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Inclusive Double-Pomeron Exchange at the Fermilab Collider

CDF Paper Seminar October 23, 2003. Inclusive Double-Pomeron Exchange at the Fermilab Collider. Authors : M.E. Convery, K. Goulianos, K. Hatakeyama The Rockefeller University Godparents : Andrey Korytov, Giorgio Bellettini, Mario Martinez-Perez PRL Draft : CDF Note 6568.

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Inclusive Double-Pomeron Exchange at the Fermilab Collider

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  1. CDF Paper Seminar October 23, 2003. Inclusive Double-Pomeron Exchange at the Fermilab Collider Authors : M.E. Convery, K. Goulianos, K. Hatakeyama The Rockefeller University Godparents : Andrey Korytov, Giorgio Bellettini, Mario Martinez-Perez PRL Draft : CDF Note 6568

  2. History of the Analysis • Analysis blessed on May 2, 2002 and May 16, 2003. • PRL Draft : CDF Note 6568 Comments from • University of Toronto group • UC Davis group • University of Illinois group • Universita di Padova group • Main Analysis Document : CDF Note 5865 • Analysis Web Page : http://www-cdf.fnal.gov/internal/people/links/KenichiHatakeyama/idpe.html Many Thanks! Kenichi Hatakeyama

  3. High Energy Particle Diffraction • Several of our collaborators have expressed an unfamiliarity with diffractive physics. • This talk will start with a brief introduction to diffraction at CDF. • Details may be found in textbooks such as this. • Also, “Diffractive interactions of hadrons at high energies”, K. Goulianos, Phys. Rep. 101, 169 (1983) would be helpful for understanding the basics of soft hadron-hadron diffraction. V. Barone, E. Predazzi, Springer Press, 2002. Kenichi Hatakeyama

  4. Shaded Area : Region of Particle Production Introduction Diffraction in high energy hadron physics refers to a reaction in which no quantum numbers are exchanged between colliding particles. Kenichi Hatakeyama

  5. CDF Publications on Diffraction in Run 1 Soft Diffraction Hard Diffraction (diffraction +hard scattering) Kenichi Hatakeyama

  6. What did we learn from hard diffraction? ND For SD dijet production, Main issue in hadronic diffraction : • Do hard diffraction processes obey QCD factorization? (Are the diffractive parton distribution functions universal?) • This question can be addressed by comparing the functions extracted from different processes. SD Kenichi Hatakeyama

  7. ~10 Main Issue in Hadronic Diffraction :Results from single diffractive (SD) dijet production CDF Collaboration, Phys. Rev. Lett. 84, 5043-5048 (2000). • The diffractive structure function measured using SD dijet events at the Tevatron is smaller than that at HERA by approximately an order of magnitude. • The discrepancy is generally attributed to additional color exchanges which spoil the “diffractive” rapidity gap. Factorization Breakdown Next Q : How is it broken? Kenichi Hatakeyama

  8. Dijet Production in DPE CDF Collaboration, Phys. Rev. Lett. 85, 4215-4220 (2000). • Dijet production by double pomeron exchange was studied by CDF. • R[DPE/SD] is larger than R[SD/ND] by a factor of about 5. The formation of the 2nd gap is not as suppressed as the 1st gap. Extract diffractive structure function from R[DPE/SD] and compare it with expectations from HERA results. Kenichi Hatakeyama

  9. The diffractive structure function measured using DPE dijets is approximately equal to expectations from HERA! Diffractive Structure Functionmeasured using DPE dijet events Factorization holds? Kenichi Hatakeyama

  10. Soft Diffraction : Regge Theory Total Cross Section Single Diffractive Cross Section σtot(mb) √s (GeV) Kenichi Hatakeyama

  11. Unitarity problem : Soft Diffraction :Inclusive (Soft) SD Results • The measured SD cross section is smaller than the Regge theory prediction by approximately an order of magnitude at the Tevatron energy. • Normalizing the integral of the pomeron flux (fIP/p) to unity yields the correct √s-dependence of σSD. Tevatron data Renormalization K. Goulianos, PLB 353, 379 (1995). Similar results were obtained for double diffraction as well. Study DPE Is the formation of the second gap suppressed? Kenichi Hatakeyama

  12. ξ , t p p = g:triple-Pomeron coupling, κ=g/β(0). Inclusive (Soft) DPE Cross Section • Regge theory prediction + factorization : • Flux renorm. model : (both gaps are suppressed.)K. Goulianos, Phys. Lett. B 353, 379 (1995). • Gap probability (Pgap) renorm. model : Pgap is renormalized. (only one gap is suppressed.) K. Goulianos, e.g. hep-ph/0110240 (2001). Kenichi Hatakeyama

  13. Analysis Strategy • Use events triggered on a leading antiproton. • ξpbar is measured by Roman Pots : ξpbarRPS. • Measure ξp (ξpbar) from BBC and calorimeters : ξpX (ξpbarX). • Calibrate ξX by comparing ξpbarRPS and ξpbarX. • Plot ξpX distribution and look for a DPE signal expected in the small ξpX region. Kenichi Hatakeyama

  14. Roman PotSpectrometer Roman Pots detect recoil antiprotons Kenichi Hatakeyama

  15. Reconstruction of ξpX Calorimeters • Cannot reconstruct ξp by RPS. • Use calorimeter towers and • BBC hits to reconstruct ξp : Calorimeters :use ET and η of towers above noise level. BBC :use hits in BBC scintillation arrays. • pT is chosen to follow the “known” pT spectrum : (J. Collins, hep-ex/9705393) The CAL+BBC method allowed us to access all the way down to the kinematic limit. BBC Kenichi Hatakeyama

  16. Data Sample and Event Selection • Roman Pot triggered data collected in 1800 GeV low luminosity runs during Run 1C (<Linst> ~ 0.2 x 1030 cm-2s-1). • Overlap event (containing SD + additional ND collisions which kill the rapidity gap signal ) rate is low (~4% ~0.5% after the cuts shown below). Kenichi Hatakeyama

  17. Monte Carlo Event Generation : MBR(CDF Note 0256, 0675, 5371. PRD 50 (1994) 5535, 5550.) SD and DPE event generation MBR min-bias MC: • Specially designed to reproduce soft-interaction results from low-energy experiments • Used to determine CDF total, SD and DD cross sections [PRL 50 (1994) 5535, 5550, PRL 87 (2001) 141802.] Detector simulation Calorimeters:not well calibrated for low pT particles. • Convert the generated particle pT to the calorimeter ET using calibrations determined specifically for low-pT particles. BBC:assume that all charged particles will trigger the BBCs. Kenichi Hatakeyama

  18. Calibration of ξX ξX distribution in every ξRPS bin is fitted to P1 : Peak P2 : Width ξX = ξRPS, (ξX is calibrated so that ξX = ξRPS.) P2/P1 = 0.57 (ξX resolution is ~60%.) Kenichi Hatakeyama

  19. ξpX Distribution • The input ξp distribution in DPE MC is 1/ξp1+ε (ε = 0.104 is obtained from p±p/π±p/K±p total cross sections). • The DPE and SD MC distributions are independently normalized to the data distribution. • The measured ξpX distribution is in agreement with the DPE+SD MC distribution. Kenichi Hatakeyama

  20. ξpX Distribution • The ξp distribution on the previous page shows “number of events per Δlogξ=0.1”; • Multiply each bin by 1/ξ to show dN/dξ. • A diffractive peak of 3 orders of magnitude is observed! Kenichi Hatakeyama

  21. Corrections to R[DPE/SD(incl)] : • ξpX resolution : • According to MC, more events with ξp>0.02 seem to fall into ξpX<0.02 than events with ξp<0.02 fall into ξpX>0.02. • R[DPE/SD(incl)] is corrected by Fresol=1.04±0.04 • Low ξpbarX enhancement: • 3~4 % of events have very low ξpbarX values although those events have 0.035< ξpbarRPS <0.095. • MC shows a similar effect, but not as pronounced as in data. • Obtain R[DPE/SD(incl)] with/without ξpbarX<0.003 cut, and take the average. Kenichi Hatakeyama

  22. Systematic Uncertainties The measured fraction is in agreement with the prediction from the renormalized gap probability model (0.21±0.02)! Kenichi Hatakeyama

  23. Comparisons with phenomenological models In agreement with the renormalized gap predictions! Kenichi Hatakeyama

  24. DPE Proton dissociation event All the particles in Y go beyond BBC so that the event is indistinguishable from “DPE” events. Proton Dissociation Events Our “DPE” signal actually consists of two classes of events; • Events in which both the proton and antiproton escape intact from the collision  typically called “DPE”. • Events in which the antiproton escapes intact from the collision, while the proton dissociates into a small mass cluster Y (MY2 <~8 GeV2)  proton dissociation events. • Particles in Y have rapidity up to y=7.5. • In 35% of events (“A”), east BBC covers up to η=5.9, MY2 < e 7.5 - 5.9 = 5 GeV2. • In 65% of events (“B”), east BBC covers up to η=5.2, MY2 < e 7.5 - 5.2 = 10 GeV2. • R[DPE/SD(incl)] is larger in “B” than in “A” by 6%. Weighted average : 8 GeV2 The contribution of proton dissociation events with 1.5<MY2<8GeV2 to R[DPE/SD(incl)] is ~15%. Kenichi Hatakeyama

  25. Good Agreement with Renormalized Gap Predictions! Soft Diffraction :Summary SD DD σ (mb) DPE SDD Gap Fraction Kenichi Hatakeyama

  26. In events with a rapidity gap, the formation of a second gap is “unsuppressed”! Summary • We have observed double pomeron exchange events in an inclusive single diffractive event sample. • The measured ξpXdistribution exhibits ~1/ξ1+ε behavior (ε = 0.104). • The measured DPE fraction in SD is : for 0.035 <ξpbar< 0.095, |tpbar|<1 GeV2, ξpX< 0.02 and MY2<~8GeV2at √s = 1800 GeV, • in agreement with the renormalized gap prediction. Consistent with results from hard diffraction Universality of the rapidity gap formation Kenichi Hatakeyama

  27. Summary + • Universality of rapidity gap formation across soft and hard diffraction processes. • Events with multiple rapidity gaps can be used to eliminate the “suppression” factor…  Facilitate QCD calculation of hard diffraction. The diffractive structure function measured using DPE dijets is approximately equal to expectations from HERA! Kenichi Hatakeyama

  28. Backups Kenichi Hatakeyama

  29. Regge Theory & Factorization Single Diffractive Cross Section Total & EL Cross Sections Kenichi Hatakeyama

  30. Unitarity Problem Single Diffractive Cross Section Total Cross Section [ε=0.104 in PLB 389 (1996) 176] The ratio σDPE/σSD reaches unity at √s~2 TeV. In data, s2ε in dσSD/dM2 1 Kenichi Hatakeyama

  31. Soft Single Diffraction Results KG&JM, PRD 59 (1999) 114017 KG, PLB 358 (1995)379 • Differential cross section agrees with Regge predictions (left) • Normalization is suppressed by flux factor integral (right) dσSD/dM2 σSDtot versus √s Kenichi Hatakeyama

  32. Renormalization Single Diffractive Cross Section In data, s2ε 1 Renormalization K. Goulianos, Phys. Lett. B 358 (1995) 379 Kenichi Hatakeyama

  33. Soft Double Diffraction Results • Differential cross section agrees with Regge predictions (left) • Normalization is suppressed by flux factor integral (right) CDF, Phys. Rev. Lett 87 (2001) 141802 dσDD/dΔη0 σDDtot versus √s Kenichi Hatakeyama

  34. Extracted σIPIPtot using FIP/p(ξ,t) from their SD analysis. The extracted σIPIPtot shows an enhancement at low MX. They attributed it to the glueball production...... Note : If the standard ε~0.1 is used, the enhancement is reduced significantly. But, the extracted σIPIPtot is overall higher than the expectation. Past Experimental Results : UA8 CollaborationNLB 514 (1998) 3, PLB 481 (2000) 177, EPJC 25 (2002) 361. Consistent with our results Kenichi Hatakeyama

  35. Beam-Beam Counters East BBC West BBC • In 35% of events (“A”), Red : Dead Channels Light blue : Channels used to reconstruct ξX • In 65% of events (“B”), East BBC West BBC Kenichi Hatakeyama

  36. Reconstruction of ξpX : BBC Use calorimeter towers and BBC hits to reconstruct ξX, BBC (ξpBBC) : use hits in BBC scintillation arrays • use only inner 3 (shaded) layers (the most-outer layer overlaps with the forward cal). • pT is chosen to follow the “known” pT spectrum • η is chosen randomly within the η range of the BBC counter which has a hit. Kenichi Hatakeyama

  37. Reconstruction of ξpX :Calorimeter Calorimeter (ξpCAL) : use ET and η of towers above the noise level ξpCAL has to be corrected for • Calorimeter non-linearity at low ET region • Particles below the applied ET threshold The correction factor for ξCAL is obtained so that ξX(median):ξRPS=1:1. Kenichi Hatakeyama

  38. ξX Calibration :ξpbarX distributions in 9 ξpbarRPS intervals ξX distribution in every ξRPS bin is fitted to P1 : Peak, P2 : Width • ξX(median) = 0.94 ξRPS • calibrated later to • obtainξX(median)=ξRPS • P2/P1 = 0.57 • (ξX resolution is ~60%.) Kenichi Hatakeyama

  39. ξpbarX Distribution We calibrated ξX so that ξX(median) : ξRPS becomes 1 : 1. The choice of P1/median/mean does NOT make a difference in R[DPE/SD(incl)], since the choice is taken into account by the ξX resolution correction, Fresol. Kenichi Hatakeyama

  40. BBC Multiplicities in MC “A” “B” • The peak at EBBC=0 in data distributions is due to DPE events. • The MBR SD MC whose dN/dη is already checked in PRD 50 (1994) 5535, shows much lower multiplicities in the east BBC. • The higher BBC multiplicities in data are presumably due to “splashes” which are hard to simulate.  In SD MBR, for east BBC hits, don’t use the information of particles generated by MBR but simulate east BBC hits according to the data east BBC multiplicities. Kenichi Hatakeyama

  41. BBC Contribution to ξX (A) (B) Kenichi Hatakeyama

  42. ξpX resolution correction • Generate ξ by using dσ/dξ from • F. Abe et al., PRD 50 (1994) 5535. • K. Goulianos & J. Montanha, PRD 59 (1999) 114017. • Smear ξ according to the form: - P2/P1 = 0.57, P1 = 0.67ξ (P1 = 0.67xmedian when P2/P1=0.57) • The number of events with ξ<0.02 increases about 4% after the smearing. Fresol=1.04±0.04 Kenichi Hatakeyama

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