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Colloquium PSI, Mai 2009
Precision calculations for LHC physics
Michael Kramer (RWTH Aachen)
Sponsored by:
SFB/TR 9 “Computational Particle Physics”, Helmholtz Alliance “Physics at the Terascale”, BMBF-
Theorie-Verbund, Marie Curie Research Training Network “Heptools”, Graduiertenkolleg “Elemen-
tarteilchenphysik an der TeV-Skala”page 1
Why precision calculations for LHC physics?
We do not need theory input for LHC discoveries
8000
6000
4000
2000
080 100 120 140
mγγ (GeV)
Higgs signal
Eve
nts
/ 500
MeV
for
105
pb-
1
HSM γγ
Simulated 2γ mass plotfor 105 pb-1 mH =130 GeV
in the lead tungstate calorimeter
D_D
_105
5c
CMS, 105 pb-1
but only if we see a resonance. . .
page 2
Why precision calculations for LHC physics?
We do not need theory input for LHC discoveries
8000
6000
4000
2000
080 100 120 140
mγγ (GeV)
Higgs signal
Eve
nts
/ 500
MeV
for
105
pb-
1
HSM γγ
Simulated 2γ mass plotfor 105 pb-1 mH =130 GeV
in the lead tungstate calorimeter
D_D
_105
5c
CMS, 105 pb-1
but only if we see a resonance. . .
page 2
Contents
Why precision calculations for LHC physics?
– lessons from the past
– prospects: Higgs & BSM searches
Theoretical tools for LHC phenomenology
– (N)NLO multi-leg calculations
– matching with parton showers & hadronization
page 3
Contents
Why precision calculations for LHC physics?
– lessons from the past
– prospects: Higgs & BSM searches
Theoretical tools for LHC phenomenology
talking about theoretical tools at PSI:
carrying coals to Newcastle. . .
page 4
Contents
Why precision calculations for LHC physics?
– lessons from the past
– prospects: Higgs & BSM searches
page 5
Why precision calculations for LHC physics?
Tevatron jet cross section at large ET
Et (GeV)
-0.5
0
0.5
1
(Dat
a -
The
ory)
/ The
ory
200 300 40010050
CTEQ3MCDF (Preliminary) * 1.03D0 (Preliminary) * 1.01
page 6
Why precision calculations for LHC physics?
Tevatron jet cross section at large ET
Et (GeV)
-0.5
0
0.5
1
(Dat
a -
The
ory)
/ The
ory
200 300 40010050
CTEQ3MCDF (Preliminary) * 1.03D0 (Preliminary) * 1.01
⇒ new physics? + ?
page 7
Why precision calculations for LHC physics?
Tevatron jet cross section at large ET
Et (GeV)
-0.5
0
0.5
1
(Dat
a -
The
ory)
/ The
ory
200 300 40010050
CTEQ3MCDF (Preliminary) * 1.03D0 (Preliminary) * 1.01
LBSM ⊇g2
M2ψγµψ ψγµψ ⇒
data − theory
theory∝ g2 E
2T
M2
page 8
Why precision calculations for LHC physics?
Tevatron jet cross section at large ET
(GeV)TInclusive Jet E0 100 200 300 400 500 600
(n
b/G
eV)
η d
T /
dE
σ2d
10-8
10-7
10-6
10-5
10-4
10-3
10-2
10-1
1
10
102
CDF Run II Preliminary
Integrated L = 85 pb-1
0.1 < |ηDet| < 0.7
JetClu Cone R = 0.7
Run II Data
CTEQ 6.1 Uncertainty
+/- 5% Energy Scale Uncertainty
⇒ just QCD. . . (uncertainty in gluon pdf at large x)
page 9
Why precision calculations for LHC physics?
Tevatron bottom quark cross section
[D0, PLB 487 (2000)]
⇒ new physics?
page 10
Why precision calculations for LHC physics?
Tevatron bottom quark cross section
[Berger et al., PRL 86 (2001)]
10-1
1
10
10 2
10 3
10 4
10 5
10 102
Sum
QCD
g → b~
D0 Data
CDF Data
√S = 1.8 TeV
mg = 14 GeV
mb = 3.5 GeV
mb = 4.75 GeV
~
~
pT (GeV)min
σ b(p T
≥ p
T )
(nb
)m
in
⇒ light gluino/sbottom production?
page 11
Why precision calculations for LHC physics?
Tevatron bottom quark cross section
[Mangano, AIP Conf.Proc, 2005]
⇒ just QCD. . . (αs, low-x gluon pdf, b→ B fragmentation & exp. analyses)
page 12
Why precision calculations for LHC physics?
Signals of discovery include
– mass peaks
– anomalous shapes of kinematic distributions
e.g. jet production at large ET
– excess of events after kinematic selection
e.g. bottom cross section
page 13
Why precision calculations for LHC physics?
Signals of discovery include
– mass peaks
– anomalous shapes of kinematic distributionse.g. jet production at large ET
– excess of events after kinematic selectione.g. bottom cross section
page 13
Why precision calculations for LHC physics?
Signals of discovery include
– mass peakse.g. Higgs searches in H → γγ/ZZ∗ final states
– anomalous shapes of kinematic distributionse.g. SUSY searches in multijet + ET,miss final states
– excess of events after kinematic selectione.g. Higgs searches in H → WW ∗ final states
Experiments measure multi-parton final states in restricted phase space region
→ Need flexible and realistic precision calculations
precise → including loops & many legs
flexible → allowing for exclusive cross sections & phase space cuts
realistic → matched with parton showers and hadronization
page 14
Why precision calculations for LHC physics?
Signals of discovery include
– mass peakse.g. Higgs searches in H → γγ/ZZ∗ final states
– anomalous shapes of kinematic distributionse.g. SUSY searches in multijet + ET,miss final states
– excess of events after kinematic selectione.g. Higgs searches in H → WW ∗ final states
Experiments measure multi-parton final states in restricted phase space region
→ Need flexible and realistic precision calculations
precise → including loops & many legs
flexible → allowing for exclusive cross sections & phase space cuts
realistic → matched with parton showers and hadronization
page 14
Searches at the LHC: outline
Examples from Higgs physics
– discovery from excess of events: pp→ H → WW
pp→ ttH→ be aware of backgrounds. . .
Examples from beyond the standard model physics:
BSM searches with multi-jet + ET,miss signatures
– no excess over SM expectations
→ exclude models / set limits on model parameters
– excess in inclusive jets + ET,miss signal (early LHC phase)
→ discriminate BSM models
– exploring BSM models (later LHC phase)
→ determine masses & spins
page 15
Searches at the LHC: outline
Examples from Higgs physics
– discovery from excess of events: pp→ H → WW
pp→ ttH→ be aware of backgrounds. . .
Examples from beyond the standard model physics:
BSM searches with multi-jet + ET,miss signatures
– no excess over SM expectations
→ exclude models / set limits on model parameters
– excess in inclusive jets + ET,miss signal (early LHC phase)
→ discriminate BSM models
– exploring BSM models (later LHC phase)
→ determine masses & spins
page 15
Higgs searches at the LHC: be aware of backgrounds
pp→ H → WW
• pp→ ttH
page 16
Higgs searches at the LHC: pp → H → WW ∗→ l+νl−ν
g
g
H
W−
W+
ν
l−
l+
ν
– neutrinos in final state
→ no invariant Higgs mass peak
– large background from QCD
process qq → WW
– exploit lepton rapidity distributions
and angular correlations to sup-
press background(Dittmar, Dreiner) 0
100
200
300
0 50 100 150 200 250
mT (GeV)
Eve
nts
/ 5 G
eV
page 17
Higgs searches at the LHC: pp → H → WW ∗→ l+νl−ν
LO background from qq scattering
������
���
���
� � ��
� �
�����
���
���
� � ��
experimental selection cuts may enhance the importance of higher-order
corrections for background processes: gg → WW → lν l′ν ′
[Binoth, Ciccolini, Kauer, MK; Duhrssen, Jakobs, van der Bij, Marquard]
W−
W+
γ, Z
ν
`
W+γ, Z, H
g
gq
q
q
g
gq
q
q
g
gd
d u
W−d
W+
ν ′
¯′
`
ν
`
ν
ν ′
¯′
ν ′
¯′
→ formally NNLO
→ but enhanced by Higgs search cuts
qq (NLO) gg corr.
σtot 1373 fb 54 fb 4%
σbkg 4.8 fb 1.39 fb 30%
page 18
Higgs searches at the LHC: pp → H → WW ∗→ l+νl−ν
LO background from qq scattering
������
���
���
� � ��
� �
�����
���
���
� � ��
experimental selection cuts may enhance the importance of higher-order
corrections for background processes:
gg → WW → lν l′ν ′
[Binoth, Ciccolini, Kauer, MK; Duhrssen, Jakobs, van der Bij, Marquard]
W−
W+
γ, Z
ν
`
W+γ, Z, H
g
gq
q
q
g
gq
q
q
g
gd
d u
W−d
W+
ν ′
¯′
`
ν
`
ν
ν ′
¯′
ν ′
¯′
→ formally NNLO
→ but enhanced by Higgs search cuts
qq (NLO) gg corr.
σtot 1373 fb 54 fb 4%
σbkg 4.8 fb 1.39 fb 30%
page 18
Higgs searches at the LHC: pp → H → WW ∗→ l+νl−ν
LO background from qq scattering
������
���
���
� � ��
� �
�����
���
���
� � ��
experimental selection cuts may enhance the importance of higher-order
corrections for background processes: gg → WW → lν l′ν ′
[Binoth, Ciccolini, Kauer, MK; Duhrssen, Jakobs, van der Bij, Marquard]
W−
W+
γ, Z
ν
`
W+γ, Z, H
g
gq
q
q
g
gq
q
q
g
gd
d u
W−d
W+
ν ′
¯′
`
ν
`
ν
ν ′
¯′
ν ′
¯′
→ formally NNLO
→ but enhanced by Higgs search cuts
qq (NLO) gg corr.
σtot 1373 fb 54 fb 4%
σbkg 4.8 fb 1.39 fb 30%
page 18
Higgs searches at the LHC: pp → H → WW ∗→ l+νl−ν
LO background from qq scattering
������
���
���
� � ��
� �
�����
���
���
� � ��
experimental selection cuts may enhance the importance of higher-order
corrections for background processes: gg → WW → lν l′ν ′
[Binoth, Ciccolini, Kauer, MK; Duhrssen, Jakobs, van der Bij, Marquard]
W−
W+
γ, Z
ν
`
W+γ, Z, H
g
gq
q
q
g
gq
q
q
g
gd
d u
W−d
W+
ν ′
¯′
`
ν
`
ν
ν ′
¯′
ν ′
¯′
→ formally NNLO
→ but enhanced by Higgs search cuts
qq (NLO) gg corr.
σtot 1373 fb 54 fb 4%
σbkg 4.8 fb 1.39 fb 30%
page 18
Higgs searches at the LHC: be aware of backgrounds
• pp→ H → WW
pp→ ttH
page 19
Higgs searches at the LHC: pp → ttH(→ bb)
g
g
H0t–,t
t
t–
b
b–
b
b–
W+
W-
q
q–'
l
ν–
+ ...
– small cross section: σ(ttH)/σ(H + X) ≈ 1/100
→ only relevant for MH ∼< 140 GeV
– distinctive final state: pp → t(→ W+b) t(→ W−b) H(→ bb)
– cross section ∝ g2ttH
→ unique way to measure top-Higgs Yukawa coupling
page 20
Higgs searches at the LHC: pp → ttH(→ bb)
theoretical uncertainty of signal ≈ 20% at NLO
[Beenakker, Dittmaier, MK, Plumper, Spira, Zerwas]
σ(pp → tt_ H + X) [fb]
√s = 14 TeV
MH = 120 GeV
µ0 = mt + MH/2
NLO
LO
µ/µ0
0.2 0.5 1 2 5200
400
600
800
1000
1200
1400
1
page 21
Higgs searches at the LHC: pp → ttH(→ bb)
invariant mass spectrum
[CMS (Benedetti et al.)]
Note N233
b-likelihood cut
0 0.1 0.2 0.3 0.4 0.5
b-likelihood cut
0 0.1 0.2 0.3 0.4 0.5
BS
/
0
0.5
1
1.5
2
2.5
3
= 115 GeVHm
= 120 GeVHm
= 130 GeVHm
b-likelihood cut
0 0.1 0.2 0.3 0.4 0.5
b-likelihood cut
0 0.1 0.2 0.3 0.4 0.5
S/B
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
Figure 8. Significance (left) and purity (right), prior to inclusion of systematic uncertainties, for
three different Higgs boson masses (115, 120 and 130 GeV/c2) as a function of the cut on the
b-tagging likelihood LbTag, for an integrated luminosity of 60 fb−1 for the semi-leptonic (muon
and electron) ttH decay channel. No mass window requirement has been applied. The error bars
indicate the statistical error due to the finite sizes of datasets. Bin-to-bin correlations also occur
here because of the sliding cut on the b-tagging likelihood.
]2Higgs mass [GeV/c
0 50 100 150 200 250 300 350
2#
eve
nts
pe
r 2
0 G
eV
/c
0
5
10
15
20
25
]2Higgs mass [GeV/c
0 50 100 150 200 250 300 350
2#
eve
nts
pe
r 2
0 G
eV
/c
0
50
100
150
200
250
300
350ttH 115ttNj
ttbb
ttZ
Figure 9. Invariant Higgs boson mass spectrum for an LbTag cut of 0.225 and mH = 115 GeV/c2,
after an integrated luminosity of 60 fb−1. Only signal events are shown at left. The combinatorial
background is shaded grey. The plot at the right adds all relevant physical backgrounds (ttZ, ttbb
and ttN j) to the ttH signal (including the combinatorial background). The contributions from all
sources are stacked on top of each other.
physical backgrounds (ttZ, ttbb and ttN j) and the ttH signal stacked on top of each other.
Due to the limited amount of available Monte Carlo statistics for the ttN j background and the
large scale factors that have to be applied to the remaining events, the statistical fluctuations
in figure 9 are large.
The preselection and selection efficiencies, together with the corresponding numbers of
expected events and signal significances, prior to consideration of systematic uncertainties,
are reported in table 4 for the channel with a muon or an electron in the final state. The table
presents results for two working points: a ‘loose’ working point, which optimizes S/√
B, and
a ‘tight’ working point, which optimizes the purity S/B.
Thus far, no mass window requirement has been used. If one applies the requirement
mH < 150 GeV/c2, the purity can be increased by about 10%, while the significance does
not change appreciably. This improvement is very minor because the shape of the Higgs
⇒ similar shapes for signal and background (tt + n jets, ttbb, ttZ)
→ counting experiment
→ precise knowledge of event rates required
page 22
Higgs searches at the LHC: pp → ttH(→ bb)
need to know backgrounds much better than 10%!
[CMS (Benedetti et al.)]
→ try to determine reducible backgrounds from data
→ need accurate theory to extrapolate into signal region
page 23
Higgs searches at the LHC: pp → ttH(→ bb)
pp→ ttbb+X at NLO [Bredenstein, Denner, Dittmaier, Pozzorini ’09]
NLOLO
σ [fb]
µ0/2 < µ < 2µ0
mt = 172.6 GeV
pp→ ttbb + X
mbb, cut
[GeV]
20018016014012010080604020
10000
1000
100
10
page 24
Searches at the LHC: outline
• Examples from Higgs physics
– discovery from excess of events: pp→ H → WW
pp→ ttH→ be aware of backgrounds. . .
Examples from beyond the standard model physics:
BSM searches with multi-jets + ET,miss signatures
– no excess over SM expectations
→ exclude models / set limits on model parameters
– excess in inclusive jets + ET,miss signal (early LHC phase)
→ discriminate BSM models
– exploring BSM models (later LHC phase)
→ determine masses & spins
page 25
BSM searches at the LHC
Many model for new physics are addressing two problems:
– the hierarchy/naturalness problem
– the origin of dark matter
→ spectrum of new particles at the TeV-scale with weakly interacting & stable particle
→ generic BSM signature at the LHC involves cascade decays with missing energy,
eg. supersymmetry
D_D
_204
7.c.
1
q
q
q
q
q~
~
~
~
—
—
—b
b
l+
l+
g
~g
W— W+t
t
t1
ν
χ1
~χ10
~χ20
Gluino/squark production event topology al lowing sparticle mass reconstruction
3 isolated leptons+ 2 b-jets+ 4 jets
+ Etmiss
~l
+
l-
Such cascade decays allow to reconstructsleptons, neutralinos, squarks, gluinos...in favorable cases with %level mass resolutions
page 26
BSM searches at the LHC
Many model for new physics are addressing two problems:
– the hierarchy/naturalness problem
– the origin of dark matter
→ spectrum of new particles at the TeV-scale with weakly interacting & stable particle
→ generic BSM signature at the LHC involves cascade decays with missing energy,
eg. supersymmetry
D_D
_204
7.c.
1
q
q
q
q
q~
~
~
~
—
—
—b
b
l+
l+
g
~g
W— W+t
t
t1
ν
χ1
~χ10
~χ20
Gluino/squark production event topology al lowing sparticle mass reconstruction
3 isolated leptons+ 2 b-jets+ 4 jets
+ Etmiss
~l
+
l-
Such cascade decays allow to reconstructsleptons, neutralinos, squarks, gluinos...in favorable cases with %level mass resolutions
page 26
BSM searches at the LHC
• simple discriminant for SUSY
searches: effective mass
Meff = ET,miss +∑4
i=1 pjetT
• excess of events with large Meff
→ initial discovery of SUSY
LHC Point 5
10-13
10-12
10-11
10-10
10-9
10-8
10-7
0 1000 2000 3000 4000Meff (GeV)
dσ/d
Mef
f (m
b/40
0 G
eV)
page 27
BSM searches at the LHC
• simple discriminant for SUSY
searches: effective mass
Meff = ET,miss +∑4
i=1 pjetT
• excess of events with large Meff
→ initial discovery of SUSY
Modern LO Monte Carlo tools predict much larger multi-jet background
What will disagreement between Monte Carlo and data mean?
→ Need precision NLO calculations to tell!
page 28
BSM searches at the LHC
• simple discriminant for SUSY
searches: effective mass
Meff = ET,miss +∑4
i=1 pjetT
• excess of events with large Meff
→ initial discovery of SUSY
Modern LO Monte Carlo tools predict much larger multi-jet background
What will disagreement between Monte Carlo and data mean?
→ Need precision NLO calculations to tell!
page 28
Precision calculations for BSM physics at the LHC
no excess over SM expectations
→ exclude models / set limits on model parameters
excess in inclusive jets + ET,miss signal (early LHC phase)
→ discriminate BSM models
exploring BSM models (later LHC phase)
→ determine masses & spins
page 29
Precision calculations for BSM physics at the LHC
no excess over SM expectations
→ exclude models / set limits on model parameters
)2
(GeV/cg~
M0 100 200 300 400 500 600
)2 (
GeV
/cq~
M
0
100
200
300
400
500
600CDF Run II Preliminary -1L=2.0 fb
no mSUGRAsolution
LEP 1 + 2
UA
1
UA
2
FNAL Run I
g~
= M
q~M
)2
(GeV/cg~
M0 100 200 300 400 500 600
)2 (
GeV
/cq~
M
0
100
200
300
400
500
600observed limit 95% C.L.
expected limit
<0µ=5, β=0, tan0A
Theoretical uncertainties includedin the calculation of the limit
page 30
Precision calculations for BSM physics at the LHC
no excess over SM expectations
→ exclude models / set limits on model parameters
] 2 [GeV/cg~
M250 300 350 400 450
NL
O C
ross
Sec
tio
n [
pb
]
-210
-110
1
10 NLO: PROSPINO CTEQ6.1M
Ren.)⊕syst. uncert. (PDF observed limit 95% C.L.
expected limit 95% C.L.
q~ = M
g~M
CDF Run II PreliminaryTheoretical uncertainties not included
in the calculation of the limit
-1L=2.0 fb
page 31
Precision calculations for BSM physics at the LHC
no excess over SM expectations
→ exclude models / set limits on model parameters
Prospino: PROduction of Suspersymmetric Particles In NlO[Beenakker, Hopker, MK, Plehn, Spira, Zerwas (’95-’08)]
page 32
Precision calculations for BSM physics at the LHC
excess in inclusive jets + ET,miss signal (early LHC phase)
→ discriminate BSM models
“look-alike models” (Hubisz, Lykken, Pierini, Spiropulu)
]
2m
ass
[GeV
/c
0
100
200
300
400
500
600
700
800
900
1000LH2 NM6 NM4 CS7
HA
HWHZ
HidH
iu
0
1χ∼
±1
χ∼0
2χ∼
Rd~Lu~Ru~Ld~
g~
1τ∼ Rl~
0
1χ∼
±1
χ∼0
2χ∼
Ru~Rd~Lu~
1τ∼Ld~Rl
~
g~
0
1χ∼
1τ∼Rl~
±1
χ∼0
2χ∼
g~
Rd~ Ru~Lu~
Ld~
– Little Higgs model LH2 and
SUSY models NM4 and CS7
give same number of events
after cuts
– “twin models” LH2 and NM6
(SUSY) have different cross
sections and event counts
→ distinguish models with
same spectrum but different
spins through event count
page 33
Precision calculations for BSM physics at the LHC
excess in inclusive jets + ET,miss signal (early LHC phase)
→ discriminate BSM models
“look-alike models” (Hubisz, Lykken, Pierini, Spiropulu)
]
2m
ass
[GeV
/c
0
100
200
300
400
500
600
700
800
900
1000LH2 NM6 NM4 CS7
HA
HWHZ
HidH
iu
0
1χ∼
±1
χ∼0
2χ∼
Rd~Lu~Ru~Ld~
g~
1τ∼ Rl~
0
1χ∼
±1
χ∼0
2χ∼
Ru~Rd~Lu~
1τ∼Ld~Rl
~
g~
0
1χ∼
1τ∼Rl~
±1
χ∼0
2χ∼
g~
Rd~ Ru~Lu~
Ld~
– Little Higgs model LH2 and
SUSY models NM4 and CS7
give same number of events
after cuts
– “twin models” LH2 and NM6
(SUSY) have different cross
sections and event counts
→ distinguish models with
same spectrum but different
spins through event count
page 33
Precision calculations for BSM physics at the LHC
excess in inclusive jets + ET,miss signal (early LHC phase)
→ discriminate BSM models
“look-alike models” (Hubisz, Lykken, Pierini, Spiropulu)
]
2m
ass
[GeV
/c
0
100
200
300
400
500
600
700
800
900
1000LH2 NM6 NM4 CS7
HA
HWHZ
HidH
iu
0
1χ∼
±1
χ∼0
2χ∼
Rd~Lu~Ru~Ld~
g~
1τ∼ Rl~
0
1χ∼
±1
χ∼0
2χ∼
Ru~Rd~Lu~
1τ∼Ld~Rl
~
g~
0
1χ∼
1τ∼Rl~
±1
χ∼0
2χ∼
g~
Rd~ Ru~Lu~
Ld~
– Little Higgs model LH2 and
SUSY models NM4 and CS7
give same number of events
after cuts
– “twin models” LH2 and NM6
(SUSY) have different cross
sections and event counts
→ distinguish models with
same spectrum but different
spins through event count
page 33
Precision calculations for BSM physics at the LHC
excess in inclusive jets + ET,miss signal (early LHC phase)
→ discriminate BSM models
“ancient wisdom”: cross sections depend on spin, e.g.
q + q → q + ¯q
σLO[qq → q¯q] =α2
sπ
s
4
27β3 (β2 = 1 − 4m2/s)
c.f. top production:
σLO[qq → QQ] =α2
sπ
s
8
27
(s+ 2m2)
s2β
→ σtop/σstop ∼ 10 at the Tevatron
page 34
Precision calculations for BSM physics at the LHC
excess in inclusive jets + ET,miss signal (early LHC phase)
→ discriminate BSM models
“ancient wisdom”: cross sections depend on spin, e.g.
q + q → q + ¯q
σLO[qq → q¯q] =α2
sπ
s
4
27β3 (β2 = 1 − 4m2/s)
c.f. top production:
σLO[qq → QQ] =α2
sπ
s
8
27
(s+ 2m2)
s2β
→ σtop/σstop ∼ 10 at the Tevatron
page 34
Precision calculations for BSM physics at the LHC
excess in inclusive jets + ET,miss signal (early LHC phase)
→ discriminate BSM models
“ancient wisdom”: cross sections depend on spin
(Kane, Petrov, Shao, Wang)
160 170 180 190 200mass HGeVL
0.5
1
5
10
50
100
CrossSection
HpbL
tst�s
tt�
CDFD0
→ no production of scalar quarks (assuming same mass and couplings as top. . . )
page 35
Precision calculations for BSM physics at the LHC
excess in inclusive jets + ET,miss signal (early LHC phase)
→ discriminate BSM models
how to discriminate “look-alike models”? (Hubisz, Lykken, Pierini, Spiropulu)
(GeV/c)T
p0 100 200 300 400 500 600 700 800 900 1000
num
ber
of e
vent
s
0
200
400
600
800
1000
1200
1400– consider ratios of event counts, e.g.
σ(pT > 250, 500, . . . GeV)/σ
→ systematic uncertainties cancel
→ normalization important
– NLO affects shape of distributions:
K ≡σNLO(pp → tt)
σLO(pp → tt)
=
1.4 (pT > 100 GeV)
0.5 (pT > 1000 GeV)
→ no proper tools to perform realistic NLO analysis of BSM decay chains
page 36
Precision calculations for BSM physics at the LHC
excess in inclusive jets + ET,miss signal (early LHC phase)
→ discriminate BSM models
how to discriminate “look-alike models”? (Hubisz, Lykken, Pierini, Spiropulu)
(GeV/c)T
p0 100 200 300 400 500 600 700 800 900 1000
num
ber
of e
vent
s
0
200
400
600
800
1000
1200
1400– consider ratios of event counts, e.g.
σ(pT > 250, 500, . . . GeV)/σ
→ systematic uncertainties cancel
→ normalization important
– NLO affects shape of distributions:
K ≡σNLO(pp → tt)
σLO(pp → tt)
=
1.4 (pT > 100 GeV)
0.5 (pT > 1000 GeV)
→ no proper tools to perform realistic NLO analysis of BSM decay chains
page 36
Precision calculations for BSM physics at the LHC
excess in inclusive jets + ET,miss signal (early LHC phase)
→ discriminate BSM models
how to discriminate “look-alike models”? (Hubisz, Lykken, Pierini, Spiropulu)
(GeV/c)T
p0 100 200 300 400 500 600 700 800 900 1000
num
ber
of e
vent
s
0
200
400
600
800
1000
1200
1400– consider ratios of event counts, e.g.
σ(pT > 250, 500, . . . GeV)/σ
→ systematic uncertainties cancel
→ normalization important
– NLO affects shape of distributions:
K ≡σNLO(pp → tt)
σLO(pp → tt)
=
1.4 (pT > 100 GeV)
0.5 (pT > 1000 GeV)
→ no proper tools to perform realistic NLO analysis of BSM decay chains
page 36
Precision calculations for BSM physics at the LHC
exploring BSM models (later LHC phase)
→ determine masses & spins
Mass measurements from cascade decays, e.g.�
�
��� � �� �
�� �
��
�
���� �
��� �� �
Allanach et al.
0
500
1000
1500
0 20 40 60 80 100 m(ll) (GeV)
Eve
nts/
1 G
eV/1
00 fb
-1→ kinematic endpoint (mmax
ll )2 = (m2χ0
2
−m2
lR)(m2
lR−m2
χ01
)/(m2
lR)
sensitive to mass differences
page 37
Precision calculations for BSM physics at the LHC
exploring BSM models (later LHC phase)
→ determine masses & spins
Mass measurements from total rate, e.g. gluino mass in SUSY models with heavy
scalars (FP dark matter scenarios)
LO
NLO
σ(pp→ gg + X) [pb]
mg[GeV]
140012001000800600
10
1
0.1
0.01
0.001
mgluino =
{785 ± 35 (LO)
870 ± 15 (NLO)
page 38
Precision calculations for BSM physics at the LHC
exploring BSM models (later LHC phase)
→ determine masses & spins
Mass measurements from total rate, e.g. gluino mass in SUSY models with heavy
scalars (FP dark matter scenarios)
(Baer, Barger, Shaunghnessy, Summy, Wang)
1000 1500 2000m
g~
0
10
20
30
40
σ (f
b)
TH
100 fb-1
errorTH ±15%TH ±15% ±100%BGBG
LE
P2
exc
lud
ed → ∆mgluino = ±8%
page 39
Precision calculations for BSM physics at the LHC
exploring BSM models (later LHC phase)
→ determine masses & spins
qL
qL
lR-
χ20
lR+ (near)
lR- (far)
χ10
no spin correlations:
0
0.5
1
1.5
2
0 50 100 150 200 250 300
tree unpol. dσ/dmql+near
mql+near[GeV]
page 40
Precision calculations for BSM physics at the LHC
exploring BSM models (later LHC phase)
→ determine masses & spins
qL
qL
lR-
χ20
lR+ (near)
lR- (far)
χ10
with spin correlations:
0
0.5
1
1.5
2
0 50 100 150 200 250 300
tree pol.tree unpol
dσ/dmql+near
mql+near[GeV]
cannot determine mql+neardistribution experimentally
→ consider charge asymmetry A = (dσ/dmql+−dσ/dmql−)/(dσ/dmql++dσ/dmql−)
page 41
Precision calculations for BSM physics at the LHC
exploring BSM models (later LHC phase)
→ determine masses & spins
qL
qL
lR-
χ20
lR+ (near)
lR- (far)
χ10
with spin correlations:
0
0.5
1
1.5
2
0 50 100 150 200 250 300
tree pol.tree unpol
dσ/dmql+near
mql+near[GeV]
cannot determine mql+neardistribution experimentally
→ consider charge asymmetry A = (dσ/dmql+−dσ/dmql−)/(dσ/dmql++dσ/dmql−)
page 41
Precision calculations for BSM physics at the LHC
exploring BSM models (later LHC phase)
→ determine masses & spins
qL
qL
lR-
χ20
lR+ (near)
lR- (far)
χ10
(Barr)
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
0 100 200 300 400 500mlq / GeV
A+-
cannot determine mql+neardistribution experimentally
→ consider charge asymmetry A = (dσ/dmql+−dσ/dmql−)/(dσ/dmql++dσ/dmql−)
page 42
Precision calculations for BSM physics at the LHC
exploring BSM models (later LHC phase)
→ determine masses & spins
qL
qL
lR-
χ20
lR+ (near)
lR- (far)
χ10
with spin correlations:
0
0.5
1
1.5
2
0 50 100 150 200 250 300
tree pol.tree unpol
dσ/dmql+near
mql+near[GeV]
page 43
Precision calculations for BSM physics at the LHC
exploring BSM models (later LHC phase)
→ determine masses & spins
qL
qL
lR-
χ20
lR+ (near)
lR- (far)
χ10
with spin correlations @ NLO:
0
0.5
1
1.5
2
0 50 100 150 200 250 300
tree pol.tree unpolNLO pol
dσ/dmql+near
mql+near[GeV]
→ radiative corrections affect shape of distributions (Horsky, MK, Muck, Zerwas)
page 44
Precision calculations for BSM physics at the LHC
exploring BSM models (later LHC phase)
→ determine masses & spins
qL
qL
lR-
χ20
lR+ (near)
lR- (far)
χ10
(Horsky, MK, Muck, Zerwas)
A (NLO)A (Born)
Mql
350300250200150100500
1
0.5
0
−0.5
−1
consider charge asymmetry A = (dσ/dmql+ − dσ/dmql−)/(dσ/dmql+ + dσ/dmql−)
→ radiative corrections cancel in charge asymmetry
page 45
Precision calculations for BSM physics at the LHC
exploring BSM models (later LHC phase)
→ determine masses & spins
consider invariant jet-mass distributions in decay chains like
pp→ g + g → qqR + qqL → qqχ01 + qqχ0
2
g
g
q
q
q
q
→ information on gluino spin in jet event shapes (MK, Popenda, Spira, Zerwas)
page 46
Precision calculations for BSM physics at the LHC
exploring BSM models (later LHC phase)
→ determine masses & spins
consider invariant jet-mass distributions in decay chains like
pp→ g + g → qqR + qqL → qqχ01 + qqχ0
2
uRuL :< Mjet >= 102 GeVuRuR :< Mjet >= 116 GeV
without spin correlations: < Mjet >= 116 GeV
with the lowest pT
Mjet calulated from the two jets
mχ1/2= 98/184 GeV
muR/L= 547/565 GeV
mg = 607 GeVSPS1a’:
1/σtot dσ/dMjet (g(→ uu(→ uχ))g(→ uu(→ uχ)) [1/GeV]
Mjet[GeV]
5004003002001000
0.01
0.009
0.008
0.007
0.006
0.005
0.004
0.003
0.002
0.001
→ information on gluino spin in jet event shapes (MK, Popenda, Spira, Zerwas)
page 47
Precision calculations for BSM physics at the LHC
exploring BSM models (later LHC phase)
→ determine masses & spins . . . or the number of extra dimensions?
consider graviton production in ADD scenarios (Arkani-Hamed, Dimopoulos, Dvali)
pp→ G+ jet → monojet signature
10−7
10−6
10−5
10−4
10−3
10−2
10−1
100
101
� � � � � � � � � � � � � � � �
pmissT ��� � �
dσ
dpmiss
T
[pb/GeV]
Z + jet
� �� �� � � � � �� �
δ = 3, Ms = 5TeVδ = 4, Ms = 5TeVδ = 5, Ms = 5TeV
→ determine number of extra dimensions δ?page 48
Precision calculations for BSM physics at the LHC
exploring BSM models (later LHC phase)
→ determine masses & spins . . . or the number of extra dimensions?
consider graviton production in ADD scenarios (Arkani-Hamed, Dimopoulos, Dvali)
pp→ G+ jet → monojet signature
10−7
10−6
10−5
10−4
10−3
10−2
10−1
100
101
� � � � � � � � � � � � � � � �
pmissT ��� � �
dσ
dpmiss
T
[pb/GeV]
Z + jet
� �� �� � � � � �� �
δ = 3, Ms = 5TeVδ = 4, Ms = 5TeVδ = 5, Ms = 5TeV
→ spoiled by QCD uncertainties. . .page 49
Precision calculations for BSM physics at the LHC
exploring BSM models (later LHC phase)
→ determine masses & spins . . . or the number of extra dimensions?
consider graviton production in ADD scenarios (Arkani-Hamed, Dimopoulos, Dvali)
pp→ G+ jet → monojet signature
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 200 400 600 800 100012001400160018002000
pT,miss
1
2
3
500 1000 1500
LO
NLO
→ include NLO-QCD corrections (Karg, MK, Li, Zeppenfeld, prelim.)
page 50
Precision calculations for BSM physics at the LHC
exploring BSM models (later LHC phase)
→ determine masses & spins . . . or the number of extra dimensions?
consider graviton production in ADD scenarios (Arkani-Hamed, Dimopoulos, Dvali)
pp→ G+ jet → monojet signature
0
0.5
1
1.5
2
2.5
3
0.1 1 10µ/µ0
σ(µ)/σ(µ0 = pT,miss)
PP → G + jet
(δ = 4, Ms = 4TeV)
LONLO
→ include NLO-QCD corrections (Karg, MK, Li, Zeppenfeld, prelim.)
page 51
Progress in SUSY precision calculations at the LHC
Sparticle production cross sections
– NLO QCD → Prospino: Beenakker, Hopker, MK, Plehn, Spira, Zerwas
(cf. Baer, Hall, Reno; Berger, Klasen, Tait)
– threshold summation for Mq , Mg∼
> 1 TeV
(Bozzi, Fuks, Klasen; Kulesza, Motyka; Langenfeld, Moch;
Beenakker, Brensing, MK, Kulesza, Laenen, Niessen)
– electroweak corrections(Hollik, Kollar, Mirabella, Trenkel; Bornhauser, Drees, Dreiner, Kim;
Beccaria, Macorini, Panizzi, Renard, Verzegnassi)
– beyond MSSM: NLO QCD for RPV SUSY(Debajyoti Choudhury, Swapan Majhi, V. Ravindran; Yang, Li, Liu, Li; Dreiner, Grab, MK, Trenkel)
Sparticle decays
– total rates → Sdecay: (Muhlleitner, Djouadi, Mambrini) plus work by many authors. . . ...
– only few results for shapes (Drees, Hollik, Xu; Horsky, MK, Muck, Zerwas)
Sparticle production ⊕ decay: generic BSM cascades (SUSY, UEDs, LH,. . . )
– so far only tree level → challenge for LHC theory community. . .
page 52
Progress in SUSY precision calculations at the LHC
Sparticle production cross sections
– NLO QCD → Prospino: Beenakker, Hopker, MK, Plehn, Spira, Zerwas
(cf. Baer, Hall, Reno; Berger, Klasen, Tait)
– threshold summation for Mq , Mg∼
> 1 TeV
(Bozzi, Fuks, Klasen; Kulesza, Motyka; Langenfeld, Moch;
Beenakker, Brensing, MK, Kulesza, Laenen, Niessen)
– electroweak corrections(Hollik, Kollar, Mirabella, Trenkel; Bornhauser, Drees, Dreiner, Kim;
Beccaria, Macorini, Panizzi, Renard, Verzegnassi)
– beyond MSSM: NLO QCD for RPV SUSY(Debajyoti Choudhury, Swapan Majhi, V. Ravindran; Yang, Li, Liu, Li; Dreiner, Grab, MK, Trenkel)
Sparticle decays
– total rates → Sdecay: (Muhlleitner, Djouadi, Mambrini) plus work by many authors. . . ...
– only few results for shapes (Drees, Hollik, Xu; Horsky, MK, Muck, Zerwas)
Sparticle production ⊕ decay: generic BSM cascades (SUSY, UEDs, LH,. . . )
– so far only tree level → challenge for LHC theory community. . .
page 52
Progress in SUSY precision calculations at the LHC
Sparticle production cross sections
– NLO QCD → Prospino: Beenakker, Hopker, MK, Plehn, Spira, Zerwas
(cf. Baer, Hall, Reno; Berger, Klasen, Tait)
– threshold summation for Mq , Mg∼
> 1 TeV
(Bozzi, Fuks, Klasen; Kulesza, Motyka; Langenfeld, Moch;
Beenakker, Brensing, MK, Kulesza, Laenen, Niessen)
– electroweak corrections(Hollik, Kollar, Mirabella, Trenkel; Bornhauser, Drees, Dreiner, Kim;
Beccaria, Macorini, Panizzi, Renard, Verzegnassi)
– beyond MSSM: NLO QCD for RPV SUSY(Debajyoti Choudhury, Swapan Majhi, V. Ravindran; Yang, Li, Liu, Li; Dreiner, Grab, MK, Trenkel)
Sparticle decays
– total rates → Sdecay: (Muhlleitner, Djouadi, Mambrini) plus work by many authors. . . ...
– only few results for shapes (Drees, Hollik, Xu; Horsky, MK, Muck, Zerwas)
Sparticle production ⊕ decay: generic BSM cascades (SUSY, UEDs, LH,. . . )
– so far only tree level → challenge for LHC theory community. . .
page 52
Precision calculations at the LHC: conclusions & outlook . . .
Signal cross sections in the SM and MSSM are (or will rather soon be) known at
NLO accuracy
– theoretical uncertainty ≈ 15% for inclusive cross sections
– larger uncertainty for exclusive observables
– can predict distributions and observables with cuts
– in general no parton showers/hadronization
Progress in matching NLO calculations with parton showers and hadronization
EWK corrections: important for high accuracy or scales �MW,Z
Many backgrounds (multi-leg processes) are only know at LO
(Need breakthrough in techniques to do pp→> 4 partons at NLO?)
First LHC data will allow us to focus on the relevant processes. . .
page 53
Precision calculations at the LHC: conclusions & outlook . . .
Signal cross sections in the SM and MSSM are (or will rather soon be) known at
NLO accuracy
– theoretical uncertainty ≈ 15% for inclusive cross sections
– larger uncertainty for exclusive observables
– can predict distributions and observables with cuts
– in general no parton showers/hadronization
Progress in matching NLO calculations with parton showers and hadronization
EWK corrections: important for high accuracy or scales �MW,Z
Many backgrounds (multi-leg processes) are only know at LO
(Need breakthrough in techniques to do pp→> 4 partons at NLO?)
First LHC data will allow us to focus on the relevant processes. . .
page 53
Precision calculations at the LHC: conclusions & outlook . . .
Signal cross sections in the SM and MSSM are (or will rather soon be) known at
NLO accuracy
– theoretical uncertainty ≈ 15% for inclusive cross sections
– larger uncertainty for exclusive observables
– can predict distributions and observables with cuts
– in general no parton showers/hadronization
Progress in matching NLO calculations with parton showers and hadronization
EWK corrections: important for high accuracy or scales �MW,Z
Many backgrounds (multi-leg processes) are only know at LO
(Need breakthrough in techniques to do pp→> 4 partons at NLO?)
First LHC data will allow us to focus on the relevant processes. . .
page 53
Precision calculations at the LHC: conclusions & outlook . . .
Signal cross sections in the SM and MSSM are (or will rather soon be) known at
NLO accuracy
– theoretical uncertainty ≈ 15% for inclusive cross sections
– larger uncertainty for exclusive observables
– can predict distributions and observables with cuts
– in general no parton showers/hadronization
Progress in matching NLO calculations with parton showers and hadronization
EWK corrections: important for high accuracy or scales �MW,Z
Many backgrounds (multi-leg processes) are only know at LO
(Need breakthrough in techniques to do pp→> 4 partons at NLO?)
First LHC data will allow us to focus on the relevant processes. . .
page 53
Precision calculations at the LHC: conclusions & outlook . . .
Signal cross sections in the SM and MSSM are (or will rather soon be) known at
NLO accuracy
– theoretical uncertainty ≈ 15% for inclusive cross sections
– larger uncertainty for exclusive observables
– can predict distributions and observables with cuts
– in general no parton showers/hadronization
Progress in matching NLO calculations with parton showers and hadronization
EWK corrections: important for high accuracy or scales �MW,Z
Many backgrounds (multi-leg processes) are only know at LO
(Need breakthrough in techniques to do pp→> 4 partons at NLO?)
First LHC data will allow us to focus on the relevant processes. . .
page 53