From the tevatron to the lhc what could lie beyond the sm
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From the TeVatron to the LHC: What could lie beyond the SM?. Monica D’Onofrio IFAE-Barcelona HEP Seminar, University of Oxford, 28 th October 2008. The Standard Model. Matter is made out of fermions: 3 generations of quarks and leptons Forces are carried by Bosons:

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From the TeVatron to the LHC: What could lie beyond the SM?

Monica D’Onofrio


HEP Seminar, University of Oxford, 28th October 2008

The Standard Model

  • Matter is made out of fermions:

    • 3 generations of quarks and leptons

  • Forces are carried by Bosons:

    • Electroweak: ,W,Z

    • Strong: gluons

  • Remarkably successful description of known phenomena:

    • predicted the existence of charm, bottom, top quarks, tau neutrino, W and Z bosons.

    • Very good fit to the experimental

    • data so far

  • but ...

University of Oxford, 10/28/2008

The missing piece: the Higgs



What is the origin of masses?

 Within SM, Higgs field gives mass to Particles (EWK symmetry breaking)

SM predicts existence of a new massive neutral particle

Not found yet!

Theory does not predict its mass

LEP limit: mH>114 GeV @ 95% CL

Indirect limit from EW data:

- Preferred value: mH = 84+34-26 GeV

- mH < 154 GeV @ 95% CL

with aS (MZ) = 0.1185±0.0026, DaS(5)had=0.02758±0.00035

University of Oxford, 10/28/2008

Beyond SM: the Unknown

The Standard Model is theoretically incomplete

  • Mass hierarchy problem

  •  radiative correction in Higgs sector

  • Unification

  • Dark Matter

  • Matter-antimatter asymmetry

  • Many possible new particles and theories

    • SuperSymmetry

    • Extra Dimension

    • New Gauge groups (Z’, W’)

    • New fermions (e*, t’, b’ …)



DmH2 ~ L2

L = Mpl ?

Can show up in direct searches or as subtle deviations in precision measurements

University of Oxford, 10/28/2008


  • Tevatron and the CDF and D0 experiments

  • Tevatron sensitivities: achievements understanding the SM

  • The SM Higgs

  • Searching for physics beyond SM

    • Supersymmetry

      • mSUGRA-inspired searches:

        • Squark/gluino

        • Chargino/neutralinos

      • GMSB-inspired searches

        • Diphoton+X

        • Delayed photon analysis

      • MSSM Higgs

    • Extra-dimension and new gauge bosons:

      • Search for high-mass resonances

  • Perspectives for the LHC

University of Oxford, 10/28/2008


The Tevatron




Highest-energy accelerator

currently operational


Peak luminosity > 3.2 *1032 cm-2 s-1

Integrated luminosity/week

 ~ 40-60 pb-1

Delivered: 5.1 fb-1

Acquired: 4.2-4.3 fb-1


University of Oxford, 10/28/2008

CDF and DØin RunII



Took >1 years of collisions to

get to stable high efficiency

Oct 08

Jan 02

University of Oxford, 10/28/2008

Tevatron Sensitivities

  • Jet cross section measurements, heavy flavor physics, inclusive W/Z

  • Precision measurements (Top properties, observation of rare processes...)

  • New Physics searches, looking for ‘the’ unexpected

Both CDF and D0 have a very rich physics program!

University of Oxford, 10/28/2008

Knowledge of the SM: QCD and EWK

  • Z(e+e-)+jets

    • Clean signature, low background

    • Test ground for Monte Carlo tools

  • W Mass and width

  • MW = 80413±48 MeV

  • GW = 2032±73MeV

  • world’s most precise single measurements!

Test of Next-to-Leading Order

perturbative QCD

  • inclusive jet cross section

    • Probing distances ~10-19 m

    • Constrains gluon PDF at high-x

University of Oxford, 10/28/2008

Knowledge of SM: top physics

Mtop = 172.4 ± 0.7 (stat) ± 1.0 (syst) GeV/c2

  • Top quark discovered at the Tevatron in 1995

  • Very extensive program on top physics:

    • Precision measurements of top mass

    • Top cross sections, properties…

University of Oxford, 10/28/2008

Knowledge of SM: rare processes

  • DiBoson cross sections

D0:s + t = 4.7 ± 1.3 pb

CDF: s + t = 2.0-2.7 pb (± 0.7 pbper analysis)

Measurements of W/Zg,

WW and WZcross sections

Consistent with NLO calculation

ZZ production  Evidence at CDF

Observation at D0!!

Consistent with NLO calculation: 1.4 ± 0.1 pb

The focus is now to uncover the unknown

University of Oxford, 10/28/2008

Evidence of Single top production

Needle in the haystack

 Model-inspired searches

  • Theory driven

  • Model-dependent optimization of event selection

  • Set limits on model parameters

 Signature-based searches

  • Signature driven

  • Optimize selection to reduce backgrounds

  • Event count; event kinematics

Every measurement we make is an attempt to find New Physics

When searching for a needle in a haystack, the hay is more important than the needle...

Many searches are extensions of SM measurements.

University of Oxford, 10/28/2008

The SM Higgs Boson

SM Higgs Production and Decay

  • Direct production gg→H

    • Highest Production rate

    • Largest background

  • Associated production ZH/WH

    • Leptonic vector boson decay helps for triggering and signal extraction

MH (GeV/c2)

  • Low Mass (MH<135 GeV/c2)

    • H→bb mode dominates

    •  WHlbb, ZHbb , ZHllbb

    • VBF Production, VHqqbb, H(with

    • 2jets), H, WH->WWW, ttH

  • High Mass (135<MH<200 GeV/c2)

    • H→WW mode dominates

University of Oxford, 10/28/2008


  • Most sensitive channel for high mass Higgs

    • gg →H → WW* and W(Z)H → W(Z)WW*

  • Unbalanced transverse energy (MET) from n

  • 2 leptons: e,,→e, (must haveopposite signs)

    • Key issue: Maximizing lepton acceptance

    • Primary backgrounds: Drell-Yan, WW

      • Higgs is scalar  leptons travel same direction

      • In t-channel WW, W are polarized along the beam direction

  • Use Matrix Element and Neural Network methods

Results at mH = 165GeV : 95%CL Limits/SM

University of Oxford, 10/28/2008

SM Higgs limits

CDF/D0 combination: High mass only

Exp. 1.2 @ 165, 1.4 @ 170 GeV

Obs. 1.0 @ 170 GeV

Tevatron exclude at 95% C.L. the

production of a SM Higgs boson of 170 GeV

Low mass combination difficult due to ~70 channels: Expected sensitivity of CDF/DØ combined: <3.0xSM @ 115GeV

A 15 GeV window [162:177] excluded @ 90% CL

University of Oxford, 10/28/2008

Searches Beyond SM



  • New spin-based symmetry relating

    fermions and bosons:

Q|Boson> = Fermion

Q|Fermion> = Boson

gaugino/higgsino mixing

  • Minimal SuperSymmetric SM (MSSM):

    • Mirror spectrum of particles

    • Enlarged Higgs sector: two doublets with 5 physical states

  • Naturally solve the

  • hierarchy problem

  • Define R-parity = (-1)3(B-L)+2s

    • R = 1 for SM particles

    • R = -1 for MSSM partners

If conserved, provides

Dark Matter Candidate

(Lightest Supersymmetric Particle)

University of Oxford, 10/28/2008


SUSY breaking

(hidden sector)


(visible sector)


Gauge fields, loop effects….

Symmetry breaking

No SUSY particles found yet:

  • SUSY must be broken

  • More than 100 parameters even in minimal (MSSM) models

  • Breaking mechanism determines phenomenologyand search strategy at colliders:

    • Direct searches or subtle deviations in precision measurements




choose a model 

Constrained MSSM models used as benchmark

University of Oxford, 10/28/2008

Sparticles mass and cross sections

1. Unified gaugino mass m1/2

2. Unified scalar mass m0

3. Ratio of H1, H2 vevs tanβ

4. Trilinear coupling A0

5. Higgs mass term sgn()

  • in mSUGRA, new superfields in “hidden” sector

  • Interact gravitationally with MSSM

  • 5 parameter at GUT scale



m (GeV)

  • Squarks and gluinos are heavy

  • Sizeable Chargino/neutralino cross sections

M(+) ~ M(02) ~ 2M(01)

M(g) ~ 3M(+)

In R parity conservation scenario,

the LSP is the neutralino (c01 )


University of Oxford, 10/28/2008

Inclusive search for squark/gluino

mSUGRA: Low tan b scenario (=5 for CDF, = 3 for D0)

Assume 5-flavors degenerate


Final state: energetic jets of hadrons and large unbalanced transverse energy(due to presence of c0)














A0 = 0, m<0

M0 [0,500 GeV/c2]

m1/2  [50,200 GeV/c2]






















Mq ~ Mg

qg final state dominates

 3 jets expected

























Mq > Mg

gg final state dominates

 4 jets expected











Mq < Mg

qq final state dominates

 2 jets expected









3 different analyses carried out with different jet multiplicities

Final selection based on Missing ET , HT = S (ETjets) and ET jets

University of Oxford, 10/28/2008


Background rejection

Data sample Cleanup

  • at least one central jet with |h|<1.1

  • minimum missing ET of 70 GeV

  • Reject beam-related backgrounds and cosmics

Rejection of SM processes

QCD-multijet: ET due to jet energy mismeasurement.

W/Z+jets with Wl or Z, DiBoson

and tt production: Signaturesvery

similar to SUSY

Define signal region based on selections

that maximize background rejection

University of Oxford, 10/28/2008

QCD multijet rejection

Missing ET from mis-reconstructed jets

 Collinear with one of the leading jets

 Apply cuts on Df (missingET-jets)

  • CDF: remaining QCD-bkg estimatated from Monte Carlo.

  • Control checks in enhanced QCD-sample

  • DØ : QCD-bkg extrapolated in data by exponential fit function


cut reversed for

at least one of

the leading jets

University of Oxford, 10/28/2008




















Top and Boson+jets rejection

Control region

  • Genuine Missing ET in the event

  • Suppressed vetoing events with:

    • jetElectromagnetic fraction > 90%, to reject electrons mis-identified as jets

    • isolated tracks collinear to missing ETto reject undetected electrons/muons

  • Modeled using Monte Carlo

  • Normalized to NLO cross section

  • Define control regions reversing lepton vetoes  checks of background estimations

    • Understanding these processes is fundamental

Control region

University of Oxford, 10/28/2008

DATA vs SM predictions


Good agreement between Observed and Expected events

Systematic uncertainties dominated by Jet Energy scale

University of Oxford, 10/28/2008

Exclusion limits: Mg -Mq andM0-M1/2 plane



Similar results for CDF and DØ

95% C.L. Exclusion limit

Results can be interpreted as a function of mSUGRA parameters

LEP limit improved in the region where 70<M0<300 GeV/c2and 130<M1/2<170 GeV/c2



For Mg=Mq → M > 392GeV/c2

Mg > 280 GeV/c2 in any case


University of Oxford, 10/28/2008

Lepton ET

Search for chargino/neutralino

mSUGRAc02c±1 pair production

Signature: three leptons and ET

  • Small cross sections (~0.1-0.5 pb)

  • Very low background:

    • Drell-Yan

    • Diboson(WW, WZ/*, ZZ/*, W)

    • Top pair production

    • QCD-multijets, W+jets

      (misidentified leptons)

e,m,tLept, tHadr

  • CDF: 5 exclusive channels

    • combinations of “tight” (t) and “loose” (l) lepton categories

      • 3-leptons (e,m,tLept)

      • 2-leptons (e,m,tLept) + iso-track T (tHadr)

    • Ordered in terms of S/B

  • DØ: 4 analyses carried out

    • ee+IsoTrk, mm+IsoTrk, em+IsoTrk, Same-sign mm






University of Oxford, 10/28/2008

3 tight leptons


c02c±1 results

47 Dilepton and trilepton control regions defined to test SM predictions


Signal region:

Missing ET > 20 GeV + topological cuts

Njet=0,1 and ETjet < 80 GeV

(4 channels)

mSUGRA Benchmark:

m0=60 GeV/c2,

m1/2=190 GeV/c2,

tan=3, A0=0, >0

Data Observed : 3

SM Expected: 4.1  0.7

Good agreement between data and SM prediction  set limit

University of Oxford, 10/28/2008

Excluded region in mSUGRA

excluded region in mSUGRA m0-m½ space for tan(β)=3, A0=0, μ>0

m0 = 60 GeV/c2


mc±1< 145 GeV/c2




Small Dm = m(c20 )-m(l), soft leptons from c20 decay

 Loss in acceptance, no exclusion

University of Oxford, 10/28/2008

Gauge Mediated Symmetry Breaking

  • SUSY breaking at scale L (10 -100 TeV). Mediated by Gauge Fields (“messengers”)

  • Gravitino very light (<< MeV) and LSP

  • Neutralino or slepton can be NLSP

  • If NLSP is neutralino

    In Rp conservation scenario:

     2 NLSP  2g + MET (+X) in final state

Snowmass p8 spectra


(taken from N. Ghodbane et al., hep-ph/0201233)

University of Oxford, 10/28/2008

gg+Missing ET

  • Assuming c01 (NLSP) short-lived

  • Very low SM background

    • Zgg nngg, Wgg lngg

  • Understanding of instrumental background challenging:

    • Mis-measured ET: use multijet data sample

    • e g misidentification: use W(en)g data

2 photons pTg > 25 GeV, |hg|<1.1

ET> 60 GeV

3 events (SM: 1.60.4)

University of Oxford, 10/28/2008

Delayed Photons

  • c01 life-time undetermined in GMSB  long-lifetime can be in ~ns range

  • Final state: Delayed photon+ET +jets

 ET> 40 GeV, pTg>25 GeV, ETjet > 35 GeV

 |h(g)|<1.1, |h(jet)|< 2.

Observed 2 events

SM Expect.: 1.30.7

M(c01)>101 GeV @ 5 ns

tc(g) in [2-10] ns range

University of Oxford, 10/28/2008

MSSM Higgs

Neutral MSSM Higgs

  • In MSSM, two Higgs doublets

    • Three neutral (h, H, A), two charged (H±)

    • Properties of the Higgs sector largely determined by mA and tanb

    • Higher-order effects introduce other SUSY parameters

  • Large Higgs production cross section at large tanb.

Higgs decays:

BR(bb) : ~90%

Huge QCD background

BR(tt) :~10%

University of Oxford, 10/28/2008

BSM Higgs: 

  • CDF and DØ  channel

    •  pure enough for direct production search

    • DØ adds associated production search: bb

  • Key issue: understanding  Id efficiency

    • Large calibration samples: W for Id optimization and Z for confirmation of Id efficiency

mA=140 GeV/c2

  • No Evidence for SUSY Higgs

    • Limits: tan vs mA

    •  generally sensitive at high tan

CDF: 

University of Oxford, 10/28/2008

Searches Beyond SM

  • More ‘Exotic’ models…

  • - Extra-Dimensions

  • New Gauge bosons

Search for high mass resonances

Example of di-lepton events

Transverse plane

  • Advantage

  • Sensitive to many BSM scenarios:

  • Extra-Dimensions

  • Extended SUSY-GUT groups

  • (SO(10),E6,E8...leading to additional gauge bosons, Z' and W')

  • R-parity violating SUSY

  • and more...

  • Di-lepton resonances have a strong track record for discovery → J/ψ, Υ, Z

    • Enlarge the possible final states looking also in dijet,ditop or dibosons!

  • Construct the pair invariant mass and look for any excesses in the high mass spectrum

University of Oxford, 10/28/2008


M2Planck ~ Rn(MD)n+2 ,MD ~ 1 TeV

‘Solves’ the hierarchy problem by postulating that we live in more than 4 dimensions.

  • Large Extra Dimensions: Arkani-Hamed, Dimopoulos, Dvali (ADD)

    • Gravity propagate in ndadditional spatial dimensions compactified at radius R

    • Effective Planck scale:

    • no narrow resonances, SM particles pair production enriched by exchanged gravitons

  • Randall-Sundrum model: Only one extra dimensions (wraped) limited by two 4-dimensional brains.

    • SM particles live in one of the brains.

    • Graviton can travel in all 5 dimensions, appears as Kaluza-Klein towers

    • dimensionless coupling (k/MPl) free parameter

University of Oxford, 10/28/2008

CDF: Central-Central (|1,2|<1) or Central-Forward (||<2) e+e- pair with ET>25 GeV

D0: EM objects pair (e+e- or gg), CC: |1,2|<1.1, CF 1.5<||<2.4

Major Backgrounds:


QCD (including W+jets)

Resonance search performed in mass range 150-1000 GeV/c2

No evidence for narrow resonances

 set limits

Search for High Mass e+e-/gg Resonance


Search for

RS Gkk resonance

University of Oxford, 10/28/2008

Exclusion limits

  • CDF (D0) exclude RS graviton with mass below 850 (900) GeV/c2 for k/MPl=0.1

    • Can interpret results in term

    • of several other scenarios

  • Limits on extended gauge groups theories: SM-like Z’: 966 GeV/c2

  • Limits on effective Planck scale in LED:

    • Expect a cross section enhancement above SM

    • Use gg, e+e-

1.29 - 2.09 TeV depending on number of ED

University of Oxford, 10/28/2008

Di-muon resonances

Spin 1 Z’-like limits

For the first time beyond one TeV for SM-Z'!

Spin 0 (RPV sneutrinos):

mass limits up to 810 GeV

Spin 2 ( RS Graviton):

mass limits up to 921 GeV

  • Looking for narrow dimuon resonance decaying

    • Could have spin 0, 1 and 2

  • Search in 1/mμμin which detector resolution is ~const:

     17% inverse mass resolution at 1 TeV

     construct templates for several signal hypothesis, add bkg and compare to data

University of Oxford, 10/28/2008

and more!

Every final state is currently investigated!!!

  • dijet resonances

    • Limits on several models, up to 1.2 TeV!

  • ditop resonances

    • limits on massive gluons and leptophobic Z' (Mz' > 760 GeV)

  • W' in tb(+c.c.) or en final state

    • world's best limit MW'→ en> 1 TeV

  • searches for t' or b'

    • fourth generation quarks not excluded by EWK

    • interesting tails in t' → Wq

    • mt' > 311 GeV

University of Oxford, 10/28/2008

8.75 fb-1

7.29 fb-1


Highest Int. Lum

Lowest Int. Lum

Final remarks

Projection curves

FY10 start

In case we don’t find new particles @ Tevatron….

~ 1.8 fb-1 delivered in FY08

FY08 start

University of Oxford, 10/28/2008

CDF and D0 have a wide and rich program of searches for SUSY. No evidence yet, but.. expect to collect and analyze up to 8 fb-1 of data in the next years.

7 TeV +

7 TeV

The Future …. now almost present

The Large Hadron Collider (LHC)

Proton- Proton Collider



First Event (9/10/2008)!

University of Oxford, 10/28/2008

Roadmap to discovery

Higgsdiscoverysensitivity (MH=130~500 GeV)

Explore SUSY to m ~ TeV

Precision SM measurements

1 fb-1

Sensitivity to 1-1.5 TeV resonances → lepton pairs

Understand SM backgroundfor SUSY and Higgs

Jet energyscalecalibration

100 pb-1

Detector calibration

Use SM processes as “standardcandles”

10 pb-1


100 pb-1

  • High-pT lepton resonances may provide the first signal of New Physics:

    • Less sensitive to calorimeter performance

University of Oxford, 10/28/2008

ATLAS preliminary

Jets measurements @ LHC


50 pb-1

Jet energy scale

largest source of systematic error

initial uncertainty ~ 5-10%

Need to reduce error for QCD test

LHC (s = 14 TeV)

10 events with Ldt = 20 pb-1



measure W/Z + jet(s) cross-section

γ/Z+jets calibration signal

University of Oxford, 10/28/2008

RP-conserving mSUGRA

ATLAS preliminary


[email protected]


The LHC is built to discover SUSY

If there, we will find it relatively soon

An example:

squark-gluino production

  • But it will take a bit of time:

  • commissioning phase to understand detector performance and “re-discover” the SM

University of Oxford, 10/28/2008

ATLAS preliminary

H  ZZ*  4l

30 fb-1

The “golden” channel

SM Higgs: a challenge!

Required luminosity for 95% C.L. exclusion

For low mass of ~120 GeV need to combine many channels with small S/B or low statistics (H  , H→, H ZZ*  4l, H→ WW*→ll )



most promising in the range 150-180 GeV, again with H → WW* →ll

 almost excluded at the Tevatron!

University of Oxford, 10/28/2008


"Whatever" is beyond the Standard Model, these are exciting times for high energy physics!



University of Oxford, 10/28/2008

Back up

Higgs reach @ Tevatron

  • With 7 fb-1

  • exclude all masses !!! [except real mass]

  • 3-sigma sensitivity 150:170

  • LHC’s sweet spot


This is very compelling


University of Oxford, 10/28/2008



  • New superfields in “hidden” sector

  • Interact gravitationally with MSSM

  • Soft SUSY breaking

5 parameters at GUT scale

1. Unified gaugino mass m1/2

2. Unified scalar mass m0

3. Ratio of H1, H2 vevs tanβ

4. Trilinear coupling A0

5. Higgs mass term sgn()

In R parity conservation scenario,

the LSP is the neutralino (c01 )

University of Oxford, 10/28/2008

2-leptons control region




10 15

DY + 

Z + fake

15 76 106

Invariant Mass (GeV/c2)


MET < 10 GeV


MET < 10 GeV

Control regions (CDF)

Dilepton and trilepton control regions defined to test SM predictions:  function of ET and the invariant mass of the 2 leading leptons

 47 in total!

University of Oxford, 10/28/2008

CDF Jet Energy Scale

Different correction factors:

  • (frel)Relative Corrections

     Make response uniform in h

  • (MPI)Multiple Particle Interactions

     Energy from different ppbar interaction

  • (fabs)Absolute Corrections

     Calorimeter non-linear and non-compensating

  • (UE)Underlying Event

     Energy associated with spectator partons

  • Jets are composite object:

  • complex underlying physics

  • depends on detector properties

PT jet(R) = [ PT jetraw(R)  frel (R) – MPI(R)]  fabs(R) - UE(R)


Total systematic uncertainties for JES: between 2% and 3%

Absolute correction factor

University of Oxford, 10/28/2008

LHC mSUGRA cross sections

  • Strongly interacting particles

  • High cross sections for gluinos andsquarksproduction

  •  Golden signature!



University of Oxford, 10/28/2008

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