LO NLO dist HTjets HAZ12 - lpthe.jussieu.frsalam/talks/repo/2011-giantK-Valencia.pdf · Gavin Salam...
Transcript of LO NLO dist HTjets HAZ12 - lpthe.jussieu.frsalam/talks/repo/2011-giantK-Valencia.pdf · Gavin Salam...
Giant K factors
Gavin Salam
CERN, Princeton & LPTHE/CNRS (Paris)
Work performed with Mathieu Rubin and Sebastian Sapeta, arXiv:1006.2144
Kick-off meeting of LHCPhenoNet Initial Training NetworkValencia, Spain, 1–4 February 2011
Many searches for New Physics (eg. SUSY) rely onLeading Order predictions for backgrounds.
eg. Z+4jet background to gluino pair production
with NLO technology rapidly becoming mature for such cases
LO often considered good to within a factor of 2NLO to within 10-20%
This talk is about cases where such “rules of thumb” fail(spectacularly)
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 2 / 16
The Z+jet process[Introduction]
Use MCFM to examinevarious properties of suchevents at LO and NLO.
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 3 / 16
The Z+jet process[Introduction]
Use MCFM to examinevarious properties of suchevents at LO and NLO.
10-2
10-1
1
101
102
103
104
200 400 600 800 1000 1200 1400dσ
/dp t
,Z [f
b / 1
00 G
eV]
pt,Z [GeV]
pp, 14 TeV
LO
NLO
pt spectrum of Z boson gets K -factor of 1.5
Fairly standard kind of occurrence
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 3 / 16
The Z+jet process[Introduction]
Use MCFM to examinevarious properties of suchevents at LO and NLO.
10-2
10-1
1
101
102
103
104
200 400 600 800 1000 1200 1400dσ
/dp t
,j1 [f
b / 1
00 G
eV]
pt,j1 [GeV]
pp, 14 TeV
LO
NLO
pt spectrum of leading jet gets K -factor of 5–10
related issues in Butterworth, Davison, Rubin & GPS ’08
Bauer & Lange ’09; Denner, Dittmaier, Kasprzik & Much ’09
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 3 / 16
The Z+jet process[Introduction]
Use MCFM to examinevarious properties of suchevents at LO and NLO.
10-2
10-1
1
101
102
103
104
200 400 600 800 1000 1200 1400dσ
/dH
T,je
ts [f
b / 1
00 G
eV]
HT,jets [GeV]
pp, 14 TeV
LO
NLO
HT ,jets ≡∑
i∈jets pt,iHT ,jets ≡∑
i∈jets pt,iHT ,jets ≡∑
i∈jets pt,i gets K -factor of up to 100
Such things are not supposed to happen with αs = 0.1!
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 3 / 16
Why the large K -factors?[Introduction]
Leading Order
αsαEW
Next-to-Leading Order
α2sαEW
LHC probes scales well above EW scale,√s ≫ MZ .
EW bosons are light. New log-enhanced topologies appear.
HT ,jets is extreme, because at LO HT ,jets ≃ pt,jet 1; NLO: HT ,jets ≃ 2pt,jet 1G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 4 / 16
Why the large K -factors?[Introduction]
Leading Order
αsαEW
Next-to-Leading Order
α2sαEW
LHC probes scales well above EW scale,√s ≫ MZ .
EW bosons are light. New log-enhanced topologies appear.
HT ,jets is extreme, because at LO HT ,jets ≃ pt,jet 1; NLO: HT ,jets ≃ 2pt,jet 1G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 4 / 16
Why the large K -factors?[Introduction]
Leading Order
αsαEW
Next-to-Leading Order
α2sαEW ln2
pt
MZ
LHC probes scales well above EW scale,√s ≫ MZ .
EW bosons are light. New log-enhanced topologies appear.
HT ,jets is extreme, because at LO HT ,jets ≃ pt,jet 1; NLO: HT ,jets ≃ 2pt,jet 1G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 4 / 16
Why the large K -factors?[Introduction]
Leading Order
αsαEW
Next-to-Leading Order
α2sαEW ln2
pt
MZ
LHC probes scales well above EW scale,√s ≫ MZ .
EW bosons are light. New log-enhanced topologies appear.
HT ,jets is extreme, because at LO HT ,jets ≃ pt,jet 1; NLO: HT ,jets ≃ 2pt,jet 1G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 4 / 16
Why the large K -factors?[Introduction]
Leading Order
αsαEW
Next-to-Leading Order
α2sαEW ln2
pt
MZ
LHC probes scales well above EW scale,√s ≫ MZ .
EW bosons are light. New log-enhanced topologies appear.
HT ,jets is extreme, because at LO HT ,jets ≃ pt,jet 1; NLO: HT ,jets ≃ 2pt,jet 1G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 4 / 16
We calculated Z+jet@NLO.
But giant K-factors are dominated by “LO” Z+2-partonpiece of Z+jet@NLO.
We know LO calculations aren’t reliable.
We’d ideally want to combine Z+jet@NLO withZ+2-jet@NLO
without double counting
without having to do full Z+jet@NNLO calculation
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 5 / 16
First try something simpler:
Take the “leading” process[Z + jet @ LO]
and add in process with one extra jet.
[i.e. include Z + 2 jets @ LO]
approximate the 1-loop Z+jet term, by requiringcancellation of all divergences
[those from singly unresolved limit of Z + 2 jets]
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 6 / 16
The LoopSim idea: n̄LO[LoopSim]
[The idea]
p3
p1
p2
Z + 2 partons
|M2(p1, p2, p3)|
◮ Identify softest or most collinear parton [with help of a jet algorithm]
◮ “Loop” it ≡ remove it from event, reshuffle other momenta;weight of looped event is (−1)× weight of tree-level event
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 7 / 16
The LoopSim idea: n̄LO[LoopSim]
[The idea]
p3
p1
p2
softest
Z + 2 partons
|M2(p1, p2, p3)|
◮ Identify softest or most collinear parton [with help of a jet algorithm]
◮ “Loop” it ≡ remove it from event, reshuffle other momenta;weight of looped event is (−1)× weight of tree-level event
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 7 / 16
The LoopSim idea: n̄LO[LoopSim]
[The idea]
p3
p1
p2
softest
Z + 2 partons
|M2(p1, p2, p3)|
+
~
~p1
p2
looped
Z + 1 parton + 1 sim. loop
−−−|M2(p1, p2, p3)|
◮ Identify softest or most collinear parton [with help of a jet algorithm]
◮ “Loop” it ≡ remove it from event, reshuffle other momenta;weight of looped event is (−1)× weight of tree-level event
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 7 / 16
The LoopSim idea: n̄LO[LoopSim]
[The idea]
p3
p1
p2
softest
Z + 2 partons
|M2(p1, p2, p3)|
+
~
~p1
p2
looped
Z + 1 parton + 1 sim. loop
−−−|M2(p1, p2, p3)|
◮ Identify softest or most collinear parton [with help of a jet algorithm]
◮ “Loop” it ≡ remove it from event, reshuffle other momenta;weight of looped event is (−1)× weight of tree-level event
This cancels all the “single-unresolved” divergences in the Z+2 events
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 7 / 16
n̄LO results (K -factors, normalised to LO)[LoopSim]
[The idea]
ptptpt of Z-boson ptptpt of jet 1 HT, jets =∑
jets pt,jHT, jets =∑
jets pt,jHT, jets =∑
jets pt,j
0.5
1
1.5
2
2.5
3
250 500 750 1000 1250
K-f
acto
r w
rt L
O
pt,Z (GeV)
MCFM 5.7, CTEQ6Mpp, 14 TeV
anti-kt, R=0.7pt,j1 > 200 GeV
LONLO–nLO (µ dep)–nLO (RLS dep)
0
2
4
6
8
10
250 500 750 1000 1250
K-f
acto
r w
rt L
O
pt,j1 (GeV)
MCFM 5.7, CTEQ6Mpp, 14 TeV
anti-kt, R=0.7pt,j1 > 200 GeV
LONLO–nLO (µ dep)–nLO (RLS dep)
1
10
100
1000
500 1000 1500 2000 2500
K-f
acto
r w
rt L
O
HT,jets (GeV)
MCFM 5.7, CTEQ6Mpp, 14 TeVanti-kt, R=0.7pt,j1 > 200 GeV
LONLO
–nLO (µ dep)–nLO (RLS dep)
When the K -factors are large, n̄LO agrees well with NLO
MLM matching also does a similar job
cf. de Aquino, Hagiwara, Li & Maltoni ’11
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 8 / 16
Differences between and LoopSim andMLM/CKKW matching:
1. Does not rely on shower (✓: simplicity; ✗: not easilyintegrated with shower MCs)
2. Does not need arbitrary separation of Z+1/Z+2/etc.
samples with (hard-to-choose) momentum cutoff
3. Can easily be extended beyond LO matching
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 9 / 16
n̄n̄LO and n̄NLO[LoopSim]
[n̄NLO]
add tree-level Z+3,cancel divergences in single + doubly unresolved limits: n̄n̄LO
p4p3
p1
p2
|M2(p1, p2, p3, p4)|
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 10 / 16
n̄n̄LO and n̄NLO[LoopSim]
[n̄NLO]
add tree-level Z+3,cancel divergences in single + doubly unresolved limits: n̄n̄LO
p4p3
p1
p2
|M2(p1, p2, p3, p4)|
+
p4~
~
~p1
p2
−|M2(p1, p2, p3, p4)|
+
~
~
~
p3
p1
p2
−|M2(p1, p2, p3, p4)|
+
provides approximation of 1-loop
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 10 / 16
n̄n̄LO and n̄NLO[LoopSim]
[n̄NLO]
add tree-level Z+3,cancel divergences in single + doubly unresolved limits: n̄n̄LO
p4p3
p1
p2
|M2(p1, p2, p3, p4)|
+
p4~
~
~p1
p2
−|M2(p1, p2, p3, p4)|
+
~
~
~
p3
p1
p2
−|M2(p1, p2, p3, p4)|
+
~
~p1
p2
+|M2(p1, p2, p3, p4)|
provides approximation of 1-loop and 2-loop contributions; total sums to zero
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 10 / 16
n̄n̄LO and n̄NLO[LoopSim]
[n̄NLO]
add tree-level Z+3,cancel divergences in single + doubly unresolved limits: n̄n̄LO
p4p3
p1
p2
|M2(p1, p2, p3, p4)|
+
p4~
~
~p1
p2
−|M2(p1, p2, p3, p4)|
+
~
~
~
p3
p1
p2
−|M2(p1, p2, p3, p4)|
+
~
~p1
p2
+|M2(p1, p2, p3, p4)|
provides approximation of 1-loop and 2-loop contributions; total sums to zero
add in (exact Z+2 @ 1-loop) − (approximate Z+2 @ 1-loop)+ extra simulated 2-loop piece to cancel new Z+2@1-loop divergences
This is n̄NLO
allows combination of Z+1@NLO with Z+2@NLOG. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 10 / 16
Testing NLO Merging, in 3 processes
1. Z@NLO with Z+j@NLO
2. Z+j@NLO with Z+2j@NLO
3. 2j@NLO with 3j@NLO
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 11 / 16
Validation: Drell-Yan lepton pt , n̄NLO v. NNLO[n̄NLO results]
[Drell-Yan]
n̄LO v. NLO
102
103
104
105
0 10 20 30 40 50 60 70 80 90 100
dσ/d
p t,m
ax [f
b/G
eV]
pt,max [GeV]
pp, 14 TeV66 < me+e- < 116 GeV
LO
NLO–nLO
Z (i.e. DY) with Z+j from MCFM & LoopSim
For pt ell &12MZ + ΓZ (giant K -factor!) it had to work
For pt,ℓ .12MZ + ΓZ it’s remarkable that it still works
Validation: Drell-Yan lepton pt , n̄NLO v. NNLO[n̄NLO results]
[Drell-Yan]
n̄LO v. NLO n̄NLO v. NNLO
102
103
104
105
0 10 20 30 40 50 60 70 80 90 100
dσ/d
p t,m
ax [f
b/G
eV]
pt,max [GeV]
pp, 14 TeV66 < me+e- < 116 GeV
LO
NLO–nLO
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
10 20 30 40 50 60 70 80 90 100K
fact
or w
rt N
LOpt,max [GeV]
pp, 14 TeV66 < me+e- < 116 GeV
NLO–nNLO (µ dep)–nNLO (RLS dep)
NNLO
NNLO from DYNNLO, Z (i.e. DY) with Z+j from MCFM & LoopSim
For pt ell &12MZ + ΓZ (giant K -factor!) it had to work
For pt,ℓ .12MZ + ΓZ it’s remarkable that it still works
Validation: Drell-Yan lepton pt , n̄NLO v. NNLO[n̄NLO results]
[Drell-Yan]
n̄LO v. NLO n̄NLO v. NNLO
102
103
104
105
0 10 20 30 40 50 60 70 80 90 100
dσ/d
p t,m
ax [f
b/G
eV]
pt,max [GeV]
pp, 14 TeV66 < me+e- < 116 GeV
LO
NLO–nLO
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
10 20 30 40 50 60 70 80 90 100K
fact
or w
rt N
LOpt,max [GeV]
pp, 14 TeV66 < me+e- < 116 GeV
NLO–nNLO (µ dep)–nNLO (RLS dep)
NNLO
NNLO from DYNNLO, Z (i.e. DY) with Z+j from MCFM & LoopSim
For pt ell &12MZ + ΓZ (giant K -factor!) it had to work
For pt,ℓ .12MZ + ΓZ it’s remarkable that it still works
n̄NLO for Z+j observables[n̄NLO results]
[Z+jet]
ptptpt of Z-boson
0.5
1
1.5
2
2.5
3
250 500 750 1000 1250
K-f
acto
r w
rt L
O
pt,Z (GeV)
MCFM 5.7, CTEQ6Mpp, 14 TeV
anti-kt, R=0.7pt,j1 > 200 GeV
LONLO–nNLO (µ dep)–nNLO (RLS dep) ◮ ptZ distribution didn’t have
giant K -factors.
◮ n̄NLO brings no benefitTo get improvement you would
need exact 2-loop terms
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 13 / 16
n̄NLO for Z+j observables[n̄NLO results]
[Z+jet]
ptptpt of jet 1
0
2
4
6
8
10
250 500 750 1000 1250
K-f
acto
r w
rt L
O
pt,j1 (GeV)
MCFM 5.7, CTEQ6Mpp, 14 TeV
anti-kt, R=0.7pt,j1 > 200 GeV
LONLO–nNLO (µ dep)–nNLO (RLS dep) ◮ ptj distribution seems to
converge at n̄NLO
◮ scale uncertainties reduced by∼ factor 2
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 13 / 16
n̄NLO for Z+j observables[n̄NLO results]
[Z+jet]
HT, jets =∑
jets pt,jHT, jets =∑
jets pt,jHT, jets =∑
jets pt,j
1
10
100
1000
500 1000 1500 2000 2500
K-f
acto
r w
rt L
O
HT,jets (GeV)
MCFM 5.7, CTEQ6Mpp, 14 TeVanti-kt, R=0.7pt,j1 > 200 GeV
LONLO
–nNLO (µ dep)–nNLO (RLS dep)
◮ Signficiant furtherenhancement for HT ,jets
◮ n̄NLO brings clear message:
HT ,jetsHT ,jetsHT ,jets is not a goodobservable!
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 13 / 16
What’s the problem with HT?[n̄NLO results]
[Z+jet]
HTHTHT (effective mass) type observables are widely used in searches
◮ HT has a steeply falling distribution (like ptj , ptZ )
◮ At each order (NLO, NNLO), an extra (soft) jet contributes to theHT sum e.g. from ISR
◮ That shifts HT up, which translates to a substantial increase in thecross section
We can test this hypothesis for plain jet events, using a truncated sum,
HT ,n =n∑
i=1
pt,jet i
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 14 / 16
HT ,n in (di)jet events[n̄NLO results]
[dijets]
HT ,2HT ,2HT ,2 HT ,3HT ,3HT ,3 HT ,∞HT ,∞HT ,∞
0
0.5
1
1.5
2
2.5
3
100 200 300 400 500 600 700 800 900
ratio
to L
O (
x µ=
1)
12− HT,2 [GeV]
pp, 7 TeV, anti-kt R=0.7
NLOJet++, CTEQ6M
LONLO
–nNLO (µ)–nNLO (RLS) 0
0.5
1
1.5
2
2.5
3
100 200 300 400 500 600 700 800 900
ratio
to L
O (
x µ=
1)
12− HT,3 [GeV]
pp, 7 TeV, anti-kt R=0.7
NLOJet++, CTEQ6M
LONLO
–nNLO (µ)–nNLO (RLS) 0
0.5
1
1.5
2
2.5
3
100 200 300 400 500 600 700 800 900
ratio
to L
O (
x µ=
1)
12− HT [GeV]
pp, 7 TeV, anti-kt R=0.7
NLOJet++, CTEQ6M
LONLO
–nNLO (µ)–nNLO (RLS)
A clear message:for a process with n objects at lowest order, use HT ,n
Do you know what gets used in your experiment’s searches?
Many writers of LHC SUSY proceedings didn’t...
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 15 / 16
Some take-home messages[Closing]
Be aware that giant K -factors existAlways look one order beyond the leading order, for example with
MLM/CKKW matching
New tool to get good predictions in such cases: LoopSimBasically an “operator” to generate approximations to unknown loops
Combine Z+j@NLO, Z+2j@NLO to get “n̄NLO” Z+jet
It sometimes works even beyond “giant-K -factor” regions
Watch out for HT
Even for simple processes, it converges very poorly
unless you define it carefully (limit number of objects in sum)
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 16 / 16
EXTRAS
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 17 / 16
Add Z+1jet, Z+2jet + shower[Extras]
[How MLM works]
Z+parton
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 18 / 16
Add Z+1jet, Z+2jet + shower[Extras]
[How MLM works]
shower Z+parton
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 18 / 16
Add Z+1jet, Z+2jet + shower[Extras]
[How MLM works]
Z+2partons
+
shower Z+parton
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 18 / 16
Add Z+1jet, Z+2jet + shower[Extras]
[How MLM works]
shower Z+2partons
+
shower Z+parton
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 18 / 16
Add Z+1jet, Z+2jet + shower[Extras]
[How MLM works]
showergenerates hard gluon
of Z+parton
v.
shower Z+2partons
+
shower Z+parton
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 18 / 16
Add Z+1jet, Z+2jet + shower[Extras]
[How MLM works]
showergenerates hard gluon
of Z+parton
v.
shower Z+2partons
+
shower Z+parton
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 18 / 16
Add Z+1jet, Z+2jet + shower[Extras]
[How MLM works]
DOUBLECOUNTING
showergenerates hard gluon
of Z+parton
v.
shower Z+2partons
+
shower Z+parton
Z + parton implicitly includes part of Z + 2 partons
It’s just that the 2nd parton isn’t always explicitly “visible”
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 18 / 16
cartoon of MLM merging of Z+j and Z+2j[Extras]
[How MLM works]
showergenerates hard gluon
of Z+parton
v.
shower Z+2partons
+
shower Z+parton
◮ MLM merging relies on parton shower to help figure out what fraction ofZ + parton is really Z + 2 partons.
◮ Our aim is to do that without the parton shower
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 19 / 16
cartoon of MLM merging of Z+j and Z+2j[Extras]
[How MLM works]
pt cut
Qmerge
ACCEPT ACCEPT REJECT
showergenerates hard gluon
of Z+parton
v.
shower Z+2partons
+
shower Z+parton
◮ MLM merging relies on parton shower to help figure out what fraction ofZ + parton is really Z + 2 partons.
◮ Our aim is to do that without the parton shower
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 19 / 16
cartoon of MLM merging of Z+j and Z+2j[Extras]
[How MLM works]
pt cut
Qmerge
ACCEPT ACCEPT REJECT
showergenerates hard gluon
of Z+parton
v.
shower Z+2partons
+
shower Z+parton
◮ MLM merging relies on parton shower to help figure out what fraction ofZ + parton is really Z + 2 partons.
◮ Our aim is to do that without the parton shower
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 19 / 16
Testing Alpgen + Herwig + MLM Matching[Extras]
[MLM results]
ptptpt of Z-boson
10-2
10-1
1
10
102
103
104
200 300 400 500 600 700 800 900 1000
dσ/d
p t,Z
[fb
/ 100
GeV
]
pt,Z [GeV]
pp, 14 TeV
LO
NLO
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 20 / 16
Testing Alpgen + Herwig + MLM Matching[Extras]
[MLM results]
ptptpt of Z-boson
10-2
10-1
1
10
102
103
104
200 300 400 500 600 700 800 900 1000
dσ/d
p t,Z
[fb
/ 100
GeV
]
pt,Z [GeV]
pp, 14 TeV
LO
NLO
Alpgen+HW6 Z+jet
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 20 / 16
Testing Alpgen + Herwig + MLM Matching[Extras]
[MLM results]
ptptpt of Z-boson
10-2
10-1
1
10
102
103
104
200 300 400 500 600 700 800 900 1000
dσ/d
p t,Z
[fb
/ 100
GeV
]
pt,Z [GeV]
pp, 14 TeV
LO
NLO
Alpgen+HW6 Z+jet
Alpgen+HW6 Z+jet/Z+2jets
All predictions similarand stable
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 20 / 16
Testing Alpgen + Herwig + MLM Matching[Extras]
[MLM results]
ptptpt of jet 1
10-2
10-1
1
10
102
103
104
200 300 400 500 600 700 800 900 1000
dσ/d
p t,j1
[fb
/ 100
GeV
]
pt,j1 [GeV]
pp, 14 TeV
LO
NLO
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 20 / 16
Testing Alpgen + Herwig + MLM Matching[Extras]
[MLM results]
ptptpt of jet 1
10-2
10-1
1
10
102
103
104
200 300 400 500 600 700 800 900 1000
dσ/d
p t,j1
[fb
/ 100
GeV
]
pt,j1 [GeV]
pp, 14 TeV
LO
NLO
Alpgen+HW6 Z+jet
Showered Z+j ≃ LO
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 20 / 16
Testing Alpgen + Herwig + MLM Matching[Extras]
[MLM results]
ptptpt of jet 1
10-2
10-1
1
10
102
103
104
200 300 400 500 600 700 800 900 1000
dσ/d
p t,j1
[fb
/ 100
GeV
]
pt,j1 [GeV]
pp, 14 TeV
LO
NLO
Alpgen+HW6 Z+jet
Alpgen+HW6 Z+jet/Z+2jets
Showered Z+j ≃ LO
Showered Z+j/Z+2j≃ NLO
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 20 / 16
Testing Alpgen + Herwig + MLM Matching[Extras]
[MLM results]
HT, jets =∑
jets pt,jHT, jets =∑
jets pt,jHT, jets =∑
jets pt,j
10-2
10-1
1
10
102
103
104
200 300 400 500 600 700 800 900 1000
dσ/d
HT
,jets
[fb
/ 100
GeV
]
HT,jets [GeV]
pp, 14 TeV
LO
NLO
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 20 / 16
Testing Alpgen + Herwig + MLM Matching[Extras]
[MLM results]
HT, jets =∑
jets pt,jHT, jets =∑
jets pt,jHT, jets =∑
jets pt,j
10-2
10-1
1
10
102
103
104
200 300 400 500 600 700 800 900 1000
dσ/d
HT
,jets
[fb
/ 100
GeV
]
HT,jets [GeV]
pp, 14 TeV
LO
NLO
Alpgen+HW6 Z+jet
Showered Z+j 6= LO
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 20 / 16
Testing Alpgen + Herwig + MLM Matching[Extras]
[MLM results]
HT, jets =∑
jets pt,jHT, jets =∑
jets pt,jHT, jets =∑
jets pt,j
10-2
10-1
1
10
102
103
104
200 300 400 500 600 700 800 900 1000
dσ/d
HT
,jets
[fb
/ 100
GeV
]
HT,jets [GeV]
pp, 14 TeV
LO
NLO
Alpgen+HW6 Z+jet
Alpgen+HW6 Z+jet/Z+2jets
Showered Z+j 6= LO
Showered Z+j/Z+2j≃ NLO
G. Salam (CERN/Princeton/LPTHE) Giant K -factors 2011-02-02 20 / 16