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Summary of K*(892) analysis, PhD thesis C. Hoehne

http://archiv.ub.uni-marburg.de/diss/z2003/0627/

CERN EDMS Id 816035

• analyzed data samples

• method, corrections

• results for pp

• results for CC, SiSi

• Appendix: Comparison of pion and kaon analysis to NA49-pp-group

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Analyzed datasets for pp collisions:

Corrections in order to extract yields for minimum bias p+p collisions (basically corresponding to yields for inelastic pp-collisions):

• multiplicity dependent scaling of events in order to correct for trigger bias

• scaling in order to correct for „0-track events“ in the N49 acceptance

• global empty target run subtraction

(For comparison to results with more complicated and detailed corrections see Appendix.)

In addition: study of p+p events at different inelasticity

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Analyzed datasets for CC and SiSi collisions:

• C target thickness of 3.05 mm corresponds to 2.4% interaction length, Si target thickness of 5.02 mm to 4.4%.

• centrality selection was: (15.3 ± 2.4)% for C+C and (12.2 ± 1.8)% for SiSi

• Number of wounded nucleons (VENUS): 14 ± 2 for C+C, 37 ± 3 for SiSi

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Fraction of C, N and Al, Si, P in beam selection:

• C – N intensity ratio: 69:31

• Al – Si – P intensity ratio: 35:41:24

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K*(892) extracted using the invariant mass method

• invariant mass calculated for real and mixed events

• distribution normalized to number of entries

• subtracted

• yield extraction by comparison to simulation

• undershoot structure due to mixing of K, pi from K* from different events – well described by simulation!

K*(892)

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Investigation of correlations due to higher lying resonances, in particular the K*2(1430)

• higher lying resonances expected (see literature) with exponential dependence of the yield on the mass

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Investigation of correlations due to higher lying resonances, in particular the K*2(1430)

• implement in simulation and investigate the effect

• only K*2(1430) shows a small effect in the K*(892) invariant mass spectrum

• baseline (solid line) pulled down in comparison to simulation without (dashed line)

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Investigation of correlations due to higher lying resonances, in particular the K*2(1430)

• simulations performed with different fractions of the K*2(1430) compared to the K*(892)

• best fit value compares well to expectation from the exponential dependence of the yield on the mass

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For the extraction of the yield K*2(1430) is taken into account

• integrated spectra

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For the extraction of the yield K*2(1430) is taken into account

• example spectra for more restricted kinematical bins as used for the extraction of pt- and y-spectra

• phantastic quality of K*(892) signal in pp data!

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Investigation of reflections from other resonances in the invariant mass spectrum

• misidentification of kaons and pions due to selection by dE/dx in a measured band around the Bethe-Bloch value

• if e.g. a proton from a (1232) decay is misidentified as K and combined with the partner pion, correlated structures appear in the background

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Investigation of reflections from other resonances in the invariant mass spectrum

• these reflections generate distortions in the remaining background after the event-mix subtraction

• difficult to quantify

• investigate by changing selection criteria

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Investigation of reflections from other resonances in the invariant mass spectrum

• pp data rather insensitive – always high quality

• strong effect seen for CC, SiSi

• with strict selection criteria (and reduced misidentification) the remaining background clearly improves

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Selection criteria of kaons and pions:

• momentum range (4-50) GeV/c for a reasonable dE/dx identification

• upper pt-cut of 1.5 GeV/c (pp) or 1 GeV/c (CC, SiSi), because for this range fitted dE/dx positions were available

• lower cut on the number of measured points on track Npoints, standard = 30, best K* results in CC, SiSifor Npoints > 100

• particle identification by selecting tracks from a fixed c∙dE/dx window around the mean dE/dx value from fits, standard c=1.5, best K* results in CC, SiSi for C=1.5 for pions and (-0.5, 1.5) ∙dE/dx for kaons

• cuts are varied for the extraction of systematic errors

• (same for subtraction of remaining background in the invariant mass signal if necessary)

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Extraction of yields

• adjust a simulation to the measured invariant mass spectrum (2-minimization), extract yield from scaling factor d: Nsignal = d∙Nsim

• F = braching ratio

• pid = particle identification probabability from dE/dx cut

• as statistics is not sufficient for a binning in y and pt, 1/y and 1/pt are replaced by fy anf fpt if integrating over y or pt respectively; fy and fpt are then extrapolation factors from the used y- and pt-range to the full y-range or infinity

• the simulation contains corrections for the geometrical acceptance (including the Npoints cut) and kaon decay in flight

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K*(892) acceptance

• no embedding simulations done as efficiency losses due to track density are negligible for pp, CC, and SiSi interactions

Note: underlying acceptance corrections for pions and kaons, and inflight-decay corrections for kaons also used for the extraction of pion and kaon yields using dE/dx fits

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Kinematic distributions and yields in minimum bias p+p collisions

• determination of the mass of K*(892) (width fixed to 50 MeV)

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Kinematic distributions and yields in minimum bias p+p collisions

• transverse momentum distributions

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Kinematic distributions and yields in minimum bias p+p collisions

• rapidity distributions

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Kinematic distributions and yields in minimum bias p+p collisions

• systematic errors determined by variation of analysis cuts

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Kinematic distributions and yields in minimum bias p+p collisions

• systematic errors determined by variation of analysis cuts

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Summary table of results

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Comparison to other experiments

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Comparison to other experiments

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Integrated yields in C+C and Si+Si collisions

• statistics lacking for the extraction of kinematic distributions

• estimate of total yield, assume rapidity distribution as for K, pt-spectra (slope) as for -meson

• extract number of K*(892) in large acceptance: 3.1 < y < 4.7 and pt < 1.5 GeV/c

• appr. 6% error of extrapolation to full acceptance taking unknown distributions into account

• variation of cuts and background estimate for systematic errors: 15% at most

• statistical errors 15-20%

• combined error 30%

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K*(892)

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K*(892)

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Summary of results:

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Appendix:

Comparison of my pp-analysis with results from the NA49-pp-group

Multiplicities of pions and kaons:

NA49 Claudia Difference

+ 3.018 3.07 +1.7%

- 2.360 2.33 -1.3%

K+ 0.227 0.238 +4.8%

K- 0.130 0.138 +6.2%

Claudia: systematic errors of 5% on and 10% on K

NA49: systematic errors on K are given xF dependent: 2.2% … 12.2 %

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NA49 pp data

Difference of sophisticated empty target run subtraction and trigger bias correction method to an (older) method applying multiplicity dependent cross section weighting factors or even simple overall scaling

→ estimate systematic error due to this correction

-production

• published data: Eur. Phys. J. C 45, 343–381 (2006)

→ sophisticated trigger bias correction and empty target run subtraction

• PhD thesis, C. Höhne, http://archiv.ub.uni-marburg.de/diss/z2003/0627/

→ multiplicity dependent scaling of events in order to correct for trigger bias, global empty target run subtraction

4 yields:

EPJC <+> = 3.018 <-> = 2.360

PhD <+> = 3.07±0.01 ± 0.15 <-> = 2.33 ±0.01 ±0.12

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pt- / mt ditribution at midrapidity

PhD

• T at midrapidity (2.77 < y < 3.23), fitted to data points from 0.3 GeV < (mt-m0) < 1.3 GeV

+ T = 167±1±10 MeV

- T = 166±1.5±10 MeV

EPJC

• see figure

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numerical values not given in the paper

no direct comparison possible

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y-distribution

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production

• published data: Physics Letters B 491 (2000) 59–66

→ no correction for y- and mt-distribution (if I remember correctly)

→ 4 yield scaled down by ratio of minimum bias pp event trigger (28.9 mb) and known inelastic pp cross section (31.7 mb)

• PhD thesis, C. Höhne, http://archiv.ub.uni-marburg.de/diss/z2003/0627/

→ multiplicity dependent scaling of events in order to correct for trigger bias, global empty target run subtraction

4 yields

PLB <> = 0.012±0.0015

PhD <> = 0.0129±0.0002±0.0013

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mt-distribution

PhD

(y-range 2.9 – 4)

T = 164±4±10 MeV

PLB

(y-range: 2.9 – 4.4)

T = 169±17 MeV

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y-distribution

PLB

y = 0.89 ± 0.06

PhD

y = 0.95 ± 0.02 ± 0.04

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Comparison to other experiments