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The experiment

The experiment. at LHC. Stefano Lami INFN Pisa on behalf of the TOTEM Collaboration. jet. b. b. jet. TOTEM Physics Overview. Total cross-section. Ultimately ~1% precision. Elastic Scattering. Over a wide t range. Forward physics.

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The experiment

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  1. The experiment at LHC • Stefano Lami • INFN Pisa • on behalf of the • TOTEM Collaboration

  2. jet b b jet TOTEM Physics Overview Total cross-section Ultimately ~1% precision Elastic Scattering Over a wide t range Forward physics Diffraction: soft and hard

  3. Physics Motivation (1) Dispersion relation fit Best fit TOTpp rises as ~ ln2 s • Predictions at 14 TeV: 90-130 mb • Available data not decisive • Aim of TOTEM: ~1% accuracy It will distinguish between several models COMPETE Collaboration fits all available hadronic data and predicts: LHC (14TeV): [PRL 89 201801 (2002)]

  4. Physics Motivation (2) … Islam Model: Elastic scattering (diffraction in general) • theoretical understanding not complete • number of approaches: Regge, geometrical, eikonal,QCD, . . . ⇒ rather incompatible predictions • intimately related to the structure of proton b* = 1540 m b* = 90 m b* = 2 m |t| Big uncertainties at large |t|: Models differ by ~ 3 orders of magnitude! 3-gluon exchange at large |t|: TOTEM will measure the 10-3< | t | ~(pq)2 <10 GeV2range with good statistics … and more

  5. p-p Interactions  = -lntg/2 x= Dp/p Non-diffractiveDiffractive Colour exchange Colourless exchange with vacuum quantum numbers dN / d  = exp (-) dN / d  = const  = -ln Incident hadrons acquire colour and break apart Incident hadrons retain their quantum numbers remaining colourless GOAL: understand the QCD nature of the diffractive exchange

  6. Elastic Scattering Single Diffraction M Double Diffraction Double Pomeron Exchange M Dominant Event Classes in p-p Collisions f ( = -lntg/2) ~65 mb~ 58 % h ~30mb ~10mb ~7 mb ~ 42 % Processes with large cross-sections ! ~1 mb << 1 mb Indicative cross-sections at 14 TeV

  7. TOTEM Experimental Apparatus • Physics requirements: forward proton detectors and large pseudorapidity coverage Roman Pots & tracking telescopes T1and T2 (inelastic evts + Vtxreco) • all detectors symmetrically on both sides of IP5 • all detectors L1 trigger capable T1: 3.1 < |h| < 4.7 T2: 5.3 < |h| < 6.5 Stefano Lami

  8. TOTEM Coverage Courtesy by Jan Kaspar Stefano Lami

  9. TOTEM Roman Pots Protons at few rad angles w. RPs at 10 + dfrom beam `Edgeless’ detectors to minimize d(sbeam~ 80 mm at RP220 w. b*=1540m) Each RP station has 2 units, 4m apart Each unit has 2 vertical insertions (‘pots’) + 1 horizontal Beam Thin window 150mm • Ongoing Detector Installation: • RP220 (147) fully (partially) equipped by June HALF OF THE RP STATION 10 silicon detector planes pitch 66mm Horizontal RP Vertical RP BPM Overlap for alignment

  10. T1 Telescope 3m • 1 station per side of IP5 • • each station: 5 planes • • each plane: 6 trapezoidal CSC detectors • • L1 trigger capability • • Cathode Strip Chamber detector • – 3 coordinates: 2 cathode strips, 1 anode wire • – Resolution ≈ 1 mm • • Primary Vtxreconstruction to discriminate • background (not beam-beam events) for the measurement of Ninel • Multiplicity measurement Installation foreseen for May/June: One arm eventually in September ¼ of T1 Stefano Lami

  11. T2 Telescope • 1 station on each side of IP5 • • each station: two halves (left/right) • • each half: 10 (5×2 back-to-back mounted) GEM detectors • • L1 trigger capability • • Triple Gas Electron Multiplier detectors • – double readout: strips (radial) and pads (coarse radial and azimuthal) • – resolution: radial 100 mm, azimuthal 0.8◦ • Vtxreco. + Multiplicity measurement Ongoing installation: fully done by May Stefano Lami

  12. TOTEM Physics and LHC Optics cross section luminosity • Feasible physics depends on running scenarios: • luminosity • beam optics (β*) • acceptance of proton detectors • precision in the measurement of scattering angle / beam divergence stot(~1%), low t elastic, stot(~5%), low t elastic, high t elastic, soft diffraction (semi)-hard diffraction hard diffraction EARLY mbb nb *(m)1540 902 0.5 L (cm2 s1) 1028 10301031 1033 TOTEM runsStandard runs Stefano Lami

  13. Details on Optics Proton transport equations: x = Lxx* + vxx* + D y = Lyy* + vyy * Optical functions: - L(effective length); - v(magnification); -D(machine dispersion) Describe the explicit path of particles through the magnetic elements as a function of the particle parameters at IP. Define t and  range (Acceptance)  = p/p;t = tx + ty; ti ~ -(pi*)2 (x*, y*): vertex position at IP (x*,y*): emission angle at IP Example Same sample of diffractive protons at different * - low *: p detected by momentum loss () - high *: p detected by trans. momentum (ty)

  14. Diffractive Proton Acceptance in (t, x): (contour lines at A = 10 %) RP220 Proton Acceptance RP 220m b*=1540 m Acceptance Detector distance to the beam: 10+0.5mm b*=90 m x resolved b = 0.5m - 2m b*=2 m -t = 0.01 GeV2 -t = 0.002 GeV2 * = 1540 m Beam 0.002 0.06 4.0 log(-t / GeV2) Low b*: see protons 0.02<x<0.2 or 2< |t| < 10 GeV2 Optics properties at RP220: 90m: see all protons 0.03 < |t| < 10 GeV2 Elastic Scattering Det. dist. 1.3 mm 6 mm

  15. Total Cross-Section and Elastic Scattering at low |t| Related by the Optical Theorem: Coulomb scattering Coulomb-Nuclear interference Nuclear scattering • a = fine structure constant • = relative Coulomb-nuclear phase G(t) = nucleon em form factor = (1 + |t|/0.71)-2 • r = Re/Im f(pp) TOTEM Approach: Measure the exp. slope B in the t-range 0.002 - 0.2 GeV2 , extrapolate d/dtto t=0,Measure total inelastic and elastic rates (all TOTEM detectors provide L1 triggers):

  16. simulated extrapolated Acceptance single diffraction Loss at low diffractive masses M detected Measurement of the Inelastic Rate • Inelastic double arm trigger: robust against background, inefficient at small M • Inelastic single arm trigger: suffers from beam-gas + halo background, best efficiency • Inelastic triggers and proton (SD, DPE): cleanest trigger, proton inefficiency to be extrapolated • Trigger on non-colliding bunches to determine beam-gas + halo rates. • Vertex reconstruction with T1, T2 to suppress background • Extrapolation of diffractive cross-section to large 1/M2 assuming ds/dM2 ~ 1/M2

  17. Combined Uncertainty in tot b* = 90 m 1540 m Extrapolation of elastic cross-section to t = 0: ± 4 % ± 0.2 % Total elastic rate (strongly correlated with extrapolation): ± 2 % ± 0.1 % Total inelastic rate: ± 1 % ± 0.8 % (error dominated by Single Diffractive trigger losses) Error contribution from (1+r2) using full COMPETE error band dr/r = 33 % ± 1.2 % Total uncertainty in stot including correlations in the error propagation: b* = 90 m : ± 5 %, b* = 1540 m : ± (1 ÷ 2) % . Slightly worse in L(~ total rate squared!) : ± 7 % (± 2 %). Precise Measurement with b* = 1540 m requires: improved knowledge of optical functions alignment precision < 50 mm

  18. b*=0.5 - 3 b*=1540 b*=90 Log(M) (GeV)‏ • Early Physics with TOTEM (Ep = 5 TeV & b* = 3m) RP220 Acceptance: - elastic scattering 1 < |t| < 12 GeV2 - diffractive protons 0.02 < x < 0.18 - resolution: σ(ξ) <∼ 6 · 10−3 very similar to Ep = 7 TeV !! DPE Protons seen for > 2% Stefano Lami

  19. 1 p 2 p p2 p1 p X  p p p  Rapidity Gap -ln MX2 =  s  Very first measurements with low b* optics • Using horizontal RPs • dSD/dM(SD events with high mass) • 0.02 <  < 0.18  2 < M < 6 TeV • (M)/M = 24 % • dDPE/dM(DPE high mass) • 250 < M < 2500 GeV • (M)/M = 2.13.5 % • Using vertical RPs:high t elastic scattering • dElastic/dt 1 < |t| < 12 GeV2 (t)  0.2 |t| SD DPE Rapidity Gap -ln1 Rapidity Gap -ln2  MX2 = 12s p1 p2 X 

  20. T1/T2: charged multiplicity • Measurement of charged multiplicity for different processes • Important also for cosmic ray physics (e.g. for MC generator validation) • Identification and measurement of rapidity gaps Acceptance: 3.1 <  < 4.7 (T1) & 5.3 <  < 6.5 (T2) () = 0.04  0.2, no mom. &  info dNch/dh [1/unit] Particelle cariche per evento minimum bias single diffractive

  21. Conclusions • TOTEMready for LHC restart • will run under all beam conditions • will need high β∗ optics → will require β∗ = 90m optics for early running • Early measurements • low*: • - study of SD and DPE at high masses • - elastic scattering at high |t| • - measurement of forward charged multiplicity • * = 90 m: • - first measurement of tot(and L ) with a precision of ~ 5% (~ 7%) • - elastic scattering in a wide |t| range • - inclusive studies of diffractive processes • - measurement of forward charged multiplicity • Later • Measurement of total pp cross-section (and L ) with a precision • of 1÷2 % (2 %) with * = 1540 m (dedicated short runs). • Measurement of elastic scattering in the range 10-3< |t| < 10 GeV2 • An extensive CMS/TOTEM Physics Programme

  22. The experiment at LHC • Backup Slides

  23. I1 I2 current terminating ring biasing ring Al - + SiO2 p+ p+ n-type bulk cut edge Al n+ 50µm Si CTS edgeless detectors Proton detection down to 10beam, + d (beam, = 80  600 m) To minimize d : detectors with highly reduced inactive edge (”edgeless”) Planar technology + CTS (Current Terminating Structure) Micro-strip Si detectors designed to reduce the inefficiency at the edge. Inefficient edge ~ 50 m 50 µm

  24. Optics and Beam Parameters • * = 90 m ideal for early running: • fits well into the LHC start-up running scenario; • uses standard injection (b* = 11m)  easier to commission than 1540 m optics • wide beam  ideal for training the RP operation (less sensitive to alignment) • * = 90 m optics proposal submitted to the LHCC and well received.

  25. p Level-1 Trigger Schemes (L = 1.6 x 1028 cm-2 s-1) RP CMS RP T1/T2 p Elastic Trigger: Single Diffractive Trigger: Double Diffractive Trigger: Central Diffractive Trigger: Minimum Bias Trigger: p p p

  26. Extrapolation to the Optical Point (t = 0) at b*=90m (extrapol. - model) / model in d/dt |t=0Statistical extrapolation uncertainty ∫ L dt = 2 nb-1(5 hours @ 1029 cm-2 s-1) Common bias due to beam divergence : – 2 % (angular spread flattens dN/dt distribution) Spread between most of the models: ±1% Systematic error due to uncertainty of optical functions: ± 3% Different parameterizations for extrapolation tested (e.g. const. B, linear continuation of B(t)):negligible impact

  27. Diffractive scattering is a unique laboratory of confinement & QCD: A hard scale + protons which remain intact in the scattering process Forward protons observed, independent of their momentum losses b ‘wee’ parton cloud - grows logarithmically Elastic soft SD hard SD soft DPE hard DPE Lorentz contracted longitudinal view p jet jet Baryonic charge r~0.5fm ln s + b h Valence quarks in a bag with r ~ 0.2fm rapidity Soft Hard Diffractive Scattering large b small b p Rapidity gap survival & ”underlying” event structures are intimately connected with a geometrical view of the scattering - eikonal approach ! 29mb? 10mb? 1mb? • Soft processes: • Coherent • interactions • impact parameter • picture. Hard processes: Jet momenta correlated with the initial parton momenta. Cross sections are large Measure (M,,t)

  28. Possibilities of r measurement asymptotic behaviour: • 1 / ln s for s   pred. ~ 0.13 at LHC • Try to reach the Coulomb region and measure interference: • move the detectors closer to the beam than 10  + 0.5 mm • run at lower energy @ √s < 8 TeV

  29. Optical Functions (* = 90 m) L = (*)1/2 sin((s)) v = (/*)1/2 cos((s)) hit distribution (elastic) x = Lxx* + vxx* +D y = Lyy* + vyy*  Idea: Lylarge Lx=0 vy= 0 y(220) = /2 x(220) =  (parallel-to-point focussing on y) (m)‏ Optical functions: - L (effective length) - v (magnification) defined by  (betatron function) and  (phase advance); - D (machine dispersion)  describe the explicit path of particles through the magnetic elements as a function of the particle parameters at IP  = p/p (x*, y*): vertex position at IP (x*,y*): emission angle at IP t = tx + ty ti~ -(pi*)2

  30. Total multiplicity in T2 (5<<7) Forward Physics: VHE Cosmic Ray Connection p-p collisions @ LHC as predicted by generators tipically used to model hadronic showers generated by VHE CR Interpreting cosmic ray data depends on hadronic simulation programs. Forward region poorly known/constr. Models differ by factor 2 or more. Need forward particle/energy measurements e.g. dN/d, dE/d…

  31. Machine Induced Background T1/T2 Detectors: • beam-gas interactions: prel. ext. ~ 14 Hz per beam; ~ 19 KHz for MB events (MB = 80 mb, L = 2.4 ·1029 cm-2 s-1)  reduced by vertex reconstruction • muon halo (expected to be very small, not yet quantified) Roman Pot Detectors: • beam halo (protons out of design orbit): ext. (* = 1540m) ~ 12·10-4/bunch  reduced by requiring coincidence between RP arms • beam-gas interactions: ext. (* = 1540m) ~ 3·10-4/bunch after cuts  reduced with cuts on track angles and multiplicities • p-p collision (at IP) background: ext (* = 1540m) ~ (0.4  2)·10-4/bunch after cuts  reduced with cuts on track angles and hit multiplicities Tot. elast. evts ~ 3 KHz (L = 1029 cm-2 s-1); prel. expt. S/B ~ (0.6  0.7)·103

  32. Expected Radiation Dose in CMS/TOTEM In 1 year @ Linst = 1034 cm-2s-1 At RPs locations =>

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