Changes made after the Physics Meeting

Author	Title	Files	Version	Figures
Ferenc Siklér	Reconstruction of low pT charged particles with the pixel detector		17 Oct
Ferenc Siklér	Reconstruction of V0s and photon conversions with the pixel detector		17 Oct

General: Magnetic field

The plot shows the B_z component as function of z coordinate at the beam-line from OSCAR_3_9_8.

The field value use in ORCA is 4 T, which leads to a ratio of 4.068/4 = 1.017. This means that the reconstructed p_T was smaller and was expected to be around 0.983 of the simulated value, explaining the p_T bias and the problems with the invariant mass spectra. The corresponding plots are changed.

CMS Note AN-2006/100: Reconstruction of low p_T charged ...

Section 2: Standard algorithm

Original text: "The standard pixel hit triplet algorithm \cite{standard} first finds hit pairs, then for each pair it predicts the range of possible coordinates ($\phi$ and $z$ or $r$) of the third hit. The method uses a straight line through the inner hit and outer hit of the pair in order to get the $z/r$ prediction. The $\phi$ prediction is simply the corresponding value of the outer hit (Fig.~\ref{fig:comparison}). Tolerances are set such that they take into account the effects of multiple scattering."

Section 3: Cluster shapes

New text: "If the maximum and the minimum move in opposite directions or if there are empty pixels in the column, the cluster is not compatible with a single particle hit. (These type of clusters might be skipped, but it was not done in this analysis.) ... (The cluster might also be skipped if it is at the boundary of a silicon unit, but it was not done in this analysis.)"

Section 4.5: p_T bias

New text: "The reconstructed $\pt$ tends to the simulated one for higher $\pt$, their ratio converges to 1. There is an increasing bias with decreasing $\pt$ and for heavier particles. It is due to the energy loss of the particle which increases with decreasing momentum and scales with $p/m$ of the particle."

CMS Note AN-2006/101: Reconstruction of V0s and photon ...

Section 1.1: Effect of fakes on secondaries

New text: "It was shown that fake rate strongly depends on the luminosity and the single event multiplicity (see~\cite{lowpt}). If the hit removal is applied to events with different amount of pile-up, the higher luminosity events will loose more possibly valid hits due to their higher fake content. This is reflected in the smaller reconstruction efficiency of V0s and photon conversions (Section~\ref{sec:various})."

Section 2.1: Definition of truncated mean dE/dx

New text: "The energy loss of the particles, in this case the easily calculable truncated mean $\dedx$ is obtained as follows. The ADC values of the each pixel clusters are summed. The sum is divided by the path of the track inside the silicon. In the end there are three values corresponding to the three hits. They are ordered in increasing order $\DeDx_1 < \DeDx_2 < \DeDx_3$ and truncated by taking the average of the lower "half" of the numbers (50\% truncation), that is $\dedx = (\DeDx_1 + 0.5\DeDx_2)/1.5$. The resulted $\dedx$ value as function of total momentum is shown in Fig.~\ref{fig:vzeroDedx}."

Section 3.2: Invariant mass distributions

New text: "The $\PKzS$ is reconstructed with the resolution of 16~MeV/$c^2$ and at an average mass of 0.496~GeV/$c^2$. This agrees with the nominal mass value. At the same time $\PgL$ and $\PagL$ have a resolution of 6~MeV/$c^2$ and they are located at 1.114~GeV/$c^2$."

Section 3.3: Mass spectra at various conditions

New text: "The histograms of pile-up events have been normalized such that they correspond to the same number of produced particles as in the single p+p case."

Additional plots requested for PTDR Addendum on Heavy Ion Physics as updates to AN-2006/100

Slides for Physics Meeting on January 16, 2007:

Caption: Reconstructed raw p_T distribution of produced particles in 25 000 minimum bias p+p events at 14 TeV energy from Pythia generator (left); and in 125 central Pb+Pb events at 5.5 TeV/nucleon energy from Hydjet generator (right). (In order to roughly match the amount of produced particles in the p+p plot, the spectra have been scaled up from 25 events with a straightforward procedure.) Pions, kaons and protons are shown separately. Simulated spectra are given with dotted lines.

Original eps versions are here:

-- FerencSikler - 25 Sep 2006