CERN - IPHC - U. Strasbourg EYNRULES-MADGRAPH · 2nd Taipei School on FEYNRULES-MADGRAPH for LHC...

Fuks Benjamin

CERN - IPHC - U. Strasbourg

Monotop phenomenology at the LHC

2nd Taipei School on FEYNRULES-MADGRAPH for LHC physics

National Taiwan Normal UniversitySeptember 04-08, 2013

Benjamin Fuks - 2nd Taipei School on FR/MG - 08.09.2013 -

Monotop phenomenology at the LHC

1

Introduction Monotops Top anomalous couplings Summary

Monotop phenomenology at the LHC Benjamin Fuks - 2nd Taipei School on FR/MG - 08.09.2013 - 2

A framework for LHC analyses: a modern way

Idea

[Christensen, de Aquino, Degrande, Duhr, BenjFuks, Herquet, Maltoni, Schumann (EPJC ’11) ]

Lagrangian

Theory

MADGRAPH 5(Matrix element generator)

PYTHIA 6/8 [Sjostrand, Mrenna, Skands (JHEP ’06, CPC’08) ]

Parton showering-hadronization

DELPHES

Detector simulation

Phenomenology

FEYNRULES

MA

DA

NA

LYS

IS 5

Tools[ Christensen, Duhr (CPC ’09) ] [ Alloul, Christensen, Degrande, Duhr, BenjFuks (in prep) ]

[ C

on

te,

Be

njF

uk

s, S

err

et

(CP

C ’

13

) ]

[Alwall, Herquet, Maltoni, Mattelaer, Stelzer (JHEP ’11) ]

[ Ovyn, Rouby, Lemaitre (’09) ]


Monotop phenomenology at the LHC Benjamin Fuks - 2nd Taipei School on FR/MG - 08.09.2013 -

Outline

3

1. Bottom-up new physics excursions: why and how

2. Monotops

3. A new search for top anomalous couplings

4. Summary



The top-down approach: pros and cons (1)

✦ The darker side: the model signatures✤ Driven by the benchmark scenarios

→ e.g., Majorana state ↔ same-sign dileptons

✤ Not typical of a specific benchmark, of a specific theory → e.g., cascade decays both in supersymmetric and extra-dimensional models

✦ The bright side: serious physical motivations✤ Fundamental theoretical ideas

→ e.g., symmetry principles✤ Addresses one or several issues of the Standard Model

→ e.g., the hierarchy problem✤ Predictions can be made through perturbation theory

→ e.g., tests at colliders

✦ The dark side: one theory ≡ hundreds of scenarios✤ In general, many new free parameters

→ e.g., the general MSSM and its 105 new free parameters✤ Benchmark choice constrained by current experimental data

→ e.g., 125 GeV Higgs, electroweak precision tests,...



The top-down approach: pros and cons (2)

✤ How to relate observations to a given model?✤ Assuming a model, how to related the observations to a specific benchmark?✤ How to disentangle models and benchmarks?

✤ Are we missing some signatures not predicted by any model?(and not phenomenologically and experimentally investigated)

THE BOTTOM-UP approach: ✤ We start from the signature✤ We construct an appropriate effective theory✤ Prospective studies at colliders



Outline

6


2. Monotops


4. Summary



7

Monotops at hadron colliders: main features

✦ The bottom-up strategy: we start from a final state signature: top + missing energy

✦Key features:✤ Missing energy (dark matter candidate)

★ Bosonic or fermonic state★ One-particle or n-particle state★ Neutral, weakly-interacting, long-lived/stable/invisible

✤ One single top quark✤ Enhanced coupling between the third generation and the others✤ Initial state: two possibilities

★ A down-type (anti)quark pair → baryon-number-violating process★ An up-type quark / gluon associated pair → flavor-changing neutral interactions

✦ Highly-suppressed in the Standard Model✤ Loop-suppression✤ GIM-suppression

Observing monotops new physics➟

[ Andrea, BenjFuks, Maltoni (PRD ’11); BenjFuks (IJMPA ’12); Agram, Andrea, Buttignol, Conte, BenjFuks (in prep) ]



8

Classifying monotop signatures (1)

✦ The missing energy is a fermion

✦ Monotop produced via (resonant or not) exchange of a new bosonic state✤ Lying in the (anti)fundamental representation of SU(3)c

✦ Examples✤ R-parity violating supersymmetry ( )✤ SU(5) theories (V = leptoquark, )✤ spin 3/2 excitations ✤ Four-fermion interactions (very heavy S or V)✤ etc...

�

S = t;� = �01

� = ⌫� ⌘




9

Classifying monotop signatures (2)

✦ The missing energy is a boson S or V

✦ Monotop produced via flavor-changing interactions (top-charm or top-up)

✦ Examples✤ R-parity conserving supersymmetry with non-minimal flavor violation ( )✤ Compressed spectrum (top produced in association with invisible superpartners)✤ Flavor-violating graviton couplings (spin 2)✤ etc...

gq ! q�01 ! t�0

1�01




10

Monotops: the Lagrangian

✦ We embed all the cases into one single Lagrangian (flavor indices understood)

L =LSM + Lkin

+ �ua0FCu

+ Vµua1FC�

µu

+ ✏ijk'idcja

qSRdk + 'iu

ia1/2SR�

+ ✏ijkXµ,i dcja

qV R�

µdk +Xµ,i uia1/2V R�

µ�

+ h.c.

Invisible scalar fieldFlavor

changing modes

Invisible vector field

Resonant modes

Invisible fermionic

fieldScalar colored

resonance

Vectorial colored

resonance




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Signal and background description

✦ Signal description✤ Leptonic top decay

★ 1 lepton + 1 b jet + missing energy★ No top mass reconstruction★ Challenging ⇒ not considered here (two different missing energy particles)

✤ Hadronic top decay (our case)★ 2 light jets + 1 b jet + missing energy★ Top reconstruction possible

A first prospective parton-level analysis (LHC-7, 1fb-1)Learning the key features necessary for a full analysis➟


Z ! ⌫⌫ + 3 jets

tt

✦ Background description✤ ⇒ irreducible background

✤ QCD multijet ⇒ misreconstructed jet (fake missing energy)

✤ W+jets, and diboson ⇒ non- or misreconstructed leptons from W’s

✤ Single top ⇒ non- or misreconstructed leptons



12

Monotops with 1 fb-1 of 7 TeV LHC data (1)

✦ Control of the non-simulated backgrounds: we rely on existing experimental works★ CMS: CERN-PH-EP-2011-65★ ATLAS: PLB 701 (2011) 186

✦ Analysis strategy✤ Large missing energy✤ Three high-quality hard jets✤ Large hadronic activity

✦ Effects on the background✤ Comparable amount of multijet, , Drell-Yan and W+jets events✤ Single top and diboson contributions highly reduced

tt


The instrumental background is expected to be highly suppressedIt is fair to consider as only source of background: . ➟ Z ! ⌫⌫ + 3 jets

✦ Additional specific monotop search strategy: we have exactly one top✤ Exactly 3 jets, with one b-tag✤ Lepton veto✤ The two light jets are issued from a W-boson (reconstructed invariant mass)✤ The three jets are issued from a top (reconstructed invariant mass)



13


✦ The key selection: the missing energy✤ Resonant and non-resonant production have different missing energy spectra

Invisible Z background

Flavor-changing modes

Resonant mode, far from threshold

Resonant mode, close to threshold

➟This selection criterion drives the sensitivity to the different modes

150 GeV selection




14

Monotops with 1 fb-1 of 7 TeV LHC data (3)✦ Analysis strategy: detailed specifications

✤ > 150 GeV (hard to detect light resonances)✤ W-boson reconstruction: 20 GeV window✤ Top reconstruction: 30 GeV window✤ b-tagging efficiency: 60 % (10% c-mistagging and 1% light jet-mistagging)

E/T

3�

Flavor-changing modes more easily

accessible

Resonant modes: depends on the

kinematical regime

Light

Heavy

➟ Light monotops are

reachable in all production modes

Heavier monotops are only visible in specific

channels➟




15

✦ Missing energy spectrum for non-resonant vectorial monotops


150 GeV selection


7 TeV, parton-level 8 TeV, reconstructed-level

W+jets and (semileptonic) contributions not negligible

(even after the cuts)

tt

Different invisible masses

Flavor-changing modes




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✦ Missing energy spectrum for scalar resonant monotops


150 GeV selection


7 TeV, parton-level

W+jets and (semileptonic) contributions not negligible

(even after the cuts)

tt

Kinematics drives the peak position

Resonant modes

8 TeV, reconstructed-level




17

Representative Feynman diagram

Only two free parameters

a


Large couplings: large masses reachable

Smaller couplings: masses of several hundreds of GeV

CDF exclusion: a=0.1;

MV < 150 GeV[PRL`12]




18


The sensitivity depends on the mass difference (as well as on the total rate)

BR( ) = 100%→ total rate independent

of the related coupling and .m�

' ! u�


Only three free parameters

a





Outline

19


2. Monotops


4. Summary



Not considered by ATLAS and CMS→ all three addressed in this talk

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Top anomalous couplings in the single top mode

✦ Monotops are highly-suppressed in the Standard Model

✦ Let us consider the associated trileptonic final state:✤ Leptonic Z-boson decay✤ Leptonic top quark decay

✦ Pros and cons for a trilepton signature:✤ Small Standard Model background✤ Lower statistics for the signal (Z and top leptonic branching fractions)

✦ We now embed new physics in top anomalous couplings

L =X

q=u,c

p2gs

gqt

⇤t�µ⌫Ta(f

Lq PL+fR

q PR)q Gaµ⌫

+gp2cW

zqt

⇤t�µ⌫(fL

q PL+fRq PR)q Zµ⌫

+g

4cW⇣zqt t�

µ(fLq PL+fR

q PR)q Zµ

�+ h.c.

[ Agram, Andrea, Conte, BenjFuks, Gelé, Lansonneur (PLB ’13) ]



21

Current bounds on top anomalous couplings

✦ Strong anomalous couplings✤ From single top processes at the production level

★ 1 lepton + 1 b jet + missing energy★ Additional kinematics information (small top transverse-momentum, ...)★ Best bounds (in terms of top rare branching ratio):

BR(t → gu) < 5.7 10-5 and BR(t → gc) < 2.7 10-4

✦ Weak anomalous couplings✤ From rare decays in top-antitop events

★ 3 lepton + 2 jets (1 b-tag) + missing energy★ Leptonic top and Z reconstruction★ Best bounds (in terms of top rare branching ratio):

BR(t → Zq) < 7. 10-4

L =X

q=u,c

p2gs

gqt

⇤t�µ⌫Ta(f

Lq PL+fR

q PR)q Gaµ⌫ +

gp2cW

zqt

⇤t�µ⌫(fL

q PL+fRq PR)q Zµ⌫

�+ h.c.

gqt/⇤

[ ATLAS, 7 TeV, 2.05 fb-1 ]

zqt/⇤

[ CMS, 8 TeV, 19.5 fb-1 ]

We will probe both couplings at the same time, as well as .➟ ⇣




22

✦ Selection strategy: exploiting the final state topology✤ 3 leptons✤ 2 of them compatible with a Z-boson (same flavor, opposite charge, invariant mass)✤ > 30 GeV✤ W-transverse mass larger than 10 GeV✤ At least one jet and exactly one b-tag✤Top reconstruction

E/T

Signal normalized to a cross section of 10 fb

We can expect a good sensitivity

Analysis strategy[ Agram, Andrea, Conte, BenjFuks, Gelé, Lansonneur (PLB ’13) ]



23


Results in terms of rare branching ratios

3�5�

Beware when comparing ...

✦ Reminder: current bounds (at the 95% C.L.)

✤ BR(t → gu) < 5.7 10-5 and BR(t → gc) < 2.7 10-4

✤ BR(t → Zu) < 7. 10-4 and BR(t → Zc) < 7. 10-4

Reminder: no limit on so far⇣

reaches 8 TeV / CMS 7 TeV 95%CL

BR(t → Zu) < 2.0 10-3 / 5.1 10-3 BR(t → gu) < 2.5 10-3 / 5.6 10-2

BR(t → Zu) < 5.6 10-3

BR(t → Zc) < 2.1 10-2 / 1.1 10-1

BR(t → gc) < 2.8 10-2 / 7.12 10-2 BR(t → Zc) < 4.0 10-2

3�[TOP-12-021]



Outline

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2. Monotops


4. Summary



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Summary

✦ We exploit the FEYNRULES - MADGRAPH - PYTHIA - DELPHES - MADANALYSIS 5 framework✤ We develop simplified models describing monotop and multitop signatures✤ We investigate their phenomenology at 7 TeV and 8 TeV

✦ Monotops✤ We study the production of a hadronic top quark in associated with missing energy✤ A large part of the parameter space can be probed by the LHC

(including fairly large masses)

✦ Top anomalous couplings✤ We use associated top-Z production to probe top anomalous couplings✤ This is a competitive channel to put extra constraints on BR(t → Zq)

CERN - IPHC - U. Strasbourg EYNRULES-MADGRAPH · 2nd Taipei School on FEYNRULES-MADGRAPH for LHC...

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