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Inclusive Diffraction at HERA From The ZEUS Experiment

Inclusive Diffraction at HERA From The ZEUS Experiment. Presented by B.Loehr on behalf of ZEUS. New data from the running period 1999-2000. The last period with the ZEUS Forward Plug Calorimeter (FPC) and the Leading Proton Spectrometer (LPS) installed.

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Inclusive Diffraction at HERA From The ZEUS Experiment

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  1. Inclusive Diffraction at HERA From The ZEUS Experiment Presented by B.Loehr on behalf of ZEUS New data from the running period 1999-2000. The last period with the ZEUS Forward Plug Calorimeter (FPC) and the Leading Proton Spectrometer (LPS) installed. Results from all three methods to extract inclusive diffractive events: • Leading proton spectrometer • The MX – method • Large rapidity gap method using data from the same running period. We attempt to get a consistent picture from these three method. Bernd Löhr, DESY Diffraction 2006 , 5-10 September , Milos Greece Page 1

  2. Extraction of diffractive events (I) 1.)Forward proton detection -> diffractively scattered proton ; the only method to measure the t-distribution Forward proton tagged events are practically free of proton dissociation background. ZEUS preliminary 0.4 0.6 0.8 1.0 They contain, however, contributions from Reggeon exchange at high xIP or low xL. xL LPS has small acceptance 2.) Thelarge (pseudo)rapidity (max) method No tracks or energy deposits in calorimeter for rapidities greater than maxor at angles less than min. Events tagged by a large rapidity are dominated by diffraction but they contain contributions from proton dissociation and from Reggeon exchange. Bernd Löhr, DESY Diffraction 2006 , 5-10 September , Milos Greece Page 2

  3. Extraction of diffractive events (II) 3.) The Mx-method (ii) Diffractive events : (i) Nondiffractive events : Uncorrelated particle emissionbetween incoming p-direction and scattered quark. At high energies and not too low MX Rapidity Property of a produced particle (iii) Nondiffractive + diffractive contributions W Poisson distr. for Dy in nondiffractive events For Fit slope b and c -> subtract nondiffractive events. Bernd Löhr, DESY Diffraction 2006 , 5-10 September , Milos Greece Page 3

  4. The ZEUS MX-Analysis (I) Example of lnMX-distributions for four kinematical bins : Diffractive data selected by the MX-method contain proton dissociative events but no contributions from Regge exchange MC-simulation : nondiffractive : DJANGOH diffractive : SATRAP proton diss.: SANG SANG adjusted to fit data which are dominated by proton dissociation Proton dissociation can be reliably calculated for MN > 2.3 GeV and has been subtracted from data The ZEUS MX-results contain contributions from proton dissociation for masses MN < 2.3 GeV. fit to data in the fit region fitted slope of of nondiffractive events Data are presented for 9 Q2-bins, 7 W-bins, and 6 MX-bins at reference values Q2ref, Wref, MXref Bernd Löhr, DESY Diffraction 2006 , 5-10 September , Milos Greece Page 4

  5. ZEUS MX – data from 1998 – 2000 (II) Mx 98-99, Mx 99-00 (prel.) | Mx 98-99 : * Published data from 1998-1999 period (ZEUS Coll., S.Chekanov et al. Nucl. Phys B 713, 3 (2005) ) | Prel. Mx 99-00: Preliminary results from 1999-2000 period. Extension of Mx 98-99 analysis to higher Q2. Mx 98-99 and Mx 99-00 analyses have common bin at Q2 = 25 GeV2 Bernd Löhr, DESY Diffraction 2006 , 5-10 September , Milos Greece Page 5

  6. ZEUS Mx 98-99, ZEUS Mx 00 (prel.) ZEUS MX– data from 1998 – 2000 (III) | Mx 98-99: * Prel. Mx 99-00: | Mx 98-99 and Mx 99-00 analyses have common bin at Q2 = 55 GeV2 Within syst. errors good agreement between Mx 98-99 and Mx 99-00 results Bernd Löhr, DESY Diffraction 2006 , 5-10 September , Milos Greece Page 6

  7. Fit W-dependence of inclusive DIS and inclusive diffractive DIS cross sections Inclusive DIS: For small x, F2 rises rapidly as x-> 0 < < < Inclusive diffractive DIS: averaged over t for small t. Inclusive DIS and inclusive diffractive DIS are not described by the same ‘Pomeron’. take as measure by ZEUS LPS Bernd Löhr, DESY Diffraction 2006 , 5-10 September , Milos Greece Page 7

  8. Ratio of total diffractive cross-section to total DIS cross-section Ratio plotted at W=220 GeV because only there the full MX range is covered by measurments r = sdiff(0.28<MX<35 GeV)/stot at W=220 GeV Within the errors of the measurements r is independent of W. Mx 98-99 Mx 99-00 (prel.) At W=220 GeV, r can be fitted by r = 0.22 – 0.034.ln(1+Q2) This logarithmic dependence of the ratio of total diffractive cross-section to the total DIS cross section indicates that diffraction is a leading twist process for not too low Q2. Bernd Löhr, DESY Diffraction 2006 , 5-10 September , Milos Greece Page 8

  9. Diffractive Cross-Section and Diffractive Structure Functions If t is not measured : (LRG and MX-method ) H1 defines : sizable only at high y ZEUS neglects the contribution from longitudinal structure function If is interpreted in terms of quark densities, it specifies the probability to find in a proton which undergoes a diffractive interaction a quark carrying a fraction x = bxIPof the proton momentum. Diffraction 2006 , 5-10 September , Milos Greece Page 9 Bernd Löhr, DESY

  10. xIPF2D(3) Results from the MxII-Analysis ZEUS Mx 99-00 (prel.) Diffraction 2006 , 5-10 September , Milos Greece Page 10 Bernd Löhr, DESY

  11. ZEUS modified BEKW Fit The ZEUS data support taking nT(Q2) = ng(Q2) = n1`ln(1+Q2/Q20) and nL= 0 Taking x0= 0.01 and Q20= 0.4 GeV2 results in the modified BEKW model (BEKW(mod)) with the 5 free papameters : cT , cL ,cg , n1T,g , g Diffraction 2006 , 5-10 September , Milos Greece Page 11 Bernd Löhr, DESY

  12. xIPF2D(3) Results from the MxI and MxII-Analyses with BEKW(mod) Fit (I) BEKW-fit (prel.): transverse qq contribution sum of all contributions > 400 points, 5 parameters c2/nD = 0.71 , total errors transverse qqg contribution longitudinal qq contribution Diffraction 2006 , 5-10 September , Milos Greece Page 12 Bernd Löhr, DESY

  13. xIPF2D(3) Results from the FPC I +II MX-Analyses with BEKW(mod) Fit: II Result of the BEKW(mod) fit xIPF2D(3) shows considerable scaling violations: from positive scaling violations over near constancy to negative scaling violations. Diffraction 2006 , 5-10 September , Milos Greece Page 13 Bernd Löhr, DESY

  14. xIPF2D(3) Results from the FPC I +II MX-Analyses with BEKW(mod) Fit ( III) ZEUS Mx 99-00 (prel.) • xIPF2D(3) exhibits : • a broad maximum around b=0.5 • which is due to the transverse • qq-contribution, • a steep rise towards small b • which is generated by the • qqg-contribution, • a longitudinal qqg-contribution • which is sizeable only at • very high band causes the structure function not to • vanish at b = 1. - - - - Diffraction 2006 , 5-10 September , Milos Greece Diffraction 2006 , 5-10 September , Milos Greece Page 14 Bernd Löhr, DESY Bernd Löhr, DESY

  15. xIPF2D(3) Results from the FPC I +II MX-Analyses with BEKW(mod) Fit (IV) ZEUS Mx 99-00 (prel.) Fixed xIP = 0.01 25 < Q2 < 190 GeV2 in one plot The 3 contributions from BEKW(mod) fit for the above Q2 values plotted - - longitudinal qq-contributions qqg-contributions The BEKW model has an effective QCD-type Q2-evolution incorporated. Diffraction 2006 , 5-10 September , Milos Greece Page 15 Bernd Löhr, DESY

  16. ZEUS Results from the LPS I Diffractive structure functions from ZEUS LPS mesurements Regge fit : t = 0.13 GeV2 t = 0.3 GeV2 ZEUS LPS 00 (prel.) ZEUS LPS 00 (prel.) Fit parameters: Diffraction 2006 , 5-10 September , Milos Greece Page 16 Bernd Löhr, DESY

  17. ZEUS Results from the LPS (II) Comparison of LPS results with recent H1 FPS results ZEUS LPS 00 (prel.), H1 FPS 06 RD = 0 -> Not shown are the normalization Uncertainties of +12/-10 % for the ZEUS LPS data and +/-10% for the H1 FPS data. The agreement is good Diffraction 2006 , 5-10 September , Milos Greece Page 17 Bernd Löhr, DESY

  18. ZEUS Results from the LRG Method (I) Events selected by : hmax < 3.0 and energy in the Forward Plug Calorimeter (FPC) < 1 GeV ZEUS LRG 00 (prel.) ZEUS LRG 00 (prel.) Results of a Regge-fit Input parameters to the Regge -fit: aIR(0) = 0.75, BIR= 2.0 GeV-2 a’IP = 0.0 GeV-2 , BIP = 7.2 GeV-2 Fit results : aIP(0) = 1.117 +/-0.005 +0.024 -0.007 Diffraction 2006 , 5-10 September , Milos Greece Page 18 Bernd Löhr, DESY

  19. ZEUS Results from the LRG Method (II) Comparison of ZEUS LRG data with LPS data ZEUS LRG 00 (prel.) ZEUS LRG 00 (prel.), ZEUS LPS 00 (prel.) The ratio LPS/LRG = 0.82 +/- 0.01(stat.) +/- 0.03(syst) it is independent of Q2and b The Regge-fit gives a good description of the ZEUS LRG data with c2/ndf = 159/185 Not shown is the normalization uncertainty of the LPS measurement of about 10%. Diffraction 2006 , 5-10 September , Milos Greece Page 19 Bernd Löhr, DESY

  20. ZEUS : Comparison of Results from the MX-, and LRG- Method (I) ZEUS MX 98-99, ZEUS MX 99-00 (prel.), ZEUS LRG 00 (prel.) In general good agreement for xIP < 0.01 For xIP > 0.01 one can expect some differences from Reggeon contributions to the LRGdata. Diffraction 2006 , 5-10 September , Milos Greece Page 20 Bernd Löhr, DESY

  21. ZEUS : Comparison of Results from the MX-, and LRG- Method (II) ZEUS MX 99-00, ZEUS MX 99-00 (prel.), ZEUS LRG 00 (prel.) Comparison of ZEUS LRG with ZEUS MX results: xIPF2D(3) as a function of Q2 ZEUS Mx 90-99 ZEUS Mx 99-00 (prel.) ZEUS LRG 00 (prel.) Reasonable agreement, maybe there is a normalization difference. Work is continuing to understand remaining differences Diffraction 2006 , 5-10 September , Milos Greece Page 21 Bernd Löhr, DESY

  22. Summary • ZEUS presented preliminary results on inclusive diffraction from • 3 different methods for the extraction of inclusive diffractive events. • Results from all 3 methods are derived from data taken during the same time. • The results span a wide range of the kinematic region up to high Q2. • There is good to reasonable agreement for the results from all 3 methods. • In particular, there is agreement for the Q2-dependence of the structure function • between the MX-method and the LRG-method. • There is also good agreement compared to results from H1 for the • LRG- and FPS method. • Work continues to understand some remaining minor differences, in particular • with respect to the relative normalisations. • We try to get a consistent picture out of the results from these three methods. Diffraction 2006 , 5-10 September , Milos Greece Page 22 Bernd Löhr, DESY

  23. Additional Material

  24. The ZEUS MX-Analysis II Demonstration that MX can be measured reliably Nondiffractive contribution from DJANGOH has logarithmic slope Nondiffractive contribution from REGGEON exchange has logarithmic slope Bernd Löhr, DESY Diffraction 2006 , 5-10 September , Milos Greece Page 5

  25. ZEUS Results from the LPS I The LPS has six Roman-Pot stations. For this analysis only the stations S4,S5,S6 have been used The measured t-region is 0.09 < |t| < 0.55 GeV2 and results are given in two intervals<|t|>=0.13 GeV2and <|t|>=0.3 GeV2. ZEUS LPS 00 (prel.) The t-distributions from the LPS data Approximately exponential shape ZEUS LPS 00 (prel.) slope b ~ 7 GeV-2,no strong Q2, b or xIP dependence Diffraction 2006 , 5-10 September , Milos Greece Page 18 Bernd Löhr, DESY

  26. Comparison of Results from ZEUS LRG 00 with H1 LRG xIP = 0.003 xIP = 0.01 ZEUS LRG 00 (prel.), H1 LRG ZEUS LRG 00 (prel.), H1 LRG The ZEUS LRG 00 data are normalized to the H1 LRG data Diffraction 2006 , 5-10 September , Milos Greece Page 22 Bernd Löhr, DESY

  27. Regge-Fit to LRG compared with MX-Data The fit curve is the Pomeron contribution from the Regge-Fit to the LRG data Diffraction 2006 , 5-10 September , Milos Greece Page A4 Bernd Löhr, DESY

  28. Regge-Fit to LRG Data Diffraction 2006 , 5-10 September , Milos Greece Page A5 Bernd Löhr, DESY

  29. MX – dependence of the diffractive cross-section at constant W Mx 89-99 Q2ds/dMX shows a rapid variation with Q2 at low MX . Q2ds/dMX tends towardsa common value at higher MX . Mx 00 This kind of scaling behaviour is reached only at higher MX for higher Q2 when MX2 becomes of the order of Q2 . Bernd Löhr, DESY Diffraction 2006 , 5-10 September , Milos Greece Page A6

  30. Comparison of MX – Results from H1 and ZEUS H1 MX data 2006 ZEUS MX I data 2005 The ZEUS data have been renormalized by a factor 0.86 so that they correspond to MN=1.6 GeV as for the H1 data Bernd Löhr, DESY Diffraction 2006 , 5-10 September , Milos Greece Page A7

  31. Extraction of diffractive events (I) 1.)Forward proton detection -> diffractively scattered proton ; the only method to measure the t-distribution Forward proton tagged events are practically free of proton dissociation background. ZEUS preliminary They contain, however, contributions from Reggeon exchange at high xIP or low xL. LPS has small acceptance 2.) Thelarge (pseudo)rapidity (max) method No tracks or energy deposits in calorimeter for rapidities greater than maxor at angles less than min. Events tagged by a large rapidity are dominated by diffraction but they contain contributions from proton dissociation and from Reggeon exchange. Bernd Löhr, DESY Diffraction 2006 , 5-10 September , Milos Greece Page 2

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