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-- TomasHreus - 23-Jul-2012

Measurement of Strange Particle Production in Underlying Events in proton-proton collisions at $\sqrt{\rm{s}} = 7 \;\rm{TeV}$

Contents:

Abstract

Measurements of the production of $K_S^0$, $\Lambda$ and ${\bar{\Lambda}}$ particles in the underlying activity of events with a $p_T$ scale ranging from 1 to 50 GeV/c are made in proton-proton collisions at $\sqrt{s}$ = 7 TeV, using data collected by the CMS experiment at the LHC. Particle production is studied with reference to the azimuthal direction of the leading set of charged particles forming a “track-jet”. A growth in the average multiplicity and average scalar $p_T$ sum of ${\rm{K}}_{\rm{S}}^{\rm{0}}$ and $\Lambda$ + ${\bar{\Lambda}}$, with $p_T^{\rm{K_S^0}}$ > 0.6 GeV/c and $p_T^{\Lambda,\bar{\Lambda}}$ > 1.5 GeV/c, within |$\eta$| < 2 and azimuthal direction transverse to that of the leading track-jet, is observed with increasing scale given by the leading track-jet $p_T$. This growth is followed by a saturation at large values of the scale. The growth and saturation are very similar to what is observed for charged primary particles. The average activity of the underlying event in primary $K_S^0$ mesons and $\Lambda$ baryons is compared to recent tunes of the PYTHIA Monte Carlo generator. The PYTHIA simulations underestimate the activity by 15-30% for$K_S^0$ mesons and by about 50% for $\Lambda$ + ${\bar{\Lambda}}$ baryons.

Kinematic fit input variables

Figure Caption
mass_k0.png mass_laal.png Distributions of invariant mass and invariant mass pulls, for the most probable particle type hypothesis determined by the kinematic fit. Backgrounds (red: misidentified $V^0$; green: non-primary $\Lambda$ or ${\bar{\Lambda}}$ from $\Xi$, $\Omega$ and $\Sigma$ cascade decays; grey: other sources) and signal (yellow) are shown as predicted by PYTHIA6 D6T. The sum of the simulated signal and background distributions is normalized to data.
masspull_k0_log.png masspull_laal_log.png
pvdist_k0_log.png pvdist_laal_log.png Distributions of the signed impact parameter with respect to the primary vertex and pulls of this variable, for the most probable particle type hypothesis determined by the kinematic fit. Backgrounds (red: misidentified $V^0$; green: non-primary $\Lambda$ or ${\bar{\Lambda}}$ from $\Xi$, $\Omega$ and $\Sigma$ cascade decays; grey: other sources) and signal (yellow) are shown as predicted by PYTHIA6 D6T. The sum of the simulated signal and background distributions is normalized to data.
pvdistsig_k0_log.png pvdistsig_laal_log.png

Uncorrected rates

Figure Caption
rates_uncorr_dphi_datamc.png Uncorrected average rate of selected V0 candidates per event, per degree and per unit pseudorapidity within -2 < $\eta$ < 2, in pp collisions at $\sqrt{s}$ = 7 TeV as a function of angular distance $\Delta\phi$ to the leading track-jet. Data and simulations of minimum bias events with different PYTHIA tunes are shown for uncorrected track-jet $p_T$ > 1 GeV/c. Top: $K_S^0$ with $p_T$ > 600MeV/c; bottom: $\Lambda$ + ${\bar{\Lambda}}$ with $p_T$ > 1.5 GeV/c.

Results

Figure Caption
rates_k0_datamc.png rates_laal_datamc.png Fully corrected average multiplicity per unit of pseudorapidity and per radian in the transverse region (-2 < $\eta$ < 2, $60^o$ < $\Delta\phi$ < $120^o$), as a function of the $p_T$ of the leading trackjet: (left) $K_S^0$ with $p_T$ > 0.6 GeV/c; (right) $\Lambda$ + ${\bar{\Lambda}}$ with $p_T$ > 1.5 GeV/c. Predictions of PYTHIA tunes are compared to the data. For data, the statistical uncertainties (error bars) and sum of statistical and systematic uncertainties (error band) are distinguished, while for simulations the total uncertainty is only shown for PYTHIA6 tune Z2 for clarity.
sumpt_k0_datamc.png sumpt_laal_datamc.png Fully corrected average scalar $p_T$ sum per unit of pseudorapidity and per radian in the transverse region (-2 < $\eta$ < 2, $60^o$ < $\Delta\phi$ < $120^o$), as a function of the $p_T$ of the leading trackjet: (left) $K_S^0$ with $p_T$ > 0.6 GeV/c; (right) $\Lambda$ + ${\bar{\Lambda}}$ with $p_T$ > 1.5 GeV/c. Predictions of PYTHIA tunes are compared to the data. For data, the statistical uncertainties (error bars) and sum of statistical and systematic uncertainties (error band) are distinguished, while for simulations the total uncertainty is only shown for PYTHIA6 tune Z2 for clarity.
k0_pt_gen_datamc.png laal_pt_gen_datamc.png Corrected $V^0$ $p_T$ distributions in the transverse region (-2 < $\eta$ < 2, $60^o$ < $\Delta\phi$ < $120^o$) for events with a leading track-jet $p_T$ > 3 GeV/c, compared to predictions from different PYTHIA tunes. Left: $K_S^0$ ; right: $\Lambda$ + ${\bar{\Lambda}}$. Error bars for data include both statistical and systematic uncertainties. Simulations are normalized to the first $p_T$ bin measured in data. Normalization factors are given in parentheses.
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PDFpdf k0_pt_gen_datamc.pdf r1 manage 23.3 K 2012-07-24 - 09:59 TomasHreus  
PNGpng k0_pt_gen_datamc.png r1 manage 21.3 K 2012-07-24 - 09:59 TomasHreus  
PDFpdf laal_pt_gen_datamc.pdf r1 manage 23.0 K 2012-07-24 - 09:59 TomasHreus  
PNGpng laal_pt_gen_datamc.png r1 manage 21.6 K 2012-07-24 - 09:59 TomasHreus  
PDFpdf mass_k0.pdf r1 manage 18.8 K 2012-07-24 - 09:51 TomasHreus  
PNGpng mass_k0.png r1 manage 20.4 K 2012-07-24 - 09:41 TomasHreus  
PDFpdf mass_laal.pdf r1 manage 18.3 K 2012-07-24 - 09:51 TomasHreus  
PNGpng mass_laal.png r1 manage 20.7 K 2012-07-24 - 09:41 TomasHreus  
PDFpdf masspull_k0_log.pdf r1 manage 18.1 K 2012-07-24 - 09:51 TomasHreus  
PNGpng masspull_k0_log.png r1 manage 15.4 K 2012-07-24 - 09:41 TomasHreus  
PDFpdf masspull_laal_log.pdf r1 manage 18.2 K 2012-07-24 - 09:51 TomasHreus  
PNGpng masspull_laal_log.png r1 manage 15.6 K 2012-07-24 - 09:41 TomasHreus  
PDFpdf pvdist_k0_log.pdf r1 manage 17.3 K 2012-07-24 - 09:51 TomasHreus  
PNGpng pvdist_k0_log.png r1 manage 18.2 K 2012-07-24 - 09:41 TomasHreus  
PDFpdf pvdist_laal_log.pdf r1 manage 20.1 K 2012-07-24 - 09:52 TomasHreus  
PNGpng pvdist_laal_log.png r1 manage 20.1 K 2012-07-24 - 09:41 TomasHreus  
PDFpdf pvdistsig_k0_log.pdf r1 manage 18.3 K 2012-07-24 - 09:51 TomasHreus  
PNGpng pvdistsig_k0_log.png r1 manage 17.5 K 2012-07-24 - 09:41 TomasHreus  
PDFpdf pvdistsig_laal_log.pdf r1 manage 19.4 K 2012-07-24 - 09:51 TomasHreus  
PNGpng pvdistsig_laal_log.png r1 manage 18.5 K 2012-07-24 - 09:41 TomasHreus  
PDFpdf rates_k0_datamc.pdf r1 manage 16.9 K 2012-07-24 - 09:59 TomasHreus  
PNGpng rates_k0_datamc.png r1 manage 20.1 K 2012-07-24 - 09:59 TomasHreus  
PDFpdf rates_laal_datamc.pdf r1 manage 17.3 K 2012-07-24 - 10:00 TomasHreus  
PNGpng rates_laal_datamc.png r1 manage 20.3 K 2012-07-24 - 09:59 TomasHreus  
PDFpdf rates_uncorr_dphi_datamc.pdf r1 manage 30.7 K 2012-07-24 - 10:00 TomasHreus  
PNGpng rates_uncorr_dphi_datamc.png r1 manage 24.3 K 2012-07-24 - 09:59 TomasHreus  
PDFpdf sumpt_k0_datamc.pdf r1 manage 17.1 K 2012-07-24 - 10:24 TomasHreus  
PNGpng sumpt_k0_datamc.png r1 manage 20.9 K 2012-07-24 - 10:23 TomasHreus  
PDFpdf sumpt_laal_datamc.pdf r1 manage 17.0 K 2012-07-24 - 10:24 TomasHreus  
PNGpng sumpt_laal_datamc.png r1 manage 20.9 K 2012-07-24 - 10:23 TomasHreus  
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