1. 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

2. R. Ströhmer RAL-PPD Seminar 9.5.07
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  1 x 1032
phase 3: 25 ns, L ~4 x  1 x 1033 cm-2s-1
Integrated luminosity end of 2008: fb-1 ?
(e.g.: 1 fb-1 = 120 effective 1032 cm-2s-1)
R. Ströhmer RAL-PPD Seminar

3. R. Ströhmer RAL-PPD Seminar 9.5.07
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

4. R. Ströhmer RAL-PPD Seminar 9.5.07
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

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?
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

6. Calorimeter noise has to be understood
Run II
V. Shary CALOR04
ETmiss spectrum contaminated by cosmics,
beam-halo, machine/detector problems, etc.
R. Ströhmer RAL-PPD Seminar

7. Material in front of calorimeter
Affects electrons and photons: energy loss, conversions
R. Ströhmer RAL-PPD Seminar

8. 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. Top events as test sample
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
If one sees the expected distribution and rate on can have confidence in the object reconstructions
R. Ströhmer RAL-PPD Seminar

10. R. Ströhmer RAL-PPD Seminar 9.5.07
SUSY Searches
Many SUSY searches
are performed in the
framework of mSUGRA
WMAP: 0.094<Ωχh2<0.129
Excluded by
b- > s
(CLEO,BELLE)
Favored by gμ−2 at the 2σ level
Muon g−2 coll.
Stau=LSP
J. Ellis et al., Phys. B565 (2003) 176.
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

11. 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

12. R. Ströhmer RAL-PPD Seminar 9.5.07
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 m n
Measure in Z -> μμ
Use in Z -> νν
R. Ströhmer RAL-PPD Seminar

13. 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
Effective Mass
Missing ET
Leading Jet PT
ATLAS
preliminary
Test with “pseudo data” using different MC parameters
Z -> nn
230 +/- 15 (pseudo-data) /- 23 (estimation)
W -> ln
190 +/- 14 (pseudo-data) /- 21 (estimation)
R. Ströhmer RAL-PPD Seminar

14. R. Ströhmer RAL-PPD Seminar 9.5.07
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
MET
jets
Et(estimated)/Et(measured)
R. Ströhmer RAL-PPD Seminar

15. 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

16. R. Ströhmer RAL-PPD Seminar 9.5.07
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

17. Expected significance
The statistical significances have been studied including background uncertainties with the likelihood ratio method
R. Ströhmer RAL-PPD Seminar

18. Determination of SUSY Parameters
264
154 , 255
137 ~
Example:
Coannihilation point
Two edges in lepton-pair-mass
Estimate background from eµ events
GeV
20.6 fb-1
MC Truth, lR
MC Truth, lL
MC Reconstructed
ATLAS Preliminary
Full sim.
R. Ströhmer RAL-PPD Seminar

19. R. Ströhmer RAL-PPD Seminar 9.5.07
Spin Measurement
First emitted lepton (“near”)
Spin:
1/2
LHCC5:
m0 =100 GeV
m1/2 =300 GeV
A0 =-300 GeV
tan(β) =2.1
sign(μ)=+
M(qlnear)
M(qlfar)
quark
ql-
quark
ql+
ql-
ql+
antiquark
antiquark
ATLAS Fast Simulation
A. J. Barr Phys.Lett.B596: ,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

20. RS Gravitons & Heavy Bosons
ATLAS
preliminary
Characterisation
Measure spin
G* Spin 2
Z’ Spin 1 p θ
graviton e
5 sigma discovery
R. Ströhmer RAL-PPD Seminar

21. 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

22. 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

23. 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

24. Search for Heavy Stable Particles
Combined β resolution for stau
gluino 300 GeV
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

25. Search for Long-Lived Neutralinos
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)
Event selection
Isolated photon pt>80 GeV
4 Jets pt> 50 GeV
missing energy > 160 GeV
not in Jet direction (Δφ>20o)
CMS
preliminary
CMS
preliminary
R. Ströhmer RAL-PPD Seminar

26. 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
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

27. Universal Extra Dimensions (UED)
CMS
preliminary
CMS
preliminary
µ: pt> 5 GeV, |η|<2.4
e: pt> 7 GeV, |η|<2.5
Z veto: one OSSF
with M<5 GeV or M>80 GeV
R. Ströhmer RAL-PPD Seminar

28. 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

29. R. Ströhmer RAL-PPD Seminar 9.5.07
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