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Jets and jet
substructure
1
Gavin Salam (CERN)with extensive use of material by Matteo Cacciari
and Gregory Soyez
TASIJune 2013
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013 2
JETSCollimated,
energetic bunches of particles
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013 3
Sterman and Weinberg, Phys. Rev. Lett. 39, 1436 (1977):
Jets date back to the late 1970s
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013 4
e+e� ! qq̄gevent at LEP
√s = 91.2 GeV, in 1990s
And they’ve been used and studied at every
collider since
event at TASSO√s = 27.4 GeV, in 1979
gluon discovery:
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013 4
e+e� ! qq̄gevent at LEP
√s = 91.2 GeV, in 1990s
And they’ve been used and studied at every
collider since
event at TASSO√s = 27.4 GeV, in 1979
gluon discovery:
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013 4
e+e� ! qq̄gevent at LEP
√s = 91.2 GeV, in 1990s
And they’ve been used and studied at every
collider since
event at TASSO√s = 27.4 GeV, in 1979
gluon discovery:
e
p>2.5
p
CTD
CAL
Yoke RMUFMUp>4 GeV
Inner chambersµ
Toroids
Outer chambersµ
BMU pt>2.5 GeV
ZEUS
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013 4
e+e� ! qq̄gevent at LEP
√s = 91.2 GeV, in 1990s
And they’ve been used and studied at every
collider since
event at TASSO√s = 27.4 GeV, in 1979
gluon discovery:
e
p>2.5
p
CTD
CAL
Yoke RMUFMUp>4 GeV
Inner chambersµ
Toroids
Outer chambersµ
BMU pt>2.5 GeV
ZEUS
CDF
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013 5
464 records foundFind all papers by ATLAS and CMS
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013 6
Pull out those that refer to one widely used jet-alg272 records found
60% of papers use jets!
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Jet usage at the LHC
7
+N
P co
rrectio
ns
Tree level Monte Carlo (N)NLO
Jets (theory tool)
MC + Tree
Jet X-sctDetector sim.
Jet X-sct
DETECTOR
Detector unfolding
CKKWMLM
BSM searches
Higgs physics
top physics
PDF fits
...
MC validation
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Two key aspects to discussing jets
8
How jets come to have the structure they do
Jets as projections[Introduction]
[Background knowledge]
jet 1 jet 2
LO partons
Jet Def n
jet 1 jet 2
Jet Def n
NLO partons
jet 1 jet 2
Jet Def n
parton shower
jet 1 jet 2
Jet Def n
hadron level
π π
Kp φ
Projection to jets should be resilient to QCD e!ects
Gavin Salam (CERN) Jets and jet substructure (1) June 2013 8 / 35
Jets as projections[Introduction]
[Background knowledge]
jet 1 jet 2
LO partons
Jet Def n
jet 1 jet 2
Jet Def n
NLO partons
jet 1 jet 2
Jet Def n
parton shower
jet 1 jet 2
Jet Def n
hadron level
π π
Kp φ
Projection to jets should be resilient to QCD e!ects
Gavin Salam (CERN) Jets and jet substructure (1) June 2013 8 / 35
Jets as projections[Introduction]
[Background knowledge]
jet 1 jet 2
LO partons
Jet Def n
jet 1 jet 2
Jet Def n
NLO partons
jet 1 jet 2
Jet Def n
parton shower
jet 1 jet 2
Jet Def n
hadron level
π π
Kp φ
Projection to jets should be resilient to QCD e!ects
Gavin Salam (CERN) Jets and jet substructure (1) June 2013 8 / 35
How we “reconstruct” jets
Why do we see jets? Parton fragmentation[Introduction]
[Background knowledge]
KL
π−
π+
π0
K+
non−perturbative
hadronisation
quark
Gluon emission:!
!sdE
E
d"
"! 1
At low scales:
!s " 1
High-energy partons unavoidably lead tocollimated bunches of hadrons
Gavin Salam (CERN) Jets and jet substructure (1) June 2013 3 / 35
jet finding interpretation
quarkanti-
quark
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Two key aspects to discussing jets
8
How jets come to have the structure they do
Jets as projections[Introduction]
[Background knowledge]
jet 1 jet 2
LO partons
Jet Def n
jet 1 jet 2
Jet Def n
NLO partons
jet 1 jet 2
Jet Def n
parton shower
jet 1 jet 2
Jet Def n
hadron level
π π
Kp φ
Projection to jets should be resilient to QCD e!ects
Gavin Salam (CERN) Jets and jet substructure (1) June 2013 8 / 35
Jets as projections[Introduction]
[Background knowledge]
jet 1 jet 2
LO partons
Jet Def n
jet 1 jet 2
Jet Def n
NLO partons
jet 1 jet 2
Jet Def n
parton shower
jet 1 jet 2
Jet Def n
hadron level
π π
Kp φ
Projection to jets should be resilient to QCD e!ects
Gavin Salam (CERN) Jets and jet substructure (1) June 2013 8 / 35
Jets as projections[Introduction]
[Background knowledge]
jet 1 jet 2
LO partons
Jet Def n
jet 1 jet 2
Jet Def n
NLO partons
jet 1 jet 2
Jet Def n
parton shower
jet 1 jet 2
Jet Def n
hadron level
π π
Kp φ
Projection to jets should be resilient to QCD e!ects
Gavin Salam (CERN) Jets and jet substructure (1) June 2013 8 / 35
How we “reconstruct” jets
Why do we see jets? Parton fragmentation[Introduction]
[Background knowledge]
KL
π−
π+
π0
K+
non−perturbative
hadronisation
quark
Gluon emission:!
!sdE
E
d"
"! 1
At low scales:
!s " 1
High-energy partons unavoidably lead tocollimated bunches of hadrons
Gavin Salam (CERN) Jets and jet substructure (1) June 2013 3 / 35
jet finding interpretation
quarkanti-
quark
Most of the content of these lectures
Core understanding
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Why do we see jets?
9
Why do we see jets? Parton fragmentation[Introduction]
[Background knowledge]
KL
π−
π+
π0
K+non−perturbative
hadronisation
quark
Gluon emission:!
!sdE
E
d"
"! 1
At low scales:
!s " 1
High-energy partons unavoidably lead tocollimated bunches of hadrons
Gavin Salam (CERN) Jets and jet substructure (1) June 2013 3 / 35
Z↵s
dE
E
d✓
✓� 1
Gluon emission
↵s ⇠ 1
Non-perturbativephysics
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Why do we see jets?
9
Why do we see jets? Parton fragmentation[Introduction]
[Background knowledge]
KL
π−
π+
π0
K+non−perturbative
hadronisation
quark
Gluon emission:!
!sdE
E
d"
"! 1
At low scales:
!s " 1
High-energy partons unavoidably lead tocollimated bunches of hadrons
Gavin Salam (CERN) Jets and jet substructure (1) June 2013 3 / 35
Z↵s
dE
E
d✓
✓� 1
Gluon emission
↵s ⇠ 1
Non-perturbativephysics
soft-collinear structure (no colour)
i
/p+ /kigs✏/ v(p)
drop /k in numerator, use /p/k + /k/p = 2p.k, /pv(p) = 0
get gsp.✏
p.kv(p) take p = (1, 0, 0, 1), k = E(cos ✓, sin ✓, 0, 1), ✏ = (sin ✓,� cos ✓, 0, 0)
square the amplitude, put in phasespace:
d3k
2E(2⇡)3! E dE dcos ✓ d�
16⇡3
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Jet finding as a form of projection
11
Jets as projections[Introduction]
[Background knowledge]
jet 1 jet 2
LO partons
Jet Def n
jet 1 jet 2
Jet Def n
NLO partons
jet 1 jet 2
Jet Def n
parton shower
jet 1 jet 2
Jet Def n
hadron level
π π
Kp φ
Projection to jets should be resilient to QCD e!ects
Gavin Salam (CERN) Jets and jet substructure (1) June 2013 8 / 35
Projection to jets should be resilient to QCD effects
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Reconstructing jets is an ambiguous task
12
Seeing v. defining jets[Introduction]
[Background knowledge]
Jets are what we see.Clearly(?) 2 jets here
How many jets do you see?Do you really want to ask yourselfthis question for 109 events?
Gavin Salam (CERN) Jets and jet substructure (1) June 2013 6 / 35
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Reconstructing jets is an ambiguous task
12
Seeing v. defining jets[Introduction]
[Background knowledge]
Jets are what we see.Clearly(?) 2 jets here
How many jets do you see?Do you really want to ask yourselfthis question for 109 events?
Gavin Salam (CERN) Jets and jet substructure (1) June 2013 6 / 35
2 clear jets
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Reconstructing jets is an ambiguous task
12
Seeing v. defining jets[Introduction]
[Background knowledge]
Jets are what we see.Clearly(?) 2 jets here
How many jets do you see?Do you really want to ask yourselfthis question for 109 events?
Gavin Salam (CERN) Jets and jet substructure (1) June 2013 6 / 35
2 clear jets 3 jets?
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013 13
Seeing v. defining jets[Introduction]
[Background knowledge]
Jets are what we see.Clearly(?) 2 jets here
How many jets do you see?Do you really want to ask yourselfthis question for 109 events?
Gavin Salam (CERN) Jets and jet substructure (1) June 2013 6 / 35
2 clear jets 3 jets?or 4 jets?
Reconstructing jets is an ambiguous task
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Make a choice: specify a jet definition
14
{pi} {jk}jet definition
particles,4-momenta,
calorimeter towers, ....
jets
• Which particles do you put together into a same jet?• How do you recombine their momenta
(4-momentum sum is the obvious choice, right?)
“Jet [definitions] are legal contracts between theorists and experimentalists’’ -- MJ Tannenbaum
They’re also a way of organising the information in an event1000’s of particles per events, up to 20.000,000 events per second
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013 16
There is no objectively "correct" clustering algorithm, but […] "clustering is in the eye of the beholder."[1] The most appropriate clustering algorithm for a particular problem often needs to be chosen experimentally, unless there is a mathematical reason to prefer one cluster model over another.
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013 17
Partitioning / centroid-based clustering
[cone algorithms]
Matteo Cacciari - LPTHE MadGraph School - May 2013 - Beijing
k-means
18
Example of a partitional algorithm1) Choose K centroids at random2) Assign objects to closest centroid, forming K clusters3) Calculate centroid (mean of distances) of each cluster, update centroids4) Check if an object in a cluster is closer to another centroid. Reallocate in case.5) Repeat from step 3 until no object changes cluster anymore.
Step 1(random centroids)
Step 2(allocate objects)
Step 3(move centroids)
Step 5(end of iteration)
[Fig
ures
by
E. G
arre
tt-M
ayer
]
Matteo Cacciari - LPTHE MadGraph School - May 2013 - Beijing
k-means
18
Example of a partitional algorithm1) Choose K centroids at random2) Assign objects to closest centroid, forming K clusters3) Calculate centroid (mean of distances) of each cluster, update centroids4) Check if an object in a cluster is closer to another centroid. Reallocate in case.5) Repeat from step 3 until no object changes cluster anymore.
One of the main shortcomings: result of final convergence can be highly sensitive to choice of initial seeds.
Also, the concept of ‘mean distance’ (to calculate the centroid) must be defined.
Step 1(random centroids)
Step 2(allocate objects)
Step 3(move centroids)
Step 5(end of iteration)
[Fig
ures
by
E. G
arre
tt-M
ayer
]
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Iterative Cone, Prog Removal (IC-PR)
60
50
40
20
00 1 2 3 4 y
30
10
pt/GeVOne of the simplest of the cone algs
e.g. CMS iterative cone
! Take hardest particle as seed for
cone axis
! Draw cone around seed
! Sum the momenta use as new
seed direction, iterate until stable
! Convert contents into a “jet” and
remove from event
Notes
! “Hardest particle” is collinear
unsafe more right away...
19
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Iterative Cone, Prog Removal (IC-PR)
60
50
40
20
00 1 2 3 4 y
30
10
pt/GeV Seed = hardest_particleOne of the simplest of the cone algs
e.g. CMS iterative cone
! Take hardest particle as seed for
cone axis
! Draw cone around seed
! Sum the momenta use as new
seed direction, iterate until stable
! Convert contents into a “jet” and
remove from event
Notes
! “Hardest particle” is collinear
unsafe more right away...
20
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Iterative Cone, Prog Removal (IC-PR)
60
50
40
20
00 1 2 3 4 y
30
10
pt/GeV Draw coneOne of the simplest of the cone algs
e.g. CMS iterative cone
! Take hardest particle as seed for
cone axis
! Draw cone around seed
! Sum the momenta use as new
seed direction, iterate until stable
! Convert contents into a “jet” and
remove from event
Notes
! “Hardest particle” is collinear
unsafe more right away...
21
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Iterative Cone, Prog Removal (IC-PR)
60
50
40
20
00 1 2 3 4 y
30
10
pt/GeV sum of momenta != seedOne of the simplest of the cone algs
e.g. CMS iterative cone
! Take hardest particle as seed for
cone axis
! Draw cone around seed
! Sum the momenta use as new
seed direction, iterate until stable
! Convert contents into a “jet” and
remove from event
Notes
! “Hardest particle” is collinear
unsafe more right away...
22
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Iterative Cone, Prog Removal (IC-PR)
60
50
40
20
00 1 2 3 4 y
30
10
pt/GeV Iterate seedOne of the simplest of the cone algs
e.g. CMS iterative cone
! Take hardest particle as seed for
cone axis
! Draw cone around seed
! Sum the momenta use as new
seed direction, iterate until stable
! Convert contents into a “jet” and
remove from event
Notes
! “Hardest particle” is collinear
unsafe more right away...
23
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Iterative Cone, Prog Removal (IC-PR)
60
50
40
20
00 1 2 3 4 y
30
10
pt/GeV Draw coneOne of the simplest of the cone algs
e.g. CMS iterative cone
! Take hardest particle as seed for
cone axis
! Draw cone around seed
! Sum the momenta use as new
seed direction, iterate until stable
! Convert contents into a “jet” and
remove from event
Notes
! “Hardest particle” is collinear
unsafe more right away...
24
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Iterative Cone, Prog Removal (IC-PR)
60
50
40
20
00 1 2 3 4 y
30
10
pt/GeV sum of momenta != seedOne of the simplest of the cone algs
e.g. CMS iterative cone
! Take hardest particle as seed for
cone axis
! Draw cone around seed
! Sum the momenta use as new
seed direction, iterate until stable
! Convert contents into a “jet” and
remove from event
Notes
! “Hardest particle” is collinear
unsafe more right away...
25
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Iterative Cone, Prog Removal (IC-PR)
60
50
40
20
00 1 2 3 4 y
30
10
pt/GeV Iterate seedOne of the simplest of the cone algs
e.g. CMS iterative cone
! Take hardest particle as seed for
cone axis
! Draw cone around seed
! Sum the momenta use as new
seed direction, iterate until stable
! Convert contents into a “jet” and
remove from event
Notes
! “Hardest particle” is collinear
unsafe more right away...
26
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Iterative Cone, Prog Removal (IC-PR)
60
50
40
20
00 1 2 3 4 y
30
10
pt/GeV Draw coneOne of the simplest of the cone algs
e.g. CMS iterative cone
! Take hardest particle as seed for
cone axis
! Draw cone around seed
! Sum the momenta use as new
seed direction, iterate until stable
! Convert contents into a “jet” and
remove from event
Notes
! “Hardest particle” is collinear
unsafe more right away...
27
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Iterative Cone, Prog Removal (IC-PR)
60
50
40
20
00 1 2 3 4 y
30
10
pt/GeV sum of momenta == seedOne of the simplest of the cone algs
e.g. CMS iterative cone
! Take hardest particle as seed for
cone axis
! Draw cone around seed
! Sum the momenta use as new
seed direction, iterate until stable
! Convert contents into a “jet” and
remove from event
Notes
! “Hardest particle” is collinear
unsafe more right away...
28
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Iterative Cone, Prog Removal (IC-PR)
60
50
40
20
00 1 2 3 4 y
30
10
pt/GeV Cone is stableOne of the simplest of the cone algs
e.g. CMS iterative cone
! Take hardest particle as seed for
cone axis
! Draw cone around seed
! Sum the momenta use as new
seed direction, iterate until stable
! Convert contents into a “jet” and
remove from event
Notes
! “Hardest particle” is collinear
unsafe more right away...
29
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Iterative Cone, Prog Removal (IC-PR)
60
50
40
20
00 1 2 3 4 y
30
10
pt/GeV Convert into jetOne of the simplest of the cone algs
e.g. CMS iterative cone
! Take hardest particle as seed for
cone axis
! Draw cone around seed
! Sum the momenta use as new
seed direction, iterate until stable
! Convert contents into a “jet” and
remove from event
Notes
! “Hardest particle” is collinear
unsafe more right away...
30
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Iterative Cone, Prog Removal (IC-PR)
60
50
40
20
00 1 2 3 4 y
30
10
pt/GeV Seed = hardest_particleOne of the simplest of the cone algs
e.g. CMS iterative cone
! Take hardest particle as seed for
cone axis
! Draw cone around seed
! Sum the momenta use as new
seed direction, iterate until stable
! Convert contents into a “jet” and
remove from event
Notes
! “Hardest particle” is collinear
unsafe more right away...
31
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Iterative Cone, Prog Removal (IC-PR)
60
50
40
20
00 1 2 3 4 y
30
10
pt/GeV Draw coneOne of the simplest of the cone algs
e.g. CMS iterative cone
! Take hardest particle as seed for
cone axis
! Draw cone around seed
! Sum the momenta use as new
seed direction, iterate until stable
! Convert contents into a “jet” and
remove from event
Notes
! “Hardest particle” is collinear
unsafe more right away...
32
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Iterative Cone, Prog Removal (IC-PR)
60
50
40
20
00 1 2 3 4 y
30
10
pt/GeV sum of momenta != seedOne of the simplest of the cone algs
e.g. CMS iterative cone
! Take hardest particle as seed for
cone axis
! Draw cone around seed
! Sum the momenta use as new
seed direction, iterate until stable
! Convert contents into a “jet” and
remove from event
Notes
! “Hardest particle” is collinear
unsafe more right away...
33
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Iterative Cone, Prog Removal (IC-PR)
60
50
40
20
00 1 2 3 4 y
30
10
pt/GeV Iterate seedOne of the simplest of the cone algs
e.g. CMS iterative cone
! Take hardest particle as seed for
cone axis
! Draw cone around seed
! Sum the momenta use as new
seed direction, iterate until stable
! Convert contents into a “jet” and
remove from event
Notes
! “Hardest particle” is collinear
unsafe more right away...
34
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Iterative Cone, Prog Removal (IC-PR)
60
50
40
20
00 1 2 3 4 y
30
10
pt/GeV Draw coneOne of the simplest of the cone algs
e.g. CMS iterative cone
! Take hardest particle as seed for
cone axis
! Draw cone around seed
! Sum the momenta use as new
seed direction, iterate until stable
! Convert contents into a “jet” and
remove from event
Notes
! “Hardest particle” is collinear
unsafe more right away...
35
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Iterative Cone, Prog Removal (IC-PR)
60
50
40
20
00 1 2 3 4 y
30
10
pt/GeV sum of momenta == seedOne of the simplest of the cone algs
e.g. CMS iterative cone
! Take hardest particle as seed for
cone axis
! Draw cone around seed
! Sum the momenta use as new
seed direction, iterate until stable
! Convert contents into a “jet” and
remove from event
Notes
! “Hardest particle” is collinear
unsafe more right away...
36
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Iterative Cone, Prog Removal (IC-PR)
60
50
40
20
00 1 2 3 4 y
30
10
pt/GeV Cone is stableOne of the simplest of the cone algs
e.g. CMS iterative cone
! Take hardest particle as seed for
cone axis
! Draw cone around seed
! Sum the momenta use as new
seed direction, iterate until stable
! Convert contents into a “jet” and
remove from event
Notes
! “Hardest particle” is collinear
unsafe more right away...
37
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Iterative Cone, Prog Removal (IC-PR)
60
50
40
20
00 1 2 3 4 y
30
10
pt/GeV Convert into jetOne of the simplest of the cone algs
e.g. CMS iterative cone
! Take hardest particle as seed for
cone axis
! Draw cone around seed
! Sum the momenta use as new
seed direction, iterate until stable
! Convert contents into a “jet” and
remove from event
Notes
! “Hardest particle” is collinear
unsafe more right away...
38
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Iterative Cone, Prog Removal (IC-PR)
60
50
40
20
00 1 2 3 4 y
30
10
pt/GeV Seed = hardest_particleOne of the simplest of the cone algs
e.g. CMS iterative cone
! Take hardest particle as seed for
cone axis
! Draw cone around seed
! Sum the momenta use as new
seed direction, iterate until stable
! Convert contents into a “jet” and
remove from event
Notes
! “Hardest particle” is collinear
unsafe more right away...
39
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Iterative Cone, Prog Removal (IC-PR)
60
50
40
20
00 1 2 3 4 y
30
10
pt/GeV Draw coneOne of the simplest of the cone algs
e.g. CMS iterative cone
! Take hardest particle as seed for
cone axis
! Draw cone around seed
! Sum the momenta use as new
seed direction, iterate until stable
! Convert contents into a “jet” and
remove from event
Notes
! “Hardest particle” is collinear
unsafe more right away...
40
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Iterative Cone, Prog Removal (IC-PR)
60
50
40
20
00 1 2 3 4 y
30
10
pt/GeV sum of momenta != seedOne of the simplest of the cone algs
e.g. CMS iterative cone
! Take hardest particle as seed for
cone axis
! Draw cone around seed
! Sum the momenta use as new
seed direction, iterate until stable
! Convert contents into a “jet” and
remove from event
Notes
! “Hardest particle” is collinear
unsafe more right away...
41
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Iterative Cone, Prog Removal (IC-PR)
60
50
40
20
00 1 2 3 4 y
30
10
pt/GeV Iterate seedOne of the simplest of the cone algs
e.g. CMS iterative cone
! Take hardest particle as seed for
cone axis
! Draw cone around seed
! Sum the momenta use as new
seed direction, iterate until stable
! Convert contents into a “jet” and
remove from event
Notes
! “Hardest particle” is collinear
unsafe more right away...
42
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Iterative Cone, Prog Removal (IC-PR)
60
50
40
20
00 1 2 3 4 y
30
10
pt/GeV Draw coneOne of the simplest of the cone algs
e.g. CMS iterative cone
! Take hardest particle as seed for
cone axis
! Draw cone around seed
! Sum the momenta use as new
seed direction, iterate until stable
! Convert contents into a “jet” and
remove from event
Notes
! “Hardest particle” is collinear
unsafe more right away...
43
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Iterative Cone, Prog Removal (IC-PR)
60
50
40
20
00 1 2 3 4 y
30
10
pt/GeV sum of momenta == seedOne of the simplest of the cone algs
e.g. CMS iterative cone
! Take hardest particle as seed for
cone axis
! Draw cone around seed
! Sum the momenta use as new
seed direction, iterate until stable
! Convert contents into a “jet” and
remove from event
Notes
! “Hardest particle” is collinear
unsafe more right away...
44
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Iterative Cone, Prog Removal (IC-PR)
60
50
40
20
00 1 2 3 4 y
30
10
pt/GeV Cone is stableOne of the simplest of the cone algs
e.g. CMS iterative cone
! Take hardest particle as seed for
cone axis
! Draw cone around seed
! Sum the momenta use as new
seed direction, iterate until stable
! Convert contents into a “jet” and
remove from event
Notes
! “Hardest particle” is collinear
unsafe more right away...
45
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Iterative Cone, Prog Removal (IC-PR)
60
50
40
20
00 1 2 3 4 y
30
10
pt/GeV Convert into jetOne of the simplest of the cone algs
e.g. CMS iterative cone
! Take hardest particle as seed for
cone axis
! Draw cone around seed
! Sum the momenta use as new
seed direction, iterate until stable
! Convert contents into a “jet” and
remove from event
Notes
! “Hardest particle” is collinear
unsafe more right away...
46
Gavin Salam (CERN) Jets and jet substructure (1) TASI, June 2013
Iterative Cone, Prog Removal (IC-PR)
60
50
40
20
00 1 2 3 4 y
30
10
pt/GeV Convert into jetOne of the simplest of the cone algs
e.g. CMS iterative cone
! Take hardest particle as seed for
cone axis
! Draw cone around seed
! Sum the momenta use as new
seed direction, iterate until stable
! Convert contents into a “jet” and
remove from event
Notes
! “Hardest particle” is collinear
unsafe more right away...
47