Download - The ALFA project in ATLAS
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The ALFA project in ATLASThe ALFA project in ATLAS
Antwerpen 25/10/07Per Grafstrom
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ATLAS FORWARD DETECTORSATLAS FORWARD DETECTORS
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Purpose of ALFAPurpose of ALFA
Additional handle on the luminosity ALFA = Absolute Luminosity For ATLAS
Measurement of tot and elastic scattering parameters
Tag proton for single diffraction
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Luminosity measurements-why? Luminosity measurements-why?
Cross sections for “Standard “ processes t-tbar production W/Z production …….
Theoretically known to better than 10% ……will improve in the future
New physics manifesting in deviation of x BR relative the Standard Model predictions
Important precision measurements Higgs production x BR tan measurement for MSSM Higgs …….
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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).
(ATLAS-TDR-15, May 1999)
Higgs couplingtan measurement
ExamplesExamples
Systematic error dominated by luminosity (ATLAS Physics TDR )
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Elastic scattering as a handle on luminosity
optical theorem: forward elastic rate + total inelastic rate:
needs large |η| coverage to get a good measurement of the inelastic rate- otherwise rely on MC in unmeasured regions
Use tot measured by others (TOTEM)
Combine machine luminosity with optical theorem
luminosity from Coulomb Scattering
ATLAS pursuing all options
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Absolute vs relative measurementAbsolute vs relative measurement
STRATEGY:
1. Measure the luminosity with most precise method at optimal conditions
2. Calibrate luminosity monitor with this measurement, which can then be used at different conditions
Relative Methods:
LUCID (dedicated luminosity monitor) BCM Min. Bias Scintillators Tile/LAr Calorimeters
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Elastic scattering at small angles
• Measure elastic rate dN/dt down to the Coulomb interference region
(à la UA4). |t|~0.00065 GeV2 or Θ ~ 3.5 microrad.This requires (apart from special beam optics)• to place detectors ~1.5 mm from LHC beam axis• to operate detectors in the secondary vacuum of a Roman
Pot • spatial resolution sx = sy well below 100 micron (goal 30
micron) • no significant inactive edge (< 100 micron)
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Elastic scatteringElastic scattering
All very simplified – we need
• Electromagnetic form factor• Proper treatment of the Coloumb-hadron interference phase• t- dependence of rho and phase• non-exponential behaviour -t dependence of the slope• Saturation effects
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tot vs sand fit to (lns) =1.0
) =2.2(best fit)
The total cross sectionThe total cross section
AlanValery Mishka
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The The ρρ parameter parameter
ρ = Re F(0)/Im F(0) linked to the total cross section via dispersion relations ρ is sensitive to the total cross section beyond the energy at which ρ is
measured predictions of tot beyond LHC energies is possible Inversely :Are dispersion relations still valid at LHC energies?
(Figures from Compete collaboration)
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The b-parameter or the forward peakThe b-parameter or the forward peak The b-parameter for lt l< .1 GeV2
“Old” language : shrinkage of the forward peak b(s) 2 ’ log s ; ’ the slope of the Pomeron trajectory ; ’ 0.25 GeV2
Not simple exponential dependence of local slope
Structure of small oscillations?
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Single DiffractionSingle Diffraction
RP
IP
240m 240m
RPRP RP
RP RP RP RP
RP
IP
240m 240m
RPRP RP
RP RP RP RPZDC
ZDC
140m
LUCID
LUCID
ZDC
ZDC
140m
LUCID
LUCID
ATLAS
ATLAS
17m 17m
elastic scattering
single diffraction
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Forward detectorsForward 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
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Trigger conditionsTrigger conditions
For the special run (~100 hrs, L=10For the special run (~100 hrs, L=102727cmcm-2-2ss-1-1))
1. ALFA trigger1. ALFA trigger coincidence signal left-right arm (elastic trigger) coincidence signal left-right arm (elastic trigger) each arm must have a coincidence between 2 stations each arm must have a coincidence between 2 stations rate about 30 Hzrate about 30 Hz
2. LUCID trigger2. LUCID trigger coincidence left-right arm (luminosity monitoring)coincidence left-right arm (luminosity monitoring) single arm signal: one track in one tube single arm signal: one track in one tube
3. ZDC trigger3. ZDC trigger single arm signal: energy deposit > 1 TeV (neutrons)single arm signal: energy deposit > 1 TeV (neutrons)
4. Single diffraction trigger4. Single diffraction trigger ALFA.AND.(LUCID.OR.ZDC) ALFA.AND.(LUCID.OR.ZDC) central ATLAS detector not considered for now (MBTS good central ATLAS detector not considered for now (MBTS good
candidate)candidate)
For the special run (~100 hrs, L=10For the special run (~100 hrs, L=102727cmcm-2-2ss-1-1))
1. ALFA trigger1. ALFA trigger coincidence signal left-right arm (elastic trigger) coincidence signal left-right arm (elastic trigger) each arm must have a coincidence between 2 stations each arm must have a coincidence between 2 stations rate about 30 Hzrate about 30 Hz
2. LUCID trigger2. LUCID trigger coincidence left-right arm (luminosity monitoring)coincidence left-right arm (luminosity monitoring) single arm signal: one track in one tube single arm signal: one track in one tube
3. ZDC trigger3. ZDC trigger single arm signal: energy deposit > 1 TeV (neutrons)single arm signal: energy deposit > 1 TeV (neutrons)
4. Single diffraction trigger4. Single diffraction trigger ALFA.AND.(LUCID.OR.ZDC) ALFA.AND.(LUCID.OR.ZDC) central ATLAS detector not considered for now (MBTS good central ATLAS detector not considered for now (MBTS good
candidate)candidate)
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Event generation and simulationEvent generation and simulation
PYTHIA6.4modified elastic
with coulomb- and ρ-termsingle diffraction
PHOJET1.1 elastic & single diffraction
beam propertiesat IP1
size of the beam spot σx,y
beam divergence σ’x,y
momentum dispersion
beam transportMadX
tracking IP1RP high β* optics V6.5
including apertures
ALFA simulationtrack reconstruction
t-spectrumξ-spectrum
luminosity determination
single diffractionL1 filter
LUCID & ZDCpre-selection
elastic scattering
(Work of Hasko Stenzel-Giessen)
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Single diffraction: trigger conditionsSingle diffraction: trigger conditions
Efficiency [%] Pythia Phojet
Preselection
ξ<0.2 97.1 94.8
ZDC [E>1 TeV] 51.5 38.7
LUCID [1 track] 45.1 57.3
[Central ATLAS E> 100 GeV] 24.9 38.7
Total preselection 75 74
RP selection
ALFA(Relative to preselection)
60.1 54.2
Total acceptance 44.9 40.1
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Hit pattern in ALFAHit pattern in ALFA
hit pattern for 10 M SD events simulated with PYTHIA + MADX for the beam transport
Dispersion
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acceptance for t and acceptance for t and ξξ
global acceptance: PYTHIA 45 % PHOJET 40.1 %
global acceptance: PYTHIA 45 % PHOJET 40.1 %
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Feedthrough for trigger photodetectors
Kapton flat cable
motherboard
MAPMT + VD + RO cards
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The fiber trackerThe fiber tracker
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ALFA 2007: a full scale detection module ALFA 2007: a full scale detection module
23 MAPMTs
10x2 for fiber detector
3x1 for overlap detector
Frame from the 2006 TB
Base plate similar to the 2006 version, but with central fixation for fiber plates and 1 free slot for triggers feed-throughNew design for the
fiber plates support
10-2-64 fiber plates:
New substrates design
3 overlaps fiber plates:
New substrates design
Trigger scintillators:
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Roman Pot Concept
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FE electronicsFE electronics
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Test Beam campaigns at DESY and at Test Beam campaigns at DESY and at CERNCERN
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DESY test beam resultsDESY test beam results
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The test beam at DESYThe test beam at DESY
the validity of the chosen detector concept with MAPMT readout
the baseline fibre Kuraray SCSF-78 0.5 mm2 square
expected photoelectric yield ~4
low optical cross-talk
good spatial resolution
high track reconstruction efficiency
No or small inactive edge
Technology appears fully appropriate for the
proposed measurement.
Conclusions from DESY test beam
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Test beam at CERNTest beam at CERN
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Test Beam at CERNTest Beam at CERN
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Time lineTime line Mechanics
Prototype tested Full production launched Delivery end February 2008
Detector A number of small prototypes tested Construction of one full detector started (1/8 of total system) Production start after validation spring 2008. Full detector in 2009
Electronics Prototypes tested Electronics corresponding to one full detector by end 2007 All electronics by end 2008
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Back up
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Simulation of the LHC set-upSimulation of the LHC set-up
elastic generatorPYTHIA6.4
with coulomb- and ρ-termSD+DD non-elastic
background, no DPE
beam propertiesat IP1
size of the beam spot σx,y
beam divergence σ’x,y
momentum dispersion
beam transportMadX
tracking IP1RP high β* optics V6.5
including apertures
ALFA simulationtrack reconstruction
t-spectrumluminosity determinationlater: GEANT4 simulation
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Acceptance 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
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L from a fit to the t-spectrumL 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
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Simulation of elastic scatteringSimulation of elastic scattering
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*
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t- and t- and ξξ-resolution: PYTHIA vs PHOJET -resolution: PYTHIA vs PHOJET
Good agreement between PYTHIA and PHOJET for the reolutions Good agreement between PYTHIA and PHOJET for the reolutions
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reconstruction biasreconstruction bias
True and reconstructed values are in average slightly shifted needs to be corrected some differences observed at small t
True and reconstructed values are in average slightly shifted needs to be corrected some differences observed at small t
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Introduction – physics case Introduction – physics case
single diffraction ppX+p:
complements the elastic scattering program measurement of cross section and differential distributions fundamental measurement, tuning of models, background
determination special detectors ALFA+LUCID+ZDC high β* optics same special run as for luminosity calibration
single diffraction ppX+p:
complements the elastic scattering program measurement of cross section and differential distributions fundamental measurement, tuning of models, background
determination special detectors ALFA+LUCID+ZDC high β* optics same special run as for luminosity calibration
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resolution for t and resolution for t and ξξ
main contribution to the resolution t: vertex smearing, beam divergence (small t), det. resolution (large t) ξ: vertex smearing and detector resolution
main contribution to the resolution t: vertex smearing, beam divergence (small t), det. resolution (large t) ξ: vertex smearing and detector resolution
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Systematic uncertainties Systematic uncertainties
generator difference, model dependence acceptance, detector corrections ± 5-10%
beam conditions, optical functions, alignment ± 2% (based on results for elastic scattering)
background (being estimated) double diffraction minimum bias beam halo
DD ≈ 2 %, MB ≈ 0.5 %, beam halo + DD/MB 1-2%
luminosity ± 3%, very best possible luminosity determination, at calibration
point!
statistical uncertainty small, expect 1.6-2.3 M accepted events
generator difference, model dependence acceptance, detector corrections ± 5-10%
beam conditions, optical functions, alignment ± 2% (based on results for elastic scattering)
background (being estimated) double diffraction minimum bias beam halo
DD ≈ 2 %, MB ≈ 0.5 %, beam halo + DD/MB 1-2%
luminosity ± 3%, very best possible luminosity determination, at calibration
point!
statistical uncertainty small, expect 1.6-2.3 M accepted events
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Conclusion & outlookConclusion & outlook
A measurement of single diffraction with ATLAS appears to be possible,
however it won’t be a precision measurement in contrast to elastic
scattering.
Combination ALFA, LUCID and ZDC Special running conditions measurement of cross section and t-, ξ-distribution not a precision measurement, 10% systematic uncertainty
achievable? goal: improve model predictions and background estimates
for central diffraction
This first pilot study must be pursued and confirmed by full simulation and
systematic studies involving the LUCID and ZDC communities. The option of
including the MBTS for tagging the diffractive system should be investigated.
A measurement of single diffraction with ATLAS appears to be possible,
however it won’t be a precision measurement in contrast to elastic
scattering.
Combination ALFA, LUCID and ZDC Special running conditions measurement of cross section and t-, ξ-distribution not a precision measurement, 10% systematic uncertainty
achievable? goal: improve model predictions and background estimates
for central diffraction
This first pilot study must be pursued and confirmed by full simulation and
systematic studies involving the LUCID and ZDC communities. The option of
including the MBTS for tagging the diffractive system should be investigated.
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Systematic errorsSystematic errors Background subtraction ~ 1 %
Background subtraction ~ 1%
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Luminosity transfer 10Luminosity transfer 102727-10-1034 34 cmcm-2-2 sec sec-1-1
Bunch to bunch resolution we can consider luminosity / bunch
~ 2 x10-4 interactions per bunch to 20 interactions/bunch
Required dynamic range of the detector ~ 20
Required background < 2 x10-4 interactions per bunch main background from beam-gas interactions Dynamic vacuum difficult to estimate but at low luminosity we will be close to
the static vacuum. Assume static vacuum beam gas ~ 10-7 interactions /bunch/m We are in the process to perform MC calculation to see how much of this will
affect LUCID
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t-resolutiont-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
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