Suppression of High-pTNeutral Pion Production in CentralPb+PbCollisions atsNN=17.3GeVRelative top+Candp+PbCollisions

Neutral pion transverse momentum spectra were measured in $p+\mathrm{C}$ and $p+\mathrm{Pb}$ collisions at $\sqrt{{s}_{NN}}=17.4\text{ }\text{ }\mathrm{GeV}$ at midrapidity ($2.3\ensuremath{\lesssim}{\ensuremath{\eta}}_{\mathrm{lab}}\ensuremath{\lesssim}3.0$) over the range $0.7\ensuremath{\lesssim}{p}_{T}\ensuremath{\lesssim}3.5\text{ }\text{ }\mathrm{GeV}/c$. The spectra are compared to ${\ensuremath{\pi}}^{0}$ spectra measured in $\mathrm{Pb}+\mathrm{Pb}$ collisions at $\sqrt{{s}_{NN}}=17.3\text{ }\text{ }\mathrm{GeV}$ in the same experiment. For a wide range of $\mathrm{Pb}+\mathrm{Pb}$ centralities (${N}_{\mathrm{part}}\ensuremath{\lesssim}300$), the yield of ${\ensuremath{\pi}}^{0}$'s with ${p}_{T}\ensuremath{\gtrsim}2\text{ }\text{ }\mathrm{GeV}/c$ is larger than or consistent with the $p+\mathrm{C}$ or $p+\mathrm{Pb}$ yields scaled with the number of nucleon-nucleon collisions (${N}_{\mathrm{coll}}$), while for central $\mathrm{Pb}+\mathrm{Pb}$ collisions with ${N}_{\mathrm{part}}\ensuremath{\gtrsim}350$, the ${\ensuremath{\pi}}^{0}$ yield is suppressed.