QCD Jet Measurements –Inclusive Jets –Rapidity Dependence –CMS Energy Dependence –Dijet...
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Transcript of QCD Jet Measurements –Inclusive Jets –Rapidity Dependence –CMS Energy Dependence –Dijet...
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
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
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
Inclusive Jets- D0
Inclusive Jets- CDF
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
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
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)
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
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.
1
dMddd3
dM dd Nevents
L M =
Dijet Mass Cross Section DD
NLO QCD in good agreement with data
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
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.
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
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
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.
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
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
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
Boson+ Jet Theory
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
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.
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
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
• 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
W + Jets: CDF
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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.
Jets) 0N(W
Jets) 1N(W10
R
W+ Jet Ratio
W + Jets: CDF
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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
Rapidity Gaps
Typical event
Hard single diffraction
Hard double pomeron
Hard color singlet
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.
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
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
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
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)
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
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