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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. First challenge: get the LHC operational.

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new particle searches at the lhc

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
slide2
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)

R. Ströhmer RAL-PPD Seminar 9.5.07

slide3
And the experiments too: huge challenge

Getting the subdetectors built, tested and installed.

Power and signal cables, detector control and monitoring

Cooling 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

R. Ströhmer RAL-PPD Seminar 9.5.07

slide4
Getting the data flowing…

First individual detectors, then combined

Commissioning the DAQ system with cosmics

Single 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

R. Ströhmer RAL-PPD Seminar 9.5.07

particle searches in a nutshell
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?

If no excess is observed:

  • What is the signal efficiency: reconstruction and trigger efficiencies
  • exclude models or parameter regions for models

R. Ströhmer RAL-PPD Seminar 9.5.07

calorimeter noise has to be understood
Run II

V. Shary CALOR04

ETmiss spectrum contaminated by cosmics,

beam-halo, machine/detector problems, etc.

Calorimeter noise has to be understood

R. Ströhmer RAL-PPD Seminar 9.5.07

material in front of calorimeter
Material in front of calorimeter

Affects electrons and photons: energy loss, conversions

R. Ströhmer RAL-PPD Seminar 9.5.07

getting efficiency from data
Getting efficiency from data

Use Zµµ 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

R. Ströhmer RAL-PPD Seminar 9.5.07

top events as test sample
3 jets with largest ∑ pT

100 pb-1

4 jets pT> 40 GeV

2 jets M(jj) ~ M(W)

Isolated lepton pT> 20 GeV

Bg: W+jets

NO b-tag !!

ETmiss > 20 GeV

Top events as test sample
  • If one sees the expected distribution and rate on can have confidence in the object reconstructions

R. Ströhmer RAL-PPD Seminar 9.5.07

susy searches
Excluded by

b- > s

(CLEO,BELLE)

Favored by gμ−2 at the 2σ level

Muon g−2 coll.

WMAP: 0.094<Ωχh2<0.129

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

Stau=LSP

SUSY Searches

Many SUSY searches

are 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

R. Ströhmer RAL-PPD Seminar 9.5.07

inclusive susy search jets missing et
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

R. Ströhmer RAL-PPD Seminar 9.5.07

backgrounds from data
m

m

n

n

Backgrounds from Data

Replace observed µ by ν

  • Z->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

R. Ströhmer RAL-PPD Seminar 9.5.07

background normalization from data
Effective Mass

Missing ET

Leading Jet PT

ATLAS

preliminary

ATLAS

preliminary

ATLAS

preliminary

Leading Jet PT

Effective Mass

Missing ET

ATLAS

preliminary

ATLAS

preliminary

ATLAS

preliminary

Background Normalization from Data
  • Systematic 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 -> nn

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

W -> ln

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

R. Ströhmer RAL-PPD Seminar 9.5.07

qcd background
jets

MET

QCD Background
  • Significant 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

Select events with:

EtMiss > 100 GeV,

dPhi(EtMiss, jet) < 0.1

ATLAS

preliminary

Et(estimated)/Et(measured)

R. Ströhmer RAL-PPD Seminar 9.5.07

inclusive susy search jets 1lepton missing et
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

R. Ströhmer RAL-PPD Seminar 9.5.07

background from data
Background from Data

Find second quantity not correlated to missing Et

General ideas:

other variable

SUSY signal

plus bg

bg

D

A

bg

B

C

bg

Missing ET

Bg in D = A x C/B

normalize to data

For ttbar-> bqqblν the top mass can

be used as second quantity

Contribution from ttbar->blνblν

is under study

R. Ströhmer RAL-PPD Seminar 9.5.07

expected significance
Expected significance
  • The statistical significances have been studied including background uncertainties with the likelihood ratio method

R. Ströhmer RAL-PPD Seminar 9.5.07

determination of susy parameters
~

~

Full sim.

20.6 fb-1

137

264

154 , 255

MC Truth, lR

MC Truth, lL

MC Reconstructed

ATLAS Preliminary

Determination of SUSY Parameters

Example:

Coannihilation point

  • Two edges in lepton-pair-mass
  • Estimate background from eµ events

GeV

R. Ströhmer RAL-PPD Seminar 9.5.07

spin measurement
Spin Measurement

First emitted lepton (“near”)

0

1/2

0

Spin:

M(qlnear)

M(qlfar)

LHCC5:

m0 =100 GeV

m1/2 =300 GeV

A0 =-300 GeV

tan(β) =2.1

sign(μ)=+

quark

ql-

quark

ql+

ql-

ql+

antiquark

antiquark

ATLAS Fast Simulation

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

More quarks than

antiquarks (pp collisions)

Remaining asymmetry:

L=500 fb-1

L=500 fb-1

After selection

Parton level x 0.6

ql-

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

ql+

No spin correlations,

no asymmetry

R. Ströhmer RAL-PPD Seminar 9.5.07

rs gravitons heavy bosons
e

graviton

p

p

θ

e

RS Gravitons & Heavy Bosons

ATLAS

preliminary

Characterisation

  • Measure spin
    • G* Spin 2
    • Z’ Spin 1

5 sigma discovery

R. Ströhmer RAL-PPD Seminar 9.5.07

effect of initial alignment
Effect of initial alignment

CMS

generator

initial

alignment

1 TeV Z’

Track-based alignment using minimum bias, Zee, 

alignment

after few fb-1

initial

alignment

R. Ströhmer RAL-PPD Seminar 9.5.07

search for heavy stable particles
Search for Heavy Stable Particles

CMS preliminary

Predicted in various models

  • Long 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

R. Ströhmer RAL-PPD Seminar 9.5.07

search for heavy stable particles1
Search for Heavy Stable Particles

R–hadrons have hadronic interaction

  • Energy/momentum mostly carried by SUSY particle
  • Hadronic interactions will change the charge of the R-hadron

ATLAS

preliminary

R. Ströhmer RAL-PPD Seminar 9.5.07

search for heavy stable particles2
Search for Heavy Stable Particles

gluino 300 GeV

Combined βresolution for stau

Event selection

  • β(dE/dx) < 0.85
    • to exclude MIPs
  • 0.6 < β(dE/dx) < 0.8
  • 0.6 < 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)

30 pb-1

CMS preliminary

gluino 600 GeV

stau

152.3 GeV

500 pb-1

500 pb-1

R. Ströhmer RAL-PPD Seminar 9.5.07

search for long lived neutralinos
Search for Long-Lived Neutralinos

Event selection

  • Isolated photon pt>80 GeV
  • 4 Jets pt> 50 GeV
  • missing energy > 160 GeV
    • not in Jet direction (Δφ>20o)

Lifetime reconstruction

  • photons 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)

CMS

preliminary

CMS

preliminary

R. Ströhmer RAL-PPD Seminar 9.5.07

universal extra dimensions ued
Universal Extra Dimensions (UED)
  • mass
    • degenerate spectrum
  • Conservation of KK parity (-1)n
    • n=1 similar to SUSY but Spin(KK) = Spin(SM)
  • 2nd excitationcan be singly produced

Long decay chains

Pair production of g1 g1 ,q1 g1 and q1 q1

Signal: 4 leptons (2 pairs OSSF), jets, and

missing energy

R. Ströhmer RAL-PPD Seminar 9.5.07

universal extra dimensions ued1
Universal Extra Dimensions (UED)

CMS

preliminary

CMS

preliminary

Z veto: one OSSF

with M<5 GeV or M>80 GeV

µ: pt> 5 GeV, |η|<2.4

e: pt> 7 GeV, |η|<2.5

R. Ströhmer RAL-PPD Seminar 9.5.07

spectacular states micro black holes
Spectacular States : Micro Black Holes
  • Large EDs
  • Micro 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

CMS

preliminary

Invariant mass [GeV/c2]

sphericity

R. Ströhmer RAL-PPD Seminar 9.5.07

conclusions
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

R. Ströhmer RAL-PPD Seminar 9.5.07

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