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TOTEM: Prospects for Total Cross-Section and Luminosity Measurements

TOTEM: Prospects for Total Cross-Section and Luminosity Measurements. M. Deile (CERN) for the TOTEM Collaboration 13.01.2011. ultimate goal: ± 1% (2011: ± 3%). Luminosity-Independent Method based on the Optical Theorem.

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TOTEM: Prospects for Total Cross-Section and Luminosity Measurements

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  1. TOTEM: Prospects for Total Cross-Section and Luminosity Measurements M. Deile (CERN) for the TOTEM Collaboration 13.01.2011 ultimate goal: ±1% (2011: ±3%) Mario Deile –

  2. Luminosity-Independent Method based on the Optical Theorem • measure the inelastic event rate Ninel(with forward tracking chambers); • measure the elastic event rate Nel(detect surviving protons with Roman Pots) • and extrapolate the cross-section dNel/dt to t = 0; • take r = Re f(0) / Im f(0)[f(0) = forward elastic amplitude] • from theory, e.g. COMPETE extrapolation: • later: try to measure r at b* ~ 1 km: elastic scattering in the Coulomb-nuclear interference region • Requirements for this method: • Beam optics providing proton acceptance at low |t| in the Roman Pots • Detector coverage at high |h| • Trigger capability for all detector systems Mario Deile –

  3. The TOTEM Detector Setup operational in 2010 installation in progress now installed operational in 2010 3.1  h  4.7 5.3  h  6.5 T1 T2 T1 “-” arm during installation Mario Deile – p. 3

  4. Acceptance for Inelastic Events • Uncertainties in inelastic cross sections large: • non-diffractive min. bias (MB): 40  60 mb • single diffraction (SD): 10  15 mb • double diffraction (DD): 4  11 mb 5 4 PHOJET s = 7 TeV 3 2 T1 T1 T2 T2 1 h Accepted event fractions: Mario Deile – p. 4

  5. Measurement of the Inelastic Rate Ninel Acceptance single diffraction A [1 / 2GeV] M [GeV] Loss at low diffractive masses M simulated extrapolated dN/d(1/M2) [1 / GeV-2] detected 1/M2 [GeV-2] Trigger Losses at s = 7 TeV, requiring 3 tracks pointing to the IP M • Correction for trigger losses: • Extrapolation of the mass spectrum: • fit dN/dM2 ~ 1/Mn with n ~ 2 • uncertainty depends on the purity of the diffractive • event sample used for the extrapolation • (e.g. errors from minimum bias events misidentified • as diffractive events) • Independent handle on low-mass diffraction: • At b* = 90 m the protons for all diffractive masses • are visible (for |t| > ~10-2 GeV2). •  total uncertainty on Ninel : 1.0 mb (1.4 %). Mario Deile –

  6. Roman Pot System: Leading Proton Detection scattering angle q Horizontal Pot Vertical Pot BPM Mario Deile – p. 6

  7. Elastic Scattering exponential region Elastic Scattering Acceptance at s = 7 TeV 7 TeV RP220: detectors at 10 s from beam centre b* = 3.5m b* = 1540m b* = 90m |t50| = 0.024 GeV2 (eN = 3.75 mm) squared 4-momentum transfer t  - p2 q2 |t50| = 0.0008 GeV2 (eN = 1 mm) Mario Deile –

  8. Preliminary t-distribution  84K elastic scattering candidate events TOTEM special run (~ 9 nb-1) s = 7 TeV * = 3.5 m RPs @ 7  (V) and 16  (H) “Raw” distribution: - No smearing corrections - No acceptance corrections - No background subtraction Syst. error sources under study: alignment, beam position and divergence, background, optical functions, efficiency, … 0.7 GeV2 Mario Deile –

  9. Elastic Scattering at low |t| Exponential Slope B(t) Cross-section 7 TeV b* = 1540 m b* = 90 m fit interval with detectors at 10 s: b* = 1540 m: |t50| = 0.0008 GeV2 b* = 90 m: |t50| = 0.024 GeV2 best parameterisation: B(t) = B0 + B1t + B2t2 Mario Deile –

  10. Extrapolation to the Optical Point (t = 0) at b* = 90 m Study at 14 TeV, eN = 3.75 mm rad (extrapol. - model) / model in d/dt |t=0Statistical extrapolation uncertainty 14 TeV 14 TeV upper bound: 0.25 GeV2 ∫ L dt = 2 nb-1 • Common bias due to beam divergence (angular spread flattens dN/dt distribution): -2% @14 TeV  -3% @7 TeV, can be corrected. • Spread between most of the models: ±1% (Islam model needs different treatment, can be distinguished at larger |t|) • Systematic error due to uncertainty of optical functions:± 1.5 % , assuming dL/L = 1% • Different parameterisations for extrapolation (e.g. const. B, linear continuation of B(t)): negligible impact Mario Deile –

  11. Acceptance versus Energy and Detector Approach • Advantage of 7 or 8 TeV w.r.t. 14 TeV: |t50| reduced  shorter extrapolation • reduced model dependence • reduced statistical uncertainty (eN = 3.75 mm rad) lower E x 0.6 closer approach x 0.4 (eN = 1 mm rad) Mario Deile –

  12. Desired Scenario for Runs at b* = 90 m (subject to discussions with MPP and collimation experts and to commissioning progress / surprises) 4 special runs (assuming E = 4 TeV): Dominated by systematics  small RP distance much more important than luminosity ! Crucial: good knowledge of the optical functions Aim: contribution from optical functions not larger than angle resolution limit from beam divergence dLy / Ly < 1.1 % or dby / by < 1.1 % dLx / Lx < 0.2 % or dbx / bx < 0.2 % (but our error estimates are based on 1%: sufficient) Mario Deile –

  13. Combined Uncertainty in tot At b* = 90 m, s = 7 TeV : • Extrapolation of elastic cross-section to t = 0: ± 2 % • Total elastic rate (strongly correlated with extrapolation): ± 1 % • Total inelastic rate: ± 1.4 % • Error contribution from (1+r2) using full COMPETE error band dr/r = 33 % (very pessimistic): ± 1.2 %  Total uncertainty in stot including correlations in the error propagation: ± 3 % Slightly worse in L (~ total rate squared!) : ± 4 % Mario Deile –

  14. Outlook: Extrapolation with the Ultimate Optics (b* = 1540 m) [Cahn, Kundrát, Lokajíček] |t50| = 0.0008 GeV2 for RP window at 10 sgood lever arm for choosing a suitable fitting function for the extrapolation to t = 0. Complication: Coulomb-nuclear interference must be included: 14 TeV !!! 7 TeV b* = 1540m where and b(t) is a function of fC(t) and fH(t). For most models: extrapolation within ± 0.2 %. Islam model needs different treatment; can be distinguished in the visible t-range. Difficulties: - very-high-b* optics at 7 or 8 TeV still to be developed (b*=1540m exists only for 14 TeV). - additional magnet powering cables needed. Mario Deile –

  15. Outlook: Measurement of r in the Coulomb-nuclear Interference Region? Aim: get also the last ingredient to stot from measurement rather than theory. (eN = 3.75 mm rad) (eN = 1 mm rad) • might be possible at 8 TeV with RPs at 8 s • incentive to develop very-high-b* optics before reaching 14 TeV !E.g. try to use the same optics principle as for 90m and unsqueeze further. Mario Deile –

  16. Summary TOTEM is ready for a first stot and luminosity measurement in 2011 with b* = 90m using the Optical Theorem. Expected precision: ~3% in stot , ~4% in L Wish: start soon with the development of the b* = 90m optics to have enough time for learning. Desired running conditions: low beam intensity, small RP distance to the beam Longer term: Measurement at the 1% level with very-high-b* optics (~1 km); might give access to the r parameter if the energy is still low (s ~ 8 TeV); needs optics development work. Mario Deile –

  17. Mario Deile –

  18. Backup Mario Deile –

  19. Elastic Scattering:  =  f(0) /  f(0) COMPETE [PRL 89 201801 (2002)] Preferred fit predicts: E710/E811: r = 0.135 ± 0.044 asymptotic behaviour:  1 / ln s for s   Mario Deile –

  20. Elastic Scattering from ISR to LHC Coulomb - nuclear interference  r “Pomeron” exchange e– B |t| ds / dt [mb / GeV2] B(s) = Bo + 2aP’ ln(s/so)  20 GeV-2 at LHC diffractive structure E710/811, CDF UA4, CDF pQCD  1/ |t|8 UA4 pp 14 TeV BSW model Block model 0 1 2 -t [GeV2] -t [GeV2] 546 GeV:CDF:0.025 < |t| < 0.08 GeV2 : B = 15.28 ± 0.58 GeV-2 (agreement with UA4(/2)) 1.8 TeV: CDF:0.04 < |t| < 0.29 GeV2 : B = 16.98 ± 0.25 GeV-2 E710: 0.034 < |t| < 0.65 GeV2 : B = 16.3 ± 0.3 GeV-20.001 < |t| < 0.14 GeV2 : B = 16.99 ± 0.25 GeV-2 , r = 0.140 ± 0.069E811: 0.002 < |t| < 0.035 GeV2 : using B from CDF, E710: r = 0.132 ± 0.056 1.96 TeV:D0: 0.9 < |t| < 1.35 GeV2 Mario Deile –

  21. Relative Luminosity Measurement • For running conditions where measurement via Optical Theorem impossible:relative measurementafter a prior absolute calibration at b* = 90 m or 1540 m. • Examples: • partial inelastic rates, e.g. (T2 left) x (T2 right): robust against beam-gas background • for running conditions with pileup: count zero-events, e.g. failing (T2 left) x (T2 right): • e.g. P(n=0) = 15 % @ L=1033 cm-2s-1 , 2808 bunches Also usable for continuous luminosity monitoring (to be studied further). Mario Deile –

  22. Measurements of stot Conflicting Tevatron measurements at 1.8 TeV: E710: stot = 72.8 ± 3.1 mb E811: stot = 71.42 ± 2.41 mb CDF: stot = 80.03 ± 2.24 mb Disagreement E811–CDF: 2.6 s Best combined fit by COMPETE: But models vary within (at least) Mario Deile –

  23. TOTEM Detector Configuration T1:3.1 < h < 4.7 T2: 5.3 <h< 6.5 CMS HF T1 10.5 m T2 ~14 m (RP2) RP1 RP3 147 m (180 m) 220 m Symmetric experiment: all detectors on both sides! Mario Deile –

  24. Level-1 Trigger Schemes RP CMS RP T1/T2 p p p Always try to use 2-arm coincidence to suppress background. Elastic Trigger: s 30 mb Single Diffractive Trigger: s 14 mb Double Diffractive Trigger: s 7 mb Central Diffractive Trigger (Double Pomeron Exchange DPE) s 1 mb Non-diffractive Inelastic Trigger: s 58 mb stot 110 mb p p Mario Deile –

  25. Acceptance Losses and Selection Losses Mario Deile –

  26. Detection of Leading Protons b = 0.5m - 2m vertical Si detector y [mm] horizontal Si detector 10 vertical Si detector x [mm] x(mm)‏ Transport equations: TOTEM: Proton Acceptance in (t, x): (contour lines at A = 10 %) RP220 (x*, y*): vertex position (x*, y*): emission angle x = p/p x resolved Example: Hit distribution @ TOTEM RP220 with b* = 90m t ~ -p2 * 2 Optics properties at RP220: Mario Deile –

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