Physics at the Tevatron: Lecture I

MarinaCobal

UniversitàdiUdine

1

Physics at Hadron Colliders Part III: W

•  Because of it’s long lifetime, the muon is basically a stable particle for us (cτ ~ 700 m)

•  It does not feel the strong interaction

–  Therefore, they are very penetrating

•  It‘s a minimum ionising particle (MIP)

–  Only little energy deposit in calorimeter

•  However, at high energies (E>0.2 TeV) muons can sometimes behave more like

electrons!

–  At high energies radiative losses begin to dominate and muons can undergo

bremsstrahlung

•  Muons are identified as a track in the muon chambers and in the

inner tracking detectors

•  Both measurements are combined for the best track results

2

Muons

3

Electrons and Photons

•  Energy deposit in calorimeter

–  “Narrow“ shower shape in EM calorimeter

–  Energy nearly completely deposited in EM calorimeter

•  Little or no energy in had calorimeter (hadronic

leakage)

•  Electrons have an associated track in inner detector

•  If there is no track found in front of calorimeter: photon

–  But be careful, photon might have converted before

reaching the calorimeter

•  Input to clustering:

–  Cells calibrated at the EM scale

•  Sum energy in EM calo, correct for losses in upstream material, longitudinal

leakage and possible other lossses between calo layers (if applicable)

–  e.g.

•  Typically need to find best compromise between best resolution and best linearity 4

( )33210 EWEEEWbE presrec ++++= λ

Cluster reconstruction Losses between PS and S1

strips

e± with energy E

Middle Back

Presampler LAr Calorimeter Upstream Material

Upstream Losses

Longitudinal Leakage

5

e/jet and γ/jet separation

•  Leakage into 1st layer of hadronic

calorimeter

•  Analyse shape of the cluster in the different

layers of the EM calo

–  “narrow“ e/γ shape vs “broad“ one from

mainly jets

•  Look for sub-structures within one cluster

–  Preshower in CMS, 1st EM layer with

very fine granularity in ATLAS

–  Very useful for π0→γγ / γ separation, 2

photons from π0 tend to end up in the

same cluster at LHC energies

jet

e or γ

cut

Transverse shower shape in 2nd EM layer (ATLAS)

ATLAS

6

Bremsstrahlung

•  Electrons can emit photons in the presence

of material •  At LHC energies:

–  electron and photon (typically) end up in the same cluster

–  Electron momentum is reduced –  E/p distribution will show large tails

•  Methods for bremsstrahlung recovery –  Gaussian Sum Filter, Dynamic

Noise Adjustment –  Use of calorimeter position to correct for

brem –  Kink reconstruction, use track

measurement before kink

7

Material in Tracker

•  Silicon detectors at hadron colliders constitute significant amounts of material, e.g. for R<0.4m –  CDF: ~20% X0 –  ATLAS: ~20-90% X0 –  CMS: ~20-100% X0

CMS CMS

8

Effects of Material on Analysis

•  Causes difficulties for e/γ identification:

–  Bremsstrahlung

–  Photon conversions

•  Constrained with data:

–  Photon conversions

–  E/p distribution

–  Number of e±e± events

9

Conversion reconstruction •  Photons can produce electron pairs in the

presence of material

•  Find 2 tracks in the inner detector from the same

secondary vertex

–  Need for outside-in tracking

•  However, can be useful:

–  Can use conversions to x-ray detector and

find material before calorimeter (i.e. tracker) ATLAS

CDF

W/Z: lepton ID

10

For electrons we need: High efficiency for isolated electrons Low misidentification of jets Measured using Z’s Electron reconstruction improved • Track, calorimeter cluster matching • Recover bremsstrahlung losses Muon Performance:MW Efficiency: 98% depending on |η| Measured using Z’s

ETmiss measured in Z→µµ events (Data vs. MC) Very good agreement over 6 orders of magnitude with overall Pythia6 normalization to data.

ATLAS-CONF-2012-101

11

Electron Identification

•  Desire: –  High efficiency for (isolated) el –  Low misidentification of jets

•  Cuts: –  Shower shape –  Low hadronic energy –  Track requirement –  Isolation

•  Performance: –  Efficiency measured from Z’s using “tag and probe” method

–  Usually measure “scale factor”: •  SF=εData/εMC (=1 for perfect MC) •  Easily applied to MC

CDF ATLAS

Loosecuts 85% 88%

Tightcuts 60‐80% ~65%

12

Lepton Momentum Scale

•  Momentum scale: –  Cosmic ray data used for detailed cell-

by-cell calibration of CDF drift chamber

–  E/p of e+ and e- used to make further small corrections to p measurement

–  Peak position of overall E/p used to set electron energy scale

•  Tail sensitive to passive material

13

Momentum/Energy Scale and Resolution

•  Systematic uncertainty on momentum scale: 0.04%

Υ→µµ

Z→µµ

Z→ee

14

Beware of Environment

•  Efficiency of e.g. isolation cut depends on

environment

–  Number of jets in the event

•  Check for dependence on distance to

closest jet

•  Decays

–  17% in muons

–  17% in electrons

–  ~65% of τ’s decay hadronically in 1- or 3-prongs

(τ±→π±ν, τ±→π±ν+nπ0 or τ±→3π±ν, τ±→3π±ν+nπ0)

•  For reconstruct hadronic taus

–  Look for “narrow“ jets in calorimeter (EM + had)

•  i.e. measure EM and hadronic radius

(measurement of shower size in η-ϕ):

∑Ecell⋅R2cell/∑Ecell

–  Form ΔR cones around tracks

•  tau cone

•  isolation cone

–  associate tracks (1 or 3) 15

Taus

16

Missing Transverse Energy •  Missing energy is not a good quantity in a hadron collider as much energy from

the proton remnants are lost near the beampipe

•  Missing transverse energy (ET) much better quantity

–  Measure of the loss of energy due to neutrinos

•  Definition:

– 

•  Best missing ET reconstruction

–  Use all calorimeter cells with true signal

–  Use all calibrated calorimeter cells

–  Use all reconstructed particles not fully reconstructed in the calorimeter

•  e.g. muons from the muon spectrometer

•  But it‘s not that easy...

–  Electronic noise might bias your ET measurement

–  Particles might have ended in cracks / insensitive regions

–  Dead calorimeter cells

–  Effects from beamhalo events

•  Corrections needed to calorimeter missing ET

–  Correction for muons

•  Recall: muons are MIPs

–  Correct for known leakage effects (cracks etc)

–  Particle type dependent corrections

•  Each cell contributes to missing ET according to the final calibration of

the reconstructed object (e, γ, µ, jet…)

–  Pile-up effects will need to be corrected for17

Missing Transverse Energy

18

Missing Transverse Energy

•  Difficulttounderstandquantity

16/12/12 C.8 A. Bettini 19

Larghezze leptoniche W

MW =g

22

8GF

!

"#

$

%&

1/2

=!"

2GF

1

sin#W=

37.3

sin#W GeV

MW

MZ

= cos!W

MW= 80 GeV M

Z! 91 GeV

Le masse (approssimativamente)

Da valore misurato di θW

W. Larghezze leptoniche (uguali per universalità). Per calcolo serve teoria

!e" = !µ" = !#" =g

2

$%&

'()

2

MW

24*=

1

2

GFMW

3

3 2*! 225 MeV

NB. In generale le larghezze dei BI sono proporzionali al cubo della massa

W: Larghezze adroniche

!cd" ! W # cd( ) = 3$ V

cd

2

!e% = 3$ 0.22

2$ !

e% & 33 MeV

mt> m

W! "

td= "

ts= "

tb= 0

Vub<<1 ! "

ub# 0 V

cb<<1 ! "

cb# 0

!us" ! W # us( ) = 3! V

us

2

"e! = 3!0.224

2!"

e! ! 35 MeV

Tre colori

!ud" ! W # ud( ) = 3$ V

ud

2

!e% = 3$ 0.974

2$ !

e% = 2.84 $ !e% & 640 MeV

!cs" ! W # cs( ) = 3$ V

cs

2

!e% = 3$ 0.99

2$ !

e% & 660 MeV

!W" 2.04 GeV

Per calcolare le larghezze in qq bisogna tener conto di • un fattore 3 perché ci sono 3 colori • la matrice di mescolamento

Due tipi di decadimento •  nella stessa famiglia •  in diverse famiglie (piccola larghezza)

Tutti gli elementi non diagonali sono piccoli, quindi W decade poco in quark di diverse famiglie

Formazione risonante di W Sia W sia Z si possono produrre in formazione con un collisore quark-(anti)quark

⇒ UA1 (CERN). Scoperta nel 1983

s = xqxqsEnergia nel CM dei quark

u + d! e"+!

e

Devono avere lo stesso colore

Devono avere la giusta chiralità

Processo principale da osservare

u + d ! e++"

e

Formazione risonante di W

u + d! e"+#

e

Vicino a risonanza ⇒ Breit e Wigner (come per e+e–)

! ud! e""

e( ) =1

9

3!

s

#ud#e"

s "MW( )

2

+ #W/ 2( )

2

Probabilità che i colori siano uguali

Piccola σmax<<< σtot≈100 mb. Le interazioni deboli sono deboli!

!max ud! e""

e( ) =!max ud ! e+"

e( )

=4!

3

1

MW

2

#ud#e"

#W

2=

4!

3

1

812

0.640$0.225

2.042

GeV-2%& '($388 µb/GeV

-2%& '( ) 8.8 nb

Sezioni d’urto Fascio di p = fascio a larga banda di partoni (q, g, e qualche q) Fascio di p = fascio a larga banda di partoni (q, g, e qualche q)

< x >!M

W

s!M

Z

s! 0.15

OK. Ce ne sono parecchi

Consideriamo l’annichilazione di un quark e un antiquark di valenza se √s=630 GeV, la frazione di quantità di moto che serve per essere in risonanza

Produzione di W da pp La larghezza della banda delle energie dei partoni >> larghezze delle risonanze W e Z Il riferimento del lab. è il cm di pp, non di qq; questa coppia, e la W o Z cui dà origine, hanno un moto longitudinale diverso da caso a caso

s = xdxus

Calcolo di sez. d’urto (incertezze di QCD e di funzioni di struttura) prevedeva a √s=630 GeV:

! pp"W " e#e( ) = 530

+170

$90pb

@ √s=630 GeV <x> = MW/√s≈0.15, quark di valenza dominano sul mare

più analogo da ud

Le sezioni d’urto crescono rapidamente con l’energia e con essa le possibilità di momento longitudinale del bosone

Formazione risonante di W e Z Nel 1978 Cline, McIntire e Rubbia proposero di trasformare l’acceleratore di protoni SpS del CERN in un anello di accumulazione pp nel quale protoni e antiprotoni potevano circolare in versi opposti, nella stessa struttura magnetica (esistente), sfruttando la simmetria CPT

Il grande problema che Rubbia e Van der Meer risolsero fu il “raffreddamento” dei pacchetti di particelle dei fasci a dimensioni abbastanza piccole nel punto di collisione

Nel 1983 si raggiunse la luminosità L=1032 m–2 s–1, sufficiente a scoprire W e Z.

Nel 1983 W e Z furono scoperte

Esercizio. Quanti eventi W→eν e Z →e+e– si rivelano in un anno con luminosità L=1032 m–2 s–1 ed efficienza di rivelazione del 50%?

I segnali La produzione di IVB è un processo raro 10–8 -- 10–9 (σtot(pp)≈ 70 mb = 7×1010 pb ) [l’interazione debole, è debole] Il potere di reiezione del rivelatore deve essere > 1010 Stati finali più frequenti sono qq

!

" #B W $ qq ( ) = 3" #B W $ l% l( ) 3 = numero di colori

Sperimentalmente q ⇒ jet Fondo enorme da

!

gg" gg, gq" gq, gq " gq , qq " qq

Gli stati finali leptonici hanno un S/N più favorevole

W → e νe e isolato, alto pT

W → µ νµ µ isolato, alto pT

Z → e– e+ 2e 2 isolati, alto pT

Z → µ–µ+ 2µ 2 isolati, alto pT

} + ν ad alto pT = grande pT mancante Rivelatore ermetico (UA1 misurava pT mancante con la precisione di qualche GeV)

Importante quantità cinematica misurata: il momento trasverso pT = componente del momento perpendicolare ai fasci

UA1. In costruzione

16/12/12

UA1. Il rivelatore centrale va al museo

16/12/12 C.8 A. Bettini 29

UA1. Prima W

W→eν

L’eliminazione delle tracce con pT< 1 GeV rende completamente pulito l’evento, sopravvivono solo elettrone e il “neutrino”

Nei calorimetri elettromagnetici le W appaiono come un deposito localizzato di energia in direzione opposta al momento mancante

Misura di MW

W→l νl pTe

e

νe

W

LAB

e

νe

W

CM. W

pTe

θ*

pe = mW/2

I momenti trasversi di q e q sono piccoli, quindi lo è anche quello della W.

pTe è il medesimo nei due riferimenti = (mW/2) sin θ*

Distribuzione angolare di decadimento nel CM nota

!

dn

d"*trasf .coordinate

# $ # # # # # dn

dpT=dn

d"*d"*

dpT

!

dn

dpT=

1

mW

2

"

# $

%

& ' 2

( pT2

dn

d)*

Picco “Jacobiano” per pTe = mW/2

Picco “Jacobiano” per pTmissing = mW/2

Il moto trasverso della W (pTW≠0) sbrodola il picco, ma non lo cancella. La misura di mW si

basa sulla misura dell’energia del picco o del fronte di discesa

W’s @ UA1

UA1 MW= 82.7±1.0(stat)±2.7(syst) GeV ΓW<5.4 GeV UA2 MW= 80.2±0.8(stat)±1.3(syst) GeV ΓW<7 GeV

33

W Boson mass •  Real precision measurement:

–  LEP: MW=80.367±0.033 GeV/c2

–  Precision: 0.04%

•  => Very challenging!

•  Main measurement ingredients:

–  Lepton pT

–  Hadronic recoil parallel to lepton: u||

•  Z→ll superb calibration sample:

–  but statistically limited:

•  About a factor 10 less Z’s than W’s

•  Most systematic uncertainties are related to

size of Z sample

–  Will scale with 1/√NZ (=1/√L)

34

How to Extract the W Boson Mass

•  Uses “Template Method”:

–  Templates created from MC simulation for different mW

–  Fit to determine which template fits best

–  Minimal χ2 ⇒ W mass!

•  Transverse mass of lepton and Met

mW=80.4 GeV +1.6 GeV - 1.6 GeV

How to Extract the W Boson Mass

•  Alternatively can fit to –  Lepton pT or missing ET

•  Sensitivity different to different systematics –  Very powerful checks in this analysis:

•  Electrons vs muons •  Z mass •  mT vs pT vs MET fits

–  The redundancy is the strength of this difficult high precision analysis

36

Hadronic Recoil Model

•  Hadronic recoil modeling

–  Tune data based on Z’s

–  Check on W’s

37

LHC signals of W’s

•  0.2-0.3 pb-1 yield clean signals of W’s and Z’s

[GeV]T m40 50 60 70 80 90 100 110 120

Eve

nts

/ 2.5

GeV

2000

4000

6000

8000

10000

12000

14000

[GeV]T m40 50 60 70 80 90 100 110 120

Eve

nts

/ 2.5

GeV

2000

4000

6000

8000

10000

12000

14000 = 7 TeV)sData 2010 (

! e"W

QCD

!# "W

-1 L dt = 36 pb$ATLAS

Systematic Uncertainties

•  Overall uncertainty 60 MeV for both analyses –  Careful treatment of correlations between them

•  Dominated by stat. error (50 MeV) vs syst. (33 MeV)

Limited by data statistics

Limited by data and theoretical understanding

Wμν

MTWµ

PTZ

µ

Mee

W signal @ LHC

40

W Boson Mass

•  World average:

MW=80399 ± 23 MeV •  Ultimate Run 2 precision:

~15 MeV

(GeV)Wm80 80.2 80.4 80.6

LEP2 average 0.033±80.376

Tevatron 2009 0.031±80.420

D0 Run II 0.043±80.402

D0 Run I 0.083±80.478

Tevatron 2007 0.039±80.432

CDF Run II 0.048±80.413

CDF Run 0/I 0.081±80.436

World average 0.023±80.399

July 09

W Boson Width

1600 2000 2400

Width of the W Boson

[MeV]W! February 2010

Measurement [MeV]W!

/ dof = 1.4 / 42"

SM* (Preliminary)

CDF-Ia 329±2,032

CDF-Ib 138±2,043

-I#D 172±2,242

CDF-II 72±2,033

-II#D 72±2,034

Tevatron Run-I/II 49±2,046

LEP-2* 83±2,196 42±World Av.* = 2,085

Spin e polarizzazione della W

Nel riferimento del c.m. della W l’energia dell’elettrone >> me. chiralità ≈ elicità

V–A ⇒W si accoppia solo a

fermioni con elicità – antifermioni con elicità +

Mom. ang. Tot. J=SW=1 Jz (iniz.) = λ = –1 Jz’ (fin.) = λ’ = –1

!

d"

d#$ d%1,%1

1[ ]2

=1

21+ cos&*( )

'

( ) *

+ ,

2

N.B. Se fosse stato V+A

!

d"

d#$ d1,1

1[ ]2

= –1

21+ cos%*( )

&

' ( )

* +

2

L’asimmetria avanti-indietro è conseguenza della violazione di P

Per distinguere V–A da V+A sono necessarie misure di polarizzazione dell’elettrone

W!" e

!#e

W Cross Section Results σTh,NNLO=2687±54pb W

•  Uncertainties: –  Experimental: 2% –  Theoretical: 2% –  Luminosity: 6%

•  Can we use these processes to normalize luminosity? –  Is theory reliable enough?

LHC W Cross Sections

•  Data agree well with theoretical

expectation

–  Uncertainties: 13% (W), 17% (Z)

–  Luminosity uncertainty 10%

44

45

WW Cross Section at Tevatron

•  WW cross section

–  Use W→µν and W→eν

–  2 leptons and missing ET

•  Result:

–  Data: σ=13.6+-3.1 pb

–  Theory: σ=12.4+-0.8 pb

•  Campbell, Ellis

Total W production x-section

•  Inclusive cross sections:

•  Experimental precision at the 1% level, especially for ratio-observables

•  Excellent agreement with NNLO QCD, both at 7 and 8 TeV

•  Many diff. distributions measured

•  Confidence in background predictions for many searches

W charge asymmetries

47

Phys. Rev. D85 (2012) 072004 CMS-PAS-EWK-11-005 arXiv:1206.2598

Sensi&vetochoicesofPDF

|l!|

0 0.5 1 1.5 2 2.5

lA

0.1

0.15

0.2

0.25

0.3

0.35 = 7 TeV)sData 2010 (

MSTW08HERAPDF1.5ABKM09JR09

-1 L dt = 33-36 pb"

Stat. uncertainty

Total uncertainty

ATLAS

W→lν

LHC is a pp-collider: 2 valence up quarks, 1 valence down quark Sea quark Valence quark Since valence quarks have high x ➡ more W+ (u dbar) than W-(ubar d) ( remember that the proton is uud) Here the PDF’ are giving very different predictions

48

(W)

! n

-jets

)"

(W +

!

-310

-210

-110

data energy scale unfolding MadGraph Z2 MadGraph D6T Pythia Z2

CMS

= 7 TeVs at -136 pb

# e$W > 30 GeVjet

TE

inclusive jet multiplicity, n

(n-1

)-jet

s)"

(W +

!

n-je

ts)

"(W

+

! 0

0.1

0.2

1 2 3 4

W/Z + jets : jet multiplicities

jets

) [pb

]je

tN!

(W +

"

1

10

210

310

410 + jets#l$W

=7 TeVsData 2010, ALPGENSHERPAPYTHIABLACKHAT-SHERPA

-1Ldt=36 pb% jets, R=0.4Tanti-k

|<4.4jet y>30 GeV, |Tjetp

ATLAS

jets

) [pb

]je

tN!

(W +

"

1

10

210

310

410

jetNInclusive Jet Multiplicity,

0! 1! 2! 3! 4!

Theo

ry/D

ata

0

1

jetNInclusive Jet Multiplicity,

0! 1! 2! 3! 4!

Theo

ry/D

ata

0

1

jetNInclusive Jet Multiplicity,

0! 1! 2! 3! 4!

Theo

ry/D

ata

0

1

Inclusive Jet Multiplicity Ratio

0!1/! 1!2/! 2!3/! 3!4/!

- 1

jets

)je

tN!

(W +

"

jets

) /

jet

N!(W

+

"

0.1

0.2

0.3

0.4 + jets#l$W

=7 TeVsData 2010, ALPGENSHERPAPYTHIABLACKHAT-SHERPA

-1Ldt=36 pb%

jets, R=0.4Tanti-k|<4.4jet y>30 GeV, |

Tjetp

ATLAS

Inclusive Jet Multiplicity Ratio

0!1/! 1!2/! 2!3/! 3!4/!

- 1

jets

)je

tN!

(W +

"

jets

) /

jet

N!(W

+

"

0.1

0.2

0.3

0.4

Goodagreementwithmul&‐partonmatrixelement+partonshowerpredic&ons

PurepartonshowerMCinadequatefordescribingmul&‐jetfinalstates

Phys. Rev. D85 (2012) 092002 JHEP 01 (2012) 010

normalizedtoσtot

!

" (W+ # n jets)

" (W+ # n -1 jets)

l l )

+ 1

-jet)

!(Z

("

) + 1

-jet)

# l

!(W

("

4

6

8

10

12

14

16 Channels combined!Data e-

Total syst. uncertainty stat. uncertainty$Total syst.

MCFM

-1 Ldt = 33 pb%

ATLAS > 20 GeV

T| < 2.5, p&|

l l )

+ 1

-jet)

!(Z

("

) + 1

-jet)

# l

!(W

("

4

6

8

10

12

14

16

Threshold [GeV]T

Jet p40 60 80 100 120 140 160 180 200

Theo

ry /

Dat

a ra

tio

0.60.8

11.21.4 PYTHIA

ALPGENMCFM

Threshold [GeV]T

Jet p40 60 80 100 120 140 160 180 200

Theo

ry /

Dat

a ra

tio

0.60.8

11.21.4

inclusive jet multiplicity, n

(W)

!(Z

)!

n-je

ts)

"(Z

+

! n

-jets

)"

(W +

!

0

0.5

1

1.5

2

data energy scale unfolding MadGraph Z2 Pythia Z2

CMS

= 7 TeVs at -136 pbe channel

> 30 GeVjetTE

1 2 3 4

X. Wu, SUSY2012, 13/08/12

inclusive jet multiplicity, n

(W)

!(Z

)!

n-je

ts)

"(Z

+

! n

-jets

)"

(W +

!

0

0.5

1

1.5

2

data energy scale unfolding MadGraph Z2 Pythia Z2

CMS

= 7 TeVs at -136 pb channelµ

> 30 GeVjetTE

1 2 3 449

Jetenergyscalesystema&cmostlycancelsout

Measurementswithsmallsystema&cuncertainty

Phys. Lett. B708 (2012) 221-240 JHEP 01 (2012) 010

W + jets/Z + jets : ratio and double ratio

!

" (W (# l$ )+1 jet)

" (Z(# ll)+1 jet)!

" (W+ # njets)

" (Z+ # njets)

" (Z)

" (W )echannel

µchannel

•  Importance of diboson production •  Sensitive to Triple Gauge Couplings (TGC): fundamental test of SM •  WWγ and WWZ allowed; ZZγ, Zγγ and ZZZ forbidden •  Search for beyond SM → anomalous coupling and resonances •  Background to Higgs and other new physics searched

•  If the TGC’s have non SM values, this shows up at large pT (short distances) •  This is a region where the background from the right diagram is small

Diboson (WW, WZ, ZZ, Wγ, Zγ) production

50

Thisprocesshas… ..thisasabackground

Diboson (WW, WZ, ZZ)

51

ATLAS-CONF-2012-025

ATLAS-CONF-2012-090

arXiv:1208.1390

WW production

52

Measure cross section in WW→2l2n channel → Need good calibration for missing ET

)[GeV]Tmiss(llETm

50 100 150 200 250 300 350

Even

ts /

20G

eV

0

50

100

150

200

250

300

350

400

450DataDibosonW+jet/dijettopDrell-Yan

!l!l"WWstat+syst#

ATLAS Preliminary-1Ldt = 4.70fb$

= 7TeVs

8TeV,CMS(3.54T−1)7TeV,ATLAS(4.7T−1)/CMS(4.92T−1)

Alreadysystema&cslimited!

!

ATLAS:53.4 ± 2.1(stat)± 4.5(syst)± 2.1(lumi) pb

CMS: 52.4 ± 2.0(stat)± 4.5(syst)±1.2(lumi) pb

NLO : 45.1± 2.8 pb

69.9± 2.8(stat)± 5.6(syst)±3.1(lumi) pb

NLO: 57.3!1.6

+2.4 pb

ATLAS-CONF-2012-025 CMS PAS SMP-12-005 CMS PAS SMP-12-013