Physics at Hadron Colliders - Uniudcobal/marina_Z_3.pdf · 1 Physics at the Tevatron: Lecture I Marina Cobal University of Udine Trieste, ﬁsica sperimentale nucleare e subnucleare

1

Physics at the Tevatron: Lecture I

Marina Cobal

University of Udine

Trieste, fisica sperimentale nucleare e subnucleare

Physics at Hadron Colliders

Part IV: Z

22/12/12

C.8 A. Bettini 2

UA1. Prima Z

Z→e+ e–

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

Il rivelatore centrale tracciante nel campo magnetico misura segno della carica e momento I calorimetri misurano l’energia degli elettroni Si controlla che E=p

Nei calorimetri elettromagnetici le Z appaiono come due depositi localizzati di energia in direzioni opposte

Dilepton mass spectra near the Z0 peak (CDF Collaboration)

More precise methods give world average values of

MZ = 91.187±0.007 GeV/c2

ΓZ = 2.490 ±0.007 GeV/c2

corresponding to a lifetime of 2.6x10-25 s

Branching ratios of leptonic decay modes of Z0 are around 3.4% for each lepton generation

Misura di MZ E1 (e–, µ–)

E2 (e+, µ+)

θ

Z0! e

+e"

m2 = E

1+ E

2( )2

!!p1+!p2( )2

= E1

2 + E2

2 + 2E1E2! p

1

2! p

2

2! 2p

1p2cos"

# 2E1E2(1! cos" )

!

m2" 4E1E2 sin

2# /2

! m2( )

m2

=! E

1( )E1

"

#$%

&'

2

+! E

2( )E2

"

#$%

&'

2

+! (( )tan( / 2

"

#$%

&'

2

!

" #100˚ tan"

2$ O(1) " misurato dalla misura delle tracce % "( ) $10

–2

Domina l’errore sulle energie (calorimetro)

! E( )E

=20%

E

! m2( )

m2

= 2! E( )E

" 4 # 6%

errore statistico su singola misura σ(m)≈2-3 GeV errore sulla scala ≈3.1 GeV (UA1); 1.7 GeV (UA2) UA1 (24 Z→ee) MZ=93.1±1.0(stat)±3.1(syst) GeV UA2 MZ=91.5±1.2(stat)±1.7(syst) GeV

! m( )m

=1

2

! m2( )

m2

" 2 # 3%

Carlo Rubbia (1934) �Simon van der Meer (1925)

•  Nobel Prize 1984 for their decisive contributions to the large project, which led to the discovery of the field particles W and Z, communicators of weak interaction

•  Nobel Prize 1979 for their contributions to the theory of the unified weak and electromagnetic interaction between elementary particles, including, the prediction of the weak neutral current

Sheldon Lee Glashow (1932) � Abdus Salam (1926 – 1996)�Steven Weinberg (1933)

8

SM last milestones

•  Discovery of a Higgs-like particle 2012

9

Z bosons

Branching Ratio

  Ovvero quante volte la Zo decade in un particolare tipo di particelle…

Leptonic decays Branching ratio

due neutrini 20 %

due elettroni 3.67 %

due muoni 3.67 %

due tau 3.67 % Quark decays Branching ratio* Total 69.9 %

2 jets ~ 40 %

3 jets ~ 24 %

4 o piu’ jets ~ 6 %

Previsioni teoriche

Trionfo del Modello Standard 1987-1988 analisi complete di tutti i dati disponibili allora concludendo che il MS è in perfetto accordo con i dati L’angolo di Weinberg deve aver lo stesso valore in ogni caso, ma nel confronto bisogna introdurre in ciascun caso delle correzioni radiative, previste dalla teoria

Le principali ! (m

t

2"m

b

2) # m

t

2lnM

H

L’accordo si perde se mt>180-200 GeV

Da misure precise di LEP di mW e mZ ⇒ mt=166±27 GeV

Udine, 10 marzo 2006 Masterclasses 2006 12

Zo → e+ e- ALEPH


Zo → µ+ µ- ALEPH


Zo → τ+ τ- ALEPH


Zo → qq ALEPH


Zo → qq DELPHI: WIRED

DELPHI:

Uno dei quattro rivelatori LEP (ALEPH, DELPHI, L3, OPAL)

Installato nel 1989

Presa dati fino al 2000

Lunghezza e diametro del cilindro: 10 m

Peso totale: 3500 ton

20 sottorivelatori

La risonanza Le sezioni d’urto dei processi e++e–→ f++f– (con f≠e, altrimenti bisogna considerare anche lo scambio nel canale t) sono al prim’ordine dovute agli scambi nel canale s

Nei pressi della risonanza (√s≈ mZ) domina lo scambio di Z nel canale s

Γe larghezza parziale in e+e– , Γf larghezza parziale in f+f–, Γ larghezza totale

!e+ +e–" f

+ + f –mZ( ) =

12#

mZ

2

$e$ f

$2al picco

! E( ) =3"

s

#e# f

s $mZ( )2

+ # / 2( )2%&'

()*

A differenza che in un collider adronico tutti gli eventi sono collisioni di oggetti elementari

18

Esempi. Sezione d’urto al picco !

e+ +e–" f

+ + f –mZ( ) =

12#

mZ

2

$e$ f

$2

! e+ + e–

" µ+ + µ–( ) =

12#

mZ

2

$e$µ

$2

=12#

912

842

24502= 5.3%10

&6 GeV

–2% 388 µb/GeV

–2 = 2.1 nb

Quante Z in µ+µ– si producono con una luminosità (tipica per LEP) L=1035m–2s–1

R = L! = 1035 m–2

s–1( )" 2.1"10#37 m2( ) = 0.02s–1

Cioè circa una al minuto

Quante Z in adroni si producono?

! e+ + e–

" adroni( ) =12#

mZ

2

$e$µ

$2

=12#

912

84 %1690

24502

= 40.2 nb

R = L! = 1035 m–2

s–1( )" 4 "10#36 m2( ) = 0.4s–1

Correzioni radiative ! Born E( ) =

3"

E2

#e# f

E $mZ( )2

+ # / 2( )2%&

'(

Quest’espressione, detta “di Born” è troppo semplificata. Ci sono importanti “correzioni radiative”. Le maggiori sono elettromagnetiche,

in linea di principio, note

Dominante: Brensstrahlung iniziale

Altre correzioni EM minori

La forma della riga

Se un elettrone o un positrone irradia un fotone l’energia della collisione diminuisce; diventa risonante √s>MZ. Coda alle alte energie δσ(picco)= 30%, δMZ≈ 200 MeV Si calcolano le correzioni “ovvie”, si corregge la curva misurata, si estraggono i parametri (massa, larghezza, altezza del picco)

MZ= 91.1875 ± 0.0021 GeV 2 ppm( )

!Z= 2.4952 ± 0.0023 GeV MS: !

Z= 2.4972 ± 0.0012 GeV[ ]

! 0= 41.540 ± 0.037 nb MS: ! 0

= 41.481± 0.014 nb"# $%

MZ come costante fondamentale, nei valori delle altre due ci sono incertezze teoriche dovute alla non conoscenza perfetta di MH, αs etc

Le larghezze parziali della Z Gli esperimenti a LEP hanno misurato • le larghezze parziali in e+e–, µ+µ–, τ+τ– • la “larghezza invisibile” cui contribuiscono tutte le generazioni di neutrini ed eventuali particelle neutre non previste • la larghezza in ≠cc individuando i vertici secondari di decadimento • la larghezza in ≠bb individuando i vertici secondari di decadimento Perfetto accordo con la teoria (e determinazione di sin2θW)

Re !"adr

"e

= 20.804 ± 0.050; Rµ !"adr

"µ

= 20.785 ± 0.033; R# !"adr

"#

= 20.764 ± 0.045

Verifica dell’universalità dell’accoppiamento debole neutro dei leptoni

!l= 83.984 ± 0.086 MeV MS: !

l= 84.042 ± 0.025 MeV[ ]

!adr= 1744.4 ± 2.0 MeV

Le larghezze parziali adroniche della Z !adr= 1744.4 ± 2.0 MeV

Negli eventi con due getti adronici non si riesce in generale a identificare la natura del quark Lo si può fare con charm e beauty che hanno vite dell’ordine del picosecondo, viaggiano dell’ordine del millimetro I rivelatori di vertice rivelano vertici secondari a qualche millimetro ⇒ decadimento di particella con c o b. Fit cinematico distingue le due

Rc! "

c/"

adr= 0.1721± 0.0030 MS: R

c= 0.1723± 0.0001[ ]

Rb! "

b/"

adr= 0.21629 ± 0.00036 MS: R

b= 0.21562 ± 0.00013[ ]

Esempio. Calcolare la distanza percorsa in una vita media da un D˚ e da un B˚ di energia 50 GeV

lB= !

B"Bc =

50

5.28#1#1.5 #10

$12 # 3#108= 4.3 mm

lD= !

D"Dc =

50

1.86#1# 4 #10

$13 # 3#108= 3 mm

Il numero di neutrini

!inv

!l

=12"R

e

MZ

2#0

$ Rl$ 3

Nν=2.9840±0.0082

• Poteva non essere intero se nuova fisica (altre particelle invisibili) • Ci sono tre famiglie, e solo tre

La larghezza totale è tanto maggiore quanto maggiore è il numero di canali aperti, in particolare il numero di neutrini (di massa <MZ/2). Ancora più sensibile è la sezione d’urto totale al picco, che dipende dalla larghezza totale

Il contributo a Γ di 3 neutrini è il 20% del totale. Conviene usare quantità che dipendono poco da correzioni radiative: σ0, MZ e il rapporto Rl=Γadr/Γl.

valore misurato

!inv" !

Z# !

adr# 3!

l$

!inv

!l

=!Z

!l

# Rl# 3

!0=12"

MZ

2

#e#adr

#Z

2$

#Z

2

#e#adr

=12"

MZ

2!0

$#Z

2

#e

2=12"R

e

MZ

2!0

!inv" 3!# = "2.7"1.5

+1.7 MeV

!0=12"

MZ

2

#adr#e

#Z

2

!!0

!0

= 2!"

Z

"Z

24

Z’s

  Z mass reconstruction   Invariant mass of two leptons

  Sets electron energy scale by comparison to LEP MZ measured value

Z signal @ LHC

Almost background free! together with good Z mass reconstruction this is another reason why Z->ll is used for many cross-checks

[GeV]eem70 80 90 100 110

Even

ts /

1 G

eV

200

400

600

800

1000

1200

1400 = 7 TeV)sData 2010 (

ee!Z

QCDATLAS

-1 L dt = 36 pb"

ee!Central Z

26

Z Boson Cross Section

  Trigger requires one electron with ET>20 GeV   Criteria at L1, L2 and L3/EventFilter

  You select two electrons in the analysis   With certain quality criteria   With an isolation requirement   With ET>25 GeV and |eta|<2.5   With oppositely charged tracks with

pT>10 GeV   You require the di-electron mass to

be near the Z:   66<M(ll)<116 GeV

=> εtotal = εtrigεrecεIDεkinεtrack

27

More Differential W/Z Measurements dσ/dy

dσ/dM

e+e–⇒W+W–. LEPII

+ +

+ correzioni radiative

Le previsioni della teoria sono pienamente soddisfatte La simmetria sottostante non è abeliana La posizione del fronte di salita dipende criticamente da MW e da GW Misure dirette al Tevatron (CDF e D0)

da !W

teor = 2.0 1+"

sM

Z

2( )#

$

%&&

'

())

GeV*"sM

Z

2( )

MW= 80.425± 0.034 GeV 42 ppm( )

!W= 2.133± 0.069 GeV

MS: !W= 2.093± 0.002 GeV[ ]

W/Z: Drell-Yan

29

W and Z production at LHC proceeds at the hard scattering level and first order via collisions of a valence quark (u,d) and a sea antiquark (Q≈100 GeV):

•  LHC parton density fractions in this process are typically 10-4 < x < 10-1.

•  Cross sections at LHC are a factor of 3 higher than at the Tevatron.

•  At LHC: > 106 W→lν events and ~ 105 Z → l+l- events per experiment and per lepton channel in 2011 data !!

ATLAS + CMS

Importance of DY

30

•  Process: production of two leptons at high PT

•  It allows the measurement of few important parameters of the SM the forward backward asymmetry AFB. measurement of sinϑW: via the measurement of asymmetry AFB measurement of the MW mass

•  W± production:

- W+ x-section larger than W-

- PDF: quark and antiquark density in protons [ud(bar)W+; u(bar) d W-] •  W+jets production

•  Production of (WW, ZZ, WZ): to study Triple Gauge coupling constants

All of this constitues background for new physics

Drell-Yan production cross sections dσ/dM

31

  Good agreement with NNLO theoretical prediction   NLO significantly undershoot the data in low M region

CMS-PAS-EWK-11-007

X. Wu, SUSY2012, 13/08/12 32

Measurementsalreadylimitedbysysandlumiuncertain1es

ATLASpointsoverlapwithCMS

GoodagreementwithNNLOpredic1on

Discrimina1ngpoweragainstdifferentPDFsets

Phys. Rev. D85 (2012) 072004 CMS-PAS-12-011

Total W and Z production x-section

Limits on Triple Gauge Coupling WWZ   Set limits to the anomalous couplings assuming an

effective Lagrangian with EW gauge and CP invariance

  WWZ coupling probed by WW and WZ

Phys. Lett. B 712 (2012) 289-308 Phys. Lett. B 709 (2012) 341–555

ICHEP,4.6K−1

Limits on Triple Gauge Coupling ZZZ and ZZγ

Z4f

-0.02 -0.01 0 0.01 0.02

! 4f

-0.04

-0.02

0

0.02

0.04

SM

No form factor assumedaTGC values outside contour excluded

Observed " 1±Expected " 2±Expected

llll# ZZ #pp

95% CL

-1 = 7 TeV, L = 5.0 fbsCMS Preliminary

  Set limits to the anomalous couplings assuming an effective Lagrangian   Use total number of events

(ATLAS) or the shape of the ZZ invariant mass (CMS)

Z5f

-0.02 -0.01 0 0.01 0.02

! 5f

-0.04

-0.02

0

0.02

0.04

SM



llll# ZZ #pp

95% CL


-1.5 -1 -0.5 0 0.5 1 1.5

Z40f

Z50f

!40f

!50f

-1Ldt = 1.02 fb"ATLAS,

#= $= 7 TeV, s


= 2 TeV$= 7 TeV, s

-1Ldt = 700 pb"LEP,

= 130~209 GeVs

-1Ldt = 1 fb"D0,

= 1.2 TeV$= 1.96 TeV, s

ATLAS

ZZ95% C.I.

CMS-PAS-SMP-12-007 Phys. Rev. Lett. 108 (2012) 041804

[GeV]WZm170-270 270-405 405-2500

Dat

a/M

C

0.51

1.5

fid WZ

!/fid W

Z!

"

0.2

0.4

0.6

0.8

1PreliminaryATLAS

= 7 TeV)sData 2011 (-1 L dt = 4.6 fb#

Monte Carlo (MC@NLO)Data Full. Uncertainty

WZ production

X. Wu, SUSY2012, 13/08/12 35

Measure cross section in WZ->3l1ν channel → very small bkg, lower statistics ATLAS new (ICHEP 2012)

CMS PAS EWK-11-010

normalizeddistribu1on(fiducial)

ATLAS(4.6K−1)

CMS(1.09K−1)

!

17.5 ± 0.6 pb

!

19.0"1.3

+1.4 (stat)± 0.8(syst)± 0.4(lumi) pb

!

17.0 ± 2.4(stat)±1.1(syst)±1.0(lumi) pb

!

17.6"0.6

+1.1 pb

ZZ production at 8 TeV

ATLAS(5.8K−1)

Four-lepton mass [GeV]100 150 200 250 300 350 400 450 500

Even

ts /

20G

eV

5

10

15

20

25

30

35ATLAS Preliminary! -1Ldt = 5.8 fb

= 8 TeVs

Datallll"ZZ

Background(d.d.)stat+syst#

-l+l-l+l"ZZ

[GeV]4lm200 400 600 800

Even

ts /

20 G

eV

0

5

10

15

20

25 DATA

ZZ

WZ/Z + jets


CMS(5.26K−1)(include2l2τ)

!

7.4 ± 0.4 pb9.3!1.0

+1.1 (stat)±!0.3

+0.4 (syst)± 0.3(lumi) pb

!

8.4 ±1.0(stat)± 0.7(syst)± 0.4(lumi) pb

!

7.7 ± 0.4 pb

ATLAS-CONF-2012-090 CMS-PAS-SMP-12-014

Limits on Triple Gauge Coupling WWZ   Set limits to the anomalous couplings assuming an

effective Lagrangian with EW gauge and CP invariance

  WWZ coupling probed by WW and WZ

Phys. Lett. B 712 (2012) 289-308 Phys. Lett. B 709 (2012) 341–555

ICHEP,4.6K−1

Limits on Triple Gauge Coupling ZZZ and ZZg

Z4f

-0.02 -0.01 0 0.01 0.02

! 4f

-0.04

-0.02

0

0.02

0.04

SM



llll# ZZ #pp

95% CL


  Set limits to the anomalous couplings assuming an effective Lagrangian   Use total number of events (ATLAS) or the

shape of the ZZ invariant mass(CMS)

Z5f

-0.02 -0.01 0 0.01 0.02

! 5f

-0.04

-0.02

0

0.02

0.04

SM



llll# ZZ #pp

95% CL


-1.5 -1 -0.5 0 0.5 1 1.5

Z40f

Z50f

!40f

!50f


#= $= 7 TeV, s


= 2 TeV$= 7 TeV, s

-1Ldt = 700 pb"LEP,

= 130~209 GeVs

-1Ldt = 1 fb"D0,

= 1.2 TeV$= 1.96 TeV, s

ATLAS

ZZ95% C.I.

CMS-PAS-SMP-12-007

Phys. Rev. Lett. 108 (2012) 041804

39

Acceptance of kinematic cuts

40

Acceptance of Kinematic Cuts: Z’s

  Some events are kinematically outside your measurement range

  E.g. at Tevatron: 63% of the events fail either pT or η cut   Need to understand how certain these 63% are   Best to make acceptance as large as possible

  Results in smaller uncertainties on extrapolation

X. Wu, SUSY2012, 13/08/12 41

Sensi1vitytodifferentPDFsetsapproaching1σ!

) [nb]-l+ l!*" BR(Z/# Ztot$

0.8 0.9 1

) [nb

]% l

!!

BR

(W#

!Wto

t$

8

9

10

11

= 7 TeV)sData 2010 (

MSTW08HERAPDF1.5ABKM09JR09

total uncertainty acc& sys &sta

uncertainty

68.3% CL ellipse area

-1 L dt = 33-36 pb'

ATLAS

) [nb]-l+ l!*" BR(Z/# Ztot$

0.8 0.9 1

) [nb

]% l

!!

BR

(W#

!Wto

t$

8

9

10

11

) [nb]-l+ l!*" BR(Z/# Zfid$

0.4 0.45 0.5 0.55

) [nb

]% l

!!

BR

(W#

!Wfid$

4

4.5

5

5.5


MSTW08HERAPDF1.5ABKM09JR09

total uncertainty sys&sta

uncertainty

68.3% CL ellipse area

-1 L dt = 33-36 pb'

ATLAS

) [nb]-l+ l!*" BR(Z/# Zfid$

0.4 0.45 0.5 0.55

) [nb

]% l

!!

BR

(W#

!Wfid$

4

4.5

5

5.5

Fiducialcrosssec1onshavenotheore1caluncertaintyfromextrapola1ontofullphasespace→be[ersensi1vity

Phys. Rev. D85 (2012) 072004 CMS-PAS-12-011

Sensitivity of W/Z cross section to PDF σB(W)vsσB(Z),fiducial

σB(W)vsσB(Z),total σB(Z)vsσB(W),total,8TeV

W/Z differential cross sections in rapidity

X. Wu, SUSY2012, 13/08/12

ImpactonthedetailedunderstandingofPDF

|y|0 0.5 1 1.5 2 2.5 3 3.5

/d|y

|!

) d!

(1/

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4CMS

= 7 TeVs at -1 L dt = 36 pb"

combined)µdata (e and

+ CT10POWHEG

|Z

|y0 0.5 1 1.5 2 2.5 3 3.5

Theo

ry/D

ata

0.91

1.1

| [pb

]Z

/d|y

!d

20

40

60

80

100

120

140

160


MSTW08

HERAPDF1.5

ABKM09

JR09

-1 L dt = 33-36 pb"-l+ l#Z

Uncorr. uncertainty

Total uncertainty

ATLAS

|l!|

0 0.5 1 1.5 2 2.5

Theo

ry/D

ata

0.91

1.1

| [pb

]l!

/d|

"d

100

200

300

400

500

600

= 7 TeV)sData 2010 (MSTW08HERAPDF1.5ABKM09JR09

-1 L dt = 33-36 pb# l$- l%

-W

Uncorr. uncertainty

Total uncertainty

ATLAS

|l!|

0 0.5 1 1.5 2 2.5

Theo

ry/D

ata

0.91

1.1| [

pb]

l!/d

|"d

300

400

500

600

700

800

= 7 TeV)sData 2010 (MSTW08HERAPDF1.5ABKM09JR09

-1 L dt = 33-36 pb# l$+ l%+W

Uncorr. uncertainty

Total uncertainty

ATLAS

normalized

Phys. Rev. D85 (2012) 072004 JHEP 10 (2011) 132

Z,W+,W−sensi1vetodifferentpartonflavourconfigura1ons

Z→l+l− W+→l+ν W−→l−ν

Z→l+l−

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 3 443

Jetenergyscalesystema1cmostlycancelsout

Measurementswithsmallsystema1cuncertainty

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

44

Summary of Boson Cross Sections

45

QCD Modeling of Process   Kinematics affected by

pT of Z boson   Determined by soft and

hard QCD radiation   tune MC to describe data

  Limitations of Leading Order Monte Carlo   Compare to NNLO

calculation

CDF

46

Comparison to Theory σTh,NNLO=251.3±5.0pb

•  Experimental uncertainty: ~2% •  Luminosity uncertainty: ~6% •  Theoretical uncertainty: ~2%

• Can use these processes to normalize luminosity absolutely  However, theory uncertainty larger at LHC and theorists don’t agree (yet)

(Martin, Roberts, Stirling, Thorne)

Documents

Physics at Hadron Colliders - Uniudcobal/marina_Z_3.pdf · 1 Physics at the Tevatron: Lecture I Marina Cobal University of Udine Trieste, ﬁsica sperimentale nucleare e subnucleare