qcd jet measurements –inclusive jets –rapidity dependence –cms energy dependence –dijet...
TRANSCRIPT
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QCD
• Jet Measurements– Inclusive Jets– Rapidity Dependence– CMS Energy Dependence– Dijet Spectra
• QCD with Gauge Bosons– Production Cross Sections– Differential Cross Sections– W/Z and Jets
• Diffractive Physics– Rapidity Gaps– Roman Pots
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Jet Variables
coscosh2
2/tanln ,, :Jet
21212,1,2
TT
T
EEM
E
Jet 2: ET2, 2, 2
Jet 1: ET1, 1, 1
= 0
2,1,2
2
1
,21
exp
TT
ii
iT
EEQ
s
Ex
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Jet Production
1P
2P
1xfi11Px
22Px
1jet
2jet
sij ̂
2xf j
,,,ˆ
,,
2
2
2
22
2211
22
2121
RFRsij
ijFjFi
QQPxPx
xfxfdxdx
2R
1.3R
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Inclusive Jets- D0
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Inclusive Jets- CDF
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Inclusive Jet Cross Section
|| < 0.5 PRL82, 2451 (1999)
0.1 < || < 0.7 Preliminary
Data and theory agreement prob 47-90%
NLO QCD describes the data well
TLdtE
NE
T
jet .vs
DD
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PRL82, 2451 (1999)
Inclusive Jet Cross Section at 1.8TeV DD
D0 and CDF data in good agreement. NLO QCD describes the data well.
Preliminary
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Rapidity Dependence of the Inclusive Jet Cross Section
s = 1.8 TeV, || < 1.5
DD
0.0 < 0.5 0.5 1.0 1.0 1.5
DØ Preliminary
d2 d
ET
d
(fb
/GeV
)
0.5 1.0
0.0 0.5
1.0 1.5
ET (GeV)
( D
ata
- T
heor
y )
/ Th e
ory
Data and NLO QCD in good agreement Extend measurement to || = 3
Refine error analysis
New
DØ Preliminary
ET (GeV)
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Ratio of Scale Invariant Cross Sections d(630)/d(1800) vs xT
DD d = (ET3/2) (d2/dETd
XT ET / (s / 2 )
DDPreliminary
•Taking different renormalizations scales in theory for 630 vs 1800 GeV produces good quantitative agreement between D0 data and NLO QCD
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Measurement of S from Inclusive Jet Production
)(),()()( 3,
22
TFRSTFRST
EBEAddE
d
NLO x-section can be parametrized as
Measuredby CDF
Obtained from JETRAD
2TE
FR
• Fitting the NLO prediction to the data determines S(ET)
• S(ET) is evolved to S(MZ) using 2-loop renormalization group equation
• Systematic uncertainties (~8%) from understanding of calorimeter response
• Measured value consistent with
world average of S(MZ)=0.119
0089.0
0078.00001.01129.0)( ZS M
New measurement of S by a single experiment & from a single observable over a wide range of Q2.
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1
dMddd3
dM dd Nevents
L M =
Dijet Mass Cross Section DD
NLO QCD in good agreement with data
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Inclusive Dijet Differential Cross Section 211
3
dddE
dT
Beam line
Trigger Jet0.1<||<0.7
Probe Jet ET>10 GeV0.1<||<0.7, 0.7<||<1.4, 1.4<||<2.1, 2.1<||<3.0
1
2
Distributions are sensitive to PDFs - CTEQ4HJ shows better agreement with data at high ET
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Inclusive Dijet Differential Cross Section DD 212,1
3
dddE
dT
Beam line
• Consider 4 ranges: 0.0<||<0.5, 0.5<||<1.0, 1.0<||<1.5, 1.5<||<2.0
• Divide data into two samples
• Measure ET of both jets
Total of 8 x-sections
||
||
||
||
D0 data agree with NLO QCD with CTEQ family PDFs within the systematic uncertainty.
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Subjet Multiplicity in Quark & Gluon JetsDD
Jet ET Jet ET
Motivation:
• Separate q jets from g jets (top, Higgs, W+Jets events)
• Test SU(3) dynamics (QCD color factors)
Measure the subjet multiplicity in quark and gluon jets
Contributions of different initial states to the cross section for fixed Jet ET vary with s
compare jets at same (ET,)produced at different s & assume relative q/g content is known.
1800GeV
100 200 300
630GeV
gg
qg
100 200 300
Method:
•Select quark enriched & gluon enriched jet sample and compare jet properties
challenge is not to bias the samples.
s
New
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Subjet Multiplicity in Quark & Gluon JetsDD
Method:
• Subjet Multiplicity M = fgMg + (1-fg )Mq
(g jet fractions fg obtained from theory)
f 630 = 33% f 1800 = 59%
• Assuming that the subjet multiplicity is independent of s (verified with MC)
Mq =
f 1800M630 - f 630M1800
f 1800- f 630
f 1800- f 630
(1-f 630)M1800 - (1- f 1800)M630
Mg =
• Use kT algorithm; unravel jets until
all subjets are separated by ycut
=.001
• Measure number of subjets for events with jets with 55<ET<100 GeV
1
1
q
g
M
MR
(sys) 0.19
0.23(stat) 04.091.1 R
Dominant uncertainties come from g jet fraction and choice of jetET
MC Prediction =1.860.08(stat)
jetsjets dN
dM
N
1
M 1 2 3 4
0.5
0.4
0.3
0.2
0.1
GeVs 1800
Quark Jets Gluon Jets
Preliminary
New
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QCD with Vector BosonsTitle:PRJ$ROOT207:[WZ.NOTES.KUMAC]W_HIST.EPS;1Creator:HIGZ Version 1.22/09Preview:This EPS picture was not savedwith a preview included in it.Comment:This EPS picture will print to aPostScript printer, but not toother types of printers.
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W&Z Production at the Tevatron
pq q
pW(Z)
l
(l )
O(s0)
• Production dominated by qq annihilation (~60% valence-sea, ~20% sea-sea)
• Due to very large pp jj production, need to use leptonic decays (BR ~ 11% (W), ~3% (Z) per mode)
W
g
q
q’
O(s)Modifications due to QCD corrections:
• Boson produced with transverse momentum ( < PT > ~ 10 GeV )
• Boson + jet events possible ( W + 1 jet ~ 7%, ETjet > 25 GeV )
• Inclusive cross sections larger (K factor ~ 18%)
• Boson decay angular distribution modified
• Distinctive event signatures• Low backgrounds
• Large Q2 (Q2 ~ Mass2 ~ 6500 GeV2)
• Well understood Electroweak Vertex
Benefits of studying QCD with W&Z Bosons:q
q’
W
g
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Production of W/Z BosonsCross section measurementstest O(2) QCD predictions for W/Z production
(pp W + X) B(W ) (pp Z + X) B(Z )
S=1.8 TeV
WB(W e)
Z B(Z ee)R=
R=10.54 0.24
S=630 GeVDØ: W e = 658 67 pb
(DØ)
(CDF)R=10.36 0.18
Preliminary
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Introduction to W, Z PT Theory
• Small PT region (QCD < PT < 10 GeV): Resum large logs
Ellis, Martinelli, Petronzio (83); Arnold & Reno (89);Arnold, Ellis, Reno (89); Gonsalves, Pawlowski, Wai (89)
Altarelli, Ellis, Greco, Martinelli (84); Collins, Soper, Sterman (85)
b-space:Parisi-Petronzio (79); Davies-Stirling (84); Collins-Soper-Sterman (85); Davies, Webber, Stirling (85); Arnold- Reno-Ellis (89); AK: Arnold-Kaufann (91); LY: Ladinsky-Yuan (94)
qt-space:Dokshitser-Diaknov-Troian (80); Ellis-Stirling (81); Altarelli-Ellis-Greco-Martinelli (84); Gonsalves-Pawlowksl-Wai (89); ERV: Ellis-Ross-Veseli (97); Ellis-Veseli (98)
• Large PT region (PT 30 GeV): Use pQCD, O(s2) calculations exist
• Very low PT region (PT ~ QCD): Non-perturbative parameters extracted from data
)(ln)ln(~
2
22
212
2
22T
Ws
T
W
T
s
T p
Mvv
p
M
pdp
d
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Boson+ Jet Theory
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Arnold-Kauffman Nucl. Phys. B349, 381 (91). O(s
2), b-
space, MRSA’ (after detector simulation)
Preliminary
dof=7/19 (pT(W)<120 GeV/c)
dof=10/21 (pT(W)<200GeV/c)
Resolution effects dominate at low PT
High PT dominated by statistics & backgrounds
DD D0 W PT measurement
Preliminary
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D0 Z PT measurementDD2/dof = 17/16
2/dof = 83/16
Ladinsky, Yuan, PRD 50, 4239 (94), O(s
2), b-space.
Arnold, Kauffman, NP B349, 381 (91), O(s
2), b-space.
Preliminary
Arnold, Reno, Nucl. Phys. B319, 37. O(s
2), MRSA’, pQCD calculation
Data resolution allows to discriminate between different models for VB production.
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CDF PT measurementsEllis, Ross, Veseli, NP B503, 309 (97). O(s), qt space, after
detector simulation.
ResBos: Balas, Yuan, PRD 56, 5558 (1997), O(s2), b-space
VBP: Ellis, Veseli, NP B511,649 (1998), O(s), qt-space
Preliminary
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RW JetW Jets
10 10
( )( )
R R
W
q
q
E ET T min
W
g
q
E ET T min
g
W
q
q
W+ Jet Production
LO
s
s
A test of NLO
W
q
q
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• Sensitive to PDF’s, higher orders
• Depends on R, ETmin due to jet definition
• Calculations of A, B from NLO DYRAD (Giele, Glover, Kosower)
R E RW JetW JetsT
10 10
( , )( )( )
min
( ) ( )minW Jets A B Es T 0 0 0
( ) ( ) ( , )min minW Jet A E B E Rs T s T 1 12
1
W+ Jet Production
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W + Jets: CDF
Title:DISK$F0:[CDF.TEMP.HENNESSY.3077]XSYS_4JET.PS;2 (Portrait A 4)Creator:HIGZ Version 1.22/09Preview:This EPS picture was not savedwith a preview included in it.Comment:This EPS picture will print to aPostScript printer, but not toother types of printers.
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W/Z + Jets: CDFTitle:DISK$F0:[CDF.TEMP.HENNESSY.3077]RFACTOR_BLESS_NEW_2 (Portrait A 4)Creator:HIGZ Version 1.22/09Preview:This EPS picture was not savedwith a preview included in it.Comment:This EPS picture will print to aPostScript printer, but not toother types of printers.
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Jets) 0N(W
Jets) 1N(W10
R
W+ Jet Ratio
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W + Jets: CDF
Title:DISK$23:[DITTMANN.PS]PS_OUT.PS;1Creator:HIGZ Version 1.22/09Preview:This EPS picture was not savedwith a preview included in it.Comment:This EPS picture will print to aPostScript printer, but not toother types of printers.
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Rapidity Gaps• D0 and CDF study hadronic events with peculiar structure - a rapidity gap
due to color-singlet exchange (pomeron). What is the Pomeron?
(gap)
p
hard single diffraction
(gap)
p
hard double pomeron
(gap)
p
hard color singlet
(gap)
p
p
p
p
p
p
} Probe thepomeronstructure
CDF and D0 made the first studies of thesetopologies.}
pomeron
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Rapidity Gaps
Typical event
Hard single diffraction
Hard double pomeron
Hard color singlet
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Hard Color-singlet Exchange Dijet Production
DD
• Count tracks and EM Calorimeter Towers in || < 1.0 for events with two jets.
jet
jet
Fraction rises with parton x
Consistent with soft color rearrangement model preferring initial quark statesInconsistent with BFKL two-gluon or massive photon/U(1) gauge boson models
Phys. Lett. B 440 189 (1998), hep-ex / 9809016
(ET > 30 GeV, s = 1800 GeV)
•Measured fraction of dijet events arising from color-singlet exchange
is .94.04(stat).12(syst)%•Too large to be explained by EW boson exchange indication of strong-interaction process.
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Double Gaps at 1800 GeV |Jet | < 1.0, ET>15 GeV
D0 PreliminaryD0 Preliminary
Demand gap on one side, measure multiplicity on opposite sideDemand gap on one side, measure multiplicity on opposite side
Gap Region 2.5<||<5.2
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Double Gaps at 630 GeV |Jet | < 1.0, ET>12 GeV
D0 PreliminaryD0 Preliminary
Demand gap on one side, measure multiplicity on opposite sideDemand gap on one side, measure multiplicity on opposite side
Gap Region 2.5<||<5.2
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Gap Region 2.5<||<5.2
• Demand gap on one side, measure Demand gap on one side, measure multiplicity on opposite sidemultiplicity on opposite side Observe an excess of double gap events
• Plot EPlot ET T distribution of the leading two jets distribution of the leading two jets for three data samples: Inclusive Two Jet for three data samples: Inclusive Two Jet sample with |sample with |JetJet|<1.0, One forward gap & |<1.0, One forward gap & Double Gap eventsDouble Gap events
ET spectra of double-gap events is harder than expected if Pomeron carries 5% of the proton’s momentum
s = 630GeV
s = 1800GeV
DØ PreliminaryDD Double Gaps at 1800 & 630 GeV
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Kinematic Characteristics of Diffractive Dijets
GeVE
GeVt
T 7
2.0||
10.004.02
GeVs 630
Absolute normalization
Stat errors only
• Diffractive Dijet spectrum is steeper
• Diffractive Dijet system recoils against pot track
• Diffractive events are cleaner (fewer 3rd jets)
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Diffractive Dijet Production
• Use roman-pot triggered data from Run 1C at 1800&630GeV
• Select events with two jets and roman pot hits
• Measure production rates and kinematic characteristics of difractive dijet events
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Diffractive to Non-Diffractive Ratio vs px
p
JetT
JetT
p p
eEeEx
02
2211
TeVs 8.1 GeVs 630
Rate of diffractive to non-diffractive events
decreases with increasing p
x