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Twenty Years of Diffraction at the Tevatron

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K. Goulianos

The Rockefeller University

EDS 2005

15-20 May 2005

Chateau de Blois, France

http://physics.rockefeller.edu/dino/my.html

Diffractive:

vacuum exchange

Non-diffractive:

color exchange

Protons retain their

quantum numbers

Protons acquire color

and break apart

Twenty Years of Diffraction at the Tevatron K. Goulianos

Twenty Years of Diffraction at the Tevatron K. Goulianos

Po’< Po

Twenty Years of Diffraction at the Tevatron K. Goulianos

- Important for understanding hadron structure and quark confinement
- Need to develop new mathematical methods
- Diffraction offers an arena on which to confront non-pQCD

pure thinking!

THEORY

phenomenology

experiment

Twenty Years of Diffraction at the Tevatron K. Goulianos

- 1960’sBNL: first observation of pp -> pX
- 1970’sFermilab fixed target, ISR, SPS
- Regge theory & factorization
- Review: KG, Phys. Rep. 101 (1983) 169
- 1980’sUA8: diffractive dijets a hard diffraction
- 1990’sTev Run-I: Regge factorization breakdown
- Tev vs HERA: QCD factorization breakdown
- 21st C Multigap diffraction: restoration of factorization
- Ideal for diffractive studies @ LHC

Twenty Years of Diffraction at the Tevatron K. Goulianos

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

Twenty Years of Diffraction at the Tevatron K. Goulianos

KG, PLB 358 (1995) 379

Twenty Years of Diffraction at the Tevatron K. Goulianos

Run-IC

Run-IA,B

Forward Detectors

BBC 3.2<h<5.9

FCAL 2.4<h<4.2

Twenty Years of Diffraction at the Tevatron K. Goulianos

93(2004)141601

Twenty Years of Diffraction at the Tevatron K. Goulianos

Hd

Fraction(%)

W

1.15 (0.55)

JJ

0.75 (0.10)

b

0.62 (0.25)

J/y

1.45 (0.25)

Fraction:

SD/ND ratio

at 1800 GeV

All ratios ~ 1%

~ uniform suppression

~ FACTORIZATION

Twenty Years of Diffraction at the Tevatron K. Goulianos

H1

CDF

Twenty Years of Diffraction at the Tevatron K. Goulianos

(KG, hep-ph/0205141)

f

y

Twenty Years of Diffraction at the Tevatron K. Goulianos

f

y

Total cross section:

power law rise with energy

~1/as

The exponential rise of sT(Dy’) is due

to the increase of wee partons with Dy’

(see E. Levin, An Introduction to Pomerons,Preprint DESY 98-120)

f

Elastic cross section:

forward scattering amplitude

y

QCD expectations

Twenty Years of Diffraction at the Tevatron K. Goulianos

t

2 independent variables:

color

factor

sub-energy x-section

gap probability

Gap probability MUST be normalized to unity!

Twenty Years of Diffraction at the Tevatron K. Goulianos

Grows slower than lns

No unitarity problem after eikonalization of the elastic amplitude

Twenty Years of Diffraction at the Tevatron K. Goulianos

- Unitarity problem:
Using factorization

and std pomeron flux

sSD exceeds sT at

- Renormalization:
Normalize the Pomeron

flux to unity

KG, PLB 358 (1995) 379

Twenty Years of Diffraction at the Tevatron K. Goulianos

Color factor:

Pomeron intercept:

lg=0.20

lq=0.04

lR=-0.5

Experimentally:

KG&JM, PRD 59 (114017) 1999

CTEQ5L

fg=gluon fraction

fq=quark fraction

Twenty Years of Diffraction at the Tevatron K. Goulianos

5 independent variables

color

factors

Gap probability

Sub-energy cross section

(for regions with particles)

Same suppression

as for single gap!

Twenty Years of Diffraction at the Tevatron K. Goulianos

Agreement with renormalized Regge predictions

DD

SDD

DPE

- One-gap cross sections are suppressed

- Two-gap/one-gap ratios are

Twenty Years of Diffraction at the Tevatron K. Goulianos

S =

Results similar to predictions by:

Gotsman-Levin-Maor

Kaidalov-Khoze-Martin-Ryskin

Soft color interactions

Twenty Years of Diffraction at the Tevatron K. Goulianos

jet

p

x

x,t

IP

p

g*

e

g*

Q2

e

reorganize

Brodsky et al. rescattering?

Factorization holds: J. Collins

Pomeron exchange

Color reorganization

Twenty Years of Diffraction at the Tevatron K. Goulianos

aP(0)-1

eg=0.20

(eq+l)/2

eq=0. 04

eR=-0.5

eq

KG, “Diffraction: a New Approach,” J.Phys.G26:716-720,2000 e-Print Archive: hep-ph/0001092

F2 ~ x-l

Twenty Years of Diffraction at the Tevatron K. Goulianos

jet

p

jet

reorganize

Twenty Years of Diffraction at the Tevatron K. Goulianos

Twenty Years of Diffraction at the Tevatron K. Goulianos

0.035 < x < 0.095

Flat x dependence

Twenty Years of Diffraction at the Tevatron K. Goulianos

R(SD/ND)

R(DPE/SD)

DSF from two/one gap:

factorization restored!

Twenty Years of Diffraction at the Tevatron K. Goulianos

Twenty Years of Diffraction at the Tevatron K. Goulianos

Question

Is the diffractive exchange BFKL-like

or simply a color rearrangement?

Twenty Years of Diffraction at the Tevatron K. Goulianos

p

p

valence quarks

antiproton

antiproton

SOFT

HARD

eg=0.20

lg=0.5

eq=0. 04

lq=0.3

eR=-0.5

deep sea

valence quarks

Derive diffractive

from inclusive PDFs

and color factors

x=x

proton

Twenty Years of Diffraction at the Tevatron K. Goulianos

- Single Diffraction
- x and Q2 dependence of FjjD
- Process dependence of FD (W, J/y)

- Double Diffraction
- Jet-Gap-Jet: Dhgap for fixed large Dhjet

- Double Pomeron Exchange
- FjjD on p-side vs x-pbar
Also:

Exclusive central production

- Dijets, cc
Other

- Tev4LHC issues

- FjjD on p-side vs x-pbar

Twenty Years of Diffraction at the Tevatron K. Goulianos

- Diffraction is a low-x QCD phenomenon subject
to color constraints.

- Multigap processes offer the opportunity
to study diffraction without complications

arising from rapidity gap survival issues.

- Regularities observed in Run 1
at the Tevatron and in results

obtained at HERA paint a picture of the Pomeron

as a composite object constructed from the

underlying inclusive pdf’s of the (anti)proton.

This picture could be further clarified and

advanced to a theory by studies at the LHC.

Twenty Years of Diffraction at the Tevatron K. Goulianos