Seesaw type III search at 8 TeV - INFN Sezione di Padovaagozzeli/Presentazioni/Pre... ·...

Seesaw type III search at 8 TeV Ezio Torassa, Sara Vanini

Andrea Gozzelino, Stefano Lacaprara, Lisa Benatowith Carla Biggio (INFN Genova) theoric support

PRE APPROVAL TALK July 24 th 2014

July 24 th 2014 1EXO-14-001 Preapproval talk

ANALYSIS NOTE AN-13-135PHYSICS ANALYSIS SUMMARY (PAS) EXO-14-001

Pre approval talk outline Motivation

Seesaw models Seesaw type III Analysis tools

Event offline selections Backgrounds: EWK prompt, Dalitz, Fake leptons

Systematics Signals

Results and their interpretations Conclusions

Documentations


AN

PAS

Table or plot included in AN-13-135 v8

Table or plot included in PAS EXO-14-001 v9

Update After July 18 th 2014


Motivation• Neutrinos oscillate. • Neutrinos are massive and mixed.• This is an evidence for physics beyond the standard model (BSM).• Left-Right-Symmetric extension (LRSM) deploys a seesaw mechanism

to give a possible explanations for the smallness of the ordinary neutrino masses LRSM has new particles: W±

R, Z’, NiR (mass M)

Standard Model Left-Right-Symmetric Extension

Gauge group SU(2)L U(1)

YSU(2)

L SU(2)

R U(1)

B-L

FermionsLH doublets: Q

L = (ui,d i)

L ; L

L = (l i,ν i)

L

RH singlets: QR = ui

R , d i

R ; L

R = l i

R

LH doublets: QL = (ui,d i)

L , L

L = (l i,ν i)

L

RH doublets: QR= (ui,d i)

R , L

R = (l i,N i)

R

Neutrinosν i

R do not exist

ν iL are massless and pure chiral

N iR

are heavy partners to the ν iL

N iR Majorana in the Minimal LRSM

Gauge bosons W±L, Z0, g W±

L,W±

R,Z0, Z´, g

Mmν


Seesaw Type I: fermion singletProduction and decay process: pp Nl+ l+W-l+ l+l+jj

Signature: two same sign same flavor leptons and two jets (j)

Seesaw Type II: scalar weak triplet (Y =2)Production and decay process: pp WR + X Nl l1 X l1l2 WR* l1l2jj

Signature: two muons or two electrons (opposite or same sign), and two jets (j)

Seesaw Type III: fermion weak triplets Σ+,Σ0,Σ− (Y=0)

LK refers to the interactions triplets - vector bosonsLY refers to the interactions higgs - triplets and higgs - fermions LM refers to the Majorana mass, including L-R interactions forbidden in SU(2)L

Seesaw Type III Lagrangian L = LSM + LK + LY + LM

Seesaw models (I)


Seesaw models (II)

where Y is the Yukawa coupling matrix, MNK is the mass of the heavy neutrino partners,

ν is the Higgs vacuum expectation value

After spontaneous symmetry breaking LY and LM terms lead to the

neutrino mass matrix charged leptons mass matrix

To obtain small mν :

•O(M) = 1014 GeV and Yukawa coupling O(1)•M «small» (~TeV) and Yukawa coupling small

In the basis where the light charged lepton mass matrix is diagonal,

the neutrino mass matrix is: the charged interaction mixings are:

KN

jkij

kij M

YYm

2)(

2νν ∑−=

j

ji

N

ijNl M

YV

2,

ν=


Seesaw statusLHC experiments have discovery potential for seesaw mechanism at electroweak scale.

Fermion isospin singletsType I

EXO-11-076 with 2011 data

Scalar tripletsType II

EXO-12-017with partial 2012 data

Fermion tripletsType III

EXO-11-073with 2011 data

Type III Seesaw with 2012 data is EXO-14-001

AN

AN


Seesaw type III model

Assuming only the lighest triplet is present (Σ+, Σ0, Σ-) and the Σ have the same mass

Small Yukawa couplings (“natural value”) Vα = 10-6 (constraints from theory and measurements)

Benchmark in flavor democratic scenario Ve = Vμ = Vτ = Vα Generalized interpretation

Studied production and decay processesAN

Predicted Σ pair cross section not dependent on Vα, Production of lepton α proportional to bα

Contributions from final states with four, five or six leptons are less than 10% respect three leptons case.

PAS


Seesaw type III signal

Seesaw type III model developed in Mathematica v9.0 with Feynman Rules v1.6.11 and UFO (Universal FeynmanRules Output)

Les Houches Events files generation in MADGRAPH 5 v1_5_7 with CTEQ6l1 Parton Distribution Functions + Pythia6 + CMSSW official Full Simulation

Production cross sections: σ (pp Σ+Σ0 ) ≈ 2 σ (pp Σ-Σ0) Production cross sections: range [123; 0.9] fb Ten mass point values for Σ+ and Σ- : range [140; 340] GeV

Processes involving Σ± have similar branching fraction (BR) The small contribution (below 10%) from decays involving Higgs boson is not implemented

AN

AN


Analysis overviewSeesaw type III signature

exactly three charged isolated leptons in the final state and charge sum ±1

Analyzed dataall 2012 proton-proton collisions data @ 8 TeV (19.7 fb-1), online selected with triggers requiring at least two leptons with transverse momentum above 17 GeV and 8 GeV, respectivelyReReco January 22nd, 2013 campaign

Offline pre selectionsExactly three charged isolated leptons (electrons or muons)Transverse momentum above 30, 20, 20 GeV, respectivelyCharge sum ±1

Background sourcesElectroweak prompt SM processes (di-boson, tri-boson)Asymmetric photon conversions (Dalitz)Non prompt leptons (“Fake”)

Seesaw type III signal search is performed doing a cut and count experiment.

Software area: CMSSW_5_3_X (analysis) | CMSSW_6_2_X (limit)


Physics objects

e / μ

Thank to the EXO electron POG contact Daniele and EXO muon POG contact Oscar

MET

Jet Thank to the EXO JME POG contact Mikko

Particle Flow algorithm that use information from all subdetectors to reconstruct objects

HT

CSV combined secondary vertex b tagging value

Lepton isolation in a cone

missing transverse energy with recommended filters applied

Iso(e) = 0.15 Iso(μ) = 0.12

0.3 (e) 0.4(μ)


Dataset sample and trigger

ReReco January 22nd, 20133 data sets

Di lepton trigger paths

AN

AN

AN


Event offline selections

Pre selections: exactly three charged isolated leptons above pT thresholds and charge sum ±1

Missing transverse energy (neutrinos in final state) MET > 50 GeV

Hadron activity (jets in final states) HT < 150 GeV

Combined Secondary Vertex (CSV) b tagging variable value, for leading pT jet CSV < 0.244

Low mass resonances veto M(ll) > 12 GeV

Z veto M(ll) < 76 GeV or M(ll) > 106 GeV

Dedicated selection Z Dalitz veto M(lll) < 76 GeV or M(lll) > 106 GeV (applied only in some categories)

Backgrounds reduction Signal preservation

Thresholds common to all mass point values for both Σ+ and Σ-

The offline selections are optimized to give the best significance value.


Electroweak prompt Standard Model contributions are evaluated with MonteCarlo simulations

SM Process σ (pb) Background

WZ 24.6 Irreducible background, three leptons in final states

ZZ 8.4 Z bosons decay into leptons, and one lepton is not detected

WWW 0.08 Irreducible background, production cross section small

All the cross sections are measured by CMS at 8 TeV, except for WWW.

Electroweak prompt backgrounds

AN

Consider EWK prompt and data events before the Z veto.93% of EWK prompt events are WZ.

WZ inclusive measured cross section overestimates the main background source in our search region (MET > 50 GeV).

From table 22


Z ee

Z μμ


AN

AN

PAS

PAS



METpT lepton 1

AN

Data undershooting the MC expectation

• Apply SUSY electroweakino (SUS-13-006) method • Normalize the main background source (WZ)• Reduce WZ events by factor -11%• Introduce systematic error on WZ: 11%• Sum in quadrature systematic errors for WZ

Update

Thank to the Internal Reader Steven’s suggestion


Electroweak prompt backgroundsIn the categories with three same flavor leptons the electric charge order is reported as an example (all combinations are considered).The third (ninth) row has muons with same sign, the fourth (tenth) row has muons with opposite sign.

AN

Statistical errors wrongly computed Update in next slide


Electroweak prompt backgroundsIn the categories with three same flavor leptons the electric charge order is reported as an example (all combinations are considered).The third (ninth) row has muons with same sign, the fourth (tenth) row has muons with opposite sign.

ANUpdate

WZ reduction not applied at this step

FSR


Photon asymmetric conversionW or Z bosons decays + final state radiation (FSR) γ + γ asymmetric conversions

Scatter plots three bodies invariant mass versus

the opposite sign same flavor lepton pair invariant mass

at pre selections

Feynman’s diagrams for asymmetric photons conversions in FSR

FSR

Remove Dalitz events or estimate through a data driven method

μe+e-μ+μ- l (l is mostly e)

AN


Dalitz contribution

C(e) = N(eel)/N(eeγ) = (2.1 ± 0.3)%C(μ) = N(μμl)/N(μμγ) = (0.7± 0.1)%

•Evaluate the conversions factors in control regions•Estimate the Dalitz events contribution in signal region for each category•Dalitz events contribution independent on the sign

AN


Fake leptons step 1“fake” leptons = non prompt isolated leptons from top-antitop, W+jets, WW+jet, Z+jets or other SM processes, not coming from primary interaction vertex.

The Fake Rate (FR) is defined as the probability for a “loose lepton” (looser criteria on isolation variable and the track impact parameter) to pass the “tight identification” selection in samples where the presence of prompt isolated leptons is suppressed, and therefore almost all leptons are candidate fakes.

STEP 1: FR determinationControl data sample: events with high hadron activityTrigger: at least one jet with pT > 60 GeV or HT > 200 GeV, and single lepton with pT > 17 GeV

Offline selections method BOne lepton and one jet in opposite direction;Jet pT > 60 GeV;MET < 20 GeV;MT(MET, pT(l)) < 20 GeV;If OSSF lepton pair, M(ll) < 76 GeV or M(ll) > 106 GeV.

Offline selections method AMET < 20 GeV;MT(MET, pT(l)) < 20 GeV;If OSSF lepton pair, M(ll) < 76 GeV or M(ll) > 106 GeV. AN

AN


Fake leptons step 1 – cross check

NOTES about FR step 1:•Two methods applied on data give compatible results.•Fake Rate is nearly stable changing the lepton isolation values.Systematic error of 50 % is safe.

•Cross check between MC truth and method B confirms the reliability of the method.

AN


Fake leptons step 2STEP 2: FR application

Consider the analysis data samples and the loose leptons definition, four possible combinations of objects are:• LLL: events with three loose, not-tight leptons; this contribution is dominated by QCD multi lepton events; it is negligible due to the requirements;• TLL: events with two loose, not-tight leptons and one tight lepton, this contribution is dominated by W+jets events;• TTL: events with one loose, not-tight lepton and two tight leptons, this contribution contains mainly WW+jet events and is the most important one;• TTT: events with three tight isolated leptons, which define the signal region for the seesaw type III exclusive search.

AN


Total background contributionAN

AN Update


SystematicsSimulation: parton distribution function knowledge, leptons momentum scale and resolution, jets energy corrections, missing transverse energy scale and resolution, pileup effects negligibleData versus simulation correction factors: trigger efficiencies, objects reconstruction, identification (ID) and isolation efficiencies.

ANAN

Systematics (new section 4.15 in AN)

ANUpdateSystematic theory error on signal 0.3%

Systematic error on WZ: 6.9% and 11%

Systematic error on integrated luminosity 2.6%



Signals

Factor k not includedFor limits applied to use NNLO cross section

AN

AN

AN Update

Text improvements


Results in ANCONCLUSIONS:

No excess of events in data with respect to the total background is found.

The analysis shows no evidence for seesaw type III model signal in 2012 CMS data.

Interpretations of results are upper limits on production cross sections (σ) times the branching fraction (BR) for the considered processes, at 95% confidence level (CL).

AN Update

Statistical error fixed WZ reduction applied

Systematic error on WZ updated


Complete results in ANAN Update

Statistical error fixed WZ reduction applied | Systematic error on WZ updated


Results in PASCONCLUSIONS:

No excess of events in data with respect to the total background is found.

The analysis shows no evidence for seesaw type III model signal in 2012 CMS data.

Interpretations of results are upper limits on production cross sections (σ) times the branching fraction (BR) for the considered processes, at 95% confidence level (CL).

PAS Update

Statistical error fixed WZ reduction applied

Systematic error on WZ updated


Results plots

Thank to the convener Sarah’s suggestions

PAS


Results interpretation - limits

Yellow (68% CL) and green (95% CL) bands reflect the combined statistical and systematic uncertainties on the background contributions.

CMS observed limit @ 7 TeV = 179 GeV improvement CMS new result

AN

AN AN

PAS


Results interpretation - limitsAN and PAS – statistical error fixed

on WZ, ZZ and WWWNo reduction applied on WZ, systematic error on WZ 6.9%

Total error bands are smaller than in the AN v8 plots, because now statistical errors are correctly computed.Observed (points) – Expected (black line) are more separated than in AN v8.

We would like to insert these plots in the AN and in the PAS, BUT a suggestion to improve came from Internal Reader



Results interpretation - limitsAN and PAS Update

AN Update

Reduction applied on WZ, systematic error on WZ 13%


Results interpretation – 2D plot

In case the Σ mix almost completely with e and μ and not with τ (i.e. close to the black line on the left plot), the analyzed data fixes that the bound on the mass is at 280 GeV.

Verified efficiencies equal for the same final states but coming from different decays chains, the number of events for the categories Nijk are calculated.N(tot) is the event number sum of the six categories contributions at mass value 240 GeV.Chosen another mass point, the search for the mixing that gives same N(tot) is performed.

AN

PAS


Conclusions

Seesaw type III search authors are seeking the pre approval

for the AN-13-135 and the PAS EXO-14-001.

The analysis will hopefully become a PAS PUB only.

Authors are available for a common PAPER with other multi lepton searches.

• Type III seesaw exclusive and dedicated search in final states with three charged isolated leptons using 2012 proton-proton collisions at 8 TeV data is performed.

• General results interpretation in agreement with theoretician is given.

• Objects definitions are in agreement with the POGs prescriptions.

• Normalization method is applied on the main electroweak background source (WZ) (similar to SUSY electroweakino analysis, SUS-13-006).

• Data-driven method to estimate the non prompt lepton contribution (fake) is in agreement with the dedicated SUSY working group.

• Fake Rate factors cross checks on MonteCarlo samples are done.

• Systematic uncertainties section completly new in AN (and PAS)

• Plots in AN with (data-MC)/MC are restored and checked.


DocumentationsGeneral twiki page: https://twiki.cern.ch/twiki/bin/viewauth/CMS/SeesawQuestions and Answers: https://twiki.cern.ch/twiki/bin/viewauth/CMS/EXO14001QA

https://twiki.cern.ch/twiki/bin/viewauth/CMS/Seesaw

https://twiki.cern.ch/twiki/bin/viewauth/CMS/EXO14001QA


Documentations in detail

Many thanks for their comments/suggestions and continued support and patience.

Link to stuffs are in the twiki page


Thank you very much


Backup materialAdditional slides


Seesaw type III signal

AN


Seesaw type III processes

AN

CHECK: The generated seesaw signal has the correct number of produced Z and W Test different combinations of the 6 seesaw signal processes (in MadGraph process card)

process 3 and process 6:* equal number of Z and W as expected * BUT the decay BF of Z are not preserved due to a MadGraph bug:BR(z>udsc)/BR(vv) = 0.673/0.327=2.0


Signal generation testSeesaw type III model developed in Mathematica v9.0 with Feynman Rules 1.6.11and UFO (Universal FeynmanRules Output)

Signal Les Houches Events files produced with Madgraph 5 v1_5_7

Process card with 6 processes (example Σ- )

1. pp > Σ- Σ0 > w- ν w+ l- > l- ν ν l+ ν l- 2. pp > Σ- Σ0 > w- ν w- l+ > l- ν ν l- ν l+ 3. pp > Σ- Σ0 > z l- w+ l- > ν ν l- l+ ν l- 4. pp > Σ- Σ0 > z l- w- l+ > ν ν l- l- ν l+ 5. pp > Σ- Σ0 > z l- w- l+ > j j l- l- ν l+ 6. pp > Σ- Σ0 > z l- w+ l- > j j l- l+ ν l-

AN

Theory: BR(Σ- > Z l-) / BR(Σ- > W- ν ) = 0.408 Z and W are constrained to decay: W > leptons (30% BR) and Z > νν, uu, dd, ss, cc (75% BR) Considering W, Z decays the number of Z over

number of W in signal Les Houches Events files is larger than 0.4 because we are excluding most of the W and including most of the Z.

a scale factor can be applied for specific channels to fix the bug.Update


Z decays generation test

z > uu ===> 0.1156z > dd ===> 0.1548z > ss ===> 0.1473z > cc ===> 0.1202z > bb ===> 0.1484z > vv ===> 0.2059z > ll ===> 0.1078

BRs are coherent with PDG values

(within statistical error for 1k events samples)

CHECK: The seesaw model integrated in MadGraph preserves SM BRsWe replaced seesaw signal processes in Madgraph process card with different combinations of Z boson decays:

Z > all (100k events): BF(z>udsc)/BF(vv) = 0.5379 / 0.2059 = 2.61BF(z>udsc)/BF(ll) = 0.5379 / 0.1078 = 4.99BF(vv)/BF(ll) = 0.2059 / 0.1078 = 1.91

Z > jj and Z > vv (1000 events): BR(z>udsc)/BR(vv) = 2.80

Z > jj and Z > ll (1000 events): BR(z>udsc)/BR(ll) = 5.17

Z > ll and Z > vv (1000 events): BR(vv)/BR(ll) = 2.08

Z > jj and Z > ll and Z > vv (1000 events): BR(z>udsc)/BR(vv) = 2.50BR(z>udsc)/BR(ll) = 5.66BR(vv)/BR(ll) = 2.27

Update


Signal validation

MET

HT

CSV b tag

AN


AN



Ele, Iso<0.15 Ele, Iso<0.20

Mu, Iso<0.12 Mu, Iso<0.20

Fake leptons step 1AN


Significance

AN

AN

Offline selections on slide 14

STUDY: significance versus leptons transverse momentum thresholds

Signal 180 GeV, sign +



Significance

AN

AN

Offline selections on slide 14

STUDY: significance after each offline selection step



NOTE: each selection improves the significance


STUDY: MET distribution after pre selections EWK prompt and other SM processes as backgrounds MC samples

Fake leptons and Dalitz contributions are NOT included.Signal 180 GeV, sign +

MET threshold 50 GeV

Not in ANCome from AN v5

MET threshold Offline selections on slide 14

MET


Selections efficiencies

AN


ANUpdate

Selections efficiencies


Category Dalitz events

μ+μ+μ- 0.3 ± 0.15 (53%)

e+e+e- Z Dalitz veto

μ+μ+e- No Dalitz

μ+e+μ- Z Dalitz veto

e+e+μ- No Dalitz

μ+e+e- 0.8 ± 0.4 (53%)

Category Dalitz events

μ-μ-μ+ 0.3 ± 0.15 (53%)

e-e-e+ Z Dalitz veto

μ-μ-e+ No Dalitz

μ-e-μ+ Z Dalitz veto

e-e-μ+ No Dalitz

μ-e-e+ 0.8 ± 0.4 (53%)

Dalitz contribution


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