We present the results of a search for diffractive dijets produced in {ital p}{ital {anti p}} collisions at {radical}s = 1.8 TeV from data collected by the Collider Detector at Fermilab using a Roman pot trigger. The dijet events exhibit additional diffractive characteristics such as rapidity gaps and boosted center-of-mass systems

CDF Collaboration

Melese, P. L.

UNT Digital Library

C O N F - C j d  og/a -- lb  Fermi National Accelerator Laboratory w /Y4QOS 0 ' 3 3 0  Diffractive Dijet Search with Roman Pots at CDF P.L. Melbsit For the CDF Collaboration The Rockefeller University New York, New York 10021 Fermi National Accelerator Laboratory P.O. Box 500, Batavia, Illinois 60510 August 1996 Presented at 1996 Annual Divisional Meeting (DPF 96) of the Division of Particles and Fields of the American Physical Society, Minneapolis, Minnesota, August 10-15, 1996. 3 Operated by Universities Research Association Inc. under Contract No. DE-ACO2-76CH03000 with the United States Department of Energy & @ S T R f m O N  OF W t S  QOCUME~JT IS VNLIMfhEE) Disclaimer This report was prepared as an account of work sponsored by an agency of the United States Government. 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Submitted to DPF96 (Augnst Minneapolis, MN) August 9,1996 DIFFRACTWE DUET SEARCH WITH ROMAN POTS AT CDF P.L. MClbe The Rockefeller University, New York, NY lOO2f  (Representing the CDF Collaboration) We present the results of a search for diffractive dijets produced in p p  collisions at 6 d . 8  TeV from data collected by the Collider Detector at Fermilab using a Roman pot trigger. The dijet events exhibit additional diffractive characteristics such as rapidity gaps and boosted center-of-mass systems. 1 Introduction Within Regge theory the pomeron trajectory is used to describe high energy Mractive processed. Assuming that the pomeron is made up of quarks and gluons and that the Hractive cross section can be factorised’ into a pomeron flux times a pomeron-proton total cross section, then the structure of the pomeron can be determined. Just as jets are used to probe the quark/gluon structure of the proton, diffractive dijets can be used to probe the structure of the pomeron. There is evidence from other experiments? that the pomeron has a hard parton distribution where the momentum is predominately shared by two gluons (“hard-gluon”) or two quarks (“hard-quark”), which may be modelled as p(1 - p ) ,  where p is the fraction of the pomeron’s momentum carried by the part‘ons. structure of the pomeron and a pomeron flux to generate ((, t ) ,  where < is the fraction of the proton’s momentum carried by the pomeron and t is the 4 momentum transfer squared. PYTIIIA then simulates the pomeron-proton interaction that produces dijets. We model Mractive interactions using POMPY‘I!, assuming a quark/gluon 2 Analysis Three Roman pot detectors were installed and used together with the CDF detector during the run 1C Tevatron run. Each Roman pot contained trig- ger scintillators and z,y position detectors using scintillating fibers read out by multichannel photomultiplier tubes. For diffractive events in which the 1 * b  antiproton loses 5% to 10% of its momentum by the emission of a pomeron (0.05 < ( < 0.10), the antiproton gets bent out of the beam into the Roman pot detectors. The 2,y track measured in the three Roman pots is projected back to the event vertex, using the accelerator magnetic transport matrix, to determine the ( , t  of the antiproton. The data sample used in the search for dxractive dijets was taken during a special low luminosity (a few x loz9 cm-2s-1) running period in which a triple Roman pot coincidence triggered the CDF readout. There are 1.53 million events with a good z,y reconstructed track and 0.05 < 6 < 0.10, consistent with coming from the CDF event vertex. These events show the expected correlations between the CDF event and the f measured in the Roman pots 55 meters away. Figure 1 (left plot) shows the expected correlation between the event mass, measured using calorimeter towers, and &, where the center-of- mass energy available in a pomeron-proton collision is 1800& GeV. Figure 1 (right plot) shows the correlation between the detected (occupied tower with the largest q) and ln(, where the she of the rapidity gap is expected to scale with lnt. In addition to the tagged antiproton, rapidity gaps are also observed in the forward detectors on the same side. Inelusive-Oiff Colorimeter Moss vs Roman-pct C Inclusive-Oiff Colorimeter Tower T- va ln(e) Figure 1: Calorimeter Mass vs and qmar vs in((). (The Lines are linear fits to the data) The Roman pot cross section at 1800 GeV was measured by C D F  in 1989. The cross section for 0.05 < 6 < 0.10 is expected to be 0.64 mb, of which the pomeron-induced diffractive component is bP - 0.15 mb and the remaind- is a non-diffractive background possibly due to Reggeon exchange. Within our Roman pot triggered sample, there are 2546 Gets defined as two jets with E+ > 10 GeV. There is significantly lower activity observed (m pidie gaps) in the forward detectors on the Roman pot side (west) compared to the east side for these Roman pot dijet events, while non-diffrsctive events are west/east symmetric. Figure 2 shows dijet variables for the dijets with Roman pot tracks com- 2 pared to a non-diffractive sample (superimposed). The mean G e t  9, (VI + 7h)/2, shows the expected boost away from the Roman pots compared to the psymmetric non-Mractive sample. The leading jet ET is similar for both Roman pot and non-diffractive dijets. The 41 - 4 2  distribution is more peaked than the non-dXractive dijets, which could be explained by the lower 4 in the dif€ractive interaction producing a smaller fraction of 3-jet events. Diffractive- Di je t  Candidates  v) 200 2 175 0 12s E 100 :.rso 2 7s n 50 25 0 v) 250 c OI-z 200 B 160 n E z 100 e 0 50 0 (E.> 1 0  CmV. O.O5CC<O. 1 0 .  ltlC.5 t I 10  1 0  Lead Jet E, (GeV) Mean q i eo 160 1 4 0  120 100 80 60 40 20 0 5 e,-*, Roman-pot Figure 2: Dijet Sample Kinematic Distributions (non-diffractive is dashed histogram). The &jet production rate is u = 0.64mbx (2546 dijets) / ( l .53~ lo6 i d )  - lpb. The rates predicted by POMPYT for a hard-gluon pomeron structure is - 6pb assuming the standard flux and - 0.7pb assuming a flux that scales with the soft single-Mractive cross section'. The comparison with the POMPYT diffractive simulation must be inter- preted with the provision that we have not proven that all these G e t s  with Roman pot tracks are due to pomeron exchange (difFractive), as opposed to other colorless Regge exchanges. References 1. K. Goalianos, Phys. Lett. B3b8 (1995) 379, and references therein. 2. A. Bnrndt ef ul. (UA8), Phys. Lett. B297 (1992) 417; H1 Collaboration, 3. F. Abe et ul. (CDF Collaboration), Phys. Rev. D50, 5535 (1994). DESY 95-36 (1995); L.E. Sincla i~  (ZEUS), HEP-EX/9606010 (1996). 3 

Diffractive dijet search with Roman pots at CDF

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Diffractive dijet search with Roman pots at CDF

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