B EYOND 'S TANDARD 'M ODEL ' AT 'LHC - - PowerPoint PPT Presentation

SLIDE 1

BEYOND'STANDARD'MODEL'AT'LHC

XXVI'Seminario'Nazionale'di'Fisica'Nucleare'e'Subnucleare'“Francesco'Romano”
 Otranto,'9G10'Giugno'2014' Lecture'2:'Exofca

Shahram'Rahatlou
 hQp://www.roma1.infn.it/people/rahatlou/

SLIDE 2

DIRECT'SEARCHES'AT'LHC

104

] 2 [GeV/c χ M

• 1

10 1 10 2 10 3 10 ] 2

• Nucleon Cross Section [cm

χ

• 45

10

• 43

10

• 41

10

• 39

10

• 37

10

• 35

10

• 33

10

• 31

10 CMS MonoJet CMS MonoPhoton CDF 2012 XENON-100 CoGeNT 2011 CDMSII 2011 CDMSII 2010 CMS = 7 TeV s

• 1

L dt = 5.0 fb

∫

a) Spin Independent Neutralino Mass [GeV] 100 150 200 250 300 Neutralino Proper Decay Length [mm] 1 10 2 10 3 10 4 10 5 10 6 10 7 10 8 10

• 1

CMS 4.9 fb = 7 TeV s )

• 1

This experiment (4.9 fb expected

• bserved

)

• 1

+ Jets (2.6 fb T E + γ γ CDF with )

• 1

(6.3 fb T E + γ γ D0 with prompt )

• 1

(4.8 fb T E + γ γ ATLAS with prompt SPS8 G ~ γ → 1 χ ∼ GMSB )=15 β , tan( Λ = 2 m M > 0 µ = 1, m N

Almost 200 papers on searches at LHC so far

SLIDE 3

Shahram Rahatlou, Roma Sapienza & INFN

EXO'SUMMARY'IN'ATLAS

105

SLIDE 4

Shahram Rahatlou, Roma Sapienza & INFN 95% CL EXCLUSION LIMITS (TEV)

CMS'EXOTICA'SUMMARY

stopped gluino (cloud) stopped stop (cloud) HSCP gluino (cloud) HSCP stop (cloud) q=2/3e HSCP q=3e HSCP neutralino, ctau=25cm, ECAL time 1 2 3 4 RS1(γγ), k=0.1 RS1(ee,uu), k=0.1 RS1(jj), k=0.1 RS1(WW→4j), k=0.1 RS1(ZZ→4j), k=0.1 bulk RS(ZZ→lljj), k=0.5 1 2 3 4 coloron(jj) x2 coloron(4j) x2 gluino(3j) x2 gluino(jjb) x2 1 2 3 4

RS Gravitons Multijet Resonances Long-Lived Particles

SSM Z'(ττ) SSM Z'(jj) SSM Z'(bb) SSM Z'(ee)+Z'(µµ) SSM W'(jj) SSM W'(lv) SSM W'(WZ→lvll) SSM W'(WZ→4j) 1 2 3 4

Heavy Gauge Bosons

j+MET, SI DM=100 GeV, Λ j+MET, SD DM=100 GeV, Λ γ+MET, SI DM=100 GeV, Λ γ+MET, SD DM=100 GeV, Λ l+MET, ξ=+1, SI DM=100 GeV, Λ l+MET, ξ=+1, SD DM=100 GeV, Λ l+MET, ξ=-1, SI DM=100 GeV, Λ l+MET, ξ=-1, SD DM=100 GeV, Λ 1 2 3 4

Dark Matter

LQ1(ej) x2 LQ1(ej)+LQ1(νj) LQ2(μj) x2 LQ2(μj)+LQ2(νj) LQ3(νb) x2 LQ3(τb) x2 LQ3(τt) x2 1 2 3 4

Leptoquarks

e* (M=Λ) μ* (M=Λ) q* (qg) q* (qγ) b* 1 2 3 4

Excited Fermions

dijets, Λ+ LL/RR dijets, Λ- LL/RR dimuons, Λ+ LLIM dimuons, Λ- LLIM single e, Λ HnCM single μ, Λ HnCM inclusive jets, Λ+ inclusive jets, Λ- 3 6 9 12 15

ADD (γγ), nED=4, MS ADD (ee,μμ), nED=4, MS ADD (j+MET), nED=4, MD ADD (γ+MET), nED=4, MD QBH, nED=4, MD=4 TeV NR BH, nED=4, MD=4 TeV Jet Extinction Scale String Scale (jj)

3 6 9 12 15

Large Extra Dimensions Compositeness

SLIDE 5

Shahram Rahatlou, Roma Sapienza & INFN

RESONANCES

• Resonances have a good record of past Nobel-worth discoveries!!

– charm and beauty

107

di-lepton mass di-photon mass

Z Extended Gauge Symm Graviton Randall-Sundrum Z,G1, γ1 Kaluza-Klein Excitations

SLIDE 6

Shahram Rahatlou, Roma Sapienza & INFN

EXTENDED'GAUGE'SYMMETRIES

• New gauge bosons predicted by many extensions of the Standard Model with extended

gauge symmetries!

– ZSSM in Sequential Standard Model with same Z0 coupling
 as in Standard Model! – Z’ψ , Z’χ , Z’η models from E6 and SO(10) GUT groups! – Left-Right symmetry model (LRM) and Alternative LRM (ALRM)! – The Kaluza-Klein model (KK) from Extra Dimension! – Little, Littlest Higgs model!

• No precise prediction for mass scale of gauge bosons!
• Discrimination of different models requires measurement of!

– cross section: limits with very little data! – mass: exact value requires a visible peak! – width: about same amount of data as for for mass! – backward-forward asymmetry: requires high statistics in order to divide events in categories!

• Backgrounds!

– relatively clean with good S/B ! – mostly tails of SM processes!

• Experimental challenges!

– detector resolution can be a key player! – 1.3% - 2.4% for electrons and 7% for muons at 1 TeV mass!

• extra care for energy/momentum reconstruction above 1 TeV

108

SLIDE 7

Shahram Rahatlou, Roma Sapienza & INFN

EXTRA'DIMENSIONS

• Hierarchy problem: MEW/MPl ~ 10−17!
• Gravity much weaker than other gauge fields!
• Possible solution: Existence of extra dimensions!!
• Gravity scale lowered to ~ 1 TeV if gravitons propagate in 4+n dimensions!

– weak in our 4D universe but strongly interacting
 in the extra dimensions!

• If ED similar to our 3+1 dimensions


Newton’s law affected!

– experimentally probed down to R < 160 microns!

• Tighter constraints if ED probed by elementary


particles!

– M = 100 GeV corresponds to distance of 10-18 m!

• Several models available with possible 


signatures to be seen at LHC!

– Graviton (and its KK modes), Black Holes

109

SLIDE 8

Shahram Rahatlou, Roma Sapienza & INFN

ORIGIN'OF'EXTRA'DIMENSIONS

110

• The idea that space has extra, hitherto unobservable

dimensions goes back to the beginning of the twentieth century, by Kaluza (1925) and Klein (1926).

• It comes naturally in string theory.

How come they are not visible today?

(A) Because they compact and sufficiently small. (B) Because we are “stuck” on the 4D world. (C) Because they are of a more bizarre kind (for example, they are discretized appropri- ately)

SLIDE 9

Shahram Rahatlou, Roma Sapienza & INFN

SMALL'COMPACT'DIMENSION

111

A compact, sufficiently small extra dimension is not visible ! A simple example of a space with one compact (circle) and one non- compact (real line) dimension: a hose of infinite length and radius R. There are two regimes: (A) At distance << R the space looks like an (infinite) two-dimensional plane.

SLIDE 10

Shahram Rahatlou, Roma Sapienza & INFN 112

(B) At distance >> R the compact direction of the hose is invisible. The hose looks one-dimensional.

R R

We will now make this intuition more precise.

SLIDE 11

Shahram Rahatlou, Roma Sapienza & INFN

WARPED'EXTRA'DIMENSION

• Randall-Sundrum scenario!

– One warped Extra dimension!

• 3D distances shrink between SM and Planck branes!
• Boundary conditions in ED give rise to periodical wave

functions
 corresponding to well separated Graviton resonances
 (aka Kaluza-Klein towers)!

• parameters of metric determine mass of new particles!

!

• Gravitons propagate in bulk!

! ! !

• Production at hadron collider via coupling


to SM paticles


113

ds2 = e−2kyηµνdxµdxν + dy 2

c=1 c=0.5 c=0.1 c=0.05 c=0.01

Drell-Yan production of a 1.5 TeV Gn and its subsequent tower states

pp → Gn → ll

Gravity Scale: Λπ = Mpl exp(krcπ) < 10 TeV Graviton Coupling c: 0.01 < c=k/MPl < 0.1 Mass 1st resonance: m1 = kx1 exp(krcπ)=3.83 Λπ c Width 1st resonance: Γ1 = ρm1 x1

2 (k/Mpl)2

jets e e G gg q q

KK

, , , , γγ µ µ

− + − +

→ →

SLIDE 12

Shahram Rahatlou, Roma Sapienza & INFN

Z’'PRODUCTION'AT'LHC

• Dominant Z’ production process via Drell-Yan process .!

! !

• Clear experimental signature!

– 2 high pt leptons with large invariant mass! – also decay in two jets but less sensitive than leptonic channels!

• in some models ttbar dominates over leptons. pretty exotic!!
• Differential cross section



 
 
 depends on !

– Z’ mass M=√s’! – Z’ rapidity Y! – Angle θ* between l- and q in the center 


• f mass of the colliding partons

114

u, d, s u, d, s γ / Z / Z’ l l

q¯ q → Z0

quark direction negative charged lepton direction

θ*!

cos"* > 0

SLIDE 13

Shahram Rahatlou, Roma Sapienza & INFN

RESONANCES

115

• Comprehensive list of signatures!

– di-leptons!

• e,mu,tau!
• lepton+MET!

– di-bosons (W/Z)!

• 3l+MET!
• 2l+2j!

– 2-photon!

• Backgrounds!

– relatively clean with good S/B ! – mostly tails of SM processes!

• Experimental challenges!

– detector resolution can be a key player! – 1.3% - 2.4% for electrons and 7% for muons at 1 TeV mass! – extra care for energy/momentum reconstruction above 1 TeV

RS1(γγ), k=0.1 RS1(ee,uu), k=0.1 RS1(jj), k=0.1 RS1(WW→4j), k=0.1 RS1(ZZ→4j), k=0.1 bulk RS(ZZ→lljj), k=0.5 1 2 3 4

RS Gravitons

SSM Z'(ττ) SSM Z'(jj) SSM Z'(bb) SSM Z'(ee)+Z'(µµ) SSM W'(jj) SSM W'(lv) SSM W'(WZ→lvll) SSM W'(WZ→4j) 1 2 3 4

Heavy Gauge Bosons

SLIDE 14

Shahram Rahatlou, Roma Sapienza & INFN

DIGELECTRONS

• Background mainly composed of Drell-Yan tail

116

Events

• 1

10 1 10

2

10

3

10

4

10

5

10

6

10

7

10

Data 2012 * γ Z/ Top quark Dijet & W+Jets Diboson Z’ SSM (1.5 TeV) Z’ SSM (2.5 TeV)

ATLAS ee → Z’

• 1

L dt = 20.3 fb

∫

= 8 TeV s

[TeV]

ee

m

0.08 0.1 0.2 0.3 0.4 0.5 1 2 3 4 Data/Expected

0.6 0.8 1 1.2 1.4

SLIDE 15

Shahram Rahatlou, Roma Sapienza & INFN

DIGMUONS

• wider peak structure!

– momentum resolution of high pt muons worse than energy resolution for high energy electrons

117 Events

• 1

10 1 10

2

10

3

10

4

10

5

10

6

10

7

10

Data 2012 * γ Z/ Top quark Diboson Z’ SSM (1.5 TeV) Z’ SSM (2.5 TeV)

ATLAS µ µ → Z’

• 1

L dt = 20.5 fb

∫

= 8 TeV s

[TeV]

µ µ

m

0.08 0.1 0.2 0.3 0.4 0.5 1 2 3 4 Data/Expected

0.6 0.8 1 1.2 1.4

SLIDE 16

Shahram Rahatlou, Roma Sapienza & INFN

LOOKING'FOR'DEVIATIONS

118

SLIDE 17

Shahram Rahatlou, Roma Sapienza & INFN

EXCLUSION'LIMITS

119

[TeV]

Z’

M

0.5 1 1.5 2 2.5 3 3.5 B [pb] σ

• 4

10

• 3

10

• 2

10

SSM

Observed limit Z’

χ

Observed limit Z’

ψ

Observed limit Z’ Observed limit Z*

SSM

Z’

χ

Z’

ψ

Z’ Z*

ATLAS = 8 TeV s

• 1

L dt = 20.3 fb

∫

ee:

• 1

L dt = 20.5 fb

∫

: µ µ

SSM

Observed limit Z’

χ

Observed limit Z’

ψ

Observed limit Z’ Observed limit Z*

SSM

Z’

χ

Z’

ψ

Z’ Z*

[TeV]

G*

M

0.5 1 1.5 2 2.5 3 3.5

Pl

M k/

0.05 0.1 0.15 0.2

Expected limit Observed limit 95% Exclusion

• 1

L dt = 20.3 fb

∫

ee:

• 1

L dt = 20.5 fb

∫

: µ µ

= 8 TeV s ATLAS

SLIDE 18

Shahram Rahatlou, Roma Sapienza & INFN

NEW'WGLIKE'BOSON

• Look for heavy W-like Jacobian peak in transverse mass!

! !

• Dominant background: W production in Standard Model!
• Now also take into account interference with SM

120

SLIDE 19

Shahram Rahatlou, Roma Sapienza & INFN

LEPTON'+'MET'SPECTRUM

121

SLIDE 20

Shahram Rahatlou, Roma Sapienza & INFN

W’'EXCLUSION'LIMIT

122

SLIDE 21

Shahram Rahatlou, Roma Sapienza & INFN

COMPOSITENESS

123

• Quarks and leptons are probed to be

elementary up to scales of 10-15 m or TeV Maybe substructure? Constituents = “preons”. ¡New ¡strong ¡gauge ¡(metacolor) interaction of scale Lambda is introduced. Concept ¡similar ¡to ¡Fermi’s ¡theory ¡of ¡beta ¡ decay

Pati & Salam, PRD 10 (1974), 2500 citations

Fermion substructure

(Compositeness)

?

May address open questions:

• Replication of SM families
• Their complex pattern of masses

and mixing angles

• Large number of fundamental

particles

SLIDE 22

Shahram Rahatlou, Roma Sapienza & INFN

PROBING'COMPOSITENESS

124

Excited leptons and quarks l, , l*, l , l** ¡ ¡, ¡…. ¡ ¡q, ¡q*, ¡q** ¡

• Sort out by mass (or spin), sharing

flavor with corresponding SM particle

• Direct evidence for fermion substruc-

ture rich spectrum of excited states

• Known l,q regarded as ground states

4 below

• Search channels in CMS

ee,

q*qg (dijet) q*ZZ

• ** ¡ ¡, ¡…. ¡ ¡q, ¡q*, ¡q** ¡
• es
• 4-fermion contact interaction (CI)

below compositeness scale l jet l l jet

Search channels: , jj

SLIDE 23

Shahram Rahatlou, Roma Sapienza & INFN

COMPOSITENESS'AND'CONTACT'INTERACTION

125

• Excited quarks and leptons!
• Both leptonic and hadronic states!

– lepton + photon (l* -> l + gamma)! – 2-jet (q* -> q glu)! – boosted Z spectrum in q* -> q Z!

• Contact interaction !

– di-jet angular analysis! – re-interpretation of di-lepton! – re-interpretation of W’

dijets, Λ+ LL/RR dijets, Λ- LL/RR dimuons, Λ+ LLIM dimuons, Λ- LLIM single e, Λ HnCM single μ, Λ HnCM inclusive jets, Λ+ inclusive jets, Λ- 3 6 9 12 15

Compositeness

SLIDE 24

Shahram Rahatlou, Roma Sapienza & INFN

COMPOSITE'LEPTONS

126

Lcontact = 2π Λ2jµjµ , jµ = f LγµfL + f

∗ Lγµf ∗ L + f ∗ LγµfL + h.c.

SLIDE 25

Shahram Rahatlou, Roma Sapienza & INFN

EXCLUSION'OF'COMPOSITE'LEPTON

127 e* (M=Λ) μ* (M=Λ) q* (qg) q* (qγ) b* 1 2 3 4

Excited Fermions

SLIDE 26

• Sh. Rahatlou

HEAVY NEUTRINO AND L-R SYMMETRY

• Parity violation built-in for the Standard Model !

– Parity violation in LRSM via symmetry breaking at 
 intermediate mass scale !

• Neutrino oscillations require massive neutrinos!

– but neutrinos mass forbidden in SM! – “See saw” mechanism in LRSM can explain small mass of 
 neutrinos via heavy partners

128

Standard Model Left-Right-Symmetric Extension (LRSM)

Gauge group

SU(2)L X U(1)Y SU(2)L X SU(2)R X U(1)B-L

Fermions

LH doublets: QL = (ui,d i)L , LL = (l i,ν i)L RH singlets: QR = ui

R , d i R , LR = l i R

LH doublets: QL = (ui,d i)L , LL = (l i,ν i)L RH doublets: QR= (ui,d i)R , LR = (l i,N i)R

Neutrinos

ν i

R do not exist

ν i

L are massless & pure chiral

Ν i

R are heavy partners to the ν i L

Ν i

R Majorana in the Minimal LRSM

Gauge bosons

W±

L, Z0, γ

W±

L,W± R, Z0, Z´, γ

SLIDE 27

Shahram Rahatlou, Roma Sapienza & INFN

HEAVY'NEUTRINO'AND'WR

• Limits approaching 3 TeV !
• Gets very interesting for theory once limits over 3 TeV!
• Enhanced cross section at 13 TeV

129

SLIDE 28

Shahram Rahatlou, Roma Sapienza & INFN

HADRONIC'RESONANCES

• Extremely rich and productive

hadronic program!

• Variety of signatures and

models explored!

– standard jets! – b-jets! – fat jets! – jet substructure for W/Z tag

130

q* q g

C C

qq,qg,gg)

q q ~ ~ ~ ~ g g

C C C C

Studied in CMS (so far)

• String resonances, S (qq,qg,gg)
• Scalar diquarks, D (qq)
• Excited quarks, q* (qg,qW,qZ)
• Axigluons, A (qq)
• Color-octet colorons, C (qq, qqqq)
• Color-octet scalar, S8 (gg,bb)
• W‘ bosons (qq,WZ)
• Z‘ bosons (qq,bb,tt)
• RPV SUSY gluinos (qqqqqq)
• RS gravitons (qq,gg,WW,ZZ)

Hadronic inspired EWK inspired Gravitation inspired RSG W W q q q q

SLIDE 29

Shahram Rahatlou, Roma Sapienza & INFN

DIJET'SPECTRUM

131

/dm (pb/GeV)

• d
• 6

10

• 5

10

• 4

10

• 3

10

• 2

10

• 1

10 1 10

)

• 1

CMS Preliminary (5 fb Fit QCD Pythia Jet Energy Scale Uncertainty

= 7 TeV s | < 1.3

• | < 2.5, |
• |

Wide Jets S (1.8 TeV) S (2.6 TeV) Q* (1.5 TeV) Q* (3.2 TeV)

Dijet Mass (GeV) 1000 1500 2000 2500 3000 3500 4000

Residuals

• 2
• 1

1 2

ss by in r m

• Lower threshold fixed by trigger requirements on single jets ~500 GeV!
• Fit data to define background shape!

– no dependence on MC prediction and modeling

SLIDE 30

Shahram Rahatlou, Roma Sapienza & INFN

BOOSTED'JETS

132

RSG W W q q q q

SLIDE 31

Shahram Rahatlou, Roma Sapienza & INFN

W/Z'TAGGED'JETS

133

SLIDE 32

Shahram Rahatlou, Roma Sapienza & INFN

DIJET'EXCLUSION'LIMITS

134

SLIDE 33

• Sh. Rahatlou

DI-JET PAIR

• Events with at least 4 jets and pt > 150 GeV!
• Sensitive to colorons at low mass

135

7!TeV! 5.0!G,1!

SLIDE 34

1 6 5 4 3 2

Shahram Rahatlou, Roma Sapienza & INFN

TRIGJET'RESONANCE

• 6 jets in several theoretical models !

– Q = g = SU(3)C Adjoint Majorana Fermion ! – R-Parity violating (No Missing ET) !

• Modeled as R-parity violating gluino 


(negligible intrinsic width)

136

state, pp → QQ → 3j + 3j.

SLIDE 35

Shahram Rahatlou, Roma Sapienza & INFN

QUADGJET'RESONANCE

• Multivariate analysis for max. QCD 


rejection!

– pt of 1st,4th, 7th, and 8 jets! – HT! – 8-jet invariant mass

137

madgraph+pythia

SLIDE 36

BLACK'HOLES?'REALLY?

138

SLIDE 37

Shahram Rahatlou, Roma Sapienza & INFN

MUCH'ADO'ABOUT'NOTHING

• Perhaps the worst case of misleading and wrong scientific information in

history prior to start of LHC!

• Too much noise about non-existent dangers based on wrong assumptions

by non-scientists!

• No way to create an black holes in the lab!
• Black hole is a term used both for astrophysical objects and solution to a

pure mathematical problem!

• Dedicated safety assessment group has studied and release a detailed

summary!

– Review of the Safety of LHC Collisions: http://arxiv.org/abs/0806.3414!

• Of course there is no danger!
• if course nothing crazy has happened!
• Unfortunately none of the newspaper has reported that idiots claiming

catastrophes were unreliable idiots with no scientific knowledge looking
 for 1-day fame

139

SLIDE 38

Shahram Rahatlou, Roma Sapienza & INFN

MICRO/QUANTUM'BLACK'HOLES'

• Black Holes are a direct prediction of Einstein’s general theory on relativity!
• If Planck scale ~TeV region, expect Quantum Black Hole production!
• Using Gauss’s law with n extra dimensions!
• For small extra dimension of size R!

!

• Relation between planck scale in 4D and 4+nD!
• Schwarzschild radius is the radius in which a confined mass would become

a black hole!

!

– Mpl = 1019 GeV in 4D implies rh << 10-35 m! – Mpl = TeV in 4+n D implies rh ~ 10-17 m !

• Occasionally protons with parton center of mass energy


could collide at a distance smaller than rh!

• such collisions satisfy the black hole definition but with tiny mass

140

V (r) ∼ M Mn+2

p

1 rn+1

V (r) ∼ M Mn+2

p

Rn 1 r .

M2

p(4) ∼ M n+2 p

Rn

rh = 1 √πMp MBH Mp

• 1

n+1

• 8Γ

n+3

2

• n + 2
• 1

n+1

MBH = √ ˆ s

SLIDE 39

Shahram Rahatlou, Roma Sapienza & INFN

PRODUCTION'AND'DECAY'OF'BLACK'HOLES

141 !

Formation: semi-classical argument

!

Partons with impact parameter less than Schwarzchild radius Rs(√s)

!

Hawking evaporation with lifetime τ~10-27 sec

!

Experimental signatures

!

High multiplicity events

!

Hadrons:Leptons ~ 5:1

!

Spherical events

!

Large missing PT

!

Could be discovered with 1 fb1 if MPl < 5 TeV! MBH >> MD Parton i Parton j

RS

area ~ πRS

2 ~ 1 TeV -2 ~ 10-38 m2 ~ 100 pb

Production rate of ~0.1 Hz at L = 1034cm-2 s-1$

Harris et al. [JHEP 08(2003) 033, JHEP 10(2003) 014] MD

2 = MPl(4+n) 2+n

Rn

SLIDE 40

Shahram Rahatlou, Roma Sapienza & INFN

SEARCHES'AT'LHC

142

• Analysis strategy: events with large transverse energy, multiple high- energy jets, leptons,

and photons!

• Main Standard Model background: QCD multijet production!
• Discrimination variable: visible transverse energy!

– scalar sum of ET for identified physics objects and MET!

• data-driven background estimate from low ST region and lower multiplicity as control sample

ST=

∑

j ,e ,μ ,γ ,MET N

pT

Only phys obj with pT > 50 GeV

SLIDE 41

Shahram Rahatlou, Roma Sapienza & INFN

CANDIDATE'MULTIJET'EVENT

143

SLIDE 42

Shahram Rahatlou, Roma Sapienza & INFN

EXCLUSION'LIMITS

• No quantum black holes observed yet!

144