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Fragmentation and correlation of hadrons in ep collisions

XXXVI International Symposium on Multiparticle Dynamics September 02–08, 2006 ,  Paraty, Rio de Janeiro, Brazil. Fragmentation and correlation of hadrons in ep collisions. Artur Ukleja (Warsaw University). on behalf of H1 and ZEUS Collaborations. Motivation DIS kinematic variables

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Fragmentation and correlation of hadrons in ep collisions

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  1. XXXVI International Symposium on Multiparticle DynamicsSeptember 02–08, 2006, Paraty, Rio de Janeiro, Brazil Fragmentation and correlation of hadrons in ep collisions Artur Ukleja (Warsaw University) on behalf of H1 and ZEUS Collaborations Motivation DIS kinematic variables and particle production Bose-Einstein correlations between and Charged particle momentum distributions Azimuthal asymmetry of particle production through the energy flow Summary

  2. XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil Motivation • Produce partons (Matrix Element) • Fragmentation (Parton Shower) • Hadronisation HADRONISATION • Measuring hadrons would contain information on: • Fragmentation properties • ( production, BEC, charged particle momentum) • Matrix Element • (charged particle momentum, azimuthal asymmetry)

  3. XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil DIS kinematic variables The photon virtuality Q2 and Bjorken variables are defined as: The CMS energy squared of the ep system: collisions at HERA give information about soft and hard processes HERA: 1994-97 1998-06

  4. XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil and particle production particle fragmentation DIS PHP

  5. XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil • Baryon-antibaryon asymmetry • Baryon to meson ratio direct resolved

  6. XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil Baryon-antibaryon asymmetry Q2>25 GeV2 0.02<y<0.95 • No evidence of baryon numbers propagated to central rapidity • Baryon and antibaryon are produced according to the same mechanism ARIADNE: with a strangeness factor of S=0.3 and 0.22

  7. XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil Baryon to meson ratio • ARIADNE (S=0.3) follows the shape of the data • Baryon to meson ratio increases at low xOBS up to 0.7, not predicted by PYTHIA (is flat at about 0.4) • For high xOBSsame baryon to meson ratio as in DIS and e+e-

  8. XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil Baryon to meson ratio (R) in PHP • R is bigger, most significantly at high pTLAB for the fireball enriched • PYTHIA predicts almost the same R for both sample • PYTHIA prediction approximately follows the measured values of R for the fireball depleted Fireball enriched Jet of the highest ET contributed at most 30% to the total hadronic ET Fireball depleted

  9. XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil BE correlations between and BEC have been observed in DIS at HERA. (gives information about hadronisation process) The two-particle correlation function is studied as: M – invariant mass of the pair Two bosons with momenta p1 , p2 produced at points r1 and r2 12 – bosons BEC as the method of determination of the size of the particle emission source

  10. XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil Bose-Einstein correlation function P(Q12) – the two-particle distribution for identical kaon pairs Pref(Q12)– the reference distribution in the absence of BEC Standard parametrisation of R(Q12) is Goldhaber-like parametrisation r – radius of the particle emission source – coherence strength factor =0 since linear behavior in the high Q12 region

  11. XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil BEC function for

  12. XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil BEC function for

  13. XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil BEC comparison with LEP A good agreement with LEP for radius ZEUS r=0.57±0.09(stat) fm ZEUS r=0.61±0.08(stat) fm

  14. XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil Charged particle momentum distributions Parton splitting in pQCD causes scaling violations in structure functions. Also seen in fragmentation functions. Test pQCD. Scaled momentum distribution is defined in the Breit Frame as: ph – momentum of charged track in the current region of Breit Frame Q – virtuality of the exchange boson

  15. XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil Scaling violations 100<Q2<20000 GeV2 0.05<y<0.6 • Number of hadrons: • increase at small xp with ↗Q

  16. XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil Charged particle momentum distributions Compared with e+e- experiments • Number of hadrons: • increase at small xp with ↗Q • decrease at large xpwith ↗Q The cause of the scaling violations is the same as for the scaling violations observed for the deep inelastic structure functions. • e+e-data show the same behavior as ep data 100<Q2<20000 GeV2 0.05<y<0.6

  17. XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil Charged particle momentum distributions Compared with LO MC predictions • CDM and PS models provide general reasonable description of the data • At high xp HERWIG predictions even fail to show scaling behavior producing a flat spectrum 100<Q2<20000 GeV2 0.05<y<0.6

  18. XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil Azimuthal asymmetry • Azimuthal asymmetry comes from: • two-body processes (BGF and QCDC) • photon polarisation • longitudinally polarized electron beam • final hadron polarisation • intrinsic parton momentum in the proton

  19. XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil Azimuthal asymmetry X X In the Born approximation for purely electromagnetic interactions with unpolarised initial electron beam the terms containing sin and sin2 vanish as a consequence of a time-reversal invariance The coefficients D and E arise from parity violating weak interactions or polarisation of the initial electron beam

  20. XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil Energy flow method Jet analysis Phys.Lett.B551(2003)226-240 Multiplicity method Phys.Lett.B481(2000)199-212 Each particle is weighted with its energy

  21. XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil Asymmetry as a function of NC DIS: 100<Q2<8000 GeV2 0.01<x<0.1 0.2<y<0.8 Energy flow method

  22. XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil Asymmetry as a function of Cut ET>2 GeV is sufficient to removed non perturbative effects Proposed by Chay et al. Phys.Lett.B269(1991)175-182

  23. XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil Summary and conclusions • Measurements: and production • BEC • charge particle momentum • have been made at HERA • ep data show the similar behavior as e+e- data • Detailes, for example: • The baryon to meson ratio increases at low xOBS up to 0.7, not predicted by PYTHIA (is flat at about 0.4) • Azimuthal asymmetry is investigated for cos , cos2 , sin , sin2 • as a function of  and ET,min • cos and cos2is significant • sin and sin2consistent with null • NLO better describe ZEUS data then LO MC predictions

  24. XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil BACK UP

  25. XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil Fireball enriched and fireball depleted Line represents the cut used to separate fireball enriched and fireball depleted Fraction of the total ET carried by two jets of highest transverse energy Fireball depleted events are dominated by dijet events carrying most of the total ET Fireball enriched and fireball depleted has about the same number of events

  26. XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil BE correlations between • good agreement with LEP for radius • higher  value then for ALEPH, DELPHI • the f0 (980) resonance is expected in the same low Q12 region where BEC are measured • small contribution of f0 (980) in data can significantly change  value • the estimation of f0 (980) in data is 10 % • the ALEPH, DELPHI removed f0 resonance

  27. XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil BE correlations between • good agreement with LEP for radius • smaller  value then for e+e- • different fragmentation processes in e±p and e+e- • proton influence is expected – ZEUS data populate mostly proton fragmentation region • K+K- can be production from 0 (1020) resonance dacay – strong signal of 0 (1020) in ZEUS data

  28. XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil Charge particle momentum distributions Compared with NLO QCD predictions The data show a clear sensitivity to the fragmentation function used in the NLO QCD predictions 100<Q2<20000 GeV2 0.05<y<0.6

  29. XXXVI International Symposium on Multiparticle Dynamics, 02–08.09.2006, Paraty, Brazil Summary and conclusions • Measurements of and production have been made at HERA • No evidence of baryon numbers propagated to central rapidity • The baryon to meson ratio increases at low xOBS up to 0.7, not predicted by PYTHIA (is flat at about 0.4) • BEC have been measured in DIS at HERA • The radius value for KS0KS0 is consistent with K±K± and with ±± • The radius value is compatible with LEP results • Scaled charge particle momentum is investigated at high Q2 • e+e-data show the same behavior as ep data • MC tuned from LEP data can successfully described ep data over large region of Q • Azimuthal asymmetry is investigated for cos , cos2 , sin , sin2 • as a function of  and ET,min • cos and cos2is significant • sin and sin2consistent with null • NLO better describe ZEUS data then LO MC predictions

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