in p+pbar collisions at sqrt{s}
in p+pbar collisions at sqrt{s}
in p+pbar collisions at sqrt{s}
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Possible signal and background sources<br />
• Non-physical sources:<br />
� Cosmic rays:<br />
� no vertex, � no ZDC.<br />
� Beam gas <strong>in</strong>teractions:<br />
�no vertex, � large multiplicities.<br />
⇒ Trigger criterion gets rid of those<br />
• Physical sources:<br />
� Peripheral nuclear A+A <strong>collisions</strong>:<br />
� large multiplicities, � large p T .<br />
� Hadronic diffractive (Pomeron-Pomeron, rapidity gap):<br />
� forward proton emission, � larger p T : p T (γγ) < p T (PP),<br />
� expect like-sign pairs too.<br />
⇒ Analysis cuts gets rid of them<br />
� Incoherent UPC: γ+n → n+J/ψ<br />
� wider p T : p T (γγ) < p T (γP), � asymmetry dN/dy,<br />
� >2 neutrons (<strong>in</strong>duced nuclear break-up) w/ same direction as J/Ψ.<br />
� Coherent UPC: γ+γ → e + e - , γ+Α → X+J/ψ, γ+A → jet(s)+A<br />
Sensitive to coherent and <strong>in</strong>coherent UPC<br />
ISSP-Erice Mickey Chiu 7/ 16
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