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QCD studies through hadronic final states at HERA

QCD studies through hadronic final states at HERA. scaled charged particle momentum distributions in DIS a s from inclusive jet in DIS 3-jet in DIS for low x multi-jet production in g p antideuteron production in DIS. Takahiro Matsumoto / KEK

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QCD studies through hadronic final states at HERA

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  1. QCD studies through hadronic final states at HERA • scaled charged particle momentum distributions in DIS • as from inclusive jet in DIS • 3-jet in DIS for low x • multi-jet production in gp • antideuteron production in DIS Takahiro Matsumoto / KEK On behalf of H1 and ZEUS collaborations Lake Louise Winter Institute 2007, 24 February, 2007

  2. Hadronic final states @HERA Jet production at HERA This talk covers recent results on: - fragmentation function - hard process QCD (as, low x) - other topics (multi-parton interaction, antideuteron) as as Cross section for HFS: Fragmentation function Parton distribution function of the proton Cross section of the hard process Regarded as hadronic correction ~ 1 + dhad in jet studies Takahiro Matsumoto

  3. Breit frame  parton from proton (for the interaction) is back scattered with the same momenta Breit frame has advantage for DIS jet analysis • Current region can be compared to e+e- experiments • Current quark and proton remnants are clearly separated • Contributions from QCD radiation can be seen in high ET jet Target region Current region [Proton remnants] Takahiro Matsumoto

  4. Jet algorithm • Longitudinally invariant kT algorithm • theoretically favored, no overlapping For each Energy Flow Object, calculate: Radius parameter [usually set to 1] dii = ET,i2 R2 dij = min[ET,i2,ET,ｊ2][Dh2 + Df2] *under Breit Frame Order all dii and dij If dii is minimum  i is regarded as jet If dij is minimum  i and j are merged, further iteration Takahiro Matsumoto

  5. Scaled charged particle momentum distributions in DIS L = 44 pb-1 (2000) • For tracks in current region of Breit frame, define: • xp = p/(Q/2) • Measurements of dn/dxp for Q <~100 GeV and full xp range H1prelim-05-133 Scaling violation is clearly observed 1/N dn/dxp Q increasing xp Agreement with e+e- experiments, and RAPGAP(PS) MC tuned to e+e- universality of quark fragmentation function Takahiro Matsumoto

  6. Inclusive jet in DIS NLO describes inclusive jets well Agreement also for smaller radius (R=0.7,0.5)  Interesting for studying jets from heavy particles asextraction for as Small uncertainty of as (main concern is theoretical part) is obtained from Q2>500GeV2 and R=1 Takahiro Matsumoto

  7. as running is clearly seen ZEUS (DESY-06-241) H1prelim-05-133 Consistent with PDG’2006: as(MZ) = 0.1176 ±0.002 Takahiro Matsumoto

  8. 3-jet in DIS for low x qjet < 20º • Low x DIS • DGLAP (kT ordering) may be insufficient to describe g radiation • 3-jet in DIS • Low Q2: 5 < Q2 < 80 GeV2 • Low x: 10-4 < x < 10-2 • 2 jets in forward • Sensitive to g radiation • Fixed order QCD prediction, O(as3) is greatly improved from O(as2) , but still discrepancy exists at small x Unordered gluon radiation would play a significant role xjet = Ejet*/Ep,beam > 0.035 L= 44pb-1 ~ as3 (usually 3-jet: ~as2) Takahiro Matsumoto

  9. Four jets in photoproduction • Test of pQCD in higer orders of as • Can adjust multi-parton interaction model to agree with data  related to LHC (underlying event) 4jet direct (tree level) Multi-jet at HERA O(aas3) Schematic view of MPI Takahiro Matsumoto

  10. ZEUS (prel.) 121 pb-1 MC without MPI underestimates the data in low Mnj region First observation of 4 jets in photoproduction HERWIG with tuned MPI describes the data well Fraction of the photon’s momentum exchanged in the interaction Takahiro Matsumoto

  11. Antideuteron production in DIS Q2 > 1 GeV2 • Antideuteron production: • Studied in nuclear experiments (PHENIX etc.), but not well known for elementary particle collisions • Search in DIS first time • Mass was calculated from dE/dx, p • Also use DCA to beam spot, Zvtx • First observation of antideuteron in DIS • N(d) = 61 ±8 ZEUS (prel.) 120 pb-1 dE/dx(mips)>2.5 Takahiro Matsumoto

  12. d/p, p/p ratios in DIS Q2 > 1 GeV2 • Ratios were measured after correction of efficiency for tracking and dE/dx cut • d/p ~ 5 x 10-4 • Consistent with gp(H1), also for U(1S)(ARGUS), pp • But d production is suppressed in e+e- • p/p ~ 1 • Asymmetry is not observed 0.3 < pT/M < 0.7, |y|< 0.4 Takahiro Matsumoto

  13. Summary • Scaled momentum in DIS in wide kinematic range  validation of fragmentation function • Inclusive jet at high Q2 DIS  measurements of strong coupling constant as • 3-jet in low Q2 DIS  QCD at low x • First observation of 4-jet in photoproduction  tuning of multi-parton interaction model • First observation of antideuteron in DIS  understanding of hadronization, coalescence Selected topics on recent results from hadronic final states at H1 and ZEUS were presented Hadronic final states allow various tests on QCD ! Takahiro Matsumoto

  14. Backup

  15. as measurements at HERA as running Takahiro Matsumoto

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