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QCD physics at HERA

QCD physics at HERA. Recent and results from:. Takahiro Matsumoto KEK, ZEUS Group. Structure function EW tests using polarized lepton Hadronic Final States. KEKPH 2007 1st March, 2007. HERA accelerator. DESY, Hamburg. Ring ~ 6.3 km.

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QCD physics at HERA

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  1. QCD physics at HERA Recent and results from: Takahiro Matsumoto KEK, ZEUS Group • Structure function • EW tests using polarized lepton • Hadronic Final States KEKPH 2007 1st March, 2007

  2. HERA accelerator DESY, Hamburg Ring ~ 6.3 km • HERA; start 1992… end June 30, 2007 • Only one ep collider in the world Proton e p 27.6 GeV 920 GeV √s = 318 GeV Electron or positron Takahiro Matsumoto

  3. Longitudinal polarized lepton • Self polarization of electrons by Synchrotron radiation (Sokolov-Ternov effect) • Use spin rotator for longitudinal polarization • Applied to H1 and ZEUS from 2002- • Polarization: • 30-40% (both for L&R) • Useful for EW tests in DIS Takahiro Matsumoto

  4. The Detectors Multi-purpose detectors with Calorimeter, Tracking system Uranium-Scintillator calorimeter Liquid-Argon calorimeter s(E)/E = 35%for hadrons s(E)/E = 50%for hadrons s(E)/E = 18%for electrons s(E)/E = 12%for electrons Both detectors provide competitive measurements on QCD Takahiro Matsumoto

  5. Luminosity (HERA-I/II) as of Feb. 20, 2007 • HERA-I (1992~2000) • e+p 110 pb-1 • e-p 15 pb-1 (on tape) • Unpolarized lepton Matured analyses, being finalized • HERA-II (2002~2007) • e+p 130 pb-1 • e-p 250 pb-1(on tape) • Longitudinally polarized lepton • Si vertex detector for b,c tagging  New results with larger statistics, new capabilities are being produced 06/07 04-06 92-00 02/03 ~70% is recorded on the tape Takahiro Matsumoto

  6. Deep Inelastic Scattering at HERA • HERA; Giant electron micro scope of the proton • Q2 up to 4 Ee Ep ~ 105 GeV2  Space resolution; 0.001 fm  Proton structure can be measured for wide kinematic range • Various QCD studies using Hadronic final states 920 GeV 27.6 GeV Takahiro Matsumoto

  7. DIS (cont’d) Related to Q2 = - (k-k’)2 x = Q2/2P•(k-k’) x P Parton Distribution Function Main source Neutral Current DIS: ~ S x (qf – qf) Small for Q2 < < MZ2 Y± = 1 ±(1-y)2, inelasticity y = Q2/xs Longitudinal component Small, 0 for LO QCD dumped with y2 F2, F3, FL Structure function of the proton Takahiro Matsumoto

  8. Kinematic regions • HERA covers wide span (~O(106) ) for Q2 and x region, compared to Fixed targets and Tevatron • Structure function: • Evolution in Q2, measured very well • Low x region is only covered by HERA  Important input for LHC ! LHC x region Takahiro Matsumoto

  9. Structure function, F2 • Sea quark is dynamically produced for high Q2 in low x  Scaling violation F2 • Predicted by DGLAP (Dokschitzer-Gribov-Lipatov-Altarelli-Parisi) evolution equation for wide kinematic region  Triumph of perturbative QCD Takahiro Matsumoto

  10. High Q2 DIS • Low Q2 • NC, mediated by g • CC, suppressed by W mass • High Q2( >> MZ2, MW2 ) • NC and CC cross sections compatible  Electroweak unification ! Neutral Current For NC, Q2 >~ MZ2 is also interesting to see effect of g/Z interference Charged Current MZ2 Takahiro Matsumoto

  11. F2, xF3 at High Q2 Y± = 1± (1-y)2 E polarization F2 = S Af x (qf + qf) = F2g- (ve + Pe ae) cZ F2gZ + O(cZ2) xF3 = S Bf x (qf- qf) = - (ae + Peve)cZ xF3gZ + O(cZ2) g(EM) gZ (EW cZ order) Z (EW cZ2 order) visible @High Q2 EW coupling vf = T3f – 2ef sin2qW, af = T3f F2gZ = S 2 efvf x ( qf + qf )  ve ~ 0 ( because 2sin2qW ~ ½) xF3gZ=S2 efaf x ( qf – qf ) Unpol data  seen in xF3 (s(e-p) – s(e+p))  af of quarks EW effect? pol data  also in F2  af, vf of quarks Takahiro Matsumoto

  12. xF3 (unpol) • xF3 at High Q2 is useful to determine valence quark PDF • complementary to neutrino DIS at Low Q2 xF3 ~ S x (qf – qf), obtained from s(e-p) – s(e+p) Takahiro Matsumoto

  13. Polarization asymmetry at High Q2 PR > 0 PL < 0 e+p A+ A- e-p First observation of parity violation in e±p NC DIS Takahiro Matsumoto

  14. Light quark EW coupling • ZEUS fit to HERA-I e±p DIS, jets + HERA-II pol e-p DIS • Consistent with SM • Better precision than H1 unpol results (especially for vu,d) • Better precision than Tevatron, LEP Takahiro Matsumoto

  15. Obtained PDF HERA-I +HERA-II • Inclusion of HERA-II data with polarization • Consistent results with HERA-I • Smaller uncertainties of PDF at High Q2 + HERA-II HERA-I  Good News for LHC Takahiro Matsumoto

  16. 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

  17. Breit frame  parton from proton (for the interaction) is back scattered with the same momenta Advantages in Breit frame: • Current region can be compared to e+e- experiments • Current quark and proton remnants are clearly separated Target region Current region [Proton remnants] Takahiro Matsumoto

  18. 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

  19. Jet analysis Breit frame • theoretically favored, no overlapping • No gluon  No PT components • Contributions from QCD radiation can be seen in high ET jet Longitudinally invariant kT algorithm Radius parameter [usually set to 1] For each Energy Flow Object, calculate dii, dij under Breit frame dii = ET,i2 R2 Order all dii and dij If dii is minimum  i is regarded as jet dij = min[ET,i2,ET,ｊ2][Dh2 + Df2] If dij is minimum  i and j are merged, further iteration Takahiro Matsumoto

  20. 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

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

  22. as measurements at HERA as running many as from jets and scaling violation in the structure function  All give consistent results Takahiro Matsumoto

  23. Low x QCD • We want to estimate LHC PDF from Tevatron and HERA data • DGLAP QCD evolution sufficiently works? • Need to care low x • Saturation? • Breakdown of DGLAP?  Study at HERA LHC Tevatron HERA Takahiro Matsumoto

  24. Evolution, Resummation • DGLAP (Dokshitzer-Gribov-Lipatov-Altarelli-Parisi) • kT ordering, describe evolution in Q2, but fails at low x • BFKL (Balitsky-Fadir-Kuraev-Lipatov) • No kT ordering, applicable to low x • CCFM (Ciafaloni-Catani-Fiorani-Marchesini) • angular ordering, describe evolution both in Q2 and x ( applicable to low x @ BFKL and High Q2 @ DGLAP) ~(lnQ2)n Gluon ladder diagram ~(ln(1/x))n BFKL: expect more energetic jets in forward Takahiro Matsumoto

  25. Extended to forward rapidity 2 < hjet < 3.5 • 0.0004 < xBj < 0.005 Forward jet L = 82pb-1 • LEPTO (DGLAP) • Disagree with data • CASCADE (CCFM) • Set 2 ( with no singular term ) is better • OK for Q2 and ET • But fail in xBj and h • ARIADNE • Color dipole model • unordered kT, but not BFKL… • Good agreement Comparison with LO+PS MC Takahiro Matsumoto

  26. Forward jet (cont’d) Comparison with NLO QCD calculation with hadronization correction • NLO, improved from LO calculation (k=s(NLO)/s(LO)~10) • Data is larger than NLO prediction, but within large theoretical uncertainty * except lowest xBj * DISENT: Fixed order QCD partonic cross section, on mass shell ME + DGLAP Takahiro Matsumoto

  27. 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 need NNLO or unordered gluon radiation? xjet = Ejet*/Ep,beam > 0.035 L= 44pb-1 ~ as3 (usually 3-jet: ~as2) Takahiro Matsumoto

  28. Four jets in photoproduction Q2 < 1 GeV2 • Test of pQCD in higer orders of as • Can adjust multi-parton interaction model to agree with data  related to LHC (underlying event) g quasi-photon 4jet direct (tree level) Multi-jet at HERA O(aas3) Schematic view of MPI Takahiro Matsumoto

  29. 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

  30. 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

  31. 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 U(1S)(ARGUS), pp • But d production is suppressed in e+e-  qq • p/p ~ 1 • Asymmetry is not observed 0.3 < pT/M < 0.7, |y|< 0.4 Takahiro Matsumoto

  32. Coalescence model Consistent with pp, pA HERA • Process dependent • Pp ~ pA ~ gp • Suppressed in e+e- and also in AA B2 ~ 1 / V (freeze out volume) Suppression in AA larger source size Recent measurements in e+e-also show the suppression (mechanism, not well known yet…) Takahiro Matsumoto

  33. Summary • Structure function in wide Q2 and x range • F2; Steep rise in F2 at low x (sea quark and gluon), well described by pQCD (DGLAP) • xF3; gZ interference at High Q2, sensitive to valence quark • Light quark EW coupling; benefit from polarized lepton • Proton PDF determination • Hadronic final states • Various QCD studies; fragmentation, as, low x, multiple parton interaction, coalescence • Many other interesting items were missed this time • Diffraction, heavy flavor, new physics search etc. • HERA, operating 15 years and end up with this year. Inclusion of HERA-II results with polarized lepton, finally will improve our knowledge on QCD Takahiro Matsumoto

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