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Study of D ++ Resonance Abundance in 158 AGeV Pb + Pb Collisions at CERN-SPS

Study of D ++ Resonance Abundance in 158 AGeV Pb + Pb Collisions at CERN-SPS. Susumu SATO. Contents 1) Introduction ~ Relativistic heavy ion collision ~ 2) Thesis motivation ~ D measurement ~ 3) Experimental setup ~ WA98 at CERN-SPS ~ 4) Data analysis ~ corrections and errors ~

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Study of D ++ Resonance Abundance in 158 AGeV Pb + Pb Collisions at CERN-SPS

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  1. Study of D++ Resonance Abundance in 158 AGeV Pb + Pb Collisions at CERN-SPS Susumu SATO Contents 1) Introduction ~ Relativistic heavy ion collision ~ 2) Thesis motivation ~ D measurement ~ 3) Experimental setup ~ WA98 at CERN-SPS ~ 4) Data analysis ~ corrections and errors ~ 5) Experimental Results ~ p,p spectra & D yield ~ 6) Discussion ~ low mt enhancement of inclusive p spectrum ~ • Summary CERN-SPS-WA98 SusumuSATO

  2. Picture of Relativistic Heavy Ion collisions [1: Before collision (g~17 at SPS)] - Lorentz contracted [2: During collision (Dt ~1fm/c)] →stopping/heating →hot/dense fireball [3: After collision] →(thermal/chemical equilibrium) →”cooling with expansion” →thermal/chemical freeze out →hadrons(p,K,p,…), e, g, …detection Fireball To understand fireball, need picture during “cooling with expansion” CERN-SPS-WA98 SusumuSATO

  3. Single Particle Spectra (pp collisions) Nucl.Phys.B100(75)237 (1)Similar shape, and (2)Similar slope for different particle species (called mt-scaling) mt– m (GeV) mt-scaling in proton – proton collisions CERN-SPS-WA98 SusumuSATO

  4. Single Particle Spectra (nucleus - nucleus collisions) Nucl.Phys.A610(96)175c (1)Different shape, and (2)Different slope for different particle species mt– m (GeV) Different shape and slope are observed. CERN-SPS-WA98 SusumuSATO

  5. Two particle HBT correlation quantum interference to measure source size (R) R C2: detection probability of two particles at the momentum of p1and p2 (R=6fm,l=1) Source size as a function of relative momentum CERN-SPS-WA98 SusumuSATO

  6. Two particle HBT correlationin nucleus nucleus collisions Transverse Direction (x,y) q Eur.Phys.J. C2(98)661 Beam Direction (z) Source size as a function also of average momentum CERN-SPS-WA98 SusumuSATO

  7. p p－ K－　 K+ p+ p－ Expanding Fireball Model (1) mass dependence of mt spectra slope NPA610(96)175 →linear mass dependence 　　　　　↓ parameterized naively T = Tf +mass・〈bf〉2 Slope(GeV) Mass(GeV/c2) Naively, Expansion Fireball is applicable ! CERN-SPS-WA98 SusumuSATO

  8. Expanding Fireball Model (2)~ example of good parameterization ~ • Single spectra: • transverse kinetic energy (mt) spectra • PRL80(98)3467 →parameterization for different particle species Tf ~139MeV, 〈bf〉~0.42c (2) Two particle HBT correlation Habilitation(’97/T.Peitzmann) →Boost invariance for expansion 〈bf〉=DR/tf ~ 0.430.16c Good explanation both for singles and two particle correlation, but not using lower mt-region CERN-SPS-WA98 SusumuSATO

  9. Thesis Motivations (1) Measurement of particle production of a new particle species; →D(1232) in 158 A GeV Pb + Pb central collisions. (2) As a basic problem to understand both single particle spectra and HBT correlation, low mt pion enhancement is observed. →By using the result of explicit measurement of D resonance, the contribution of D to low mt enhancement is acquired, then aiming to get footing of the validity of the expanding fireball model. CERN-SPS-WA98 SusumuSATO

  10. Authors Contributions Design of experimental detector ●Time-of-Flight (TOF) detector ●Optimal alignment of chambers in magnetic spectrometer Construction, test, installation, and operation of detectors ●TOF detector ●Streamer tube tracking (STD) detector ●Start counter Programming of control and reconstruction software ●HV control for TOF ●Online monitoring for TOF, STD ●Momentum reconstruction Physics Analysis ●Pion and proton single spectrum ●Yield of D(1232) resonance CERN-SPS-WA98 SusumuSATO

  11. D++ Δ++ resonance ●Lowest resonance of nucleon ● M ~ 1232MeV (in Breit-Wigner function） ●ct ~ 1.8 fm; (G~111MeV) ● Isospin3/2, Spin 3/2 ● Decay into pion and proton with >99% branching ratio Pt(mt)(GeV/c) 0.8 p 0.4 p+ 0 y 0 -1 1 ● Decayed pion gives lower transverse kinetic energy CERN-SPS-WA98 SusumuSATO

  12. LEDA(EM.Cal.) TOF (Stop counter) ZDC(Had.Cal.) Streamer Tube Det. PAD Cham. MIRAC(Had.Cal.) Magnet PMD 21.5m Start Beam ( 208Pb:158AGeV) Target (208Pb: 0.239mg/cm2) +P.ball, SPMD WA98 experimental setup Characterize Fireball from various aspects • [Hadron] momentum + PID; w/Mag. Spectr. • [Photon] Eg; w/EM.Cal. • [Hadron] global ET, E0; w/Had.Cal. • [Photon] mult. distr.; w/PMD • [Charged particle] mult. distr.; w/SPMD, P.ball CERN-SPS-WA98 SusumuSATO

  13. Detector resolutions (p, Tstart, Ttof) N s~30ps start sT~1.3mm, s//~2.1mm (PAD1) sT~2.6mm,s// ~7.0mm(STD1) σp / p 10k 2% 5k Tdif (ns) 1.5% -0.4 0.4 0 N s~85ps 800 tof 1% ～1% at 2GeV/c 0.5% 400 0 Ttof (ns) 0 1 2 3 4 5 p(GeV/c) 0.8 -0.8 0 Magnetic spectrometer is in good operation CERN-SPS-WA98 SusumuSATO

  14. Particle Identification 8 p p+ σm2(GeV/c2)2 p(GeV/c) 6 K＋ ~0.02 (GeV/c2)2 at 2GeV/c for π 4 2 0.10 0 0 0.5 1 1.5 0.05 m2(GeV2/c4) 0.00 0 1 2 3 4 p(GeV/c) • Clear Particle Identification by ToF method CERN-SPS-WA98 SusumuSATO

  15. Parameterization [1]for p+, p single particle spectra Kinematical parameters Lorentz invariant differential yield Transverse kinetic energy (longitudinal) rapidity if f symmetry : Lorentz invariant CERN-SPS-WA98 SusumuSATO

  16. Geometrical Acceptance mt-m(GeV) Fireball (←ytarget =0) ycm=2.9 (ybeam=5.8 →) Measure around mid-rapidity, where hot fireball is expected the most. CERN-SPS-WA98 SusumuSATO

  17. Data selection • Event selection Single beam (3s in ADCstart) FEE linear region (5.7% in Tdynamic) not after-chamber-spark (0.8sec) event ADCstart 2 [ch] •Track selection image on target (3s in B// direction) image on TOF2 (2.5s on 2-D plane) •PID selection m2 (2.5s in the p) ADCstart 1 [ch] CERN-SPS-WA98 SusumuSATO

  18. ec eg Y X y mt Geometrical acceptance and Efficiency correction By the Monte Carlo Simulation (GEANT3.15) PAD2 PAD1 p+ Averaged eff. ePAD1 83% ePAD2 80% eSTD1 91% eSTD2 97% STD1 STD2 p CERN-SPS-WA98 SusumuSATO

  19. Single spectra (*) Nucl.Phys.610(96)175 mt-m(GeV) Consistent shapes with other experiments CERN-SPS-WA98 SusumuSATO

  20. Parameterization [2]for D yield by invariant mass method Invariant mass Invariant mass distribution Invariant mass (GeV) should be evaluated CERN-SPS-WA98 SusumuSATO

  21. Mixed Event technique example EVENT 2 p p+ p p+ p p+ EVENT 1 p p+ p p+ p p+ Mixed events: p and p+ from different events paired in 100 every events Invariant mass (GeV) Combinatorial background is assumed to be proportional to mixed events CERN-SPS-WA98 SusumuSATO

  22. Two normalization methods • Tail method normalize only in higher minv region (2) Breit-Wigner + Background method normalize in any minv region, assuming YieldD++ follows Relativistic Breit-Wigner Invariant Mass (GeV) (PRL79(’97)4354) q:relative momentum of the pair in its C.M. frame,m:180MeV/c Two methods should be consistent CERN-SPS-WA98 SusumuSATO

  23. E0=1.2370.006 G=0.0860.014 (GeV) Tail method Invariant mass (GeV) Clear yield can be extracted by tail method CERN-SPS-WA98 SusumuSATO

  24. Breit-Wigner + Background method Invariant mass (GeV) Again, clear yield can be extracted by B.W.+BG. method CERN-SPS-WA98 SusumuSATO

  25. Poisson <Np> =2.6 Nev. 2k 1k 0 2 4 6 0 Np 0.10 Np=2 Np=3 Np=4 0.022 0.022 0.018 ND / ev. 0.05 0 Mth. (GeV) 1.4 1.5 1.6 1.7 1.4 1.5 1.6 1.7 1.4 1.5 Systematic error of ND / ev. on extraction method • Breit-Wigner • + B.G. method: 0.022 (2) Tail method: 0.021 (3)Local multiplicity (Np) on TOF Less dependence on extraction parameters CERN-SPS-WA98 SusumuSATO

  26. For , Statistical Error Error propagation gives ( 50.0% ) ( 49.9% ) ( < 0.1% ) Major contribution of error is large Combinatorial Back Ground CERN-SPS-WA98 SusumuSATO

  27. Isospin consideration Factor from Np/ND++ to Nnucleon/ND is 2.0. CERN-SPS-WA98 SusumuSATO

  28. Yield summary table At SPS, delta yield is, for the first time, directly measured CERN-SPS-WA98 SusumuSATO

  29. Population ratio: Δ/ nucleon 100 PLB477 (2000) 37-44 (%) 80 Δ(1232) nucleon 60 40 Acquired from D / p, Isospin correction done for 20 0 1 10 100 Ebeam(AGeV) Higher population is seen at SPS CERN-SPS-WA98 SusumuSATO

  30. Low mt enhancement in Pb + Pb (1) 103 p+ 102 Neighboring several points for local mt slope 10 1 mt– m (GeV) 0 0.2 0.4 0.6 0.8 1 Low mt enhancement is seen in local mt slope (Next) CERN-SPS-WA98 SusumuSATO

  31. Low mtenhancement in Pb + Pb (2) Local slope (GeV) Center of fitting region in mt– m (GeV) The mt enhancement is seen in p+spectrum in Pb + Pb collisions CERN-SPS-WA98 SusumuSATO

  32. pp collisions 100 p+ at mid-rapidity Nucl.Phys.B100(’75)237 Fitting Line y=aexp(-x/b) a=82.5±3.7 b=0.153±0.003 c2/n.d.f=8.8/6 10 1 0 0.2 0.4 0.6 mt– m (GeV) pp collision is described well in mt exponential CERN-SPS-WA98 SusumuSATO

  33. p+ D++ D++ p p+ Candidates of low mt enhancement (1) Collective motion e.g. Collective radial expansion (2) Coulomb effect  Repulsion/Attraction from Charges Pt(mt)(GeV/c) (3) Resonance decay 0.8 p D decay gives lower mt p by kinematics 0.4 p+ 0 y 0 -1 1 There are more than one candidates CERN-SPS-WA98 SusumuSATO

  34. Collective motion (Thermal+expansion) PRL80(’98)3467 Describing well for different particle species except low mtp, and shape of p is little affected by collective motion T=139MeV 〈b〉=0.42c consistent also with two particle HBT correlation mt– m (GeV) Dashed line: exponential for eye guide p spectra shape is little affected by Collective motion CERN-SPS-WA98 SusumuSATO

  35. 2.0 w/Coulomb 1.0 No Coulomb 0 0 0.2 0.4 Coulomb effect Coulomb Low mt Enhance mt– m (GeV) Low mt enhancement is seen in both charge, and Coulomb effect appears as difference between p+ and p–. CERN-SPS-WA98 SusumuSATO

  36. (a.u.) Contribution of Δ Resonance D included evaluation Δ( invariant mass) with a factor (1+α) →consistent with simulation + thermal model T=139 MeV, 〈b〉=0.42c mt– m (GeV) “thermal source” + “Δ resonance decay” is consistent with the low-mt enhancement of π＋. CERN-SPS-WA98 SusumuSATO

  37. Conclusion • For the systematic study of hadron production in 158 A GeV Pb + Pb collision, magnetic spectrometer with good PID capability is constructed. • At 158 A GeV Pb + Pb collisions, p+ and p inclusive single mt spectra are measured. Inverse slopes are 142  3 MeV (fitting region: mt – m > 0.2 GeV) for p+ and 251  25 MeV for proton. In the pion spectrum, clear low mt enhancement is observed. • (3) 158 AGeVPb + Pbcollisions,D resonance yield • is, for the first time, measured directly. The D/nucleon ratio is 0.62  0.28 (stat.)  0.16 (sys.). • (4) Spectrum shape with consideration of D decay on thermal expanding fireball follows low-mt enhancement of π＋. The additional factor is consistent with a cascade simulation that gives contribution of D decay with re-scattered proton. CERN-SPS-WA98 SusumuSATO

  38. Dat AGS (not directly measured) andMeasured PID at SPS PLB351(95)93 in RQMD At AGS, good description with D decay At SPS, D is not measured, while AGS tells its importance CERN-SPS-WA98 SusumuSATO

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