From the ATLAS electromagnetic calorimeter to SUSY

Freiburg, 15/06/05Dirk ZerwasLAL Orsay

• Introduction• ATLAS EM-LARG• Electrons and Photons• SUSY measurements• Reconstruction of the fundamental parameters• Conclusions

Introduction• LHC: CERN’s proton-proton collider at 14TeV• 2800 bunches of 1011 protons• bunch crossing frequency: 40.08MHz • Low Luminosity: 1033cm-2/s meaning 10fb-1 per experiment (3 years)• High Luminosity 1034cm-2/s meaning 100fb-1 per experiment (n years)• SLHC: most likely 1035cm-2/s meaning 1000fb-1 per experiment (2015+)• startup for physics: late 2007

Two multipurpose detectors: ATLAS, CMS

The experimental challenges of the LHC environment:• bunch crossing every 25ns • 22 events par BX (fast readout, 40MHz 200Hz, event-size 1.6MB)• High radiation FE electronics difficult (military and/or space technology)and with that do precision physics!

Physics at the LHC

Process Events/s Events/year other machines

Weν 15 108 104 LEP/ 107 TeV.Z ee 1.5 107 107 LEPtt 0.8 107 104 TeVatronbb 105 1012 108 Belle/BabarQCD jets 102 109 107

pT>200GeV

If the machine works well:

Factory of Z, W, top and QCD jets. Will be limited quickly by systematics!

Measurements:• W mass to 20MeV needs control of the linearity/energy scale (0.02% energy scale)• Higgs mass measurement (if etc) in γγ• SUSY precision measurements with leptonsStringent requirements on the energy scale, uniformity and linearity of the ATLAS-EM Calorimeter response! Startup date getting closer, need to prove that we understand and are prepared Calo!

You have heard already much about the physics from Sven Heinemeyer, Tilman Plehn, Christian Weiser,… plus in-house expertise on ATLAS-Tracker, ATLAS-Muons, Higgs physics,…..so try to find things of added value not covered so far: Calo+SUSYreco

The ATLAS Electromagnetic Calorimeter

Liquid Argon Sampling Calorimeter:• lead (+s.s.) absorbers (1.1, 1.5mm Barrel)• liquid Argon gap 2.2mm 2kV (barrel)• varying gap and HV in the endcap• accordion structure no dead area in φ • “easy” to calibrate

R 4m

φ

Z 3.2m

Z 0mR 2.8m

Granularity (typical Δη X Δφ ):Presampler = 0.025x0.1 (up to η=1.8)Strips = 0.003x0.1 (EC )Middle = 0.025x0.025 (main energy dep)Back = 0.05 x0.025

The barrel and endcap EM-calorimeters!Some numbers:2048 barrel absorbers2048 barrel electrodesgiving 32 barrel modules (4years of production and assembly)16 endcap modulesAll assembled and inserted in their cryostatsBarrel cryostat in pit waiting for electronics

Thickness: 24-30X0

Barrel

Endcaps

Calibration of the ATLAS EM calorimeter

General Strategy and Sequence for electrons and photons:• Calibration of Electronics

• necessitates a good understanding of the physics and calibration signal• Corrections at the cluster level:

• position corrections • correction of local response variations• corrections for losses in upstream (Inner detector) material and longitudinal leakage

• Refinement of corrections depending on the particle type (e/γ)• uniformity 0.7% with a local uniformity in ΔηXΔφ=0.2x0.4 better than 0.5% • inter-calibrate region with Zee

What can be studied where?• Calibration of electronics studied in testbeam• Corrections at cluster level: testbeam and ATLAS simulations• uniformity: testbeam• Zee: simulation

The best Monte Carlo is the DATA! For ATLAS:Testbeam TestbeamMC ATLASMC ATLAS

ATLAS series modules in testbeam

1998-2002: prototype and single module tests at CERN:4 ATLAS barrel modules3 ATLAS endcap modulesSingle electron beams20-245GeV

Studies of:• energy resolution• linearity• uniformity• particle ID

2004: combined testbeam endcap and barrel including tracking and muons

FE electronicsSitting directly on the feedthroughas in ATLAS

Electronics:• bipolar signal • time to peak 50ns (variable)• 40MHz sampling of 5 samples (125ns)• three gain system 1/9.5/10(automatic choice)

From 5 samples in time to one “energy”:Optimal Filtering coefficients:• exponential versus linear• different entry points • inductance effect: parallel versus serial• electronic gains

The Signal/Electronics Calibration

Calibration signal : ~0.2%

Physics signal

0 1.4

L non-uniform:2-3 % effecton E along

Preamp + shaper (3gains) + SCA

60

30

10

L (nH)

Hamac SCA: Atlas Calorimeter Electronics.

Sampling of 3x4 signals at 40MHz, 13.5 bits of dynamic range with simultaneous write and read in rad-hard technology (DMILL).

Same type of chip used in digital oscilloscope: keep the high dynamic range and increase the sampling rate and bandwidth while using the cheapest technology on the market: 0.8µ pure CMOS (patent filed in April 2001).

Instruments are based on the MATACQ chip which is a sampling matrix able to sample data at 2GS/s over 2560 points and 12 bits of dynamic range with a very low power consumption compared to standard systems.

This structure has first been used in the design of the new digital oscilloscope family of Metrix (0X7000). This product is the first autonomous 12-bit scope on the market. Award for technology transfer to industry of the SFP (DPG)

Also used in a 4-channel VME and GPIB board. The latter offers the 2GS/s – 12bits facility with low power at low cost. It’s perfectly suited for high dynamic range precise measurements in harsh environments (CAEN).

Digression:From physics to industry.

Dominique Breton LAL-Orsay, Eric Delagnes CEA-Saclay

Cluster Corrections

Clustering with fixed size• Correct position S-shape in eta• Correct phi offset• S shape eta in strips• local energy variations phi (accordion)• local energy variations eta

Testbeam: phi modulation Endcap:

ATLAS simulation: S-shape

Variation of correction as function of η under control (smooth behaviour)

Cluster Corrections: longitudinal weighting

Non-negligeable amount of material before the calorimeterReconstruction needs to optimise simultaneously energy resolution and linearity.Method based on Monte Carlo and tested with data in one point η= 0.68:

impactcellbremleaki

caloi

visVisPS

VisPS

rec fEfdepthfEEdEEEcEEbEaE 3,1

5.01 ).()).(1).().().)(().()((

Correct for energyloss upstream ofPresampler(cryostat+beam linematerial)

Energy lost between PS and calo(Cable/board)

Small dependence of calo sampling fraction+ lateral leakage with energy

Longitudinalleakage depthfunction of depth only

fbrem extracted from simulation and beam transport of H8 beam line, not present in ATLAS

1.5 X0, 3.6 %@10 GeV 0.9 X0, 4.1 %@10 GeV > 30 X0, 0.3 %@10 GeV

EPS = energy in presamplerEi =energy in calorimeter compartments

Linearity

Achieved better than 0.1 % over 20-180 GeV but : - done only at one position in a setup with less material than in ATLAS and no B field-No Presampler in Endcap (ATLAS) for >1.8

Systematics at low energy ~0.1 %

Dedicated setup was used in 2002 to have a very precise beam energy measurement : - Degaussing cycle for the magnet to ensure B field reproducibility ateach energy (same hysteresis) - Use a precise Direct Current-Current Transformer with a precision of 0.01 % - Hall probe from ATLAS-Muon in magnet to cross-check magnet calibration lots of help from EA-team (I. Efthymiopoulos) Limitation of calorimeter linearity measurement is 0.03 % from beam energy knowledge - Absolute energy scale is not known in beam test to better than ~1 %- Relative variation is important

Energy resolution

Resolution at =0.68 Local energy resolution well understood since Module 0 beam tests and well reproduced by simulation : Uniformity is at 1% level quasi onlinebut achieving ATLAS goal (0.7 %) difficult

Good agreement for longitudinal shower development between data and testbeam MC

Cluster Energy CorrectionsIn ATLAS: use a simplified formula:E(corr) = Scale(eta)*(Offset(eta)+W0(eta)*EPS+E1+E2+W3(eta)*E3)

3x7

0.1%-0.2% spread from 10GeV to 1TeV over all eta remember testbeam was 1point: proof that the method works!

10GeV

50GeV

100GeV

Energy resolution in ATLAS Simulation

100GeVresolution

X0 in frontof strips

Energy resolution in ATLAS wrt testbeam 20% worseTypically 2-4 X0 in front of calorimeterGood correlation with resolution

Current method at the limit of its sensitivityFor historians: wrt TDR 25% degradation, but in TDR simulation Inner Detector Material description incomplete

Barrel uniformity @ 245 GeV in testbeam

In beam setup, one feedthrough had qualityproblem ( open symbols) due to largeresistive cross talk (non-ATLAS FT). > 7 is ATLAS like and can be used as reference : uniformity better than 0.5 %Energy scale differs by 0.13 %

quality of module construction is excellent

rms0.62%

0.45%

4.5‰0.49%

Module P13

Module P13 > 7

Module P15 > 7

Module P13Energy resolution

Similar results for endcap modules

Position/Direction measurements in TB

245 GeV Electrons ~550 μmat =0

~250 μmat =0

mid

strip

H γγ vertex reconstructed with 2-3 cm accuracy in ATLAS in z Precision of theta measurement 50mrad/sqrt(E)

Good agreement of data and simulation

Z~5mm

Z~20mm

Zee

• uniformity 0.2x0.4 ok in testbeam• description of testbeam data by Monte Carlo satisfactory• make use of Zee Monte Carlo and Data in ATLAS for intercalibration of regions• 448 regions in ATLAS (denoted by i)• mass of Z know precisely• Ei

reco = Eitrue(1+αi)

• Mijreco =Mij

true(1+(αi+αj)/2)• fit to reference distribution (Monte Carlo!!!)• beware of correlations, biases etc…

At low (but nominal) luminosity, 0.3% of intercalibration can be achieved in a week (plus E/P later on)! Global constant term of 0.7% achievable!

Mass resolution of Higgs bosons

Hγγ120.96GeVσ= 1.5GeVH γγ

Note that the generated Higgs mass is 120GeV:Effect: calibration with electrons, so the photon calibration is off by 1-2%Getting from Electron to photon in ATLAS will require MC!

H ZZ 4e:Mass scale correct within 0.1GeV σ=2.2GeV

Particle Identification/jet rejection

Dijet cross section ~1mbZ ee 1.5 10-6 mbW eν 1.5 10-5 mbNeed a rejection factor of 105 for electronsUse the shower shape in the calorimeter

Use the trackerUse the combination of the calo+tracker

Cut based analysis gives for electrons an efficiency of about 75-80% with a rejection factor of 105

Multivariate techniques are being studied for possible improvements(likelihood, neural net, boost decision tree)

Soft electrons

Two possibilities for seeded electron reconstruction• calo• trackerReconstruction of electrons close to jets difficult, and interesting (b-tagging) especially for soft electrons. Dedicated algorithm:• builds clusters around extrapolated impact point of the tracks• calculates properties of the clusters• PDF and neural net for ID• useful per se as well as for b-tagging

Hbbpions

e id efficiency = 80% Pion rejection in: J/Psi : 1050±50 WH(bb) : 245±17 ttH : 166 ±6

J/Psi

WH

ttH

What can we do now with all that?

Supersymmetry

3 neutral Higgs bosons: h, A, H1 charged Higgs boson: H±

and supersymmetric particles:

spin-0 spin-1/2 spin-1

Squarks:

qR, qL

q

Gluino: g g

Sleptons:

ℓR, ℓL

ℓ

h,H,A Neutralino χi=1-4

Z, γ

H± Charginos:χ±

i=1-2 W±

~~

~~

The parameters of the Higgs sector:• mA : mass of the pseudoscalar Higgs boson• tanβ: ratio of vacuum expectation values• mass of the top quark• stop (tR, tL) sector: masses and mixing

~

~ ~

Theoretical limit:mh 140GeV/c2

Many different models:• MSSM (minimal supersymmetric extension SM)• mSUGRA (minimal supergravity)• GMSB• AMB• NMSSM

Conservation of R-parity• production of SUSY particules in pairs• (cascade) decays to the lightest sparticle • LSP stable and neutral: neutralino (χ1)• signature: missing ET

See talks by Sven and Tilman: Here only a reminder for completeness sake

At the LHC

Large cross section for squarks and gluinos of several pb, i.e. several kEventssum jet-PT and ET effective massSquarks and gluinos up to 2.5TeV “straight forward”Largest background for SUSY is SUSY (but…)

Large masses means long decay chainsSelection: multijet with large PT (typically 150,100,50 GeV) and OS-SF leptonsInvariant masses jet-lepton, lepton-lepton, lepton-lepton-jet related to masses

SM

SUSY

SUSY at the LHC (and ILC)

Moderately heavy gluinos and squarks

light sleptons

Heavy and light gauginos

Higgs at the limitof LEP reach

τ1 lighter than lightest χ± :• χ± BR 100% τν• χ2 BR 90% ττ • cascade:qL χ2 q ℓR ℓ q ℓ ℓ qχ1

visible

m0 = 100GeV m1/2 = 250GeV A0 = -100GeV tanβ =10 sign(μ)=+favourable for LHC and ILC (Complementarity)

~

~

~~

~

Examples of measurements at LHC

Gjelsten et al: ATLAS-PHYS-2004-007/29

From edges to masses: System overconstrainedplus other mass differences and edges…

Using the kinematical formula (no use of model) and a toy MC for the correlated energy scale error: • energy scale leptons 0.1%• energy scale jets 1%Mass determination for 300fb-1 (thus 2014):

Coherent set of “measurements”for LHC (and ILC) “Physics Interplay of the LHC and ILC”Editor G. Weiglein hep-ph/0410364

Polesello et al: use of χ1 from ILC (high precision) in LHC analyses improves the mass determination

From Mass measurements to Parameters

SFITTER (R. Lafaye, T. Plehn, D. Z.): tool to determine supersymmetric parameters from measurementsModels: MSUGRA, MSSM, GMSB, AMB

The workhorses:• Mass spectrum generated by SUSPECT (new version interfaced) or SOFTSUSY• Branching ratios by MSMLIB• NLO cross sections by Prospino2.0• MINUIT

The Technique:• GRID (multidimensional to find a non-biased seed, configurable)• subsequent FIT

Other approaches:• Fittino (P. Bechtle, K. Desch, P. Wienemann)• Interpolation (Polesello)• Analytical calculations (Kneur et al, Kalinowski et al)• Hybrid (Porod)

Beenakker et al

SPS1a ΔLHC ΔILC ΔLHC+ILC

m0 100 3.9 0.09 0.08

m1/2 250 1.7 0.13 0.11

tanβ 10 1.1 0.12 0.12

A0 -100 33 4.8 4.3

Results for MSUGRA

Start SPS1a LHC ILC LHC+ILC

m0 100 1TeV 1TeV 1TeV

m1/2 250 1TeV 1TeV 1TeV

tanβ 10 50 50 50

A0 -100 0GeV 0GeV 0GeV

• Convergence to central point• errors from LHC %• errors from ILC 0.1%• LHC+ILC: slight improvement• low mass scalars dominate m0

Two separate questions:• do we find the right point?

• need and unbiased starting point• what are the errors?

Once a certain number of measurements are available, start with the most constrained model

Sign(μ) fixed

Masses versus Edges

need correlations to obtain the ultimate precision from masses….

SPS1a ΔLHC masses

ΔLHCedges

m0 100 3.9 1.2

m1/2 250 1.7 1.0

tanβ 10 1.1 0.9

A0 -100 33 20

Δm0 Effect on mℓR Effect on mℓℓ

1GeV 0.7/5=0.14 0.4/0.08=5

• use of masses improves parameter determination!• edges to masses is not a simple “coordinate” transformation:

Similar effect for m1/2

Sign(μ) fixed

Total Error and down/up effect

Higgs sleptons Squarks,gluinos Neutralinos, charginos

3GeV 1% 3% 1%

Theoretical errors (mixture of c2c and educated guess):

Running down/up• spectrum generated by SUSPECT• fit with SOFTSUSY (B. Allanach)• central values shifted (natural)• m0 not compatible

SPS1a ΔLHC+ILCexp

ΔLH+ ILCth

m0 100 0.08 1.2

m1/2 250 0.11 0.7

tanβ 10 0.12 0.7

A0 -100 4.3 17

Including theory errors reducessensitivity by an order of magnitude

SPS1a SoftSUSYup ΔLHC+LC

m0 100 95.2 1.1

m1/2 250 249.8 0.5

tanβ 10 9.82 0.5

A0 -100 -97 10

Higgs error: Sven Heinemeyer et al.

Between MSUGRA and the MSSM

Start with MSUGRA, then loosen the unification criteria,less restricted model defined at the GUT scale:• tanβ, A0, m1/2 , m0

sleptons, m0squarks, mH

2 , μ• experimental errors only

SPS1a LHC ΔLHC

m0sleptons 100 100 4.6

m0squarks 100 100 50

mH2 10000 9932 42000

m1/2 250 250 3.5

tanβ 10 9.82 4.3

A0 -100 -100 181

• Higgs sector undetermined • only h (mZ) seen

• slepton sector the same as MSUGRA• light scalars dominate determination of m0

• smaller degradation in other parameters, but still % precision

The highest mass states do not contain the maximum information in the scalar sector, but they do in the Higgs sector!

Sfitter-team and Sabine Kraml

MSSM

MSSM fit:bottom-up approach24 parameters at the EW scale

LHC or ILC alone:• certains parameters must be fixedLHC+ILC:• all parameters fitted• several parameters improved

Caveat:• LHC errors ~ theory errors• ILC errors << theory errorsSPA project: improvement oftheory predictions and standardisation

LHC ILC LHC+ILC

With more measurements available: fit the low energy parameters

Impact of TeVatron Data?

With Volker Buescher (Uni Freiburg): • 2008 too early for Higgs to γγ with 10fb-1 at LHC• only central cascade SUSY measurements are available: χ1, χ2, qL, ℓR

• Higgs is sitting on the edge of LEP exclusion • WH+ZH 6 events per fb-1 and experiment at TeVatron• end of Run: Δmh = ± 2GeV• adding background: Δmh = ± 4-5GeV

•A hint of Higgs from the TeVatron would help the LHC at least the first year! • mtop from TeVatron with 2GeV precision makes impact on fit negligible

Higgs mass from γγ

~~

No Higgs, edges from the LHC:m0 = 100 ± 14 GeV m1/2 = 250 ± 10 GeVtanβ = 10 ± 144 A0 = -100.37 ± 2400 GeV

Higgs hint plus edges from the LHC:m0 = 100 ± 9 GeVm1/2 = 250 ± 9 GeVtanβ = 10 ± 31 A0 = -100 ± 685 GeV

And the Egret point?Wim de Boer: astro-ph/0408272EGRET: on Compton gamma ray observatory, measured high energy gamma ray flux.Compatible with Standard Model, but also SUSY:m0 =1400 GeV m1/2 = 180 GeV A0=700 GeV tanβ = 51 μ > 0

0

WMAP

EGRET

Stau coannihilation

mA resonance

Bulk

Incomp. withEGRET data

StauLSP

No EWSB

Dominant Processes at the LHC:

m0 =1400 ± (50 – 530)GeV m1/2 = 180 ± (2-12) GeV A0 =700 ± (181-350) GeV tanβ= 51 ± (0.33-2)

Measurements:• Higgs masses h,H,A• mass difference χ2-χ1

• mass difference g- χ2

Sufficient for MSUGRA

~

Uncertainties:• b quark mass• t quark mass• Higgs mass prediction

Les Houches 2005: P. Gris, L. Serin, L.Tompkins, D.Z.

Tri-lepton signal promissing

Conclusions

• Construction of ATLAS-EM calorimeter modules finished• Testbeam studies have driven the improvement of the understandingof the combined optimisation of linearity and resolution of the calorimeter • EM calibration under control• electron (and photon identification) are at the required levelwith multivariate approaches under study • SFitter (and Fittino) will be essential to determine SUSY’s fundamentalparameters

• mass differences, edges and thresholds are more sensitive than masses• the LHC will be able to measure the parameters at the level %• LC will improve by a factor 10• LHC+LC reduces the model dependence• EGRET: in MSUGRA, LHC has enough potential measurements to confront the hypothesis

Many thanks to Laurent Serin for his help in the preparation of the talk!