luminosity measurments roadmap for luminosity determinations relative luminosity monitors

Luminosity measurments

• roadmap for luminosity determinations

• relative luminosity monitors

• luminosity from machine parameters

• luminosity from physics processes

• luminosity from elastic scattering

• how to access luminosity information

Dresden 15.05.2008 luminosity measurements, H.Stenzel 2

roadmap for luminosity determinations

from machine parameters (2008)

● absolute luminosity at start-up will uniquely come from the machine● expected precision is 20-30%● this will improve with special dedicated runs, 10% is feasible

from physics processes (2009)

● using γ γ →μμ (not discussed here)● using W/Z counting: 3-5% can be reached

from elastic scattering (>2009)

● with the optical theorem ● with small-angle scattering in the Coulomb region ● 3% accuracy is anticipated

combinations of all above ...

from machine parameters (2008)

● absolute luminosity at start-up will uniquely come from the machine● expected precision is 20-30%● this will improve with special dedicated runs, 10% is feasible

from physics processes (2009)

● using γ γ →μμ (not discussed here)● using W/Z counting: 3-5% can be reached

from elastic scattering (>2009)

● with the optical theorem ● with small-angle scattering in the Coulomb region ● 3% accuracy is anticipated

combinations of all above ...


relative luminosity monitor: LUCID

Cherenkov light is emitted at 3o and is read-out after 3 reflections on the inner tube walls.

Dresden 15.05.2008 luminosity measurements, H.Stenzel 4M. Bruschi – INFN Bologna (ITALY)

Off-line

On and Off-line

On and Off-line


other luminosity monitors

● MBTS (limited lifetime)● TILE calorimeter (Monitoring/Minimum Bias path)● LARG (current in HV lines)● Beam Condition Monitor

precision of about 1% on relative luminosity is expected

● MBTS (limited lifetime)● TILE calorimeter (Monitoring/Minimum Bias path)● LARG (current in HV lines)● Beam Condition Monitor

precision of about 1% on relative luminosity is expected


Luminosity from machine parameters

yxeff

eff

A

A

fNNL

4

21

Simplest case, beams colliding head-on, Gaussian beam profilesSimplest case, beams colliding head-on, Gaussian beam profiles

In presence of a crossing angle the luminosity is reduced by

In presence of a crossing angle the luminosity is reduced by

FfkN

L

F

N

b

z

4

21

2

2

Dresden 15.05.2008Dresden 15.05.2008 R.Bailey, DESY, December 2007R.Bailey, DESY, December 2007 77

Overall commissioning strategy for protons (estOverall commissioning strategy for protons (estdd. 2005). 2005)

Hardware commissioning

Machine checkout

Beam commissioning

43 bunch operation

75ns ops

25ns ops IInstall Phase II and MKB

25ns ops II

Stage A B C

No beam Beam

D

I.I. Pilot physics runPilot physics run First collisionsFirst collisions 43 bunches, no crossing angle, no squeeze, moderate intensities43 bunches, no crossing angle, no squeeze, moderate intensities Push performancePush performance Performance limit 10Performance limit 103232 cm cm-2-2 s s-1-1 (event pileup) (event pileup)

II.II. 75ns operation75ns operation Establish multi-bunch operation, moderate intensitiesEstablish multi-bunch operation, moderate intensities Relaxed machine parameters (squeeze and crossing angle)Relaxed machine parameters (squeeze and crossing angle) Push squeeze and crossing angle Push squeeze and crossing angle Performance limit 10Performance limit 103333 cm cm-2-2 s s-1-1 (event pileup) (event pileup)

III.III. 25ns operation I25ns operation I Nominal crossing angleNominal crossing angle Push squeezePush squeeze Increase intensity to 50% nominalIncrease intensity to 50% nominal Performance limit 2 10Performance limit 2 103333 cm cm-2-2 s s-1-1

IV.IV. 25ns operation II25ns operation II Push towards nominal performancePush towards nominal performance

*

bk

N

Optimise

Pileup

Losses

Beampower

Complexity

Minimise

)( *


Luminosity from beam parameters

Adjustment of the orbits to equalize the position differences left/right of the IP, determination of the overlap integral.

Tuning based on Beam position monitors with ~ 50 μm resolution.

Adjustment of the orbits to equalize the position differences left/right of the IP, determination of the overlap integral.

Tuning based on Beam position monitors with ~ 50 μm resolution.

Optimize luminosity in separation scans (Van der Meer-method)

Optimize luminosity in separation scans (Van der Meer-method)

LEP example


Expected precision from machine parameters

Factors entering in the luminosity calculation:

● beam current (intensity) 1-2%● crossing angle (reduction factor) ● hour glass effect (1% at high lumi, ß*=0.55m)● bunch-by-bunch variations● non-gaussian beam shapes ● suppression of tails by scraping

A precision of 10% can be reached

● ... and can be further reduced with dedicated runs/special studies● at start-up a precision of 20-30% can be expected● ultimately a few % level is not unrealistic,● at the ISR an error of < 1% was achieved!

Important: cross calibration of machine- and experiment-based methods!

More info: H.Burkhardt and P.Grafstrom, LHC Project Report 1019

Factors entering in the luminosity calculation:

● beam current (intensity) 1-2%● crossing angle (reduction factor) ● hour glass effect (1% at high lumi, ß*=0.55m)● bunch-by-bunch variations● non-gaussian beam shapes ● suppression of tails by scraping

A precision of 10% can be reached

● ... and can be further reduced with dedicated runs/special studies● at start-up a precision of 20-30% can be expected● ultimately a few % level is not unrealistic,● at the ISR an error of < 1% was achieved!

Important: cross calibration of machine- and experiment-based methods!

More info: H.Burkhardt and P.Grafstrom, LHC Project Report 1019


Luminosity from W/Z counting

● large cross section, high rate● clean experimental signature (leptonic modes) ● precise theoretical calculations

● large cross section, high rate● clean experimental signature (leptonic modes) ● precise theoretical calculations

a

BNLdt

th

Recent results on W/Z counting in CSC note: experimental systematic uncertaintydominated by acceptance, is 2-3%

(accounts for ISR, kT, UE, EW and PDF uncertainties)

Recent results on W/Z counting in CSC note: experimental systematic uncertaintydominated by acceptance, is 2-3%

(accounts for ISR, kT, UE, EW and PDF uncertainties)

For 1fb-1For 1fb-1

eeZ


theoretical cross section

QCD NNLO calculation for inclusive W/Z production, perturbative uncertainty fromscale variations is about 1% .

QCD NNLO calculation for inclusive W/Z production, perturbative uncertainty fromscale variations is about 1% .

However, 2-loop EW corrections are important at large pT, no complete QCD x EW are available!

However, 2-loop EW corrections are important at large pT, no complete QCD x EW are available!

EW corrections


theoretical cross section: PDF uncertainty

PDF-uncertainty using CTEQ6.6:3.3-3.5% using NLO+NLL

PDF-uncertainty using CTEQ6.6:3.3-3.5% using NLO+NLL

New NNLO MRSW2006 compared to MRST2004 (6% change)

New NNLO MRSW2006 compared to MRST2004 (6% change)

Currently a 3-5% accuracy of luminosity from W/Z seems in reachand will improve in the course of LHC....

Currently a 3-5% accuracy of luminosity from W/Z seems in reachand will improve in the course of LHC....


elastic scattering with ALFAelastic scattering with ALFA• Absolute• Luminosity• For • ATLAS


The elastic t-spectrum

schematically

ALFA simulation


Luminosity from elastic scattering

Our baseline method for the absolute luminosity calibration requires themeasurement of elastic scattering in the Coulomb-nuclear interference region down to t ≈6·10-4GeV2

Our baseline method for the absolute luminosity calibration requires themeasurement of elastic scattering in the Coulomb-nuclear interference region down to t ≈6·10-4GeV2

2

222/

2

22

2

16

14

c

e

t

e

t

cL

FFLdt

dN

tBtot

tBtot

NC

This is only possible if ALFA can be operated very close to the beam ≈12σ under optimal beam conditions.Alternatively at larger t the optical theorem can be used:

This is only possible if ALFA can be operated very close to the beam ≈12σ under optimal beam conditions.Alternatively at larger t the optical theorem can be used:

0

22

0

2 16

1,

1

16

,0Im4

t

el

tot

tot

t

el

totN

dtdR

RL

R

dtdR

RLtF

tot

tot

tot

Requires μrad anglemeasurements and detector distance to beam ≈1.5 mm!

Requires μrad anglemeasurements and detector distance to beam ≈1.5 mm!

Requires measurements of the total rate and extra-polation of elastic rate to 0!

Requires measurements of the total rate and extra-polation of elastic rate to 0!


How to measure the total inelastic rate?

From the CSC note on minimum bias:From the CSC note on minimum bias:

MBTS acceptanceMBTS acceptance SCT+PixelSCT+Pixel

Systematicuncertainty ≈3%+ physics modeluncertainties

Systematicuncertainty ≈3%+ physics modeluncertainties


Single diffraction with forward detectors

RP

IP

240m 240m

RPRP RP

RP RP RP RPZDC

ZDC

140m

LUCID

LUCID

ZDC

ZDC

140m

LUCID

LUCID

ATLAS

ATLAS

17m 17m

single diffraction

Cross sections[mb] Pythia Phojet

Elastic scattering 34.2 (modified)

22.2 (default)34.5

Single diffraction 14.3 11.0

Double diffraction 10.2 4.1

Minimum bias

non-diffractive54.7 67.9

Total cross section 101 119

Complement central detector measurement of single diffraction with measurements in the forward region to get the total rate.

In addition for the Luminosity there is an uncertainty of the extrapolation of the elastic slope to t=0~1% (TOTEM)

Complement central detector measurement of single diffraction with measurements in the forward region to get the total rate.

In addition for the Luminosity there is an uncertainty of the extrapolation of the elastic slope to t=0~1% (TOTEM)


Elastic scattering in the CNI region

2

,

2

,

2

2222*

yeffxeff

yx

L

y

L

xp

ppt

t reconstruction:

hit pattern for 10 M elastic events simulated with PYTHIA + MADX for the beam transport

2

sin

effL

special optics parallel-to-point focusing high β*


acceptance

Global acceptance = 67%at yd=1.5 mm, including losses in the LHC aperture.Require tracks 2(R)+2(L) RP’s.

distance of closest approach to the beam

radGeVTOT

EMa

t

Nf

Cf

5.324106

8

|||| :Region Coulomb

Detectors have to be operated as close as possible to the beam in order to reach the coulombregion!

-t=6·10-4 GeV2

decoupling of L and σTOT

only via EM amplitude!


t-resolution

The t-resolution is dominated by the divergence of the incoming beams.

σ’=0.23 µrad

ideal case

real world

2*231

ˆ pppt


L from a fit to the t-spectrum

2

222/

2

22

2

16

14

c

e

t

e

t

cL

FFLdt

dN

tBtot

tBtot

NC

input fit errorcorrelation

L 8.10 1026 8.151 1026 1.77 %

σtot 101.5 mb 101.14 mb 0.9% -99%

B 18 Gev-2 17.93 Gev-20.3%

57%

ρ 0.15 0.143 4.3% 89%

Simulating 10 M events,running 100 hrsfit range 0.00055-0.055

large stat.correlation between L and other parameters


systematic uncertainties for the luminosity

Details are give in the ALFA TDR CERN-LHCC-2008-006

and in ATL-LUM-PUB-2007-001


How to get your cross-section?

Marjorie Shapiro


The concept of luminosity blocks

Marjorie Shapiro


How to get the luminosity for your sample

Marjorie Shapiro

More info: Luminosity Working Group https://twiki.cern.ch/twiki/bin/view/ATLAS/LuminosityGroupLTF report: http://cdsweb.cern.ch/record/970678

https://twiki.cern.ch/twiki/bin/view/ATLAS/LuminosityGroup


Conclusion

Expected precision of luminosity measurements

● relative monitoring to 1% (LUCID)

● initial absolute calibration from machine parameters 20-30%

● improving with special runs to 10% or better

● W/Z production yield 3-5% calibration, likely to improve with LHC data

● elastic scattering in the CNI region and/or with the optical theorem will yield a 3% accuracy

Expected precision of luminosity measurements

● relative monitoring to 1% (LUCID)

● initial absolute calibration from machine parameters 20-30%

● improving with special runs to 10% or better

● W/Z production yield 3-5% calibration, likely to improve with LHC data

● elastic scattering in the CNI region and/or with the optical theorem will yield a 3% accuracy

Dresden 15.05.2008Dresden 15.05.2008 R.Bailey, DESY, December 2007R.Bailey, DESY, December 2007 2727

Staged commissioning plan for protonsStaged commissioning plan for protons

Hardware commissioning

450 GeV and 7TeV

2008 Machine checkout

Beam commissioning

450 GeV

Machine checkout

Beam commissioning

7TeV

43 bunch operation

Shutdown

B C

No beam Beam

ShutdownMachine checkout

Beam Setup

75ns ops 25ns ops I Shutdown

2009

No beam Beam

A


Forward detectors

80% acceptance

GeV 2.7E

6.1|η|5.4

90% acceptance

GeV 60 n, TeV 1E

8.3|η|

(elastic) 67% acceptance

99%efficiency

14|η|10


acceptance for t and ξ

global acceptance:PYTHIA 45 %PHOJET 40.1 %

global acceptance:PYTHIA 45 %PHOJET 40.1 %

luminosity measurments roadmap for luminosity determinations relative luminosity monitors

Documents

absolute luminosity

luminosity calculation

luminosity measurments

lineluminosity measurements

machine parameters factors

beam parameters adjustment

machine parametersluminosity

beam position monitors