jetography, like photography · jetography, like photography fine detail on boarding pass — shoot...
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Jetography, like photography
◮ Fine detail on boarding pass —shoot from close up, focus =40cm
[look for gate]
◮ Keep focus at 40cm
◮ Reset focus to 3mCatch correct plane
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 2 / 19
Jetography, like photography
◮ Fine detail on boarding pass —shoot from close up, focus =40cm
[look for gate]
◮ Keep focus at 40cm
◮ Reset focus to 3mCatch correct plane
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 2 / 19
Jetography, like photography
◮ Fine detail on boarding pass —shoot from close up, focus =40cm
[look for gate]
◮ Keep focus at 40cm
◮ Reset focus to 3mCatch correct plane
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 2 / 19
Jetography, like photography
◮ Fine detail on boarding pass —shoot from close up, focus =40cm
[look for gate]
◮ Keep focus at 40cm
◮ Reset focus to 3mCatch correct plane
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 2 / 19
Small v. large jet radius (R)
Small jet radius Large jet radius
single parton @ LO: jet radius irrelevant
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 3 / 19
Small v. large jet radius (R)
Small jet radius
θ
Large jet radius
θ
perturbative fragmentation: large jet radius better(it captures more)
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 3 / 19
Small v. large jet radius (R)
Small jet radius
KL
π−π+
π0
K+
non−perturbativehadronisation
θ
Large jet radius
KL
π−π+
π0
K+
non−perturbativehadronisation
θ
non-perturbative fragmentation: large jet radius better(it captures more)
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 3 / 19
Small v. large jet radius (R)
Small jet radius
UE
KL
π−π+
π0
K+
non−perturbativehadronisation
θ
Large jet radius
UE
KL
π−π+
π0
K+
non−perturbativehadronisation
θ
underlying ev. & pileup “noise”: small jet radius better(it captures less)
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 3 / 19
Small v. large jet radius (R)
Small jet radius Large jet radius
multi-hard-parton events: small jet radius better(it resolves partons more effectively)
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 3 / 19
Jet pt v. parton pt : perturbatively?
The question’s dangerous: a “parton” is an ambiguous concept
Three limits can help you:
◮ Threshold limit e.g. de Florian & Vogelsang ’07
◮ Parton from color-neutral object decay (Z ′)
◮ Small-R (radius) limit for jet
One simple result (small-R limit)
〈pt,jet − pt,parton〉
pt=
αs
πlnR ×
{
1.01CF quarks0.94CA + 0.07nf gluons
+O (αs)
only O (αs) depends on algorithm & process
cf. Dasgupta, Magnea & GPS ’07Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 4 / 19
Jet pt v. parton pt : hadronisation?
Hadronisation: the “parton-shower” → hadrons transition
Method:
◮ “infrared finite αs” / infrared renormalons a la Dokshitzer & Webber ’95
Korchemsky & Sterman ’94
Seymour ’97
Main result
〈pt,jet − pt,parton−shower 〉 ≃ −0.4 GeV
R×
{
CF quarksCA gluons
cf. Dasgupta, Magnea & GPS ’07
coefficient holds for anti-kt; see Dasgupta & Delenda ’09 for kt alg.
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 5 / 19
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 6 / 19
Underlying Event (UE)
“Naive” prediction (UE ≃ colour dipole between pp):
∆pt ≃ 0.4 GeV ×R2
2×
{
CF qq dipoleCA gluon dipole
Perugia 2011 Pythia tune:
∆pt ≃ 5 − 10 GeV ×R2
2
This big coefficient motivates special effort to understand interplaybetween jet algorithm and UE: “jet areas”
How does coefficient depend on algorithm?
How does it depend on jet pt? How does it fluctuate?
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 7 / 19
Underlying Event (UE)
“Naive” prediction (UE ≃ colour dipole between pp):
∆pt ≃ 0.4 GeV ×R2
2×
{
CF qq dipoleCA gluon dipole
Perugia 2011 Pythia tune:
∆pt ≃ 5 − 10 GeV ×R2
2
This big coefficient motivates special effort to understand interplaybetween jet algorithm and UE: “jet areas”
How does coefficient depend on algorithm?
How does it depend on jet pt? How does it fluctuate?
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 7 / 19
What R is best for an isolated jet?
PT radiation:
q : 〈∆pt〉 ≃αsCF
πpt lnR
Hadronisation:
q : 〈∆pt〉 ≃ −CF
R· 0.4 GeV
Underlying event:
q, g : 〈∆pt〉 ≃R2
2·2.5−15 GeV
Minimise fluctuations in ptptpt
Use crude approximation:
〈∆p2t 〉 ≃ 〈∆pt〉2
E.g. to reconstruct mX ∼ (ptq + ptq)
Xpp
q
q
q
q
in small-R limit (!)
NB: full calc, correct fluct: Soyez ’10
What R is best for an isolated jet?
PT radiation:
q : 〈∆pt〉 ≃αsCF
πpt lnR
Hadronisation:
q : 〈∆pt〉 ≃ −CF
R· 0.4 GeV
Underlying event:
q, g : 〈∆pt〉 ≃R2
2·2.5−15 GeV
Minimise fluctuations in ptptpt
Use crude approximation:
〈∆p2t 〉 ≃ 〈∆pt〉2
50 GeV quark jet
⟨δp t
⟩2 pert +
⟨δp t
⟩2 h +
⟨δp t
⟩2 UE [G
eV2 ]
R
LHCquark jetspt = 50 GeV
0
5
10
15
20
25
30
0.4 0.5 0.6 0.7 0.8 0.9 1 1.1
⟨δpt⟩2pert
⟨δpt⟩2h
⟨δpt⟩2UE
in small-R limit (!)
NB: full calc, correct fluct: Soyez ’10
What R is best for an isolated jet?
PT radiation:
q : 〈∆pt〉 ≃αsCF
πpt lnR
Hadronisation:
q : 〈∆pt〉 ≃ −CF
R· 0.4 GeV
Underlying event:
q, g : 〈∆pt〉 ≃R2
2·2.5−15 GeV
Minimise fluctuations in ptptpt
Use crude approximation:
〈∆p2t 〉 ≃ 〈∆pt〉2
1 TeV quark jet
⟨δp t
⟩2 pert +
⟨δp t
⟩2 h +
⟨δp t
⟩2 UE [G
eV2 ]
R
0
10
20
30
40
50
0.4 0.5 0.6 0.7 0.8 0.9 1 1.1
⟨δpt⟩2pert ⟨δpt⟩
2UE
LHCquark jetspt = 1 TeV
in small-R limit (!)
NB: full calc, correct fluct: Soyez ’10
What R is best for an isolated jet?
PT radiation:
q : 〈∆pt〉 ≃αsCF
πpt lnR
Hadronisation:
q : 〈∆pt〉 ≃ −CF
R· 0.4 GeV
Underlying event:
q, g : 〈∆pt〉 ≃R2
2·2.5−15 GeV
Minimise fluctuations in ptptpt
Use crude approximation:
〈∆p2t 〉 ≃ 〈∆pt〉2
1 TeV quark jet
⟨δp t
⟩2 pert +
⟨δp t
⟩2 h +
⟨δp t
⟩2 UE [G
eV2 ]
R
0
10
20
30
40
50
0.4 0.5 0.6 0.7 0.8 0.9 1 1.1
⟨δpt⟩2pert ⟨δpt⟩
2UE
LHCquark jetspt = 1 TeV
in small-R limit (!)
NB: full calc, correct fluct: Soyez ’10
At low pt, small RRR limits relative impact of UE
At high pt, perturbative effects dominate overnon-perturbative → RbestRbestRbest ∼ 1.
Dijet mass: scan over R [Pythia 6.4]
R = 0.31/
N d
n/db
in /
2
dijet mass [GeV]
qq, M = 100 GeV
arXiv:0810.1304
0
0.02
0.04
0.06
0.08
60 80 100 120 140
SISCone, R=0.3, f=0.75Qw
f=0.24 = 24.0 GeV
Resonance X → dijets
Xpp
q
q
q
q
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 9 / 19
Dijet mass: scan over R [Pythia 6.4]
R = 0.31/
N d
n/db
in /
2
dijet mass [GeV]
qq, M = 100 GeV
arXiv:0810.1304
0
0.02
0.04
0.06
0.08
60 80 100 120 140
SISCone, R=0.3, f=0.75Qw
f=0.24 = 24.0 GeV
Resonance X → dijets
Xpp
q
q
q
q
jet
jet
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 9 / 19
Dijet mass: scan over R [Pythia 6.4]
R = 0.41/
N d
n/db
in /
2
dijet mass [GeV]
qq, M = 100 GeV
arXiv:0810.1304
0
0.02
0.04
0.06
0.08
60 80 100 120 140
SISCone, R=0.4, f=0.75Qw
f=0.24 = 22.5 GeV
Resonance X → dijets
Xpp
q
q
q
q
jet
jet
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 9 / 19
Dijet mass: scan over R [Pythia 6.4]
R = 0.51/
N d
n/db
in /
2
dijet mass [GeV]
qq, M = 100 GeV
arXiv:0810.1304
0
0.02
0.04
0.06
0.08
60 80 100 120 140
SISCone, R=0.5, f=0.75Qw
f=0.24 = 22.6 GeV
Resonance X → dijets
Xpp
q
q
q
q
jet
jet
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 9 / 19
Dijet mass: scan over R [Pythia 6.4]
R = 0.61/
N d
n/db
in /
2
dijet mass [GeV]
qq, M = 100 GeV
arXiv:0810.1304
0
0.02
0.04
0.06
0.08
60 80 100 120 140
SISCone, R=0.6, f=0.75Qw
f=0.24 = 23.8 GeV
Resonance X → dijets
Xpp
q
q
q
q
jet
jet
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 9 / 19
Dijet mass: scan over R [Pythia 6.4]
R = 0.71/
N d
n/db
in /
2
dijet mass [GeV]
qq, M = 100 GeV
arXiv:0810.1304
0
0.02
0.04
0.06
0.08
60 80 100 120 140
SISCone, R=0.7, f=0.75Qw
f=0.24 = 25.1 GeV
Resonance X → dijets
Xpp
q
q
q
q
jet
jet
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 9 / 19
Dijet mass: scan over R [Pythia 6.4]
R = 0.81/
N d
n/db
in /
2
dijet mass [GeV]
qq, M = 100 GeV
arXiv:0810.1304
0
0.02
0.04
0.06
0.08
60 80 100 120 140
SISCone, R=0.8, f=0.75Qw
f=0.24 = 26.8 GeV
Resonance X → dijets
Xpp
q
q
q
q
jet
jet
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 9 / 19
Dijet mass: scan over R [Pythia 6.4]
R = 0.91/
N d
n/db
in /
2
dijet mass [GeV]
qq, M = 100 GeV
arXiv:0810.1304
0
0.02
0.04
0.06
0.08
60 80 100 120 140
SISCone, R=0.9, f=0.75Qw
f=0.24 = 28.8 GeV
Resonance X → dijets
Xpp
q
q
q
q
jet
jet
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 9 / 19
Dijet mass: scan over R [Pythia 6.4]
R = 1.01/
N d
n/db
in /
2
dijet mass [GeV]
qq, M = 100 GeV
arXiv:0810.1304
0
0.02
0.04
0.06
0.08
60 80 100 120 140
SISCone, R=1.0, f=0.75Qw
f=0.24 = 31.9 GeV
Resonance X → dijets
Xpp
q
q
q
q
jet
jet
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 9 / 19
Dijet mass: scan over R [Pythia 6.4]
R = 1.11/
N d
n/db
in /
2
dijet mass [GeV]
qq, M = 100 GeV
arXiv:0810.1304
0
0.02
0.04
0.06
0.08
60 80 100 120 140
SISCone, R=1.1, f=0.75Qw
f=0.24 = 34.7 GeV
Resonance X → dijets
Xpp
q
q
q
q
jet
jet
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 9 / 19
Dijet mass: scan over R [Pythia 6.4]
R = 1.21/
N d
n/db
in /
2
dijet mass [GeV]
qq, M = 100 GeV
arXiv:0810.1304
0
0.02
0.04
0.06
0.08
60 80 100 120 140
SISCone, R=1.2, f=0.75Qw
f=0.24 = 37.9 GeV
Resonance X → dijets
Xpp
q
q
q
q
jet
jet
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 9 / 19
Dijet mass: scan over R [Pythia 6.4]
R = 1.31/
N d
n/db
in /
2
dijet mass [GeV]
qq, M = 100 GeV
arXiv:0810.1304
0
0.02
0.04
0.06
0.08
60 80 100 120 140
SISCone, R=1.3, f=0.75Qw
f=0.24 = 42.3 GeV
Resonance X → dijets
Xpp
q
q
q
q
jet
jet
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 9 / 19
Dijet mass: scan over R [Pythia 6.4]
R = 1.31/
N d
n/db
in /
2
dijet mass [GeV]
qq, M = 100 GeV
arXiv:0810.1304
0
0.02
0.04
0.06
0.08
60 80 100 120 140
SISCone, R=1.3, f=0.75Qw
f=0.24 = 42.3 GeV
1
1.5
2
2.5
3
0.5 1 1.5ρ L
from
Qw f=
0.24
R
qq, M = 100 GeV
arXiv:0810.1304
SISCone, f=0.75
After scanning, summarise “quality” v. RRR. Minimum ≡ BESTpicture not so different from crude analytical estimate
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 9 / 19
Scan through qq mass values
mqq = 100 GeV
1
1.5
2
2.5
3
0.5 1 1.5
ρ L fr
om Q
w f=0.
24
R
qq, M = 100 GeV
arXiv:0810.1304
SISCone, f=0.75
Best R is at minimum of curve
◮ Best R depends strongly onmass of system
◮ Increases with mass, just likecrude analytical prediction
NB: current analytics too crude
NB: 100,000 plots for various jet algorithms, narrow qq and gg resonancesfrom http://quality.fastjet.fr Cacciari, Rojo, GPS & Soyez ’08
Other related work: Krohn, Thaler & Wang ’09; Soyez ’10
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 10 / 19
Scan through qq mass values
mqq = 150 GeV
1
1.5
2
2.5
3
0.5 1 1.5
ρ L fr
om Q
w f=0.
24
R
qq, M = 150 GeV
arXiv:0810.1304
SISCone, f=0.75
Best R is at minimum of curve
◮ Best R depends strongly onmass of system
◮ Increases with mass, just likecrude analytical prediction
NB: current analytics too crude
NB: 100,000 plots for various jet algorithms, narrow qq and gg resonancesfrom http://quality.fastjet.fr Cacciari, Rojo, GPS & Soyez ’08
Other related work: Krohn, Thaler & Wang ’09; Soyez ’10
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 10 / 19
Scan through qq mass values
mqq = 200 GeV
1
1.5
2
2.5
3
0.5 1 1.5
ρ L fr
om Q
w f=0.
24
R
qq, M = 200 GeV
arXiv:0810.1304
SISCone, f=0.75
Best R is at minimum of curve
◮ Best R depends strongly onmass of system
◮ Increases with mass, just likecrude analytical prediction
NB: current analytics too crude
NB: 100,000 plots for various jet algorithms, narrow qq and gg resonancesfrom http://quality.fastjet.fr Cacciari, Rojo, GPS & Soyez ’08
Other related work: Krohn, Thaler & Wang ’09; Soyez ’10
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 10 / 19
Scan through qq mass values
mqq = 300 GeV
1
1.5
2
2.5
3
0.5 1 1.5
ρ L fr
om Q
w f=0.
24
R
qq, M = 300 GeV
arXiv:0810.1304
SISCone, f=0.75
Best R is at minimum of curve
◮ Best R depends strongly onmass of system
◮ Increases with mass, just likecrude analytical prediction
NB: current analytics too crude
NB: 100,000 plots for various jet algorithms, narrow qq and gg resonancesfrom http://quality.fastjet.fr Cacciari, Rojo, GPS & Soyez ’08
Other related work: Krohn, Thaler & Wang ’09; Soyez ’10
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 10 / 19
Scan through qq mass values
mqq = 500 GeV
1
1.5
2
2.5
3
0.5 1 1.5
ρ L fr
om Q
w f=0.
24
R
qq, M = 500 GeV
arXiv:0810.1304
SISCone, f=0.75
Best R is at minimum of curve
◮ Best R depends strongly onmass of system
◮ Increases with mass, just likecrude analytical prediction
NB: current analytics too crude
NB: 100,000 plots for various jet algorithms, narrow qq and gg resonancesfrom http://quality.fastjet.fr Cacciari, Rojo, GPS & Soyez ’08
Other related work: Krohn, Thaler & Wang ’09; Soyez ’10
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 10 / 19
Scan through qq mass values
mqq = 700 GeV
1
1.5
2
2.5
3
0.5 1 1.5
ρ L fr
om Q
w f=0.
24
R
qq, M = 700 GeV
arXiv:0810.1304
SISCone, f=0.75
Best R is at minimum of curve
◮ Best R depends strongly onmass of system
◮ Increases with mass, just likecrude analytical prediction
NB: current analytics too crude
NB: 100,000 plots for various jet algorithms, narrow qq and gg resonancesfrom http://quality.fastjet.fr Cacciari, Rojo, GPS & Soyez ’08
Other related work: Krohn, Thaler & Wang ’09; Soyez ’10
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 10 / 19
Scan through qq mass values
mqq = 1000 GeV
1
1.5
2
2.5
3
0.5 1 1.5
ρ L fr
om Q
w f=0.
24
R
qq, M = 1000 GeV
arXiv:0810.1304
SISCone, f=0.75
Best R is at minimum of curve
◮ Best R depends strongly onmass of system
◮ Increases with mass, just likecrude analytical prediction
NB: current analytics too crude
NB: 100,000 plots for various jet algorithms, narrow qq and gg resonancesfrom http://quality.fastjet.fr Cacciari, Rojo, GPS & Soyez ’08
Other related work: Krohn, Thaler & Wang ’09; Soyez ’10
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 10 / 19
Scan through qq mass values
mqq = 2000 GeV
1
1.5
2
2.5
3
0.5 1 1.5
ρ L fr
om Q
w f=0.
24
R
qq, M = 2000 GeV
arXiv:0810.1304
SISCone, f=0.75
Best R is at minimum of curve
◮ Best R depends strongly onmass of system
◮ Increases with mass, just likecrude analytical prediction
NB: current analytics too crude
NB: 100,000 plots for various jet algorithms, narrow qq and gg resonancesfrom http://quality.fastjet.fr Cacciari, Rojo, GPS & Soyez ’08
Other related work: Krohn, Thaler & Wang ’09; Soyez ’10
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 10 / 19
Scan through qq mass values
mqq = 4000 GeV
1
1.5
2
2.5
3
0.5 1 1.5
ρ L fr
om Q
w f=0.
24
R
qq, M = 4000 GeV
arXiv:0810.1304
SISCone, f=0.75
Best R is at minimum of curve
◮ Best R depends strongly onmass of system
◮ Increases with mass, just likecrude analytical prediction
NB: current analytics too crude
NB: 100,000 plots for various jet algorithms, narrow qq and gg resonancesfrom http://quality.fastjet.fr Cacciari, Rojo, GPS & Soyez ’08
Other related work: Krohn, Thaler & Wang ’09; Soyez ’10
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 10 / 19
Scan through qq mass values
mqq = 4000 GeV
1
1.5
2
2.5
3
0.5 1 1.5
ρ L fr
om Q
w f=0.
24
R
qq, M = 4000 GeV
arXiv:0810.1304
SISCone, f=0.75
Best R is at minimum of curve
◮ Best R depends strongly onmass of system
◮ Increases with mass, just likecrude analytical prediction
NB: current analytics too crude
NB: 100,000 plots for various jet algorithms, narrow qq and gg resonancesfrom http://quality.fastjet.fr Cacciari, Rojo, GPS & Soyez ’08
Other related work: Krohn, Thaler & Wang ’09; Soyez ’10
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 10 / 19
Scan through qq mass values
mqq = 4000 GeV
1
1.5
2
2.5
3
0.5 1 1.5
ρ L fr
om Q
w f=0.
24
R
qq, M = 4000 GeV
arXiv:0810.1304
SISCone, f=0.75
Best R is at minimum of curve
◮ Best R depends strongly onmass of system
◮ Increases with mass, just likecrude analytical prediction
NB: current analytics too crude
NB: 100,000 plots for various jet algorithms, narrow qq and gg resonancesfrom http://quality.fastjet.fr Cacciari, Rojo, GPS & Soyez ’08
Other related work: Krohn, Thaler & Wang ’09; Soyez ’10
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 10 / 19
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 11 / 19
http://quality.fastjet.fr/
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 12 / 19
Experimental results
ATLAS dijet mass
2000 3000 4000
1
10
210
310
410
510 DataBackground
[GeV]jjReconstructed m2000 3000 4000
Eve
nts
Sig
nific
ance
-2
0
2
ATLAS Preliminary
-1 = 13.0 fbdt L ∫ = 8 TeVs
CMS dijet mass
(pb/G
eV
)jj
/dm
!d
-810
-710
-610
-510
-410
-310
-210
-110
1
10
Data
Fit
QCD MC
JES Uncertainty
CMS Preliminary-1 = 8 TeV , L= 19.6 fbs
| < 1.3jj"#| < 2.5 , |"|
> 890 GeV , Wide Jetsjjm
A / C (3.6 TeV)
W’ (1.9 TeV)
Dijet Mass (GeV)
1000 1500 2000 2500 3000 3500 4000 4500 5000 5500
Da
ta!
(Data
-Fit)/
-4-3-2-101234
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 13 / 19
Highest mass central dijet event atthe LHC: 5.15 TeV!
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 14 / 19
Dijet Mass (GeV)1000 2000 3000 4000 5000 6000
No
rmalized
yie
ld/G
eV
0
0.0005
0.001
0.0015
0.002
0.0025
0.003
0.0035
0.004
0.0045 QuarkQuark
QuarkGluon
GluonGluon
CMS Simulation Preliminary
= 8 TeV, WideJetss
| < 1.3jj
η∆| < 2.5 & |η|
Expected resonance limits [TeV]7 TeV, 5 fb−1, published
ATLAS CMSX → (R = 0.6) (wide)
q∗ qg 2.94 3.05string qg 4.29 3.47octet scalar gg 1.97 2.24W ′ qq 1.74 1.78
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 15 / 19
Expected resonance limits [TeV]7 TeV, 5 fb−1, published
ATLAS CMSX → (R = 0.6) (wide)
q∗ qg 2.94 3.05string qg 4.29 3.47octet scalar gg 1.97 2.24W ′ qq 1.74 1.78
CMS “wide jets”:
We [...] select the two AK5 jets with the highest pT in the event (leading AK5 jets).
Then we add the Lorentz vectors of all other AK5 jets with pT > 10 GeV and |η| < 2.5 to
the closest AK5 leading jet, if within ∆R =< 1.1, to obtain the two leading wide jets.
The parameter ∆R sets the maximum size of the wide jet.
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 15 / 19
Why do the experiments have a |∆ηjj | < 1.3 cut?
see blackboard!
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 16 / 19
Why do the experiments have a |∆ηjj | < 1.3 cut?
see blackboard!
Bottom line: if you’re looking for a hadronically decaying
resonance, never use jets far in rapidity the CoM systemof the resonance
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 16 / 19
pp → ttpp → ttpp → ttsimulated with Pythia, displayed with Delphes
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 17 / 19
6 partons v. 6 jets?
Alpgen pp → tt → 6q
0
0.2
0.4
0.6
0.8
1
0 0.5 1 1.5
R
fraction of pp→tt→6q events with all Rqq > R
pp, 7 TeV
Alpgen partons
no pt cut on quarks
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 18 / 19
6 partons v. 6 jets?
Alpgen pp → tt → 6q
0
0.2
0.4
0.6
0.8
1
0 0.5 1 1.5
R
fraction of pp→tt→6q events with all Rqq > R
pp, 7 TeV
Alpgen partons
require all ptq > 10 GeV
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 18 / 19
6 partons v. 6 jets?
Alpgen pp → tt → 6q
0
0.2
0.4
0.6
0.8
1
0 0.5 1 1.5
R
fraction of pp→tt→6q events with all Rqq > R
pp, 7 TeV
Alpgen partons
require all ptq > 20 GeV
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 18 / 19
6 partons v. 6 jets?
Alpgen pp → tt → 6q
0
0.2
0.4
0.6
0.8
1
0 0.5 1 1.5
R
fraction of pp→tt→6q events with all Rqq > R
pp, 7 TeV
Alpgen partons
require all ptq > 30 GeV
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 18 / 19
6 partons v. 6 jets?
Alpgen pp → tt → 6q
0
0.2
0.4
0.6
0.8
1
0 0.5 1 1.5
R
fraction of pp→tt→6q events with all Rqq > R
pp, 7 TeV
Alpgen partons
require all ptq > 20 GeV
Herwig pp → tt → hadronsDistribution of number of jets
0
1
2
3
4
0 2 4 6 8 10 12
dσ/d
nje
ts [a
rb. u
nits
]
number of jets
pp, 7 TeVHerwig 6.5 (no UE)
anti-kt R=0.5
pt,jet > 20 GeV
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 18 / 19
Take-home messages
◮ We can (sort of) calculate the relation between jet pt and parton pt
◮ That guides us in how to “focus” jets◮ generally want small R and low pt , because UE is large◮ larger R at high pt ’s◮ smaller R helps resolve multi jets, as in tt, SUSY, black holes, etc.
ATLAS mostly uses R = 0.4; also R = 0.6
CMS mostly uses R = 0.5; also R = 0.7 & “wide” jets
◮ Large di/multi-jet mass is not enough when looking for signals — QCDvery enhanced at small angles, signals aren’t
◮ Relation between number of partons & number is non-trivial at highmultiplicities
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 19 / 19
EXTRAS
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 20 / 19
Robustness: Mtop varies with R?
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
150 160 170 180 190 200
1/n
dn/d
m
reconstructed mt [GeV/c2]
kt
Pythia 6.325, mt = 175 GeV/c2
R=0.4tt -> bqq+bµνµ
no UE
with UE
Mtop
Game: measure top mass to 1 GeVexample for Tevatron
mt = 175 GeV
◮ Small R : lose 6 GeV to PTradiation and hadronisation, UEand pileup irrelevant
◮ Large R : hadronisation and PTradiation leave mass at∼ 175 GeV, UE adds 2− 4 GeV.
Is the final top mass (after W jet-energy-scale and Monte Carlo unfolding)independent of R used to measure jets?
Flexibility in jet finding gives powerful cross-check of systematic effects
cf. Seymour & Tevlin ’06
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 21 / 19
Robustness: Mtop varies with R?
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
150 160 170 180 190 200
1/n
dn/d
m
reconstructed mt [GeV/c2]
kt
Pythia 6.325, mt = 175 GeV/c2
R=0.5tt -> bqq+bµνµ
no UE
with UE
Mtop
Game: measure top mass to 1 GeVexample for Tevatron
mt = 175 GeV
◮ Small R : lose 6 GeV to PTradiation and hadronisation, UEand pileup irrelevant
◮ Large R : hadronisation and PTradiation leave mass at∼ 175 GeV, UE adds 2− 4 GeV.
Is the final top mass (after W jet-energy-scale and Monte Carlo unfolding)independent of R used to measure jets?
Flexibility in jet finding gives powerful cross-check of systematic effects
cf. Seymour & Tevlin ’06
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 21 / 19
Robustness: Mtop varies with R?
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
150 160 170 180 190 200
1/n
dn/d
m
reconstructed mt [GeV/c2]
kt
Pythia 6.325, mt = 175 GeV/c2
R=0.6tt -> bqq+bµνµ
no UE
with UE Game: measure top mass to 1 GeVexample for Tevatron
mt = 175 GeV
◮ Small R : lose 6 GeV to PTradiation and hadronisation, UEand pileup irrelevant
◮ Large R : hadronisation and PTradiation leave mass at∼ 175 GeV, UE adds 2− 4 GeV.
Is the final top mass (after W jet-energy-scale and Monte Carlo unfolding)independent of R used to measure jets?
Flexibility in jet finding gives powerful cross-check of systematic effects
cf. Seymour & Tevlin ’06
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 21 / 19
Robustness: Mtop varies with R?
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
150 160 170 180 190 200
1/n
dn/d
m
reconstructed mt [GeV/c2]
kt
Pythia 6.325, mt = 175 GeV/c2
R=0.7tt -> bqq+bµνµ
no UE
with UE Game: measure top mass to 1 GeVexample for Tevatron
mt = 175 GeV
◮ Small R : lose 6 GeV to PTradiation and hadronisation, UEand pileup irrelevant
◮ Large R : hadronisation and PTradiation leave mass at∼ 175 GeV, UE adds 2− 4 GeV.
Is the final top mass (after W jet-energy-scale and Monte Carlo unfolding)independent of R used to measure jets?
Flexibility in jet finding gives powerful cross-check of systematic effects
cf. Seymour & Tevlin ’06
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 21 / 19
Robustness: Mtop varies with R?
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
150 160 170 180 190 200
1/n
dn/d
m
reconstructed mt [GeV/c2]
kt
Pythia 6.325, mt = 175 GeV/c2
R=0.8tt -> bqq+bµνµ
no UE
with UE Game: measure top mass to 1 GeVexample for Tevatron
mt = 175 GeV
◮ Small R : lose 6 GeV to PTradiation and hadronisation, UEand pileup irrelevant
◮ Large R : hadronisation and PTradiation leave mass at∼ 175 GeV, UE adds 2− 4 GeV.
Is the final top mass (after W jet-energy-scale and Monte Carlo unfolding)independent of R used to measure jets?
Flexibility in jet finding gives powerful cross-check of systematic effects
cf. Seymour & Tevlin ’06
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 21 / 19
Robustness: Mtop varies with R?
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
150 160 170 180 190 200
1/n
dn/d
m
reconstructed mt [GeV/c2]
kt
Pythia 6.325, mt = 175 GeV/c2
R=1.0tt -> bqq+bµνµ
no UE
with UE Game: measure top mass to 1 GeVexample for Tevatron
mt = 175 GeV
◮ Small R : lose 6 GeV to PTradiation and hadronisation, UEand pileup irrelevant
◮ Large R : hadronisation and PTradiation leave mass at∼ 175 GeV, UE adds 2− 4 GeV.
Is the final top mass (after W jet-energy-scale and Monte Carlo unfolding)independent of R used to measure jets?
Flexibility in jet finding gives powerful cross-check of systematic effects
cf. Seymour & Tevlin ’06
Gavin Salam (CERN) Jets and jet substructure (3) TASI, June 2013 21 / 19