Jorge Barreto Low_x Prague1 Status of Diffractive Physics at DØ Run II Jorge Barreto Instituto de Física - UFRJ Rio de Janeiro – RJ - Brazil Outline  Color Singlet Exchange  Diffractive Z Production  The FPD: Diffractive Scattering  Conclusions

Jorge Barreto Low_x Prague2 Color Singlet Exchange (Diffraction)  The Tevatron collides protons and antiprotons at √s = 1.96 TeV at a crossing rate of 1.7 MHz  About 40% of the total pp cross-section is elastic or diffractive scattering  Diffractive processes involve the exchange of a color singlet: –Quantum numbers of the vacuum –Often referred to as Pomeron exchange  Diffractive studies used to probe nature of the Pomeron p I p J1J1 J2J2 X X X P  Experimental Signature –Rapidity Gap: absence of particles or energy above threshold in some region of rapidity in detector –Tagged proton: p or p scattered at small angle from the beam measured in a detector far from the interaction (p f ) (p i ) |t| = (p f – p i ) 2  = 1 – p f / p i

Jorge Barreto Low_x Prague3 Measuring Rapidity Gaps at DØ Run II  Use the following detectors to identify rapidity gaps: –Forward Calorimeters –Luminosity Monitors (LM) VC: 5.2 < |  < 5.9 LM: 2.7 < |  < 4.4 pp Forward Calorimeter

Jorge Barreto Low_x Prague4 Calorimeter FH EM CH LM 2.7 LM range 4.4 Cells arranged in layers: – electromagnetic (EM) – fine hadronic (FH) – coarse hadronic (CH) 2.6 Esum range  Sum E of Cells in EM and FH layers above threshold: E EM > 100 MeV E FH > 200 MeV Liquid argon/uranium calorimeter IP

Jorge Barreto Low_x Prague5 Calorimeter Energy Sum Areas normalized to 1 empty events physics samples  Compare 'empty event' sample with physics samples: – Empty event sample: random trigger. Veto LM signals and primary vertex, i.e. mostly empty bunch crossings – Physics samples: minimum bias (coincidence in LM), jet and Z→μμ events Log 10 (cell energy sum / GeV): 10 GeV  Use energy sum to distinguish proton break-up from empty calorimeter:  Esum < 10 GeV for current study  Final value will be optimized using full data sample WORK IN PROGRESS

Jorge Barreto Low_x Prague6  Inclusive Z→μμ selection: –di-muon (|η|<2) or single muon (|η|< ~1.6) trigger –2 muons, p T > 15GeV, opposite charge –at least one muon isolated in tracker and calorimeter –cosmics cuts DØ Run II preliminary Summer 2003 M μμ (GeV)  Run I publication ”Observation of diffractively produced W and Z bosons in pp Collisions at sqrt(s)=1.8 TeV”, Phys. Lett. B 574, 169 (2003) Nine single diffractive Z→e+e- events. No result in muon channel.  Run II: first search for forward rapidity gaps in Z→μ+μ- events Search for Z→μμ in Diffraction

Jorge Barreto Low_x Prague7 Z Mass of rapidity gap candidates  Add Esum requirement to define gap  Invariant mass peak consistent with Drell-Yan/Z events  Will be able to compare Z boson kinematics (p T, p z, rapidity) 89.8 ± 0.1 GeV 89.6 ± 1.0 GeV No GapGap WORK IN PROGRESS

Jorge Barreto Low_x Prague8 Z→μμ with rapidity gaps: Summary  Preliminary definition of rapidity gaps at DØ Run II  Study of Z→μ+μ- events with a rapidity gap signature  Current Status –Evidence of Z events with a rapidity gap signature –Quantitative studies of gap definition, backgrounds, efficiency in progress  Plans –Measurement of the fraction of diffractively produced Z events –Diffractive W→μν, W/Z→ electrons, jets and other channels –Use tracks from Forward Proton Detector outgoing proton side outgoing anti-proton side muon

Jorge Barreto Low_x Prague9 Forward Proton Detector Layout  9 momentum spectrometers each composed of 2 Scintillating fiber detectors housed in (Roman Pots) can be brought close (~6 mm) to the beam.  Reconstruct scattered protons and anti-protons to calculate their momentum fraction and scattering angle –Much better resolution than available with gaps alone  Combine tracks with central high-p T scattering (main detector)  Cover a kinematic region 0 < |t| < 3 GeV 2 never before explored at Tevatron energies Z(m) D S Q2Q2 Q3Q3 Q4Q4 S A1A1 A2A2 P 1U P 2I P 2O P 1D p p D2 D Veto Q4Q4 Q3Q3 Q2Q2 |t| = (p f – p i ) 2 = – 2k 2 (1 – cos  ) ~  2 (small angles)  = 1 – x p = 1 – p f / p i < 0.05 (diffraction)

Jorge Barreto Low_x Prague10 FPD Detector Setup  6 layers per detector in 3 planes and a trigger scintillator  U and V at 45 degrees to X, 90 degrees to each other  Layers in a plane offset by ~2/3 fiber. Fibers in each layer of a plane taken together define a segment (0.27mm) used to define hits.  2 detectors in a spectrometer. Hits used to define tracks. 0.8 mm 3.2 mm 1 mm mm U U’ X X’ V V’ Trigger

Jorge Barreto Low_x Prague11 Detector Hit Resolutions  Starting in January 2004, all 18 detectors regularly inserted (dipoles since February 2003)  Commissioning underway on quadrupoles  Resolutions calculated by the difference of the x value of a hit calculated from u/v segments compared to the x value of the x segment show that most of the detectors are working as expected WORK IN PROGRESS

Jorge Barreto Low_x Prague12 FPD Dipole Data Analysis (Diffraction)  Read out using AFE (Analog Front End) board  Trigger minimum of one jet with p T > 25 GeV and North luminosity counters not firing  Harsh multiplicity cut applied on number of segments (1) allowed to fire to help deal with spray background  This correlation is from a small sample pbar p halo pbar halo (0,0) x y beam D2D1 D0 WORK IN PROGRESS X_D1 X_D2 Y_D1 Y_D2 WORK IN PROGRESS

Jorge Barreto Low_x Prague13 Dipole Diffraction Acceptance  Fair agreement between data and MC Simple MC Geometrical Acceptance (14σ from beam) Data (No Cuts) flat |t| distribution WORK IN PROGRESS

Jorge Barreto Low_x Prague14 Dipole Tagged Dijets  Comparison of dijet events with (dashed) and without (solid) tags in the dipole detectors –areas normalized to one  Studies underway to calibrate detectors and refine tag definition WORK IN PROGRESS

Jorge Barreto Low_x Prague15 Summary  The full FPD system has been installed and is working as designed  Full commissioning studies –Detector alignment and calibration  Initial analysis using FPD data: –Dijets using dipole tags –Z→ μμ using tags –(elastics!)  Initial definition of a gap in the calorimeter made  Evidence of Z→ μμ with gap signature found, further work needed to finalize results and interpretation in terms of diffractive physics p IP IP p

Jorge Barreto Low_x Prague16   E Soft Diffraction and Elastic Scattering: Inclusive Single Diffraction Elastic scattering (t dependence) Total Cross Section Centauro Search Inclusive double pomeron Search for glueballs/exotics Hard Diffraction: Diffractive jet Diffractive b,c,t, Higgs Diffractive W/Z Diffractive photon Other hard diffractive topics Double Pomeron + jets Other Hard Double Pomeron topics Rapidity Gaps: Central gaps+jets Double pomeron with gaps Gap tags vs. proton tags Topics in RED were studied with gaps only in Run I 1000 tagged events expected in Run II DØ Run II Diffractive Topics