NotesChanges < CMS

---+++!!Changes made after the Physics Meeting

| *Author* | *Title* | *Files* | *Version* | *Figures* |
| Ferenc Siklér | Reconstruction of low p<sub>T</sub> charged particles with the pixel detector | [[%ATTACHURL%/LowPtTracking.pdf][%ICON{pdf}%]] | 17 Oct | [[%ATTACHURL%/LowPtTracking.tgz][%ICON{zip}%]] |
| Ferenc Siklér | Reconstruction of V0s and photon conversions with the pixel detector | [[%ATTACHURL%/VzeroReconstruction.pdf][%ICON{pdf}%]] | 17 Oct | [[%ATTACHURL%/VzeroReconstruction.tgz][%ICON{zip}%]] |

%TOC%

---++++General: Magnetic field

The plot shows the B<sub>z</sub> component as function of z coordinate at the beam-line from OSCAR_3_9_8.

%ATTACHURL%/oscarMagneticField.png

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<sub>T</sub> was smaller and was expected to be around 0.983 of the simulated value, explaining the p<sub>T</sub> bias and the problems with the invariant mass spectra. The corresponding plots are changed.

---++++CMS Note AN-2006/100: Reconstruction of low p<sub>T</sub> 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<sub>T</sub> 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."

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

Slides for Physics Meeting on January 16, 2007: [[%ATTACHURL%/Sikler_update.pdf][%ICON{pdf}%]]

| %ATTACHURL%/ppmulti.png | %ATTACHURL%/PbPbmulti_scaled.png |

*Caption:* Reconstructed raw p<sub>T</sub> 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: [[%ATTACHURL%/ppmulti.eps][%ICON{ps}%]] [[%ATTACHURL%/PbPbmulti_scaled.eps][%ICON{ps}%]]


-- Main.FerencSikler - 25 Sep 2006

Attachments

Topic attachments
I	Attachment	History	Action	Size	Date	Who
eps	PbPbmulti.eps	r5 r4 r3 r2 r1	manage	28.1 K	2007-01-04 - 22:13	FerencSikler
png	PbPbmulti.png	r5 r4 r3 r2 r1	manage	12.5 K	2007-01-04 - 22:13	FerencSikler
png	PbPbmulti_per.png	r2 r1	manage	12.9 K	2006-12-19 - 05:57	FerencSikler
png	ppmulti_per.png	r2 r1	manage	12.5 K	2006-12-19 - 05:58	FerencSikler

This topic: CMS > CMSTrackerSoftware > NotesInPreparation > NotesChanges
Topic revision: r18 - 2007-01-14 - FerencSikler

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