A Search for Excited Quark Production at H1

Andrew Rimmer

IoP Conference University of Liverpool 1 March 2005 Contents of talk

„ Introduction to HERA and H1 „ Phenomenology of excited quarks „ Event selections „ Control distributions „ Final distributions „ Some results „ Conclusions

IoP Conference 2 March 2005 Centre of mass energy = 320 GeV

IoP Conference 3 March 2005 The H1 Detector

IoP Conference 4 March 2005 Compositeness and Excited Quarks

Many BSM theories predict a new layer of substructure:

Quarks and Leptons as composite particles?

This could lead to excited states of SM particles

HERA is an ideal place to look for these

IoP Conference 5 March 2005 Phenomenology of Excited Quarks μν σ Lagrangian modelsτ the interactions of excited quarks with SM particles: μν

μν ⎡ a λa ⎤ = 1 * a + ′ ′ Y + a + Lint FR ⎢gf W g f B gs fs Gμν ⎥FL h.c. 2Λ ⎣ 2 2 2 ⎦

Λ is the compositeness scale ′ f , f and fs are form factors, allowing arbitrary couplings to the SM gauge groups

IoP Conference 6 March 2005 Production is possible at HERA via electroweak coupling at low Q2

Look for photon, W and Z decays. Tevatron has better handle on gluons.

Assume that fs= 0 to prevent gluon couplings from dominating

IoP Conference 7 March 2005 Currently concentrating on decay to Jet + Photon. This is possible in s-channel and u-channel at H1.

IoP Conference 8 March 2005 Outline of analysis

Event selection

2 level selection:

1) Loose selection: - Control distributions

2) Tight final selection: - Final plots - Efficiencies and limits

IoP Conference 9 March 2005 Main pre-selection cuts

„ At least 1 photon/electron „ Elec Pt > 10 GeV „ At least 1 Jet „ Jet Pt >10 GeV „ Cut out inefficient regions of detector „ Background rejection using topological filters

IoP Conference 10 March 2005 IoP Conference 11 March 2005 IoP Conference 12 March 2005 Main final selection cuts

„ Photon Pt > 20 Gev „ Jet Pt > 20 GeV „ Jet Theta < 90 degrees „ Photon Theta < 90 degrees „ Jet and Photon back to back in r-phi „ No track linked to the photon within 20cm, except for theta < 25 degrees „ Invariant Mass > 50 GeV

IoP Conference 13 March 2005 IoP Conference 14 March 2005 Jet + photon data candidate

IoP Conference 15 March 2005 95 % confidence level limits were calculated on the Cross section * branching ratio of q* Æ q + photon

Statistical and systematic errors taken into account

qÆ q + gamma

IoP Conference 16 March 2005 Conclusions

No evidence for q* seen in 99-00 data

Limits on cross sections calculated

Still to do

Calculate limits on the coupling (f / lambda)

Look at other q* decay channels

IoP Conference 17 March 2005 Selection Efficiencies for Jet + Photon channel

Mass 50 75 100 125 150 175 200 225 250 275 300 (GeV)

Eff (this 0 39 44 49 53 55 56 58 59 59 58 analysis)

Eff (94-97 22 33 36 -- 42 -- 41 -- 40 -- -- analysis)

IoP Conference 18 March 2005