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Multiplicity structure in inclusive and diffractive deep-inelastic ep collisions

XIII Workshop on Deep-Inelastic Scattering 2005, Madison, Wisconsin. Multiplicity structure in inclusive and diffractive deep-inelastic ep collisions. Tinne Anthonis University of Antwerpen, Belgium. Outline Introduction Kinematic dependencies of DDIS Comparison DIS/DDIS

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Multiplicity structure in inclusive and diffractive deep-inelastic ep collisions

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  1. XIII Workshop on Deep-Inelastic Scattering 2005, Madison, Wisconsin Multiplicity structure in inclusive and diffractive deep-inelastic ep collisions Tinne Anthonis University of Antwerpen, Belgium Outline Introduction Kinematic dependencies of DDIS Comparison DIS/DDIS Conclusions

  2. Motivation • H1 analysis on 94 DDIS data: • Dependence of <n> on MX • H1 analysis on 2000 DDIS data: • Large statistics allowsmore differential study: W, Q2,  dependences at fixed MX • Compare DIS and DDIS

  3. Multiplicity structure Charged particle multiplicity of the hadronic final state • Shape of multiplicity distribution P(n) • Independent emission of single particles: Poisson distribution • Deviations from Poisson reveal correlations and dynamics • Mean multiplicity <n> of charged particles • Rapidity spectra • Koba-Nielsen-Olesen (KNO) scaling (z) • energy scaling of the multiplicity distribution • (z) = <n> Pn vs z = n/<n>

  4. Diffraction: ep ! e’XY ~ 10% of DIS events have a rapidity gap Cross section: Reduced cross section:

  5. Models for diffraction Combine QCD/Regge theory: resolved IP model • Proton infinite momentum frame • Colourless IP is built up of quarks/gluons • Based on QCD and Regge factorization: • Needs subleadingIR component

  6. Models for diffraction cont’d Colour dipole approach • In proton rest frame: * splits up in qq dipole • Model the dipole cross section: Saturation model Golec-Biernat and Wusthoff (GBW)

  7. Data selection DIS and DDIS • 2000 nominal vertex data: 46.65 pb-1 • Data corrected via Bayesian unfolding procedure: • DIS MC: DJANGOH 1.3, proton pdf CTEQ5L • DDIS MC: RAPGAP resolved pomeron DIS selection: • Good reconstruction of scattered electron • Kinematic cuts: • 0.05 < yav < 0.65 • 5 < Q2 < 100 GeV2 • 80 < W < 220 GeV DDIS selection: • Rapidity gap: • No activity in the forward detectors • max < 3.3 • Kinematic cuts: • 4 < MX < 36 GeV • xIP < 0.05

  8. Track selection • Primary vertex fitted tracks • 15 <  < 165 and pT > 150 MeV • Boost to hadronic *p CMS • Acceptance: • Resolution: tracks with * > 1 * *

  9. Multiplicity structure results Charged particles with *>1 in *p CMS frame • Multiplicity distribution and moments • Q2 dependence of <n> in DIS/DDIS at fixed W •  dependence of <n> in DDIS at fixed MX • W dependence of <n> in DDIS at fixed MX • Comparison of DIS and DDIS • Rapidity spectra • KNO scaling

  10. Kinematic relations DIS ymax=ln (W/m) W2 ~ Q2/x DDIS  = Q2/(Q2+MX2) gap ~ ln (1/xIP)

  11. Q2 dep. of <n> in DIS/DDIS at fixed W • <n> vs Q2 • DIS/DDIS data (at fixed MX) • No dependence on Q2 • Fit <n>: <n> = a + b log(Q2)

  12. Q2 dep. of dn/d(y-ymax) in DIS at fixed W • dn/d(y-ymax) vs y-ymax • ymax= ln(W/m) • Weak Q2 dependence (scaling violations in QCD) DIS: <n> predominantly function of W, not Q2

  13. Q2 dep. of dn/d(y-ymax) in DDIS at fixed W • dn/d(y-ymax) vs y-ymax • ymax= ln(W/m) • Weak Q2 dependence • Weak W dependence DDIS: <n> predominantly function of MX, not Q2

  14. dependence of <n> • Intuitive picture: expect no  dependence (no Q2 dependence measured)

  15. dependence of <n> low <n> • * fluctuation models: relative fraction of q and g fragmentation depends strongly on  high <n>

  16. dep. of <n> at fixed MX in DDIS • MX kept fixed • No  dependence DDIS: <n> predominantly function of MX, not Q2 or 

  17. W dependence of <n>? • Change of W means change the ‘gap’ • Gap ~ ln(1/xIP) • Investigate <n> dependence on xIP

  18. Wdep. of <n> at fixed MX in DDIS • Change W: change xIP • Regge factorisation: diffractive pdf’s independent of xIP • Breaking of Regge factorisation • In resolved IP model: pomeron + reggeon

  19. Wdep. of <n> at fixed MX in DDIS • Fit <n>: <n> = a + b log(W2) • Regge factorisation breaking expected in multiple scattering models • Effects predicted to diminish with increasing Q2 ( shorter interaction time) Factorisation breaking within errors, not dependent on Q2

  20. Comparison DIS/DDIS: rapidity spectra • dn/d(y-ymax) vs y-ymax • Central region: particle density similar for DIS and high MX DDIS • Lowest MX bin: systematically different

  21. Comparison DIS/DDIS: KNO scaling • Negative particles • (z) = <n> Pn vs z = n/<n> • Approximate KNO scaling for DIS and DDIS • Shape of KNO distribution similar for DIS and DDIS

  22. Conclusions Charged particle multiplicity • studied for DIS and DDIS • <n> in DIS depends only on W, not Q2 or x • <n> in DDIS depends mainly on MX and W, not Q2 or  • DIS and DDIS: rapidity spectra similar for highest MX • DIS and DDIS: approximate KNO scaling Kinematic dependencies Comparison DIS and DDIS

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