Narrow Results

Using new data on pion production in p+p interactions from the NA49 experiment, it is demonstrated that the detailed features of double differential pion cross sections are well reproduced over most of the phase space from the decay of a representative sample of known mesonic and baryonic resonances.

Thirteen resonances reaching up to spin four tensor-mesons and including the newly measured N* states up to the N*(1680) have been used. The p_T integrated Feynman x_F distributions in the high-x_F region 0.4 < x_F < 0.9 are quantitatively reproduced as well as the p_T distributions up to 2 GeV/c and beyond at all x_F.

In both these phase space regions direct effects of parton dynamics such as valence quark fragmentation or parton scattering are generally evoked in order to provide a basis of understanding. The saturation of the measured yields by resonance decay casts a doubt on these assumptions.

We argue that $p_T$ distribution data from the LHC on the invariant differential yield of the charged primary particles in $pp$ collisions at $\sqrt{s}=0.9\mathrm{\text{TeV}},2.76\mathrm{\text{TeV}},7\mathrm{\text{TeV}}$ and in Pb–Pb collisions at $\sqrt{s_{NN}}=2.76$TeV with six centrality bins contains several $p_T$ regions with special properties. These distributions were analyzed by fitting the data with exponential functions. We conclude that the regions reflect features of fragmentation and hadronization of partons through the string dynamics. The nuclear transparency results in negligible influence of the medium in the III region ($p_T>17-20\mathrm{\text{GeV/c}}$), which has highest $p_T$ values. The effects and changes by the medium start to appear weakly in the II region ($4-6\mathrm{\text{GeV/c}}<p_T<17-20\mathrm{\text{GeV/c}}$) and become stronger in the I region ($p_T<4-6\mathrm{\text{GeV/c}}$). It seems that the II region has highest number of strings. The increase in string density in this region could lead to fusion of strings, appearance of a new string and collective behavior of the partons in the most central collisions. These phenomena can explain anomalous behavior of the Nuclear Modification Factor in the II region. We propose the II region as a possible area of Quark Gluon Plasma formation through string fusion. The first $p_T$ regions are the ones with the maximum number of hadrons and minimum number of strings due to direct hadronization of the low energy strings into two quark systems–mesons.