ATLAS cavern LHC physics : the first year(s) - Nikhef · PDF fileLHC physics : the first...

LHC physics : LHC physics : the first year(s) the first year(s) ……..

• Introduction (experiments, construction status, ...)• Physics potential with the first 10 fb-1

(a few examples …) • Some comments on comparison/links with Tevatron

F. Gianotti, NIKHEF, 12/03/2004

ATLAS cavern

Fabiola Gianotti (CERN)March 12, 2004

• pp (mainly) √s = 14 TeV• Start-up : April 2007• Initial/low luminosity L ≤ 1033 cm-2 s-1

≤ 2 minimum bias/x-ing “Tevatron-like” environment• Design/high luminosity L = 1034 cm-2 s-1 (after ~ 3 years)~ 20 minimum bias/x-ing fast (≤ 50 ns) rad hard detectors

Note : 10 fb-1 collected in 107 s ≡ 3 months at 1033 , i.e. in one year assuming 30% running efficiency


Here :ATLAS and CMS

TOTEM

ALICE : heavy ions,p-ions

ATLAS and CMS :pp, general purpose

ATLAS and CMS :pp, general purpose

LHCb : pp, B-physics

27 Km ring 1232 dipoles B=8.3 T

The machine


First full LHC cell (~ 120 m long) : 6 dipoles + 4 quads Successful tests at nominal current (12 kA)

~ 200 dipoles produced

ATLASA Toroidal Lhc ApparatuS

Length : ~45 m Radius : ~12 m Weight : ~ 7000 tons


•• Tracking (|η|<2.5, B=2T) :-- Si pixels and strips-- Transition Radiation Detector (e/π separation)

• Calorimetry (|η|<5) :-- EM : Pb-LAr-- HAD: Fe-scintillator (central), Cu/W-LAr (fwd)

• Muon Spectrometer (|η|<2.7) :air-core toroids with muon chambers (standalone capabilities)


CMSCompact Muon Solenoid

Length : ~22 m Radius : ~7 m Weight : ~ 12500 tons

•• Tracking (|η|<2.5, B=4T) : Si pixels and strips

• Calorimetry (|η|<5) :-- EM : PbWO4 crystals-- HAD: brass-scintillator (central+ end-cap),

Fe-Quartz (fwd)

• Muon Spectrometer (|η|<2.5) : return yoke ofsolenoid instrumented with muon chambers

ATLAS CMS

MAGNET (S)Air-core toroids + solenoid in inner cavityCalorimeters outside field 4 magnets

SolenoidCalorimeters inside field1 magnet

TRACKERSi pixels+ stripsTRD → particle identificationB=2Tσ/pT ~ 5x10-4 pT ⊕ 0.01

Si pixels + stripsNo particle identificationB=4T σ/pT ~ 1.5x10-4 pT ⊕ 0.005

EM CALOPb-liquid argonσ/E ~ 10%/√E uniformlongitudinal segmentation

PbWO4 crystals σ/E ~ 2-5%/√Eno longitudinal segmentation

MUON Air → σ/pT < 10 % at 1 TeVstandalone; larger acceptance

Fe → σ/pT ~ 5% at 1 TeVcombining with tracker

HAD CALO Fe-scint. + Cu-liquid argon (10 λ) σ/E ~ 50%/√E ⊕ 0.03

Brass-scint. (> 5.8 λ +catcher)σ/E ~ 100%/√E ⊕ 0.05



Solenoid ready/tested ATLAS MAGNETS

End-cap toroid vacuum vessels

All components ready, integration started

All eight barrel coil conductors/casings/cryostats ready, but integration on critical path (heat shields) First coil in the pit in July 2004


ATLAS INNER DETECTORCarbon-fibre pixel support structure

SCT end-cap system test

Pixels : module production startedSCT : > 50 % (10%) of barrel (end-cap) modules produced,

assembly/integration started(but some delays accumulated …)

TRT : all barrel modules completedassembly of second end-cap on critical path

TRT end-cap wheel


Barrel EM inside the cryostat

Assembly of first EM end-cap(now completed)

Hadron Tiles

Hadron LAr

EM LAr

Forward LArSolenoid

Barrel cryostat

Endcap cryostat

Module production and (cold) tests completedEmphasis on assembly and integration: barrel (including solenoid) and one end-cap ready, second end-cap completed in June

ATLAS CALORIMETERS

First 8 Tilecal modules installedin the pit on March 1st


ATLAS MUON CHAMBERSFinal chambers and alignment system on CERN H8 test beam line

End-capBarrel

Alignment

MDT, TGC : ~ 80% of (bare) chambers readyRPC: -- ~ 45% produced (but need to increase production rate)

-- extensive aging tests ongoing


F. Gianotti, NIKHEF, 12/03/2004 CMS magnet yoke

INSTALLATION

ATLAS installation in the pit: Beg. 2004 - July 2006CMS installation in the pit : Mid 2005 – End 2006

ATLAS installation scheme

CMS compact and modular yoke pieces can beassembled, instrumented and tested on surface and then transferred in the cavern (in ~ 4 months)after magnet test mid 2005.

CMS installation scheme


CMS MUON CHAMBERSInstallation test of barrel chamber

Installation of end-cap chamber support

90%/40%/25% of CSC/DT/RPC chambers assembled

Coil main parameters :Length : 12.5 m Diameter : 6 mStored energy : 2.7 GJ~ 56 km of conductor

CMS MAGNET

Coil made of 5 coil modules : CB-2 and CB-1 ready; 70% of winding completed


CB0 CB-1

Conductor producedMagnet test in surface hall by mid ‘05


Inner barrel (TIB) system test

5.4 m

End cap –TECPixel

2.4 m

Inner Disks –TID

Inner Barrel –TIB

Outer Barrel –TOB

CMS INNER DETECTOR

End-cap (TEC) system test

Production of hybrids and part ofsensors started (some problems with thicker sensors). Need to speed up module production

210 m2, 15000 modules

CMS CALORIMETERBarrel :-- ~ 25k crystals out of 62k delivered-- 12 bare supermodules (out of 36) ready

Electronics:Production started after change of front-end chipand readout architecture.

Schedule of crystal production is still a concern(esp. for end-cap)


Barrel supermodule (1700 crystals)

Module of 200 crystals

Hadronic barrel completed

Forward calorimeter : quartz fibre insertion

Forward calorimeterfinished


Extensive beam tests have been and will be made Electron E-resolutionfrom test beam datadata


ATLAS (Pb-LAr) final modules

CMS(crystals)prototype

pT (π0) ~ 50 GeV

R (π0)π0 rejection from photon test beam data

Data : <R> = 2.60 ± 0.05

MC : <R> = 2.82 ± 0.10(preliminary)

επ vs εe20 GeV

ATLAS TRT prototype

Using 4mm stripsin 1st compartmentof barrel ECAL


RPC over |η|<1.6 (instead of |η|< 2.1)4th layer of end-cap chambers missing

Which detectors the first year ?

2 pixel layers/disks instead of 3

TRT acceptance over |η|< 2 (instead of |η|< 2.4)

Both experiments: deferrals of high-level Trigger/DAQ processors

LVL1 output rate limited to50 kHz CMS (instead of 100 kHz)

~ 25 kHz ATLAS (instead of 75 kHz)

Impact on physics visible but acceptableMain loss : B-physics strongly reduced (single µ threshold pT> 14-20 GeV)


Which physics the first year(s) ?

Expected event rates at production in ATLAS or CMS at L = 1033 cm-2 s-1

Process Events/s Events for 10 fb-1 Total statistics collectedat previous machines by 2007

W→ eν 15 108 104 LEP / 107 Tevatron

Z→ ee 1.5 107 107 LEP

1 107 104 Tevatron

106 1012 – 1013 109 Belle/BaBar ?

gg~~

tt

bb

H m=130 GeV 0.02 105 ?

m= 1 TeV 0.001 104 ---

Black holes 0.0001 103 ---m > 3 TeV(MD=3 TeV, n=4)

Already in first year, large statistics expected from:-- known SM processes → understand detector and physics at √s = 14 TeV-- several New Physics scenarios


Implications for light Higgs(assuming the same luminosity/detector/analysis)

qq WH lν bb gg H WWqq ZH ll bb lν lνmH=120 GeV mH=160 GeV

S(14)/S(2) ≈ 5* ≈ 30B(14)/B(2) ≈ 25 ≈ 6S/B(14)/S/B(2) ≈ 0.2 ≈ 3S/√B(14)/ S/√B(2) ≈ 1 ≈ 7

*Acceptance ~ 2 times larger at Tevatron(physics is more central, less initial-state g radiation)

EW cross-sections (e.g. qq W, Z, WH) : LHC/Tevatron ~ 10QCD cross-sections (e.g. tt, gg H) : LHC/Tevatron ≥ 100 (because of gluon PDF)

e/jet ~ 10–3 √s = 2 TeVe/jet ~ 10–5 √s = 14 TeV pT > 20 GeV


First goals ….

• Understand and calibrate detector and trigger in situ using well-known physics samples e.g. - Z → ee, µµ tracker, ECAL, Muon chambers calibration and alignment, etc.

- tt → blν bjj 104 evts/day after cuts jet scale from W jj, b-tag performance, etc.

• Understand basic SM physics at √s = 14 TeV first checks of Monte Carlos (hopefully well understood at Tevatron)

e.g. - measure cross-sections for e.g. minimum bias, W, Z, tt, QCD jets (to ~ 10-20 %),events features, particle multiplicities, pT and mass spectra, angular distributions, etc.

- measure top mass (to 5-7 GeV) give feedback on detector performance (jet scale …)Note : statistical error negligible after few days run

…. and then …

• Prepare the road to discovery:-- measure backgrounds to New Physics : e.g. tt and W/Z+ jets (omnipresent …)-- look at specific “control samples” for the individual channels:

e.g. ttjj with j ≠ b “calibrates” ttbb irreducible background to ttH ttbb

• Look for New Physics potentially accessible in first year (e.g. SUSY, …)

Note: if mH < 120 GeV : fast Higgs discovery may be crucial in case of competition with TevatronThis may be the most difficult physics goal for first year …


Standard Model Higgs

F. Gianotti, NIKHEF, 12/03/2004 Full GEANT simulation, simple cut-based analyses

mH > 114.4 GeVhere discovery easier with H → 4l

mH ~ 115 GeV 10 fb-1

total S/ √B ≈ 2.23.14+

−

H → γγ ttH → ttbb qqH → qqττ(ll + l-had)

S 130 15 ~ 10B 4300 45 ~ 10

S/ √B 2.0 2.2 ~ 2.7

includednot 2 σσ factor K

LO

NLO ≈≡−

ATLAS

Remarks:Each channel contributes ~ 2σ to total significance → observation of all channelsimportant to extract convincing signal in first year(s)

The 3 channels are complementary → robustness:

H → γγ

b

b

ttH → tt bb → blν bjj bb

H

τ

τ

qqH → qqττ


• different production and decay modes• different backgrounds• different detector/performance requirements:

-- ECAL crucial for H → γγ (in particular response uniformity) : σ/m ~ 1% needed-- b-tagging crucial for ttH : 4 b-tagged jets needed to reduce combinatorics-- efficient jet reconstruction over |η| < 5 crucial for qqH → qqττ :

forward jet tag and central jet veto needed against background

Note : -- all require “low” trigger thresholdsE.g. ttH analysis cuts : pT (l) > 20 GeV, pT (jets) > 15-30 GeV

-- all require very good understanding (1-10%) of backgrounds

mH > 130 GeV : H → ZZ(*) → 4l


ATLASATLAS

Requires good lepton E, p resolutionand identification. Gold-plated channelat LHC (~ background free …)

Measurement of the SM Higgs mass at the LHC (not for the first year …)

Expected experimental systematic errors included,but no theoretical uncertainty.


mh < 135 GeVmA ≈ mH ≈mH± at large mA

MSSM Higgs bosons h, H, A, H ±

-- A, H, H± cross-section ~ tg2β-- best sensitivity from A/H → ττ, H± → τν

(not easy the first year …)-- A/H µµ experimentally easier

(esp. at the beginning)

5σ discovery curves


Measurement of tg β

Not for the first year …

• Large variety of channels and signatures accessible • bbA/H 4b is more difficult than at the Tevatron(because of huge QCD background)

5σ contours

4 Higgs observable3 Higgs observable2 Higgs observable1 Higgs observable


H, A → µµ, ττH± → τν , tb

h

After several years ….

Assuming decays to SM particles only

Here only h (SM - like) observable at LHC, unless A, H, H± → SUSY → LHC may miss part of the MSSM Higgs spectrumObservation of full spectrum may require high-E (√s ≈ 2 TeV) Lepton Collider

SUPERSYMMETRY (SUSY) ≡ symmetry between fermions (matter) and bosons (forces)

•• All SM particles p have SUSY partner with same couplings and quantum numbers except

p~1/2- (p)spin )p~(spin =


SM particle SUSY partner spin

l sleptons 0q squarks 0g gluino 1/2W± (+Higgs) charginos χ±

1,2 1/2γ, Z (+Higgs) neutralinos χ0

1,2,3,4 1/2

l~

q~g~

Particle spectrum in minimal models(MSSM)

+ 5 Higgs : h, H, A, H±

mh < 135 GeV

•• R-Parity (multiplicative quantum number) = + 1 (-1) SM (SUSY) particles If conserved : -- SUSY particles produced in pairs

-- Lightest Supersymmetric Particle (LSP) is stableLSP ≡ χ0

1 weakly interacting dark matter candidate-- all SUSY particles decay to LSP

•• Motivations : unification matter-forces/fermions-bosons is beautiful; allows incorporationof gravity; can stabilize Higgs mass; allows unification of forcesat GUT scale; provides candidate for cold dark matter; not ruled out bypresent data; predicts light Higgs as favoured by data, etc.

SUSY searches at LHC

e.g. qq

q~

q~gαsαs

gggqqq ~~ ,~~ ,~~• Dominant processes : production strong production → huge cross-section

e.g. for ~ 104 events produced in one year at low L

TeV 1~ )g~ ,q~( m

g~ ,q~•• heavy → cascade decays

→ spectacular signatureswith many jets, leptons + missing E

→ easy to extract SUSY signal from SM backgrounds at LHC

χ01

Z

q

q

χ02

q~g~

weakly interacting → not detected→ missing energy in final state


SUPERSYMMETRY


gggqqq ~~ ,~~ ,~~Large cross-section → ≈ 100 events/day at 1033 forSUSY could be found quickly

TeV 1~ )g~ ,q~( m

5σ discovery curves

~ one year at 1034: up to 2.8 TeV

~ one year at 1033 : up to 2.3 TeV

~ one month at 1033 : up to 2 TeV

Multijet + ETmiss (most powerful and

model-independent signature if R-parity conserved)

Events for 10 fb-1 signalbackground

(GeV) )(jet p E M4

1iiT

missTeff ∑

=

+=

GeV 400 ~ )g~ ,q~( m≅ Tevatron reach

ET(j1) > 80 GeVET

miss > 80 GeV

signalEvents for 10 fb-1background

(GeV) )(jet p E M4

1iiT

missTeff ∑

=

+=

TeV 1 ~ )g~ ,q~( mATLAS

Peak position correlated to MSUSY ≡ ))g~( m ),q~( (mmin

From Meff peak, first/fast measurement of SUSY mass scale to ≈ 20% (10 fb-1, mSUGRA)


Detector/performance requirements:-- calorimeter coverage and hermeticity for|η|<5-- calorimeter energy scale calibration to ~5%-- “low” Jet+ET

miss trigger thresholds for low masses at overlap with Tevatron region (~400 GeV)

g~

b~

b

b

ml

±l

01

~χ

02

~χ±l

~

With more time and data: precise SUSY measurements(not for the first year ….)


•• ATLAS and CMS should be able to perform precise measurements of SUSY final state → determine sparticle masses and fundamental parameters of theory with precision ≈ 10% or better in many cases (at least in minimal models)

• Method: measure end-points of reconstructed mass spectra at each step of (long) squark/gluino decay chains. End-points depend only on involved masses only (pure kinematics ….) “model-independent” measurements

• LSP is not directly observable but its mass can be constrained indirectly fromother measurements in final state constraints on cold dark matter

GeV 700 ~)q~( mGeV 800 ~)g~( m

GeV 120 ~)( m 10χ

Ex. : LHC “Point 5” :


ATLAS100 fb-1

LHC Point 5

m (ll) spectrumend-point : 109 GeVexp. precision ~0.3%

m (llj)min spectrumend-point: 552 GeVexp. precision ~1 %

m (l±j) spectrumend-point: 479 GeVexp. precision ~1 %

Lq~ → q χ02

R~l

l χ01

l

m (llj)max spectrumthreshold: 272 GeVexp. precision ~2 %

GeV 121 157, 232, 690,)χ ,~ ,χ ,q~( m 120

R0

L =l

Example ofa typical chain:


Precision~ 10%

∆m (χ01) / m(χ0

1)

Lq~ → q χ02

R~l

l χ01

l

h χ01

bbPutting all constraints together: m (bbj), m(ll), m(llj)max, m(llj)min, m(lj)

Sparticle mass Expected precision 100 fb-1

squark left ± 3%χ0

2 ± 6%slepton mass ± 9%χ0

1 ± 12%

From fit of mSUGRA to all experimentalmeasurements at Point 5 can deduce cold darm matter relic density:

Ωχ h2 = 0.2247 ± 0.0035

Micromegas 1.1 (Belanger et al.)+ ISASUGRA 7.58

ATLAS

A lot !!!What can the LHC learn from the Tevatron data ?

All physics results are useful and exciting (mW, mtop, B-physics, possible discoveries ….)

F. Gianotti, NIKHEF, 12/03/2004 ΣET (Gev)

New UE tuning< ΣET > ~ 222 GeV

Old UE tuning< ΣET > ~ 135 GeV

Less glamorous but equally important :

• general tuning of MC with data : minimum bias, underlying event, jet shapes, jetfragmentation (e.g. jet π0 ), jet algorithms (e.g. cone vs k⊥ as done by D0), PDF (g, b-quark, …)

ATLAS : ΣET in Z ττ events

• measurements of specific processes relevant to LHC, e.g. :-- tt, ttj (j=q,c,b), W/Z+jets, QCD multijets : omnipresent backgrounds in ~ all LHC searches-- γγ, γj : backgrounds to H γγ-- etc. etc.

• performance studies : τ-reconstruction and τ/jet separation, jet veto in e.g. W+jets events(for VBF at LHC), lepton absolute energy scale (can CDF/D0 achieve 0.4‰ as required for ∆mW~ 30 MeV ?), b-jet scale, etc.


Note : backgrounds at LHC will be measured with combination of data and MCAt the beginning, the data statistics will be limited

impact of MC prediction will be high

How fast can the LHC discover something new depends also on the Tevatron data


Conclusions

• LHC offers potentially an impressive physics programme right from the beginning.Event statistics : 1 day at LHC at 1033 ≡ 10 years at previous machines in some casesMachine luminosity performance will be the crucial issue in first year(s)

• Detector construction is progressing well, although few items are on critical path(e.g. ATLAS barrel toroid, CMS crystals)

• Lot of emphasis on test beams (individual sub-detectors, several sub-detectors together) and on construction quality checks results indicate that the detectors “as built” should give a good starting-point performance.

• However, a lot of data (and time …) will be needed at the beginning to:-- commission the detector and trigger in situ -- reach the performance needed to optimize the physics potential-- understand standard physics at √s = 14 TeV and compare to MC predictions-- measure backgrounds to possible New Physics

• SUSY may be discovered “quickly”, light Higgs more difficult … and what about surprises ?

• Contributions from Tevatron studies and data will be very important, especially in the initial phase to reach quickly the “discovery mode” and extract a convincing “early” signal

Back-up slides



• ~ 200 dipoles produced • most reached 8.3 T with < 2 quenches



staged

Guiding physics principles:-- all sub-detectors needed already in 1st year-- physics potential decreases fast with decreasing η coverage

(e.g. H → γγ significance decreases linearly)-- full radial redundancy in tracking less crucial at ~ 1033

⊕ Technical (e.g. installation) and schedule constraints

Which detector the first year ?

staged

stagedin part

staged

staged

Staged detector components:-- 1 pixel layer -- TRT outer end-cap-- Gap scintillator-- EEL/EES MDT and half CSC-- Part of forward shielding-- Part of LAr ROD -- Large part of HLT/DAQ

processors

Summary of physics impact of staging initial detector

Staged items Main impact during Effectfirst run on

1 pixel layer ttH → ttbb ~8% loss in significance

Gap scintillator H → 4e ~8% loss in significance

MDT A/H → 2µ ~5% loss in significancefor m~ 300 GeV

Trigger processors B-physics program jeopardisedHigh-pT physics no safety margin

(e.g. for EM triggers)

Requires 10-15% more integrated luminosity to compensate.


Complete detector needed at high luminosity:-- robust pattern recognition (efficiency, fakes rate) in the

presence of pile-up and radiation background-- muon measurement -- powerful b-tag-- robustness against detector aging and L > 1034

-- precise measurements (e.g. light Higgs) may require low trigger thresholds

at (very) high pT

-- HLT/DAQ deferrals limit available networking and computing for HLT → limit LVL1 output rate-- Large uncertainties on LVL1 affordable rate vs money (component cost, software performance, etc.)


Selections (examples …) LVL1 rate (kHz) LVL1 rate (kHz) LVL1 rate (kHz)L= 1 x 1033 L= 2 x 1033 L= 2 x 1033

Real thresholds set for no deferrals no deferrals with deferrals95% efficiency at these ET An example for illustration…

MU6,8,20 23 19 0.82MU6 --- 0.2 0.2EM20i,25,25 11 12 122EM15i,15,15 2 4 4J180,200,200 0.2 0.2 0.2 3J75,90,90 0.2 0.2 0.2 4J55,65,65 0.2 0.2 0.2 J50+xE50,60,60 0.4 0.4 0.4 TAU20,25,25 +xE30 2 2 2MU10+EM15i --- 0.1 0.1Others (pre-scaled, etc.) 5 5 5

Total ~ 44 ~ 43 ~ 25

LVL1 designed for 75 kHz→ room for factor ~ 2 safety

Likely max affordable rate,no room for safety factor

LVL1 menus and rates (indicative only …)


L = 2∗1033 cm-2 s-1 Threshold (GeV) Rate (kHz) Threshold

(GeV) Rate (kHz)

Inclusive muon 20 0.8

0.2

12.0

4.0

0.6

0.4

2.0

Inclusive tau 86 2.2

Two taus 59-59 1.0

Elecron + Jet 21-45 0.8

5.0

~ 25 (no safety margin)

Two muons 6

2.714

3

29

17

177, 86,70

88-46

Inclusive electron 25

0.9

3.3

1.3

3.0

2.3

Two electrons 15

1 Jet, 3 Jet, 4 Jet 200, 90, 65

Jet + ET miss 60-60

tau + ET miss 25-30

0.9

~16 (factor ~3

safety margin)

Others (pre-scaled, calibration, …)

Total

ATLAS CMS

B-physics programme strongly reduced (e.g. B J/ψ ( ee) KOS , hadronic channels)

Which data samples ? Total trigger rate to storage at 2 x 1033

reduced from ~ 540 Hz (HLT/DAQ TP, 2000)to ~ 200 Hz (now)

High-Level-Trigger output


Selection (examples …) Rate to storage at 2x1033 (Hz) Physics motivations (examples …)

e25i, 2e15i ~ 40 (55% W/b/c → eX) Low-mass Higgs (ttH, H→ 4l, qqττ)µ20i, 2µ10 ~ 40 (85% W/b/c → µX) W, Z, top, New Physics ? γ60i, 2γ20i ~ 40 (57% prompt γ) H → γγ, New Physics

(e.g. X → γ yy mX~ 500 GeV ) ?j400, 3j165, 4j110 ~ 25 Overlap with Tevatron for new

X → jj in danger …j70 + xE70 ~ 20 SUSY : ~ 400 GeV squarks/gluinosτ35 + xE45 ~ 5 MSSM Higgs, New Physics

(3rd family !) ? More difficult high L2µ6 (+ mB ) ~ 10 Rare decays B → µµX

Others ~ 20 Only 10% of total ! (pre-scaled, exclusive, …)Total ~ 200 No safety factor included.

“Signal” (W, γ, etc.) : ~ 100 Hz

Best use of spare capacity when L < 2 x 1033 being investigated

Here ≥5σdiscovery ofbbA/H → 4bpossible at Tevatron with15 fb-1


The main challenges and the ATLAS/CMS detector requirements

√s = 14 TeVL = 1034 cm–2 s–1

Discovery reach for new particles up to m ≈ 5 TeV

-- > 100 times larger than Tevatron Run 2-- bunch spacing 25 ns 25 ns

Event rate in ATLAS, CMS :


N = L x σinel (pp) ≈ 1034 cm–2 s–1 x 70 mb≈ 109 interactions/s

ATLAS

~ 25 inelastic (low-pT) events (“minimum bias”)produced on average in the detectors ateach bunch crossing → pile-up

First 2-3 years: L = 1033 cm–2 s–1

( “low luminosity” phase)

Best channels at LHC :

Hg

g

t


CMS

100 fb-1

mH < 150 GeV : H → γγ

Requires excellent EM calorimetry(E-resolution, γ/π0 separation)

mH > 130 GeV :

ATLASATLAS

H → ZZ(*) → 4e, 4µ

Requires good lepton E, p resolutionand identification. Gold-plated channelat LHC

mH ~ 130 GeV 10 fb-1

total S/√B ≈ 6

H → γγ qqH → qqττ H → 4l qqH → qqWW(ll + l-had)

S 120 ~ 8 ~ 5 18B 3400 ~ 6 < 1 15

S/ √B 2.0 ~ 2.7 2.8 3.9

l= e,µ

includednot 2 factorK ≈−

• 4 complementary channels for physics and for detector requirements• S/√B < 3 per channel (except qqWW counting channel) → observation of all channels

important in first year• H → 4l low rate but very clean: small background, narrow mass peak

Detector requirements: -- ≥ 90% e, µ efficiency at low pT (analysis cuts : pT

1,2,3,4 > 20, 20, 7, 7, GeV) -- σ /m ~ 1%, tails < 10% → E, p measurement and resolution in ECAL and tracker at low pT


First pp collisions : collect data for calibration and to understand “basic” physics

Well-known, clean processes from standard trigger menu: e.g.- Z → ee : ECAL inter-calibration, absolute E-scale to ~ 0.1%, etc.- Z → µµ : p-scale in tracker and Muon Spectrometer, etc.- tt → blν bjj : absolute jet-scale from W → jj (~1%), study b-tag,

reconstruction of complex final states (for ttH), etc.

~ 6 x 104 evts/dayafter cuts

~ 104 evts/day after cuts, S/B ~ 65


Additional lower-thresholds samples (pre-scaled triggers) :

• Minimum-bias events : pp interaction properties, MC tuning, LVL1 efficiency,radiation background in Muon chambers, etc.

• QCD jets (20 ≤ ET ≤ 400 GeV) : QCD cross-sections and MC tuning, trigger efficiency, calorimeter inter-calibration, jet algorithms, background to Higgs, SUSY, etc.

• Inclusive e± pT > 10 GeV : trigger efficiency, ECAL calibration, ID alignment, E/p, e± reconstruction at low-pT, etc.

• Inclusive µ± pT > 6 GeV : trigger efficiency, µ± reconstruction at low-pT,E-loss in calorimeters, ID alignment, etc.

~ 107 eventsper sampleneeded

These are only few examples …

≥ 10% of total trigger rateunder normal operation(more at the beginning)


ChannelChannel Main backgroundMain background S/BS/B backgroundbackgroundsystematicssystematics for 5for 5σσ

Proposed technique/commentsProposed technique/comments

H->γγ Irreduc. γγReducible γj

2-3% 0.4% Side-bands stat Err ~0.5% for 30-100 fb-1

ttH H->bb ttjj 30% 6% Mass side-bandsAnti b-tagged ttjj ev. Under study J.Cammin

H->ZZ*-> 4 lep ZZ->4l and ττll 3-6 60% Mass side-bandsStat Err <30% 30fb-1

H->WW*->llνν WW*, tW 30-50% 6% No mass peakBkg enriched region ?

Study to be performed

VBF channelsIn general

Rejection QCD/EW Study forward jet tag and central jet veto Use EW ZZ and WW leptonicStudy to be performed

VFB H->WW tt, WW, Wt 50-200% 10% Bkg. enriched samples with discr. VariablesStudy to be performed

VBF H->ττ Zjj, tt 50-400% 10% Missing Et calibrationZ-> ττ (mass tails ?)

Study to be performed

MSSM (bb)H/A->ττ

Z->ττ, Wj 25% tgβ=15 MA=300

5% Mass side-bandsStat Err ~5% 30fb-1

MSSM(bb)H/A -> µµ

Z/γ*->µµ 12% tgβ=15 MA=150

~2% Mass side-bandsStat Err ~2% 30fb-1

• Cracks :-- can be monitored with Z ( ll) + jets-- impact minimised by ET

miss isolation, removal of jets in cracks


Events with ETmiss > 50 GeV

these 2 events contain a high-pT neutrino

if leading jet undetected

reconstructed

Z ( µµ) + jetfull simulation

• “Poor” initial calorimeter calibration may increase trigger rates impact on low-mass SUSY (Very) pessimistic uncorrected non-compensation simulated by + 20% enhancement of EM scale + 50% rate for ET

miss > 80 GeV

Muon RPC ageing test at X5


• The test is going on continuously and is now reaching the limit of 3 Atlas years (90 mC/cm2) including the safety factor of 5-10

• The gas closed loop system has been mounted and will be gradually introduced for 4 out of the 6 detector layers that are under test. The other two will remain in open flow

• Detection efficiencies are good• A modest increase of the source off current is observed• In July and August the set up has to be removed from X5 for ATLAS MDT and

other non ATLAS users testing >>> long time required for reaching the limit of 10 Atlas years

RPC Ageing test 3 production 3 production RPCsRPCs currently ageing at currently ageing at the CERN Gamma Irradiation Facilitythe CERN Gamma Irradiation Facility

Aim to integrate 300 mC/cm2

10 Atlas Years with safety factor > 5Measurement still ongoingPrevious tests on RPC prototype showed good efficiency and time resolution after 8 ATLAS years

F. Gianotti, NIKHEF, 12/03/2004 Last week

Expected impact of “realistic/pessimistic” initial detector performance

One example : ATLAS EM calorimeter

H → γγ : constant term ctot ≤ 0.7% over |η| < 2.5 needed

Strategy to achieve this goal

By construction (e.g. mechanical tolerances): expect cL (≡ “local” constant term) ≈ 0.5% over ∆η x ∆ϕ =0.2 x 0.4 448 channels

in total

Source Expected contribution to cL(over ∆η x ∆ϕ = 0.2 x 0.4)

Geometry (e.g. residual Accordion modulation) 0.25-0.35 %Mechanics (absorber and gap thickness) < 0.25%Calibration (amplitude uniformity, ~ 0.4 %

difference physics-calibration)

Total 0.5-0.6%

There are~ 400 such regionsin |η| < 2.5


Beam tests of 4 (out of 32) barrel modules and 3 (out of 16) end-cap modules in 2001-2002:from first results step is achieved


Scan of a barrel module with 245 GeV e-

r.m.s. ≈ 0.67% over ~ 500 spots

“On-line” uniformity : ~ 1.3%Uniformity after corrections(e.g. optimal filtering) : ~ 0.67 %

over ~ half module

Uniformity after correctionsover ∆η x ∆ϕ = 0.2 x 0.4 : ~ 0.55%

1 barrel module:∆η x ∆ϕ = 1.4 x 0.4 ≡~ 3000 channels

ϕη

rate ~ 1 Hz at 1033, ~ no background, allows standalone ECAL calibration Z → ee eventsIn situ calibration with

ctot = cL ⊕ cLR cLR ≡ long-range response non-uniformities of the 400 regions(module-to-module variations, different upstream material, etc.)

(from full simulation)

~ 250 e± per region needed to achieve cLR ≤ 0.4% ctot = 0.5% ⊕ 0.4% ≤ 0.7%

~ 105 Z → ee events (few days of data taking at 1033)


conservative : implies very poor knowledge of upstream material (to factor ~2)

Nevertheless, let’s consider the worst (unrealistic ?) scenario : no corrections applied

• cL = 1.3 % measured “on-line” non-uniformity of individual modules• cLR = 1.5 % no calibration with Z → ee ctot ≈ 2%

H → γγ significance mH~ 115 GeVdegraded by ~ 25%

Pion E-resolutionfrom test beam datadata

e and π beams down to~ 1 GeV now available at CERN

ATLAS LAr hadronic end-cap series modules

G4 G3 data

CMS ECAL+HCAL barrel prototypes

~ 100% /√E

~ 70% /√E

G4

data

2004 : several ATLAS “combined tests” :-- Pixels + SCT + TRT-- end-cap EM + end-cap hadronic + forward-- ID + barrel EM + Tilecal + Muon chambers


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