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ISMD 2005, Kromeriz Czech Republic Aug.9-15 1 Measurement of identified particle production at RHIC An Tai University of California at Los Angeles For.

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Presentation on theme: "ISMD 2005, Kromeriz Czech Republic Aug.9-15 1 Measurement of identified particle production at RHIC An Tai University of California at Los Angeles For."— Presentation transcript:

1 ISMD 2005, Kromeriz Czech Republic Aug Measurement of identified particle production at RHIC An Tai University of California at Los Angeles For the STAR Collaboration

2 ISMD 2005, Kromeriz Czech Republic Aug Outline Introduction Results from in 200 GeV Au+Au collisions at RHIC new mechanism for hadronization Results from in 200 GeV dAu collisions at RHIC an important reference Heavy flavor production Summary

3 ISMD 2005, Kromeriz Czech Republic Aug A Pictorial View of Micro-Bangs at RHIC Thin Pancakes Lorentz =100 Nuclei pass thru each other < 1 fm/c Huge Stretch Transverse Expansion High Temperature (?!) The Last Epoch: Final Freezeout-- Large Volume What are properties of matter formed at RHIC ?

4 ISMD 2005, Kromeriz Czech Republic Aug J/ D K* K p d, HBT v 2 saturates T saturates T saturates Q2Q2 time Identified particles probing the matter properties PID in STAR: TPC: tracking p,K,π …. BEMC electron … * ToF patch p,K,π, electron. Δφ π/30, -1 < η < 0

5 ISMD 2005, Kromeriz Czech Republic Aug STAR Particle Identification Electron identification: TOFr |1/ß-1| < 0.03 TPC dE/dx electrons!!! electrons

6 ISMD 2005, Kromeriz Czech Republic Aug Examples of mass plots |y|<1 0.4

7 ISMD 2005, Kromeriz Czech Republic Aug Identified Spectra in Simpler Systems Theoretical understanding of p+p reference not completely under control NLO calculations fail, especially for baryons: poorly constrained fragmentation functions? Other hadronization schemes ? fragmentation functions from e + e - data, hep-ph/

8 ISMD 2005, Kromeriz Czech Republic Aug /K 0 s in Au+Au and pp –baryon abnormally (1)Baryon is enhanced at intermediate pt region with respective to meson in AA (2) At higher pt, the ratios seem to approach that in pp (3) Recombination/coalescence models at intermediate pt vs fragmentation at higher pt Central 0-5% Peripheral 60-80%

9 ISMD 2005, Kromeriz Czech Republic Aug How recombination/coalescence works Efficient way to produce baryons at intermediate pt when parton density is high

10 ISMD 2005, Kromeriz Czech Republic Aug Study of nuclear effects N part – No of participant nucleons N coll – No of binary nucleon- nucleon collisions

11 ISMD 2005, Kromeriz Czech Republic Aug Nuclear effects in AA Nuclear suppression seen for both baryon and meson Nuclear suppression seen for both baryon and meson The suppression is stronger for mesons than for baryons The suppression is stronger for mesons than for baryons The effect is grouped by particle type (baryon vs meson), supporting recombination/coalesc ence picture The effect is grouped by particle type (baryon vs meson), supporting recombination/coalesc ence picture STAR Preliminary Au+Au Energy Loss: Partonic or hadronic interaction ? Suppression: Initial state or final state effect ? q q

12 ISMD 2005, Kromeriz Czech Republic Aug Φ production probing early state m Φ ~1019 MeV/c 2 ; m Λ ~1116 MeV/c 2 ; m Ks ~498 MeV/c 2 May determine whether the particle dependence of the nuclear modification factor is grouped by the particle mass or particle type Possible production mechanism: (1) ggg -> (2) s sbar -> (3) K+K- -> Small cross section for scattering with hadronic medium sensitive to source properties of early time.

13 ISMD 2005, Kromeriz Czech Republic Aug Φ production dynamics N( )/K - independent of collision centralities. K + K - Φ is not a dominant channel Φ does not pick up as much as transverse flow as proton

14 ISMD 2005, Kromeriz Czech Republic Aug R cp of Φ meson in AA Au+Au STAR preliminary Species dependence at intermediate pt region is verified Species dependence at intermediate pt region is verified The suppression can not be due to later hadronic processes The suppression can not be due to later hadronic processes

15 ISMD 2005, Kromeriz Czech Republic Aug K 0 s,, : 0.4 – 6 GeV/c; : 0.6 – 5 GeV/c. Statistical errors only. Double exponential fit function d+Au as a reference

16 ISMD 2005, Kromeriz Czech Republic Aug Rcp in dAu Cronin effect is seen in dAu system Same baryon/meson separation in dAu as in AuAu collisions Recombination/coalescence modes work in d+Au ? Rcp in AA is lower than that in dAu the suppression is due to final state effect dAu 200 GeV STAR Preliminary AuAu 200 GeV

17 ISMD 2005, Kromeriz Czech Republic Aug Heavy flavor measurements D 0 K (B.R=3.8%) D* ± D 0 π(B.R=68% 3.8% (D 0 K ) = 2.6% ) D* ± 2.4

18 ISMD 2005, Kromeriz Czech Republic Aug Charm cross section at RHIC (1) NLO pQCD calculations tuned for low energy points under-predict the ccbar production cross section at RHIC (2) The Pythia prediction with the Peterson fragmentation function is softer than the measured electron spectrum Phys. Rev. Lett. 94 (2005) π+A 350 GeV/c

19 ISMD 2005, Kromeriz Czech Republic Aug Heavy Flavor R AA --- Challenge to radiative picture? Suppression is approximately the same as for hadrons Where is b contribution ? M. Djordjevic, et. al. nucl-th/

20 ISMD 2005, Kromeriz Czech Republic Aug Summary STAR has a vigorous program which is pushing our measured probes more and more sensitive to the early stage of the formed medium Nuclear effects at intermediate pt show particle type dependence, supporting recombination/coalescence as dominant processes for hadronization Strong suppression of high pt hadron production is observed for both light and heavy quarks, which demonstrates the formation of strongly-interacting dense medium at RHIC.

21 ISMD 2005, Kromeriz Czech Republic Aug

22 ISMD 2005, Kromeriz Czech Republic Aug Dead cone effect---Radiative Energy Loss of Heavy Quarks See also Armesto et al, Phys. Rev. D71 (2005) Coupling of heavy quarks to the medium reduced due to mass Expectation: even for high medium density, higher R AA for single electrons from heavy flavor than for light hadrons

23 ISMD 2005, Kromeriz Czech Republic Aug /2K 0 s in d+Au Close to Au+Au most peripheral ratio (60-80%) No significant centrality dependence in d+Au

24 ISMD 2005, Kromeriz Czech Republic Aug Electron ID in STAR – EMC 1.TPC for p and dE/dx e/h ~ 500 (p T dependent) 2.Tower E p/E e/h ~ 100 (p T dependent) 3.Shower Max Detector (SMD) shape to reject hadrons e/h ~ 20 4.e/h discrimination power ~ 10 5 Works for p T > 1.5 GeV/c electronshadrons

25 ISMD 2005, Kromeriz Czech Republic Aug Inclusive Single Electrons p+p/d+Au Inclusive non-photonic spectra : How to assess the background? PHENIX 1: cocktail method PHENIX 2: converter method STAR: measurement of main background sources (TPC !!!) ToF + TPC: 0.3 GeV/c < p T < 3 GeV/c TPC only: 2 < p T < 3.5 GeV/c EMC + TPC: p T > 1.5 GeV/c

26 ISMD 2005, Kromeriz Czech Republic Aug Photonic Single Electron Background Subtraction in pp and dAu Method: 1.Select an primary electron/positron (tag it) 2.Loop over opposite sign tracks anywhere in TPC 3.Reject tagged track when m < m cut ~ 0.1 – 0.15 MeV/c 2 4.Cross-check with like-sign Rejection Efficiency: Simulation/Embedding background flat in p T weight with measured 0 spectra (PHENIX) conversion and 0 Dalitz decay reconstruction efficiency ~60% Relative contributions of remaining sources: PYTHIA/HIJING + detector simulations Invariant Mass Square Rejected Signal Opening Angle conversion and 0 Dalitz decay reconstruction efficiency : ~60% at p T >1.0 GeV/c

27 ISMD 2005, Kromeriz Czech Republic Aug Photonic Single Electron Background Subtraction p T dependent hadron contamination (10-30%) subtracted Excess over background

28 ISMD 2005, Kromeriz Czech Republic Aug Non-Photonic Single Electron Spectra in p+p and d+Au

29 ISMD 2005, Kromeriz Czech Republic Aug Nuclear Effects R dAu ? Nuclear Modification Factor: Within errors compatible with R dAu = 1 … … but also with R dAu (h ) NOTE: R dAu for a given p T comes from heavy mesons from a wide p T range p(D) > p(e) (~ 2-3) makes interpretation difficult hadrons

30 ISMD 2005, Kromeriz Czech Republic Aug D 0 Mesons in d+Au Mass and Width consistent with PDG values considering detector effects: mass=1.867±0.006 GeV/c 2 ; mass(PDG)=1.8645± GeV/c 2 mass(MC)=1.865 GeV/c 2 width=13.7±6.8 MeV width(MC)=14.5 MeV

31 ISMD 2005, Kromeriz Czech Republic Aug Obtaining the Charm Cross-Section cc D 0 Mesons –Requires fit to data points for extrapolation functional form? error on extrapolation –Requires the knowledge of N D0 /N cc Non-Photonic Single Electrons –What functional form ? PYTHIA does not describe data –tweaking it is not satisfactory NLO/FONLL not reliable for p T < F = R = m c p T D STAR Combine both measurements –Fraction of covered ?

32 ISMD 2005, Kromeriz Czech Republic Aug Obtaining the Charm Cross-Section cc Combined fit: –Assume D 0 spectrum follows a power law function –Generate electron spectrum using particle composition from PDG N D0 /N cc ~ Decay via routines from PYTHIA –Assume that only normalization scale different between the various D meson p T spectra is different (D 0, D*, D, …) From D 0 mesons alone: –N D0 /N cc ~ –Fit function from exponential fit to m T spectra In both cases for d+Au p+p: – pp inel = 42 mb –N bin = (Glauber) –|y|<0.5 to 4 : f = (simulations) –R dAu =

33 ISMD 2005, Kromeriz Czech Republic Aug Obtaining the Charm Cross-Section cc pp Charm Cross-Section From D 0 alone: cc = mb From combined fit: cc = mb

34 ISMD 2005, Kromeriz Czech Republic Aug Discrepancy between STAR and PHENIX ? STAR from d+Au: cc = mb (PRL94,062301) PHENIX from p+p (preliminary): cc = (+0.332, 0.281) mb PHENIX from min. bias Au+Au: cc = mb (PRL94,082301) Reality check: mb and mb are not so bad given the currently available statistics (soon be more!) pp p SPS, FNAL (fixed target) and ISR (collider) experiments

35 ISMD 2005, Kromeriz Czech Republic Aug Discrepancy between STAR and PHENIX ? 90% 15% Combined fit of STAR D 0 and PHENIX electrons: No discrepancy: cc = mb STAR: PRL 94, (2005) PHENIX p+p (QM04): S. Kelly et al. JPG30(2004) S1189

36 ISMD 2005, Kromeriz Czech Republic Aug Consequences of High Cross-Section: J/ Recombination Statistical model (e.g. A. Andronic et. al. PLB 571,36(2003)) : Large cc yield in one heavy ion collision J/ production through recombination possible J/ enhancement Statistical model In stat models: cc typically from pQCD calculations Consequence of STAR cc (from d+Au) much larger enhancement (~3- 10) for J/ production in central Au+Au collisions PHENIXs upper limit would invalidate the expectation from large cc ?!

37 ISMD 2005, Kromeriz Czech Republic Aug NLO/FONLL Recent calculations in NLO (e.g. R. Vogt et al. hep-ph/ ) –Since m0 heavy quark production is a hard process –Calculations depend on: quark mass m c factorization scale F (typically F = m or 2m) renormalization scale R (typically R = F ) parton density functions (PDF) –Total cross-section depends only on m c, not kinematic quantities –Hard to obtain large with R = F (which is used in PDF fits) –For p T spectra m (for calculations m p T integrated direct calculated Fixed-Order plus Next-to-Leading-Log (FONLL) –designed to cure large logs for p T >> m c where mass is not relevant –FONLL higher over most p T than NLO (also tot ) K factor (NLO NNLO) ?

38 ISMD 2005, Kromeriz Czech Republic Aug NLO/FONLL from hep-ph/

39 ISMD 2005, Kromeriz Czech Republic Aug Charm Total Cross Section Can we confirm or rule out Cosmic Ray experiments? (Pamir, Muon, Tian Shan) under similar conditions? NPB (Proc. Suppl.) 122 (2003) 353 Nuovo Ciment. 24C (2001) 557 X. Dong USTC –NLO calculations under-predict current cc at RHIC –More precise data is needed high statistics D mesons in pp

40 ISMD 2005, Kromeriz Czech Republic Aug Comparison: Non-Photonic Electrons with NLO FONLL calculations: Charm: scaled by STAR / FONLL Bottom: derived from fit of sum to data Errors used: data + FONLL uncertainty bands Plenty of room for bottom !!!

41 ISMD 2005, Kromeriz Czech Republic Aug Can We Disentangle Charm from Bottom ? Method I: Finding the Secondary Vertex –Requires excellent resolution of vertex tracker (< 50 m) –Survival probability P(x) depends on M/c D ~ 15 MeV/ m B ~ 11 MeV/ m (B lives long but is heavy) –Works only at high p but bb is dominated by p T e < 4 GeV/c Method II: Identifying the Ks from the semileptonic decay –If a K is present within certain kinematical region around the e the ratio of opposite/same sign pairs (K + e - + K - e + )/(K - e - + K + e + ) is –charm (c e K anything): ~ 55:1 (PYTHIA) –bottom (b e K anything): ~ 1:6 (PYTHIA) –works only in pp and requires large acceptance + high p T PID Method III: Subtracting e evaluated from measured D spectra –Requires knowledge of D spectra out to very high p T Need D spectra out to 11 GeV/c to describe electrons at p T ~ 5 GeV/c

42 ISMD 2005, Kromeriz Czech Republic Aug High-p T D 0 -Meson Spectra in d+Au How is it done ? –Assumptions: p T spectra of D 0, D*, D same shape –D 0 K defines low p T points –D 0 K defines one high-p T point –Combined allow power law fit –functional form allows to move D* and D spectra into place –cross-check with known ratios OK –Problem: D*/D 0 and D / D 0 not well known (p T, s dependent ?) Note: spectrum depends on one point: D 0 K

43 ISMD 2005, Kromeriz Czech Republic Aug High-p T D-Meson Spectra in d+Au Headache: Spectra very hard (too hard) –Fragmentation function function (Peterson FF needs c = b ) ? –Yield at 10 GeV/c only factor 3 below CDF (LO/NLO ~ 10) ? Intensive systematic studies of D 0 K of many people over many month …

44 ISMD 2005, Kromeriz Czech Republic Aug High-p T D-Meson Spectra in d+Au Until we found the problem … –very, very, subtle effect –Downside: combined low to high-p T D 0 spectra is gone ratios not well enough known cannot normalize D*, D to D 0 appropriately any more Upper limits from D 0 K (90% CL) Note: D* itself is still valid!!! Now a standalone spectra. Doesnt affect possibility of studying R AA in Au+Au

45 ISMD 2005, Kromeriz Czech Republic Aug Thermalization of heavy quarks ? v 2 of non-photonic electrons in Au+Au

46 ISMD 2005, Kromeriz Czech Republic Aug Strong Elliptic Flow at RHIC Strong elliptic flow at RHIC (consistent with hydro limit ?) –scaling with Number of Constituent Quarks (NCQ) partonic degrees of freedom !? –v 2 /n(p T /n) shows no mass and flavor dependence –Strong argument for partonic phase with thermalized quarks Whats about charm? –Naïve kinematical argument: need M q /T ~ 7 times more collisions to thermalize –v 2 of charm closely related to R AA

47 ISMD 2005, Kromeriz Czech Republic Aug Charm Elliptic Flow from the Langevin Model –Diffusion coefficient in QGP: D = T/M momentum drag coefficient) –Langevin model for evolution of heavy quark spectrum in hot matter –Relates collisional energy loss and elliptic flow v 2 –pQCD gives D (2 T) 6(0.5/ s ) 2 AMPT: (C.M. Ko) =10 mb =3 mb

48 ISMD 2005, Kromeriz Czech Republic Aug Charm Elliptic Flow through Resonance Effects Van Hees & Rapp, PRC 71, (2005) –Assumption: survival of resonances in the QGP –Introducing resonant-heavy-light quark interactions –heavy particle in heat bath of light particles (QGP) + fireball evolution time-evolved c p T spectra in local rest frame Nearly thermal: T ~ 290 MeV Including scalar, pseudoscalar, vector, and axial vector D mesons gives: σ cqcq (s 1/2 =m D )6 mb Cross-section is isotropic the transport cross section is 6 mb, about 4 times larger than from pQCD t-channel diagrams

49 ISMD 2005, Kromeriz Czech Republic Aug How to Measure Charm v 2 Best: D mesons need large statistics, high background not now Alternative: Measure v 2 of electrons from semileptonic charm decays –Emission angles are well preserved above p = 2 GeV/c –2-3 GeV Electrons correspond to 3-5 GeV D-Mesons

50 ISMD 2005, Kromeriz Czech Republic Aug Measuring v 2 of Non-Photonic Electrons Analysis –Same procedures as for single electrons (incl. background subtraction) –… but with much harder cuts (plenty of statistics) –special emphasis on anti-deuteron removal –reaction plane resolution ~ 30% Consistency check: PYTHIA + MEVSIM (flow generator) through analysis chain D 0 (input) e ± 0 e e (input) e ±

51 Phenix : Min. Bias Star: 0-80% STAR: stat. errors only Corrected for residual e ± contaminations from π decays with v 2 max =17% Phenix: nucl-ex/ (QM2004) nucl-ex/ (submitted to PRC) Star: J. Phys. G (Hot Quarks 2004) J. Phys. G (SQM 2004) v 2 of Non-Photonic Electrons Indication of strong non-photonic electron v 2 consistent with v 2 (c) = v 2 (light quark) smoothly extending from PHENIX results Teany/Moor D (2 T) = 1.5 expect substantial suppression R AA Greco/Ko Coalescence model (shown above) appears to work well

52 ISMD 2005, Kromeriz Czech Republic Aug Argonne National Laboratory Institute of High Energy Physics - Beijing University of Bern University of Birmingham Brookhaven National Laboratory California Institute of Technology University of California, Berkeley University of California - Davis University of California - Los Angeles Carnegie Mellon University Creighton University Nuclear Physics Inst., Academy of Sciences Laboratory of High Energy Physics - Dubna Particle Physics Laboratory - Dubna University of Frankfurt Institute of Physics. Bhubaneswar Indian Institute of Technology. Mumbai Indiana University Cyclotron Facility Institut de Recherches Subatomiques de Strasbourg University of Jammu Kent State University Institute of Modern Physics. Lanzhou Lawrence Berkeley National Laboratory Massachusetts Institute of Technology Max-Planck-Institut fuer Physics Michigan State University Moscow Engineering Physics Institute City College of New York NIKHEF Ohio State University Panjab University Pennsylvania State University Institute of High Energy Physics - Protvino Purdue University Pusan University University of Rajasthan Rice University Instituto de Fisica da Universidade de Sao Paulo University of Science and Technology of China - USTC Shanghai Institue of Applied Physics - SINAP SUBATECH Texas A&M University University of Texas - Austin Tsinghua University Valparaiso University Variable Energy Cyclotron Centre. Kolkata Warsaw University of Technology University of Washington Wayne State University Institute of Particle Physics Yale University University of Zagreb 545 Collaborators from 51 Institutions in 12 countries STAR Collaboration

53 ISMD 2005, Kromeriz Czech Republic Aug Motivation II the Cronin effect in pA, d+Au collisions Nuclear Modification factor R AA or R CP Should the Cronin effect be influenced by the final state particle formation dynamics? Recombination models! p q h A traditional models : Multiple parton/hardon scatterings in initial state Recombination/ Coalescence: Final state effect

54 ISMD 2005, Kromeriz Czech Republic Aug STAR Detector at RHIC Time Projection Chamber Forward TPCs pion, kaon, proton and electron : identified using ionization energy loss technique. Other particles are reconstructed from them.

55 ISMD 2005, Kromeriz Czech Republic Aug Data Set and Cuts STAR d+Au 200GeV Minimum Bias data Event Selection: |VertexZ| < 50cm, Primary vertex found, good run ~ 10M events after the cuts. Centrality definition in STAR: 0-20%(Nch>=17), 20-40%(17>Nch>=10), %(Nch<10) Nch (Uncorrected # of charged Forward TPC-Au side, -3.8< <-2.8)

56 ISMD 2005, Kromeriz Czech Republic Aug Invariant mass plots |y|<1 0.4

57 ISMD 2005, Kromeriz Czech Republic Aug K 0 s,, : 0.4 – 6 GeV/c; : 0.6 – 5 GeV/c. Statistical errors only. Double exponential fit function better than the exponential function ( low p T )and the power-law ( high p T ). m T Spectra and fits in d+Au

58 ISMD 2005, Kromeriz Czech Republic Aug Compare various fit functions

59 ISMD 2005, Kromeriz Czech Republic Aug The mean p T s are little dependence of Number of Charged Particles. The mean p T s increase with Number of Charged Particles vs. Number of Charged Particles dAu Minbias

60 ISMD 2005, Kromeriz Czech Republic Aug /K 0 s in Au+Au and pp Au+Au and 200 GeV Au+Au most peripheral Recombination models Central 0-5% Peripheral 60-80% R.J.Fries et al Phys. Rev. C V.Greco et al Phys. Rev. C

61 ISMD 2005, Kromeriz Czech Republic Aug /2K 0 s in d+Au No significant centrality dependence in d+Au Close to Au+Au most peripheral ratio (60-80%) Soft+Hard Reco may work in d+Au

62 ISMD 2005, Kromeriz Czech Republic Aug R cp in Au+Au 200 GeV Suppression R cp s are grouped into Mesons (K 0 s, ) and Baryons (, ). Particle-type dependence! STAR Preliminary

63 ISMD 2005, Kromeriz Czech Republic Aug R AB charged hadrons in d+Au STAR d+Au : Cronin enhancement Au+Au : Suppression

64 ISMD 2005, Kromeriz Czech Republic Aug K 0 s R cp of K 0 s / / / in d+Au STAR R cp s are grouped into Mesons (K 0 s, ) and Baryons (, ). Particle-type dependence again! Cronin effect Final state formation dynamics (Recombination model ) R cp difference between BM.

65 ISMD 2005, Kromeriz Czech Republic Aug R cp of K/ /p in d+Au D. Kotchetkov, QM2004 PHENIX B-M dependence: (, K) vs. (p, ) STAR TOF measurement B-M dependence: (, K) vs. (p)

66 ISMD 2005, Kromeriz Czech Republic Aug R AA in low energy p+A collisions s =27.4GeV P.B Straub,PRL 68, 452(1992) R w/Be in p+A collisions W: tungsten Be: beryllium s =38.8GeV R w/Be : Mesons (2 quarks): Mesons (2 quarks): kaon and pion ~ 1.5; Baryons (3 quarks): Baryons (3 quarks): proton ~ 2.5 Particle-type dependence ?? ~1.4 ~1.5 ~2.5

67 ISMD 2005, Kromeriz Czech Republic Aug Summary Measured productions for 4 identified particles(K 0 s,,, ) in d+Au collisions at RHIC; /K 0 s ratio increases with multiplicity. –dAu ratio is close to AuAu most peripheral (60-80%) –Recombination models are in qualitative agreement with the data. pA Nuclear modification factor, R AB, shows Cronin effect –Baryon–Meson(B-M) dependence?. Au+Au Nuclear modification factor, R CP, shows B-M difference and suppression. –Consistent with parton recombination + jet quenching. d+Au Nuclear modification factor, also shows B-M difference and Cronin effect. –PHENIX : (K/ vs. p/ ), STAR : (K 0 s / vs. ) –Cronin: Final state particle formation dynamics (recombination)

68 ISMD 2005, Kromeriz Czech Republic Aug centrality dependence centrality dependence 1), K, p mean transverse momentum increase in more central collisions; 2) Heavier mass particle increase faster than lighter ones as expected from hydro type collective flow; 1), K, p mean transverse momentum increase in more central collisions; 2) Heavier mass particle increase faster than lighter ones as expected from hydro type collective flow; 3) -meson seems flow differently.


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