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Multiplicity structure in inclusive and diffractive deep-inelastic ep collisions

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binah
22 diapositives · 394 Views · Sep 10, 2014

This workshop highlights a comprehensive analysis of multiplicity structures in inclusive and diffractive deep inelastic scattering (DDIS) using data from H1. Key findings demonstrate that the mean multiplicity of charged particles is primarily influenced by the invariant mass MX and the total energy W, rather than the virtuality Q². The results include comparisons of DDIS and DIS processes, exploring rapidity spectra, KNO scaling, and the significant correlations that arise from the data. The implications of these findings for theoretical models, including Regge and QCD approaches, are discussed.

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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