Rijssenbeek – 27-Feb-04 ATLAS General – 1

ATLAS Detectors for Luminosity ATLAS Detectors for Luminosity Measurement and MonitoringMeasurement and Monitoring

Letter of IntentLetter of IntentContributors to this Letter of Intent:

Andrew Brandt, Bryan Caron, Brian Cox, Jaroslav Cvach, Ilias Efthymiopoulos, Angeles Faus-Golfe, Per Grafström, Maurice Haguenauer, Vincent Hedberg, Christian Joram, Jerry Lamsa, Milos Lokajicek, Michael Moll, Stanislav Nemecek, Jim Pinfold, Jan Soukup, Stefan Tapprogge, Valery Telnov, Sebastian White

Thanks for assistance from LHC Machine experts: Ralph Assman, Bernard Jeanneret, André Verdier

Thanks to TOTEM Colleagues for information on the Roman Pot Stations

Topics:• Baseline Method and Requirements• Optics Solution and Machine Conditions• Roman Pot Detectors• Luminosity Monitor LUCID• Other Luminosity Methods• Costs and Participants

Rijssenbeek – 27-Feb-04 ATLAS General – 2

Luminosity MeasurementLuminosity MeasurementLuminosity MeasurementLuminosity Measurement• Goal:

– Measure L with ≲2% accuracy

• Luminosity needed for:– Precision comparison with theory:

bb, tt, W/Z, jet, …, H, SUSY, …• Cross sections gives additional info;

will help disentangle SUSY scenarios– Precision comparison with other expt’s

• Luminosity from:– LHC Machine parameters (~5-10%)– Optical theorem: forward elastic rate

+ total inelastic rate: needs ~full |η| coverage

– Rates of well-calculable processes:e.g. QED, QCD,

• need DEDICATED Luminosity monitor

Relative precision on the measurement of HBR for various channels, as function of mH, at Ldt = 300 fb–1. The dominant uncertainty is from Luminosity: 10% (open symbols), 5% (solid symbols).

(ATL-TDR-15, May 1999)

Rijssenbeek – 27-Feb-04 ATLAS General – 3

LL from the Optical Theorem from the Optical Theorem•Luminosity from the machine: accuracy goal 5%, probably limited

by:• extrapolation of x , y (or , x , y) from measurements of beam profiles

elsewhere to IP• beam-beam effects at IP, effect of crossing angle at IP, …• Van der Meer scans à la ISR? Cross checks with HI running?

•Using the Optical Theorem and the total inelastic rate: (Method pursued by TOTEM/CMS)

– ATLAS does NOT have sufficient forward coverage to measure Ninel well enough…

2

0 0

2

2

2

0

( )1(1 ) ;

16

( )(1 )

16 ( / )

el el inelto eltot

t t

inel el

el t

td dN N N

dt dt

N N

dN dt

L

L

L

Need to reach tmin0.01 GeV2

1,..,2835

1,..,2835

21 21 2

* * *4 4 /Intersection Area of 1 ,2

i ii bi i

i x y N

f N N f k NN Nf

i i

L

Rijssenbeek – 27-Feb-04 ATLAS General – 4

Luminosity from Coulomb Luminosity from Coulomb ScatteringScattering

• Elastic scattering at micro-radian angles:

• Required reach in t: tmin t(|fC|=| fN|) 8EM/tot 6×10–4 GeV2 θmin 3.5 μrad

– Requires: • small intrinsic beam angular spread at IP small emittance

•detectors close to the beam, at large distance from IP

•parallel-to-point optics, insensitive to transverse vertex smearing and with large effective lever arm Leff

2

2 2tot

0

2e

4t

C Nb

t

dNf f i

dt t

LL

Rijssenbeek – 27-Feb-04 ATLAS General – 5

Experimental TechniqueExperimental Technique• independence of vertex position:

– parallel-to-point focusing: ydet = M11,yy* + M12,y y* with:

M11,y = (/*) [cos *sin] ( ψ(s) ≡ 0∫s ds/β(s) )

M12,y = (*) sin (* = value at IP)

optimum: M11= 0, M12 large: sit at (s) = (n ½), n=0,1,2,… and make * 0, * largethen: ydet = M12 y* = (*) y* = Leff,y y*

• limit on minimum |t|min:*min = dmin/Leff, tmin = (*min pb)2 , with dmin = nσy = nσ(N/γ)

tmin pb2nσ

2(N/γ) /*

Thus: maximize *; minimize nσ and N

y*

y*

parallel-to-point focusing

s

ydet

IP Leff

Rijssenbeek – 27-Feb-04 ATLAS General – 6

Beam Halo: limit on Beam Halo: limit on nnσσ

• Beam halo is a serious concern for Roman Pot operation– determines the distance of closest approach dmin

of (sensitive part of) detector: nσ = dmin/σbeam: 9 ≤ nσ ≤ 15

– expected halo rate (43 bunches, Np=1010, εN = 1.0 μm, nσ=10): 6 kHz

nσ-reach?

(RA LHC MAC 13/3/03)

Rijssenbeek – 27-Feb-04 ATLAS General – 7

EmittanceEmittance• Emittance can be reduced to 1.0×10–6 m (std: 3.75×10–6

m)– Recent LHC information:

emittance εN, number of protons/bunch Np , and collimator opening nσ,coll (in units of σ) are related via a resistive (collimator) wall instability limit criterion:

– Thus: εN ≥ 1.5×10–6 m (for Np=1010, nσ,coll=6 )

– For nσ=10: if tmin= pb2nσ

2ε/β*≤ 4×10–4 then: β* ≳ 2500 m

• beam size at detector: d = √(βdεN/γ) ,

– Beam safety: kσd ≳ 1.0-1.5 mm then: βd ≳ 100 m

p 223 5/2

,coll N

1.6 10N

n

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2625 m Optics (A. Faus-Golfe et 2625 m Optics (A. Faus-Golfe et al.)al.)

β

[m]

D

[m

]

• Smooth path to injection optics exists

• All Quads are within limits

• Q4 is inverted w.r.t. standard optics!

* * *N

, 11, 12,

11, 12,

4 2 2mi x

d

m

d

,d

n a

0 563.

2625m, 0.61mm, 0.229μrad ( 1 μm)

120.8m, , , 130μm

81.

1m

0.168 143.17 m, , m

4 10 GeV 0.1

, 0 GeV

y y

x x

y

x

M M

M M

t t

} Leff

Rijssenbeek – 27-Feb-04 ATLAS General – 9

Roman Pot LocationsRoman Pot Locations

240 m

TOTEM Pot

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Requirements for Roman Pot Requirements for Roman Pot DetectorsDetectors

• “Dead space” d0 at detector’s edge near the beam the beam: d0 ≲ 200 m (full/flat efficiency away from edge)

• Detector resolution: d = 30 m

• Same d = 30 m relative position accuracy between opposite detectors (e.g. partially overlapping detectors, …)

• Radiation hardness: 100 Gy/yr

• Operate with the induced EM pulse from circulating bunches (shielding, …)

• Rate capability: O(Mhz) (40 MHz); time resolution t = O(1 ns)

• Readout and trigger compatible with DAQ

• Other:– Simplicity, Cost

– extent of R&D needed, time scale, manpower, …

– issues of LHC safety and controls

Rijssenbeek – 27-Feb-04 ATLAS General – 11

Roman Pot DetectorsRoman Pot Detectors• Square scintillator strips

– Kuraray 0.5 mm × 0.5 mm

– 10 layers per coordinate– 50 μm offset between layers

• Readout: – MultiAnode PMT, or– Avalanche Photodiodes

• Trigger:– scintillator panes (possibly

subdivided?)– Trigger latency: MARGINAL!

p from IP RP: 800 ns signal RP CTP: 1000 ns trigger formation: 100 ns TOTAL: 1900 ns > 1.8μsremains to be sorted out… halo inter calibration planes

(well away from beam)

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Detector Performance Detector Performance SimulationsSimulations

• first simulation results:– strip positioning σfiber ≈ 20 μm

– light and photo-electron yield: Npe = <dE/dx> dfiber (dnγ/dE) εA εT εC gR εQ εd ≈ 5 p.e. marginal !

Baseline detector:SCSF-38 (=428 nm),

0.5 mm square. MAPMT

Alternative configuration:SCSF-3HF (=530 nm),

0.5 mm square. GM-APD

<dE/dx> specific energy loss of a MIP in scintillator

200 keV/mm 200 keV/mm

dfiber active thickness of fiber 0.48 mm 0.48 mm

dn/dE scintillation light yield 8.3 / keV 8.3 / keV

A geometrical acceptance 0.042 0.042

T attenuation in fiber 0.85 0.85

C coupling efficiency fiber/photodetector

0.8 0.8

gR Gain due to reflection from rear end

1.4 1.4

Q quantum efficiency photodetector

0.2 0.15 (0.3 in future ?)

d detection efficiency (electronics/DAQ)

0.85 0.85

Npe Photoelectron yield 5.4 4 (8 in future ?)

Rijssenbeek – 27-Feb-04 ATLAS General – 13

Tracking Simulation Tracking Simulation (multiplexing)(multiplexing)

• normal incidence tracks; assume: – fiber readout multiplexing (4/1)

– fiber position smearing: 20 μm

– fiber efficiency 85-95%

The hits of the 10 planes are projected in a histogram. The real hits can clearly be distinguished from the randomly distri-buted multiplexed hits.

Track traversing the fiber planes. The detection efficiency/fiber is 95%. All 10 hit fibers and the 30 multiplexed fibers give a signal.

Spatial resolution of a fiber plane for a detection efficiency per fiberof 85%. On average 8.2 fibers are hit (plus 24.6 multiplexed fibers). The Gaussian fit indicates a resolution of 25.4 mm.

Rijssenbeek – 27-Feb-04 ATLAS General – 14

Proof of Principle (M. Proof of Principle (M. Haguenauer et al.)Haguenauer et al.)

• Test beam hodoscope for CMS:– 1x1 mm2

– multiplexed MAPMT readout

Fibres KURARAY

a

b

amoy= 0,5 mm± 0,06 mm

bmoy= 0,05 mm± 0,01 mm

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 20 40 60 80 100 120 140

mm

a

b

Rijssenbeek – 27-Feb-04 ATLAS General – 15

Luminosity Performance Luminosity Performance SimulationsSimulations

• Baseline optics, with baseline detector resolutions

• smearing of hits on the detector plane caused by•detector resolution (30 μm) – negligible contribution

•beam angular spread (σθ* = 0.23 μrad)

• transverse vertex smearing (σ* = 0.42 mm),

– vertical coordinate: σ(y) = 0.23 μrad × 563 m = 127 μmvertical smearing reduces acceptance near the detector edge

– horizontal coordinate: σ(x) = 0.23 μrad × 143 m 0.42 mm × 0.168 = 32 μm 71 μm = 87 μmNote: taking the combination of left and right arms, the vertex smearing drops out (there is no detector edge in x!)

Rijssenbeek – 27-Feb-04 ATLAS General – 16

Simulated Elastic ScatteringSimulated Elastic Scattering• Inner ring:

t = 0.0007 GeV2

• Outer ring: t = 0.0010 GeV2

• Reconstruct θ*: 2 2*

2 2

, ,

x y

eff x eff y

x y

L L

Rijssenbeek – 27-Feb-04 ATLAS General – 17

Simulated dNSimulated dNelel/dt and Naïve Fit/dt and Naïve Fit

• 10 M evts with±45° fiducial cut on φ*

• NO systematics on beam optics!

• Only 1 station/arm

5M events Generated~90 hr at L=1027 cm-2s-1

Fit Results (χ2/NDF=1442/1467): σtot = 98.7±0.8 mb (100) ρ = 0.148±0.007 (0.15) B = 17.90±0.12 GeV-2 (18) L = (1.11±1.6%) 1027cm-2s-1 (1.09×1027)

Range for fitting: 0.00056 <|t|<0.030 GeV2

↖ (pθmincos45º)2

~4M events ‘Measured’ dN/d|t|

Rijssenbeek – 27-Feb-04 ATLAS General – 18

Luminosity MonitoringLuminosity Monitoring• LUCID: (Jim Pinfold et XVI al.: Alberta, Lund, Montreal, Regina, Saclay)

– Dedicated detector:•bundle of projective Cerenkov cones: 5 layers of 40 tubes each• low mass (6 kg), rad hard (C4F10 gas?), quartz fiber readout

– 40 MHz capability:• linearity required over 2x10-4 – 20 interactions/crossing•Cross-Calibration at low L = 1027:

– non-beam-beam backgrounds, e.g. beam-gas, can be important at low L!!

– Counts primary particles (only Č-photon statistics)•Mostly insensitive to non-primary particles

total signal #charged prim’s interactions/crossing L

– LUCID should operate at start-up (machine diagnostics)• can be calibrated absolutely later…

may be used in rapidity-gap vetoing (under study), etc…

• proof of principle: CLC at CDF! (e.g. S. Klimenko et al., NIM A441 (2000) 266)

• Preliminary approval by ATLAS EB last year (EB mtg, June 2002)

Rijssenbeek – 27-Feb-04 ATLAS General – 19

Services In/Out

ToUXA

PMTs

Inner radius of LUCID ~8 cm, outer radius ~16cm

~17< |z| <~18.5 m5.4< || <6.1

LUCID

ATLAS – Luminosity Monitor ATLAS – Luminosity Monitor (J. Pinfold

et al.)

Rijssenbeek – 27-Feb-04 ATLAS General – 20

LUCID - Simulation LUCID - Simulation Geant4 Simulation: Variation of #photons vs. muon incidence angle (measured at the tube centre)

Front

(J. Pinfold et al.)

prototypes Aug’03

~2 cmØ,1.5m tubes

Rear – ShowingWinston Cones

#photons/20 GeV μ at photo-detector: 70(1.5 m Č) x0.8(Cone acc.) x0.6(Fiber acc.) x0.4(att. 20 m fiber) = 15

Rijssenbeek – 27-Feb-04 ATLAS General – 21

Lucid Performance SimulationsLucid Performance Simulations• PYTHIA-6

(MSEL=2, MSUB995)=1,

MSTP(82)=0) events generated with increasing numbers of pileup

• Perfect linearity, with little sensitivity for secondaries

• Proof of Principle: the CDF CLC device

Number of Interactions/Crossing

Num

ber

of A

xi-L

inea

r T

rack

s/C

ross

ing/

Arm

single track/tube peak

Rijssenbeek – 27-Feb-04 ATLAS General – 22

Cross CalibrationCross Calibration• CNI calibration: L = 1028 cm–2s–1

(~2×10–4 evts/crossing)

• Standard runs: L = 1033-34 cm–2s–1

• LUCID resolves bunches: calibration must be transferred from 2×10–4 to about 20 evts/crossing

• Thus: non-beam-beam background rejection must be excellent at low L; note: beam-gas Np; beam-beam Np

2

• Remains to be studied in detail!

Rijssenbeek – 27-Feb-04 ATLAS General – 23

LL from other Physics Signals from other Physics SignalsUse well-calculable QED/QCD signals as Physics Monitors: L 2-4%

• QED: pp (p+*)+(p+*)p+()+p (A.Shamov & V.Telnov, hep-ex/0207095)

– Signal: (μμ)-pair with |η(μ)|<2.5, pT(μ)≳ 5-6 GeV, pT(μμ) 0≃• small rate ~1pb (~0.01 Hz at L=1034)

off-line: preliminary estimate δL 2%≃ for 10 fb–1

• Clean: backgrounds from DY, b,c-decays: handled by appropriate offline cuts.• uncertainties: μ trigger acceptance & efficiency, …

– Full simulation studies in progress (Alberta, SACLAY)

• QCD: W/Zleptons (Dittmar, Pauss, Zurcher, PRD56 (1997) 7284)

– High rate: Wlν : ~60 Hz at L=1034 (ε =20%)– Gives relevant parton luminosity directly… – Current “theory” systematics: σW/Zc 4% (V. Khoze et al., hep-ph/0010163)

– Detection systematics:• Trigger/Selection eff’s, Backgrounds (and L-dependence) seem manageable

– Detailed study for ATLAS detector needed (Alberta, SACLAY)

Both processes will be used – at very least as cross checks…

Rijssenbeek – 27-Feb-04 ATLAS General – 24

Cost Estimates & ParticipantsCost Estimates & Participants• LUCID:

– tubes: 70 KCHF

– Fibers and readout: 130 KCHF

– Infrastructure: 130 KCHF

– R&D: 60 KCHF

– TOTAL: ~400 KCHF

• Roman Pots:– RP Units: 220 KCHF

– Q4 Polarity inverter: 30 KCHF

– Scintillating Fiber Dets: 180 KCHF

– Readout and controls: 280 KCHF

– Materials: 80 KCHF

– R&D: 100 KCHF

– TOTAL: ~900 KCHF

• Institutions: Alberta, Arlington, CERN, Manchester, Montreal, Paris: Ecole Polytechnique, Prague, Stony Brook,Toronto, Montreal,

Rijssenbeek – 27-Feb-04 ATLAS General – 25

SummarySummary• ATLAS aims to determine absolute L in special high-β* runs

measuring Coulomb scattering– The CNI normalization is very challenging but seems

attainable in principle – critically dependent on control of the beam and backgrounds

– Roman Pot detectors: no show stoppers• This normalizes a dedicated L-monitor: the Č-detector LUCID

– LUCID prototyping is well underway: no show stoppers• Other processes will be employed as well:

• W/Z production, • double-photon exchange di-muon production, • machine L measurements, aided by HI experience… • …

• Time Table:– LoI draft available, LHCC submission in a few weeks– LHCC presentation in May

• Experience with RPs will help us prepare expansion of the ATLAS program with Central and Forward Diffraction…