DIS 2001 Bologna Hard Diffraction at DØ Run I and Run II Christophe Royon DØ Collaboration / DAPNIA-SPP Saclay, UT Arlington, Brookhaven

Diffraction p p  p p p p  p (p) + X p p  p (p) + j j p p  p p + j j

Central Calorimeter End Calorimeter Central Drift Chamber (Tracking) n trk = # charged tracks with |  | < 1.0 Hadronic Calorimeter EM Calorimeter n cal = # EM towers with E T > 200 MeV and |  | < 1.0 (use E for |  | > 2.0) DØ Calorimeter and Tracking

..... L0 Detector beam

Event Displays

Hard Single Diffraction  or Measure Multiplicity here Measure Gap Fraction: *Forward Jet Trigger 2-12GeV Jets |  |>1.6 *46K events (1800 GeV) *26K events (630 GeV) * Inclusive Jet Trigger 2-15(12)GeV Jets |  |<1.0 *14K events (1800 GeV) *27K events (630 GeV) Study SD Characteristics: *Single Veto Trigger 2-15(12)GeV Jets 1800 GeV (22K,38K) 630 GeV (1K,24K)

Single Diffractive Results D0 Preliminary Data Sample Measured Gap Fraction (#Diffractive Dijet Events/#All Dijets) 1800 Forward Jets0.65% % % 1800 Central Jets0.22% % % 630 Forward Jets1.19% % % 630 Central Jets0.90% % % * Forward Jets Gap Fraction > Central Jets Gap Fraction * 630GeV Gap Fraction > 1800GeV Gap Fraction Data Sample Ratio 630/1800 Forward Jets /1800 Central Jets Fwd/Cent Jets Fwd/Cent Jets  or Measure Multiplicity here

MC Rate Comparison D0 Preliminary Evt Sample Hard Gluon Flat Gluon Quark 1800 FWD JET (2.2  0.3)% (2.2  0.3)% (0.8  0.1)% 1800 CEN JET (2.5  0.4)% (3.5  0.5)% (0.5  0.1)% 630 FWD JET (3.9  0.9)% (3.1  0.9)% (2.2  0.5)% 630 CEN JET (5.2  0.7)% (6.3  0.9)% (1.6  0.2)% Evt Sample Soft Gluon DATA 1800 FWD JET (1.4  0.2)% (0.65  0.04)% 1800 CEN JET (0.05  0.01)% (0.22  0.05)% 630 FWD JET (1.9  0.4)% (1.19  0.08)% 630 CEN JET (0.14  0.04)% (0.90  0.06)% f visible =  gap · f predicted * Hard Gluon & Flat Gluon rates higher than observed in data (HG 1800fwd  gap~ 74%±10%, SG 1800fwd  gap ~22%±3%)   gap *Add multiplicity to background data distribution *Fit to find percent of signal events extracted  Find predicted rate POMPYT·2 / PYTHIA *Apply same jet  cuts as data, jet ET>12GeV *Full detector simulation

D0 Preliminary Event Sample Soft Glu DATA 630/1800 FWD 1.4   /1800 CEN 3.1   FWD/CEN 30.   FWD/CEN 13.   0.1 * Hard Gluon & Flat Gluon forward jet rate is lower than central jet rate -- and lower than observed in data *Quark rates and ratios are similar to observed *Combination of Soft Gluon and harder gluon structure is also possible for pomeron structure Event Sample Hard Glu Flat Glu Quark 630/1800 FWD 1.7    /1800 CEN 2.1    FWD/CEN 0.9    FWD/CEN 0.8    and 1800 GeV Ratios

n cal Peak at (0,0) indicates diffractive W with a signal on the 1% level n L0   e Measure Mult. Here Measure Mult. Here Diffractive W  s =1800 GeV n cal n L0

Demand gap on one side, measure multiplicity on opposite sideDemand gap on one side, measure multiplicity on opposite side DØ Preliminary Gap Region 2.5<|  |<5.2 Double Gaps at 630 GeV

Gap Summary Observed and measured forward gaps in jet events at  s = 630 and 1800 GeV. Rates much smaller than expected from naïve Ingelman-Schlein model. Require a different normalization and significant soft component to describe data. Large fraction of proton momentum frequently involved in collision. Observed jet events with forward/backward gaps at  s = 630 and 1800 GeV Observed W and Z boson events with gaps Finalizing papers and attempting to combine results

The Forward Proton Detector A series of momentum spectrometers used to measure t and  of scattered protons and anti-protons Gives ability to trigger on scattered proton in t,  bins -- allows large data samples without large bandwidth Full DØ detector is used to measure hard scattering

momentum spectrometers allowing measurement of Series of 18 Roman Pots forms 9 independent proton momentum and angle. 1 Dipole Spectrometer ( p )  min 8 Quadrupole Spectrometers (p or p, up or down, left or right) t > t min Q4 D S Q3S A1A2 P 1 UP p p Z(m) D1 Detector Bellows Roman Pot FPD Layout p Beam pFpF P Q2 P 1 DN D2 Q4Q3Q2

Physics Topics with the FPD 1) Diffractive jet production 2) Hard double pomeron exchange 3) Diffractive heavy flavor production 4) Diffractive W/Z boson production 5) New physics 6) Inclusive double pomeron 7) High-|t| elastic scattering 8) Total cross section 9)Inclusive single diffraction 10) Higgs production in double diffraction FPD allows DØ to maximize Run II physics

Run II Event Displays Hard Diffractive Candidtate Hard Double Pomeron Candidate

Acceptance Quadrupole ( p or ) Dipole ( only) Dipole acceptance better at low |t|, large  Cross section dominated by low |t|  Quadrupole Dipole M X (GeV) GeV M X (GeV)   Geometric  Acceptance

Quadrupole + Dipole Spectrometers The combination of quadrupole and dipole spectrometers gives: 1) Detection of protons and anti-protons a) tagged double pomeron events b) elastics for alignment, calibration, luminosity monitoring c) halo rejection from early time hits 2) Acceptance for low and high |t| 3) Over-constrained tracks for understanding detectors and backgrounds

Parts are degreased and vacuum degassed Plan to achieve Torr Will use Fermilab style controls Bakeout castle, then insert fiber detectors Constructed from 316L Stainless Steel Roman Pot Castle Design Detector 50 l/s ion pump Beam Worm gear assembly Step motor

Thin window and flange assembly Bellows Detector is inserted into cylinder until it reaches thin window Motor Flange connecting to vacuum vessel Threaded Cylinder Roman Pot Arm Assembly

Castle Prototype

Six planes (u,u’,v,v’,x,x’) of 800  scintillator fibers (’) planes offset by 2/3 fiber The Detector 20 channels/plane(U,V)’ 16 channels/plane(X,X’) 112 channels/detector 2016 total channels 80  theoretical resolution

Data Taking No special conditions required Read out Roman Pot detectors for all events (can’t miss ) A few dedicated global triggers for diffractive jets, double pomeron, and elastic events Use fiber tracker trigger board -- select , |t| ranges at L1, readout DØ standard Reject fakes from multiple interactions (Ex. SD + dijet) using L0 timing, silicon tracker, longitudinal momentum conservation, and scintillation timing Obtain large samples (for 1 fb -1 ): ~ 1K diffractive W bosons ~ 3K hard double pomeron ~500K diffractive dijets with minimal impact on standard DØ physics program

Measurements Using the FPD Observation of hard diffractive processes. Measure cross sections dominated by angular dispersion 15% error for (reduced with unsmearing). Measure kinematical variables with sensitivity to pomeron structure ( , E T, …) Use Monte Carlo to compare to different pomeron structures and derive pomeron structure. Combine different processes to extract quark and gluon content.

FPD Installation and Commissioning All of the castles are installed and tested since March 1st, All the tunnel electronics is installed and cables will all be laid. The dipole spectrometer is instrumented with full detectors and phototubes. The vertical spectrometers and one horizontal spectrometer are instrumented with pseudodetectors (trigger scintillators only) to study halo. We are ready to take data with a Phase I (10 spectrometers) FPD (in May, 2 detectors and 8 pseudo-detectors and in late summer, 10 detectors fully equipped).

Pot Motion: LVDT vs. Encoder

Overall Conclusions Much expected at RunII using the Forward Proton Detector DØ has made significant progress in hard diffraction in Run I