More Like this

1. Observation of triple J/ψ meson production in proton-proton collisions

   https://doi.org/10.1038/s41567-022-01838-y  

   Tumasyan, A. ; Adam, W. ; Andrejkovic, J. W. ; Bergauer, T. ; Chatterjee, S. ; Damanakis, K. ; Dragicevic, M. ; Del Valle, A. Escalante ; Frühwirth, R. ; Jeitler, M. ; et al ( March 2023 , Nature Physics)

   Protons consist of three valence quarks, two up-quarks and one down-quark, held together by gluons and a sea of quark-antiquark pairs. Collectively, quarks and gluons are referred to as partons. In a proton-proton collision, typically only one parton of each proton undergoes a hard scattering – referred to as single-parton scattering – leaving the remainder of each proton only slightly disturbed. Here, we report the study of double- and triple-parton scatterings through the simultaneous production of three J/ψmesons, which consist of a charm quark-antiquark pair, in proton-proton collisions recorded with the CMS experiment at the Large Hadron Collider. We observed this process – reconstructed through the decays of J/ψmesons into pairs of oppositely charged muons – with a statistical significance above five standard deviations. We measured the inclusive fiducial cross-section to be$$27{2}_{-104}^{+141}\,{{{\rm{(stat)}}}}\,\pm 17\,{{{\rm{(syst)}}}}\,{{{\rm{fb}}}}\,$$$272_{-104}^{+141}\mathrm{(stat)}\pm 17\mathrm{(syst)}\mathrm{fb}$, and compared it to theoretical expectations for triple-J/ψmeson production in single-, double- and triple-parton scattering scenarios. Assuming factorization of multiple hard-scattering probabilities in terms of single-parton scattering cross-sections, double- and triple-parton scattering are the dominant contributions for the measured process.

    

   more » « less
2. Reduction of the electroweak correlation in the PDF updating by using the forward–backward asymmetry of Drell–Yan process

   https://doi.org/10.1140/epjc/s10052-022-10280-6  

   Yang, Siqi ; Fu, Yao ; Liu, Minghui ; Zhang, Renyou ; Hou, Tie-Jiun ; Wang, Chen ; Yin, Hang ; Han, Liang ; Yuan, C. -P. ( April 2022 , The European Physical Journal C)

   We propose a new observable for the measurement of the forward–backward asymmetry$$(A_{FB})$$$\left(A_{\mathrm{FB}}\right)$in Drell–Yan lepton production. At hadron colliders, the$$A_{FB}$$$A_{\mathrm{FB}}$distribution is sensitive to both the electroweak (EW) fundamental parameter$$\sin ^{2} \theta _{W}$$${sin}^2{\theta }_W$, the weak mixing angle, and the parton distribution functions (PDFs). Hence, the determination of$$\sin ^{2} \theta _{W}$$${sin}^2{\theta }_W$and the updating of PDFs by directly using the same$$A_{FB}$$$A_{\mathrm{FB}}$spectrum are strongly correlated. This correlation would introduce large bias or uncertainty into both precise measurements of EW and PDF sectors. In this article, we show that the sensitivity of$$A_{FB}$$$A_{\mathrm{FB}}$on$$\sin ^{2} \theta _{W}$$${sin}^2{\theta }_W$is dominated by its average value around theZpole region, while the shape (or gradient) of the$$A_{FB}$$$A_{\mathrm{FB}}$spectrum is insensitive to$$\sin ^{2} \theta _{W}$$${sin}^2{\theta }_W$and contains important information on the PDF modeling. Accordingly, a new observable related to the gradient of the spectrum is introduced, and demonstrated to be able to significantly reduce the potential bias on the determination of$$\sin ^{2} \theta _{W}$$${sin}^2{\theta }_W$when updating the PDFs using the same$$A_{FB}$$$A_{\mathrm{FB}}$data.

    

   more » « less
3. $$X(3872)$$transport in heavy-ion collisions

   https://doi.org/10.1140/epja/s10050-021-00435-6  

   Wu, Biaogang ; Du, Xiaojian ; Sibila, Matthew ; Rapp, Ralf ( April 2021 , The European Physical Journal A)

   The production of the$$X(3872)$$$X\left(3872\right)$ particle in heavy-ion collisions has been contemplated as an alternative probe of its internal structure. To investigate this conjecture, we perform transport calculations of the$$X(3872)$$$X\left(3872\right)$ through the fireball formed in nuclear collisions at the LHC. Within a kinetic-rate equation approach as previously used for charmonia, the formation and dissociation of the$$X(3872)$$$X\left(3872\right)$ is controlled by two transport parameters,i.e., its inelastic reaction rate and thermal-equilibrium limit in the evolving hot QCD medium. While the equilibrium limit is controlled by the charm production cross section in primordial nucleon-nucleon collisions (together with the spectra of charm states in the medium), the structure information is encoded in the reaction rate. We study how different scenarios for the rate affect the centrality dependence and transverse-momentum ($$p_T$$$p_T$) spectra of the$$X(3872)$$$X\left(3872\right)$. Larger reaction rates associated with the loosely bound molecule structure imply that it is formed later in the fireball evolution than the tetraquark and thus its final yields are generally smaller by around a factor of two, which is qualitatively different from most coalescence model calculations to date. The$$p_T$$$p_T$ spectra provide further information as the later decoupling time within the molecular scenario leads to harder spectra caused by the blue-shift from the expanding fireball.

    

   more » « less
4. Coulomb-free 1S0 p − p scattering length from the quasi-free p + d → p + p + n reaction and its relation to universality

   https://doi.org/10.1038/s42005-023-01221-0  

   Tumino, Aurora ; Rapisarda, Giuseppe G. ; La Cognata, Marco ; Oliva, Alessandro ; Kievsky, Alejandro ; Bertulani, Carlos A. ; D’Agata, Giuseppe ; Gattobigio, Mario ; Guardo, Giovanni L. ; Lamia, Livio ; et al ( May 2023 , Communications Physics)

   The Coulomb-free¹S₀proton-proton (p-p) scattering length relies heavily on numerous and distinct theoretical techniques to remove the Coulomb contribution. Here, it has been determined from the half-off-the-energy-shellp-pscattering cross section measured at center-of-mass energies below 1 MeV using the quasi-freep + d → p + p + nreaction. A Bayesian data-fitting approach using the expression of the s-wave nucleon-nucleon scattering cross section returned ap-pscattering length$${a}_{pp}=-18.1{7}_{-0.58}^{+0.52}{| }_{stat}\pm 0.0{1}_{syst}$$$a_{pp}=-18.17_{-0.58}^{+0.52}{\mid }_{stat}\pm 0.01_{syst}$fm and effective ranger₀ = 2.80 ± 0.05_stat ± 0.001_systfm. A model based on universality concepts has been developed to interpret this result. It accounts for the short-range interaction as a whole, nuclear and residual electromagnetic, according to what the s-wave phase-shiftδdoes in the description of low-energy nucleon-nucleon scattering data. We conclude that our parameters are representative of the short-range physics and propose to assess the charge symmetry breaking of the short-range interaction instead of just the nuclear interaction. This is consistent with the current understanding that the charge dependence of nuclear forces is due to different masses of up-down quarks and their electromagnetic interactions. This achievement suggests that these properties have a lesser than expected impact in the context of the charge symmetry breaking.

    

   more » « less
5. Searching for dark photon dark matter in LIGO O1 data

   https://doi.org/10.1038/s42005-019-0255-0  

   Guo, Huai-Ke ; Riles, Keith ; Yang, Feng-Wei ; Zhao, Yue ( December 2019 , Communications Physics)

   Dark matter exists in our Universe, but its nature remains mysterious. The remarkable sensitivity of the Laser Interferometer Gravitational-Wave Observatory (LIGO) may be able to solve this mystery. A good dark matter candidate is the ultralight dark photon. Because of its interaction with ordinary matter, it induces displacements on LIGO mirrors that can lead to an observable signal. In a study that bridges gravitational wave science and particle physics, we perform a direct dark matter search using data from LIGO’s first (O1) data run, as opposed to an indirect search for dark matter via its production of gravitational waves. We demonstrate an achieved sensitivity on squared coupling as$$\sim\! 4\times 1{0}^{-45}$$$~4\times 10^{-45}$, in a$$U{(1)}_{{\rm{B}}}$$$U{\left(1\right)}_B$dark photon dark matter mass band around$${m}_{{\rm{A}}} \sim 4\,\times 1{0}^{-13}$$$m_A~4\times 10^{-13}$eV. Substantially improved search sensitivity is expected during the coming years of continued data taking by LIGO and other gravitational wave detectors in a growing global network.

    

   more » « less