Diffractive production of gluino bound states at the LHC

Tim Coughlin - in collaboration with Jeff Forshaw and Andy Pilkington

The

Institute of 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 -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 (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 ’ (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 ¥

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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 (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).