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 Ralf Seidl
      To study the strong interaction in nucleon structure and fragmentation


Fragmentation functions

Fragmentation functions describe the transition of high energetic, massless and asymptotically-free partons into confined, massive final-state hadrons. It is therefore at the haert of the remaining open questions about confinement and the formation of mass via the strong interaction, QCD. As non-perturbative objects, fragmentation functions cannot be calculated from first principles and need to be measured in experiment. The most straightforward access to fragmentation functions comes from electron-positron annihilation, where the initial process is very well understood and hadrons only appear in the final state. I have been extracting fragmentation functions in particular at the Belle experiment with about 1fb-1 of accumulated data and hope to continue working on the Belle II experiment. Apart from trying to understand QCD via fragmentation, fragmentation functions also a great tool to in accessing the nucleon structure. Unpolarized fragmentation functions allow to get information about the parton flavor of unpolarized or polarized distribution functions. Transverse spin depedendent fragmentation functions (Collins and interference FFs) are the nearly only tool to get the nucleon's transversity distribution. For transverse momentum dependent distribution functions, such as the Sivers function, the Boer-Mulders function and several others also require explicitly transverse momentum dependent fragmentation functions.

fragmentation illustration


Ongoing Fragmentation Research activities:

  • update of single and di-hadron analysis with improved ISR correction, additional fractional energy definitions and parent analysis
  • finalization of kaon related Collins measurements in multi-dimensional analysis
  • cross sectins for vector meson and other resonances
  • jet related analysis, including transverse momentum dependence and jet-shape

  • single hadronkt dihadron hadronkt single hadron jet kt


    Previous results:

  • Transverse momentum dependent production cross sections of charged pions, kaons and protons in e+e- annihilation at 10.58 GeV (RIKEN press release, Japanese) and PRD 99, 112006(32 citations)
  • di-hadron fragmentation for pion and kaon pairs as a function of mass and combined fractional energy PRD 96 (2017), 032005 (22 citations)
  • di-hadron fragmentation for pion and kaon pairs as a function of fractional energies of the hadrons PRD 92 (2015), 092007 (22 citations)
  • Precision Measurement of Charged Pion and Kaon Differential Cross Sections in e+e- Annihilation at s=10.52  GeV PRL 111 (2013) 062002 (80 citations)
  • Observation of transverse polarization asymmetries of charged pion pairs in $e^+e^-$ annihilation near $\sqrt{s}=10.58$ GeV (Interference fragementation functions) PRL 107 (2011) 072004 (131 citations)
  • Measurement of Azimuthal Asymmetries in Inclusive Production of Hadron Pairs in e+e- Annihilation at s**(1/2) = 10.58-GeV (Collins fragmentation functions) PRD 78 (2008) 032011 (260 citations) PRL 96 (2006) 232002 (305 citations)

  • Photo IFF asymmetries IFF asymmetries

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    Last modified Wed Jan 4 13:34:09 JST 2023