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

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

Ingelman-Schlein lPropose Hard Diffraction possibility in 1985 lFactorization 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) lThe Pomeron to leading order is proposed to have a minimal structure of two gluons in order to have quantum numbers of the vacuum A A* B J1J1 J2J2 P X G. Ingelman and P. Schlein, Phys. Lett. B 152, 256 (1985) My first trip to DESY was April 1987 to meet Gunnar, begin work on PYTHIA 4.8X, precursor to POMPYT

UA8

UA8 = UA2 + Roman-pot Spectrometer

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

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

Diffractive Deep Inelastic Scattering e p HERA Proton energy = 920 GeV Electron energy = 27.5 GeV  s=318 GeV Q 2 = virtuality of photon = = (4-momentum exchanged at e vertex) 2 t = (4-momentum exchanged at p vertex) 2 typically: |t|<1 GeV 2 W = invariant mass of photon-proton system x IP = fraction of proton’s momentum taken by Pomeron =  in Fermilab jargon  = Bjorken’s variable for the Pomeron = fraction of Pomeron’s momentum carried by struck quark LRG IP Q2Q2 t W X e’ p’ ** e p 920 GeV 27.5 GeV  s  320 GeV ZEUS pe X e 

p’p e e’ IP dPDF 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) 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) VM,  exclusive dijets…Higgs x’ x p p  GPD Two fundamental physics quantities can be accessed in diffractive DIS: dPDFs and GPDs Rather than IP exchange: probe diffractive PDFs of proton

Applying dPDFs to FNAL/LHC Requires Care CDF data Extrapolation from HERA F2DF2D 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”)

CDF Run 1-0 ( ) Elastic, single diffractive, and total cross 546 and 1800 GeV Roman Pot Spectrometers Roman Pot Detectors  Scintillation trigger counters  Wire chamber  Double-sided silicon strip detector Results  Total cross section  tot ~ s   Elastic cross section d  /dt ~ exp[2  ’ ln s ]  shrinking forward peak  Single diffraction Breakdown of Regge factorization Additional Detectors Trackers up to |  | = 7

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

DESY seminar Oct on DØ Hard Diffraction leads to collaboration with young Brian Cox   E DØ Run I Gaps     Pioneered central gaps between jets: Color-Singlet fractions at  s = 630 & 1800 GeV; Color-Singlet Dependence on , E T,  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

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

DØ Observation of Diffractive W/Z lObserved clear Diffractively produced W and Z boson signals lEvents have typical W/Z characteristics lBackground from fake W/Z gives negligible change in gap fractions Sample Diffractive Probability Background All Fluctuates to Data Central W( )% 7.7  Forward W( )% 5.3  All W( – 0.17)% 7.5  All Z ( )% 4.4  n cal n L0 Diffractive W and Z Boson Signals Central electron WForward electron W All Z n cal n L0 n cal n L0 Phys. Lett. B 574, 169 (2003)

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 DØ Run II Diffractive Topics Topics in RED were studied with gaps only in Run I

Event Selection: Z→μ+μ- Events Two Good (P T > 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. Diffractive Z Production Demand Activity North and SouthForward Gap (North or South)  Candidate Diffractive Z Events DØ Prelim

Forward Proton Detector z [m] Dipole SpectrometerQuadrupole Spectrometers |t| ~ 0.0 GeV 2 |t| > 0.8 GeV 2  > 0.04  > 0.0  18 Pots integrated into DØ readout and inserted every store since Jan 2004  Simultaneously tag/reconstruct protons and antiprotons Quadrupole Magnets Separator Dipole Magnets Separator P DOWN Spectrometer Dipole Spectrometer A UP Spectrometer A DOWN Spectrometer P UP Spectrometer IP Nine independent spectrometers each consisting of two detectors  Reconstruct particle tracks from detector (scintillating fiber) hits Scattered antiprotonsScattered Protons Quadrupole Magnets 78 nsec109 nsec78 nsec109 nsec 200 nsec

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

Elastics/Halo Background A1UA2U P2DP1D P Pbar LM VC Elastic 78 nsec 109 nsec 78 nsec 109 nsec A1UA2U P2DP1D LM VC Proton Halo - 78 nsec nsec In-time Bit set if pulse detected (above threshold) in in-time window Halo Timing Bit set if pulse detected in early time window double halo could be background to elastics

Large  * Store Physics Goals: 1.Low-t elastic scattering 2.Low-t single diffractive and double pomeron scattering Two day run of accelerator at injection tune  *=1.6 m 1x1 bunch Lum=0.5E30 Estimated t range accessible with injection tune pot position integrated luminosity

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

(no jet E T dependence either)

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

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?