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1. Forming molecular states with hadronic rescattering

   https://doi.org/10.1140/epja/s10050-021-00650-1  

   Ilten, Philip; Utheim, Marius (January 2022, The European Physical Journal A)

   Abstract A method for modelling the prompt production of molecular states using the hadronic rescattering framework of the general-purpose Pythia event generator is introduced. Production cross sections of possible exotic hadronic molecules via hadronic rescattering at the LHC are calculated for the $$\chi _{c1}(3872)$$ χ c 1 ( 3872 ) resonance, a possible tetraquark state, as well as three possible pentaquark states, $$P_c^+(4312)$$ P c + ( 4312 ) , $$P_c^+(4440)$$ P c + ( 4440 ) , and $$P_c^+(4457)$$ P c + ( 4457 ) . For the $$P_c^+$$ P c + states, the expected cross section from $$\Lambda _b$$ Λ b decays is compared to the hadronic-rescattering production. The $$\chi _{c1}(3872)$$ χ c 1 ( 3872 ) cross section is compared to the fiducial $$\chi _{c1}(3872)$$ χ c 1 ( 3872 ) cross-section measurement by LHCb and found to contribute at a level of $${\mathcal {O}({1\%})}$$ O ( 1 % ) . Finally, the expected yields of $$\mathrm {P_c^{+}}$$ P c + production from hadronic rescattering during Run 3 of LHCb are estimated. The prompt background is found to be significantly larger than the prompt $$\mathrm {P_c^{+}}$$ P c + signal from hadronic rescattering. 

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2. Two-particle angular correlations in e+e− collisions to hadronic final states in two reference coordinates at Belle

   https://doi.org/10.1007/JHEP03(2023)171  

   Chen, Y-C; Lee, Y-J; Chang, P; Adachi, I; Aihara, H; Al_Said, S; Asner, D M; Atmacan, H; Aulchenko, V; Aushev, T; et al (March 2023, Journal of High Energy Physics)

   A<sc>bstract</sc> We present the analysis of two-particle angular correlations using coordinate systems defined with the conventional beam axis and the event thrust axis. We propose the latter as a good representation for the correlation structure interpretation in thee⁺e⁻collision system. Thee⁺e⁻collisions to hadronic final states at center-of-mass energies of$$ \sqrt{s} $$ $\sqrt{s}$= 10.52 GeV and 10.58 GeV are recorded by the Belle detector at KEKB. In this paper, results on the first dataset are supplementary to the previous Belle publication [1]. At the same time, the latter is the first two-particle correlation measurement at collision energy on theΥ(4S) resonance and is sensitive to its decay products. Measurements are reported as a function of the charged-particle multiplicity. Finally, a qualitative understanding of the correlation structure is discussed using a combination of Monte Carlo simulations and experimental data. 

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3. Heavy quark transverse momentum dependent fragmentation

   https://doi.org/10.1007/JHEP05(2024)002  

   Dai, Lin; Kim, Chul; Leibovich, Adam K (May 2024, Journal of High Energy Physics)

   A<sc>bstract</sc> In this paper, we investigate the heavy quark (HQ) mass effects on the transverse momentum dependent fragmentation function (TMDFF). We first calculate the one-loop TMDFF initiated by a heavy quark. We then investigate the HQ TMDFF in the limit where the transverse momentum,q_⊥is small compared to the heavy quark mass,q_⊥≪mand also in the opposite limit whereq_⊥≫m. As applications of the HQ TMDFF, we study the HQ transverse momentum dependent jet fragmentation function, where the heavy quark fragments into a jet containing a heavy hadron, and we investigate a heavy hadron’s transverse momentum dependent distribution with respect to the thrust axis ine⁺e⁻collisions. 

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4. Measuring the polarization of boosted, hadronic W bosons with jet substructure observables

   https://doi.org/10.1007/JHEP05(2025)028  

   De, Songshaptak; Rentala, Vikram; Shepherd, William (May 2025, Journal of High Energy Physics)

   A<sc>bstract</sc> In this work, we present a new technique to measure the longitudinal and transverse polarization fractions of hadronic decays of boostedWbosons. We introduce a new jet substructure observable denoted asp_θ, which is a proxy constructed purely out of subjet energies for the parton level decay polar angle of theWboson in its rest-frame. The distribution of this observable is sensitive to the polarization ofWbosons and can therefore be used to reconstruct theWpolarization in a way that is independent of the production process — assuming Standard Model (SM) rules governing decays. We argue that this proxy variable has lower reconstruction errors as compared to the other proxies that have been used by the experimental collaborations, especially for large boosts of theW-boson. As a test case, we study the efficacy of our technique on vector boson scattering (VBS) processes at the high luminosity Large Hadron Collider. We find that with only SM production channels, measuring the longitudinal polarization fraction is likely to be challenging even with 10 ab⁻¹of data. We suggest further strategies and scenarios that may improve the prospects of measurement of the hadronicWpolarization fraction. 

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5. Detection of Molecular Clouds in the PeVatron Candidate Source LHAASO J0341+5258 by the Nobeyama 45-m Radio Telescope

   https://doi.org/10.3847/1538-4357/adb7df  

   Tsuji, Naomi; Takekawa, Shunya; Mori, Kaya; Mitchell, Alison; Zhang, Shuo; Bangale, Priyadarshini; DiKerby, Stephen; Ergin, Tülün; Woo, Jooyun; Safi-Harb, Samar; et al (April 2025, The Astrophysical Journal)

   Abstract We report a new CO observation survey of LHAASO J0341+5258, using the Nobeyama Radio Observatory 45-m telescope. LHAASO J0341+5258 is one of the unidentified ultra-high-energy (UHE;E> 100 TeV) gamma-ray sources detected by LHAASO. Our CO observations were conducted in 2024 February and March, with a total observation time of 36 hr, covering the LHAASO source (∼0 $\stackrel{\text{°}}{.}$3–0 $\stackrel{\text{°}}{.}$5 in radius) and its surrounding area (1° × 1 $\stackrel{\text{°}}{.}$5). Within the LHAASO source extent, we identified five compact (<2 pc) molecular clouds at nearby distances (<1–4 kpc). These clouds can serve as proton–proton collision targets, producing hadronic gamma rays via neutral pion decays. Based on the hydrogen densities (700–5000 cm⁻³) estimated from our CO observations and archived Hidata from the Dominion Radio Astrophysical Observatory survey, we derive the total proton energy ofW_p(E> 1 TeV) ∼ 10⁴⁵erg to account for the gamma-ray flux. One of the molecular clouds appears to be likely associated with an asymptotic giant branch (AGB) star with an extended CO tail, which may indicate some particle acceleration activities. However, the estimated maximum particle energy below 100 TeV makes the AGB-like star unlikely to be a PeVatron site. We conclude that the UHE emission observed in LHAASO J0341+5258 could be due to hadronic interactions between the newly discovered molecular clouds and TeV–PeV protons originating from a distant SNR or due to leptonic emission from a pulsar wind nebula candidate, which is reported in our companion X-ray observation paper. 

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