We present the transverse momentum (p) spectra for identified charged pions, protons and anti-protons from p+p and d+Au collisions at s=200 GeV. The spectra are measured around midrapidity (|y|<0.5) over the range of 0.3<p<10 GeV/c with particle identification from the ionization energy loss and its relativistic rise in the time projection chamber and time-of-flight in STAR. The charged pion and proton + anti-proton spectra at high p in p+p and d+Au collisions are in good agreement with a phenomenological model (EPOS) and with next-to-leading order perturbative quantum chromodynamic (NLO pQCD) calculations with a specific fragmentation scheme and factorization scale. We found that all proton, anti-proton and charged pion spectra in p+p collisions follow x-scaling for the momentum range where particle production is dominated by hard processes (p≳2 GeV/c). The nuclear modification factor around midrapidity is found to be greater than unity for charged pions and to be even larger for protons at 2<p<5 GeV/c.
Physics Letters B
- Pub Date:
- June 2006
- Nuclear Experiment;
- High Energy Physics - Phenomenology;
- Nuclear Theory
- 19 pages and 8 figures, published version and mT scaling included