The STAR experiment

Abstract: The parton-to-hadron transition, known as hadronization, is dominated by non-perturbative Quantum Chromodynamics (QCD) effects and thus challenging to study from first-principle calculations. On the other hand, experimental studies of observables sensitive to hadronization could provide valuable input. The charge correlator ratio r_c studies the charge correlation between the leading two hadrons in jets and is sensitive to hadronization effects. With data taken at sqrt{s}=200 GeV at STAR, we measure r_c in p+p collisions to probe for string-like fragmentation. These measurements, compared with various model predictions, are expected to distinguish between phenomenological model descriptions for hadronization in vacuum.

Figures: 

Fig. 2. Closure test that shows r_c vs jet p_T before any correction, after mistagged subtraction, and after all steps of correction. 

Fig. 3. Fully corrected r_c vs jet p_T, compared to event generator predictions. 

Conclusions: In summary, to probe for string-like fragmentation, we measure of r_c as a function of jet p_T in sqrt{s}=200 GeV p+p collisions at STAR. On average, the data show that leading charged particles in jets are more likely to be opposite signs than same sign. (In data, opposite signs occur 65% of the time and same sign 35% of the time. In PYTHIA these fractions are 68% to 32%). Compared with predictions from event generators, the fully corrected data show a weaker correlation between the leading and subleading tracks in jets. The significant difference between HERWIG and PYTHIA in their relative fractions of fragmentation vs. resonance decays might explain why their predictions for r_c are similar despite different approaches to fragmentation.

Preliminary results: page