Multi boson production Paolo Mastrandrea PIC 2009 Kobe 8/31/2009 - 9/2/2009

Multi boson productionMulti boson production

Paolo MastrandreaPaolo Mastrandrea

PIC 2009PIC 2009

Kobe 8/31/2009 - 9/2/2009Kobe 8/31/2009 - 9/2/2009

PIC 2009 - Kobe - 8/31/2009 Paolo Mastrandrea - FNAL 2

Diboson productionDiboson production

• Associated production of 2 vector bosons (, W, Z) can occur via:

– particle-antiparticle annihilation (t-channel)

– boson self-interactions or Triple Gauge Coupling (TGC) (s-channel)

t-channel s-channel


Why is diboson interesting?Why is diboson interesting?

• Measure coupling between W,Z and to test SM prediction;

• unique probe for Triple Gauge Coupling (TGC);

• observing TGCs not permitted in the SM or anomalous TGCs would be a sign of new physics;

• signature similar to Higgs (not in this presentation).

• All presented analysis from Tevatron:

– most updated;

– highest q2 available;

– techniques in LHC perspective.


Triple Gauge CouplingsTriple Gauge Couplings

• anomalous Triple Gauge Couplings (aTGCs):

– can affect cross-section and kinematics observables (i.e. lepton or

boson pT distributions);

– can depend on q2.

Coupling Decay

VWW(V = Z,)

WWNot present at LEP

WWZ

WWLep and Tevatron

ZWW

Z* and ZZ*Z

Absent in SMZZ

ZZ* and ZZZ*ZZ

ZZZ



• VWW: 14 independent couplings (7 each for ZWW and WW); can be reduced to 5 assuming C and P conservation and electromagnetic gauge invariance.

– Common set (, Z, , Z, gZ1);

– gauge invariance: Z = gZ1 - ( - 1)tan2W and Z = ;

– in SM at the tree level = Z = gZ1 = 1 and = Z = 0;

– = - 1 ; g = g - 1.

[ LEP2 arXiv:hep-ex/0612034v2 ]



• Z* and ZZ* : deviations from SM couplings may be described by

8 parameters hVi (i = 1,..4; V = , Z)

• ZZ* and ZZZ* : deviations from SM couplings may be described

by 4 parameters f Vi (i = 4, 5; V = , Z)

[ LEP2 arXiv:hep-ex/0612034v2 ]


Analysis techniquesAnalysis techniques

• Leptons for clear signatures;

• now start using jets;

• increasing statistics is pushing close/beyond LEP limits on aTCGs parameters.

Wl Wjj Zl+l- Z Zjj

Wl WW

Wjj WW --

Zl+l- WZ WZ ZZ

Z WZ WZ ZZ --

Zjj WZ -- ZZ ZZ --

Wg -- Zg Zg --


ZZ

• Z

• Copious non-collision background:

– a pointing alghoritm which exploits the transverse and longitudinal energy distributions in the EM calorimeter and central preshower

detector is used to evaluate zEM;

– reject events with |zEM - zV| > 10 cm.

• 5.1 s.d. significance - First Tevatron observation

D0 3.6fb-1

(ppZ)Br(Z) , ET>90GeV , Missing ET > 70 GeV [fb]

data 32 ± 9 (stat.+syst.) ± 2 (lumi.)

SM prediction 39 ± 4 fb

Events selection

Trigger high-ET single EM cluster

Photon ET>90 GeV , ||<1.1 , n=1

Neutrino Missing ET>70 GeV


ZZ - aTGC - aTGC

• Photon ET spectrum in data compared

to MC signal + background expectation for a grid of pairs of anomalous coupling parameters;

• 1 and 2-dimensional bounds obtained setting all other parameters to SM prediction;

• limits on Z* and ZZ* aTGC.

Parameter

95% C.L.

|h30| [-0.033, +0.033]

|h40| [-0.0017, +0.0017]

|hZ30| [-0.033, +0.033]

|hZ40| [-0.0017, +0.0017]

(h30 = 0.09 and h

40 = 0.005)

World's best


WW

• Wl

• Sensitive to WW aTGC

CDF 1fb-1

Selection criteria We W

Lepton ET>25GeV, ||<1.1 pT>20GeV/c, ||<1.1

Neutrino Missing ET>25 GeV Missing ET>20 GeV

Transverse mass 30 < MT < 120 GeV/c2

Photon ET > 7 GeV, ||<1.1

(ppW)Br(Wl) , (l=e,) , ET>7GeV [pb]

data 18.03 ± 0.65 (stat.) ± 2.55 (syst.) ± 1.05 (lumi.)

SM prediction 19.3 ± 1.4


WW

• W+Xl+X, (l=e,)

• Limits on WW aTGC

Selection criteria We W

Lepton ET>25GeV pT>20GeV/c

Neutrino Missing ET>25 GeV Missing ET>20 GeV

Transverse mass MT > 40 GeV/c2

Photon ET > 8 GeV, Rl>0.7

(ppW+X)Br(Wl) , ET>8GeV, Rl>0.7 [pb]

data 14.08 ± 1.6 (stat.) ± 1.0 (syst.) ± 1.0 (lumi.)


D0 162pb-1

Parameter 95% C.L.

[-0.88, +0.96]

[-0.20, +0.20]


WWWW

• W+W-l+l'-l' , events selection:

– high-pT e and trigger paths;

– 2 opposite charge leptons (e, ).

• Background reduction:

– no jets with ET>15GeV and ||<2.5;

– missing ET not alligned with leptons or jets - reduces DY background;

– Mll > 16 GeV to suppress h.f. contribution.

• Event-by-event matrix element probability density functions are used to build a likelihood ratio discriminant.

• Binned likelihood fit to extract (ppWW).

CDF 3.6fb-1


WWWW

• Matrix element probability density functions pdf:

– xobs - This represents the observed lepton momenta vectors as

well as the two transverse components of the missing ET.

– 1/<> - This is a normalization factor based on the total leading order cross section and detector

acceptances.

– - This refers to the leading-order cross section.

– y - The true lepton 4-momenta which are integrated over.

– - Detector efficiencies and acceptances.

– G - A generalized detector resolution function.

• Likelihood ratio:

– where i are the background processes modeled and ki is the

relative fraction of the i-th mode such that the sum over all ki

equals 1.

[All distributons in backup]


WWWW

• Cross section extracted using a binned likelihood fit which includes gaussian constraints for systematics.

• Correlation between systematics taken into account.

(ppWW) [pb]

data 12.1 ± 0.9 (stat.) +1.6-1.4 (syst.+lumi.)



WW - aTGCWW - aTGC

• The efficiency at a given leading lepton pT is similar for

any given coupling - allow to avoid full simulation for every possible coupling

• The resulting efficiency curve is then applied to MCFM NLO matrix element simulations for a grid of values of the couplings parameters

• The measured leading lepton pT distribution is fitted to extract limits on Z, gZ

1 and


WWWW

• W+W-l+l'-l'

• aTGC limits extracted

comparing the lepton pT

distributions with MC simulations for different

sets of (, , gZ1)

D0 1.0 fb-1

(ppWW) [pb]

data 11.5 ± 2.1 (stat.+syst.) ± 0.7 (stat.)

SM prediction [13.0, 13.5]

Parameter 95% C.L.

[-0.54, +0.83]

[-0.14, +0.18]

gZ1 [-0.14, +0.30]


WZWZ

• WZl'l'l+l-

• extended categories of charged leptons to increase acceptance

(ppWZ) [pb]

data 4.3 +1.3-1.0 (stat.) ± 0.2 (sysy.) ± 0.3 (lumi.)

NLO prediction 3.7 ± 0.3

CDF 1.9fb-1


WZ - aTGCWZ - aTGC

• Z pT distribution is sensitive to aTGC

• Efficiency independent from aTGC couplings

• Z pT distribution fitted to for every combination of simulated parameters to extract limits

95% C.L. Z gZ1 Z

=1.5 TeV [-0.14, 0.15] [-0.14, 0.25] [-0.81, 1.29]

=2.0 TeV [-0.13, 0.14] [-0.13, 0.23] [-0.76, 1.18]

Expected limit

[-0.15, 0.16] [-0.18, 0.28] [-0.68, 1.00]


ZZZZ

• Zl+l-l'+l-';

• extended categories of charged leptons to increase acceptance.

CDF 4.8fb-1

(ppZZ) [pb]

data 1.56 +0.80-0.63 (stat.) ± 0.25 (sysy. + lumi.)



ZZZZ

• ZZl+l-l'+l'-

• 5.4 s.d. significance

(ppZZ) [pb]

data 1.75 +1.27-0.86 (stat.) ± 0.08 (sysy.) ± 0.10 (lumi.)


D0 1.7 fb-1


ZW, ZZZW, ZZ

• ZW/ZZl+l-jj;

• extended categories of charged leptons to increase acceptance;

• signal fraction extracted by an unbinned fit to dijet mass distribution.

CDF 1.9fb-1

95% CL limit(ppZZ)

[pb](ppZW)

[pb]

140<pT(Z)<210 GeV/c 0.280 0.234

pT(Z)>210 GeV/c 0.077 0.135co

ntr

ol r

egio

nco

ntr

ol r

egio

n aTGCaTGC

SMSM

pT(Zl+l-) GeV/c


ZW, ZZ - aTGCZW, ZZ - aTGC

• ZW/ZZl+l-jj .

• aTGC limits extracted

comparing Mjj distribution to

MC simulation.

95% C.L. Limit g

=1.5 TeV

Expected [-0.16, 0.26] [-0.88, 1.16] [-0.14, 0.15]

Measured

[-0.22, 0.32] [-1.09, 1.40] [-0.18, 0.18]

=2.0 TeV

Expected [-0.15, 0.24] [-0.81, 1.07] [-0.13, 0.13]

Measured

[-0.20, 0.29] [-1.01, 1.27] [-0.16, 0.17]

95% C.L. Limit f4Z f5

Z f4 f5

=1.2 TeV

Expected [-0.11, 0.11] [-0.12, 0.11] [-0.11, 0.11] [-0.12, 0.11]

Measured

[-0.12, 0.12] [-0.13, 0.12] [-0.10, 0.10] [-0.11, 0.11]


WZ, WWWZ, WW

• WW/WZljj , l = e,.• Event selection:

– 1 lepton with ET>20GeV and ||<1.2;

– missing ET>25GeV;

– ≥ 2 jet with ET>20GeV, ||<2.4, <2.5;

– MTW>30GeV/c2;

– pT(jj)>40GeV/c.

• Diboson fraction extracted by a binned fit to Mjj distribution.

• 4.6 s.d. significance (expected 4.9 s.d.)

CDF 3.9fb-1

(ppWV) , V=W,Z [pb]

data 14.4 ± 3.1 (stat.) ± 2.2 (sysy. + lumi.)


WZ, WWWZ, WW

• WW/WZljj , l = e,.

• Matrix element technique to maximize the use of collected information in signal-background discrimination.

• 5.4 s.d. significance (expected 5.1 s.d.).

CDF 2.7fb-1

(ppWV) , V=W,Z [pb]

data 17.7 ± 3.1 (stat.) ± 2.4 (sysy. + lumi.)


VV->Missing EVV->Missing ETT+jj+jj

• Search for and l final states.

• Acceptance for WW, WZ and ZZ events.

• Event selection:

– Missing ET > 60 GeV;

– 2 jets ET > 25 GeV, || < 2.0;

– Missing ET significance > 4;

– Missing ET-jet > 0.4.

• Missing ET model to enanche QCD rejection.

• Sysytematic uncertaintiy on V+jj background shape checked with +jj events.

(ppVV) , V=W,Z , with one Vjj [pb]

data 18.0 ± 2.8 (stat.) ± 2.4 (sysy.) ± 1.1 (lumi.)


j

j

, lep

CDF 3.5fb-1


… … and what about LHC ?and what about LHC ?

• Tevatron:– proton-antiproton s = 1.96 TeV– L = 31032 cm-2s-1

[arXiv:0901.0512 ; CERN-OPEN-2008-020 ]

• LHC:– proton-proton s = 14 TeV– L = 1034 cm-2s-1


… … and what about LHC ?and what about LHC ?

• Example on WW, =2TeV

[arXiv:0901.0512 ; CERN-OPEN-2008-020 ]

Experiment

s [TeV] L [fb-1] gZ1

D01.96

1.0 [-0.54, +0.83] [-0.14, +0.18] [-0.14, +0.30]

CDF 3.6 [-0.57, +0.65] [-0.14, +0.15] [-0.22, +0.30]

ATLAS 14

0.1 [-0.476, +0.512] [-0.564, +0.775] [-0.741, +1.177]

1 [-0.240, +0.251] [-0.259, +0.421] [-0.355, +0.616]

10 [-0.088, +0.089] [-0.074, +0.165] [-0.149, +0.309]

30 [-0.056, +0.054] [-0.052, +0.100] [-0.149, +0.251]


ConclusionsConclusions

• Diboson program is wide and exciting

• Tevatron is producing mature results

• … even more in the next LHC era!


BackupBackup


WWWW

• Matrix element probability density functions pdf:

Documents

Multi boson production Paolo Mastrandrea PIC 2009 Kobe 8/31/2009 - 9/2/2009