perspectives of model-independent searching for z’ boson at modern hadron colliders

Perspectives ofPerspectives ofmodel-independent searchingmodel-independent searching

for Z’ bosonfor Z’ bosonat modern hadron collidersat modern hadron colliders

A.GulovA.GulovDnipropetrovsk Univ.Dnipropetrovsk Univ.

Perspectives of model-independent searching for Z’ boson at modern hadron collidersPerspectives of model-independent searching for Z’ boson at modern hadron colliders

Z’ boson as a scenario of ‘new physics’ Z’ boson as a scenario of ‘new physics’ beyond the SMbeyond the SM

What can be taken from the What can be taken from the theorytheory??

What can be taken from What can be taken from previous previous experimentsexperiments at high energies (LEP)? at high energies (LEP)?

What can be expected at modern hadron What can be expected at modern hadron colliders (colliders (Tevatron, LHCTevatron, LHC)?)?


Z’ is a new Z’ is a new heavy neutral vectorheavy neutral vector particle beyond the SM particle beyond the SM

Popular in the theory:Popular in the theory:

It is predicted by lots of models designed for energies It is predicted by lots of models designed for energies up to the Plank scale (GUTs, Extended gauge groups)up to the Plank scale (GUTs, Extended gauge groups)

Popular in HEP experiments:Popular in HEP experiments:

It can easily arise in the annihilation of SM fermions as It can easily arise in the annihilation of SM fermions as an intermediate off-shell or on-shell statean intermediate off-shell or on-shell state

It can decay into the SM charged leptons preferable It can decay into the SM charged leptons preferable for precision measurements in experimentsfor precision measurements in experiments


Z’ is predicted by lots of models designed for energies Z’ is predicted by lots of models designed for energies up to the Plank scale (GUTs, Extended gauge groups):up to the Plank scale (GUTs, Extended gauge groups):

<200 GeV<200 GeV

1 TeV - …1 TeV - …

……

The Plank scaleThe Plank scale

SMSM

U’(1) (?)U’(1) (?)

SU(2)SU(2)L L SU(2) SU(2)R R U(1) U(1) B-LB-L

SU(5)SU(5) U(1) U(1) U(1) U(1)

Z’ as the ZZ’ as the Z

… … models … models … models …models … models … models …

LRLR

,,SSMSSM

SO(10)SO(10)

(?)(?)

(Super)string (Super)string modelsmodels

(?)(?)

Decoupling of Decoupling of new particlesnew particles

An update of the particle content:An update of the particle content:

+ (?) Z’, W’, heavy fermions, + (?) Z’, W’, heavy fermions, heavy scalarsheavy scalars

An update of the An update of the particle content particle content again: again:

+ (?)+ (?)

(?)(?)

Contact couplingsContact couplings + Resonances+ Resonances The distant future which can be ever (never) reachedThe distant future which can be ever (never) reached


Z’ is predicted by lots of models designed for energies Z’ is predicted by lots of models designed for energies up to the Plank scale (GUTs, Extended gauge groups):up to the Plank scale (GUTs, Extended gauge groups):

<200 GeV<200 GeV

1 TeV - …1 TeV - …

……

The Plank scaleThe Plank scale

SMSM

U’(1) (?)U’(1) (?)

SU(2)SU(2)L L SU(2) SU(2)R R U(1) U(1) B-LB-L

SU(5)SU(5) U(1) U(1) U(1) U(1)

Z’ as the ZZ’ as the Z

… … models … models … models …models … models … models …

LRLR

,,SSMSSM

SO(10)SO(10)

(?)(?)

(Super)string (Super)string modelsmodels

(?)(?)

Decoupling of Decoupling of new particlesnew particles

An update of the particle content:An update of the particle content:

+ (?) Z’, W’, heavy fermions, + (?) Z’, W’, heavy fermions, heavy scalarsheavy scalars

An update of the An update of the particle content particle content again: again:

+ (?)+ (?)

(?)(?)

Contact couplingsContact couplings + Resonances+ Resonances The distant future which can be ever (never) reachedThe distant future which can be ever (never) reached

Typical phenomenologyTypical phenomenology instead of 100(0…) possible modelsinstead of 100(0…) possible models


Phenomenological (model independent) description of the Z’ boson:Phenomenological (model independent) description of the Z’ boson:

Some general parameterization of the Z’ couplings to the SM particlesSome general parameterization of the Z’ couplings to the SM particles

General theoretical reasons can be taken into accountGeneral theoretical reasons can be taken into account

How the generic Z’ boson can manifest itself in experiments?How the generic Z’ boson can manifest itself in experiments?

Z’ boson can be visible in one observable amplifying the signal, but it Z’ boson can be visible in one observable amplifying the signal, but it can be easily missed in another one. The optimal observables have to can be easily missed in another one. The optimal observables have to be found.be found.

Model-independent constraints from recent experiments can help to Model-independent constraints from recent experiments can help to estimate the discovery potential of future experiments. The combined estimate the discovery potential of future experiments. The combined constraints from different experiments are also possibleconstraints from different experiments are also possible

How signals of the Z’ boson can be separated from another possible How signals of the Z’ boson can be separated from another possible ‘new physics’ (Gomel STU team @ NPQCD-2011).‘new physics’ (Gomel STU team @ NPQCD-2011).


Only one Z’Only one Z’ at 1-10 TeV at 1-10 TeV

Below 1-10 TeV the Below 1-10 TeV the Z’ is decoupled, and Z’ is decoupled, and the theory is reduced the theory is reduced to the SM (THDM)to the SM (THDM)

General theoretical assumptions which General theoretical assumptions which can be taken into accountcan be taken into account

It is enough to parameterize:It is enough to parameterize:

Z’ interactions to the SM fermionsZ’ interactions to the SM fermions

Z’ couplings to scalarsZ’ couplings to scalars (determine (determine Z-Z’ mixing)Z-Z’ mixing)


Z’ interactions to the SM fermionsZ’ interactions to the SM fermions

Z-Z’ mixing related to the Z’ Z-Z’ mixing related to the Z’ couplings to scalarscouplings to scalars

Only one Z’Only one Z’ at 1-10 TeV at 1-10 TeV

Below 1-10 TeV the Below 1-10 TeV the Z’ is decoupled, and Z’ is decoupled, and the theory is reduced the theory is reduced to the SM (THDM)to the SM (THDM)

Interactions of the Interactions of the renormalizable typesrenormalizable types(potential (potential current) current)

Abelian Z’Abelian Z’(Z’ interactions to (Z’ interactions to W,Z are due to the Z-W,Z are due to the Z-Z’ mixing only)Z’ mixing only)


The contact couplings describe the phenomenology The contact couplings describe the phenomenology at low energies:at low energies:

f

Z

Zff

Z

Zf v

m

mva

m

ma

'' 4,

4

2'

2'

),,(),,(

'

Z

ffffff

Z

ffffff

m

vvvaaa

ms

vvvaaa

ffffffZff

What is the number of unknown constants?What is the number of unknown constants?

These couplings were These couplings were constrained by the LEP constrained by the LEP experimentsexperiments


2 constants2 constants ( (aa, , vv) ) 12 fermion species12 fermion species (charged (charged lepton, neutrino, u-quark, d-quark lepton, neutrino, u-quark, d-quark 3 generations) = 3 generations) = 24 parameters24 parameters

+ + mixing anglemixing angle = = 25 parameters25 parameters

Phenomenology of contact couplingsPhenomenology of contact couplings

+ + Z’ massZ’ mass = = 26 parameters26 parameters

Beyond the phenomenology of contact couplingsBeyond the phenomenology of contact couplings

Too many parameters!Too many parameters!


2 constants2 constants ( (aa, , vv) ) electron, muon, u-quark, d-quark electron, muon, u-quark, d-quark = = 8 parameters8 parameters

+ + mixing anglemixing angle = = 9 parameters9 parameters




Too many parameters!Too many parameters!

Successful data fits need 1-2 parametersSuccessful data fits need 1-2 parameters


Universality? Universality? Nobody knows…Nobody knows…

Neglecting mixing angle? Neglecting mixing angle? It is small, It is small, but it but it generally affects the Z couplings to the SM generally affects the Z couplings to the SM particles producing effects of the same order particles producing effects of the same order as Z’ states.as Z’ states.

Some theoretical motivation is necessary to Some theoretical motivation is necessary to reduce the number of unknown parameters.reduce the number of unknown parameters.

One of One of the general requirementsthe general requirements on the Z’ on the Z’ couplings is the couplings is the renormalizabilityrenormalizability of the theory of the theory including this particleincluding this particle


RenormalizabilityRenormalizability (in the form of RGE for scattering (in the form of RGE for scattering amplitudes)amplitudes)

++ The parameterizationThe parameterization of the Abelian Z’ couplings of the Abelian Z’ couplings

== RelationsRelations between the Z’ couplings between the Z’ couplings

Due to the decoupling, we need no additional Due to the decoupling, we need no additional information about other new heavy particlesinformation about other new heavy particles

The relations cover a huge number of Z’ models The relations cover a huge number of Z’ models (model independence)(model independence)


The relationsThe relations

f f * is the SU(2)-partner of * is the SU(2)-partner of ff..

TT33ff is the weak isospin. is the weak isospin.

The axial-vector coupling is universal. It also The axial-vector coupling is universal. It also determines the Z-Z’ mixing angle.determines the Z-Z’ mixing angle.

There is only one independent vector coupling for each There is only one independent vector coupling for each SU(2) doublet.SU(2) doublet.

YgTaavav ffffff

~~, 3**


1 constant1 constant v v 6 SM fermion doublets6 SM fermion doublets = =6 parameters6 parameters

+ + universal universal aa (determining also the mixing angle) = (determining also the mixing angle) = 7 parameters7 parameters




Instead of 26 parameters!Instead of 26 parameters!


1 constant1 constant vv electron, muon, u(d)-quark = electron, muon, u(d)-quark = 3 parameters3 parameters

+ + aa (mixing angle) = (mixing angle) = 4 parameters4 parameters




We can try to fit dataWe can try to fit data


Constraints from the LEP data.Constraints from the LEP data.

ee++ee-- ++--, , ++-- aa22,,vveevv,,vveeaa,,vvaa

special 1-param. observable, LEP2: special 1-param. observable, LEP2: 11 hint: hint: aa2 2 = 1.30 = 1.30 10 10-5-5

Constraint on Z-Z’ mixing from LEP1: Constraint on Z-Z’ mixing from LEP1: 11 hint: hint: aa2 2 = 1.25 = 1.25 10 10-5-5

ee++ee-- ee++ee-- aa22,,vvee22,,vveeaa

special 1-parameter observable: special 1-parameter observable: 22 hint: hint: vvee2 2 = 2.24 = 2.24 10 10-4-4

general 2-parameter fit at 95%CL: general 2-parameter fit at 95%CL: no hint:no hint: vvee22<< 1.69 1.69 10 10-4-4


The current knowledge about Z’ couplingsThe current knowledge about Z’ couplings Max. likelihood value:Max. likelihood value:

95% CL intervals:95% CL intervals:

0 < a0 < a2 2 < 3.61 < 3.61 10 10-4-4

4 4 10 10-5-5 < v< vee2 2 < 1.69 < 1.69 10 10-4-4

0 < V0 < V,,,u,c,t,u,c,t2 2 < < 4 4 10 10-4-4

(suppose from the observation of no signals in the hadronic channel)(suppose from the observation of no signals in the hadronic channel)

aa2 2 = 1.3 = 1.3 10 10-5-5


Z’ @ Tevatron and LHCZ’ @ Tevatron and LHC

Searching for the (narrow) resonance in the Drell-Yan Searching for the (narrow) resonance in the Drell-Yan process:process:

pp or pppp or pp Z’ Z’ ee++ee- - ,, ++--

pp or pppp or pp qqqq Z’ Z’ ee++ee- - ,, ++--

Parton model (PDFs)Parton model (PDFs) Our knowledge about Our knowledge about Z’ couplingsZ’ couplings

Observables Observables

(cross-(cross-section)section)


We can estimate:We can estimate:

Z’ width (total)Z’ width (total)

Partial Z’ widths (BRs)Partial Z’ widths (BRs)

Z’ production cross-sectionZ’ production cross-section

Limits on the Z’ mass, discovery limits, …Limits on the Z’ mass, discovery limits, …


Estimation Scheme #1Estimation Scheme #1

All the Z’ couplings are varied in their 95% CL All the Z’ couplings are varied in their 95% CL intervals. This gives the widest intervals for intervals. This gives the widest intervals for predicted observables. predicted observables. The data outside of The data outside of these predictions are excluded by LEPthese predictions are excluded by LEP (not (not the Abelian Z’ boson, something else)the Abelian Z’ boson, something else)

““95% CL Scheme”95% CL Scheme”


Estimation Scheme #2Estimation Scheme #2

The maximum-likelihood value is used for the axial-The maximum-likelihood value is used for the axial-vector coupling. The other Z’ couplings are varied in vector coupling. The other Z’ couplings are varied in their 95% CL intervals. This gives predictions their 95% CL intervals. This gives predictions under under the assumption that the real hint of the Z’ boson has the assumption that the real hint of the Z’ boson has been observed by the LEP 2 databeen observed by the LEP 2 data. These are our . These are our expectations concerning the Abelian Z’ boson.expectations concerning the Abelian Z’ boson.

““Max. Likelihood (M.L.) Scheme”Max. Likelihood (M.L.) Scheme”


Z’ Width: calculationZ’ Width: calculation

Can be calculated by the optical theorem:Can be calculated by the optical theorem:

'

''''

)(Im

Z

ZZZZ m

mG

f

favffvfafZ avFvFaFaF ,2

,2

,2

.vect.scal'

3

''

TeV1~

ZZ m

At the one-loop level (corresponding to Z’ decays into 2 particles):At the one-loop level (corresponding to Z’ decays into 2 particles):

Estimated value of this quantity is Estimated value of this quantity is practically independent of the Z’ practically independent of the Z’ massmass


Z’ Width: results (95%C.L. and M.L. schemes)Z’ Width: results (95%C.L. and M.L. schemes)

TeV7.1GeV500

~GeV170GeV50

~GeV5.8GeV5.2

~

:TeV5.1

'

'

'

'

Z

Z

Z

Zm

M.L.

95%C.L.


Z’ Partial Widths: results (M.L. scheme)Z’ Partial Widths: results (M.L. scheme)

%5.2)bosons'BR(

%98 toup)'BR(

%21)'BR(%04.0

Z

qqZ

eeZ

e+e- +-qq

%6.0)bosons'BR(

%98)'BR(%50

%41)'BR(

:GeV50~

Z

qqZ

eeZ


Z’ @ TevatronZ’ @ Tevatron

The Z’ production cross-section can be estimatedThe Z’ production cross-section can be estimated (details will be given by (details will be given by [email protected]@NPQCD2011))

Our predictions can be compared withOur predictions can be compared with the Tevatron results and the model predictions the Tevatron results and the model predictions

The lower limit on the Z’ mass can be obtainedThe lower limit on the Z’ mass can be obtained


Z’ @ Tevatron: Z’ @ Tevatron:

D0 D0 ee++ee-- vs M.L. estimate vs M.L. estimate D0 D0 ++-- vs M.L. estimate vs M.L. estimate



CDF CDF ee++ee-- vs M.L. estimate vs M.L. estimate



The Z’ hint observed by the LEP 2 data can be the The Z’ hint observed by the LEP 2 data can be the Abelian Z’ boson with the mass between 400 GeV Abelian Z’ boson with the mass between 400 GeV and 1.15 TeV.and 1.15 TeV.

It can be still hidden as the resonance in the It can be still hidden as the resonance in the Tevatron experiments.Tevatron experiments.

The popular set of model are completely covered The popular set of model are completely covered by our model-independent bounds.by our model-independent bounds.


Z’ @ LHCZ’ @ LHCThe Z’ production cross-section can be estimated The Z’ production cross-section can be estimated (details will be given by (details will be given by [email protected]@NPQCD2011))

Our predictions can be comparedOur predictions can be compared with with the model predictionsthe model predictions

The discovery limit for the Abelian Z’ boson can be The discovery limit for the Abelian Z’ boson can be obtained (obtained ([email protected]@NPQCD2011))


SummarySummary The model-independent relations for the Z’ couplings exist. The The model-independent relations for the Z’ couplings exist. The

number of unknown Z’ parameters can be significantly reducednumber of unknown Z’ parameters can be significantly reduced

The Z’ width and the production cross-sections in proton-The Z’ width and the production cross-sections in proton-(anti)proton collisions can be estimated from the LEP2 (anti)proton collisions can be estimated from the LEP2 constraints on the Z’ couplings.constraints on the Z’ couplings.

The Z’ hint observed by the LEP 2 data can be the Abelian Z’ The Z’ hint observed by the LEP 2 data can be the Abelian Z’ boson with the mass between 400 GeV and 1.15 TeV (by boson with the mass between 400 GeV and 1.15 TeV (by Tevatron results). We have good chances to discover it at Tevatron results). We have good chances to discover it at modern hadron colliders.modern hadron colliders.

We have new model-independent results which are We have new model-independent results which are complementary to the usual model-dependent schemes.complementary to the usual model-dependent schemes.


Related publications and talks:Related publications and talks:

with V.Skalozub:with V.Skalozub: Int. Journal of Modern Physics A 25, 5787–5815 (2010)Int. Journal of Modern Physics A 25, 5787–5815 (2010)

with A.Kozhushko:with A.Kozhushko:

will be published in May, 2011will be published in May, 2011

also A.Kozhushko@NPQCD-2011also A.Kozhushko@NPQCD-2011

Dnipr. Natnl. Univ. team with Gomel State Techn. Dnipr. Natnl. Univ. team with Gomel State Techn. Univ. team:Univ. team:

A.Tsytrinov @ NPQCD-2011A.Tsytrinov @ NPQCD-2011

perspectives of model-independent searching for z’ boson at modern hadron colliders

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