COMPASS Hadron Trigger Meeting Munich Feb.11, 08 Trigger-relevant Summary of Physics Goals by Martin Faessler, Munich Feb 11, 08 Physics Goals (Hadron spectroscopy): Search for ￭ glueballs and hybrids in ￭ central production and diffractive projectile excitation

COMPASS Hadron Trigger Meeting Munich Feb.11, 08 Key actor: the Pomer(anchuk)on minimal Pomeron more sophisticated Pomeron, gluonic ladder

COMPASS Hadron Trigger Meeting Munich Feb.11, 08 Production of glueballs X and hybrids A΄ by means of Pomerons Central production by double Pomeron exchange → Diffractive projectile A excitation by single Pomeron exchange →

COMPASS Hadron Trigger Meeting Munich Feb.11, 08 Rapidity distribution in hadron hadron collisions at very high energy – Feynmans view 1972 rapidity y = ln((E+p z )/m T ) instead of Feynman-x F dn/dy = const (plateau) ←→ dn/dx = const/x

COMPASS Hadron Trigger Meeting Munich Feb.11, 08 Rapidity distribution in ordinary inelastic interaction ←Hadron A ←Hadron B ← AB inelastic interaction (minimum bias)

COMPASS Hadron Trigger Meeting Munich Feb.11, 08 Wanted: 2mb Diffractive proj. excitation → (0.01mb DPE) central production Background reactions: 4mb elastic→ 16mb ordinary inelastic→ 2mb diffractive target exitation→

COMPASS Hadron Trigger Meeting Munich Feb.11, 08 Some useful formulae for diffractive or central production of resonances with given mass M Given M (e.g. M= 2GeV) of resonance decaying into 2 final state particles m 1, m 2 (e.g. ηπ) y beam ≈ ln( 2E beam /m beam ) (e.g. π beam of 190 GeV: y beam = 7.9) Diffractive projectile excitation: y(M) ≈ ln(2E beam /M) = 5.2 Central production y(M) ≈ ln(2ν/M) where ν= E beam –E leading Approximate y - range of decay particles with mass m i : ln(m i /M) < y – y(M) < ln(M/m i ) 2.7 π 1.2 η At our beam energy, the rapidity gaps which separate centrally or diffractively produced particles from the leading p and/or π are not large. This makes life more difficult

COMPASS Hadron Trigger Meeting Munich Feb.11, 08 Longitudinal laboratory momentum distributions for isotropic decay of a diffractively excited πη resonance of mass M= 1.4 GeV for pion beam momentum 190 GeV (Monte Carlo Ismail Uman)

COMPASS Hadron Trigger Meeting Munich Feb.11, 08 Trigger strategies Sofar, goal was To select elastic proton vertex (beam,RPD, beam killer) +To exclude potentially incomplete events (sandwich veto) +To reduce elastic events (elastic veto, multiplicity trigger) Good for diffractive projectile excitation and central production +To enhance central production (forward hodoscope) Need to consider whether and how to select specific states (3π, K + K -, ηη) by trigger (multiplicity trigger, calo trigger?)