural-parity-exchange transitions, which is compatible with zero within experimental uncertainties. The results provide important input for modelling Generalised Parton Distributions (GPDs). In particular, they may allow one to evaluate in a model-dependent way the role of parton helicity-flip GPDs in exclusive [Formula omitted] production.

We report on a measurement of Spin Density Matrix Elements (SDMEs) in hard exclusive ρ 0 meson muoproduction at COMPASS using 160 GeV/ c polarised μ + and μ - beams impinging on a liquid hydrogen target. The measurement covers the kinematic range 5.0 GeV/ c 2 < W < 17.0 GeV/ c 2 , 1.0 (GeV/ c ) 2 < Q 2 < 10.0 (GeV/ c ) 2 and 0.01 (GeV/ c ) 2 < p T 2 < 0.5 (GeV/ c ) 2 . Here, W denotes the mass of the final hadronic system, Q 2 the virtuality of the exchanged photon, and p T the transverse momentum of the ρ 0 meson with respect to the virtual-photon direction. The measured non-zero SDMEs for the transitions of transversely polarised virtual photons to longitudinally polarised vector mesons ( γ T ∗ → V L ) indicate a violation of s -channel helicity conservation. Additionally, we observe a dominant contribution of natural-parity-exchange transitions and a very small contribution of unnatural-parity-exchange transitions, which is compatible with zero within experimental uncertainties. The results provide important input for modelling Generalised Parton Distributions (GPDs). In particular, they may allow one to evaluate in a model-dependent way the role of parton helicity-flip GPDs in exclusive ρ 0 production.

In 2022, the COMPASS collaboration performed semi-inclusive measurements of deep-inelastic muon-scattering on a transversely polarised deuteron (6LiD) target. From these data, transverse-spin-dependent dihadron asymmetries are extracted using pairs of oppositely charged hadrons. These asymmetries are directly sensitive to the quark transversity distributions and provide an independent handle on these fundamental quantities with respect to the Collins asymmetries measured in single-hadron production. The present results significantly improve upon the previous COMPASS deuteron measurements, which were the only available deuteron data worldwide, and reach a statistical precision comparable to that of the existing proton results from COMPASS. A small but nonzero asymmetry is observed at large Bjorken-x, consistent with theoretical expectations. A point-by-point extraction of the valence-quark transversity distributions yields, in particular, a substantially improved determination of the d-quark transversity. These measurements represent a major step towards a complete flavour mapping of the transverse-spin structure of the nucleon.

The pseudorapidity distribution of charged hadrons produced in Au+Au collisions at a center-of-mass energy of \\(\\sqrt{s_\\mathrm{NN}} = 200\\) GeV is measured using data collected by the sPHENIX detector. Charged hadron yields are extracted by counting cluster pairs in the inner and outer layers of the Intermediate Silicon Tracker, with corrections applied for detector acceptance, reconstruction efficiency, combinatorial pairs, and contributions from secondary decays. The measured distributions cover \\(|\\eta| < 1.1\\) across various centralities, and the average pseudorapidity density of charged hadrons at mid-rapidity is compared to predictions from Monte Carlo heavy-ion event generators. This result, featuring full azimuthal coverage at mid-rapidity, is consistent with previous experimental measurements at the Relativistic Heavy Ion Collider, thereby supporting the broader sPHENIX physics program.

This paper reports measurements of the transverse energy per unit pseudorapidity (\\(dE_{T}/d\\eta\\)) produced in Au+Au collisions at \\(\\sqrt{s_{NN}} = 200\\) GeV, performed with the sPHENIX detector at the Relativistic Heavy Ion Collider (RHIC). The results cover the pseudorapidity range \\(\\left|\\eta\\right| < 1.1\\) and constitute the first such measurement performed using a hadronic calorimeter at RHIC. Measurements of \\(dE_{T}/d\\eta\\) are presented for a range of centrality intervals and the average \\(dE_{T}/d\\eta\\) as a function of the number of participating nucleons, \\(N_{\\mathrm{part}}\\), is compared to a variety of Monte Carlo heavy-ion event generators. The results are in agreement with previous measurements at RHIC, and feature an improved granularity in \\(\\eta\\) and improved precision in low-\\(N_{\\mathrm{part}}\\) events.

The PHENIX experiment at the Relativistic Heavy Ion Collider has measured low-mass vector-meson (\\(+\\) and \\(\\)) production through the dimuon decay channel at forward rapidity \\((1.2<|y|<2.2)\\) in$p$ $+$ $p\\( and Au\\)+\\(Au collisions at \\)\\sqrt{s_{_{NN}}}=200\\(~GeV. The low-mass vector-meson yield and nuclear-modification factor were measured as a function of the average number of participating nucleons, \\)\\langle N_{\\rm part}\\rangle\\(, and the transverse momentum \\)p_T\\(. These results were compared with those obtained via the kaon decay channel in a similar \\)p_T\\( range at midrapidity. The nuclear-modification factors in both rapidity regions are consistent within the uncertainties. A comparison of the \\)\\omega+\\rho\\( and \\)J/\\psi\\( mesons reveals that the light and heavy flavors are consistently suppressed across both \\)p_T\\( and \\){\\langle}N_{\\rm part}\\rangle\\(. In contrast, the \\)\\phi$meson displays a nuclear-modification factor consistent with unity, suggesting strangeness enhancement in the medium formed.

We measured the strange-meson spectrum in the scattering reaction \\(K^{-}+p \\rightarrow K^{-}\\pi^{-}\\pi^{-}+p\\) with the COMPASS spectrometer at CERN. Using the world's largest sample of this reaction, we performed a comprehensive partial-wave analysis of the mesonic final state. It substantially extends the strange-meson spectrum covering twelve states with masses up to 2.4 GeV/\\(c^2\\). We observe the first candidate for a crypto-exotic strange meson with \\(J^{P}=0^{-}\\) and find \\(K_3\\) and \\(K_4\\) states consistent with predictions for the ground states.

A new and detailed measurement of the cross section for hard exclusive neutral-pion muoproduction on the proton was performed in a wide kinematic region, with the photon virtuality \\(Q^2\\) ranging from 1 to 8 (GeV/\\(c\\))\\(^\\, 2\\) and the Bjorken variable \\(x_ Bj\\) ranging from 0.02 to 0.45. The data were collected at COMPASS at CERN using 160 GeV/\\(c\\) longitudinally polarised \\(^+\\) and \\(^-\\) beams scattering off a 2.5 m long liquid hydrogen target. From the average of the measured \\(^+\\) and \\(^-\\) cross sections, the virtual-photon--proton cross section is determined as a function of the squared four-momentum transfer between the initial and final state proton in the range 0.08 (GeV/\\(c\\))\\(^\\, 2\\) \\(< |t| <\\) 0.64 (GeV/\\(c\\))\\(^\\, 2\\). From its angular distribution, the combined contribution of transversely and longitudinally polarised photons are determined, as well as transverse--transverse and longitudinal--transverse interference contributions. They are studied as functions of four-momentum transfer \\(|t|\\), photon virtuality \\(Q^2\\) and virtual-photon energy \\(\\). The longitudinal--transverse interference contribution is found to be compatible with zero. The significant transverse--transverse interference contribution reveals the existence of a dominant contribution by transversely polarized photons. This provides clear experimental evidence for the chiral-odd GPD \\(E_T\\). In addition, the existence of a non-negligible contribution of longitudinally polarized photons is suggested by the \\(|t|\\)-dependence of the cross section at \\(x_ Bj < \\) 0.1 . Altogether, these results provide valuable input for future modelling of GPDs and thus of cross sections for exclusive pseudo-scalar meson production. Furthermore, they can be expected to facilitate the study of next-to-leading order corrections and higher-twist contributions.