Absence of Suppression in Particle Production at Large Transverse Momentum in $\sqrt{s_{NN}}=200\mathrm{G}\mathrm{e}\mathrm{V}$ $d+\mathrm{A}\mathrm{u}$ Collisions

Transverse momentum spectra of charged hadrons with $p_T<8\mathrm{G}\mathrm{e}\mathrm{V}/c$ and neutral pions with $p_T<10\mathrm{G}\mathrm{e}\mathrm{V}/c$ have been measured at midrapidity by the PHENIX experiment at BNL RHIC in $d+\mathrm{A}\mathrm{u}$ collisions at $\sqrt{s_{NN}}=200\mathrm{G}\mathrm{e}\mathrm{V}$. The measured yields are compared to those in $p+p$ collisions at the same $\sqrt{s_{NN}}$ scaled up by the number of underlying nucleon-nucleon collisions in $d+\mathrm{A}\mathrm{u}$. The yield ratio does not show the suppression observed in central $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions at RHIC. Instead, there is a small enhancement in the yield of high momentum particles.

Figure 1

Midrapidity $p_T$ spectra for charged hadrons and ${\pi }^0$. Total uncertainties are shown. The ${\pi }^0$ below $5\mathrm{G}\mathrm{e}\mathrm{V}/c$ are from minimum bias triggered events, and above from photon triggered events. Lines show fits to reference spectra from $p+p$ collisions, and open points show the $p+p$ ${\pi }^0$ spectrum measured by PHENIX [17].

Figure 2

Nuclear modification factor $R_{dA}$ for ${\pi }^0$ in the PbGl and PbSc calorimeters in minimum bias $d+\mathrm{A}\mathrm{u}$. The bands around the data points show systematic errors which can vary with $p_T$, while the shaded band around unity indicates the normalization uncertainty. The nuclear modification factor $R_{AA}$ in 10% most central $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions is also shown.

Figure 3

Top: Nuclear modification factor $R_{dA}$ for $(h^{+}+h^{-})/2$ in minimum bias $d+\mathrm{A}\mathrm{u}$ compared to $R_{AA}$ in the 10% most central $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions. Inner bands show systematic errors which can vary with $p_T$, and outer bands include also the normalization uncertainty. Bottom: Comparison of $R_{dA}$ for $(h^{+}+h^{-})/2$ and the average of the ${\pi }^0$ measurements in $d+\mathrm{A}\mathrm{u}$. The bar at the left indicates the systematic uncertainty in common for the charged and ${\pi }^0$ measurements.

Figure 4

Ratio of $R_{dA}$ in minimum bias $d+\mathrm{A}\mathrm{u}$ and $R_{pA}$ from neutron tagged $d+\mathrm{A}\mathrm{u}$ collisions for $(h^{+}+h^{-})/2$ and ${\pi }^0$. The band shows the uncertainty on the number of binary collisions; all other systematic errors cancel.