Diffractive and Exclusive Production of Dijets and W/Z at...
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Low x 2008, Kolymbari-Crete, Greece Diffractive and Exclusive JJ and W/Z at CDF K. Goulianos 1
Diffractive and Exclusive Production of Dijets
and W/Z at CDF
K. GoulianosThe Rockefeller Universityand the CDF collaboration
Low x 2008, Kolymbari-Crete, Greece Diffractive and Exclusive JJ and W/Z at CDF K. Goulianos 2
A bit of history…Diffraction in the70s the Pomeron unveiled!
Opening night at Chez Leon - Fermilab (1989)
(right) Greg Snow on violin (Ph.D thesis: first observation of diffractive γ dissociation)
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At the Gorge of Samaria (1980)
w/R. Feynman – a day of jokes!
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Contents IntroductionDijetsW/Z
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Introduction
SD DD DPE SDD=SD+DD
pp
JJ, ee, μμ, γγ
Soft and hard diffraction @ CDF
JJ, b, J/ψ,
W
exclusive
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SD kinematics
MX
ξ,t
η
dN/dη
pMX
p p’
p’rap-gap
Δη=-lnξ
0
Lpξ ⋅
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Breakdown of factorization –
Run I
~8
ZEUS and H1 vs. CDF
ξxβ =H1
ZEUS
CDFKG, PLB 358 (1995) 379
1dtdξξ)(t,f0.1
ξIP/p
0
tmin
=∫ ∫−∞=
σTsd
~ 8
softγ*e
pp p
pp
hard
Magnitude:
same suppression factor in soft and hard diffraction!Shape of β
distribution:
ZEUS, H1, and Tevatron
–
why different shapes?
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All fractions ~ 1% (differences due to kinematics)
~ uniform suppression~ FACTORIZATION !
Hard diffractive fractions –
Run I
η
dN/dη
gap)( ++→ Xpp
1.45 +/-
0.25J/ψ
0.62 +/-
0.25b
0.115 +/-
0.55W
0.75 +/-
0.10JJ
Fraction %Fraction:SD/ND ratio@ 1800 GeV
FACTORIZATION !
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Multi-gap diffraction –
Run Irestoring factorization
0.1 1
0.1
1
10
100
β
FD jj(β
)
from DPE/SD , 0.01 ≤ ξ ≤ 0.03
from SD/ND , 0.035 ≤ ξ ≤ 0.095
p
p
ND jetjet
0p
p
p
IP
SD jetjet
p
0
p
p
IP
IP
DPE jetjet
p p
η0ηp_ ηp
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
w/preliminary pdf’s
from
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( )ξ1
β1~ξβ,FD
jj ⋅ Pomeron
dominated
constantdξ
dσincl ∝
( ) 0.10.90.11.0Djj ξ
1β
1ξβ,F ±± ⋅∝
ξ
& β
dependence of FDjj
– Run I
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Diffractive structure function –
Run II Q2
-
dependence
ETjet ~ 100 GeV !
Small Q2 dependence in region 100<Q2<10 000 GeV2where each dσND/dET dσND/dET vary by a factor of ~104
The Pomeron evolves as the proton !
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Diffractive structure function –
Run II t -
dependence
No diffraction dipsNo Q2 dependence in slopefrom inclusive to Q2~104
GeV2
Fit dσ/dt
to a double exponential:
Same slope over entire region of0 < Q2
< ~ 10 000 GeV2
across soft and hard diffraction!
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Looks like…
… the underlying diffractive PDF on a hard scale is similar to the proton PDF except for small differences - presumably due to the requirement of combining with the soft PDF to form a spin 1 color singlet with vacuum quantum numbers.
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Diffractive W/Z production
W, Z
p
p
pIP
W, Z
p
p
pIP
Diffractive W production probes the quark content of the Pomeron– To leading order,
the W is produced by a quark in the Pomeron
Production by gluons is suppressed by a factor of αS, and can be distinguished from quark production by an associated jet
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Diffractive W/Z -
motivation
• In Run I, by combining diffractive dijet production with diffractive W production we determined the quark/gluon content of the Pomeron ===
• In Run II we aim at determining the diffractive structure function for a more direct comparison with HERA.
• To accomplish this we use:New forward detectorsNew methodologyMore data
Phys Rev Lett 78, 2698 (1997)Fraction of W events due to SD Rw=[1.15±0.51(stat)±0.20(syst) ]%
for ξ<0.1 integrated over t
DIS @ JJ
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The DF II detectors
RPS acceptance ~80% for 0.03 < x < 0.1 and |t| < 0.1
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The MiniPlugs
@ CDF
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Using RPS information:
No background from gaps due to multiplicity fluctuationsNo gap survival probability systematicsThe RPS provides accurate event-by-event ξ measurementDetermine the full kinematics of diffractive W production by
obtaining ην
using the equation:
where
This allows the determination of:W mass xBj
Diffractive structure function
νηTcalRPS es
Eξξ −/=−
Diffractive W/Z analysis
η
towers
Tcal es
Eξ −∑=
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W/Z selection requirements
cm60|Z|GeV120M40
GeV25MGeV25(pE
vtx
WT
T
μT
eT
<<<
>/>
cm60|Z|
GeV116M66
GeV25(pE
GeV25(pE
vtx
Z
μ2T
e2T
μ1T
e1T
<
<<
>
>
Standard W/Z selection
Diffractive W/Z selectionRPS trigger counters - MIPRPS track - 0.03< ξ <0.10, |t|<1 W 50 < MW(ξRPS,ξcal) < 120Z ξcal < 0.1
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Reconstructed diffractive W mass
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Rejection of multiple interaction events
ND dijetw/soft SDoverlap
ND dijetw/soft SDoverlap
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Diffractive W/Z resultsRW (0.03 < ξ < 0.10, |t|<1)= [0.97 ± 0.05(stat) ± 0.11(syst)]%
Run I: RW =1.15±0.55 % for ξ<0.1 estimate 0.97±0.47 % in 0.03 < ξ < 0.10 & |t|<1)
RZ (0.03 < x < 0.10, |t|<1)= [0.85 ± 0.20(stat) ± 0.11(syst)]%
DØ Phys Lett B 574, 169 (2003) Rw=[5.1±0.51(stat)±0.20(syst)]%gap acceptance Agap=(0.21±4)%
uncorrected for Agap
RW=[0.89+0.19-0.17 ]% RZ=[1.44+0.61-0.52 ]%
Stay connected tor results on FDW/Z
CDF PRL 78, 2698 (1997)Rw=[1.15±0.51(stat)±0.20(syst)]% gap acceptance Agap=0.81
uncorrected for Agap
Rw=(0.93±0.44)%(Agap calculated from MC)
CDF/DØ Comparison – Run I (ξ < 0.1)
EXCLUSIVE JJ & HIGGS BOSONS
22H )'pp'p(pM −−+= ΔM~(1-2) GeV Determine spin of H
gap gap
b
b -jet
-jet
ηp p
H
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Exclusive dijet and Higg production
H
DPEMC
ExHuMEURL: http://link.aps.org/abstract/PRD/v77/e052004 DOI: 10.1103/PhysRevD.77.052004
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The DPE data sample
η
towers
TCALpbar e
sEξ −∑=
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Kinematic distributions
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Exclusive dijet signal
dijet
mass fraction –
all jets
Exclusive b-jets are suppressedas expected (JZ
= 0 selection rule)Excess observed over POMWIG MC prediction at large Rjj
b-jet dijet
mass fraction
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Underlying event
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Jet1 vs. Jet2: signal and background regions
DATA
POMWIG
A: signal regionB: background region
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Background region
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Inclusive DPE W/LRG-p data vs. MC
Shape of excess of events at high Rjjis well described by both ExHuME & DPEMC
ExHuME
(KMR): gg gg process(based on
LO pQCD)DPEMC: exclusive DPE MC
based on Regge
theory
Rjj
ExHuME DPEMCexclusive MC models
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HF suppression vs. inclusive signal
HF suppression
Invert HF vertically and compare with 1-MC/DATAgood agreement observed
HF vs. incl
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ExHuME vs. DPEMC and vs. data
Measured x-sections favor ExHuME
KMR x 1/3 agrees with dataWithin theoretical uncertainty of +/- factor of 3
σjjexcl/σincl approx. independent of ET
min
WHY?
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Exclusive dijet x-section vs. Mjj
curve: ExHuME
hadron-level exclusive dijet
cross sections vs. dijet
mass points: derived from CDF excl. dijet
x-sections using ExHuME
Stat. and syst. errors are propagated
from measured cross section uncertainties using Mjj
distribution
shapes of ExHuME
generated data.
SUMMARY HIGGS ?
Introductiondiffractive PDF looks like proton PDF
Diffractive W/Z – RPS dataW diffractive fraction in agreement with Run IW/Z diffractive fractions equal within errorNew techniques developed to enable extracting
the diffractive structure function in W production
Exclusive dijet/(Higgs?) productionResults favor ExHuME over DPEMCPhys. Rev. D 77, 052004 (2008)
DIJET
W/Z
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BACKUPMeasurements with the MiniPlugsDynamic alignment of RPS detectorsET
jet calibration
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Measurements w/the
MiniPlugs
ADC counts in MiniPlug towersin a pbar-p event at 1960 GeV.• “jet” indicates an energy cluster
and may be just a hadron.• 1000 counts ~ 1 GeVMultiplicity of SD and ND events
ENERGY
MP TOWER
STRUCTURE
MULTIPLICITY
@ POSITION
NIM A 430 (1999)
NIM A 496 (2003)
NIM A 518 (2004)
seEΣξ
iηiTiCAL
−
=
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Dynamic Alignment of RPS DetectorsMethod:
iteratively adjust the RPS X and Y offsets from the nominal beam axis until a maximum in the b-slope is obtained @ t=0.
Limiting factors1-statistics2-beam size3-beam jitter
@ CDF W/lowlum
data
μm30±
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ETjet
Calibration
Xjjξ - RPSξ = ξΔ
-0.1 -0.05 0 0.05 0.1
Raw Jets (dotted)Entries 160Mean 0.02438RMS 0.01115
Xjjξ - RPSξ = ξΔ
-0.1 -0.05 0 0.05 0.1
Eve
nts
0
10
20
30
40
50
60
70
80 Raw Jets (dotted)Entries 160Mean 0.02438RMS 0.01115L5 Corrected Jets (dashed)Entries 293Mean 0.004665RMS 0.01315L7 Corrected Jets (shaded)Entries 360Mean 0.00269RMS 0.01364
L5 Corrected Jets (dashed)Entries 293Mean 0.004665RMS 0.01315
Raw Jets (dotted)Entries 160Mean 0.02438RMS 0.01115
CDF Run II Data
> 10 GeVjet1,2TE
< 5 GeVjet3TE
0.095≤ RPSξ ≤0.035 | < 5.9gapη3.6 < |
> 0.8jj
R
s
iη- eiT E
i=1,2∑
= Xjjξ
Calibrate Etjet
or ξ, as you wish!
use RPS information to check jet energy corrections
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thank you