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Forward Physics at LHC: Total Cross-section and Low-x Dynamics

This text discusses the forward physics experiments at LHC, including topics like total cross-section with a precision of 1%, low-x dynamics, diffractive phenomena, and leading particle and energy flow in the forward direction.

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Forward Physics at LHC: Total Cross-section and Low-x Dynamics

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  1. LHC Forward Physics Experiments: ALICE ATLAS CMS FP420 (R&D project) LHCf TOTEM Jim Whitmore Penn State University DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  2. LHC Forward Physics • Total cross-section (and luminosity) with a precision of 1% • Elastic pp scattering • in the range: 10-3 < |t| = (p )2 < 10 GeV2 • Forward Physics: • Low-x dynamics • Diffractive phenomena: • Soft and Hard • Inclusive and exclusive Double Pomeron Exchange (DPE) • Leading particle and energy flow in the forward direction • pA, AA, gg and gp processes (sorry, I will not cover these topics) Many of these topics can be studied best at startup luminosities DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  3. “We are not studying a possibility of forward physics with LHCb at the moment” +LHCf +FP420 +TOTEM DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  4. Forward Detectors • General philosophy: • Additional detectors near the IP • Proton (Roman Pot) detectors: • want to detect small scattering angles (~few mrad:) • and the beam divergence • so want large values of b*. However, luminosity • want small b* • So expect a selection ofb* values (0.5-1540 m) • RP detectors at 140-220 m from IP • Need to go to 420 m→the “cold” region DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  5. Roman Pot acceptance M2=x1x2s - 240 m  = proton momentum loss = Dp/p Reconstruct  with roman pots  < 0.1  O(1) TeV “Pomeron beams“ TOTEM (ATLAS) FP420 Low *: (0.5m): Lumi 1033-1034cm-2s-1 220m: 0.02 <  < 0.2 300/400m: 0.002 <  < 0.02 Detectors in the 420 m region are needed to access the low  values (A. deRoeck) DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  6. TOTEM + CMS Experimental Apparatus T1:3.1 < h < 4.7 T2: 5.3 <h< 6.5 CMS Castor 5.25< <6.5 IP5 10.5 m T1 T2 ~14 m CASTOR (CMS) IP5 RP1 (147 m) RP2 (180 m) (later option) RP3 (220 m) DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  7. T1 Telescope 3.1< |h| <4.7 • 5 planes with measurement of three coordinates per plane. • 3 degrees rotation and overlap between adjacent planes • Primary vertex reconstruction • Trigger with CSC wires ~3 m T2 Telescope Digital r/o pads 5.3< lhl < 6.5 GEM (Gas Electron Multiplier) Telescope: 10 ½-planes 13.5 m from IP Analog r/o circular strips DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  8. reconstructed track Tracks BPM 0 Roman Pots Test beam data: reconstructed tracks in y u,v info RP in SPS beam and the detector is measuring the halo • Roman Pot unit: • - Vertical and horizontal pots mounted as close as possible • - TOTEM at the RP: sbeam ≈ 80 mm • - Leading proton detection at distances down to 10sbeam + d • Need “edgeless” detectors that are efficient up to the physical edge to minimize “d” • Currently two tech. (5-10 mm and 40-50 mm dead areas) DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  9. Forward Detectors in ATLAS Roman Pots at 240 m Cerenkov Counter (LUCID) = a lumi monitor at 5.4 << 6.1 + neutral energy at zero degrees (I. Efthymiopoulos) IP1 DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  10. Running Scenarios TOTEM (V. Avati, M. Deile) DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  11. pp total cross sectionand luminosity monitor TOTEM-CMS ATLAS DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  12. pp total cross section pp total Cross-Section Luminosity-independent measurement using the Optical Theorem: (M. Deile) • Measure the total rate (Nel+Ninel) , sdiff ~ 18 mb and min. bias ~65 mb, with an expected precision of 0.8 % (running for 1 day at L = 1.6 x 1028cm-2s-1). • Extrapolate the elastic cross-section to t = 0: systematics dominated: 0.5 % (statistical error after 1 day: 0.07 %) • ρ =Re f(0)/Im f(0) unknown; using COMPETE pred.: 0.2 % 1 % (r= 0.1361±0.0015+0.0058-0.0025) DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  13. pp total Cross-Section • Current models predictions: 90-130 mb • Aim of TOTEM: ~1% accuracy (~1 mb) [PRL 89 201801 (2002)] Cudell et al. COMPETE Collaboration fits all available hadronic data and predicts: LHC: DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  14. ATLAS’s Plans: ATLAS submitted a Letter of Intent to complement the experiment with a set of forward detectors for luminosity measurement and monitoring as part of a two stage scenario: • Short time scale • Roman Pots at 240 m from IP1 • Probe the elastic scattering in the Coulomb interference region • Dedicated detector for luminosity monitoring – LUCID • Used also to transfer the calibration from 1027 1034 Goal: Determine absolute luminosity at IP1 (2-3% precision) 2. Longer time scale • Study opportunities for diffractive physics with ATLAS • Propose a diffractive physics program using additional detectors (I. Efthymiopoulos) DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  15. Physics interest -- ATLAS Luminosity Measurement – Why? • Important for (precision) comparison with theory: • e.g. bb, tt,W/Z, n-jet,… cross-section deviations from SM could be a signal for new physics Systematic error dominated by the luminosity measurement (ATLAS-TDR-15, May 1999) (I. Efthymiopoulos) DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  16. pp elastic scattering TOTEM DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  17. Elastic scattering – from ISR to Tevatron ~1.5 GeV2 DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  18. Photon - Pomeron interference  r Multigluon (“Pomeron”) exchange  e– B |t| ds/dt [mb / GeV2]  t  p2q2 diffractive structure pQCD wide range of predictions pp 14 TeV BSW model -t [GeV2] ~1 day (1) (3) pp elastic scattering cross-section 104 per bin of 10-3 GeV2 B(s) = B0 + 2aP’ ln (s/s0) ~ 20 GeV-2 at LHC ~ 1/|t|8 BSW = Bourrely, Soffer and Wu b*=18 m L = 3.6 x 1032 cm-2 s-1 (3) b* = 1540 m L = 1.6 x 1028 cm-2 s-1 (1) DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  19. Elastic Scattering Models (eg. Islam et al) • Observations: • fwd diffraction cross section increases • diffractive peak shrinks • interference dip moves to smaller t • at –t  1 GeV2: • ds/dt  1/t8 • (3-gluon exchange) • little s dependence  1/t8 Islam et al BSW Desgrolard et al DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  20. Elastic Scattering- el/tot Rdiff=[sel(s) +sSD(s) + sDD(s)]/stot(s) Rel = sel(s)/stot(s) 0.3 0.30 0.4 0.375 0.2 0.3 0.1 0.2 4 5 6 3 4 6 3 5 log(s/s0) • sel  30% of stot at the LHC ? • sSD + sDD  10% of stot (= 100-150mb) at the LHC ? (M. Deile) DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  21. Low-x at the LHC LHC: due to the high energy can reach small values of Bjorken-x in structure of the proton F(x,Q2) Processes:  Drell-Yan  Prompt photon production  Jet production  W production If rapidities below 5 and masses below 10 GeV can be covered  x down to 10-6-10-7 Possible with T2 upgrade in TOTEM (calorimeter, tracker) 5<< 6.7 ! Proton structure at low-x !! Parton saturation effects? (A. deRoeck) DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  22. Diffractive physics ALICE TOTEM CMS F420 project DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  23. Double Pomeron exchange: Single diffraction: X X X 2 gluon exchange with vacuum quantum numbers “Pomeron” p p  p X p p  p X p Double diffraction: Y p p  X Y The accessible physics is a function of the integrated luminosity (M. Ruspa) DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  24. T1,T2 T1,T2 Roman Pots Roman Pots TOTEM+CMS CMS + TOTEM: Acceptance largest acceptance detector ever built at a hadron collider 90% (65%) of all diffractive protons are detected forb* = 1540 (90) m 107 min bias events, incl. all diffractive processes, in 1 day with b* =1540 m Total TOTEM/CMS acceptance Charged particles b*=90m dNch/dh ZDC RPs CMS central T1 HCal T2 CASTOR Energy flux dE/dh b*=1540m Pseudorapidity: = ln tg /2 DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  25. Soft Diffractive Event rates ALICE is studying the possibility of implementing a trigger requiring a rapidity gap on both sides of a central region of 1.5 units of rapidity. The selection can include EM energy deposition in the PHOS, protons in the HMPID (RICH), or electrons identified with the TRD, opening the possibility to study heavy flavour production in double diffractive events. DPE: pp  pXp Acc = 27.8% for detecting both protons (b* = 90 m) DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  26. diffractive system X proton:p1’ proton:p2’ rapidity gap rapidity gap hmin hmax DPE Dh2= – ln x2 Dh1= – ln x1 Events/GeV-day Exchange of color singlets (“Pomerons”)  rapidity gaps Dh Measure > 90 (65)% of leading protons with RPs at b* = 1540 (90) m and diffractive system X with T1, T2 and CMS. Scenario (2) (4) b* (m) = 1540 90 DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  27. hard M u jet 1 (pT 1) p d jet 2 (pT 2) u jet 3 (pT 3) hard g g p p hard Double Pomeron Exchange M Hard Diffractive Events Diffractive events with high pT particles produced • Double pomeron Ex: pp  pjjXp • = 1 mb pT > 10 GeV • Acc = 29.3% (for b* =90 m, prel.) (V. Avati) Single diffraction: pp  p + 3j DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  28. p H p Exclusive Double Pomeron Exchange TOTEM-CMS FP420 (with ATLAS/CMS) DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  29. Exclusive Double Pomeron Exchange Quantum numbers are defined for exclusive particle production Gluonic states c , b , Higgs, supersymmetric Higgs,….. MX2 = x1 x2 s Motivation from KMR calculations (e.g. hep-ph 0111078) • Selection rules mean that central system is (to a good approx) 0++ • H→b-bbar: QCD b-bbar bkgd suppressed by Jz=0 selection rule • If you see a new particle produced exclusively with proton tags you know its quantum numbers • Tagging the protons means excellent mass resolution (~ GeV) irrespective of the decay products of the central system • Proton tagging may be the discovery channel in certain regions of the MSSM Trigger studies were discussed by M. Ruspa DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  30. SUSY Higgs: h, H, A, (H+, H--) Tasevsky et al Diffractive: H bb Yuk. coupling, DMH, 0++ 5s Inclusive: H,A tt wide bump L=60 fb-1 mH=140 mH=160 From A. Martin’s parallel session talk DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  31. From A. Martin’s parallel session talk Alan’s Conclusions There is a very strong case for installing proton taggers at the LHC, far from the IP ---- it is crucial to get the missing mass DM of the Higgs as small as possible The diffractive Higgs signals beautifully complement the conventional signals. Indeed there are significant SUSY Higgs regions where the diffractive signals are advantageous ---determining DMH, Yukawa Hbb coupling, 0++ determinn ---searching for CP-violation in the Higgs sector s(pp  p + H + p) ~ 3 fb at LHC for SM 120 GeV Higgs • L(LHC)~60 fb-1~10 observable events after cuts + efficiency • Higgs needs L ~ 1033 cm-2 s-1, i.e. a running scenario forb*= 0.5 m: • trigger problems in the presence of overlapping events (see M. Ruspa’s talk) • install additional Roman Pots in cold LHC region (420 m) at a later stage DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  32. FP420 Project The aim of FP420 is to install high precision silicon tracking and fast timing detectors close to the beams at 420 m from ATLAS and/or CMS. FP420 turns the LHC into a glue-glue collider where you know the beam energy of the gluons to ~ 2 GeV. With nominal LHC beam optics @ 1033-34 cm-2s-1: • 220 m: 0.02 <  < 0.2 • 420 m: 0.002 <  < 0.02 12 s = M2 With √s = 14TeV, MH = 120 GeV on average:  0.009  1% Hence the need for FP420 (See B. Cox’s talk in the diffractive parallel session) DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  33. Forward physics:connection to cosmic rays ALICE TOTEM LHCf DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  34. Issues in UHE cosmic rays 1. Spectrum / GZK Cutoff 29th ICRC Pune DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  35. Xmax(g/cm2) Energy (eV) Issues in UHE cosmic rays 2. Composition p Measurements of the very forward energy flux (including diffraction) and of the total cross section are essential for the understanding of cosmic ray events At LHC pp energy: 104 cosmic events km-2 year-1 > 107 events at the LHC in one day Fe (O. Adriani) DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  36. UHE Cosmic Rays g p Fe 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/constrained Models differ by factor 2 or more Need forward particle/energy measurements e.g. dE/d… DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  37. Model Predictions: pp at the LHC Predictions in the forward region within the CMS/TOTEM acceptance DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  38. LHCf Measurement of Photons and Neutral Pions in the Very Forward Region of LHC Simulation of an atmospheric shower due to a 1019 eV proton. (O. Adriani) • The dominant contribution to the energy flux is in the very forward region • In this forward region the highest energy measurements of p0 cross section were done by UA7 (E=1014 eV, y = 5÷7) The direct measurement of the p production cross section as function of pT is essential to correctly estimate the energy of the primary cosmic rays (LHC: 1017 eV) DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  39. 140 m 140 m Beam line LHCf Experimental Method:2 independent detectors on both sides of IP INTERACTION POINT Detector II Tungsten Scintillator Silicon mstrips Detector I Tungsten Scintillator Scintillating fibers IP1 (ATLAS) • The vacuum tube contains two counter-rotating beams. The beams transition from one beam in each tube to two beams in the same tube. • Detectors will be installed in the TAN region, 140 m away from the Interaction Point, in front of luminosity monitors • Charged particle are swept away by magnets • LHCf will cover up to y → ∞ (O. Adriani) DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  40. There are plans at the LHC for a wide range of Forward and Diffractive measurements that can be achieved at a variety of different luminosities: Measure total cross-section stotwith a precision of1% Measure elastic scattering in the range10-3 <|t|< 8 GeV2 A study of soft and hard diffractive physics: semi-hard diffraction (pT > 10 GeV) hard diffraction Inclusive DPE Studies of Exclusive Double Pomeron Exchange events Studies of very forward particle production Connection with UHE Cosmic ray phenomena Special exotics (centauro’s, DCC’s in the forward region) Summary DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  41. Extra slides DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  42. Elastic Scattering:  = Re f(s,0)/Im f(s,0) TOTEM •  Ref+(s,0)/Imf+(s,0) (analyticity of the scattering amplitude via dispersion relations) • constant/lns with s DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  43. Pile-up: numbers! PHOJET: ALL PROCESSES 110 mb NONDIF.INELASTIC 51 mb ELASTIC 33 mb DOUBLE POMERON 1.95 mb SINGLE DIFFR.(1) 7.66 mb SINGLE DIFFR.(2) 7.52 mb DOUBLE DIFFRACT. 9.3 mb 1 mb = 100 events/s @ 10 29 cm-2 s-1 Number of pileup events per bunch crossing = = Lumi* cross section * bunch time width * total lhc bunches / filled bunches = = 1034 cm-2 s-1 * 104 (cm^2/m^2) * 10-28 (m2 / b) * 51 mb * 10-3 (b/mb) * 25 (ns) * 10-9 (s/ns) * 3564 / 2808  17 This number is valid in the central detector region, but must be corrected for the elastic and diffractive cross section in the forward region! • Number of pileup events per bunch crossing = • = Lumi* cross section * bunch time width * total lhc bunches / filled bunches = • = 1034 cm-2 s-1 * 104 (cm^2/m^2) * 10-28 (m2 / b) * 110 mb * 10-3 (b/mb) * 25 (ns) * 10-9 (s/ns) * 3564 / 2808  35 • 1x1032  0 • 1x1033 3.5 • 2x1033 7 Selection of diffractive events with rapidity gap selection only possible at luminosities below 10 33 cm-2s-1, where event pile-up is absent DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  44. TOTEM Experiment (symmetric about IP5) RP T1 & T2 RP DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  45. FP420 Acceptance and Resolution 3 mm + 3 mm 3 mm 25 mm 30 mm 5 mm 7.5 mm 10 mm 22 mm DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006 MB apertures

  46. Active edges: X-ray measurement Add here photo of RP Signal [a.u.] 5mm deadarea 150 mm Strip 1 Strip 2 Detector 1 Detector 2 Edgeless silicon detectors for the RP 10 planes/pot Planar technology: Testbeam 40 m dead area 66 mm pitch 10 mm dead area 50 mm dead area active edges (“planar/3D”) planar technology CTS (Curr. Termin. Struct.) DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  47. Diffraction at b* = 1540 m Acceptance RP at 220 m kinematically excluded • Diffractive protons are observed in a large x-t range: • x=Dp/p; t=-(pq)2 • 90% are detected • -t > 2.5x10-3 GeV2 • 10-8 < x < 0.1 • x resolution ~5x10-3 acc. < 10% DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  48. Diffraction at b* = 90 m Acceptance Resolution in x: s(x) = 4x10-4 (prel.) L<2x1031 cm-2s-1 DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

  49. Diffraction at b* = 0.5 m DIS2006 XIV International Workshop on Deep Inelastic Scattering Tsukuba, Japan, 20-24/April/2006

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