Leading Protons measured at -420m, -220m & -147m from the CMS

1. Leading Protons measured at -420m, -220m & -147m from the CMS Forward Physics at the LHC Castor Leading Protons measured at +147m, +220m and +420m from the CMS T2 CMS T1 T1 T2 Castor Leading protons: RP’s at 147m, 220m and ±420m Rap gaps & Fwd particle flows: T1 & T2 spectrometers Fwd energy flows: Castor & ZDC Veto counters at: 60m & 140m? CMS + Totem + fp420 -unique fwd experiment Low-x Workshop 2006 Risto Orava Lisbon 28. June – 2. July 2006

2. T1:3.1 < h < 4.7 T2: 5.3 <h< 6.5 T1 T2 CASTOR (CMS) RP1 (147 m) RP2 (180 m) RP3 (220 m) Experimental layout 10.5m 14m ZDC

3. Collar Table T2 GEM CASTOR T2 Telescope 10 detector planes on each side of IP

4. LHC Experiments: pT-h coverage CMS fwd calorimetry up to |h|  5 + Castor + ZDC 1000 CMS ATLAS 100 T1 T1 pT (GeV) ALICE LHCb 10 T2 T2 1 microstation microstation RP RP 0.1 veto veto pTmax~ s exp(-h) -12 -10 -8 -6 -4 -2 0 +2 +4 +6 +8 +10 +12 h The base line LHC experiments will cover the central rapidity region. TOTEMCMS+will complement the coverage in the forward region.

5. ”b*=1540m”, ”90m”, ”18m”, ”2m”, ”0.55m”,...protons b*=1540m: optimized for small –t b*=90m: optimum for soft & semihard diffraction b*=2m,18m: useful for hig-t elastics b*=0.55m: required for hard diffraction, Higgs,...

6. A new tool for leading proton simulation • A Geant3 simulation package for the • leading particles has been worked out by • Jerry Lämsä. • This b-version is being validated and • includes all the beam elements that are • relevant for tracing the leading particles • originating at the IP (5 or 1) up to the • 420 lp detector location. • To be used for acceptance, resolution • and background studies. Note: The illustration above only describes the outgoing lp’s.

7. TOTEM measurements CMS Tracking & Calorimety TOTEM Castor, ZDC, 420m TOTEM Castor, ZDC, 420m • Total pp cross section with a • precision of  1% • Elastic pp scattering: • 10-3  t = (p)2  10 GeV2 • Leading particles: • 210-3    2  10-1 • Particle flows, rap gaps: • 3.1    4.7 and 5.3    6.5 • Investigate diffractive & forward phenomena together with CMS+ (= CMS+Castor+ZDC+fp420m) HERA and Tevatron studies as guidance! Note: Rapidity coverage could be further improved by veto counters at 60m to 140m, microstations at 19m etc.

8. Elastic cross section: Significance dsel/dt yields: • pp interaction radius (slope of the dsel/dt distribution) • with the measurement of the total inelastic rate - the total pp cross section, • A test of the Coulomb-nuclear Interference (expected to have an effect over large interval in –t). • A measurement of the ratio of the real and imaginary parts of the forward pp scattering amplitude, r = ReA(s,t)/ImA(s,t) •  Through dispersion relations, a precise measurement of r will constrain stot at substantially higher energies

9. Elastic cross section: Measurements • The leading proton detectors at ‘147’ and ‘220’ meters from the Interaction Point (IP5)[1]. • The nominal TOTEM beam optics set-up has high b* (b*  1540 m) and no crossing angle • at the IP for optimizing the acceptance and accuracy at small values of t down to -tmin  2  10-3 GeV2. • The -t distribution is extrapolated to -t = 0  the total proton-proton cross section by the Optical • theorem to better than 1%. • With the custom optics of b* = 90 m, a first quick measurement of the elastic cross section dsel/dt •  extrapolation to the Optical point with an accuracy of a few percent. • Short runs with other LHC custom optics set-ups, such as the ‘injection’ optics (b* = 18 m), or stage-1 • 'pilot' run optics (b* = 2 m) allow measurements up to -t  10  15 GeV2. • Runs with a reduced center-of-mass energy will allow an analysis of energy dependence, • comparisons with the Tevatron results and a precise measurement of ther parameter. [1] The detector locations at 145 and 149 meters from IP5 are here referred as the ‘147’ meter location and the ones at  218 and  222 meters from IP5 as the ‘220’ meter location. [2] The closest approach to the beam is of the order of a few mm’s (10s + 0.5 mm) and depends on the measurement location and used beam optics scheme (see 1.2).

10. TOTAL & DIFFRACTIVE CROSS SECTIONS stot and sSD total pp cross section single diffractive cross section TOTEM TOTEM random choice of models – for a review, see KMR-05 sSDmb stotmb LHC LHC s GeV s GeV figs. from Sapeta • measurement of sSD to 10% allows tests • of diffractive models • measurement of stot to 1% will distinguish • between different models • stot (lns)eas s   • = 0, 1, 2, or - 0.08 ??

11. Total cross section: Significance • pp cross section measurements at Tevatron energies are • ambiguous and the energy dependece of stot poorly constrained •  Even a total cross section which decreases with energy, cannot • be ruled out…) •  A precise measurement of stot at the LHC will discriminate • between fundamentally different theoretical scenarios. • With a simultaneous measurements of the elastic and inelastic • rates, the luminosity can be accurately defined •  precision physics studies.

12. The ”minimum-bias” events should be understood, too... The minimum-bias energy flows populate the forward detectors ... while the central detectors are floded by a large multiplicity of soft particles... Underlying events probed by the forward tags.

13. Acceptance in  & -t vs. Run Scenario Acceptance of leading protons produced in Central Diffractive events (Phojet) 30% acc. contours log Acceptance b* = 2m FP420m b* = 90m b* = 1540m b* = 1540m b* = 90m b* = 2m log(-t) log(-t) b* = 90m: CD protons detected by their scattering angle in the vertical RP detectors, -t  3 10-2 GeV2, almost independently of ,  50% of CD protons seen (standard LHC injection optics, p-to-p in vertical plane  horizontal displacement proportional to  & vx positon/CMS) b* = 1540m: -t  1 10-3 GeV2,  85% of CD protons seen (very low –t reach) b* = 2m: CD protons seen in the horizontal detectors, only, 0.02    0.1, -t  2 GeV2, poor acceptance (high –t) (420m RP’s with min  0.002 would help!)

14.  acceptance vs. Run Scenario at 220m • Nominal Totem optics: • 85% of lp’s seen • Custom optics I (b* = 90m): • 50% of lp’s seen • Machine development phase (b* = 2 – 10m): • a few % of lp’s seen

15. Acceptance in  & MX vs. Run Scenario 90m optics:  50% of CD protons seen, L  2  1030 cm-2s-1, i.e.  1 pb-1 in a few days. Acceptance  dN/d Acceptance  dN/dM 1540m A = 1 1540m 90m 90m A = 1 2m 2m  MX (GeV) For hard diffraction need nominal optics: diffractive protons with   0.02 (0.002 at 420m location) seen, L = 1032-1033 cm-2s-1 yields 1 – 10 fb-1 in a year.

16. 90 m optics:  resolution Resolution in  is dominated by: (1) vertex position (30 mm precision by CMS assumed), (2) beam position (50 mm assumed) s() Including all uncertainties Vx position: 30 mm assumed Beam position: 50 mm assumed Detector resolution: 10 mm assumed 

17. Single diffraction: Significance • Single diffractive dissociation to a large mass system, M*, is not fully • understood: • Both the triple-Pomeron based description and prediction of "multi-Reggeon" • events - events with a few large rapidity gaps - lead to sSD that grows faster • than stot. • A measurement of sSD and the cross section of multiple large rapidity gaps at the LHC will test the proposed models (see CDF/Dino and KMR). • For understanding the asymptotics of the strong interaction amplitude, it is • crucial to measure the -t-dependence of sSD. • Vanishing of triple-Pomeron coupling, G3ℙ, at -t  0, might cure the problem of • excessive sSD • A measurement of the cross section dsSD/dt at t  0, would test the 'weak coupling' scenario

18. Single diffraction: Significance... • Measurement of the location of the diffractive minimum (predicted as • a result of the destructive interference between the pole and cut • contributions) •  further testing of the 'weak coupling' scheme. • ‘Screening corrections' due to multi-loop Pomeron graphs • gap survival factor S2 0 when s , or gap size Dh ? • investigate the dependence of S2 on c.m.s. energy, gap size and the number of gaps. • SD dominated by the periphery of the interaction disk? • particles produced within the diffractive system have smaller average transverse momenta (compared to the secondaries at energies s  M*)?

19. Single diffraction: Measurements • Based on tagging leading protons and rapidity gaps in inelastic events. • The cross sections are typically large, short special runs with the ‘nominal’ TOTEM • high b* optics conditions (b*  1540 m) yield excellent statistics. • The pilot runs with b* = 90 m, 18 m - 2 m, planned for the initial stages of the • LHC operation, suit well for measurements of soft diffractive scattering. • About 85% (50%) of the diffractive protons with the nominal b* = 1540 m (special • b* = 90 m) are registered and with a diffractive mass, M*, acceptance better than • 50% down to M* = 3 GeV (1.2 GeV?). • The diffractive systems are measured over the full azimuthal angle and the • diffractive protons within the acceptance of the elastic ones. • At low diffractive masses, the acceptance could be – importantly - extended down • to 1.2 GeV (?) by installing additional veto counters at ± 60 to ± 140m.

20. Single diffractive energy flows populate the forward detectors ...while much of the soft particle multiplicities are seen in the central system.

21. Double diffractive energy flows populate the forward detectors ...while much of the soft particle multiplicities are seen in the central system.

22. Extending acceptance in M* by veto counters simulations by J. Lämsä

23. ≥ 50% for M* ≥ 3.4 (1.4) GeV high-b* ≥ 50% for h ≥ 8.8 high-b* ≥ 50% for h ≥ 9.4 low-b* ≥ 50% for M* ≥ 3.4 (1.4) GeV low-b*

24. Veto efficiency for N(1440)D++p- high-b* Veto efficiency for N(1440)pp0/np+ high-b* Veto efficiency for N(1440)D++p- low-b* Veto efficiency for N(1440)pp0/np+ low-b*

25. Semi-hard diffraction: Significance CDF & D0 results for SD/incl. ratio • Soft diffractive dynamics + objects signifying the hard scale: high ET jets, heavy quarks, • heavy bosons, new heavy particles? •  measurement up to rapidities of h  6 probes quark and gluon structure of diffraction[1] • The ratio b xBj/ interpreted as the momentum fraction of a parton within the Pomeron. [1] However, it is known that in low impact parameter reactions, a single Pomeron does not dominate diffraction...

26. Single diffraction: Strategy • The kinematics of these events is defined by the invariant mass and • pseudorapidity of the diffractive system. • The measurement aims at reconstructing the produced hard objects • within the full acceptance region of the TOTEMCMS+ set-up. • Semi-hard diffractive events are recorded during the custom and nominal • runs with b 1540 m, 90 m, 18 m and 0.55m for diffractive masses of • M > 3 (1.1) GeV

27. Low-x physics: Significance • The detection of low-x processes is based on tagging the objects (jets, heavy quarks, heavy bosons) that signify a hard scale in both central and forward rapidities. • TOTEMCMS could test a number of specific predictions based on the optical low-x model by Frankfurt, Strikman and Weiss by measuring: • The type of leading particles: nucleons and N* states. • Transverse momenta of the leading particles for p 1 GeV/c. • Correlations between the transverse momenta of leading hadrons. • Particle flows for particles in the fractional momentum region of z  0.02 - • 0.05 in both fragmentation regions (long range rapidity correlations) and • particle/energy flows of h = 4 - 6.

28. Low-x measurements: Strategy • The aim of the TOTEMCMS set-up is to measure jets at rapidities h  6 up to transverse energies of ET  10 GeV to reach x  10-6  transform LHC into a deeply inelastic scattering (DIS) machine. • Correlations between the forward (x  10-2) and central jets (x  10-2), heavy • quarks and heavy bosons  proton - parton configurations in three dimensions. • Forward jets in triggering for new phenomena in high-ET central processes. • The CASTOR calorimeter covers the pseudorapidity region of 5.4 h  6.7, • similar to the coverage of the T2 tracking station  measure the forward jets. • With a modest (veto)detector upgrade, the rapidity acceptance could be • extended up to h 11  reach x  10-8 .

29. Central diffraction: Significance • A good environment for the production of • exotic meson states (glueballs, hybrids,...) • via gg  M in • pp  p + M + p • - 90 m optics could be used for this! • A strong coupling for glueballs and hybrids • as a result of the assumed two-gluon • exchange? • High statistics studies possible with the • 'gluon collider' mode of the LHC. • Here azimuthal correlations with the quasi- • elastic pair of leading protons can be • particularly significant.

30. Central diffraction: Significance... • Heavy quark systems could be produced exclusively in CED (see KMR); • - First indications have been reported by the CDF Collaboration at the Tevatron… •  b0(1P) (m = 9859.9  1.0 MeV), with an upper limit of Br(g(1S)) = 6%. • - The decay upsilon subsequently decays into l +l - with ~2.5% branching ratio into each lepton species • The signature is remarkable: nothing but l +l –g in the entire central detector. - The low E of the photon complicates the trigger, however…

31. Central Diffraction • The Hard Central Exclusive Diffractive (CED) processes: • pp  p + MX + p, • will extend the physics programme at the LHC. • The process facilitates both QCD asymptotics and searches for physics beyond the • standard model. • Rapidity gaps (when available) provide a clean environment for investigating the • signal events experimentally. • A colour singlet state, MX, is produced with a minimal background from soft secondary particles; LHC is turned into a gluon factory. For low mass CD interactions, short runs with the custom optics (b* = 90 m and 1540 m). For the CED Higgs events (central masses below 250 GeV), the leading proton measurement stations at 420 m and the nominal LHC optics with b*  0.55 m is required. For central masses in excess of 250 GeV, low-b* conditions together with the leading proton measurement at the 220 m location are needed.

32. Central Diffraction: Mass resolution for +220m-220m Increasing symmetry of the proton pairs

33. A historical note.... 5.13 CED Mass Measurement at 420m... Mass resolution vs. central mass assuming DxF/xF = 10-4 DM = (1.5 - 3.0) GeV (DxF/xF = (1-2)10-4) Mass resolution (GeV) stable result since 2001 symmetric case:  65% of the data Helsinki group/J.Lamsa, R.O. 20 GeV < MX < 160 GeV (MXmax determined by the aperture of the last dipole,B11, MXmin by the minimum deflection = 5mm) Central Mass (GeV) Workshop on Diffractive Physics 4. – 8. February 2002 Rio de Janeiro, Brazil

34. Beam halo: beam protons diffusing out from the closed orbit Beam-gas: inelastics (fixed tgt exp!) from beam-gas interactions (simulated from upstream TAS to lp locations): rate < a few 100 Hz pp inelastics: forward particle flow from IP5 the main worry *=0.55m, 220m RP Angular selection to reject beam-gas Background in leading proton measurement Single arm background rates from p-p coll. (preliminary)

35. A trigger for diffraction - high b* Basic Constraints for Event Rates: LvL-One: ~1kHz HLT: 1- 100 Hz1 • Custom (Low Luminosity) Optics Runs: • Elastic Trigger: ±l(eading) p(roton)_220  lp_220 ( ±T1/T2) • Single Diffraction Trigger: ±lp_220  T1/T2 • prescaling required for soft events (lp background + elastics) • Asymmetric Central Diffraction trigger: ±lp_147 lp_220 T1/T2 • Symmetric Central Diffraction trigger: ±lp_220  lp_220  ±T1/T2 • prescaling required for soft events (ET build-up due to noise in calorimetry) • ”Minimum Bias” trigger: ±T1/T2  T1/T2 • - T1/T2 will see all the inelastics  prescale ! 1 Note: These rate constraints are due to the base line CMS trigger electronics – significant improvements can be envisaged...

36. A trigger for diffraction - low b* Basic Constraints for Event Rates: LvL-One: ~1kHz HLT: 1- 100 Hz1 • Nominal (high luminosity ~ 2 1033) Optics Runs: • Elastic Trigger: ±lp_220  lp_220  ±T1/T2 • - optimal for high-t elastics (options: collinearity requirement) • Single Diffraction Trigger: ±lp_220  T1/T2  ±T1/T2 • limited x-acceptance of the lp’s • Asymmetric Central Diffraction trigger: ±lp_147  lp_220  ±T1/T2 • higher rates but degraded MX resolution (options: acollinearity requirement) • Symmetric Central Diffraction trigger: ±lp  lp  ±T1/T2 • optimum MX resolution • - LvL-1 efficiency limited by min(jet(ET)) (ET build-up due to noise in calorimetry ≥ 20 GeV) • ”Minimum Bias” trigger: ±T1/T2  T1/T2 • - T1/T2 will see all the inelastics  prescale !

37. A trigger for diffraction Example • Rate constraints: • <1kHz @ L1 • <100Hz on tape for special runs • DPE and SD rates studied • DPE scheme: 2 protons + activity in • T1/T2 • SD scheme: 1 proton + activity in • T1/T2 opposite side • -SD more sensitive to background • For DPE: left-right anti-collinearity • required • Note: More studies on low-pT (<20GeV) jets would help • ejet ~ 50% for pT>20 GeV • ejet ~100% for pT>50GeV

38. pp  p + H(120) + p bb CJJ (ET > 40 GeV/J)  ±lp220  e = 12% FJJ (ET > 40 GeV/J)  ±lp220

39. TOTEMCMS Physics Reach TIME?

40. Physics priorities vs. the initial phases of the LHC – Elastic scattering & stot • b* = 2m-18m?? • dsel/dt (large –t) • (2) b* = 90m • dsel/dt (moderate –t) • stot & L(quick & dirty?) • (3) b* = 0.55m • dsel/dt (large –t) • (4) b* = 1540m • dsel/dt (small –t) • stot & L (TOTEM TDR) TIME?

41. Physics priorities vs. the initial phases of the LHC – Single diffraction & low-x CMS Tracking & Calorimety • b* = 2m -18m?? • dsSD/dxdt (limited acc.) • (2) b* = 90m • dsSD/dxdt (50% acc.) • semi-hard diffraction • low-x phenomena • (3) b* = 0.55m • dsSD/dxdt (limited acc.) • low-x phenomena • (4) b* = 1540m • dsSD/dxdt (85% acc.) TOTEM Castor, ZDC, 420m TOTEM Castor, ZDC, 420m TIME?

42. Physics priorities vs. the initial phases of the LHC – Central diffraction • b* = 2m, 6m, 18m?? • dsCD/dMXdt (hard CD?) • (2) b* = 90m • dsCD/dMXdt (soft & semihard CD) • (3) b* = 0.55m • dsCD/dMXdt (hard CD, discoveries) • (4) b* = 1540m • dsCD/dt (soft CD, x-t coverage!) TIME?