Forward Protons from the SPS to the Tevatron

1. Forward Protons from the SPS to the Tevatron Andrew Brandt, University of Texas at Arlington Thanks for slides: Koji Terashi, Dino Goulianos, Mike Albrow, Rainer Wallny Michele Arneodo, and others DOE, NSF, UTA, Texas ARP for support Physics Seminar May 17, 2006 DESY

2. Examples of Soft Diffraction Elastic “dip” Structure from Phys. Rev. Lett. 54, 2180 (1985). Elastic Single Diffraction • Modeled by Regge Theory • Analysis of poles in the complex angular momentum plane give rise to trajectories that describe particle exchange • P.D.B. Collins, An Introduction to Regge Theory and High Energy Physics, Cambridge Univ. Press, Cambridge 1977 • Non-perturbative QCD Prior to 1985 all diffraction was soft diffraction

3. Ingelman-Schlein A* A P J2 X J1 B • Propose Hard Diffraction possibility in 1985 • Factorization allows us to look at the diffractive reaction as a two step process. Hadron A emits a Pomeron (pomeron flux) then partons in the Pomeron interact with hadron B in a standard QCD gg hard scattering. (basis of POMPYT, POMWIG MC’s) • The Pomeron to leading order is proposed to have a minimal structure of two gluons in order to have quantum numbers of the vacuum My first trip to DESY was April 1987 to meet Gunnar, begin work on PYTHIA 4.8X, precursor to POMPYT G. Ingelman and P. Schlein, Phys. Lett. B 152, 256 (1985)

4. UA8

5. UA8 = UA2 + Roman-pot Spectrometer

6. UA8 Dijet Production in Diffraction A. Brandt et al., P.L. B 297 (1992) 417 (196 citations!) Hard Diffraction exists! Pomeron has a “super-hard” component. x(2-jet)

7. CDF Confirms UA8 Result K. Hatakeyama’s thesis, Rockefeller 2003

8. Q2 = virtuality of photon = = (4-momentum exchanged at e vertex)2 t = (4-momentum exchanged at p vertex)2 typically: |t|<1 GeV2 W = invariant mass of photon-proton system xIP = fraction of proton’s momentum taken by Pomeron= x in Fermilab jargon b = Bjorken’s variable for the Pomeron = fraction of Pomeron’s momentum carried by struck quark e’ e Q2 e g* p Proton energy = 920 GeV Electron energy = 27.5 GeV s=318 GeV W X LRG IP p p’ t HERA ZEUS X e p 27.5 GeV e 920 GeV Dh s  320 GeV Diffractive Deep Inelastic Scattering

9. VM, g, exclusive dijets…Higgs g* x x’ GPD p p Two fundamental physics quantities can be accessed in diffractive DIS: dPDFs and GPDs e’ 1) Diffractive PDFs: probability to find a parton of given x in the proton under condition that proton stays intact – sensitive to low-x partons in proton, complementary to standard PDFs (ingredient for all inclusive diffractive processes at Tevatron and LHC) e dPDF IP p p’ Rather than IP exchange: probe diffractive PDFs of proton • 2) Generalised Parton Distributions (GPD) • quantify correlations between parton • momenta in the proton; t-dependence • sensitive to parton distribution in • transverse plane • When x’=x, GPDs are proportional to the • square of the usual PDFs • (ingredient for all exclusive diffractive processes)

10. F2D Extrapolation from HERA CDF data Applying dPDFs to FNAL/LHC Requires Care GPDs and diffractive PDFs measured at HERA cannot be used blindly in pp (or ) interactions. In addition to the hard diffractive scattering, there are soft interactions among spectator partons. They fill the rapidity gap and reduce the rate of diffractive events. Multi-Pomeron-exchange effects (a.k.a. “renormalization”, “screening”,“shadowing”, “damping”, “absorption”)

11. CDF Run 1-0 (1988-89) Elastic, single diffractive, and total cross sections @ 546 and 1800 GeV Roman Pot Spectrometers • Roman Pot Detectors • Scintillation trigger counters • Wire chamber • Double-sided silicon strip detector Additional Detectors Trackers up to |h| = 7 • Results • Total cross section stot ~ se • Elastic cross section ds/dt ~ exp[2a’ lns]  shrinking forward peak • Single diffraction Breakdown of Regge factorization

12. SSC is a four letter word in Texas 1992 Small-x Workshop

13. f Dh h h E   DØ Run I Gaps • Pioneered central gaps between jets: Color-Singlet fractions at s = 630 & 1800 GeV; Color-Singlet Dependence on Dh, ET, s (parton-x).PRL 72, 2332(1994); PRL 76, 734 (1996); • PLB 440, 189 (1998) • Observed forward gaps in jet events at s = 630 & 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. • PLB 531, 52 (2002) • Observed W and Z boson events with gaps: measured fractions, properties first observation of diffractive Z. • PLB 574, 169 (2003) • Observed jet events with forward/backward • gaps at s = 630 and 1800 GeV DESY seminar Oct. 1997 on DØ Hard Diffraction leads to collaboration with young Brian Cox

15. Diffractive W Boson CDF {PRL 78 2698 (1997)} measured RW = 1.15 ± 0.55% where RW = Ratio of diffractive/non-diffractive W a significance of 3.8 DIFFW signal Predicts 15-20% of W’s are diffractively produced

16. DØ Observation of Diffractive W/Z Diffractive W and Z Boson Signals • Phys. Lett. B 574, 169 (2003) • Observed clear Diffractively produced W and Zbosonsignals • Events have typical W/Z characteristics • Background from fake W/Z gives negligible change in gap fractions nL0 ncal nL0 ncal Central electron W Forward electron W Sample Diffractive Probability Background All Fluctuates to Data Central W (1.08 + 0.19 - 0.17)% 7.7s Forward W (0.64 + 0.18 - 0.16)% 5.3s All W(0.89 + 0.19 – 0.17)% 7.5s All Z (1.44 + 0.61 - 0.52)% 4.4s nL0 ncal All Z

17. DØ Run II Diffractive Topics Soft Diffraction and Elastic Scattering: Inclusive Single Diffraction Elastic scattering (t dependence) Inclusive double pomeron Search for glueballs/exotics Hard Diffraction: Diffractive jet Diffractive b,c ,t Diffractive W/Z Diffractive photon Other hard diffractive topics Double Pomeron + jets Other Hard Double Pomeron topics Exclusive Production of Dijets Topics in RED were studied with gaps only in Run I

18. Diffractive Z Production Event Selection:Z→μ+μ- Events Two Good (PT > 15GeV) Oppositely Charged Tracks Both Identified as muons BKGD Rejection: Min one muon Isolated in Tracker and Calorimeter (suppress Heavy Flavour BKGD), Cosmic Ray Rejection. Demand Activity North and South Forward Gap (North or South) DØ Prelim DØ Prelim Candidate Diffractive Z Events

19. Forward Proton Detector Nine independent spectrometers each consisting of two detectors Scattered antiprotons Scattered Protons AUP Spectrometer PUP Spectrometer Dipole Magnets Quadrupole Magnets Quadrupole Magnets Separator Separator z [m] Dipole Spectrometer IP ADOWN Spectrometer PDOWN Spectrometer 109 nsec 78 nsec 78 nsec 109 nsec 200 nsec  Reconstruct particle tracks from detector (scintillating fiber) hits Dipole SpectrometerQuadrupole Spectrometers |t| ~ 0.0 GeV2 |t| > 0.8 GeV2 x > 0.04 x > 0.0  18 Pots integrated into DØ readout and inserted every store since Jan 2004 Simultaneously tag/reconstruct protons and antiprotons

20. TDC’S! Brown U. Hardware commissioned by Manchester Engineers

21. LM A1U A2U Elastic VC Pbar P 109 nsec 78 nsec P1D P2D LM 78 nsec 109 nsec A1U A2U VC Proton Halo -109 nsec -78 nsec P1D P2D Elastics/Halo Background double halo could be background to elastics In-time Bit set if pulse detected (above threshold) in in-time window Halo Timing Bit set if pulse detected in early time window

22. Large * Store pot position integrated luminosity Two day run of accelerator at injection tune *=1.6 m 1x1 bunch Lum=0.5E30 Estimated t range accessible with injection tune • Physics Goals: • Low-t elastic scattering • Low-t single diffractive • and double pomeron • scattering

23. Hit Maps from 1x1 Store Large b* store (4647) (no low b squeeze) Typical Store pots typically 9-15 from beam 20 Million events; first results this summer/fall

25. (no jet ET dependence either)

27. CDF Exclusive Dijets in Run I Dijet Mass fraction PRL 85 (2000) 4215 Expected shape of signal events Exclusive dijet limit: sjj (excl.) < 3.7 nb (95% CL) Theoretical expectation (KMR) ~1 nb

34. Hard Diffraction has come a long way from UA8 days (from the SPS to Fermilab via HERA) SPS: Jets, FNAL: W/Z, at LHC: Higgs?