Diffractive production of gluino bound states at the LHC
Tim Coughlin - in collaboration with Jeff Forshaw and Andy Pilkington
Institute of Physics, Particle Physics 2006 - University of Warwick. Overview.
Gluino bound state production with forward tagged Protons
The Durham Model
Long-lived gluinos
Gluino bound states
Results Gluino bound state production with forward tagged Protons
• Looked at central exclusive diffractive production with forward protons, pp → p + X + p, where X is a bound state of gluinos. Here each + denotes a rapidity gap.
• Requires proton detectors ∼ 200 m down the beam pipe. These would be complimentary to proposed detectors at 420 m (FP420) and are already planned for CMS. The Durham Model
• Perturbative QCD model of pp → p + X + p due to
Khoze, Martin and Ryskin ¤ (hep-ph/0111078). ¡ £¢
• We use the ExHuME Monte Carlo to calculate cross-sections (Monk and Pilkington hep-ph/0502077).
• ExHuME factorizes the cross-section into two parts: - dσˆ(ˆs, y) from the hard gluon-fusion sub-process. - An ‘effective luminosity’ part, dL(ˆs, y)/dydsˆ, from the rest of the diagram. dσ dL(ˆs, y) = dσˆ(ˆs, y) dydsˆ dydsˆ The sub-process cross-section
• Considering scattering through very small angles and protons intact after interaction, hence:
- There is an effective Jz = 0 selection rule on the fusing gluons (z is along the proton collision axis). - Central system is produced in a colour singlet state.
• The effective luminosity is normalised such that the sub-process amplitude is averaged over gluon helicities and colours:
1 1 ++ −− Msubprocess = 2 M + M NC − 1 2 Long-lived gluinos
• Possible in ‘Split Supersymmetry’ (Arkani-Hamed and Dimopoulos hep-th/0405159).
- Scalar super-partner are massive ( 1 TeV). - Sfermions and one finely tuned Higgs are allowed to have TeV scale masses. - Hence gluino can be long-lived since it decays through the scalar super-partners. Gluino bound states (1)
• From parity and angular momentum considerations and because the gluino is a Majorana particle, the lowest available state (for this 3 process) is the P0 state.
• In the non-relativistic limit binding between two colour singlet gluinos is described by a coulomb-like potential.
−3α (Q) V (r) = s g˜g˜ r • We choose the scale Q to be set by the typical bound state radius, Q = 1/hri, with hri = 5a0.
• However Khoze, Martin and Ryskin, who have also studied this, chose a0 as their typical size. So all results are given at both scales. Gluino bound states (2)
• The sub-process amplitude is then a super-position of amplitudes for open production, weighted by a Schr¨odinger-like wave function. In the centre of mass frame:
Z d3p M(gg → G˜) ∝ ψ˜∗(p)M(gg → g˜g˜; p) (2π)3
• The cross-section in the centre of mass frame is:
2 2 5 σˆ = 12.82π αs(mg˜)αs(Q) δ(ˆs − 2mg˜). Total bound state production cross-section
Total cross-sections from ExHuME (a cross-section of 0.1 fb gives ≈ 10 events for one year of high luminosity running)
10 CTEQ6M + Scale 1 (fb)
σ CTEQ6M + Scale 2
MRST2002 + Scale 1
MRST2002 + Scale 2
1
500 600 700 800 900 1000 M (GeV) Decay, hadronization and backgrounds
• Decay the bound state, isotropically in its rest frame, to two gluon jets. Then hadronize using PYTHIA.
• Cut on the jet transverse momentum, p⊥ > 150 GeV, to simulate
the ATLAS trigger acceptance.
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• Considered gg → gg ¢¡¤£
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sub-process (using ExHuME) ¢¡¤£
and “double pomeron ¥
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fusion” (using POMWIG) as §
backgrounds. ¦ Background elimination - rapidity cut
Make a cut on the rapidity of the central system, |∆η| = 1, to reduce the gluon-gluon background.
ExHuME_GluinoBallDeltaJetEta
η 0.5 ∆ dN d 1
N ExHuME_GluinoBall 0.45
0.4 ExHuME_GG
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0 -2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 ∆η Background elimination - dijet mass-fraction cut
Make a cut on the dijet mass-fraction, Rjj, of 0.9, to reduce the double pomeron fusion background.
ExHuME_GluinoBallRJJ JJ σ d dR ExHuME_GluinoBall
2 10 Pomeron
10
1
10-1
0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1 RJJ Invariant mass of the central system
Invariant mass plot (for 250 GeV gluinos) after cuts and with detector resolution smearing (there’s a peak!):
MassTotal σ d dM
0.07
0.06
0.05
0.04
0.03
0.02
470 480 490 500 510 520 530 M Constraints on the gluino lifetime and mass
Collider limits If gluinos long-lived (on collider timescales) then mg˜ > 170 GeV from searches at the Tevatron (Hewett et. al. hep-ph/0408248).
Cosmological constraints on the gluino lifetime • Early Universe cosmology can place upper bounds on the gluino lifetime. 6 • Plot corresponds to τg˜ < 10 s for mg˜ < 500 GeV and τg˜ < 100 s for mg˜ > 500 GeV (Arvanitaki et. al. hep-ph/0504210).