Measurement of charm production at central rapidity in proton-proton collisions at $\sqrt{s} = 2.76$ TeV

The $p_{\rm T}$-differential production cross sections of the prompt (B feed-down subtracted) charmed mesons D$^0$, D$^+$, and D$^{*+}$ in the rapidity range $|y|<~0.5$, and for transverse momentum $1<~ p_{\rm T} <~12$ GeV/$c$, were measured in proton-proton collisions at $\sqrt{s} = 2.76$ TeV with the ALICE detector at the Large Hadron Collider. The analysis exploited the hadronic decays D$^0 \rightarrow $K$\pi$, D$^+ \rightarrow $K$\pi\pi$, D$^{*+} \rightarrow $D$^0\pi$, and their charge conjugates, and was performed on a $L_{\rm int} = 1.1$ nb$^{-1}$ event sample collected in 2011 with a minimum-bias trigger. The total charm production cross section at $\sqrt{s} = 2.76$ TeV and at 7 TeV was evaluated by extrapolating to the full phase space the $p_{\rm T}$-differential production cross sections at $\sqrt{s} = 2.76$ TeV and our previous measurements at $\sqrt{s} = 7$ TeV. The results were compared to existing measurements and to perturbative-QCD calculations. The fraction of cdbar D mesons produced in a vector state was also determined.

Figures

Figure 1

Invariant-mass spectrum of $\Dzero+\overline{\Dzero}$ (left) and $\Dplus$ + D$^-$ (centre) candidates, and invariant-mass difference, $\Delta m = m_{K \pi \pi} - m_{K \pi}$, for $\Dstar$ + D$^{*-}$ candidates (right) in pp collisions at $\sqrts=2.76~$TeV.
[png]   [pdf]   [eps]

Figure 2

Acceptance $\times$ efficiency $\times 2 y_{\rm fid}$ for $\Dzero$ (left), $\Dplus$ (centre) and $\Dstar$ (left) as a function of $\pt$, where $2 y_{\rm fid}$ is the fiducial acceptance (see text).
[png]   [pdf]   [eps]

Figure 3

Top : $\pt$-differential cross section for prompt $\Dzero$, $\Dplus$, and $\Dstar$ mesons in pp collisions at $\sqrts=2.76 $TeV compared with FONLL[7, 27] and GM-VFNS [6, 31] theoretical predictions. Bottom: the ratio of the measured cross section and the central FONLL and GM-VFNS calculations.
[png]   [pdf]   [eps]

Figure 4

Top : $\pt$-differential cross section for prompt $\Dzero$, $\Dplus$, and $\Dstar$ mesons in pp collisions at $\sqrts=2.76~$TeV compared with the scaling of the ALICE measurement at $\sqrts=7~$TeV. Bottom : Ratio of the $\sqrts=2.76~$TeV cross section and the $\sqrts=7~$TeV measurement scaling, where the filled boxes represent the scaling uncertainties and the empty boxes the measurement systematics.
[png]   [pdf]   [eps]

Figure 5

Left: The fraction P$_{\rm v}$ of c$\bar{\rm d}$ D mesons created in a vector state to vector and pseudoscalar prompt D mesons [8, 11, 12, 34-37]. The weighted average of the experimental measurements reported in Ref.[38] and of the LHC data [11, 12] shown in the figure is P$_{\rm v} = 0.60 \pm 0.01$, and is represented by a solid yellow vertical band. Right: Energy dependence of the total nucleon-nucleon charm production cross section [12, 13, 42-44]. In case of proton-nucleus (pA) or deuteron-nucleus (dA) collisions, the measured cross sections have been scaled down by the number of binary nucleon-nucleon collisions calculated in a Glauber model of the proton-nucleus or deuteron-nucleus collision geometry. The NLO MNR calculation [45] (and its uncertainties) is represented by solid (dashed) lines.
[png]   [pdf]   [eps]
[png]   [pdf]   [eps]