road to discovery: lecture 2

eno, Road to Discovery, L2 1

Road to Discovery: Lecture 2

Sarah EnoU. Maryland

14 Jun 09


New Physics• Many models for new physics• Many predict similar signatures• Let’s do a quick survey of fashionable new models and then

talk about the challenges that come from different signatures– Higgs?– SUSY?– Extra dimensions?– Little higgs?– New strong dynamics?– Compositeness?

14 Jun 09


General Observations

• only SM Higgs has a well-defined signal (like top, single top, etc)• Want big cross section and clean signature (final state with high pT leptons or other dramatic signature)• The earliest results may come from something that couples to gluons

14 Jun 09


WHAT IS IT?

Nevertheless, it is useful to study specific models. Kind of like the silly but necessary “problems” you solve while you are still doing course work.

Nature.comEXCESS IN LEPTON+MET+JETS• understanding of top production properties needs work?• understanding of W plus jets properties needs work?• susy?• beta.ne.1 LQ?• b’?Need the whole view of the elephant to disentangle

While challenging, will try to emphasize signatures as much as possible. It would be depressing to put a large amount of effort excluding SUSY LM1 when there is a beta=0.5 LQ in the data.

14 Jun 09


Higgs in 1 slide• standard model requires a scalar particle with mass in the terascale region that couples to mass -> diboson final states• (almost) guaranteed to be there (caveat: see, for example, technicolor) • doesn’t couple directly to gluons and take a hit in boson branching fractions to leptons. Tough luck!

Signature: Mostly di-boson events (for more signatures, lecture 3)

14 Jun 09


SUSY in 1 Slide

• a boson for every fermion, a fermion for every boson • we don’t know the mechanism that breaks susy -> creative theorists can produce almost any signature from SUSY.• rare decay searches (proton decays, b->sgamma, fcnc, lepton family number violation, precision EWK, etc) do give us some hard constraints• easiest way around is r-parity and degenerate masses for the 1st and 2nd generation sfermions. R-parity conveniently also gives a dark matter candidate. Degeneracy gives boost to cross section.• with these, still have a wide variety of signatures (strongly depends on mass hierarchy and splittings) but generally contain MET• squarks/gluinos couple to gluon, so could be an early discovery?

What spin is a saraheno?

Signature: X+MET (X usually has jets)

14 Jun 09


Extra Dimensions in a few slides

Original motivation: Solve the problem of why the planck scale and the electroweak scale are so different. We know the Planck scale comes from looking at Newton’s Law

1 22N

m mF G

R=

Mplanck

=1/ GN =1.2x1016TeV

If there were more than 3 spatial dimension), especially some rolled up ones too small for us to see (and only gravity operated in the extra ones) , this would become

M( )

planck

2=M*

2+nRn

Adjust R and n so that M* can be the EWK scale (1 TeV)

“ADD”“large extra dimensions”

14 Jun 09

R =1030n−17 1TeV

m*⎛⎝⎜

⎞⎠⎟

1+2n 1mm n=2


ADD

Signature: mono-X (X=jets, photons, etc), blackholes

Particles in the wrapped-up extra dimensions act like particle in box from undergrad QM. Massless ground state is the standard 4d graviton : tower of (massive) states. Sum of the tower of gravitons with effective coupling (1/M*2) give reasonable bremsstrahlung cross section.

14 Jun 09


TeV sized extra dimensions

TeV-1 size ED. (1 TeV=2x10-19m)Allow other particles to propagate in these (small) extra dimensions. Get KK tower of states.

mr

n = m02 +

n⋅nRc

2

⎛

⎝⎜⎞

⎠⎟

1/2 Dimension of n is number of extra dimensions (d). From precision EWK, for d=5, Rc

-1>4TeV

Signature: high mass copies of SM gauge bosons, like Zprimes. If all particles can propagate in the extra dimensions (requires k-parity), get UED.If other SM particles propogate in the ED, can get HSCP

14 Jun 09


Extra dimensions in 3 slides

Signature: towers of spin 2 resonance that decays to di-fermions and di-bosons (zprime-like, but also γγ decay) mass splittings of O(TeV) and variable width14 Jun 09


Compositeness in 1 slide

Phys. Rev. Lett 23,930 (1969)

Discovery that proton is a composite object

14 Jun 09


Potpourri in 1 slideMany other well-motivated theories• left-right symmetric models (neutrino mass) -> Wprimes, Zprimes, massive neutrinos• Hidden Valley• unification

14 Jun 09


DiscoveryWhat can we discover?• if it has no background and 100% e*A, need at least 5 events: 15 fb xsct• typical 10-80% acceptance 20-150 fb• above Tevatron reach -> gg initial state with M>100 or qq state with M>600 GeV

Examples of things with “no” backgrounds• heavy stable charged particles (HSCP)• blackholes• Zprime to ee, mumu

300 pb at 14 TeV

14 Jun 09


Bumps

Or do they?

pentaquark

Bump hunting is one of the easiest kinds of searches to do. Low background bump hunting is even easier.

They provide fool-proof discovery

Discovery of the Z

14 Jun 09


Heavy Bosons to ee, μμPredicted in many theories: TeV-1 ED, RS ED, little higgs, L-R symmetric, etc.

Main background is DY production. Smoothly and quickly falling with mass.

14 Jun 09


Heavy Boson

To get the best result, take a little care• resolution, bias for tracks (muons) sensitive to alignments• high energy muons brem• hard to check efficiencies/resolutions/scale from data at high energy• calorimeter could saturate at the highest energy• calorimeter isolation, had/em cut could lose efficiency at high energyMight not cause you to miss signal, but might not get as high a significance as you like (would be bad if the experiment across the ring got a higher significance)

14 Jun 09


Cross sections

M=1000 GeV sigma=.23 pb acc*eff=0.67 N=46M=1250 GeV sigma= 0.083 pb acc*eff=0.68 N=17M = 1500 GeV sigma = 0.033 pb acc*eff=0.69 N=7

10 TeV

14 Jun 09


AlignmentAlignment effect (startup conditions 100 pb-1)Mass resolution:7-8 (10) % at 1 (2) TeV

Loss of signal efficiency due to charge mis-ID:

Ideal: 0.98300 mm: 0.971000 mm: 0.88

3

Statistical significance related to sharpness of peak related to resolution

14 Jun 09

A specific Analysis

CMS PAS EXO-08-004

CMS BSM 07-002

ATLAS Phys TDR

CMS PAS EXO-08-001

High pt electron reconstruction Efficiencies relative to acceptance:

Example: selection for Z’ ee:- 2 electrons in |η| < 2.5, pt > 30 GeV - electron ID (cluster-track matching)- e isolated in tracker/ECAL/HCAL

electron Pt (GeV)

Main backgrounds:Drell-Yan (irreducible)ttbar, W+jets, QCD (reducible)

CMS: after selection

Mee (GeV)

Tevatron limit is: 700-1000 GeV

Z’ ee

e-m method:Use e-m events from the 2 W decaysttbar e-m = 2* ttbar ee For 100 pb-1: expect 16.1 ttbar bgdetermined by expected sample of 42.5 e-m events

CMS: Data Driven methods for ttbar background estimation

b-tagging method:Ntt can be extracted from N(1b tag)or N(2b tag) + e(b) From n2/n1 + geom acceptance forone or two b-quarks can extract e(b) (0.20± 0.09)

Z’ ee and Z’ mm

Discovery potential for Z’ ee Discovery potential for Z’ mm

CMS

Z' (SSM)

Z' (Y)

Z' (SSM)

Z' (Y)

Mee (GeV)

L (pb-1)

Gravitons and Technicolor mesons

Discovery potential for RS Gravitons:

Discovery potential for Strawman model Technicolor mesons:

CMS G mm

M(G) (GeV)

M(G) (GeV)

M(rT and w

T) (GeV)

Stat +syst

Stat only

L (

fb-1)

G

co

up

ling

c=0.1

c=0.01


Other high mass, low background resonances

Can also look for other kinds of high mass resonances, some more, some less motivated.eq, eν, eγ, eμ, … (etc etc etc)

14 Jun 09


wprimeVery similar to Zprime search. Backgrounds continuum W production and W’s from ttbar production.

14 Jun 09

lepton and jet CMS PAS EXO-08-006

Main background: Drell-Yan and ttbar production

Look for topologies with 2 same flavour leptons and at least 2 jets, and no missing Et Two models investigated: 1) Leptoquark pair production 2) Heavy W

R and heavy neutrino production

MN=M(j1j2 l2), M(W

R)=m(j1j2l1l2)

2 resonance structure

M(jl) = M(LQ)

ATLAS Phys TDR

Leptoquark pair production searchATLAS Phys TDR

Oppositely charged leptons of same flavour and at least two jets

Example: selection for the first generation LQ:- e1,e2 with |η| < 2.5, Pt < 20 GeV, electron ID, - two jets (DR=0.4 cone algo), |η| < 4.5, Pt < 20 GeV - DR(e-j) < 0.1

Mjl=M(LQ) choose combination such M

1 closest to M

2

+ M(ee) >120 GeV+ S > 490 GeV

M(lj) (GeV)

M(lj) (GeV)

ST (GeV)

M(LQ) (GeV)

All plots for L=100 pb-1


Dijet searchesAll though cross section is strong, can still be challenging due to • large SM background • poor jet energy resolution (compared to e,mu resolutions) and eta-dependent JES that can further degrade resolution until it is understood and removed. • tails on resolution due to FSRHow can we make this more robust and do it with early data?

14 Jun 09


Dijet Mass ResolutionExample: CMS

• Resolution for corrected CaloJets– 9% at 0.7 TeV – 4.5% at 5 TeV

• Tails due to FSR (gluon)

2 TeV Z’

|η| < 1.3

Corrected CaloJets

GenJets

Natural Width

Resolution

14 Jun 09


Dijet Resonances in Rate vs. Dijet Mass Measure rate vs. corrected dijet mass and look for resonances.

Use a smooth parameterized fit or QCD prediction to model background

Strongly produced resonances can be seen Convincing signal for a 2 TeV excited quark in 100 pb-1

Tevatron excluded up to 0.78 TeV.

QCD Backgound Resonances with 100 pb-1

Spectrum falling quickly enough that will not really see bump (remember Z to bbbar)

14 Jun 09


Dijet Resonances with Dijet Ratio• All resonances have a more isotropic decay angular distribution than QCD

– Spin ½ (q*), spin 1 (Z’), and spin 2 (RS Graviton) all flatter than QCD in dN / dcosq*.

• Dijet ratio is larger for resonances than for QCD.– Because numerator mainly low cos q*, denominator mainly high cos q*

QCD

Dijet Ratio vs MassDijet Angular Distributions

14 Jun 09


Dijet Resonances with Dijet Ratio• Dijet ratio from signal + QCD compared to statistical errors for QCD alone

– Resonances normalized with q* cross section for |h|<1.3 to see effect of spin.

• Convincing signal for 2 TeV strong resonance in 100 pb-1 regardless of spin.

• Promising technique for discovery, confirmation, and eventually spin measurement.

Dijet Ratio for q* Dijet Ratio for Spin ½, 1, 2

14 Jun 09


Contact Interaction

14 Jun 09


Inclusive Jet PT and Contact Interactions

• Contact interactions create large rate at high PT and immediate discovery possible– Error dominated by jet energy scale (~10%) in early running (10 pb-1)

• DE~ 10% not as big an effect as L+= 3 TeV for PT>1 TeV.– PDF “errors” and statistical errors (10 pb-1) smaller than E scale error

• With 10 pb-1 we can see new physics beyond Tevatron exclusion of L+ < 2.7 TeV.

Rate of QCD and Contact Interactions Sensitivity with 10 pb-1

Sys Err.

PDF Err.

14 Jun 09

Way out on the tails

Once Voyager got out there, that Neptune had rings was very clear.


Heavy stable charged particles

14 Jun 09


Small beta

14 Jun 09

Thesis: Andrea Rizzi

β =p

E≈

p

m

Beta =1 : arrive at CMS muon chambers at t=13 nsBeta = 0.3: arrives at CMS muon chambers at t=38 ns (25 ns later)


HSCP

CMS

14 Jun 09


HSCP

14 Jun 09


Stopped r-hadronsStopped muons from the ICARUS T600 module (http://arxiv.org/abs/hep-ex/0309023)

Muon ranges out in calorimeter, then decays to an electron (plus neutrinos)Hadronized gluino ranged out and then decays to Jet(s) (+MET)

14 Jun 09


Long-lived neutrinos to jet(s)(+MET)

Look for odd shaped jets when there is no beam in the detector

14 Jun 09

eno, Road to Discovery, L2 4214 Jun 09


Long-lived gluinos

14 Jun 09


Sensitivity

300 GeV gluino and 100 GeV neutralino

14 Jun 09

Black holes

From background-free due to simplicity to background free due to complexity.


Extra Dimensions and Black Holes

The Planck scale is the one at which gravitation interactions become large.If gravity becomes strong at the TeV scale, the results could be quite exciting.If there are extra dimensions, the formula for the Schwarzschild radius becomes

rs(4+n) =

1

π M*

MBH

M*

8Γ((n+ 3) / 2n+ 2

⎛

⎝⎜⎞

⎠⎟⎛

⎝⎜⎞

⎠⎟

1/ (n+1)

(M* =2TeV ,MBH =4TeV ,r =100 fm)

Cross section could be large at current limits on M*, n (see 0809.2571, 0709.1107,0802.2218), 1 -1800 fb.Quickly evaporate by emitting all types of particles democratically.

15 fb for background-free14 Jun 09

0802.2218

The big Picture:Heisenberg-‘t Hooft

SUSY08, Seong Chan Park

distance

energy

~ 1/x p ~x GE

PM

1/pl pll M

UV-IR duality

Trans-Planckian Domain E>>Mp-gravity dominance-new windows of bh production open-Classical gravity!!

Classical Gravity

Quantum Gravity

0~ ( / )nQG Pl l

Planck domain E~Mp-Quantum Gravity-String theory-no concrete prediction , yet

Sub-Planckian domain E<<Mp-gauge interaction-(broken)SUSY-GUT

Stolen from: Seong Chan Park (SNU)

Black Hole’s Life made simple

?

Time

Balding Phase

Spin Down Phase

Schwarzschild Phase

Planck Phase

(Production of BHs.Study “Dynamics” required.)

(Losing energy and angular momentum:60-80% Energy lost For D>4, to mostly gluons, anisotropic)

(Losing Mass: 20-40% energy, spherical, to every fields)

(Remnant ???, Stringy study required )

SUSY08, Seong Chan Park




Black holes

Simulation of a black hole event with MBH ~ 8 TeV in CMS

~ Spherical events: Many high energy jets leptons, photons etc.

Ecological comment: BH’s will decay within ~ 10-27 secs Detectors, electronics (and rest of the world) are safe!!

4 dim. : Rs << 10-35 m4+n dim. : Rs ~ 10-19 mRS = schwartzschild radius

14 Jun 09

Search for Black HolesATLAS Phys TDRSignal MC: Charybdis, M

pl = 1 TeV

d=2,4,7 and MBH

= from 5 to 14 TeV

Robust discovery reach potential for BH is difficultbecause of the semi-classical assumption used,only valid well above M

Pl M

BH > 5 TeV

Selection:Object = e,m,g or jetPt>15 GeV + ID+isolation (lepton/g) Pt>20 GeV (jet)

Search for Black HolesIt’s a log plot

road to discovery: lecture 2

Documents

early discovery

x met x

dramatic signature

monox x

extra ones

ewk scale

planck scale

susy lm1