New Particle Searches at the LHC SUSY - Inclusive search - Backgrounds - SUSY parameters Resonances...

New Particle Searches at the LHC

• SUSY- Inclusive search- Backgrounds - SUSY parameters

• Resonances in the Drell-Yan mass distribution • Heavy long-lived particles• Universal Extra Dimensions• Black holes

R. Ströhmer RAL-PPD Seminar 9.5.07 2

First challenge: get the LHC operational

Still on course for engineering run fall 2007: system commissioning single beam operations at 450 GeV collisions at 450 x 450 GeV, no ramp, no squeeze low luminosity: ATLAS/CMS commissioning

First collisions at 14 TeV: June 2008 ? after system and beam commissioning 26 weeks of proton-proton physics run in 2008 phase 1: 43 bunches, L ~ 5 x 1030 phase 2: 75 ns, L ~2.5 x 1031 1 x 1032 phase 3: 25 ns, L ~4 x 1032 1 x 1033 cm-2s-1

Integrated luminosity end of 2008: 0.5 - 1 fb-1 ? (e.g.: 1 fb-1 = 120 effective days @ 1032 cm-2s-1)


And the experiments too: huge challenge

Getting the subdetectors built, tested and installed.Power and signal cables, detector control and monitoringCooling pipes, cryogenic installations, magnets…

CMS: lowered central part (YB0) February 28th , rest soon will run in 2007 without ECAL endcap and pixels rest going well

ATLAS: on a tight schedule to run almost complete in 2007 No TRT at high ||, some muon chambers missing

Both will have reduced trigger/DAQ capabilities initially


Getting the data flowing…

First individual detectors, then combinedCommissioning the DAQ system with cosmicsSingle beam in LHC: beam halo

Use: debug cabling errors initial alignment first intercalibration: uniformity to few %

Data processing: Grid, Tier-1, Tier-2 etc

Challenge: get processing of HUGE quantities of data going Data Challenges, Calibration Challenges, Computing System Commissioning (ATLAS 2007)

ATLAS: CSC exercise should lead to notes CMS: published physics TDR in summer 06

5


Particle Searches in a Nutshell

Look for excess of events over Standard Model expectation

- Multiple or high pt leptons, jets and missing transverse energy

If excess is observed:Is the instrumental background understood?

Is the expected SM background understood?

Which models predict the excess?- How can we distinguish between models and

measure model parameters?

eeZ

If no excess is observed:What is the signal efficiency: reconstruction and trigger efficiencies

exclude models or parameter regions for models


Calorimeter noise has to be understood

Run IIV. Shary CALOR04

ETmiss spectrum contaminated by cosmics,

beam-halo, machine/detector problems, etc.


Material in front of calorimeter

Affects electrons and photons: energy loss, conversions


Getting efficiency from data

Use Zµµ to study muons

select one muon with tight requirements

both muons from Z

don’t require quantity you want to test from second muon- tracking efficiency

- muon chamber efficiency

- trigger efficiency


Top events as test sample

If one sees the expected distribution and rate on can have confidence in the object reconstructions

Isolated lepton pT> 20 GeV

ETmiss > 20 GeV

4 jets pT> 40 GeV

NO b-tag !!

2 jets M(jj) ~ M(W)

3 jets with largest ∑ pT

100 pb-1

Bg: W+jets


SUSY SearchesMany SUSY searchesare performed in the framework of mSUGRA

Aim of SUSY searches• Find SUSY (or something new)• Measure quantities (e.g. mass differences)• Prove that it is SUSY• Determine model parameters

WMAP: 0.094<Ωχh2<0.129

Excluded by b- > s(CLEO,BELLE)

0,0,10tan 0 A

Favored by gμ−2 at the 2σ levelMuon g−2 coll.

Stau=LSP

J. Ellis et al., Phys. B565 (2003) 176.


Inclusive SUSY Search (Jets + missing Et)

Calculate effective mass from jet pt and missing transverse energy

Background estimates increased by Matrix Element Monte Carlo w.r.t. showering MC prediction

Main backgrounds - Z(νν) + Jets

- W + Jets

- ttbar

Backgrounds have to be estimated or checked with data


Backgrounds from Data

Replace observed µ by νZ->µµ- clean sample- correct shape- small statistics

W->µν- large statistics- problem: needs clean

W+6jet sample

Measure in Z -> μμ

Use in Z -> νν


Background Normalization from DataSystematic uncertainties due to: Renormalization scale, factorization scale,

PDF mostly effect normalization and not shape.Same normalization for Z->νν, Z->µµ, W->νµ

Determine normalization from Z->µµ and apply to Z->νν, W->νµ

Test with “pseudo data” using different MC parameters

Z 230 +/- 15 (pseudo-data) 200 +/- 23 (estimation)

190 +/- 14 (pseudo-data) 185 +/- 21 (estimation)

W l

Effective Mass

Effective Mass

Missing ET

Missing ET

Leading Jet PT

Leading Jet PT

ATLAS

preliminary

ATLAS

preliminary ATLAS

preliminary

ATLAS

preliminary

ATLAS

preliminary

ATLAS

preliminary


QCD BackgroundSignificant part with real missing Et from b- and c- decays

Estimate effect of mismeasured jet energy with fast Monte Carlo- get transfer function from full detector simulation

- get transfer function from data where missing Et points in jet direction

MET

jets

Select events with: EtMiss > 100 GeV, dPhi(EtMiss, jet) < 0.1

Et(estimated)/Et(measured)

ATLASpreliminary


Inclusive SUSY Search (Jets+1lepton+missing Et)

Strong reduction of background due to lepton requirement

Main background is ttbar - important contribution from blνblν with one missing lepton for MT>100

GeV


Background from Data

Find second quantity not correlated to missing Et General ideas:

SUSY signal plus bg

A

B C

D

Missing ET

other variable

bg

bg bg

Bg in D = A x C/B

normalize to data

For ttbar-> bqqblν the top mass canbe used as second quantity

Contribution from ttbar->blνblνis under study


Expected significance

The statistical significances have been studied including background uncertainties with the likelihood ratio method


Determination of SUSY Parameters

Example:Coannihilation point

Two edges in lepton-pair-mass

Estimate background from eµ events

20.6 fb-1

MC Truth, lRMC Truth, lLMC Reconstructed

ATLAS Preliminary

Full sim.

01,

02

~ llll LR 264 154 , 255 137

~ ~

GeV


Spin Measurement

01

02

~ ~ ~ ~ llqllqqq nearRL

First emitted lepton (“near”)0 1/2 0

More quarks thanantiquarks (pp collisions)Remaining asymmetry:

LHCC5:LHCC5:mm00 =100 GeV =100 GeV

mm1/21/2 =300 GeV =300 GeV

AA00 =-300 GeV =-300 GeV

tan(tan(ββ) =2.1 ) =2.1 sign(sign(μμ)=+)=+

M(qlfar)quark

antiquark

ql-

ql+ql-

ql+

M(qlnear)

antiquark

quark

No spin correlations,no asymmetry

After selection

Parton level x 0.6

L=500 fb-1

ATLAS Fast Simulation

ql+

L=500 fb-1

SPS1a Non-zero M(ql) asymmetry may be observed with 30fb-1

ql-

A. J. Barr Phys.Lett.B596: 205-212,2004

Spin:


RS Gravitons & Heavy Bosons

pp

θ

gravitone

e

CharacterisationMeasure spin

- G* Spin 2- Z’ Spin 1

5 sigma discovery

eeZATLASpreliminary


Effect of initial alignment

generator initialalignment

CMS

1 TeV Z’

Track-based alignment using minimum bias, Zee,

initial alignment

alignment after few fb-1


Search for Heavy Stable Particles

Predicted in various modelsLong lived stau as next to lightest particle in GMSB

R-hadrons in Split-SUSY- Colored SUSY particle

hadronizes (e.g. gluino)

Determination of mass from momentum and velocity (β)

β can be determined in the range from 0.6 – 0.8 by:

- Energy loss in the tracker- Time of flight in the muon

system

CMS preliminary

CMS preliminary



R–hadrons have hadronic interactionEnergy/momentum mostly carried by SUSY particle

Hadronic interactions will change the charge of the R-hadron

ATLASpreliminary



Event selection β(dE/dx) < 0.85

- to exclude MIPs

0.6 < β(dE/dx) < 0.80.6 < β(TOF) < 0.8 m(dE/dx) > 30 GeV

- to reject slow standard model particles

number of tracker hits > 10- to eliminate fake tracks and

optimize the quality of dE/dx

pt cut at:- 150 GeV (300 GeV gluino)- 200 GeV (600 GeV gluino)- 80 GeV (152.3 GeV stau)

expect< 25 BG events at L= 500 pb-1

- (zero unweighted MC events)

Combined β resolution for stau

CMS preliminary

gluino 300 GeV

gluino 600 GeV stau 152.3 GeV

500 pb-1

500 pb-1

30 pb-1


Search for Long-Lived Neutralinos

Event selectionIsolated photon pt>80 GeV

4 Jets pt> 50 GeV

missing energy > 160 GeV- not in Jet direction (Δφ>20o)

• Lifetime reconstructionphotons from neutralino with finite lifetime are not pointing to primary vertex.

shape of energy deposition in calorimeter depends on photon direction.

sensitivity to log(c)

CMSpreliminary

CMSpreliminary


Universal Extra Dimensions (UED)

mass- degenerate spectrum

Conservation of KK parity (-1)n

- n=1 similar to SUSY but Spin(KK) = Spin(SM)

2nd excitation can be singly produced

Pair production of g1 g1 ,q1 g1 and q1 q1

Signal: 4 leptons (2 pairs OSSF), jets, andmissing energy

Long decay chains


Z veto: one OSSFwith M<5 GeV or M>80 GeV

Universal Extra Dimensions (UED)

µ: pt> 5 GeV, |η|<2.4e: pt> 7 GeV, |η|<2.5

CMSpreliminary

CMSpreliminary


Spectacular States : Micro Black Holes

Large EDsMicro black hole decaying via Hawking radiation

- Photons + Jets + …

We will certainly know something funny is happening

- Large multiplicities- Large ET- Large missing ET- Highly spherical

compared to BGs

Theory uncertainty limits interpretation

- Geometrical information difficult to disentangle

CMSpreliminary

Invariant mass [GeV/c2]

sphericity


Conclusions

ATLAS & CMS have significant discovery potential for physics beyond the standard model

New physics could already show up in early data

In order to claim a discovery on needs to understand the background - detector performance- standard model processes

discovery of “something” is only first step, the second is to distinguish between models and determine parameters

New Particle Searches at the LHC SUSY - Inclusive search - Backgrounds - SUSY parameters Resonances...

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Transcript of New Particle Searches at the LHC SUSY - Inclusive search - Backgrounds - SUSY parameters Resonances...