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Forward Physics with the TOTEM  CMS at the LHC

This paper discusses diffractive scattering, elastic scattering, and other phenomena in high energy physics using data from TOTEM and CMS experiments at the LHC. It explores the connection between underlying event structures and a geometrical view of scattering.

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Forward Physics with the TOTEM  CMS at the LHC

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  1. Forward Physics with the TOTEMCMS at the LHC Risto Orava XIII ISVHECRI Pylos, Greece, 6-12 September 2004 R.Orava

  2. Diffractive Scattering probes the hadronic vacuum ‘wee’ partons  lns Elastic soft SDE hard SDE hard CD Longitudinal view p jet lnMX2 Baryonic charge distribution-soliton r  0.4fm jet Valence quarks in a bag with r  0.1fm lns h Rapidity gap survival & ”underlying” event structures are intimately connected with a geometrical view of the scattering - eikonal approach! p Soft diffractive scattering Hard diffractive scattering ’Glansing’ scattering of proton fields R.Orava

  3. sel - Models B32 at the black disc limit? The black disc limit reached at 108 GeV? 20 at the LHC, b2  1.6fm2 • Forward elastic slope shrinks • effective interaction radius of proton grows ( lns) The values of the slopes agree with the optical picture, i.e. with a fully absorbing disc of radius R for which B = R2/4. For a proton with R  1/mp (mp = p meson mass): B  13 GeV-2 However: Scattering on a black disc: sel/stot = ½, while the data (at s corresponding to B 13 GeV-2) gives sel/stot = 0.17... • the proton is semi-transparent • QCD colour transparency! Mixture of scattering states with different absorption probabilities is required for diffractive scattering to take place. 0.3 at the LHC  0.17

  4. stot - Models Total cross sections show universal rise at high energies: stot s0.08 However: - Global fits cannot discriminate between Regge theory ( se) and s-channel picture leading to  logs behaviour.

  5. Total Cross Section - TOTEM TOTEM

  6. Diffractive Cross Sections are Large Rel = sel(s)/stot(s) Rdiff = [sel(s) + sSD(s) + sDD(s)]/stot(s) 0.30 0.375 • sel  30% of stot at the LHC ? • sSD + sDD  10% of stot (= 100-150mb) at the LHC ?

  7. Photon - Pomeron interferencer Pomeron exchange (~exp Bt) diffractive structure pQCD Ldt = 1033 & 1037 cm2 Studying elastic scattering an soft diffraction requires special LHC optics. These will yield large statistics. ds/dt (mb/GeV2) high-t (* = 1540 m & 18 m)

  8. Additional forward coverage opens up new complementary physics program at the LHC • Investigate QCD:stot, elastic scattering, soft & hard diffraction, multi- rapidity gap events (see: Hera, Tevatron, RHIC...) - confinement. • Studies with pure gluon jets: gg/qq… - LHC as a gluon factory! • Gluon density at small xBj (10-6 – 10-7) – “hot spots” of glue in vacuum? • Gap survival dynamics, proton parton configurations (pp3jets+p) – underlying event structures • Diffractive structure: Production of jets, W, J/, b, t, hard photons, • Parton saturation, BFKL dynamics, proton structure, multi-parton scattering • Search for signals of new physics based on forward protons + rapidity gaps Threshold scan for JPC = 0++ states in: pp  p+X+p – spin-parity of X! (LHC as the e+e- linear collider in gg-mode.) • Extension of the ‘standard’ physics reach of the CMS experiment into the forward region • Luminosity measurement with DL/L 5 %

  9. As a Gluon Factory LHC could deliver... • О(100k) high purity (q/g = 1/3000) gluon jets with ET >50 GeV • in 1 year; gg-events as “Pomeron-Pomeron” luminosity monitor • Possible new resonant states, e.g. Higgs (О(100) H  bb events per • year with mH = 120 GeV, L=1034)*, glueballs, quarkonia 0++ (b ), • gluinoballs - background free environment (bb, WW & t+t- decays) • Invisible decay modes of Higgs (and SUSY)! • CP-odd Higgs • Squark & gluino thresholds well separated • - practically background free signature: multi-jets & ET • - model independence (missing mass!) [expect O(10) events for gluino/squark masses of 250 GeV] • - an interesting scenario: gluino as the LSP with mass window 25-35 GeV(S.Raby) • O(10) events with isolated high mass ggpairs, extra dimensions

  10. TOTEM Physics Scenarios Proton b* (m) rapidity gap L(cm-2s-1) inelastic activity jet g,e,m,t L, D++,... TOTEM & CMS TOTEM & CMS TOTEM & CMS elastic scattering 1540 18 beam halo? 1028 -1032 total cross section inelastic acceptance 1540 1028 -1033 soft diffraction 1540 200-400 gap survival L, K±, ,... 1029 -1031 mini-jets? 200-400 0.5 jet acceptance central & fwd W, Z, J/,... hard diffraction 1031 -1033 200-400 0.5 di-jet backgr central pair b-tag, g, J/,... DPE Higgs, SUSY,... 1031 -1033 trigger 200-400 0.5 mini-jets resolved? central & fwd jets di-leptons jet-g,... low-x physics 1031 -1033 exotics (DCC,...) p± vs. po multiplicity jet anomalies? leptons g’s,...? 0.5 1031 -1033 R.Orava

  11. Correlation with the CMS Signatures • e, g, m, t, and b-jets: • tracking: |h| < 2.5 • calorimetry with fine granularity: |h| < 2.5 • muon: |h| < 2.5 • Jets, ETmiss • calorimetry extension: |h| < 5 • High pT Objects • Higgs, SUSY,... • Precision physics (cross sections...) • energy scale: e & m 0.1%, jets 1% • absolute luminosity vs. parton-parton luminosity via • ”well known” processes such as W/Z production? R.Orava

  12. The Large Hadron Collider (LHC) pp collisions at 14 TeV LHC is built into 27 km the LEP tunnel • 5 experiments • 25 ns bunch spacing •  2835 bunches • 1011 p/bunch • Design Luminosity: • 1033cm-2s-1 -1034cm-2s-1 • 100 fb-1/year 23 inelastic events per bunch crossing CMS/TOTEM ALICE LHC-B ATLAS Planned Startup on Spring 2007

  13. The ‘Base Line’ CMS experiment • Tracking • Silicon pixels • Silicon strips • Calorimeters • PbW04 crystals • for Electro-magn. • Scintillator/steel • for hadronic part • 4T solenoid • Instrumented iron • for muon detection • Coverage • Tracking • 0 < || < 2.7 • Calorimetry • 0 < || < 5 A Hugeenterprise. Main program: EWSB, Searches Beyond SM physics at ~90o

  14. Total TOTEM/CMS acceptance (b*=1540m) RPs microstation at 19m? Important part of the phase space is not covered by the generic designs at LHC. TOTEM  CMS Covers more than any previous experiment at a hadron collider. Charge flow information value low: - bulk of the particles crated late in space-time leading protons leading protons Energy flow information value high: - leading particles created early in space-time TOTEM + CMS In the forward region (|h > 5): few particles with large energies/small transverse momenta.

  15. The Experimental Signatures: pp  p + X + p - vertex position in the transverse plane? b-jet Detector Detector CMS p2’ p1’ _ - b-jet - resolution in x ? -beam energy spread? Aim at measuring the: • Leading protons on both sides down to D  1‰ • - Rapidity gaps on both sides – forward activity – for |h| > 5 • Central activity in CMS

  16. Relative precision on the measurement of HBR for various channels, as function of mH, at Ldt = 300 fb–1. The dominant uncertainty is from Luminosity: 10% (open symbols), 5% (solid symbols). (ATL-TDR-15, May 1999) In addition: The signatures of new physics have to be normalized: The Luminosity Measurement Luminosity relates the cross sectionsof a given process by: L = N/s A process with well known, calculable and large s (monitoring!) with a well defined signature? Need complementarity. Measure simultaneously elastic (Nel) & inelastic rates (Ninel), extrapolateds/dt  0, assumer-parameter to be known: (1+r2) (Nel + Ninel)2 L = 16p dNel/dt|t=0 Ninel = ?  Need a hermetic detector. dNel/dtt=0 = ?  Minimal extrapolation to t0: tmin 0.01

  17. Inelastic cross section Event selection: • trigger from T1 or T2 (double arm o single arm) • Vertex reconstruction (to eliminate beam-gas bkg.) Extrapolation for diffractive events needed Lost events simulated extrapolated Acceptance Loss at low masses detected

  18. longer Q2 extrapolation smaller x Low-x Physics at the LHCResolving Confinement of quarks & gluons? J. Stirling

  19. Puzzles in High Energy Cosmic Rays Cosmic ray showers: Dynamics of the high energy particle spectrum is crucial Interpreting cosmic ray data depends on hadronic simulation programs Forward region poorly known Models differ by factor 2 or more Need forward particle/energy measurements e.g. dE/d…

  20. How to manage with the high-pT 'bread-and-butter' signatures of the nomenclature: The “Underlying Event” inHard Scattering Processes Min-Bias Min-Bias • LHC: most of collisions are “soft’’, outgoing particles roughly in the same direction as the initial protons. • Occasional “hard’’ interaction results in large transverse momentum outgoing partons. • The “Underlying Event’’ is everything but the two outgoing Jets, including : initial/final gluon radiation beam-beam remnants secondary semi-hard interactions • Unavoidable background to be removed from the jets before comparing to NLO QCD predictions

  21. To Reach the Forward Physics Goals We Need: • Leading Protons • Extended Coverage of Inelastic Activity • CMS

  22. Need to Measure Inelastic Activity and Leading Protons over Extended Acceptance in , ,  and –t. Measurement stations (Roman Pots) at locations optimized vs. the LHC beam optics. Both sides of the IP. LP1 LP2 LP3 147 m 180 m 220 m Measure the deviation of the leading proton location from the nominal beam axis () and the angle between the two measurement locations (-t) within a doublet. Acceptance is limited by the distance of a detector to the beam. Resolution is limited by the transverse vx location (small ) and by beam energy spread (large ). For Higgs, SUSY etc. heavier states need LP4,5 at 300-400m!

  23. TOTEM beam optics Fortotneed to measure elastic scattering at very small t (~ 10–3)  measure scattering angles down to a few mrad. Proton trajectory: y(s) = Ly(s) qy* + vy(s)y*,L(s) = [b(s)  b*]1/2 sin m(s) x(s) = Lx(s)qx* + vx(s)x* + Dx(s) x, v(s) = [b(s) / b*]1/2 cos m(s) • Maximise Lx(s), Ly(s)at RP location • Minimise vx(s), vy(s)at RP location (parallel-to-point focussing: v=0) •  High-* optics: for TOTEM * = 1540 m (vx 0, vy  0 at 220 m) • Consequences: • low angular spread at IP:s(q*x,y) = e / b*  0.3 mrad • large beam size at IP:s*x,y = e b*  0.4 mm (if eN = 1 mm rad)  Reduced # of bunches (43 & 156) to avoid parasitical interactions downstream. LTOTEM= 1.6 x 1028 cm-2 s-1 & 2.4 x 1029 cm-2 s-1

  24. Diffraction at high b*: Acceptance Luminosity 1028-1030cm-2s-1 (few days or weeks) • more than 90% of all diffractive protons are seen! • proton momentum can be measured with a resolution of few 10-3

  25. TOTEM ROMAN POT IN CERN TEST BEAM

  26. Dispersion function - low * optics (CMS IR) horizontal offset = Dx ( = momentum loss) Dx x y For a 2.5 mm offset of a   0.5 % proton, need dispersion  0.5 m.  Proton taggers to be located at > 250 m from the IP (i.e. in a ”cryogenic section” of the LHC). Optical function  in x and y (m) Dispersion in horizontal plane (m) CMS

  27. Potential locations for measuring the leading protons from O(100 GeV) mass DPE. Cryogenic (”cold”) region (with main dipole magnets) location of currently planned TOTEM pots!! 420 m 308/338 m 220 m CMS Dispersion suppressor Matching section Separation dipoles Final focus

  28. Microstation – Next Generation Roman Pot -station concept (Helsinki proposal) Silicon pixel detectors in vacuum (shielded) Very compact A solution for 19m, 380 & 420m? Movable detector

  29. Leading Proton Detection 0m 147m 180m 220m 308m 338m 420 430m D2 Q4 Q5 Q6 Q7 B8 Q8 B9 Q9 B10 Q10 B11 IP    D1    Q1-3      x = 0.02   Jerry & Risto

  30. TOTEM Detector Layout 215m 300m 420m y(mm) y(mm) y(mm) x(mm) x(mm) x(mm) Leading diffractive protons seen at different detector locations (b* = 0.5m)

  31. CMS tracking is extended by forward telescopes on both sides of the IP CMS T1-CSC: 3.1 < h < 4.7 T2-GEM: 5.3 <h< 6.5 T3-MS: 7.0 <h< 8.5 ? T1 T2 10.5 m CASTOR ~14 m T3? ~19 m - A microstation (T3) at 19m is an option.

  32. Forward Tracking Stations T1,T2&T3 • T1: 5 planes of CSC • coverage: 3.1 <  < 4.7 & full azimuthal • spatial resolution better than 0.5 mm • T2: 5 planes of silicon/GEM detectors • coverage: 5.3 <  < 6.7 & full azimuthal • spatial resolution better than 20 m IP 7.5 m 3.0 m T1 detector HF Castor  IP T2 T3? 13.6 m 0.4 m

  33. The process: pp  p + H + p h p 10 p1 p’ Dh 5 b-jet 0++ q1 b - H 0 q2 b 0++ - b-jet -5 Dh p2 p” -10 p MH2 = (p1 + p2 – p’ – p”)2  x1x2s (at the limit, where pT’ & pT” are small) x1 = 1-p’q1/p1q1  1-p’/p1x2 = 1-p”q2/p2q2  1-p”/p2

  34. Leading proton studies at low * • GOAL: New particle states in Exclusive DPE • L > few 10 32 cm2 s1 for cross sections of ~ fb (like Higgs) • Measure both protons to reduce background from inclusive • Measure jets in central detector to reduce gg background • Challenges: • M  100 GeV  need acceptance down to ’s of a few ‰ • Pile-up events tend to destroy rapidity gaps  L < few 10 33 cm2 s1 • Pair of leading protons  central mass resolution  background • rejection A study by the Helsinki group in TOTEM.

  35. Central Diffraction produces two leading protons, two rapidity gaps and a central hadronic system. In the exclusive process, the background is suppressed and the central system has selected quantum numbers. Survival of the rapidity gaps?1 JPC = 0++ (2++, 4++,...) MX212s Measure the parity P = (-1)J: ds/d 1 + cos2 2p  Gap Jet+Jet Gap 0 hmin h hmax Mass resolution  S/B-ratio R.Orava 1 V.A.Khoze,A.D.Martin and M.G.Ryskin, hep-ph/0007359

  36. Higgs Mass – New EW Fit Results LEP Search: MH 114.4 GeV EW fits: MH = 117 GeV 95% CL: MH < 251 GeV +67 -45 With the new top-mass measurements, the best fit for the Higgs mass is not excluded.

  37. Cross Section For a 5s signal at the LHC need: 30fb-1 SUSY h0 30fb 300fb-1 3fb Relatively small cross section but clean and model independent signature

  38. Higgs Branching Ratios Could invisible decay modes be seen by the central diffractive process?

  39. ”Base Line” Higgs Searches  50 pb Dominated by gluon fusion: Swamped by QCD background - have to use rare Higgs decay modes or associated production below the WW threshold.

  40. Mass Acceptance Both protons are seen with  45 % efficiency at MX = 120 GeV Some acceptance down to: MX = 60 GeV 308m & 420m locations select symmetric proton pairs  acceptance decreases. All pp p + X + p 308 m 420 m MX = 120 GeV e 45% All detectors combined MX = 60 GeV e 30% 308m e 15% 420m MX (GeV)

  41. Momentum loss resolution at 420 m Resolution improves with increasing momentum loss Dominant effect: transverse vertex position (at small momentum loss) and beam energy spread (at large momentum loss, 420 m)/detector resolution (at large momentum loss, 215 m & 308/338 m) proton momentum loss proton momentum loss

  42. Running Scenarios 1: High & Intemediate b* - low b* physics will follow...

  43. SUMMARY: TOTEM opens up Forward Physics to the LHC TOTEMCMS covers more phase space than any previous experiment at a hadron collider. • Fundamental precision measurements on elastic scattering, total cross section and QCD: • non-perturbative structure of proton • studies of pure gluon jets – LHC as a gluon factory • gluon densities at very small xBj… • parton configurations in proton • Searches for signals of new physics: • Threshold scan of 0++ states in exclusive central diffraction: Higgs, • SUSY (mass resolution crucial for background rejection) • Extension of the ‘standard’ physics reach of CMS into the fwd region & Precise luminosity measurement

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