DIFFRACTION 2012, Lanzarote, Canary Islands, Spain

DIFFRACTIVE DIJET PRODUCTION AT CDF 

Konstantin Goulianos 

(for the CDF II Collaboration) 

Diffraction 2012 Lanzarote Diffractive Dijet Production at CDF K. Goulianos 

1

CONTENTS 

Introduction / motivation 

Diffractive dijets 

Summary 


2

STUDIES OF DIFFRACTION IN QCD 

Non-diffractive 

color-exchange gaps 

exponentially suppressed 

Diffractive 

Colorless vacuum exchange 

large-gap signature 

Incident hadrons 

acquire color 

and break upart 

rapidity gap 

p 

Incident hadrons retain 

their quantum numbers 

remaining colorless 

CONFINEMENT 

Goal: probe the QCD nature of the diffractive exchange 

P 

O 

M 

E 

R 

O 

N 

p p p p 


3

DEFINITIONS 

SINGLE DIFFRACTION 

x,t 

M X 

p p’ 

xp 

p 

1- x L 

ξ 

CAL 

ξ 

 

Σ 

 

all 

i1 

M 2 X 

s 

E 

i-tower 

T 

since no radiation 

no price paid for increasing 

diffractive gap size 

s 

e 

 

η i 

 

 

 

dσ 

d Δη 

 

 

 

t0 

p’ 

Rap-gap 

Dh=-lnx 

constant 

dσ 

dξ 

0 

dN/dh 

ln ln s 

dσ 1 

 

2 2 

1 

ξ 

ln Mx 2 


dM 

M X 

M 

4

DIFFRACTION AT CDF 

Elastic scattering s T =Im f el (t=0) Total cross section 

f 

gap 

h 

OPTICAL 

THEOREM 

f 

h 

SD DD DPE /CD SDD 

Single Diffraction or 

Single Dissociation 

Double Diffraction or 

Double Dissociation 

Double Pom. Exchange or 

Central Dissociation 

Single + Double 

Diffraction (SDD) 

JJ, b, J/y, W 

p 

exclusive 

JJ…ee…mm...gg 

p 


5

540 GeV 

1800 GeV 

FACTORIZATION BREAKING IN 

SOFT DIFFRACTION 

diffractive x-section suppressed relative 

to Regge prediction as √s increases 

p 

p 

x,t 

p’ 

M 

Factor of ~8 (~5) 

suppression at 

√s = 1800 (540) GeV 

RENORMALIZATION 

√s=22 GeV 

C 

D 

F 

see KG, PLB 358, 379 (1995) 

Question: 

does factorization breaking 

affect t-distributions? 


6

Run I 

Hard diffraction 

pp 

 

( 

 

X) 

 

gap 

or gap 

p pbar 

Fraction: 

SD/ND ratio 

@ 1800 GeV 

JJ 

W 

Fraction % 

0.75 +/- 0.10 

1.15 +/- 0.55 

dN/dh 

hard 

b 

J/y 

0.62 +/- 0.25 

1.45 +/- 0.25 

h 

All fractions ~ 1% 

(differences due to kinematics) 

‣ ~ FACTORIZATION ! 

FACTORIZATION ! 


7

Diffractive dijets in Run I 

H1 

CDF 

~20 

~8 ~8 

All hard-diffraction processes in Run I were found to be suppressed by 

a factor of ~8 relative to predictions based on HERA-measured PDFs. 


8

Excusive dijets 

Calibrate diffractive Higgs production models 

Phys. Rev. D 77, 052004 (2008) 


9

THE CDF II DETECTOR 

PLAN VIEW 

|h|

The RPS 


11

The MiniPlugs 

overlap bgnd (BG) is reduced by including the MPs in the x CAL evaluation 


12

Dynamic Alignment of RPS 

Method: iteratively adjust the RPS X and Y offsets from the 

nominal beam axis until a maximum in the b-slope is obtained @ t=0. 

±2 mm 

Limiting factors 

1-statistics 

2-beam size 

3-beam jitter 

±2 mm 

use RPStrk data 

width~ 2 mm/√N 

N~1 K events 

DX,DY = ± 60 m 


13

x CAL vs x RPS 

slice 


14

Why select 0.05

RPS ACCEPTANCE 

0.05 < x

t >1 GeV 2 : asymmetric t-distributions as 

a tool for evaluating bgd at high t 

schematic view of fiber tracker 

25 mm 

t-distributions 

7.5 mm 

12.5 mm 

x 

2.5 mm 

Y 

p p 

• • 

2 mm 

Y = 7.5 mm 

bgnd = 

20 evts/GeV 2 

‣ tracker’s upper edge: |t|=2.3 GeV 2 , estimated from t~q 2 

‣ the lower edge is at |t|= 6.5 GeV 2 (not shown) 

‣ background level: region of Y track >Y o data for |t|>2.3 GeV 2 


17

Diffractive dijet results 

http://arxiv.org/abs/1206.3955 


18

Measurement of F jj 

SD 


19

x CAL vs x RPS 

As RPS tracking was not available for all analyzed data, we used x CAL and 

calibrated it vs x RPS from data in which RPS tracking was available. 

A linear relationship is observed between x CAL vs 

x RPS in the region of x CAL of the measurement 


20

Average E T 

jet 

and h Jet 

The SD and ND E T 

Jet 

distributions are nearly identical 

The SD h* distribution is shifted towards the c.m.s of the Pomeron-proton collision 


21

Azimuthal angle difference of jets 

Left: the SD distributions are more back-to-back 

Right: the SD multiplicity is peaked at zero, while the ND is peaked at 9. 


22

x Bj Distributions vs 

=100 GeV 2 

The Run I result is confirmed. 

‣ The drop-off on the rhs is due to the 

different range of the calorimeters in 

Run I and Run II. 

The Bjorken-x distributions vary by only a factor of ~2 

over a range of of 2 orders of magnitude! 


23

t-Distributions and Slopes vs for –t

t-Distributions for -t

Result of the week 


26

EXCLUSIVE Dijet Excl. Higgs THEORY CALIBRATION 

_ 

p 

p 

} JJ 

PRD 77, 052004 (2008) 

Exclusive dijets 


27

CDF 4 LHC 

Larger Energy Larger ET 

‣ Multigap diffraction 

‣ Diffractive Higgs production 

The CDF measurements are having an impact on all LHC physics 

the MBR (Minimum Bias Rockefeller) simulation is now in PYTHIA8 


28

Summary 

We measured SD to ND ratios in dijet production vs Bjorken-x 

for up to 10 4 GeV 2 and –t > 4 GeV 2 

We find: 

nearly identical E T 

jet 

distributions for SD and ND events 

small dependence as a function of Bjorken-x 

no dependence of the b-slopes at low t 

t distributions compatible with DL at low t 

at high t the distributions lie increasingly higher than DL, 

becoming approximately flat for –t >2 GeV 2 

compatible with a diffraction minimum at –t >2.5 GeV 2 

Our findings are compatible with models of diffraction in 

which the hard scattering is controlled by the PDF of the 

recoil antiproton, while the rapidity gap formation is governed 

by the color-neutral soft exchange. 

Thank you for your attention 


29

BACKUP 


30

Data samples 


31

Ratio of SD to ND events vs E T * 

TABLE III 

Diffractive Dijet Production at CDF 

K. Goulianos 

32

Slopes of t-didtributions 


33

RIGGERS AND EVENT SAMPLES 


34

The end! 


35

DIFFRACTION 2012, Lanzarote, Canary Islands, Spain

Create successful ePaper yourself

Delete template?

Save as template?