Diffractive results from CDF

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1 International Journal of Modern Physics A Vol. 3, No. 8 (5) 543 ( ages) c World Scientific Publishing Comany DOI:.4/S775X5438 Diffractive results from CDF Konstantin Goulianos Exerimental High Energy Physics, The Rockefeller University, 3 York Avenue, NY 65, USA dino@fnal.gov Received 3 Setember 4 Published 6 February 5 We resent a reference review of diffractive results from CDF for collisions at s = 54, 63, 8, and 96 GeV at the Tevatron, ublished in 9 PRL/PRD aers from 994 to. Both soft and hard diffractive results are included for single and/or double dissociation, central diffraction or double Pomeron exchange (where both the roton and antiroton remain intact), multi-ga diffraction (a combination of single and double dissociation), elastic scattering, and the total cross-section, which through the otical theorem is related to the imaginary art of the forward elastic scattering amlitude. In each review, we include the comarisons made by CDF with theoretical redictions. Keywords: Diffraction; CDF; Tevatron. PACS numbers:.4.nn, 3.85.Dz, t. Introduction We resent a reference review of the diffractive results ublished by the CDF Collaboration (CDF) using data collected during Tevatron Collider oerations. The order of resentation of the aers in this review does not follow the chronological order of ublication, but is rather organized by the class of hysics rocesses studied. This format has been chosen in order to rovide a better understanding of the interrelationshis between aers in the same hysics class. The review addresses the following hysics rocesses: I II III Elastic and Total Cross-Sections; Soft Diffraction; Hard Diffraction; A Single/Double Diffraction, B Hard Central Diffraction/Double Pomeron Exchange (DPE), C Raidity Gas Between Jets. 543-

2 K. Goulianos For each aer, we resent a brief descrition of the imortant findings and their hysics significance, and in most cases we include figures showing the key results. I. Elastic and total cross-sections () Measurement of small angle antiroton roton elastic scattering at s = 546 and 8 GeV (994). () Measurement of the antiroton roton total cross-section at s = 546 and 8 GeV (994). II. Soft diffraction (3) Measurement of single diffraction dissociation at s = 546 and 8 GeV (994). 3 (4) Double Diffraction Dissociation at the Fermilab Tevatron Collider (995). (5) Central Pseudoraidity Gas in Events with a Leading Antiroton at the Fermilab Tevatron Collider (3). 5 (6) Inclusive Double Pomeron Exchange at the Fermilab Tevatron Collider (4). 6 III. Hard diffraction A. Hard single/double diffraction (7) Observation of Diffractive W-Boson Production at the Fermilab Tevatron (997). 5 (8) Measurement of Diffractive Dijet Production at the Fermilab Tevatron (997). 6 (9) Observation of Diffractive b-quark Production at the Fermilab Tevatron (). 9 () Diffractive Dijets with a Leading Antiroton in bar- Collisions at s = 8 GeV (). () Observation of Diffractive J/ψ Production at the Fermilab Tevatron (). 3 () Diffractive Dijet Production at s = 63 and 8 GeV at the Fermilab Tevatron (). 4 (3) Diffractive W and Z Production at the Fermilab Tevatron (). 8 (4) Diffractive Dijet Production in Collisions at s =.96 TeV (). 9 B. Hard central diffraction/double Pomeron exchange (5) Dijet Production by Double Pomeron Exchange at the Fermilab Tevatron (). (6) Observation of Exclusive Dijet Production at the Fermilab Tevatron Collider (8)

3 Diffractive results from CDF C. Raidity gas between jets (7) Observation of Raidity Gas in Collisions at.8 TeV (995). 4 (8) Dijet Production by Color-Singlet Exchange at the Fermilab Tevatron (998). 7 (9) Events with a Raidity Ga between Jets in Collisions at s = 63 GeV (998). 8. Reference Reviews by Paer.. I () : Measurement of small angle antiroton roton elastic scattering at s = 546 and 8 GeV (994) Antiroton roton elastic scattering was measured at energies of s = 546 and 8 GeV in the range of four-momentum transfer squared.5 < t <.9 GeV. The data are well described by the exonential form e bt with a sloe b = 5.8 ±.58 (6.98 ±.5 GeV ) at s = 8 (546) GeV. The measured elastic scattering cross-sections are, resectively, σ el =.87 ±.3 and 9.7 ±.75 mb. It is recommended that this aer be read together with the aers of the antiroton roton total cross-section, I (), and single diffraction dissociation, I (3), as there are common analysis issues and cross-references among all three aers... I () : Measurement of the antiroton roton total cross-section at s = 546 and 8 GeV (994) In this aer, CDF reorts a measurement of the roton antiroton total crosssection σ T at energies of s = 546 and 8 GeV. Using the luminosity-indeendent method, values of σ T = 6.6 ±.93 mb at s = 546 GeV and 8.3 ±.4 mb at 8 GeV were obtained. In this energy range, the ratio σ el /σ T increases from. ±. to.46 ±.4. In order to understand the data analysis that led to the results resented in this aer, one should also read the aers of antiroton roton elastic scattering, I (), and single diffraction dissociation, I (3), as there are common issues and cross-references among all these three aers..3. I (3) : Measurement of single diffraction dissociation at s = 546 and 8 GeV (994) 3 Results form measurements of the diffraction dissociation differential cross-section d σ SD /dm dt for X at s = 546 and 8 GeV, M /s <, and t.4 GeV are reorted. The results are comared to theoretical redictions and to extraolations from exerimental results at lower energies. This aer should be consulted together with the aers of the measurements of the antiroton roton elastic scattering, I (), and the total cross-section, I (), as there are common data analysis issues among them, the details of which are not resented in each one aer

4 K. Goulianos.4. II (4) : Double diffraction dissociation at the Fermilab Tevatron Collider (995) Results are resented from a measurement of double diffraction dissociation in collisions at the Fermilab Tevatron collider. The roduction cross-section for events with a central seudoraidity ga of width η > 3 (overlaing η = ) is found to be 4.43 ±. (stat) ±.8 (syst) mb [3.4 ±. (stat) ±.9 (syst) mb] at s = 8 [63] GeV. The results are comared with revious measurements and with redictions based on Regge theory and factorization. Figure is a schematic diagram of the double diffraction dissociation rocess. In Fig., the total diffraction dissociation cross-sections σ DD (mb) for η > 3., extraolated from the measured regions to η > 3., are comared to the UA5 adjusted results and to Renormalized-Ga (RENORM) redictions (see cation). IP M M η min dn dη η max ln M ln M ln s η Fig.. Schematic diagram and event toology in seudoraidity sace of a double diffractive interaction. σ DD (mb) for η > 3. CDF UA5 (adjusted) Regge Renormalized ga 3 s (GeV) Fig.. The total double diffractive cross-section for ( )+ X +X versus s comared with redictions from Regge theory based on the trile-pomeron amlitude and factorization (solid curve), and from the renormalized ga robability model [K. Goulianos, arxiv:he-h/34] (dashed curve)

5 Diffractive results from CDF.5. II (5) : Central seudoraidity gas in events with a leading antiroton at the Fermilab Tevatron Collider (3) 5 The fraction of events with a large seudoraidity ga η within the seudoraidity region available to the roton dissociation roducts X in + + X is resented. For a final state of fractional momentum loss ξ and four-momentum transfer squared t within.6 < ξ <.9 and t <. [.] GeV at s = 8 [63] GeV, the fraction of events with η > 3 is found to be.46 ±. (stat) ±.4 (syst) [.84 ±. (stat) ±.43 (syst)]. They are comared with ga fractions measured in minimum bias collisions and with theoretical exectations. Figure 3 is a schematic diagram of the central seudoraidity ga rocess. In Fig. 4, the ratios of the measured cross-sections are comared to Regge and Renormalized-Ga (RENORM) redictions [K. Goulianos, arxiv:he-h/34]. IP t IP t M M η min η max ln M ln M ln/ξ ln s ln s η Fig. 3. Schematic diagram and event toology in seudoraidity sace of a SDD (single diffraction lus ga) interaction, + +GAP +M +GAP+M, with a leading outgoing antiroton of fractional momentum loss ξ, associated with a seudoraidity ga η = ln, and a ga ξ within the region of η sanned by ln s = ln s ln. ξ ga fraction η > 3. CDF: one-ga/no-ga CDF: two-ga/one-ga Regge rediction Renorm-ga rediction -ga - -ga 3 sub-energy s --, (GeV) Fig. 4. Ratios of SDD (single-diffraction lus ga) to single-diffractive rates (filled circles) and double-diffractive to total cross-sections (oen circles) as a function of the collision energy of the sub-rocess, Pomeron-roton and, resectively. The uncertainties are mainly due to systematic effects, which are highly correlated among all four data oints. The dashed lines are redictions from Regge theory and the solid lines from the renormalized ga robability model [K. Goulianos, arxiv:he-h/34]

6 K. Goulianos.6. II (6) : Inclusive double-omeron exchange at the Fermilab Tevatron Collider (4) 6 A study of the reaction + + X + Y at s = 8 GeV is resented, where is detected in a RPS and Y is a roton or roton dissociation system of masssquared MY 8 GeV. In events with a of fractional momentum loss.35 < ξ <.95 and four-momentum transfer squared t <. GeV, the fractional momentum loss ξ X of the roton or system Y, evaluated from the momenta of the articles comrising X, behaves as /ξ X at small ξ X, as exected for DPE. The fraction of events with ξ X <. is.94 ±. (stat) ±. (syst). Schematic diagrams of event toologies for SD and DPE are shown in Fig. 5, and a histogram of the measured differential event sectrum versus ξ X is dislayed and comared to Renormalized-Ga (RENORM) MC redictions in Fig. 6. dn/dη X IP X (a) X η Y IP P I Y X (b) Fig. 5. Schematic diagrams and event toologies for (a) single diffraction, + + X, and (b) DPE, + + X + Y ; the filled areas are η regions of article roduction. M X ( GeV ) Number of Events er logξ = Data DPE MC SD MC DPE+SD MC s = 8 GeV.35 ξ-.95 t-. GeV ξ X Fig. 6. Distribution of roton fractional momentum loss ξ X, measured from calorimeter and beam beam counter information, for events with a leading of.35 < ξ RPS <.95 and t <. GeV ; the curves are from a Monte Carlo simulation of SD (dotted), DPE (dashed) and total (solid) contributions normalized to the data oints; the DPE events were generated for ξ <

7 Diffractive results from CDF.7. III A (7) : Observation of diffractive W-boson roduction at the Fermilab Tevatron (997) 5 This aer reorts the first observation of diffractively roduced W bosons. In a samle of W eν events roduced in collisions at s =.8 TeV, an excess of events with a forward raidity ga is found, which is attributed to diffraction. The robability that this excess is consistent with nondiffractive roduction is. 4 (3.8σ). The relatively low fraction of W + Jet events observed within this excess imlies that mainly quarks from the omeron, which mediates diffraction, articiate in W roduction. The diffractive to nondiffractive W roduction ratio is found to be R W = (.5 ±.55)%. Quote from aer: We searched for a diffractive W signal by analyzing the correlations between the η of the electron, η e, or the sign of its charge, C e, and the multilicity of one or the other of the Beam Beam Counters (BBCs). Each event enters into two distributions, one with η e η BBC < (angle-correlated) or C e η BBC < (charge-correlated), and the other with η e η BBC > (angle-anticorrelated) or C e η BBC > (charge-anticorrelated). A doubly-correlated (anticorrelated) distribution is the BBC multilicity distribution for events with η e C e > and η e η BBC < (η e η BBC > ). The main result reorted in this aer, indicating a ga signal in the diffractive to nondiffractive event ratio, is shown in Fig R (%) ACCEPTANCE 4 6 UPPER BOUND OF BBC MULTIPLICITY.5 (a) 4 6 UPPER BOUND OF BBC MULTIPLICITY (b) Fig. 7. (a) Diffractive to nondiffractive W roduction ratio (not corrected for BBC occuancy or one-vertex cut efficiency) as a function of uer bound BBC multilicity. The solid line asses through the N B = oint, which we use as our result; (b) ga-accetance for angle-ga and charge-ga doubly correlated (solid) and anticorrelated (dashed) diffractive events with an electron within η <

8 K. Goulianos.8. III A (8) : Measurement of diffractive dijet roduction at the Fermilab Tevatron (997) 6 The observation and measurement of the rate of diffractive dijet roduction at the Fermilab Tevatron collider at s =.8 TeV is reorted. In events with two jets of E T > GeV,.8 < η < 3.5 and η η >, it is found that the diffractive to nondiffractive roduction ratio is R JJ = [.75 ±.5 (stat) ±.9 (syst)]%. By comaring this result, in combination with the measured rate for diffractive W boson roduction reorted reviously, with redictions based on a hard artonic omeron structure, the Pomeron gluon fraction is determined to be f g =.7 ±.. Figures 8 and 9 show the method of extracting the signal and the hysics significance of the results, resectively. NUMBER OF EVENTS TOWERS BBC HITS 8 Fig. 8. Beam beam counter multilicity (BBC hits) versus forward calorimeter tower multilicity in the seudoraidity regions 3. < η (BBC) < 5.9 and.4 < η (tower) < 4. oosite the dijet system.. MOMENTUM FRACTION OF HARD PARTONS IN POMERON CDF- DIJETS CDF-W UA8 ZEUS GLUON FRACTION OF HARD PARTONS IN POMERON Fig. 9. Momentum fraction versus gluon fraction of hard artons in the omeron evaluated by comaring measured diffractive rates with Monte Carlo redictions based on the standard omeron flux and assuming that only hard omeron artons articiate in the diffractive rocesses considered. Results are shown for ZEUS (dashed dotted), UA8 (dashed) and the CDF-dijet and CDF-W measurements. The CDF-W result is shown for two (dotted) or three (solid) light quark flavors in the omeron. The shaded region is used in the text to extract the quark to gluon fraction of the omeron and the standard flux discreancy factor

9 Diffractive results from CDF.9. III A (9) : Observation of diffractive b-quark roduction at the Fermilab Tevatron () 9 In this aer, CDF reorts a measurement of the fraction of b-quarks roduced diffractively in collisions at s =.8 TeV. Diffraction is identified by the absence of articles in a forward seudoraidity region. From events with an elec- < GeV within the seudoraidity region tron of transverse momentum 9.5 < e T η <., the ratio of diffractive to total b-quark roduction rates is found to be R bb = [.6 ±.9 (stat).6 (syst)]. This result is comarable in magnitude to corresonding ratios for W and dijet roduction, but significantly lower than exectations based on factorization. In Fig., it is seen that this measurement, along with the diffractive dijet 6 and W 5 roduction measurements, restricts the gluon fraction of the Pomeron to a region comatible with that of the ZEUS result determined from e collisions at HERA [M. Derrik et al., Z. Phys. C 68, 569 (995)]. The value obtained by CDF is f CDF g = D (MEASURED / PREDICTED)..8.6 ZEUS.4 CDF-b CDF-W. CDF-DIJET GLUON FRACTION IN POMERON Fig.. The ratio, D, of measured to redicted diffractive rates as a function of the gluon content of the Pomeron. The redictions are from POMPYT using the standard Pomeron flux and a hard Pomeron structure. The CDF-W curves were calculated assuming a three-flavor quark structure for the Pomeron. The black cross and shaded ellise are the best fit and σ contour of a least square two-arameter fit to the three CDF results

10 K. Goulianos.. III A () : Diffractive dijets with a leading antiroton in bar- collisions at s = 8 GeV () Results are reorted from a study of events with a leading antiroton of beam momentum fraction.95 < x F <.965 and four-momentum transfer squared t < 3 GeV roduced in collisions at s = 8 GeV at the Fermilab Tevatron collider. Aroximately % of the events contain two jets of transverse energy E jet T > 7 GeV. Using the dijet events, the diffractive structure function of the antiroton is evaluated and comared with exectations based on results obtained in diffractive dee inelastic scattering exeriments at the DESY e collider HERA. The main result resented in this aer is the measurement of the diffractive structure function F jj D (β), which is shown in Fig. along with two H measurements, H fit- and H fit-3 [T. Ahmed et al., Phys. Lett. B 348, 68 (995); C. Adloff et al., Z. Phys. C 76, 63 (997)]. F D JJ (β) H fit- H fit-3 ( Q = 75 GeV ) CDF data E Jet, T > 7 GeV.35 <ξ<.95 t <. GeV.. Fig.. Data β distribution (oints) comared with exectations from the arton densities of the roton extracted from diffractive dee inelastic scattering by the H Collaboration. The straight line is a fit to the data of the form β n. The lower (uer) boundary of the filled band reresents the data distribution obtained by using only the two leading jets (u to four jets of E T > 5 GeV) in evaluating β. The dashed (dotted) lines are exectations from the H fit (fit 3). The systematic uncertainty in the normalization of the data is ±5%. β 543-

11 Diffractive results from CDF.. III A () : Observation of diffractive J/ψ roduction at the Fermilab Tevatron () 3 In this aer, CDF reorts the first observation of diffractive j/ψ( µ + µ ) roduction in collisions at s =.8 TeV. Diffractive events are identified by their raidity ga signature. In a samle of events with two muons of transverse momentum µ T > GeV/c within the seudoraidity region η <., the ratio of diffractive to total J/ψ roduction rates is found to be R J/ψ = [.45 ±.5]%. The ratio R j/ψ (x) is resented as a function of x-bjorken. By combining it with the reviously CDF measured corresonding ratio R jj (x) for diffractive dijet roduction, a value of.59 ±.5 is extracted for the gluon fraction of the diffractive structure function of the roton. Figure shows the ratio of SD to ND events versus x-bjotken. Integrating the x bj distributions for R jj and R J/ψ in the region.4 x. (kinematic boundaries for full accetance) yields [R jj (x)/r J/ψ (x)] ex =.7±.7 (stat). The gluon fraction of the diffractive structure function of the (anti)roton is found to be fg D =.9±.4 (stat)±.6 (syst), which is consistent with the value.54±.5 obtained by combining the results of diffractive W, dijet, and b-quark roduction, as discussed in Sec..9. R ( SD / ND ) - J/ψ Data Dijet Data x min =.4 x max =ξ min = X-Bjorken Fig.. Ratios of diffractive to total J/ψ (circles) and dijet (triangles) rates er unit ξ (ξ ) as a function of x-bjorken of the struck arton of the ( ) adjacent to the raidity ga. 543-

12 K. Goulianos.. III A () : Diffractive dijet roduction at s = 63 and 8 GeV at the Fermilab Tevatron () 4 The subject of this aer is the measurement of the diffractive structure function Fjj D of the antiroton, obtained from a study of dijet events roduced in association with a leading antiroton in collisions at s = 63 GeV at the Fermilab Tevatron. The ratio of Fjj D at s = 63 GeV to Fjj D obtained from a similar measurement at s = 8 GeV is comared with exectations from QCD factorization and other theoretical redictions. Also reorted in this aer is a measurement of the ξ (x-pomeron) and β (x of arton in Pomeron) deendence of Fjj D at s = 8 GeV. In the region.35 < ξ <.95, t < GeV, and β <.5, Fjj D (β, ξ) is found to be of the form β.±. ξ.9±., which obeys β-ξ factorization. The results of this measurement are summarized in Fig. 3, which dislays on (left) the diffractive structure functions F jj D versus β at s = 53 and 8 GeV, and on (right) the ξ deendence (fractional momentum loss of the leading ) of the arameters that characterize F jj D (see figure cation). The diffractive structure functions at the two energies are similar, excet for an overall suression at s = 8 GeV relative to 6 GeV. F D jj (β) - 63 GeV 8 GeV E T Jet, > 7 GeV E T > GeV.35 <ξ<.95 t <. GeV - β n Dijet, F D jj (β, ξ) β= (a) E T Jet, > 7 GeV t <. GeV (b) Dijet 7 Inclusive ξ Inclusive, /N incl dn/dξ Fig. 3. (left) The diffractive structure function versus β, F D jj (β), integrated over the range.35 < ξ <.95 and t <. GeV and exressed er unit ξ, at s = 63 GeV (black oints) and 8 GeV (oen circles). The errors are statistical only. The lines are fits of the form β n with the arameter n common at both energies. In the fit region, the systematic uncertainty in the ratio of the 63 to 8 GeV data is +3 3 %. (right) Distributions versus ξ for 8 GeV data: (a) the arameter n of a fit to the diffractive structure function of the form Fjj D(β, ξ) ξ = Cβ n for β <.5; (b) the diffractive structure function at β =. fitted to the form Fjj D(β, ξ) β=. = Cξ m (circle-oints and curve), and the inclusive single-diffractive distribution (triangles). The errors shown are statistical. 543-

13 Diffractive results from CDF.3. III A (3) : Diffractive W and Z roduction at the Fermilab Tevatron () 8 This aer reorts measurements of the fraction of events with a W or Z boson which are roduced diffractively in collisions at s =.96 TeV. The data used are from.6 fb of integrated luminosity collected with the CDF II detector equied with a RPS that detects the from + + [X + W/Z]. It is found that (.97 ±.)% of W s and (.85 ±.)% of Zs are roduced diffractively in a region of antiroton or roton fractional momentum loss ξ of.3 < ξ <. and four-momentum transferred squared t of < t < (GeV/c). The events in which the roton scatters diffractively while the antiroton dissociates, + [X + W/Z] +, are accounted for by doubling the measured roton dissociation fraction. Also reorted in this aer are searches for W and Z roduction in DPE, + + [X + W/Z] +, and for exclusive Z roduction, + + Z +. No signal is seen above background for either one of these two rocesses. The results are comared with theoretical exectations. A schematic diagram of diffractive W and Z roduction is shown in Fig. 4. The main results are summarized in Fig. 5: on the left, the lot shows distributions of various datasets used for extracting the signal, while the lot on the right shows the W mass distribution extracted from the diffractive event samle. IP q W,Z X IP g q W,Z X Fig. 4. Diffractive W roduction: (left) through quarks, and (right) through gluons. ) number of events /( GeV/c W e/µ ν - L=.6 fb fit M =8.9 ±.7 GeV/c W diff M W (GeV/c ) Fig. 5. (left) ξ cal for W and Z events with a RPS track; the dotted histogram is the distribution of nondiffractive (ND) Z events normalized to the data Z-distribution in the region. < log ξ cal <.4. (right) Reconstructed MW diff with a Gaussian fit

14 K. Goulianos.4. III A (4) : Diffractive dijet roduction in collisions at s =.96 TeV () 9 This aer reorts results from a comrehensive study of diffractive dijet roduction in collisions at s =.96 TeV using the CDF II detector at the Fermilab Tevatron collider. A data samle from 3 b of integrated luminosity collected by triggering on a high transverse energy jet, E jet T, in coincidence with a recoil antiroton detected in a RPS is used to measure the ratio of single-diffractive to inclusive-dijet event rates as a function of x of the interacting arton in the antiroton, the Bjorken-x (x Bj ), and a Q (E jet T ) in the ranges 3 < x Bj < and < Q < 4 GeV, resectively. Results are resented for the region of momentum-loss fraction.3 < ξ <.9 and a four-momentum transfer squared t > 4 GeV. The t deendence is measured as a function of Q and x Bj and comared with that of inclusive single diffraction dissociation. Only weak x Bj and Q deendencies in the ratio of single diffractive to inclusive event rates are found, and no significant Q deendence in the diffractive t distributions. This is in effect a measurement of the diffractive structure function in collisions. The rocess is shown in Fig. 6. Secial forward detectors are used, including a RPS, and a MiniPlug calorimeter: Fig. 7. (a) (b) (c) Fig. 6. Leading order schematic diagrams and event toologies in seudoraidity (η) versus azimuthal angle (φ) for diffractive dijet roduction rocesses studied by CDF: (a) single diffraction, (b) double diffraction, and (c) DPE; the dot-filled rectangles reresent regions where article roduction occurs. CDF-II m DIPOLEs EBS QUADs QUADs EBS DIPOLEs 57m to CDF-II-center (z=) TRACKING SYSTEM CCAL PCAL MP CLC BSC RPS Fig. 7. Schematic lan view of the CDF II central (CDF-II) and forward detectors

15 Diffractive results from CDF The main results are resented in Figs. 8 and 9. Figure 8 shows that the ratio of the diffractive to nondiffractive dijet event rates, which in LO is roortional to the ratio of the resective structure functions (NLO corrections are exected to be of O(%)), varies by less than a factor of two over a Q range of 3 and Fig. 9 resents the t distribution, which is nearly indeendent of Q over a wide range of Q values. Ratio ( SD / ξ ) / ND - χ / ndf 3.3 / Const.3 ±.966 sloe.3 ± < ξ Q CAL <.9 * * jet jet <E T >, <E T >=(E T +E T )/ -3 overall syst. uncertainty: ± % (norm), ± 6% (sloe) -3 - x - Fig. 8. The ratio of diffractive to nondiffractive dijet event rates as a function of x Bj (momentum fraction of arton in the antiroton) for different values of Q ET. The quoted overall systematic uncertainty of ±% is due to the uncertainties R and r listed in Table III. 9 Bj ) - (GeV and b sloe arameters b RPS.5< ξ <.8 -t <. GeV - 3 b b 4 Q (GeV ) Corrected events er.5 GeV 4 3.5< ξ RPS <.8 RPS inclusive systematics (±3%) RPS Jet (Q ~9 GeV ) DL model t GeV Fig. 9. (left) The sloe arameters b and b of a fit to the form dσ/dt = N (A e b t +A e b t ), with A /A =. for SD events of different Q values (right) t-distributions for two samles of SD RPS track events within the region.5 < ξ RPS <.8 corrected for RPS accetance after background subtraction: (circles) RPS inclusive and (triangles) RPS Jet ( Q 9 GeV ). The curve reresents the distribution exected for soft SD in the DL (Donnachie Landshoff) model [Phys. Lett. B 58, 63 (], and references therein) normalized to the RPS data within t.5 GeV

16 K. Goulianos.5. III B (5) : Dijet roduction by double omeron exchange at the Fermilab Tevatron () This aer reorts the first observation of dijet events with a DPE toology roduced in collisions at s = 8 GeV. The events are characterized by a leading antiroton, two jets in the central seudoraidity region, and a large raidity ga on the outgoing roton side. Results are resented on jet kinematics and roduction rates, comared with corresonding results from single diffractive and inclusive dijet roduction, and tests of factorization are erformed. Process diagrams and results are resented in Figs. and, resectively. jet jet IP (a) η _ jet jet η η IP IP (b) Fig.. Illustration of event toologies in seudoraidity, η, and associated Pomeron-exchange diagrams for dijet roduction in (a) single diffraction and (b) DPE. The shaded areas on the left reresent articles not associated with the jets (underlying event). R(x) er unit ξ - - R (x) / ξ R DPE SD R SD ND.5 Jet, 7 < E T < GeV.35 <ξ- <.95. <ξ <.3 t- <. GeV -3 ξ x Fig.. Ratios of DPE to SD (SD to ND) dijet event rates er unit ξ (ξ ), shown as oen (filled) circles, as a function x-bjorken of artons in the ( ). The errors are statistical only. The SD/ND ratio has a normalization systematic uncertainty of ±%. The insert shows R(x) er unit ξ versus ξ, where the tilde over the R indicates the weighted average of the R(x) oints in the region of x within the vertical dashed lines, which mark the DPE kinematic boundary (left) and the value of x = ξ min (right)

17 Diffractive results from CDF.6. III B (6) : Observation of exclusive dijet roduction at the Fermilab Tevatron Collider (8) 7 A mini-review of this aer aears in: K. Goulianos, Central Exclusive dijet roduction at the Tevatron, Int. J. Mod. Phys. A (IJMPA), World Scientific Publishing Comany. Free access on-line ublication: htts://arxiv.org/submit/3985/view For comleteness, the abstract of the above mini-review is coied below: Abstract. We resent a reference review of central exclusive dijet roduction in collisions, where the roton and antiroton emerge intact, and only two jets of transverse energy above a certain threshold are resent in the final state. The results are ublished in two aers by the Collider Detector at Fermilab (CDF) Collaboration, a PRL () and a PRD (8), based on data collected at s =.8 TeV and.96 TeV, resectively, and a D Collaboration aer from studies at.96 TeV. In all three cases redictions for the cross-section of Higgs boson roduction are discussed, a rocess that roceeds via a similar mechanism as dijet roduction. Roman Pot Sectrometers equied with tracking detectors are used to measure the outgoing antiroton (CDF and D) and roton (D), and secial forward detectors are emloyed to hel reduce backgrounds and enrich the data in diffractive and exclusive dijet events..7. III C (7) : Observation of raidity gas in collisions at.8 TeV (995) 4 In collisions at s =.8 TeV jet events are found with a raidity ga toology. The number of hadrons in the raidity interval η D between leading-jet cones is samled by charged tracks with P T > MeV/c. An excess of trackless events beyond that exected in a smooth multilicity distribution is observed. In a control region outside η D no excess is seen. For η D >.8, the fraction of excess trackless events, consistent with estimates based on exchange of color-singlet digluons, is R(ga) = σjet(ga) σ jet =.85 ±. (stat) +.4. (syst). The signal is extracted by fitting data in the η-region between the jets (G) and the background regions that contain the jets (N), Fig.. Fig.. (left) φ versus η hase sace, and (right) (a) ga and (b) no-ga regions

18 K. Goulianos.8. III C (8) : Dijet roduction by color-singlet exchange at the Fermilab Tevatron (998) 7 This aer reorts a new measurement of dijet roduction by color-singlet exchange in collisions at s =.8 TeV at the Fermilab Tevatron. In a samle of events with two jets of transverse energy E jet T > GeV, seudoraidity in the range.8 < η jet < 3.5, and η η <, it is found that a fraction R =.3 ±. (stat) ±. (syst)% have a seudoraidity ga within η < between the jets that can be attributed to color-singlet exchange. The fraction R shows no significant deendence on E jet T or on the seudoraidity searation between the jets. The color-singlet signal is extracted using events with jets on oosite sides of the η <. region from the correlation of calorimeter towers versus tracks, as shown in Fig. 3 (left). The signal is contained mostly in the region of events with zero-tracks and less than three calorimeter towers. In Fig. 3(c), the ratio of ga to control-samle no-ga events (normalized to be unity on average) is lotted versus / of the η searation between the jets. It is seen that the ga signal becomes increasingly more dominant as η η / increases. Events Number of Tracks Number of Towers Normalized Ratio Normalized Ratio (E () T +E () T )/ (GeV) (a) (GeV) E T (3) (b) η -η / (c) Fig. 3. (left) Track versus tower multilicity distribution for events in the N vertex oositeside dijet samle with N track < 5 and N tower < within η <.. The bins with zero tracks and, or towers contain an excess of events above the exectation from an extraolation from the bins with N track >. This excess is attributed to events from color-singlet exchange. (right) Normalized (to be unity on average) ratios of ga (solid oints) and control samle events (oen circles) over all events versus: (a) the average E T of the two leading jets, (b) the E T of the third jet, and (c) half the η searation between the two leading jets

19 Diffractive results from CDF.9. III C (9) : Events with a raidity ga between jets in collisions at s = 63 GeV (998) This aer reorts a measurement of the fraction of dijet events with a raidity ga between jets roduced by a color-singlet exchange in collisions at s = 63 GeV at the Fermilab Tevatron. In events with two jets of transverse energy E jet T > 8 GeV, seudoraidity in the range.8 < η jet < 3.5, and η η <, the color-singlet exchange fraction is found to be R = [.7±.7 (stat)±.6 (syst)]%. Comarisons are made with results obtained at s = 8 GeV and with theoretical exectations. The color-singlet exchange signal is extracted by comaring the track and calorimeter tower multilicity distributions for oosite-side (OS, η η < ) dijet events, which are rich in signal, and same-side ones (SS, η η > ), which are dominated by nondiffractive events. The ratio of OS to SS events, normalized to the SS ones, is lotted in Fig. 4 versus the number of tracks (left) and towers (right). A clear signal is seen in both cases in the regions of N track > and N tower < 3, resectively. Number of Events Number of Events Number of Tracks Number of Towers (a) (b) D=(N OS -N SS )/N SS D=(N OS -N SS )/N SS Number of Tracks - Number of Towers (c) (d) Fig. 4. (to) Multilicity distributions (a) for tracks and (b) for calorimeter towers in the regions η <.9 for oosite-side (OS, η η < ) dijet events (solid lines), and η <.5 ( η <.) for tracks (towers) for same-side (SS, η η > ) dijet events (dashed lines); (bottom) the bin-by-bin difference between OS and SS events normalized to the number of SS events. The SS distribution is scaled to the OS one by the ratio of OS/SS events for N track > in (a) and N tower > in (b)

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