Strange Particle Production in pp collisions at √s = 0.9 and 7 TeV

Abstract

The spectra of strange hadrons are measured in proton-proton collisions, recorded by the CMS experiment at the CERN LHC, at centre-of-mass energies of 0.9 and 7 TeV. The KS, Λ, and Ξ particles and their antiparticles are reconstructed from their decay topologies and the production rates are measured as functions of rapidity and transverse momentum, pT. The results are compared to other experiments and to predictions of the PYTHIA Monte Carlo program. The pT distributions are found to differ substantially from the PYTHIA results and the production rates exceed the predictions by up to a factor of three.

This paper can be retrieved from several sources including:

The presented results can also be found:

The paper is an updated version of an analysis originally released in the summer of 2010. The twiki for the old (superseded) analysis can be found at PhysicsResultsQCD10007PAS.

Figures from the paper are available below. Right click the image to obtain the .png version and left click to obtain the PDF version. In some cases, the description also contains a link to a root macro file.

Figure 1 left Figure 1 right
Figure 1. The π+π invariant mass distribution from data collected at √s = 0.9 TeV (left) and 7 TeV (right). The solid curves are fits to a double Gaussian and quadratic polynomial. The dashed curves show the quadratic background contribution


Figure 2 left Figure 2 right
Figure 2. The pπ (+c.c.) invariant mass distribution from data collected at √s = 0.9 TeV (left) and 7 TeV (right). The solid curves are fits to a double Gaussian and a background function given by AqB where q = M − (mp + mπ). The dashed curves show the background contribution.


Figure 3 left Figure 3 right
Figure 3. The Λπ (+c.c.) invariant mass distribution from data collected at √s = 0.9 TeV (left) and 7 TeV (right). The solid curves are fits to a double Gaussian and a background function given by Aq1/2 + Bq3/2 where q = MΛπ − (mΛ + mπ). The dashed curves show the background contribution.


Figure 4 left Figure 4 right
Figure 4. Total efficiencies, including acceptance, trigger and event selection, reconstruction and particle selection, and other decay modes, as a function of |y| (left) and pT (right) for KS, Λ, and Ξ produced promptly in the range |y|<2. Error bars come from Monte Carlo statistics.


Figure 5 left Figure 5 middle Figure 5 right
Figure 5. KS, Λ, and Ξ corrected decay time distributions at √s =0.9 and 7 TeV. The values of the lifetimes, derived from a fit with an exponential function (solid line), are shown in the legend along with the world-average value. The error bars and uncertainties on the lifetimes refer to the statistical uncertainty only.


Figure 6 top-left Figure 6 top-right
Figure 6 middle-left Figure 6 middle-right
Figure 6 bottom-left Figure 6 bottom-right
Figure 6. KS (top), Λ (middle), and Ξ (bottom) production per NSD event versus |y| (left) and pT (right). The inner vertical error bars (when visible) show the statistical uncertainties, the outer the statistical and point-to-point systematic uncertainties summed in quadrature. The normalization uncertainty is shown as a band. Three Pythia predictions are overlaid on the |y| distributions. The solid curves in the pT distributions are fits to the Tsallis function as described in the paper. Root macros are available for the KS rapidity distribution, the KS pT distribution, Λ rapidity distribution, the Λ pT distribution, the Ξ rapidity distribution, and the Ξ pT distribution.


Figure 7
Figure 7. Ratio of MC production to data production of KS (top), Λ (middle), and Ξ (bottom) versus pT at √s = 0.9 TeV (open symbols) and √s = 7 TeV (filled symbols). Results are shown for three Pythia predictions at each centre-of-mass energy. To reduce clutter, the uncertainty, shown as a band, is included for only one of the predictions (D6T) at each energy. This uncertainty includes the statistical and point-to-point systematic uncertainties added in quadrature but does not include the normalization systematic uncertainty. Figure is available in root macro format.


Figure 8 left Figure 8 right
Figure 8. N(Λ)/N(KS) (left) and N(Ξ)/N(Λ) (right) in NSD events versus pT. The inner vertical error bars (when visible) show the statistical uncertainties, the outer the statistical and all systematic uncertainties summed in quadrature. Results are shown for three Pythia predictions at each centre-of-mass energy. The plots are available in root macro format: left plot and right plot.


Figure 9
Figure 9. KS (top), Λ (middle), and Ξ (bottom) production per event versus pT. The error bars on the CMS results show the combined statistical, point-to-point systematic, and normalization systematic uncertainties. The error bars on the CDF (hep-ex/1101.2996), ALICE (hep-ex/1012.3257), and STAR (PRC75,064901,2007) results show the combined statistical and systematic uncertainties. The CMS, CDF, and STAR results are normalized to NSD events while the ALICE results are normalized to all inelastic events. Figure is available in root macro format.


Figure 10
Figure 10. Ratio of Λ to KS production (top) and Ξ to Λ production (bottom) versus pT. The CMS, ALICE (hep-ex/1012.3257), and STAR (PRC75,064901,2007) error bars include statistical and systematic uncertainties. The CDF error bars include the statistical uncertainties for N(Λ)/N(KS) (PRD72,052001,2005) and the statistical and systematic uncertainties for N(Ξ)/N(Λ) (hep-ex/1101.2996). The CDF N(Λ)/N(KS) bin sizes are doubled to reduce fluctuations. For experiments in which the binning for Λ and Ξ is different (ALICE and STAR), bins are merged to provide common bin ranges in the N(Ξ)/N(Λ) distribution. Figure is available in root macro format.


Figure 11
Figure 11. Average pT for KS (top), Λ (middle), and Ξ (bottom), as a function of the centre-of-mass energy. The CMS measurements are for |y| < 2. The other results are from UA5 in ZPC41,179,1988; PhysRept154,247,1987; NPB328,36,1989; NPB258,505,1985; PLB151,309,1985 (ppbar collisions covering |y| < 2.5, |y| < 2, and |y| < 3 for KS, Λ, and Ξ, respectively), E735 in PRD46,2772,1992 (ppbar collisions using tracks with -0.36<η<1.0), STAR in PRC75,064901,2007 (pp collisions covering |y|<0.5), and ALICE in hep-ex/1012.3257 (pp collisions covering |y| < 0.75 for KS and Λ and |y| < 0.8 for Ξ).Some points have been slightly offset from the true energy to improve visibility. The vertical bars indicate the statistical and systematic uncertainties (when available) summed in quadrature. Figure is available in root macro format.


Figure 12
Figure 12. The central rapidity production rate for KS (top), Λ (middle), and Ξ (bottom), as a function of the centre-of-mass energy. The previous results are from UA5 in ZPC41,179,1988; NPB258,505,1985; (ppbar), CDF in PRD40,3791,1989 (ppbar), STAR in PRC75,064901,2007 (pp), and ALICE in hep-ex/1012.3257 (pp). The CMS, UA5, and STAR results are normalized to NSD events. The CDF results are normalized to events passing their trigger and event selection defined chiefly by activity in both sides of the detector, at least four tracks, and a primary vertex. The ALICE results are normalized to all inelastic events. Some points have been slightly offset from the true energy to improve visibility. The vertical bars indicate the statistical uncertainties for the UA5 and CDF results and the combined statistical and systematic uncertainties for the CMS, ALICE, and STAR results. Figure is available in root macro format.


Figure 13 left Figure 13 right
Figure 13. The production ratios N(Λ)/N(KS) (left) and N(Ξ)/N(Λ) (right) in NSD events versus |y|. The inner vertical error bars (when visible) show the statistical uncertainties, the outer the statistical and all systematic uncertainties summed in quadrature. Results are shown for three Pythia predictions at each centre-of-mass energy. The plots are available in root macro format: left plot and right plot.

-- KevinStenson - 20-Apr-2011

Topic attachments
I Attachment History Action Size Date Who Comment
PDFpdf XiMass_selected_data_7.pdf r1 manage 10.2 K 2011-04-20 - 23:17 KevinStenson Cascade mass plot at 7 TeV
PNGpng XiMass_selected_data_7.png r1 manage 27.4 K 2011-04-20 - 23:15 KevinStenson Cascade mass plot at 7 TeV
PDFpdf XiMass_selected_data_900.pdf r1 manage 10.4 K 2011-04-20 - 23:17 KevinStenson Cascade mass plot at 0.9 TeV
PNGpng XiMass_selected_data_900.png r1 manage 30.2 K 2011-04-20 - 23:15 KevinStenson Cascade mass plot at 0.9 TeV
PDFpdf averagept_vs_roots.pdf r1 manage 7.4 K 2011-04-21 - 19:59 KevinStenson Average pT of Kshort, Lambda, and Cascade vs centre-of-mass energy
PNGpng averagept_vs_roots.png r1 manage 34.5 K 2011-04-21 - 19:58 KevinStenson Average pT of Kshort, Lambda, and Cascade vs centre-of-mass energy
PDFpdf dNdy_vs_roots.pdf r1 manage 6.9 K 2011-04-21 - 20:00 KevinStenson Midrapidity production vs centre-of-mass energy
PNGpng dNdy_vs_roots.png r1 manage 33.0 K 2011-04-21 - 20:00 KevinStenson Midrapidity production vs centre-of-mass energy
C source code filec fig10.C r1 manage 39.7 K 2011-04-21 - 22:51 KevinStenson Production ratios vs pT compared to other experiments
C source code filec fig11.C r1 manage 31.6 K 2011-04-21 - 22:51 KevinStenson Average pT of Kshort, Lambda, and Cascade vs centre-of-mass energy
C source code filec fig12.C r1 manage 22.9 K 2011-04-21 - 22:52 KevinStenson Midrapidity production vs centre-of-mass energy
C source code filec fig13_left.C r1 manage 31.1 K 2011-04-21 - 22:52 KevinStenson Lambda/Kshort vs rapidity
C source code filec fig13_right.C r1 manage 32.4 K 2011-04-21 - 22:53 KevinStenson Cascade/Lambda vs rapidity
C source code filec fig6_botleft.C r1 manage 33.1 K 2011-04-21 - 22:47 KevinStenson Cascade rapidity distribution
C source code filec fig6_botright.C r1 manage 245.0 K 2011-04-21 - 22:47 KevinStenson Cascade pT distribution
C source code filec fig6_midleft.C r1 manage 32.5 K 2011-04-21 - 22:48 KevinStenson Lambda rapidity distribution
C source code filec fig6_midright.C r1 manage 250.7 K 2011-04-21 - 22:48 KevinStenson Lambda pT distribution
C source code filec fig6_topleft.C r1 manage 31.9 K 2011-04-21 - 22:48 KevinStenson Kshort rapidity distribution
C source code filec fig6_topright.C r1 manage 236.2 K 2011-04-21 - 22:48 KevinStenson Kshort pT distribution
C source code filec fig7.C r1 manage 194.2 K 2011-04-21 - 22:49 KevinStenson Ratio of MC to data pT distributions for Kshort, Lambda, and Cascade
C source code filec fig8_left.C r1 manage 61.3 K 2011-04-21 - 22:49 KevinStenson Lambda/Kshort vs pT
C source code filec fig8_right.C r1 manage 59.6 K 2011-04-21 - 22:50 KevinStenson Cascade/Lambda vs pT
C source code filec fig9.C r1 manage 52.9 K 2011-04-21 - 22:51 KevinStenson pT distributions compared to other experiments
PDFpdf ks_yield_data_7000.pdf r1 manage 15.5 K 2011-04-20 - 23:16 KevinStenson Kshort mass plot at 7 TeV
PNGpng ks_yield_data_7000.png r1 manage 29.1 K 2011-04-20 - 23:13 KevinStenson Kshort mass plot at 7 TeV
PDFpdf ks_yield_data_900.pdf r1 manage 15.5 K 2011-04-20 - 23:15 KevinStenson Kshort mass plot at 0.9 TeV
PNGpng ks_yield_data_900.png r1 manage 29.7 K 2011-04-20 - 23:12 KevinStenson Kshort mass plot at 0.9 TeV
PDFpdf kslife_sum_log.pdf r1 manage 16.1 K 2011-04-20 - 23:49 KevinStenson Kshort lifetime distribution
PNGpng kslife_sum_log.png r1 manage 30.2 K 2011-04-20 - 23:48 KevinStenson Kshort lifetime distribution
PDFpdf kspt_cor_data_perevt_log.pdf r1 manage 17.5 K 2011-04-21 - 19:46 KevinStenson Kshort pT distribution
PNGpng kspt_cor_data_perevt_log.png r1 manage 35.7 K 2011-04-21 - 19:46 KevinStenson Kshort pT distribution
PDFpdf ksy_cor_datamc_perevt.pdf r1 manage 6.2 K 2011-04-21 - 19:45 KevinStenson Kshort rapidity distribution
PNGpng ksy_cor_datamc_perevt.png r1 manage 29.2 K 2011-04-21 - 19:45 KevinStenson Kshort rapidity distribution
PDFpdf lamOverKsMC_pt_sys.pdf r1 manage 10.3 K 2011-04-21 - 19:55 KevinStenson Lambda/Kshort vs pT
PNGpng lamOverKsMC_pt_sys.png r1 manage 41.3 K 2011-04-21 - 19:54 KevinStenson Lambda/Kshort vs pT
PDFpdf lamOverKsMC_y_sys.pdf r1 manage 6.1 K 2011-04-21 - 21:06 KevinStenson Lambda/Kshort vs rapidity
PNGpng lamOverKsMC_y_sys.png r1 manage 22.6 K 2011-04-21 - 21:05 KevinStenson Lambda/Kshort vs rapidity
PDFpdf lam_yield_data_7000.pdf r1 manage 13.2 K 2011-04-20 - 23:17 KevinStenson Lambda mass plot at 7 TeV
PNGpng lam_yield_data_7000.png r1 manage 30.2 K 2011-04-20 - 23:14 KevinStenson Lambda mass plot at 7 TeV
PDFpdf lam_yield_data_900.pdf r1 manage 13.3 K 2011-04-20 - 23:16 KevinStenson Lambda mass plot at 0.9 TeV
PNGpng lam_yield_data_900.png r1 manage 29.3 K 2011-04-20 - 23:14 KevinStenson Lambda mass plot at 0.9 TeV
PDFpdf lamlife_sum_log.pdf r1 manage 17.0 K 2011-04-20 - 23:50 KevinStenson Lambda lifetime distribution
PNGpng lamlife_sum_log.png r1 manage 32.5 K 2011-04-20 - 23:49 KevinStenson Lambda lifetime distribution
PDFpdf lampt_cor_data_perevt_log.pdf r1 manage 18.2 K 2011-04-21 - 19:49 KevinStenson Lambda pT distribution
PNGpng lampt_cor_data_perevt_log.png r1 manage 36.2 K 2011-04-21 - 19:49 KevinStenson Lambda pT distribution
PDFpdf lamy_cor_datamc_perevt.pdf r1 manage 6.4 K 2011-04-21 - 19:47 KevinStenson Lambda rapidity distribution
PNGpng lamy_cor_datamc_perevt.png r1 manage 28.2 K 2011-04-21 - 19:47 KevinStenson Lambda rapidity distribution
PDFpdf pt_datadata_comp.pdf r1 manage 18.9 K 2011-04-21 - 19:57 KevinStenson pT distributions compared to other experiments
PNGpng pt_datadata_comp.png r1 manage 49.2 K 2011-04-21 - 19:56 KevinStenson pT distributions compared to other experiments
PDFpdf pt_datamc_comp.pdf r1 manage 17.5 K 2011-04-21 - 19:54 KevinStenson Ratio of MC to data pT distributions for Kshort, Lambda, and Cascade
PNGpng pt_datamc_comp.png r1 manage 63.5 K 2011-04-21 - 19:53 KevinStenson Ratio of MC to data pT distributions for Kshort, Lambda, and Cascade
PDFpdf ptrat_datadata_comp.pdf r1 manage 17.0 K 2011-04-21 - 19:57 KevinStenson Production ratios vs pT compared to other experiments
PNGpng ptrat_datadata_comp.png r1 manage 43.0 K 2011-04-21 - 19:57 KevinStenson Production ratios vs pT compared to other experiments
PDFpdf v0effpt_sum.pdf r1 manage 10.2 K 2011-04-20 - 23:47 KevinStenson Efficiency vs pT for Kshort, Lambda, and Cascade
PNGpng v0effpt_sum.png r1 manage 28.6 K 2011-04-20 - 23:46 KevinStenson Efficiency vs pT for Kshort, Lambda, and Cascade
PDFpdf v0effy_sum.pdf r1 manage 6.3 K 2011-04-20 - 23:48 KevinStenson Efficiency vs |y| for Kshort, Lambda, and Cascade
PNGpng v0effy_sum.png r1 manage 22.0 K 2011-04-20 - 23:47 KevinStenson Efficiency vs |y| for Kshort, Lambda, and Cascade
PDFpdf xiOverLamMC_pt_sys.pdf r1 manage 9.8 K 2011-04-21 - 19:55 KevinStenson Cascade/Lambda vs pT
PNGpng xiOverLamMC_pt_sys.png r1 manage 36.9 K 2011-04-21 - 19:55 KevinStenson Cascade/Lambda vs pT
PDFpdf xiOverLamMC_y_sys.pdf r1 manage 6.4 K 2011-04-21 - 21:07 KevinStenson Cascade/Lambda vs rapidity
PNGpng xiOverLamMC_y_sys.png r1 manage 24.8 K 2011-04-21 - 21:06 KevinStenson Cascade/Lambda vs rapidity
PDFpdf xilife_sum_log.pdf r1 manage 14.1 K 2011-04-20 - 23:51 KevinStenson Cascade lifetime distribution
PNGpng xilife_sum_log.png r1 manage 29.8 K 2011-04-20 - 23:50 KevinStenson Cascade lifetime distribution
PDFpdf xipt_cor_data_perevt_log.pdf r1 manage 18.4 K 2011-04-21 - 19:51 KevinStenson Cascade pT distribution
PNGpng xipt_cor_data_perevt_log.png r1 manage 38.4 K 2011-04-21 - 19:50 KevinStenson Cascade pT distribution
PDFpdf xiy_cor_datamc_perevt.pdf r1 manage 6.6 K 2011-04-21 - 19:50 KevinStenson Cascade rapidity distribution
PNGpng xiy_cor_datamc_perevt.png r1 manage 27.8 K 2011-04-21 - 19:50 KevinStenson Cascade rapidity distribution
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