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Central Diffraction at the LHC – an Update

Central Diffraction at the LHC – an Update. acceptance & central mass resolution bench mark process: pp  p + X + p.

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Central Diffraction at the LHC – an Update

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  1. Central Diffraction at the LHC – an Update • acceptance & central mass resolution • bench mark process: pp  p + X + p CERN-DESY Workshop 2004/2005 Risto Orava UH & HIP/TOTEM 11-13 October 2004 CERN

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

  3. Event Characteristics: ds/dt & xmin x acceptance? -t < 1 GeV2 DPE PHOJET (MH = 120 GeV) DPE PHOJET (MH = 120 GeV) dN/dxmin dN/dt -t (GeV2) xmin SN/dt SN/dxmin -t (GeV2) xmin  dN/dt  exp(-10t)  should detect p’s down to x  10-3

  4. Event Characteristics: Where do the decay b-jets go? Asymmetric pair of protons A typical – symmetric - pair of protons DPE PHOJET (MH = 120 GeV) DPE PHOJET (MH = 120 GeV) dN/dhbmax xpmin 0.002 dN/dhbmax xpmax 0.02 Symmetric pairs dominate Asymmetric pair of protons hbmax hbmax SN/dhbmax SN/dhbmax xpmax 0.02 xpmin 0.002 hbmax hbmax  All the b-jets are confined within h 5.

  5. 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.

  6. 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 created 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.

  7. 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 140 GeV Higgs as a bench mark. A study by the Helsinki group in TOTEM.

  8. Leading proton acceptance & resolution studies • pp  p + X + p simulated using PHOJET1.12 • Protons tracked through LHC6.2 optics using MAD8 • Uncertainties included in the study: • Initial conditions at the interaction point • Conditions at detector location • Transverse vertex position (x,y = 16 11 m) • Beam energy spread (E = 10-4) • Beam divergence ( = 30 rad) T. Mäki, MSc (eng.)thesis;HIP-2003-11/EXP • Position resolution of detector (x,y = 10 m) • Resolution of beam position determination (x,y = 5 m) • Off-sets at detector locations Update by Jerry Lamsa & RO

  9. Uncertainties of The Initial Conditions • LHC beams • beam energy spread (RF, field values, ground movement...) • resolution of the beam position measurement • - absolute beam position • Interaction vertex • spread of the coordinates (x,y,z) • uncertainty of the scattering angle

  10. 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

  11. Need to Measure Inelastic Activity and Leading Protons over Extended Acceptance in , ,  and –t. Measurement stations (RP’s/mS’s) 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!

  12. TOTEM ROMAN POT IN CERN TEST BEAM

  13. 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

  14. (Note: CMS measures IP independently to 10mmx10mmx15mm)

  15. Jorg Wenninger, CERN -04

  16. Leading proton acceptance clock-wise • Detector locations at • 220 m (dotted) • 308/338 m (dashed) • 420 m (solid) • With (an optimistic?) assumption on approach: • 10beam + 0.1 mm • acceptance down to 0.2 % acceptance proton momentum loss counter clock-wise acceptance proton momentum loss

  17. 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

  18. 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

  19. Dispersion function - low * optics (CMS IR) horizontal offset = Dx ( = momentum loss) 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). Dx Optical function  in x and y (m) Dispersion in horizontal plane (m) CMS

  20. 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) clockwise proton momentum loss counter-clockwise proton momentum loss

  21. 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)

  22. Mass resolution at the 308m and 420m locations MX = 140 GeV Ds/s= 1.2%  0.9% IP: 16mm  11mm IP: 16mm  11mm Ds/s= 1.3%  1.0%

  23. MX = 140 GeV Ds/s= 6.4%  4.6% IP: 16mm  11mm

  24. Conclusions pp  p + X + p is an excellent bench mark process for forward physics! Need to retain experimental approach with the challenges of (1) detectors beyond 250m, (2) acceptance. Ongoing further work concentrates on: • - Updating central mass acceptance & resolution studies • Improvements in acceptance: Asymmetric pairs • Improvements in resolution: Independent IP measurement • Tagging/triggering • H  W+W- • Novel analysis methods - DLM

  25. Preliminary results on L1 triggering of a 120 GeV Higgs ”High” luminosity (1034cm-2 s-1) ”Low” luminosity (1033cm-2 s-1) 500 Hz 500 Hz Feasible Difficult • Efficiency includes ”usefulness” cuts (protons & b-jets seen) • Will be repeated with complete CMS trigger simulation • Improvements should be possible by using also T2 & CASTOR

  26. 120 GeV Higgs Level 1 Trigger Selection • Based on combined likelihood functions of: • Sum() & difference of jet ET • Sum & difference of jet  • Difference of jet phi () • Forward scalar ET (3 <  < 5) (”rapidity gaps”) () () most selective trigger variables Sum of jet ET’s

  27. Background events (106 events) generated by Phojet: (4) Non-diffractive: pp  non-diffractive (5) Single diffractive: pp  pp* (6) Double diffractive: pp  p*p* The event types (1) – (6) were used to calculate the trigger efficiencies. Both charged and neutral particles were considered. The protons: Protons assumed to have 1% energy loss and 110-140 GeV central mass) The trigger: (1) Rapidity gap of at least two units of h on each side of the event with 2.5 < |h| < 7. (2) Transverse energy, ET, is required to be ET > 100 GeV within |h| < 2.5. (3) Rapidity gaps of Dh=2 in the region 5<|h<7 were also assessed.

  28. H  W+W- under study...

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