ATLAS Forward Detectors for Luminosity Measurement and Monitoring

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 ATLAS Forward Detectors for Luminosity Measurement and Monitoring Letter of Intent, March 22,

ATLAS Forward Detectors for Luminosity Measurement and Monitoring Letter of Intent, March 22, 2004 ATLAS Collaboration Acknowledgement Many thanks to a number of colleagues for helping us in preparing this Letter of Intent: ¢ G. Arduni, R. Assman, F. Bordry, O. Bruning, B. Jeanneret, K. Potter, A. Verdier for the understanding of issues related to LHC machine and operations, ¢ K. Dahlerup-Petersen, J-C Guillaume, T. Kurtyka , D. Macina, Y. Muttoni, R. Ostojic , C. Rathjen and R. Veness for helping to understand the layout and interface issues, and ¢ the TOTEM Colleagues for giving us access to the Roman Pot drawings and explaining the interface issues involved LHCC Open Session - May 12 2004

Outline ¢ Introduction ¾ why measure luminosity ¾ different methods ¢ Luminosity from Coulomb

Outline ¢ Introduction ¾ why measure luminosity ¾ different methods ¢ Luminosity from Coulomb scattering ¾ the experimental technique ¾ the necessary beam conditions ¢ Roman Pot detector requirement and the proposed detector ¢ Luminosity performance simulation ¢ A dedicated ATLAS luminosity monitor – LUCID ¢ Scheduling and Interface issues with the LHC ¢ Cost estimates ¢ Conclusions LHCC Open Session - May 12 2004 2

Luminosity Measurement – WHY ? ¢ Cross sections for “Standard “ processes ¾ t-tbar

Luminosity Measurement – WHY ? ¢ Cross sections for “Standard “ processes ¾ t-tbar production ¾ W/Z production ¾ ……. 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 ¾ Higgs production x BR ¾ tan measurement for MSSM Higgs ¾ ……. LHCC Open Session - May 12 2004 3

Luminosity Measurement – WHY ? (cont. ) Examples Higgs coupling tan measurement Relative precision

Luminosity Measurement – WHY ? (cont. ) Examples Higgs coupling tan measurement Relative precision on the measurement of H BR for various channels, as function of m. H, at Ldt = 300 fb– 1. The dominant uncertainty is from Luminosity: 10% (open symbols), 5% (solid symbols). (ATLAS-TDR-15, May 1999) Systematic error dominated by luminosity (ATLAS Physics TDR ) LHCC Open Session - May 12 2004 4

Luminosity Measurement ¢ Goal: ¾ measure L with ≲ 2 -3% accuracy ¢ Absolute

Luminosity Measurement ¢ Goal: ¾ measure L with ≲ 2 -3% accuracy ¢ Absolute luminosity from: ¾ LHC Machine parameters (~5 -10%) ¾ rates of well-calculable processes: e. g. QED, QCD ¾ optical theorem: forward elastic rate + total inelastic rate: ¡ needs ~full |η| coverage-ATLAS coverage limited ¾ luminosity from Coulomb Scattering ¢ Relative luminosity a DEDICATED luminosity monitor is needed LHCC Open Session - May 12 2004 5

Luminosity from other Physics Signals ¢ QED: pp (p+ *)+(p+ *) p+( )+p ¾

Luminosity from other Physics Signals ¢ QED: pp (p+ *)+(p+ *) p+( )+p ¾ signal: (μμ)-pair with |η(μ)|<2. 5, p. T(μ)≳ 5 -6 Ge. V, p. T(μμ) ≃ 0 ¡ small rate ~1 pb (~0. 01 Hz at L=1034) ¡ clean: backgrounds from DY, b, c- decays can be handled by appropriate offline cuts ¡ uncertainties: μ trigger acceptance & efficiency, … ( A. Shamov & V. Telnov, hep-ex/0207095) ¾ full simulation studies in progress (Alberta, SACLAY) ¢ QCD: W/Z leptons ¾ high rate: W ℓν : ~60 Hz at L=1034 (ε = 20%) ¡ current “theory” systematics: PDF and parton cross sections 4% ¡ gives relevant parton luminosity directly… ¡ detection systematics: trigger/acceptance/identification efficiency/ backgrounds ¡ detailed study for ATLAS detector needed (Alberta, SACLAY) ¢ Both processes will be used LHCC Open Session - May 12 2004 6

Luminosity from Coulomb Scattering ¢ Elastic scattering at micro-radian angles: ¾ L directly determined

Luminosity from Coulomb Scattering ¢ Elastic scattering at micro-radian angles: ¾ L directly determined in a fit (along with TOT, r, and b) effectively a normalization of the luminosity from the exactly calculable Coulomb amplitude ¢ Required reach in t : ¢ Requires: ¾ ¾ small intrinsic beam angular spread at IP insensitive to transverse vertex smearing Parallel–to–point focusing large effective lever arm Leff detectors close to the beam, at large distance from IP LHCC Open Session - May 12 2004 7

Experimental Technique ¢ Independence of vertex position: y* IP parallel-to-point focusing ydet y *

Experimental Technique ¢ Independence of vertex position: y* IP parallel-to-point focusing ydet y * Leff ¢ Limit on minimum |t|min: ¢ The main potential difficulties are all derived from the above ¾ Leff, y large detectors must be far away form the IP potential interference with machine hardware ¾ small tmin ¡ * large special optics ¡ small emittance ¡ small nσ halo under control and the detector must be close to the beam LHCC Open Session - May 12 2004 8

Roman Pot Locations One Roman Pot Station per side on left and right from

Roman Pot Locations One Roman Pot Station per side on left and right from IP 1 Each RP station consists of two Roman Pot Units separated by 3. 4 m, centered at 240. 0 m from IP 1 LHCC Open Session - May 12 2004 9

Very high * (2625 m) optics ¢ Solution with following characteristics ¢ At the

Very high * (2625 m) optics ¢ Solution with following characteristics ¢ At the IP y, d = 119 m, y, d = 126 m x, d = 88 m, x, d = 109 m (for N =1 m rad) D [m] ¢ At the detector β [m] = 2625 m * = 610 m , * = 0. 23 rad ¢ Detector at 1. 5 mm or 12 tmin =0. 0004 Ge. V 2 ¢ Smooth path to injection optics exists ¢ All Quads are within limits ¢ Q 4 is inverted w. r. t. standard optics! Endorsed by LTC Compatible with TOTEM optics see LEMIC minutes 9/12/2003 LHCC Open Session - May 12 2004 10

Emittance ¢ Emittance of ~1× 10– 6 m rad needed to reach Coulomb region

Emittance ¢ Emittance of ~1× 10– 6 m rad needed to reach Coulomb region ¢ Nominal LHC emittance: 3. 75× 10– 6 m rad ¢ Emittances achieved during MD’s in SPS: ¾ Vertical plane 1. 1× 10– 6 m rad and Horizontal plane 0. 9× 10– 6 m rad for 7 x 1010 protons per bunch ¾ 0. 6 -0. 7× 10– 6 m rad obtained for bunch intensities of 0. 5× 1010 protons per bunch ¢ However ¾ Preserve emittance into LHC means that injection errors must be controlled (synchrotron radiation damping might help us at LHC energy) ¾ 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 Best parameter space from beam tuning sessions LHCC Open Session - May 12 2004 11

Beam Halo: limit on nσ ¢ Beam halo is a serious concern for Roman

Beam Halo: limit on nσ ¢ Beam halo is a serious concern for Roman Pot operation ¢ it determines the distance of closest approach dmin of (sensitive part of) detector: nσ = dmin/σbeam: 9 ≤ nσ ≤ 15 (RA LHC MAC 13/3/03) nσ-reach? ¢ Expected halo rate (43 bunches, Np=1010, εN = 1. 0 μm rad, nσ=10): 6 k. Hz LHCC Open Session - May 12 2004 12

Requirements for Roman Pot Detectors ¢ “Dead space” d 0 at detector’s edge near

Requirements for Roman Pot Detectors ¢ “Dead space” d 0 at detector’s edge near the beam : d 0 ≲ 100 (full/flat efficiency away from edge) ¢ Detector resolution: d = 30 m ¢ Same d = 10 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 the experiment DAQ ¢ Other: ¾ simplicity, cost ¾ extent of R&D needed, time scale, manpower, … ¾ issues of LHC safety and controls LHCC Open Session - May 12 2004 13

Roman Pot Detectors ¢ Square scintillating fibres ¾ Kuraray 0. 5 mm × 0.

Roman Pot Detectors ¢ Square scintillating fibres ¾ Kuraray 0. 5 mm × 0. 5 mm fibers ¾ 10 layers per coordinate ¾ 50 μm offset between layers scintillator plate for triggering y-measurement detector x-measurement detector halo inter calibration planes (well away from beam) LHCC Open Session - May 12 2004 14

Trigger - readout Photodetectors ¢ Multi. Anode PMT, or Avalanche Photodiodes Trigger ¢ Basic

Trigger - readout Photodetectors ¢ Multi. Anode PMT, or Avalanche Photodiodes Trigger ¢ Basic trigger menu: ¾ left-side (right-side) up (down) detector right-side (left-side) down (up) detector Read out ¢ The RP detector and LUCID pipelines can be made sufficiently deep to avoid any latency problems ¢ If additional hard scattering veto is required, we can read the whole ATLAS but the L 1 trigger latency has to be respected ¾ this may require special timing for the luminosity runs LHCC Open Session - May 12 2004 15

Detector Performance Simulations First simulation results ¢ strip positioning σfiber ≈ 20 μm ¢

Detector Performance Simulations First simulation results ¢ strip positioning σfiber ≈ 20 μm ¢ light and photo-electron yield: Npe = <d. E/dx> dfiber (dnγ/d. E) εA εT εC g. R εQ εd Baseline detector SCSF-38 (l=428 nm) 0. 5 mm square MAPMT Alternative configuration SCSF-3 HF (l=530 nm) 0. 5 mm square GM-APD 200 ke. V/mm active thickness of fiber 0. 48 mm scintillation light yield 8. 3 / ke. V <d. E/dx> specific energy loss of a MIP in scintillator dfiber dng/d. E A geometrical acceptance 0. 042 T attenuation in fiber 0. 85 C coupling efficiency fiber/photodetector 0. 80 g. R Gain due to reflection from rear end 1. 4 e. Q quantum efficiency photodetector 0. 18 0. 15 (0. 3 in future ? ) d detection efficiency (electronics/DAQ) 0. 85 Photoelectron yield 4. 9 4 (8 in future ? ) Npe LHCC Open Session - May 12 2004 16

Luminosity Performance Simulations ¢ Baseline optics, with baseline detector resolutions ¢ Smearing of hits

Luminosity Performance Simulations ¢ 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), ¾ vertical coordinate: σ(y) = 0. 23 μrad × 559 m = 127 μm vertical smearing reduces acceptance near the detector edge ¾ horizontal coordinate: σ(x) = 0. 23 μrad × 143 m 0. 42 mm × 0. 168 = 32 μm 71 μm = 87 μm Note: ¡ taking the combination of left and right arms, part of the vertex smearing drops out ¡ there is no detector edge in x LHCC Open Session - May 12 2004 17

Simulated Elastic Scattering Inner ring: t = -0. 0007 Ge. V 2 Outer ring:

Simulated Elastic Scattering Inner ring: t = -0. 0007 Ge. V 2 Outer ring: t = -0. 0010 Ge. V 2 ¢ Reconstruct θ*: LHCC Open Session - May 12 2004 18

Simulated d. Nel/dt and simple fit Event generation: ¢ 5 M events generated corresponding

Simulated d. Nel/dt and simple fit Event generation: ¢ 5 M events generated corresponding to ~90 hr at L 1027 cm-2 s-1 ¢ NO systematics on beam optics! ¢ Only 1 Roman Put unit/arm Simple fit ¢ range for fitting: ¾ 0. 00056 < |t| < 0. 030 Ge. V 2 ¢ ~4 M events “measured” for d. N/dt LHCC Open Session - May 12 2004 19

Luminosity Monitoring ¢ We propose a dedicated detector- LUCID “LUminosity measurement using Cerenkov Integrating

Luminosity Monitoring ¢ We propose a dedicated detector- LUCID “LUminosity measurement using Cerenkov Integrating Detector” ¢ Bundle of projective Cerenkov tubes around the beam pipe LHCC Open Session - May 12 2004 20

Luminosity monitoring LUCID ¢ There are 200 gas filled (C 4 F 10) Cerenkov

Luminosity monitoring LUCID ¢ There are 200 gas filled (C 4 F 10) Cerenkov tubes per end. ¢ Use Al lined Carbon fibre Cerenkov tubes for heat resistance. ¢ The tubes are deployed in 5 layers of increasing diameter ¾ each row has 40 tubes. ¢ Tube orientation allows some position sensitivity LHCC Open Session - May 12 2004 21

Luminosity monitoring LUCID Services In/Out To UXA PMTs LUCID ~17< |z| <~18. 5 m

Luminosity monitoring LUCID Services In/Out To UXA PMTs LUCID ~17< |z| <~18. 5 m 5. 4< | | <6. 1 Inner radius of LUCID ~8 cm, outer radius ~16 cm LHCC Open Session - May 12 2004 22

Luminosity monitoring LUCID ¢ Sensitive to right particles -- Much more light from primary

Luminosity monitoring LUCID ¢ Sensitive to right particles -- Much more light from primary particles than secondaries & soft particles: ¾ shorter paths (secondaries moving across detector) ¾ Cerenkov thresholds ¢ No Landau fluctuations for Cerenkov Light emission. . expect a narrow single particle peak (SPP) ¢ Excellent amplitude resolution ¾ one can count particles (even in the same tube) ¾ no saturation ¢ Excellent time resolution (~140 ps measured at CDF) ¾ distinguish number of interactions by time (follow bunches). ¢ Radiation hard, low mass ¢ The LUCID approach has been tested at CDF ¢ Linear relationship between luminosity and tracks LHCC Open Session - May 12 2004 23

CDF luminosity monitor CLC LHCC Open Session - May 12 2004 24

CDF luminosity monitor CLC LHCC Open Session - May 12 2004 24

Scheduling ¢ ATLAS considers the dedicated runs for the luminosity measurement as a second

Scheduling ¢ ATLAS considers the dedicated runs for the luminosity measurement as a second priority, likely just following the initial years of running, when the LHC operation is well understood ¢ Nevertheless, if early luminosity runs will be scheduled, ATLAS will put its best effort to participate and have the luminosity detectors and all the installation completed ¢ Independently of the year of data-taking, we would like to factor out the installation of the Roman Pot Units with the detectors, and resolve all the interface issues with the LHC machine as soon as possible in order to follow the LHC machine installation in the tunnel and minimize any potential impact ¢ ATLAS is prepared to submit an ECR with all the installation details already in May 2004 should this Letter of Intent be encouraged to proceed LHCC Open Session - May 12 2004 25

ECR - Interface issues with LHC machine ¢ ATLAS plans to use the same

ECR - Interface issues with LHC machine ¢ ATLAS plans to use the same RP unit design as TOTEM therefore for the major part of the interface issues the same solutions will be adopted ¢ The ECR will be focused on the issues concerning the RP installation at IP 1, namely: ¾ Layout modification for the DQR location to accommodate the two RP units ¡ displace DQR-2 by 100 mm and DQR-3 by 200 mm towards Q 6 ¾ Installation of a polarity switch for the Q 4 quadrupole ¾ Modification in the vacuum tube for the one beam to allow openings for the RPs ¡ special vacuum pieces and flanges to connect to the RPs ¡ until the RP units are actually installed, the space will be filled with vacuum pipes ¾ Cable routing and space in the trays between the RP location and the USA 15 The above has been discussed with the relevant experts and represents minor modifications LHCC Open Session - May 12 2004 26

Cost Estimates & Participants Item Cost (KCHF) LUCID Roman Pot system Cerenkov tubes 68.

Cost Estimates & Participants Item Cost (KCHF) LUCID Roman Pot system Cerenkov tubes 68. 0 Quartz fibers 62. 0 Readout 62. 0 Infrastructure 125. 0 R&D 62. 0 Total 379. 0 RP units 220. 0 Q 4 polarity inverters 60. 0 Scintillating fiber detectors 175. 0 Readout 650. 0 Integration 75. 0 R&D 100. 0 Total 1280. 0 LHCC Open Session - May 12 2004 Participating institutes: (as a subsystem, fully part of the ATLAS collaboration) University of Alberta CERN Ecole Polytechnique Institute of Physics Academy of Science, Czech Republic University of Manchester University of Montreal University of Texas University of Toronto University of Valencia SUNY Stony Brook 27

Conclusion ATLAS Baseline ¢ Absolute Luminosity measurement using Coulomb Normalization ¾ the CN normalization

Conclusion ATLAS Baseline ¢ Absolute Luminosity measurement using Coulomb Normalization ¾ the CN normalization is very challenging but seems attainable ¡ critically dependent on control of the beam and backgrounds ¾ Roman Pot detectors: no show stoppers ¢ Luminosity monitoring using LUCID ¾ LUCID prototyping is well underway ¢ Cross checks with: ¾ ¾ ¾ W/Z rates double photon exchange production of muon pairs elastic slope of d. N/dt|t=0 plus machine L machine parameters alone others… ¢ Experience with this may prepare us for expanding towards a Forward Physics program with ATLAS as a possible future upgrade LHCC Open Session - May 12 2004 28

¢Back up slides LHCC Open Session - May 12 2004 29

¢Back up slides LHCC Open Session - May 12 2004 29

Summary on emittance and beam halo issues “Looks feasible but no guarantees can be

Summary on emittance and beam halo issues “Looks feasible but no guarantees can be given” However, if we don’t reach the Coulomb region the effort is not in vain we can still: ¢ Use tot as measured by TOTEM/CMS and get the luminosity by measuring elastic scattering in a moderate t-range( -t=0. 01 Ge. V 2 ) and use the Optical theorem for the rest ¢ Use the luminosity measured by machine parameters and again via the Optical theorem get tot and all other cross sections relative to tot with a factor 2 better precision than from the machine parameters LHCC Open Session - May 12 2004 30

Luminosity transfer 1027 -1034 cm-2 sec-1 ¢ Bunch to bunch resolution we can consider

Luminosity transfer 1027 -1034 cm-2 sec-1 ¢ Bunch to bunch resolution we can consider luminosity / bunch ~ 2 x 10 -4 interactions per bunch to 20 interactions/bunch ¢ Required dynamic range of the detector ~ 20 ¢ Required background < 2 x 10 -4 interactions per bunch ¾ main background from beam-gas interactions ¾ Dynamic vacuum difficult to estimate but at low luminosity we will be close to the static vacuum. ¾ Assume static vacuum beam gas ~ 10 -7 interactions /bunch/m ¾ We are in the process to perform MC calculation to see how much of this will affect LUCID LHCC Open Session - May 12 2004 31

LUCID Performance Simulations ¢ Simulation of a 20 Ge. V muon incident along the

LUCID Performance Simulations ¢ Simulation of a 20 Ge. V muon incident along the axis of a LUCID Cerenkov tube gives ~320 photons and ~230 photons are collected at the Winston cone exit. ¢ PYTHIA-6 events generated with increasing numbers of pileup ¢ Perfect linearity, with little sensitivity for secondaries LHCC Open Session - May 12 2004 32

Statement of the machine group on the feasibility/possible problems about chosen beam optics ?

Statement of the machine group on the feasibility/possible problems about chosen beam optics ? LHCC Open Session - May 12 2004 33

BPM nearby the RPs For protection and optimization it might be good to install

BPM nearby the RPs For protection and optimization it might be good to install beam position monitors in the near of the RP station. Has this been considered ? ¢ Certainly a good possibility we should study in detail ¢ The BPM's can help in a first setting up of the beam ¾ note that there are BPMs (cold) next to each quadrupole at ~10 m distance from the RPs ¢ However for the final alignment with high precision we must rely upon data from our own detectors in the RP (overlap detectors) ¢ Given our space constraints we have to carefully evaluate the additional complexity that will be introduced, including cost LHCC Open Session - May 12 2004 34