Diffractive physics simulation for LHC

1
Diffractive physics simulation for LHC

• Marek Taševský (Physics Inst. Prague)
• In collaboration with Ch.Royon, A.Kupco,
  M.Boonekamp
• Low-x workshop - Lisbon 29/06 2006

Upgrade of 240 m RP in ATLAS
2
Forward physics in ATLAS

• Originally oriented to
• 1. Luminosity calibration using Roman pots of
  Totem type
• 2. Luminosity monitoring using integrated
  Cerenkov det. LUCID
• To access the diffraction physics, the RPs need
  to be upgraded
• to detect the diffractive protons and to stay the
  radiation hardness.
• Hard diffraction, Soft diffraction, Double
  Pomeron Exchange can
• be studied using the central detector RPs.
• Participating institutes
• Saclay (Ch.Royon, M.Boonekamp, L.Shoeffel,
  O.Kepka et al.)
• Prague (A.Kupco, M.T., V.Juránek, M.Lokajícek)
• Stony Brook (Michael Rijsenbeek)
• Cracow (group being formed)

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Double Pomeron Exch. Higgs Production
Exclusive DPE Higgs production pp? p H p
3-10 fb Inclusive DPE Higgs production
pp ? pXHYp 50-200 fb
-jet
(W)
E.g. V. Khoze et al M. Boonekamp et al. B. Cox et
al. V.Petrov et al.
gap
gap
H
h
p
p
-jet
(W)
Advantages of Exclusive
Mh² measured in RP via missing mass as ?1?2s
bb Jz0 suppression of gg-gtbb bg WW bg
almost negligible
bb L1-trigger of central CMS220 RP type
extensively studied by CMS/Totem group. WW
Extremely promising for Mhgt130 GeV. Relevant
triggers already exist. Better Mh resolution for
higher Mh.
4
DPE Higgs event generators

• DPEMC 2.4 (M.Boonekamp, T.Kucs, Ch.Royon,
  R.Peschanski)
• - Bialas-Landshof model for Pomeron flux
  within proton
• - Rap.gap survival probability 0.03
• - Herwig for hadronization
• - ExclusiveInclusive processes
• 2. EDDE 1.2 (V.Petrov, R.Ryutin)
• - Regge-eikonal approach to calculate soft
  proton vertices
• - Sudakov factor to suppress radiation into
  rap.gap
• - Pythia for hadronization
• 3. ExHuMe 1.3.1 (J.Monk, A.Pilkington)
• - Durham model for exclusive diffraction
  (pert.calc. by KMR)
• - Improved unintegrated gluon pdfs
• - Sudakov factor to suppress radiation into
  rap.gap rap.gap
• survival prob.0.03
• - Pythia for hadronization

All three models available in the fast CMS
simulation
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Roman Pot acceptances on CMS side
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Upgrade of 240 (220) m RP in ATLAS

• Main goal is to extend the forward physics
  program in ATLAS by very
• rich diffraction physics using the existing place
  for RPs at or close to
• 240 m. Complementary to FP420 program.
• o 220 or 240 m? Study the acceptances of RPs
  using MAD-X (complex
• program used by beam division)
• o What type of detector?
• o Whats the effect of the collimator at Q5 to be
  put at high lumi?

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Proton tracking in LHC

• MAD-X (beam division)
• LHC optics v6.5, low ß
• Hector (Piotrzkowski, Favereau, Rouby from
  UCLouvain)
• LHC optics v6.5, low ß
• Beam apertures included, kickers switched off
• Linear approximation for effects of dispersion
• FPtrack (Bussey from Uni Glasgow)
• LHC optics v6.5, low ß
• Beam apertures and kickers included
• Exact magnet formulae for effects of dispersion
• All MAD-X pictures made by Sasha Kupco from Prague

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Elastic events at 240 m RPs
FPTRACK
MAD-X
HECTOR
Beam 1
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Diffractive events at 240 m RP
FPTRACK
MAD-X
HECTOR
Beam 1
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Diffractive events using MAD-X
220 m
240 m
420 m

• MAD-X tracking
• Beam 1
• ß0.55m LHC optics, v6.5
• 420 has opposite orientation than 220 (240)

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Diffractive events at 420 m RP
FPTRACK
MAD-X
Beam 1
Orientation opposite because of opposite
conventions in MAD-X and FPTRACK
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Beam spots using MAD-X
Numbers agree with those based on s(s)
vß(s)e Simulated parameters Trans.vtx
position sx,y 16 µm Beam en. spread sE 0.77
GeV Beam divergence s?x,?y 30 µrad
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Acceptance for 220 m RPs (beam1)

• 0.02 steps in ?
• t0.0 and 0.05 GeV²
• 2x2 cm² detector has
• acceptance of upto ? 0.16

• Detailed look at low ?
• 0.005 steps in ?
• sx 96 µm

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Acceptance for 240 m RPs (beam1)

• 0.02 steps in ?
• t0.0 and 0.05 GeV²
• 2x2 cm² detector has
• acceptance of upto ? 0.14

• Detailed look at low ?
• 0.005 steps in ?
• sx 125 µm

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Hit maps at 216 and 224 m RPs
- Test of the idea of using a displacement for
the L1 trigger to suppress beam halo. - No
uniform shift direction between 216 and 224 m
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First study of pile-up at 240 m RP
Pile-up generated by Pythia msel2
(diffr.non-diffr. processes, but DPE
missing) Assume 2x2 cm²active volume and 20 s
for distance from beam 2.5 of PU protons seen
in RP at 240 m -gt expect about 1 PU event/BX at
highest luminosity
Beam 1
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Roman Pots
Idea follow Totem design Acceptance studies
showed the horizontal pots only are
needed Restudy the supports
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Detectors

• - Very good space resolution ( µm) useful to
  distinguish halo from signal.
• - Very good timing resolution ( O(10) ps) useful
  to distinguish pile-up
• vertices from signal ones.
• - Good readout time (5 ns)
• Si strips / Micromegas
• 1) Si strips
• Advantage fast readout (5
  ns)
• Disadvantage sensitivity of
  Si signal to EM noise
• Timing provided by Cerenkov
  counters
• 2) Micro-Mesh-Gaseous Structure
• Advantage timing resolution
  of 1 ns,
• space
  resolution of 15 µm
• good
  behaviour in radiative env.
• 
  insensitive to EM noise
• Disadvantage gas
  circulation in tunnel (safety problem?
• the
  volume will be very small)

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Summary

• The project has started this year. All institutes
  need to submit
• it by October.
• 2) MAD-X installed and working in Prague
• Acceptance studies ongoing.
• Fast simulation existing (beam parameters
  smeared, the detector ones to follow)
• 3) Roman Pots will use the Totem design. Need to
  decide what type
• of sensitive detectors to put in. They need
  to be included in ATLAS L1 trigger.
• 4) This project is complementary to FP420 and a
  natural follow-up
• of existing luminosity program in ATLAS. The
  forward physics
• programmes move ahead on both sides, CMS and
  ATLAS.

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• BACKUP SLIDES

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• Difference between DPEMC and (EDDE/ExHuMe) is an
  effect of
• Sudakov suppression factor growing as the
  available phase space for
• gluon emission increases with increasing mass of
  the central system

Models predict different physics potentials !
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Effect of pile-up events

• What is the number of fake signal events per
  bunch crossing (Nfake/BX)
• caused by PU events?
• Selection criteria for signal events (Higgs in
  DPE)
• 2 protons in RPs, each on opposite side x Jet
  cuts x Mass window
• For the moment (till I get the final results),
  assume we can factorize the
• task the above way
• Nfake NRP Jet cuts
  Mass window
• Estimate of NRP 1.Rough-but-Fast
• 2.Precise-but-Slow
• All RP acceptances are taken as means.
  

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Phojet generation of PU events

• All processes 118 mb
• Non-diff.inelastic 68 mb
• Elastic 34 mb
• Single Diffr.(1) 5.7 mb
• Single Diffr.(2) 5.7 mb
• Double Diffr. 3.9 mb
• DPE 1.4 mb
• Number of pile-up events per bunch crossing (BX)
  ? NPU
• Lumi x cross section x bunch time width LHC
  bunches/filled bunches
• 1034cm-2s-1x104cm2/m2 x 10-28m2/b x 110mb x
  10-3b/mb x 2510-9s
• X 3564/2808 35
• 51033 17.6 , 21033 7.0, 11033 3.5,
  11032 0

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NRP estimate precise method

• Mix PU events with signal or bg using FAMOS
• Sum RP acceptances over all possible proton pairs
  in all PU events
• in one BX and then look at mean over all
  signal or bg events.
• NPU properly smeared using Poisson dist.
• E.g. NRP420 ltSiNPU(n) SjNPU(n)
  AL420(i)xAR420(j)gtn5k signal or bg events
• Mean nr.of PU events with 2
  ps seen in opposite 420 RPs
  

ltNPUgt NRP420 NRP220 NRPcomb NRPtotal combinatorics
3.5 0.003 0.016 0.016 0.034
7.0 0.010 0.045 0.053 0.10
17.6 0.045 0.220 0.280 0.54
25.0 0.080 0.420 0.560 1.03
35.0 0.155 0.807 1.040 2.00