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An estimate of the K + cross section in the reaction C+C @ 2 AGeV

An estimate of the K + cross section in the reaction C+C @ 2 AGeV. A. Sadovsky Forschungszentrum Rossendorf, Dresden HADES PID meeting Ř e ž 12-14 th December 2005. Motivation Selection of K + and π ± mesons Registration efficiency correction Relative cross section normalisation

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An estimate of the K + cross section in the reaction C+C @ 2 AGeV

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  1. An estimate of the K+ cross sectionin the reaction C+C @ 2 AGeV A. Sadovsky Forschungszentrum Rossendorf, Dresden HADES PID meeting Řež 12-14th December 2005 • Motivation • Selection of K+and π±mesons • Registration efficiency correction • Relative cross section normalisation • Influence of trigger conditions • Comparison with KaoS (minimum bias conditions)

  2. Selection of K+(MdcSegment Fit and Vertex cuts) HMdcSeg1 χ2cut HMdcSeg2 χ2cut RMdcSeg1 [mm] RMdcSeg1 [mm] ZMdcSeg1 [mm] ZMdcSeg1 [mm]

  3. Selection of K+ (matching with META and cuts on β2·dE/dx) Counts MDC-META matching cut

  4. Selection of K+(Runge Kutta χ2-cut and p vs. m2-plot) All cuts, but RK remove ≈80% of MetaMatch track candidates χ2RK cut remove ≈30% from left over After all quality cuts only about 15% left to be used for K+ selection see below: No cuts After all cuts, but χ2RK After all cuts and χ2RK

  5. Selection of K+(slices with different momentum)

  6. Registration efficiency correction for K+ (simulation) Pluto: 10*106 only K+tracks (T=88 MeV, βr=0.3) hGeant with realistic settings for Nov02 DST with Hydra: Nov02/gen3-like Analysis, K+ cuts (micro DST‘s) like for real data

  7. p [MeV/c] (Sector 0) ° Registration efficiency correction for K+(TOF/TOFINO) Ratio of K+ counts distribution after Pluto /PGHAC (Pluto+Geant+Hydra+Analysis+Cuts)

  8. Selected K+ Counts Nov02/gen3 DST 166 106 events 3686 tracks identified as K+ in S0+S3 Background contribution less than 30% i.e. N(K+)/N(bg) = 2562/1124 = 2.3 Average significance = 42.2 N(K+) =124 N(bg) = 31 m [MeV/c2]

  9. Selection of π±(same quality cuts as for K+) • π±PID selection: • only for TOF region • graphical cut • 300<p<1000 [MeV/c] • π- 40° <  < 72° • π+ 46° <  < 82° • (SIM)  admixture of other particles < 3% TOF

  10. π±(registration efficiency correction) Tracking efficiency (hit registration and algorithm) Decays (for unstable particles) Registered (EXP) Corrected (EXP)

  11. Cross section(how-to approach) Target, beam intensity and trigger conditions Correction efficiency of hit registration, tracking performance and quality selection (cuts)

  12. Cross section(extrapolation to 4π) While measuring only a part of total phase space one needs extrapolation: Technique for Ntot /Npart correction is Pluto or URQMD generator

  13. Cross section(relative normalisation) C+C@1.8AGeV pion cross sections are from KaoS (F.Laue at al. Eur.Phys.J., 397-410, A9, 2000) π+ π- No corrections are taken into account (background, trigger, energy scaling) !!!

  14. Cross section correction(beam energy scaling) C+C pion cross section Scaling from KaoS 1.8AGeV  2.0AGeV (C.Sturm at al. PRL, 86:39-42, 2001) Factor 1.106 to be used π±and K+ cross sections

  15. b Multiplicity trigger(normalisation to minimum bias) Nov02 – C+C@2AGeV experiment 85% events multiplicity trigg ≥ 4 15% events multiplicity trigg ≥ 2 Apartdepends on impact parameter b Apart2 Apart1 Apart α=1 for π (P.Senger NP, A685, 2001) α=1.64 for K+ taken from measurements NiNi@1.0AGeV, NiNi@1.8AGeV R.Barth at al. (PRL, 78, 1997) Applied for C+C@2AGeV <Apart> = f(<b>) cut-off approx. w. „solid sphere model“

  16. Multiplicity trigger(normalisation to minimum bias) C+C@2AGeVsimulation 107 UrQMD events impact parameter distribution for minimum bias events and for events providing at least 2 (or 4) charged tracks in HADES acceptance (22°<  < 86°) <bm2&π>=3.146 [fm] (15%) <bm2&K>=2.480 [fm] mean impact parameter <bm4&π>=2.569 [fm] (85%) <bm4&K>=2.155 [fm] <bmin.b> =3.888 [fm] <btriggπ>=2.66 [fm] <btriggK>=2.20 [fm] “solid sphere model” approximation <Apart> = f(<b>) <Apart>min.b.=6.00 <Apart>triggπ=11.26 <Apart>triggK=13.75 Enhancement compared with minimum bias K+/pion ratio is influenced by the multiplicity trigger compared to minimum bias:

  17. Electron trigger(LVL2 / LVL1 trigger normalisation) C+C@2AGeVexperiment Nov02/gen3 DST 166 106 events LVL1 fraction=53.78% LVL2 fraction=46.22% using π+ yeld in registration area (300<p<1000) MeV/c (46° <  < 82°) (w/o registration eff. correction) (with registration eff. correction) If normalising by LVL1 events (1.000) x 53.78% + (0.899) x 46.22% = 95.37% Considering LVL1+LVL2 events together leads to lower π+ yeld estimate=>correction Assuming the same behavior for K+ one corrects for 1.0/0.954=1.048 when taking into account LVL2 events (as LVL1 events). Finally normalisation of LVL2 to LVL1trigger gives scaling factor 1.048

  18. K+ total cross section(at minimum bias conditions) x 0.765 Background (-23.5% for K+ in TOF) x 1.106 π± scaling (1.8  2.0)AGeV x 1/2.08 Multiplicity trigger (LVL1) ? 1.048 Electron trigger (LVL2) admixture Errors of approximations are not included The corresponding KaoS measurement for C+C@2AGeV (F.Laue PRL, 82,1999) HADES measurement is 42% larger

  19. BACKUPSLIDES

  20. Motivation • K+ production in collisions of C+C @ 2AGeV is a rare process • Strong requirements to tracking and detector performance • Survey HADES potential towards rare hadronic channels • Supplementary independent measurement to KaoS and FOPI • Investigation of strangeness production and ratio

  21. Results K+ Pluto K+ experiment corrected pt [MeV/c] pt [MeV/c] Y Y =88° =88° Binning N1 Binning N2 =44° =44° pt [MeV/c] pt [MeV/c] =18° =18° Y0=Y/Ycm-1 Y0=Y/Ycm-1

  22. mt-m0 spectra (binning N1) TB=62.4±3.1 [MeV] TB=60.6±1.6 [MeV] TB=60.7±1.2 [MeV] TB=69.9±1.2 [MeV] TB=80.7±1.9 [MeV] TB=72.2±1.3 [MeV] NB: Errors are stat. Full bins selection from p-acceptance. Fit function:

  23. mt-m0 spectra (binning N2) TB=53.4±1.6 [MeV] TB=59.4±1.5 [MeV] TB=61.0±1.1 [MeV] TB=71.0±1.3 [MeV] TB=82.0±2.5 [MeV] TB=82.4±1.5 [MeV] NB: Errors are stat. Full bins selection from p-acceptance. Fit function:

  24. Preliminary results from mt-m0 spectra Binning N1 Binning N2 TB [MeV] TB [MeV] Y0 Y0 dN/dY0 dN/dY0 Y0 Y0 • Systematic errors are not taken into account • Absolute normalization for dN/dY0 is not provided yet

  25. Comparison with other experiments (EkinCM-spectra) HADES C+C@2AGeV vs. KaoS C+C@1.8AGeV KaoS data scanned from F.Laue et al. PRL 82(1999)1640 T=(70.4±3.2) MeV Normalization of HADES data not performed yet

  26. Comparison with other experiments (mt-m0 spectra) HADES C+C@2AGeV vs. FOPI Ru+Ru(Zr)@1.69AGeV FOPI data and fits: dissertation of K. Wisniewski HADES extends (mt-m0) - range compared to FOPI Normalization of HADES data not performed yet

  27. Comparison with other experiments (mt-m0 spectra) HADES C+C@2AGeV vs. FOPI Ni+Ni@1.93AGeV FOPI data and fits NPA 625(1997)755 HADES extends (mt-m0) - range compared to FOPI Ni+Ni@1.93AGeV C+C@2AGeV C+C@2AGeV -1.3<Y0<-1.1 x1000 (Ni+Ni) -0.9<Y0<-0.7 x10 (Ni+Ni) -1.3<Y0<-1.1 x100 (Ni+Ni) -0.8<Y0<-0.6 x10 (C+C) -0.7<Y0<-0.5 x1 (Ni+Ni) -0.6<Y0<-0.4 x1 (C+C) Normalisation of HADES data not performed yet

  28. Results (Simulation Nov02/gen3) Simulation C+C@2AGeV (Nov02/gen3) 71·106 events 3026 K+ tracks (incl. bg<15%) The same cuts and correction as for experimental data K+ Pluto pt [MeV/c] Y =88° Binning N1 =88° Binning N2 =44° =44° pt [MeV/c] pt [MeV/c] =18° =18° Y0=Y/Ycm-1 Y0=Y/Ycm-1

  29. Results from simulation mt-m0 spectra Binning N1 Binning N2 TB [MeV] TB [MeV] Y0 Y0 dN/dY0 dN/dY0 Y0 Y0 • Systematic errors are not taken into account • Absolute normalisation for dN/dY0 is not provided yet

  30. Summary and outlook • K+ identification with HADES • possible for 250MeV<p<500MeV (TOFINO), 200MeV<p<700MeV (TOF) • 2562 K+ from 166*106 events • Y and mt spectra deduced • Slope parameters are in agreement with previous experiments • KaoS measured K+ production from C+C system at beam kinetic energies: • 1.8 AGeV for (28°,52°) and (56°,64°), N(K+)=17000 • 2.0 AGeV for (28°,44°), N(K+)=11000 • HADES extends the acceptance of C+C towards target rapidity at • 2.0 AGeV for (30°,83°), N(K+)= 2562 • (HADES specific measurement -0.9<Y0<-0.7) • To do list: • Absolute normalization to the beam particles • Investigation of systematical errors influence

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