Andrew Brandt – September Small-x 2003 – 1 Forward Physics with ATLAS Luminosity measurement for ATLAS Forward Physics with ATLAS D.Bocian, M.Boonekamp, A.Brandt, E.Brash, B.Caron, K.De, I.Efthymiopoulos, A.Faus-Golfe, P.Grafstrom, W.Guryn, M.Haguenauer, A.Hamilton, V.Hedberg, B.Jeanneret, J.Lamsa, C.Leroy, M.Lokajicek, G.Lolos, J-P.Martin, J.McDonald, Z.Papandreou, J.Pinfold, M.Rijssenbeek, E.Rosenberg, V.Simak, J.Soukup, H.Takai, V.Telnov, S.Tapprogge, W.Turner, S.Valkar, J.Velasco, A.Verdier, S.White, Y.Yao Thanks to: Michael Rijssenbeek for his slides!.

Andrew Brandt – September Small-x 2003 – 2 Luminosity Measurement Goals of the ATLAS Luminosity and Forward Physics Group: – Measure L with ≲ 2% accuracy – Study opportunities for diffractive physics with ATLAS Most important LHC characteristics: Luminosity L and CM Energy  s Luminosity measurement needed for: – Precision comparison with theory: e.g.:  bb,  tt,  W/Z,  jet, …,  H,  SUSY, … Cross section gives additional info – Precision comparison with other expt’s Luminosity from: – LHC Machine parameters (~5-10%) – Rates of well-calculable processes Dedicated Luminosity monitor: LUCID Relative precision on the measurement of  H  BR for various channels, as function of m H, at  L dt = 300 fb –1. The dominant uncertainty is from Luminosity: 10% (open symbols), 5% (solid symbols). (ATL-TDR-15, May 1999)

Andrew Brandt – September Small-x 2003 – 3 The ATLAS Detector Calorimetry: TAS R Barrel FCAL LUCID Tracking EndCap RP ZDC/TAN Diffraction/Proton Tagging Region y 109  -chambers Tracking: ATLAS has insufficient forward coverage for Total Rate measurement

Andrew Brandt – September Small-x 2003 – 4 Services In/Out To UXA PMTs Inner radius of LUCID ~7 cm, outer radius ~20cm ~17< |z| <~19 m 5.2< |  | <6.2 LUCID ATLAS – Luminosity Monitor ATLAS – Luminosity Monitor (J. Pinfold et al.)

Andrew Brandt – September Small-x 2003 – 5 Baseline Luminosity with CNI optics and Coulomb Normalization – Roman Pots at m – Scintillating strip detectors – Integrate into L1 Trigger LUCID for relative L monitoring Dedicated detector: bundle of projective Cerenkov cones: 5 layers of 40 tubes each low mass (6 kg), rad hard, quartz fiber readout  proof of principle: CLC at CDF! Cross checks with: – W/Z rates – Double photon exchange production of muon pairs – Elastic slope of dN/dt| t=0 plus machine L – others…

Andrew Brandt – September Small-x 2003 – 6 Extensions Diffractive cross sections – need RP pairs at intermediate locations: 90, 150 m – possibly forward calorimetry (TAS region) Large- |t| studies ( t in dip region and beyond) – need RP pairs at intermediate locations: 90, 150 m and smaller? DPE Higgs production… – need additional RP pairs at cryogenic locations: 330 m, 420 m – forward calorimetry (TAS region) might be attractive…

Andrew Brandt – September Small-x 2003 – 7 Coulomb Normalization of L Possible with very high β* (≥ 2500 m) optics (3500m now dead):  *=3500 m optics: A. Faus-Golfe, M. Haguenauer, J. Velasco, "Luminosity determination using Coulomb scattering at the LHC", presented at EPAC2002, June 2002 Normalization of the scattering amplitude at t  0 to the exactly calculable Coulomb amplitude: determines Luminosity L directly (and measure σ tot, ρ 0, b, … )  L / L ~ 2% (UA4 experience) Need closest possible approach to the beam Very-small-angle detectors in Roman Pots UA4 ?? LHC ISR RHIC Caveat: Phase and shape of F N (s,t) ! V.Kandrát, M.Lokajíček, PL B 544 (2002) 132.

Andrew Brandt – September Small-x 2003 – 8 Elastic Scattering in CNI Regime Need: t min  t CNI = 8  EM /  tot  7  10 –4 GeV 2 For ε N ≃1  10  m, k σ =15, t min = p B m p k σ 2 ε N  β* = 6  10 –4 GeV 2   * ≳ 2500 mε N ≃1  10  mk σ =15p B m p k σ 2 ε N  β* Detector: beam size (rms)  d = √(β d ε N  ), k σ  d ≳ 1.5 mm   d ≳ 80 m Roman Pot detectors between Q5-Q6 or Q6-Q7 (z m) – L eff  500 m,  =x /L eff, x ∈ {~1.5 mm, 25 mm}  t min = (p  min ) 2  4×10 –4 GeV 2 t max  (p  max ) 2  0.12 GeV 2 – Precision needed:  t/t ≃ 1‰   x  O (10  m)  need “self-calibrating” detectors –  L / L  2% Positions at z >300 m possible, but difficult 240 m 220 m dN/dt shape is crucial!

Andrew Brandt – September Small-x 2003 – 9 June Workshop on Roman Pot Detectors Parallel effort on RP detectors… Aim: focus on a (single?) appropriate technology for TOTEM/CMS and ATLAS or via the Luminosity and Forward Physics WG webpage

Andrew Brandt – September Small-x 2003 – 10 Requirements for Roman Pot Detectors “Dead space” d 0 at detector’s edge near the beam the beam: d 0 ≲ 100  m (full/flat efficiency away from edge) Detector resolution:  d = 30  m (10  m for p leading measurement) Same  d = 30  m (10  m) relative position accuracy between opposite detectors (e.g. partially overlapping detectors, …) Radiation hardness: 100 Gy/yr ( Gy/yr at full L ) Operate with the induced EM pulse from circulating bunches (shielding, …) Rate capability: O (Mhz) (40 MHz); time resolution  t = O (ns) Readout and trigger compatible with ATLAS TDAQ Other: – Simplicity, Cost – extent of R&D needed, time scale, manpower, … – issues of LHC safety and controls

Andrew Brandt – September Small-x 2003 – 11 Forward Physics Interest… Possible extension of ATLAS baseline physics: (Soft) Diffractive cross sections are large: –  el  26 mb,  SD   DD  13 mb (i.e. close to Pumplin bound!) – need only modest L Elastic and Total cross section measurements: –  tot,  elastic,   Re(f N )/Im(f N ), d  el /d t | N dip/structure in d  /d t at | t |≈0.5 GeV 2 ? Regge Pomeron & Odderon à la D&L transition to pQCD at | t | ≈ 8 GeV 2 – Roman Pots at m

Andrew Brandt – September Small-x 2003 – 12 Single and Double Diffraction Soft Pomeron Exchange: production of a forward colorless system… P exchange  Study of QCD Requires: – Accurate p leading measurement (    E <<0.10, small | t | ) – Forward & Central measurement – large range for rapidity gap detection… Needs additional forward coverage for case of ATLAS…  NO plans so far… IP p (ξ, t) M 2 = ξ s I P

Andrew Brandt – September Small-x 2003 – 13 Central (hard) Diffraction Double Pomeron Exchange: production of a central colorless bosonic system… Requires: – Accurate p leading measurement (    E <<0.10 ) – Central measurement, e.g. M = gg, H, … – Rapidity gap detection… Δη =  lnξ Simulations by S. Tapprogge et al., (Helsinki Group, preprint HIP-2003/EXP) Predictions for ex(in)clusive production: – “Calibrated” with TeVatron data – Predictions for LHC vary – Many talks/discussions on DPE at this conference:  DPE is THE main argument (towards the Hi-P T community) for doing Forward Physics at LHC! IP IP p (ξ 1 ) p (ξ 2 ) M 2 = ξ 1 ξ 2 s

Andrew Brandt – September Small-x 2003 – 14 Acceptance for Central Production Combined acceptance of:     All detectors m m ____ 215 m alone -  -  420 m alone without 308 / 338 m location: % loss in acceptance J.Kalliopuska, J.Mäki, N.Marola, R.Orava, K.Österberg, M.Ottela, S.Tapprogge; Helsinki Group, preprint HIP /EXP IP IP p (ξ 1 ) p (ξ 2 ) M 2 = ξ 1 ξ 2 s

Andrew Brandt – September Small-x 2003 – 15 Resolution on Central Mass Simple method: Use estimate from most distant station first 420 m 308 m 215 m ~ 4%  1% (small   large  ) Only exclusive process simulated J.Kalliopuska, J.Mäki, N.Marola, R.Orava, K.Österberg, M.Ottela, S.Tapprogge; Helsinki Group, preprint HIP /EXP

Andrew Brandt – September Small-x 2003 – 16 Measurement of Central Diffraction requires TWO additional very small angle detector pairs at very large distance: – 308/338 m, and 420 m; i.e. in COLD part of LHC needs to break into LHC cryostats! μStations? – accuracy: O (10 μm), and edge-less – Hi- L running: rad-hard detectors  need VERY strong physics arguments to convince LHC(C)!

Andrew Brandt – September Small-x 2003 – 17 Summary - Plans Luminosity Baseline: CNI measurement + LUCID – Coulomb normalization seems possible – intensive optics studies (with LHC/TOTEM – V. Avati) continue – Development of Roman Pots and Detectors (with LHC/TOTEM – M. Oriunno) Luminosity Monitoring: LUCID well underway: Other Monitors: – Double photon muon pair process: simulation underway… – W/Z production monitors: needs detailed study… Forward Physics: – Detailed simulation study is very promising (Helsinki preprint) – presumes Roman Pots for ATLAS (as for CNI; and beyond 300 m??) – Initial trigger studies for 215 m (just enough time) Preparing a draft internal proposal (Fall ’03) Next meeting at Orsay, Sept. 29 th ( Manchester in December)