qcd and vector boson + jets measurements with atlas · 2015. 3. 12. · atlas kristof schmieden les...

Les Rencontres de Physique de la Vallee d‘Aoste, La Thuile, March 2015

QCD and Vector Boson + jets measurements

with ATLAS

Kristof Schmieden, on behalf of the ATLAS collaboration

Kristof Schmieden Les Rencontres de Physique de la Vallee d‘Aoste - March 2015

The Summary at the Beginning

2

pp

total

80 µb−1

JetsR=0.4

|y |<3.0

0.1 < pT < 2 TeV

DijetsR=0.4

|y |<3.0y∗<3.0

0.3 < mjj < 5 TeV

W

fiducial

35 pb−1

njet ≥ 0

njet ≥ 1

njet ≥ 2

njet ≥ 3

njet ≥ 4

njet ≥ 5

njet ≥ 6

njet ≥ 7

Z

fiducial

35 pb−1

njet ≥ 0

njet ≥ 1

njet ≥ 2

njet ≥ 3

njet ≥ 4

njet ≥ 5

njet ≥ 6

njet ≥ 7

t̄t

total

njet ≥ 0

njet ≥ 4

njet ≥ 5

njet ≥ 6

njet ≥ 7

njet ≥ 8

tt−chan

total

WW+WZtotal

WW

total

γγ

fiducial

4.9 fb−1

Wt

total

2.0 fb−1

WZ

total

13.0 fb−1

ZZ

total

t̄tγ

fiducial

1.0 fb−1

Wγ

fiducial

njet=0

Zγ

fiducial

njet=0

t̄tW

total

t̄tZ

total

95% CL

upper

limit

ZjjEWK

fiducial

H→γγ

fiducial

W±W±jj

EWK

fiducial

ts−chan

total

95% CL

upper

limit

0.7 fb−1

σ[p

b]

10−3

10−2

10−1

1

101

102

103

104

105

106

1011

LHC pp√s = 7 TeV

Theory

Data 4.5 − 4.7 fb−1

LHC pp√s = 8 TeV

Theory

Data 20.3 fb−1

Standard Model Production Cross Section Measurements Status: July 2014

ATLAS Preliminary Run 1√s = 7, 8 TeV

pp

total

80 µb−1

JetsR=0.4

|y |<3.0

0.1 < pT < 2 TeV

DijetsR=0.4

|y |<3.0y∗<3.0

0.3 < mjj < 5 TeV

W

fiducial

35 pb−1

njet ≥ 0

njet ≥ 1

njet ≥ 2

njet ≥ 3

njet ≥ 4

njet ≥ 5

njet ≥ 6

njet ≥ 7

Z

fiducial

35 pb−1

njet ≥ 0

njet ≥ 1

njet ≥ 2

njet ≥ 3

njet ≥ 4

njet ≥ 5

njet ≥ 6

njet ≥ 7

t̄t

total

njet ≥ 0

njet ≥ 4

njet ≥ 5

njet ≥ 6

njet ≥ 7

njet ≥ 8

tt−chan

total

WW+WZtotal

WW

total

γγ

fiducial

4.9 fb−1

Wt

total

2.0 fb−1

WZ

total

13.0 fb−1

ZZ

total

t̄tγ

fiducial

1.0 fb−1

Wγ

fiducial

njet=0

Zγ

fiducial

njet=0

t̄tW

total

t̄tZ

total

95% CL

upper

limit

ZjjEWK

fiducial

H→γγ

fiducial

W±W±jj

EWK

fiducial

ts−chan

total

95% CL

upper

limit

0.7 fb−1

σ[p

b]

10−3

10−2

10−1

1

101

102

103

104

105

106

1011

LHC pp√s = 7 TeV

Theory

Data 4.5 − 4.7 fb−1

LHC pp√s = 8 TeV

Theory

Data 20.3 fb−1

Standard Model Production Cross Section Measurements Status: July 2014

ATLAS Preliminary Run 1√s = 7, 8 TeV

di-Boson results: see K. Bachas and J. Gao talks on Thursday


Motivation: jets and V+jets

3

• Jet production in association with W/Z bosons is dominated by strong interactions:

• Number of jets:• Sensitive to pQCD effects → parton shower

• Jet transverse momentum• Sensitive to higher order ME, QCD & EWK!

• Angular separation and invariant mass of leading jets• Sensitive to higher order ME & pQCD effects

• Clean leptonic signature of V decay

QCD radiation

Z-boson Bremsstrahlung

Non resonant

• Jet inclusive measurement:• QCD dominated• sensitive pQCD effects PDFs, ...

jetsN

0≥ 1≥ 2≥ 3≥ 4≥

Rel

ativ

e U

ncer

tain

ty

00.05

0.10.150.2

0.250.3

0.350.4

0.450.5

)) + jets-e+ e→))/(Z(ν e→(W(Statistical UncertaintyTotal Systematic UncertaintyJetsElectronMETUnfoldingBackgrounds

ATLAS


Motivation: Ratio Measurements σ(W+jets) / σ(Z+jets)

4

• Probes kinematic differences of jet-system recoiling against W or Z

• Many uncertainties cancel!• Experimental:• Positively correlated uncertainties (Energy scales / backgrounds / Jet uncertainties)

• Prediction:• Scale & PDF uncertainties• Parton shower / hadronization

σ(W+jets) / σ(Z+jets)

jetsN

0≥ 1≥ 2≥ 3≥ 4≥ 5≥ 6≥ 7≥

Rel

ativ

e U

ncer

tain

ty

00.05

0.10.150.2

0.250.3

0.350.4

0.450.5

) + jetsν e→W(Statistical UncertaintyTotal Systematic UncertaintyJetsElectronMETUnfoldingBackgrounds

ATLAS

σ(W+jets)


• W + jets cross section (Accepted by EPJC; arXiv:1409.8639) (Sep. 2014)

• W + jets/Z + jets cross section ratio (Eur. Phys. J. C (2014) 74:3168)

• Z + b-jets cross section (JHEP10(2014)141) (Nov. 2014)

• Inclusive Jet cross section (arXiv:1410.8857) (Oct. 2014)

• Differential 3 Jet measurement (arXiv:1411.1855) (Nov. 2014)

• Z + jets cross section (JHEP 07 (2013) 032) (not discussed)

• W +b-jets cross section (JHEP 06 (2013) 084)

• W +c-jets cross section (JHEP 05 (2014) 068)

Recent ATLAS measurements

5

• All shown results are obtained using the data measured in 2011 (4.6fb-1 @ 7 TeV)

http://arxiv.org/abs/1409.8639


http://arxiv.org/abs/arXiv:1411.1855



• Several Monte Carlo generators used to calculate predictions• Alpgen:

• Multiparton LO ME generator for SM processes • Special emphasis on multijet final states: explicitly takes helicity correlations of intermediate gauge bosons and final state particles into account• PS by external program

• Sherpa• Multiparton LO ME, provides complete hadronic final states, sophisticated ME/PS merging

• BlackHat + Sherpa for PS• Evaluates QCD one-loop matrix elements for up to 4 final state jets

• HEJ• All-order summation of perturbative terms• Any number of hard jets > 2, jet rates (up to 4 jets) fully matched to tree-level accuracy.

• MEPS@NLO• Merge resumed logs from PS with fixed order ME calculation• Jets evolve with PS, cross section accurate to Born level

• NLOJET• NLO pQCD (fixed order) calculations, including hadronisation and electroweak corrections

Theory Predictions - overview of tools

6

Results for W+jets and Ratio W/Z + jets measurements

arXiv:1409.8639 &

Eur. Phys. J. C (2014) 74






















• W→lν• Exactly 1 lepton• pT > 25GeV,|η| < 2.4 / 2.47 (µ/e)

• ETmiss > 25 GeV• mT > 40 GeV

• Jets:• pT > 30 GeV• |y| < 4.4• Removed if overlapping with lepton ΔR > 0.4

Event Selection

8

• Z→ll• Exactly 2 leptons with opposite charge• pT > 20GeV, |η| < 2.4 / 2.47 (µ/e)

• ΔR(l,l) > 0.2• 66 ≤ mll ≤ 116 GeV

• Jets:• pT > 30 GeV• |y| < 4.4• Removed if overlapping with lepton ΔR > 0.4

Z+jets cross section JHEP 07 (2013) 032

Event selection:

Lepton:

Electron channel:

pT > 20 GeV,

|h | < 2.47 (excluding

1.37 < |h | < 1.52)

Muon channel:

pT > 20 GeV,

|h | < 2.4

Z ! `` criteria:

Exactly 2 OS leptons

�R(`,`) > 0.2

66 m`` 116 GeV

Jet criteria:

pT > 30 GeV

|y | < 4.4 GeV

Jet overlap removal:

�R(`, jet) > 0.5

jetN 0≥ 1≥ 2≥ 3≥ 4≥ 5≥ 6≥ 7≥

Even

ts /

bin

10

210

310

410

510

610

710 -1 L dt = 4.6 fb∫) + jets-µ+µ →*(γZ/

jets, R = 0.4,tanti-k| < 4.4jet > 30 GeV, |yjet

Tp

= 7 TeV)sData 2011 (* + jets (ALPGEN)γZ/* + jets (SHERPA)γZ/

TopElectroweakMulti-jets

ATLAS

jetN 0≥ 1≥ 2≥ 3≥ 4≥ 5≥ 6≥ 7≥

MC

/ D

ata

0.81

1.2 ALPGEN SHERPA

[GeV]µµ

Tp

0 100 200 300 400 500

>je

t<N

0.5

1

1.5

2

2.5

3

3.5-1 L dt = 4.6 fb∫

) + jets-µ+µ →*(γZ/ jets, R = 0.4,tanti-k

| < 4.4jet > 30 GeV, |yjetT

p

= 7 TeV)sData 2011 (Z+jets(ALPGEN)Z+jets(SHERPA)

ATLAS

[GeV]µµ

Tp

0 100 200 300 400 500

MC

/ D

ata

0.9

1

1.1 ALPGEN SHERPA

A. Ruiz (CERN) JVMO 2014 17 July 2014 11

jetsN0 1 2 3 4 5 6 7 8

Even

ts

10

210

310

410

510

610

710

810

910

1010 -1 = 7 TeV, 4.6 fbsData, (ALPGEN)ν e→W

ttOther

ee→ZMultijets

(SHERPA)ν e→W

Pred sysstat⊗Pred sys

ATLAS

jetsN0 1 2 3 4 5 6 7 8

Pred

/ D

ata

0.5

1

1.5

arXiv:1409.8639 & Eur. Phys. J. C (2014) 74




• BlackHat and ALPGEN give good description of data for Njets < 5

Inclusive number of jets

9

jetsN0≥ 1≥ 2≥ 3≥ 4≥ 5≥ 6≥ 7≥

) [pb

]je

ts(W

+Nσ

-210

-110

1

10

210

310

410

510

610 ATLAS jets, R=0.4,tanti-k

| < 4.4j > 30 GeV, |yjT

p

) + jetsν l→W(Data,

-1 = 7 TeV, 4.6 fbs+SHERPAATHLACKB

HEJALPGENSHERPAMEPS@NLO jetsN

0≥ 1≥ 2≥ 3≥ 4≥ 5≥ 6≥ 7≥

Pred

. / D

ata

0.60.8

11.21.4 +SHERPAATHLACKB

ATLAS

jetsN0≥ 1≥ 2≥ 3≥ 4≥ 5≥ 6≥ 7≥

Pred

. / D

ata

0.60.8

11.21.4 HEJ

jetsN0≥ 1≥ 2≥ 3≥ 4≥ 5≥ 6≥ 7≥

Pred

. / D

ata

0.60.8

11.21.4 ALPGEN

jetsN0≥ 1≥ 2≥ 3≥ 4≥ 5≥ 6≥ 7≥

Pred

. / D

ata

0.60.8

11.21.4

SHERPA

MEPS@NLO

jetsN0≥ 1≥ 2≥ 3≥ 4≥

)je

tsZ+

Nσ

)/(je

tsW

+Nσ(

8

10

12

14

16

18ATLAS

jets, R=0.4,tanti-k| < 4.4j > 30 GeV, |yj

Tp

)) + jets-l+ l→))/(Z(ν l→(W(-1=7 TeV, 4.6 fbsData,

+SHERPAATHLACKBALPGEN+HERWIGSHERPA

jetsN0≥ 1≥ 2≥ 3≥ 4≥

NLO

/ Da

ta

0.80.9


jetsN0≥ 1≥ 2≥ 3≥ 4≥

MC

/ Dat

a

0.80.9

11.11.2 ALPGEN

jetsN0≥ 1≥ 2≥ 3≥ 4≥

MC

/ Dat

a

0.80.9

11.11.2 SHERPA

W → lν

Ratio measurement

• Trend toward large Njets (Alpgen & Sherpa) • still compatible with data within the large errors

• In ratio measurement: deviation of Sherpa prediciton becomes significant

arXiv:1409.8639 & Eur. Phys. J. C (2014) 74




• Alpgen and Sherpa describe data well

• BH and LoopSim underestimate high pT cross section

Transverse Momentum of Leading Jet (≥ 1 jet)

10

W → lν

(leading jet) [GeV]jT

p100 200 300 400 500 600 700 800 900 1000

[1/G

eV]

j T/d

p1j≥

W+

σd

-510

-410

-310

-210

-110

1

10

210

310 ATLAS jets, R=0.4,tanti-k

| < 4.4j > 30 GeV, |yjT

pScaled Predictions

1 jet≥) + ν l→W(Data,


BH+S Excl. SumLoopSimALPGENSHERPAMEPS@NLO


p100 200 300 400 500 600 700 800 900 1000

Pred

. / D

ata

0.60.8

11.21.4 BH+S BH+S Excl. Sum

ATLAS


p100 200 300 400 500 600 700 800 900 1000

Pred

. / D

ata

0.60.8

11.21.4 LoopSim


p100 200 300 400 500 600 700 800 900 1000

Pred

. / D

ata

0.60.8

11.21.4 ALPGEN


p100 200 300 400 500 600 700 800 900 1000

Pred

. / D

ata

0.60.8

11.21.4

SHERPA

MEPS@NLO


p100 200 300 400 500 600 700

)j T/d

p1j≥

Z+σ

)/(d

j T/d

p1j≥

W+

σ)(d

1j≥(1

/R

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2ATLAS


Tp

1 jet≥)) + -l+ l→))/(Z(ν l→(W(-1=7 TeV, 4.6 fbsData,



p100 200 300 400 500 600 700

NLO

/ Da

ta

0.80.9

11.11.21.3 +SHERPAATHLACKB


p100 200 300 400 500 600 700

MC

/ Dat

a

0.80.9

11.11.21.3 ALPGEN


p100 200 300 400 500 600 700

MC

/ Dat

a

0.80.9

11.11.21.3 SHERPA

Ratio measurement

arXiv:1409.8639 & Eur. Phys. J. C (2014) 74




• Pronounced offset in HEJ prediction

• Ratio is modeled well, except for very low pT

Transverse Momentum of Leading Jet (≥2 jets)

11

W → lν


p100 200 300 400 500 600 700

[1/G

eV]

j T/d

p2j≥

W+

σd

-410

-310

-210

-110

1

10

210ATLAS


TpScaled Predictions



HEJALPGENSHERPAMEPS@NLO (leading jet) [GeV]j

Tp

100 200 300 400 500 600 700

Pred

. / D

ata

0.60.8


ATLAS


p100 200 300 400 500 600 700

Pred

. / D

ata

0.60.8

11.21.4 HEJ


p100 200 300 400 500 600 700

Pred

. / D

ata

0.60.8

11.21.4 ALPGEN


p100 200 300 400 500 600 700

Pred

. / D

ata

0.60.8

11.21.4

SHERPA

MEPS@NLO


p100 200 300 400 500

)j T/d

p2j≥

Z+σ

)/(d

j T/d

p2j≥

W+

σ)(d

2j≥(1

/R

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2ATLAS


Tp




p100 200 300 400 500

NLO

/ Da

ta

0.80.9



p100 200 300 400 500

MC

/ Dat

a

0.80.9

11.11.21.3 ALPGEN


p100 200 300 400 500

MC

/ Dat

a

0.80.9

11.11.21.3 SHERPA

Ratio measurement

arXiv:1409.8639 & Eur. Phys. J. C (2014) 74




Angular separation of jets

12

W → lν

j1,j2 RΔ

1 2 3 4 5 6

j1

,j2 R

Δ/d

2j≥

W+

σd

1

10

210

310

ATLAS jets, R=0.4,tanti-k

| < 4.4j > 30 GeV, |yjT

pScaled Predictions



HEJALPGENSHERPAMEPS@NLO j1,j2 RΔ

1 2 3 4 5 6

Pred

. / D

ata

0.60.8


ATLAS

j1,j2 RΔ

1 2 3 4 5 6

Pred

. / D

ata

0.60.8

11.21.4 HEJ

j1,j2 RΔ

1 2 3 4 5 6

Pred

. / D

ata

0.60.8

11.21.4 ALPGEN

j1,j2 RΔ1 2 3 4 5 6

Pred

. / D

ata

0.60.8

11.21.4

SHERPA

MEPS@NLO

j1,j2 RΔ

1 2 3 4 5

)j1

,j2 R

Δ/d

2j≥Z+σ

)/(d

j1,j2

RΔ

/d2j≥

W+

σ)(d

2j≥(1

/R

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2ATLAS


Tp



j1,j2 RΔ1 2 3 4 5

NLO

/ Da

ta

0.80.9


j1,j2 RΔ1 2 3 4 5

MC

/ Dat

a

0.80.9

11.11.21.3 ALPGEN

j1,j2 RΔ1 2 3 4 5

MC

/ Dat

a

0.80.9

11.11.21.3 SHERPA

• sensitive to hard parton radiation at large angles • ME / PS matching

• MEPS@NLO: trend at large separation• ALPGEN: trend over full range

Ratio measurement

arXiv:1409.8639 & Eur. Phys. J. C (2014) 74



Z + b-jets

JHEP10(2014)141


• Important BG for associated Higgs production with H → bb and BSM models

• 2 schemes used in pQCD calculations: 4 and 5 flavors in initial state• (a) only existent in 5 flavor scheme• sensitive to b-quark PDF

Motivation

14

considers parton densities of gluons and of the first two quark generations in the proton.

The other is the five-flavour number scheme (5FNS), which allows a b-quark density in the

initial state and raises the prospect that measurements of heavy flavour production could

constrain the b-quark parton density function (PDF) of the proton. In a calculation to all

orders, the 4FNS and 5FNS methods must give identical results; however, at a given order

differences can occur between the two. A recent discussion on the status of theoretical

calculations and the advantages and disadvantages of the different flavour number schemes

can be found in Ref. [1].

Next-to-leading-order (NLO) matrix element calculations have been available for as-

sociated Z+b and Z+bb̄ production at parton-level for a number of years [2–4]. The

leading order (LO) Feynman diagrams shown in Figure 1 illustrate some of the contribut-

ing processes. Full particle-level predictions have existed at LO for some time, obtained

by matching parton shower generators to LO multi-leg matrix elements in the 4FNS [5,6],

5FNS [7], or both [8]. More recently, a full particle-level prediction for Z+ ≥ 2 b-jets at

NLO in the 4FNS with matched parton shower has become available [9, 10]. The same

framework can also be used to provide a full particle-level prediction for Z+ ≥ 1 b-jet at

NLO in the 5FNS. In this article data are compared with several theoretical predictions

following different approaches.

Differential measurements of Z+b-jets production have been made in proton-antiproton

collisions at√s=1.96 TeV by the CDF and D0 experiments [11, 12] as well as inclusively

in√s=7 TeV proton-proton collisions at the LHC by the ATLAS and CMS experiments

[13, 14]. The results presented in this paper significantly extend the scope of the previous

ATLAS measurement, which used around 36 pb−1of data recorded in 2010. The current

analysis takes advantage of the full sample of√s=7 TeV proton-proton collisions recorded

in 2011, corresponding to an integrated luminosity of 4.6 fb−1, and uses improved methods

for b-jet identification to cover a wider kinematic region. The larger data sample allows

differential production cross-section measurements of a Z boson with b-jets at the LHC.

These complement the recently reported results of associated production of a Z boson with

two b-hadrons at√s=7 TeV by CMS [15].

A total of 12 differential cross-sections are presented here, covering a variety of Z boson

and b-jet kinematics and angular variables sensitive to different aspects of the theoretical

b

b

Z

g

(a)

q

q

b

b

Z

(b)

q Z

b

bq

(c)

Figure 1. Leading order Feynman diagrams contributing to Z+b-jets production. Process 1(a) isonly present in a 5FNS calculation, while 1(b) and 1(c) are present in both the 4FNS and 5FNScalculations.

– 2 –

JHEP10(2014)141


• Sensitivity to PDF• In particular N flavors

• Shape of b-jet pT fairly well described

Z+b-jets: Results

15

(Zb) [pb]σ

0 1 2 3 4 5 6

(stat.)-1 = 7 TeV, 4.6 fbsData syst.)⊕ (stat.-1 = 7 TeV, 4.6 fbsData

NLO MSTW2008⊗MCFM CT10⊗MCFM NNPDF2.3⊗MCFM

MSTW2008⊗aMC@NLO 4FNS MSTW2008⊗aMC@NLO 5FNS

LO multileg CT10⊗SHERPA

CTEQ6L1⊗ALPGEN+HJ

ATLAS1 b-jet≥Z+

(a)

(Zbb) [pb]σ

0 0.1 0.2 0.3 0.4 0.5 0.6





CTEQ6L1⊗ALPGEN+HJ

ATLAS2 b-jet≥Z+

(b)

Figure 6. Cross-sections for (a) Z+ ≥ 1 b-jet, and (b) Z+ ≥ 2 b-jets. The measurement is shown asa vertical blue line with the inner blue shaded band showing the corresponding statistical uncertaintyand the outer green shaded band showing the sum in quadrature of statistical and systematicuncertainties. Comparison is made to NLO predictions from mcfm interfaced to different PDF setsand amc@nlo interfaced to the same PDF set in both the 4FNS and 5FNS. The statistical (innerbar) and total (outer bar) uncertainties are shown for these predictions, which are dominated by thetheoretical scale uncertainty calculated as described in the text. Comparisons are also made to LOmulti-legged predictions from Alpgen+Herwig+Jimmy and Sherpa; in this case the uncertaintybars are statistical only, and smaller than the marker.

– 22 –

2

[pb/

GeV

]b-

jets

/N ) Td(

b-je

t p(Zb)

σd

-410

-310

-210

-110

aData-1 = 7 TeV, 4.6 fbs

MCFMaMC@NLO 5FNSaMC@NLO 4FNSALPGEN+HJSHERPA

ATLAS 1 b-jet≥Z+

Data

NLO

0.60.8

11.21.4

[GeV]Tb-jet p30 40 50 210 210×2

Data

LO m

ultile

g

0.40.60.8

11.2

(a)

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4

[pb]

b-je

ts/N

d(b-

jet |

y|)

(Zb)

σd

0.5

1

1.5

2

2.5

3

3.5

4aData

-1 = 7 TeV, 4.6 fbsMCFMaMC@NLO 5FNSaMC@NLO 4FNSALPGEN+HJSHERPA

ATLAS 1 b-jet≥Z+

Data

NLO

0.60.8

11.21.4

b-jet |y|0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4

Data

LO m

ultile

g

0.40.60.8

11.2

(b)

Figure 7. The inclusive b-jet cross-section σ(Zb) × Nb-jet as a function of b-jet pT (a) and|y| (b). The top panels show measured differential cross-sections as filled circles with statistical(inner) and total (outer bar) uncertainties. Overlayed for comparison are the NLO predictionsfrom mcfm and amc@nlo both using the MSTW2008 PDF set. The shaded bands represents thetotal theoretical uncertainty for mcfm and the uncertainty bands on amc@nlo points representthe dominant theoretical scale uncertainty only. Also overlaid are LO multi-legged predictions forAlpgen+Herwig+Jimmy and Sherpa. The middle panels show the ratio of NLO predictions todata, and the lower panels show the ratio of LO predictions to data.

– 23 –

(Zb) [pb]σ

0 1 2 3 4 5 6





CTEQ6L1⊗ALPGEN+HJ

ATLAS1 b-jet≥Z+

(a)

(Zbb) [pb]σ

0 0.1 0.2 0.3 0.4 0.5 0.6





CTEQ6L1⊗ALPGEN+HJ

ATLAS2 b-jet≥Z+

(b)

Figure 6. Cross-sections for (a) Z+ ≥ 1 b-jet, and (b) Z+ ≥ 2 b-jets. The measurement is shown asa vertical blue line with the inner blue shaded band showing the corresponding statistical uncertaintyand the outer green shaded band showing the sum in quadrature of statistical and systematicuncertainties. Comparison is made to NLO predictions from mcfm interfaced to different PDF setsand amc@nlo interfaced to the same PDF set in both the 4FNS and 5FNS. The statistical (innerbar) and total (outer bar) uncertainties are shown for these predictions, which are dominated by thetheoretical scale uncertainty calculated as described in the text. Comparisons are also made to LOmulti-legged predictions from Alpgen+Herwig+Jimmy and Sherpa; in this case the uncertaintybars are statistical only, and smaller than the marker.

– 22 –

Good agreement in 5 FNS (≥ 1b)

Bad agreement in 5 FNS! (≥ 2b)

≥ 1b

≥ 2b

4FNS

5FNS

4FNS

5FNS

JHEP10(2014)141

Inclusive Jet Double Differential Measurement

arXiv:1410.8857


• Anti-kt reconstruction algorithm, radius R=0.4 (0.6)• Jets calibrated using insitu methods• pT > 100 GeV & |y| < 3

• Data from 2011 and 2010 are consistent

Inclusive Jet Double Differential Measurement

17

[GeV]Tp

210 310

[pb/

GeV

]y

d Tp/dσ2 d

-2010

-1710

-1410

-1110

-810

-510

-210

10

410

710

1010ATLAS

=7 TeVs, -1 dt=4.5 fbL ∫=0.4R jets, tanti-k

uncertaintiesSystematic

EW corr.×Non-pert. corr. ×NLOJET++ (CT10)

)0 10×| < 0.5 (y|)-3 10×| < 1.0 (y |≤0.5 )-6 10×| < 1.5 (y |≤1.0 )-9 10×| < 2.0 (y |≤1.5 )-12 10×| < 2.5 (y |≤2.0 )-15 10×| < 3.0 (y |≤2.5

Double differential cross sections:

0.6

0.8

1

1.2

1.4 | < 0.3y|

0.6

0.8

1

1.2

1.4 | < 0.8y |≤0.3

[GeV]Tp

210 3100.60.8

11.21.4 | < 1.2y |≤0.8

0.6

0.8

1

1.2

1.4 | < 2.1y |≤1.2

[GeV]Tp

210 3100.60.8

11.21.4 | < 2.8y |≤2.1

Rat

io

Rat

io ATLAS-1 dt = 36 pbL ∫2010 :

-1 dt = 4.5 fbL ∫2011 :

=7 TeVs

=0.4R jets, tanti-k

uncertainty2011 syst. and stat.


• Larger dataset: extension to higher pT values (2 TeV), reduces systematics

NLOJET prediction matched well with double differential

measured cross section

arXiv:1410.8857

Comparison of 2011 and 2010 data:


• Dominant systematic uncertainty:• Jet Energy Scale

• Data compared to NLOJET prediction with several different PDF sets (including corrections for non perturbative and electroweak effects):

• Only ABM11 PDF shows significant deviations from measured values

• Fairly good agreement for all other tested PDF sets

• Similar results for R=0.6

• Quantitative comparison including correlations of uncertainties• All information published

Impact on PDFs

18

0.6

0.8

1

1.2| < 0.5y|

0.6

0.8

1

1.2| < 1.0y |≤0.5

[GeV]Tp

210 310

0.81

1.21.4 | < 1.5y |≤1.0

0.5

1

1.5

2 | < 2.0y |≤1.5

0.5

1

1.5

2 | < 2.5y |≤2.0

[GeV]Tp

210 310

0.5

1

1.5

2 | < 3.0y |≤2.5

Theo

ry /

data

Theo

ry /

data ATLAS

= 7 TeVs

-1 dt = 4.5 fbL ∫

=0.4R jets, tanti-k

NLOJET++maxTp =

Rµ =

Fµ

EW corr.Non-pert and

Data

1.5HERAPDF

CT10

= 5fnABM11

0.6

0.8

1

1.2| < 0.5y|

0.6

0.8

1

1.2| < 1.0y |≤0.5

[GeV]Tp

210 310

0.81

1.21.4 | < 1.5y |≤1.0

0.5

1

1.5

2 | < 2.0y |≤1.5

0.5

1

1.5

2 | < 2.5y |≤2.0

[GeV]Tp

210 310

0.5

1

1.5

2 | < 3.0y |≤2.5

Theo

ry /

data

Theo

ry /

data ATLAS

= 7 TeVs

-1 dt = 4.5 fbL ∫

=0.4R jets, tanti-k

NLOJET++maxTp =

Rµ =

Fµ


Data

MSTW 2008

CT10

NNPDF 2.1

arXiv:1410.8857


• Comparison of Perugia 2011 and AUET2B tunes

• Perugia tune yields consistently larger cross section prediction than AUET2B

• Shape well reproduced by POWHEG

• Similar Results for R=0.6

ME+PS element generator vs. pQCD calculation

19

0.6

0.8

1

1.2| < 0.5y|

0.6

0.8

1

1.2| < 1.0y |≤0.5

[GeV]Tp

210 310

0.81

1.21.4 | < 1.5y |≤1.0

0.5

1

1.5

2 | < 2.0y |≤1.5

0.5

1

1.5

2 | < 2.5y |≤2.0

[GeV]Tp

210 310

0.5

1

1.5

2 | < 3.0y |≤2.5

Theo

ry /

data

Theo

ry /

data ATLAS

= 7 TeVs

-1 dt = 4.5 fbL ∫

=0.4R jets, tanti-k

POWHEG+PYTHIA

BornTp =

Rµ =

FµCT10,

Data

EW corr.×2011

Perugia

EW corr.×Non-pert. corr.

×(CT10) NLOJET++

EW corr.×AUET2B

arXiv:1410.8857

3 Jet Production

arXiv:1411.1855





















• Double differential measurement in Rapidity and tri-jet mass

• Dominating systematic uncertainty: JES

• Good agreement with prediction over 7 orders of magnitude!

3 Jet Production

21

[GeV]jjjm400 1000 2000 3000

/d|Y

*| [p

b/G

eV]

jjj/d

mσ2 d

-610

-410

-210

1

210

410 ATLAS-1L dt = 4.5 fb∫

= 7 TeVs

R = 0.4tkanti-

non-pert. corr×CT 10⊗NLO QCD

)0 |Y*|<2 (x10 )12<|Y*|<4 (x10 )24<|Y*|<6 (x10 )36<|Y*|<8 (x10 )48<|Y*|<10 (x10

Event Selection:

• Anti-kt reconstruction algorithm, radius R=0.4 (0.6)

• Jets calibrated using insitu methods

• At least 3 jets with• pT > 50 GeV & |y| < 3• leading jet: pT > 150 GeV• sub-leasing jet: pT > 100 GeV

• |Y*| = |y1 - y2| + |y2 - y3| + |y1 - y3|

arXiv:1411.1855




• Similar picture to previous analysis

• ABM11 PDF yield systematically lower predictions, in particular in low rapidity region

• Good agreement for R=0.4

• Shifted prediction/data ratio for R=0.6 towards lower values

3 Jet Production - PDF impact

22

[GeV]jjjm210×4 310 310×2

Pred

ictio

n/Da

ta

0.60.8

11.21.4 |Y*|<2

[GeV]jjjm210×4 310 310×2

0.60.8

11.21.4 2<|Y*|<4

[GeV]jjjm210×4 310 310×20.40.60.8

11.21.41.6 6<|Y*|<8 [GeV]jjjm210×4 310 310×2

0.6

0.8

1

1.2

1.4 4<|Y*|<6

[GeV]jjjm210×4 310 310×20.40.60.8

11.21.41.6 8<|Y*|<10

ATLAS-1 L dt = 4.5 fb∫

= 7 TeVs R = 0.4tkanti-

DATA Uncert.TotalStatistical

non-pert. corr.× PDF⊗NLO QCD

NNPDF 2.3ABM 11HERA 1.5

[GeV]jjjm210×4 310 310×2

Pred

ictio

n/Da

ta

0.60.8

11.21.4 |Y*|<2

[GeV]jjjm210×4 310 310×2

0.60.8

11.21.4 2<|Y*|<4

[GeV]jjjm210×4 310 310×20.40.60.8

11.21.41.6 6<|Y*|<8 [GeV]jjjm210×4 310 310×2

0.6

0.8

1

1.2

1.4 4<|Y*|<6

[GeV]jjjm210×4 310 310×20.40.60.8

11.21.41.6 8<|Y*|<10





NNPDF 2.3ABM 11HERA 1.5

R=0.4

R=0.6

arXiv:1411.1855




• Inclusive Jet production and the association with Vector Bosons contain interesting physics!

• Many results from ATLAS• Few are shown:• W+jets: large sensitivity to higher order ME corrections, PS and merging technique. Still room for improvements!

• W/Z + jets ratios: smaller uncertainties, well modeled by generators

• Z+b-jets: sensitivity to PDFs and initial state description

• Inclusive Jets: good agreement with fixed-order NLOpQCD calculations + corrections (non perturbative & EWK) and ME + matched PS

• 3 Jet production: similar to inclusive Jets: ABM11 PDF shows deviations from measurement in low Y* region;

for R=0.6: ratio theory / data systematically lower compared to R=0.4

Conclusions

23

BACKUP


• Promt, isolated photon production cross section

• Shape well described by Pythia and Herwig

• Absolute cross section predicted lower than measuremed

• PDF uncertainties become important for high ET • Good agreement with NLO pQCD predictions

Promt Photon Production

25

[GeV]isoTE

-10 -5 0 5 10 15 20 25 30 35 40

Entri

es /

GeV

0

20

40

60

80

100

120

140

160

180

200310×

=7 TeVsData 2011 γtight

γnon-tight

|<1.37γη>100 GeV |γ

TE

ATLAS

-1 L dt = 4.6 fb∫

0 0.5 1 1.5 2 2.5

50

100

150

200

250

300

350

400

0 0.5 1 1.5 2 2.5 [p

b]γ η

/ d

σd

100

200

300

400

0 0.5 1 1.5 2 2.5 [p

b]γ η

/ d

σd

100

200

300

400>100 GeVγ

TE =7 TeVsData 2011 PYTHIA (MRST 2007 LO*)HERWIG (MRST 2007 LO*)

NLO (Jetphox) CT10Total uncertaintyScale uncertaintyNLO (Jetphox) MSTW2008nlo

-1 L dt = 4.6 fb∫

ATLAS

0 0.5 1 1.5 2 2.50.7

0.8

0.9

1

1.1

1.2

|γη|0 0.5 1 1.5 2 2.5

0.8

1

1.2Th

eory

/Dat

a100 200 300 400 500 600 700 800 900 1000

-510

-410

-310

-210

-110

1

10

1002003004005006007008009001000

[pb/

GeV

]γ T

/ d

Eσ

d

-510

-410

-310

-210

-110

1

10

1002003004005006007008009001000

[pb/

GeV

]γ T

/ d

Eσ

d

-510

-410

-310

-210

-110

1

10

|<1.37γη|

=7 TeVsData 2011 PYTHIA (MRST 2007 LO*)HERWIG (MRST 2007 LO*)

NLO (Jetphox) CT10Total uncertaintyScale uncertainty

NLO (Jetphox) MSTW2008nlo

-1 L dt = 4.6 fb∫

ATLAS

100 200 300 400 500 600 700 800 900 10000.50.60.70.80.9

11.11.21.31.4

[GeV]γTE

100 200 300 400 500 600 700 800 900 10000.60.8

11.21.4

Theo

ry/D

ata


• Ratio well described by all generators

• Good description by HEJ for single channel

Invariant di-jet mass

26

W → lν

[GeV]12m0 500 1000 1500 2000

[1/G

eV]

12/d

m2j≥

W+

σd

-510

-410

-310

-210

-110

1

10


| < 4.4j > 30 GeV, |yjT

pScaled Predictions



HEJALPGENSHERPAMEPS@NLO [GeV]12m

0 500 1000 1500 2000

Pred

. / D

ata

0.60.8


ATLAS

[GeV]12m0 500 1000 1500 2000

Pred

. / D

ata

0.60.8

11.21.4 HEJ

[GeV]12m0 500 1000 1500 2000

Pred

. / D

ata

0.60.8

11.21.4 ALPGEN

[GeV]12m0 500 1000 1500 2000

Pred

. / D

ata

0.60.8

11.21.4

SHERPA

MEPS@NLO

[GeV]12m0 100 200 300 400 500 600 700 800 900 1000

)12

/dm

2j≥Z+σ

)/(d

12/d

m2j≥

W+

σ)(d

2j≥(1

/R

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2ATLAS


Tp



[GeV]12m0 100 200 300 400 500 600 700 800 900 1000

NLO

/ Da

ta

0.80.9


[GeV]12m0 100 200 300 400 500 600 700 800 900 1000

MC

/ Dat

a

0.80.9

11.11.21.3 ALPGEN

[GeV]12m0 100 200 300 400 500 600 700 800 900 1000

MC

/ Dat

a

0.80.9

11.11.21.3 SHERPA

Ratio measurement

Kristof Schmieden Les Rencontres de Physique de la Vallee d‘Aoste - March 2015 27

[GeV]TH500 1000 1500 2000

[1/G

eV]

T/d

H1j≥

W+

σd

-610

-510

-410

-310

-210

-110

1

10

210

310

410ATLAS


TpScaled Predictions



BH+S Excl. SumLoopSimALPGENSHERPAMEPS@NLO

[GeV]TH500 1000 1500 2000

Pred

. / D

ata

0.5

1

1.5 BH+S BH+S Excl. Sum

ATLAS

[GeV]TH500 1000 1500 2000

Pred

. / D

ata

0.5

1

1.5 LoopSim

[GeV]TH500 1000 1500 2000

Pred

. / D

ata

0.5

1

1.5 ALPGEN

[GeV]TH500 1000 1500 2000

Pred

. / D

ata

0.5

1

1.5

SHERPA

MEPS@NLO

Inclusive Jets - HT

Kristof Schmieden Les Rencontres de Physique de la Vallee d‘Aoste - March 2015 28

| (leading jet)j|y0 0.5 1 1.5 2 2.5 3 3.5 4

j/d

y1j≥

W+

σd

1

10

210

310


| < 4.4j > 30 GeV, |yjT

pScaled Predictions



ALPGENSHERPAMEPS@NLO

| (leading jet)j|y

0 0.5 1 1.5 2 2.5 3 3.5 4

Pred

. / D

ata

0.60.8


ATLAS

| (leading jet)j|y

0 0.5 1 1.5 2 2.5 3 3.5 4

Pred

. / D

ata

0.60.8

11.21.4 ALPGEN

| (leading jet)j|y0 0.5 1 1.5 2 2.5 3 3.5 4

Pred

. / D

ata

0.60.8

11.21.4

SHERPA

MEPS@NLO

Inclusive Jets - Rapidity Leading Jet


Inclusive Jets Double Differential Measurement

29

0.6

0.8

1

1.2

1.4 | < 0.3y|

0.6

0.8

1

1.2

1.4 | < 0.8y |≤0.3

[GeV]Tp

210 3100.60.8

11.21.4 | < 1.2y |≤0.8

0.6

0.8

1

1.2

1.4 | < 2.1y |≤1.2

[GeV]Tp

210 3100.60.8

11.21.4 | < 2.8y |≤2.1

Rat

io

Rat

io ATLAS-1 dt = 36 pbL ∫2010 :

-1 dt = 4.5 fbL ∫2011 :

=7 TeVs

=0.6R jets, tanti-k



[GeV]Tp

210 310

[pb/

GeV

]y

d Tp/dσ2 d

-2010

-1710

-1410

-1110

-810

-510

-210

10

410

710

1010ATLAS

=7 TeVs, -1 dt=4.5 fbL ∫=0.6R jets, tanti-k

uncertaintiesSystematic

EW corr.×Non-pert. corr. ×NLOJET++ (CT10)

)0 10×| < 0.5 (y|)-3 10×| < 1.0 (y |≤0.5 )-6 10×| < 1.5 (y |≤1.0 )-9 10×| < 2.0 (y |≤1.5 )-12 10×| < 2.5 (y |≤2.0 )-15 10×| < 3.0 (y |≤2.5

• Anti-kt reconstruction algorithm, radius R=0.6 • Jets calibrated using local hadronic calibration weights (LCW)• pT > 100 GeV & |y| < 3

• Data from 2011 and 2010 are consistent

• NLOJET prediction matched well with double differential measurement


Impact of PDFs

30

0.6

0.8

1

1.2| < 0.5y|

0.6

0.8

1

1.2| < 1.0y |≤0.5

[GeV]Tp

210 310

0.81

1.21.4 | < 1.5y |≤1.0

0.5

1

1.5

2 | < 2.0y |≤1.5

0.5

1

1.5

2 | < 2.5y |≤2.0

[GeV]Tp

210 310

0.5

1

1.5

2 | < 3.0y |≤2.5

Theo

ry /

data

Theo

ry /

data ATLAS

= 7 TeVs

-1 dt = 4.5 fbL ∫

=0.6R jets, tanti-k

NLOJET++maxTp =

Rµ =

Fµ


Data

1.5HERAPDF

CT10

= 5fnABM11

0.6

0.8

1

1.2| < 0.5y|

0.6

0.8

1

1.2| < 1.0y |≤0.5

[GeV]Tp

210 310

0.81

1.21.4 | < 1.5y |≤1.0

0.5

1

1.5

2 | < 2.0y |≤1.5

0.5

1

1.5

2 | < 2.5y |≤2.0

[GeV]Tp

210 310

0.5

1

1.5

2 | < 3.0y |≤2.5

Theo

ry /

data

Theo

ry /

data ATLAS

= 7 TeVs

-1 dt = 4.5 fbL ∫

=0.6R jets, tanti-k

NLOJET++maxTp =

Rµ =

Fµ


Data

MSTW 2008

CT10

NNPDF 2.1

• Dominant systematic uncertainty:• Jet Energy Scale

• Data compared to NLOJET prediction with several different PDF sets (including corrections for non perturbative and electroweak effects):

• Only ABM11 PDF shows significant deviations from measured values

• Fairly good agreement for all other tested PDF sets

• Similar results for R=0.4


ME element generator vs. pQCD calculation

31

0.6

0.8

1

1.2| < 0.5y|

0.6

0.8

1

1.2| < 1.0y |≤0.5

[GeV]Tp

210 310

0.81

1.21.4 | < 1.5y |≤1.0

0.5

1

1.5

2 | < 2.0y |≤1.5

0.5

1

1.5

2 | < 2.5y |≤2.0

[GeV]Tp

210 310

0.5

1

1.5

2 | < 3.0y |≤2.5

Theo

ry /

data

Theo

ry /

data ATLAS

= 7 TeVs

-1 dt = 4.5 fbL ∫

=0.6R jets, tanti-k

POWHEG+PYTHIA

BornTp =

Rµ =

FµCT10,

Data

EW corr.×2011

Perugia

EW corr.×Non-pert. corr.

×(CT10) NLOJET++

EW corr.×AUET2B

• Comparison of Perugia 2011 and AUET2B tunes

Perugia tune yields consistently larger cross section prediction than AUET2B

• Shape well reproduced by POWHEG

• Similar Results for R=0.4


3 Jet Production - R=0.6

32

[GeV]jjjm400 1000 2000 3000

/d|Y

*| [p

b/G

eV]

jjj/d

mσ2 d

-610

-410

-210

1

210

410 ATLAS-1L dt = 4.5 fb∫

= 7 TeVs

R = 0.6tkanti-

non-pert. corr×CT 10⊗NLO QCD

)0 |Y*|<2 (x10 )12<|Y*|<4 (x10 )24<|Y*|<6 (x10 )36<|Y*|<8 (x10 )48<|Y*|<10 (x10


3 Jet Production - more PDFs

33

[GeV]jjjm210×4 310 310×2

Pred

ictio

n/Da

ta

0.60.8

11.21.4 |Y*|<2

[GeV]jjjm210×4 310 310×2

0.60.8

11.21.4 2<|Y*|<4

[GeV]jjjm210×4 310 310×20.40.60.8

11.21.41.6 6<|Y*|<8 [GeV]jjjm210×4 310 310×2

0.6

0.8

1

1.2

1.4 4<|Y*|<6

[GeV]jjjm210×4 310 310×20.40.60.8

11.21.41.6 8<|Y*|<10





CT 10MSTW 2008GJR 08

[GeV]jjjm210×4 310 310×2

Pred

ictio

n/Da

ta

0.60.8

11.21.4 |Y*|<2

[GeV]jjjm210×4 310 310×2

0.60.8

11.21.4 2<|Y*|<4

[GeV]jjjm210×4 310 310×20.40.60.8

11.21.41.6 6<|Y*|<8 [GeV]jjjm210×4 310 310×2

0.6

0.8

1

1.2

1.4 4<|Y*|<6

[GeV]jjjm210×4 310 310×20.40.60.8

11.21.41.6 8<|Y*|<10





CT 10MSTW 2008GJR 08

Electroweak production of V+jets


• Production via purely electroweak processes is rare• Mainly interested in:

Motivation - EWK production

35

• What we can learn from them?• Probe triple and quadratic gauge boson self-interactions• Can be used in a model independent approach to explore new physics, that modifies gauge boson self-interactions (anomalous couplings)

• Probe the nature of the EW symmetry breaking, testing the unitarization in VV scattering by HVV contribution (VBS)

• Understand irreducible background to Higgs and beyond-SM searches• Constrain MC modeling of QCD-initiated processes in VBF-like regions

Vector Boson fusion Vector Boson scattering


Zjj: VBF - strategy of measurement

36

Baseline

pTj1> 55 GeV pT

j2> 45GeV

High pT or high mass

pTj1> 85 GeV

pTj2> 75GeV

mjj > 1TeV

Search mjj > 250 GeV

pTll> 20 GeV

pTbal<0.15

Njets gap= 0

Control mjj > 250 GeV

pTbal,3<0.15

Njetgap>= 1

pTll> 20 GeV

Z

Z Z

• Measure inclusive (QCD+EW) Zjj cross section and differential distributions in 5 fiducial regions with varying sensitivity to the EW component:

• 3 regions with simple topologies:

• “baseline”

• “high pT” and “high mass” • probe impact of EW component

• 2 ad hoc selections:• “search region” and “control region”

• Extract electroweak component cross section from “search region”, constraining background modeling (QCD Zjj) from “control region”

• Set limits on anomalous triple gauge couplings


• Electroweak production becomes important!• Overestimated in Sherpa

• Sherpa predicts harder mass spectrum

• Powheg is in good agreement with data

Zjj: VBF - Results

37

0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5

[pb]

Zjj

σ

-110

1

10ATLAS

-1 L dt = 20.3 fb∫ = 8 TeVs

Data 2012Powheg (Zjj) + Sherpa (VZ)

baselineT

high p search control high mass

theo

ryσ

data

σ0.80.9

11.1

Figure 4. Fiducial cross-section measurements for inclusive Zjj production in the Z ! `+`�

decay channel, compared to the Powheg prediction for strong and electroweak Zjj production andthe small contribution from ZV production predicted by Sherpa. The (black) circles represent thedata and the associated error bar is the total uncertainty in the measurement. The (red) trianglesrepresent the theoretical prediction, the associated error bar (or hatched band in the lower plot) isthe total theoretical uncertainty on the prediction.

• 1

�

· d�

d|�y| : The normalised distribution of the di↵erence in rapidity between the two

leading jets, |�y|.

• 1

�

· d�

d|��(j,j)| : The normalised distribution of the di↵erence in azimuthal angle between

the two leading jets, ��(j, j).

The distributions sensitive to the di↵erence in t-channel colour flow between electroweak

and strong production of Zjj events include:

• 1

�

· d�

dN

gapjet

: The normalised distribution of the number of jets, Ngap

jet

, with pT

> 25 GeV

in the rapidity interval bounded by the two highest-pT

jets.

• 1

�

· d�

dp

balanceT

: The normalised distribution of the pT

-balancing distribution, pbalanceT

(see

eq. 6.2).

• The fraction of events that contain no additional jets with pT

> 25 GeV in the

rapidity interval bounded by the two highest-pT

jets (the jet veto e�ciency) as a

function of mjj

and |�y|.

• The average number of jets with pT

> 25 GeV in the rapidity interval bounded by

the two highest-pT

jets, hNgap

jet

i, as a function of mjj

and |�y|.

• The fraction of events with pbalanceT

< 0.15 (pbalanceT

cut e�ciency) as a function of

mjj

and |�y|.

– 14 –

0 500 1000 1500 2000 2500 3000

jjdmσd

σ1

-710

-610

-510

-410

-310


= 8 TeVsbaseline region

Data (2012)

Sherpa Zjj (QCD + EW)

Sherpa Zjj (QCD)

Powheg Zjj (QCD + EW)

Powheg Zjj (QCD)

0 500 1000 1500 2000 2500 3000

D

ata

Sher

pa

1

1.5

2

[GeV]jjm0 500 1000 1500 2000 2500 3000

D

ata

Pow

heg

1

1.5

(a)

500 1000 1500 2000 2500 3000

jjdmσd

σ1

-710

-610

-510

-410

-310


= 8 TeVssearch region

Data (2012)

Sherpa Zjj (QCD + EW)

Sherpa Zjj (QCD)

Powheg Zjj (QCD + EW)

Powheg Zjj (QCD)

500 1000 1500 2000 2500 3000

D

ata

Sher

pa

0.81

1.2

[GeV]jjm500 1000 1500 2000 2500 3000

D

ata

Pow

heg

0.81

1.2

(b)

Figure 6. Unfolded 1� · d�

dmjjdistribution in the (a) baseline and (b) search regions. The data

are shown as filled (black) circles. The vertical error bars show the size of the total uncertaintyon the measurement, with tick marks used to reflect the size of the statistical uncertainty only.Particle-level predictions from Sherpa and Powheg are shown for combined strong and electroweakZjj production (labelled as QCD+EW) by hatched bands, denoting the model uncertainty, aroundthe central prediction, which is shown as a solid line. The predictions from Sherpa and Powheg forstrong Zjj production (labelled QCD) are shown as dashed lines.

in electroweak Zjj production.

In the baseline region, the Powheg prediction is accurate to NLO in perturbative QCD

and better describes the data at the highest values of mjj

and |�y| than Sherpa, which is

accurate to LO. In particular, Sherpa predicts too large a fraction of events at large mjj

and |�y|, a feature also seen in previous measurements at the LHC and Tevatron [57, 58].

In the search region, the veto on additional jet activity means that both Sherpa and Powheg

are accurate only to LO. Despite this, both predictions give a satisfactory description of

the data if both strong and electroweak Zjj production are included. The contribution

from electroweak Zjj production is evident at high mjj

and high |�y| in the search region

for both event generators.

The unfolded 1

�

· d�

dN

gapjet

, 1

�

· d�

dp

balanceT

and 1

�

· d�

d|��(j,j)| distributions are shown in the

high-mass region in figure 8. Quark/gluon radiation from the electroweak Zjj process is

much less likely than in the strong Zjj process because there is no colour flow between the

two jets. The contribution from electroweak Zjj production is clear in the low-multiplicity

region of the 1

�

· d�

dN

gapjet

distribution for both Powheg and Sherpa, demonstrating the ef-

– 17 –

baseline regionsearch region used to get aTGC limits


Limit on anomalous triple gauge coupling

38

• Zjj sensitive to TGC• Sensitivity to new physics modifying gauge boson self-interaction

• Generic aTGC couplings parametrized by effective Lagrangian

• 3 contributing couplings• g1,Z, λZ, κZ

• Limits weaker but complementary than those from di-boson production• Di-boson: all 3 bosons have time-like momentum• Here 2 W have space-like momentum

Table 7. The 95% confidence intervals obtained on the aTGC parameters from counting thenumber of events with mjj > 1 TeV in the search region. Observed and expected intervals, labelled‘obs’ and ‘exp’ respectively, are presented for unitarisation scales of ⇤ = 6 TeV and ⇤ = 1. Theparameter �g1,Z refers to the deviation of g1,Z from the SM value.

aTGC ⇤ = 6 TeV (obs) ⇤ = 6 TeV (exp) ⇤ = 1 (obs) ⇤ = 1 (exp)

�g1,Z

[�0.65, 0.33] [�0.58, 0.27] [�0.50, 0.26] [�0.45, 0.22]

�Z

[�0.22, 0.19] [�0.19, 0.16] [�0.15, 0.13] [�0.14, 0.11]

the Lagrangian that contain a derivative of the W -boson field. Table 7 shows the 95%

confidence intervals obtained on the anomalous coupling parameters �Z

and g1,Z

. The

limits are not as stringent as those set in WZ production [72], which are approximately a

factor of three smaller in the �Z

coupling, for example.

9 Summary

Fiducial cross sections for electroweak Zjj production have been presented for proton-

proton collisions atps = 8 TeV, using a dataset corresponding to an integrated luminos-

ity of 20.3 fb�1 collected by the ATLAS experiment at the Large Hadron Collider. The

background-only model has been rejected above the 5� level and these measurements con-

stitute observation of the electroweak Zjj process. The measured cross sections are in good

agreement with the Standard Model expectation and limits have been set on anomalous

triple gauge couplings. In addition, cross sections and di↵erential distributions have been

measured for inclusive Zjj production in five fiducial regions. The cross-section measure-

ments are all in good agreement with the prediction from Powheg for Zjj production. The

di↵erential distributions are sensitive to the electroweak component of Zjj production, as

well as the modelling of strong Zjj production in the extreme phase-space regions probed.

The data are compared to theoretical predictions from the Sherpa and Powheg event gen-

erators. Neither prediction is able to fully reproduce the data for all distributions and

the data can be used to constrain the theoretical modelling in these extreme phase-space

regions.

Acknowledgements

We thank CERN for the very successful operation of the LHC, as well as the support

sta↵ from our institutions without whom ATLAS could not be operated e�ciently. We

also thank Stefan Hoeche and Frank Krauss for insight and cross-checks related to the

interference between electroweak and strong Zjj production as predicted by the Sherpa

event generator.

We acknowledge the support of ANPCyT, Argentina; YerPhI, Armenia; ARC, Aus-

tralia; BMWF and FWF, Austria; ANAS, Azerbaijan; SSTC, Belarus; CNPq and FAPESP,

Brazil; NSERC, NRC and CFI, Canada; CERN; CONICYT, Chile; CAS, MOST and

– 31 –

95% confidence intervals

W�

W+Z

q

q

q0

µ+, e+

µ�, e�

q0

(a) vector boson fusion

W±

Z

q

q

q0

q0

µ+, e+

µ�, e�

(b) Z-boson bremsstrahlung

Z

Z

q

q

q

µ+, e+

µ�, e�

q

(c) non-resonant `+`�jj

Figure 1. Representative leading-order Feynman diagrams for electroweak Zjj production at theLHC: (a) vector boson fusion (b) Z-boson bremsstrahlung and (c) non-resonant `+`�jj production.

the additional jets arising as a result of the strong interaction. Production of Zjj events via

the t-channel exchange of an electroweak gauge boson is a purely electroweak process and is

therefore much rarer. Electroweak Zjj production in the leptonic decay channel is defined

to include all contributions to `+`�jj production for which there is a t-channel exchange

of an electroweak gauge boson [1, 2]. These contributions include Z-boson production

via vector boson fusion (VBF), Z-boson bremsstrahlung and non-resonant production, as

shown in figure 1. The VBF process is of particular interest because of the similarity to

the VBF production of a Higgs boson and the sensitivity to anomalous WWZ triple gauge

couplings.2

This paper presents two measurements of Zjj production using 20.3 fb�1 of proton-

proton collision data collected by the ATLAS experiment [3] at a centre-of-mass energy ofps = 8 TeV:

1. Measurements of fiducial cross sections and di↵erential distributions of inclusive Zjj

production. These measurements are performed in five fiducial regions with di↵erent

sensitivity to the electroweak component. Inclusive Zjj production is dominated by

the strong production process, an example of which is shown in figure 2(a). The data

therefore provide important constraints on the theoretical modelling of QCD-initiated

processes that produce VBF-like topologies.3

2. Observation of electroweak Zjj production and measurements of the cross section in

two fiducial regions. Limits are also placed on anomalous WWZ couplings.

These measurements are performed using a combination of the Z ! e+e� and Z ! µ+µ�

decay channels.

Using electroweak Zjj production as a probe of colour-singlet exchange and as a val-

idation of the vector boson fusion process has been discussed extensively in the litera-

ture [1, 4, 5]. A previous measurement by the CMS Collaboration showed evidence for

2The VBF process cannot be isolated due to a large destructive interference with the electroweak Z-

boson bremsstrahlung process. The contribution to the electroweak cross section from non-resonant `+`�jj

production is less than 1% after applying the selection criteria used in this analysis.3Inclusive Zjj production contains a small (percent-level) contribution from diboson events (figure 2(b)).

– 2 –


• Strategy of the measurement is about the same as for EW Zjj:

• Measure inclusive (QCD+EW) W±W±jj cross section in 2 fiducial regions • (“inclusive region” and “VBS region”): varying sensitivity to the EW component

• Extraction on the EW W±W±jj production from the “VBS region”

• Set limits on anomalous quadratic gauge couplings

Vector Boson scattering

39

q

q

q0

W+

W+

q0

q

q

q0

W+

W+

q0

q

q

q0

W+

W+

q0

q

q

q0

W+

W+

q0

Self-interaction Higgs contribution Non resonant

Electroweak process:Sensitive to anomalous quartic gauge couplings


• First evidence for VBS

• BG only hypothesis excluded at 4.5σ• Counted 34 events, ~16 BG events

• Measurement in agreement with SM prediction

Vector Boson Scattering

40

4

Inclusive Region VBS Regione

±e

±e

±µ

±µ

±µ

±e

±e

±e

±µ

±µ

±µ

±

Prompt 3.0 ± 0.7 6.1 ± 1.3 2.6 ± 0.6 2.2 ± 0.5 4.2 ± 1.0 1.9 ± 0.5Conversions 3.2 ± 0.7 2.4 ± 0.8 – 2.1 ± 0.5 1.9 ± 0.7 –Other non-prompt 0.61 ± 0.30 1.9 ± 0.8 0.41 ± 0.22 0.50 ± 0.26 1.5 ± 0.6 0.34 ± 0.19W

±W

±jj Strong 0.89 ± 0.15 2.5 ± 0.4 1.42 ± 0.23 0.25 ± 0.06 0.71 ± 0.14 0.38 ± 0.08

W

±W

±jj Electroweak 3.07 ± 0.30 9.0 ± 0.8 4.9 ± 0.5 2.55 ± 0.25 7.3 ± 0.6 4.0 ± 0.4

Total background 6.8 ± 1.2 10.3 ± 2.0 3.0 ± 0.6 5.0 ± 0.9 8.3 ± 1.6 2.6 ± 0.5Total predicted 10.7 ± 1.4 21.7 ± 2.6 9.3 ± 1.0 7.6 ± 1.0 15.6 ± 2.0 6.6 ± 0.8Data 12 26 12 6 18 10

TABLE II: Estimated background yields, observed number of data events, and predicted signal yields for the three channelsare shown with their systematic uncertainty. Contributions due to interference are included in the W

±W

±jj electroweak

prediction.

[GeV]jjm

Even

ts/5

0 G

eV

-110

1

10

210 Data 2012 Syst. Uncertainty

jj Electroweak±W± Wjj Strong±W± W

Prompt Conversions Other non-prompt

ATLAS = 8 TeVs, -120.3 fb

[GeV]jjm200 400 600 800 1000 1200 1400 1600 1800 2000Da

ta/B

ackg

roun

d

0

5

Data/BkgBkg Uncertainty(Sig+Bkg)/Bkg

FIG. 1: The mjj distribution for events passing the inclu-sive region selections except for the mjj selection indicatedby the dashed line. The black hatched band in the upper plotrepresents the systematic uncertainty on the total prediction.On the lower plot the shaded band represents the fractionaluncertainty of the total background while the solid line andhatched band represents the ratio of the total prediction tobackground only and its uncertainty. The W

±W

±jj predic-

tion is normalized to the SM expectation.

production, and the fiducial cross sections in the two re-gions (�fid) are measured by combining the three decaychannels in a likelihood function. Systematic uncertain-ties are taken into account with nuisance parameters.

The signal e�ciency in each fiducial region is definedas the number of expected signal events after selectionsdivided by the number of events passing the respectivefiducial region selections at particle level. The e�ciencyaccounts for the detector reconstruction, migration intoand out of the fiducial volume, identification, and triggere�ciency; it is 56%, 72%, 77% for the inclusive region and57%, 73%, 83% for the VBS region in the e±e±, e±µ±,

|jjyΔ|0 1 2 3 4 5 6 7 8 9

Even

ts

5

10

15

20

25

30 Data 2012 Syst. Uncertainty

jj Electroweak±W± Wjj Strong±W± W

Prompt Conversions Other non-prompt

ATLAS = 8 TeVs, -120.3 fb

> 500 GeVjjm

FIG. 2: The |�yjj | distribution for events passing all inclu-sive region selections. The |�yjj | selection is indicated by adashed line. The W

±W

±jj prediction is normalized to the

SM expectation.

µ±µ± channels respectively. The e�ciency also accountsfor the contribution of leptonic ⌧ decays, which are notincluded in the fiducial cross-section definition: 10% ofsignal candidates are expected to originate from leptonic⌧ decays. The uncertainty on the signal e�ciency is dom-inated by the jet reconstruction uncertainty of 6%.

The measured fiducial cross section for strong and elec-troweak W±W±jj production in the inclusive region is�fid = 2.1± 0.5(stat)± 0.3(syst) fb. The measured fidu-cial cross section for electroweak W±W±jj production,including interference with strong production in the VBSregion, is �fid = 1.3± 0.4(stat)± 0.2(syst) fb. The mea-sured cross sections are in agreement with the respectiveSM expectations of 1.52± 0.11 fb and 0.95± 0.06 fb.

Additional contributions to W±W±jj production canbe expressed in a model-independent way using higher-dimensional operators leading to anomalous quarticgauge boson couplings (aQGCs). The measured crosssection in the VBS fiducial region is used to set lim-its on aQGCs a↵ecting vertices with four interactingW bosons. The Whizard event-generator [39] is used

]-4 [TeV4Λ / S,0f-800 -600 -400 -200 0 200 400 600 800

]-4

[TeV

4Λ

/ S,

1f

-2000

-1000

0

1000

2000 ATLAS��20.3 fb-1, s = 8 TeV�pp → W± W± jj�K-matrix unitarization

68% CL95% CLexpected 95% CLStandard Model

confidence intervals

aQGC interpretation:

[fb]VBS.WW σ

-1 -0.5 0 0.5 1 1.5 2 2.50

0.2

0.4

0.6

0.8

1

±e±e

±µ±e

±µ±µ

Combination

4.0 [fb]± 1.0 ±0.4

0.25 [fb]± 0.6 ±1.3

0.15 [fb]± 0.8 ±1.7

0.2 [fb]± 0.4 ±1.3

ATLAS=8 TeVs,-120.3 fb

0.06 [fb]±=0.95 VBSWWσSM

NLO, POWHEG-BOX, CT10


Conclusion EWK production

41

Electroweak prod.: evidence of VBS, sensitive to anomalous coupling no deviation from SM predictions observed

qcd and vector boson + jets measurements with atlas · 2015. 3. 12. · atlas kristof schmieden les...

Documents