Diffraction at CDF
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Diffraction at CDF12th International Conference on Elastic and Diffractive ScatteringForward Physics and QCD – Blois2007
Hamburg, Germany, 21-25 May 2007
K. GoulianosThe Rockefeller
University(for the CDF
collaboration)
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Contents
Introduction Diffractive structure function Exclusive Production
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p-p InteractionsDiffractive:
Colorless exchange with vacuum quantum numbers
Non-diffractive:Color-exchange
Incident hadrons retain their quantum numbersremaining colorless
Incident hadrons acquire colorand break apart
POMERON
Goal: understand the QCD nature of the diffractive exchange
rapidity gap
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Definitions
p
MX
dN/d,t
p
MX
pp’
p’rapgap
=-ln
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Diffraction at CDF
Elastic scattering Total cross section
SD DD DPE SDD=SD+DD
T=Im fel (t=0)
OPTICALTHEOREM
GAP
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Rapidity Gaps in Fireworks
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CDF Run-I0 (1988-89)Elastic, 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
Roman Pots with Trackers up to || = 7
CDF-I
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Regge theory SD exceeds T at
Renormalization Pomeron flux integral (re)normalized to unity
Total SD x-section )(Mσξ)(t,f
dtdξ
σd 2XpIPIP/p
SD2
KG, PLB 358 (1995) 379
TeV.2s
1dtdξξ)(t,f0.1
ξ
IP/p
0
tmin
2~ sSD
Pomeron flux
Factorization
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A Scaling Law in Diffraction
KG&JM, PRD 59 (1999) 114017
Factorization breaks down so as to ensure M2-scaling!
12
2
2 )(M
s
dM
d
renormalization
1
Independent of S over 6 orders of magnitude in M2 !
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CDF Run-IRun-IC Run-IA,B
Forward DetectorsBBC 3.2<<5.9 FCAL 2.4<<4.2
beam
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Double Diffraction Dissociation
One central gap
Double Pomeron Exchange
Two forward gaps
SDD: Single+Double Diffraction One forward gap+ one central gap
Central and Multigap Diffraction
Rate for second diffractive gap is not suppressed!
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All ratios ~ 1% ~ uniform suppression
~ FACTORIZATION !
Diffractive Fractions
gap)( Xpp
1.45 (0.25)J/
0.62 (0.25)b
0.75 (0.10)JJ
1.15 (0.55)W
Fraction(%)Fraction:SD/ND ratioat 1800 GeV
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Diffractive non/Factorization
R(SD/ND)
R(DPE/SD)DSF from two/one gap:factorization restored!
The diffractive structure function measured on the proton side in events with a leading antiproton is NOT suppressed relative to predictions
based on DDIS
=momentum fractionof parton in Pomeron
=xBj/
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Run II results
CDF-II detectors Diffractive structure function Exclusive Production
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CD-II Detectors ROMAN POT DETECTORS
BEAM SHOWER COUNTERS:Used to reject ND events
MINIPLUG CALORIMETER
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The MiniPlugs @ CDF
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DIFFRACTIVE STRUCTURE FUNCTION
)(xF
)(xF
)(xRate
)(xRate)R(x
BjNDjj
BjSDjj
BjNDjj
BjSDjj
Bj
Systematic uncertainties due to energy scale and resolutioncancel out in the ratio
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Diffractive Dijet Signal
s
eEξ towersall
ηTCAL
Overlap events: mainly ND dijets plus SD low RPS trigger
- Bulk of data taken with RPS trigger but no RPS tracking- Extract from calorimeter information- Calibrate calorimetric using limited sample of RPS tracking data- Subtract overlap background using a rescaled dijet event sample- Verify diffractive range by comparing RPS with CAL
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Alignment of RPS using Data
maximize the |t|-slope determine X and Y offsets
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CAL Calibration
overlap eventssignal region
cal distribution for slice of RPS
/ mean ~ 30% RPSCAL ξ0.04)(0.97ξ
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Dijet Properties
SD boosted opposite to
pbar
p
p
jet
jet
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ET distributions
120 GeV
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Diffractive Structure Function:Q2 dependence
ETjet ~ 100 GeV !
Small Q2 dependence in region 100 < Q2 < 10,000 GeV2
Pomeron evolves as the proton!
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Diffractive Structure Function:t- dependence
No diffraction dips No Q2 dependence in slope from inclusive to Q2~104 GeV2
Fit d/dt to a double exponential:
Same slope over entire region of 0 < Q2 < 4,500 GeV2
across soft and hard diffraction!
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valence quarks
antiproton
x=
Hard Diffraction in QCD
proton
deep sea
Derive diffractivefrom inclusive PDFsand color factors
antiproton
valence quarks
p
p
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EXCLUSIVE PRODUCTION
H
Measure exclusive jj & Calibrate predictions for H production rates @ LHC
Bialas, Landshoff,Phys.Lett. B 256,540 (1991)Khoze, Martin, Ryskin,Eur. Phys. J. C23, 311 (2002); C25,391 (2002);C26,229 (2002)C. Royon, hep-ph/0308283B. Cox, A. Pilkington,PRD 72, 094024 (2005)OTHER…………………………
Search for exclusive dijets:Measure dijet mass fraction
Look for signal as Rjj 1
rscalorimeteallM
MR
X
jjjj
Search for exclusive 3 candidate events found 1 (+2/-1) predicted from ExHuME MC estimated ~1 bgd event from 0 0 ,
KMR: H(LHC) ~ 3 fbS/B ~ 1 if M ~ 1 GeVDiscovery channel
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Exclusive e+e- Production
p
p
p
p
ee
PRL 98, 112001 (2007)
pb
syststat
LPAIR 01.071.1
pb )(3.0)(6.1 5.03.0exp
nobservatio 5.5
(QED) MC LPAIR with agrees
First observation in hadron colliders
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Exclusive Dijet Signal
b-tagged dijet fraction Dijet fraction – all jets
Exclusive b-jets are suppressedby JZ= 0 selection rule
Excess over MC predictions at large dijet mass fraction
DIJETS
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RJJ(excl): Data vs MC
Shape of excess of events at high Rjj
is well described by both models
ExHuME (KMR): gggg process uses LO pQCD
Exclusive DPE (DPEMC) non-pQCD based on Regge theory
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jjexcl: Exclusive Dijet Signal
COMPARISONInclusive data vs MC @ b/c-jet data vs inclusive
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JJexcl : x-section vs ET(min)Comparison with hadron level predictions
ExHuME (red)Exclusive DPE in DPEMC (blue)
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JJexcl : cross section predictionsExHuME Hadron-Level Differential Exclusive Dijet Cross Section vs Dijet Mass (dotted/red): Default ExHuME prediction
(points): Derived from CDF Run II Preliminary excl. dijet cross sections
Statistical and systematic errors are propagated from measured cross section uncertainties using ExHuME Mjj distribution shapes.
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SummaryCDF - what we have learnt
M2 – scaling d/M2 not a function of s multigap diffraction restoration of factorization! flavor independence of diffractive fractions small Q2 dependence of SD/ND xBJ-distributions t-distributions independent of Q2 exclusive dijet cross sections favor theperturbative QCD over the DPE approachLHC - what to do Elastic and total cross sections & -value High mass (4 TeV) and multi-gap diffraction Exclusive production (FP420 project)For a QCD perspective, see Tuesday’s talk on:“Pomerom Intercept and Slope: the QCD connection”