New particle searches at the lhc
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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

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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


New particle searches at the lhc

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


New particle searches at the lhc

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


New particle searches at the lhc

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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