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Delphi Luminosity Determination and Final Focus Options

Explore the situation at Delphi at LEP, focusing on luminosity determination and final focus options for improving beam dynamics and performance. Discussing current challenges, mitigation strategies, and future plans for optimization.

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Delphi Luminosity Determination and Final Focus Options

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  1. Brainstorming regarding final focus options What do we need? What can we get? M. Koratzinos 2 December 2013

  2. Situation at Delphi at LEP Delphi had a: • silicon vertex detector • A small angle tagger (SAT) replaced by the small angle tile calorimeter (STIC) for absolute luminosity determination • and a very small angle tagger (VSAT) after the last FF quad for relative luminosity determination • A final focus superconducting quadrupole (QSC) 4m from the IP

  3. Reminder: DELPHI and VSAT QSC was at L* ~4m VSAT placed 8m from IP

  4. VSAT location – x view Beam pipe: 12cm diameter

  5. The DELPHI STIC two cylindrical detectors placed on either side of the DELPHI interaction region at a distance of 220 cm, covering an angular region between 29 and 185 mrad in polar angle (from 6.5 to 42 cm in radius).

  6. The DELPHI silicon tracker Innermost layer at R=63mm

  7. recap • DELPHI beam pipe: 12cm diameter • QSC 4m from the IP, next to beam pipe • Angle of last quadrupole: 15mrad (cm) 10 25mrad QSC 5 15mrad 0 1 3 5 2 4 6 (m)

  8. The current status of the TLEP FF effort • First attempt with L* of 3.5m does not yet work (one needs a lot of improvements): • Momentum acceptance (especially at the –ve side) is only ~0.5% • Dynamic aperture insufficient • But beam size at 15 sigma at the quadrupole is ~10mm!!

  9. mitigation • We have three mitigation scenarios: • We relax the condition on L* (3.5m) • We relax the condition on Beta* (1mm) • We do none of the above and try harder • Relaxing the condition on beta* (for me personally!) is not an option as it directly affects the luminosity

  10. L* of 2m • We have tried to change the position of the last quadrupole – move it closer to the IP – from 3.5m to 2m • This improves dynamic aperture, but not the momentum acceptance • It is currently not clear if this is the way to go (might be!)

  11. Strategy • We would like to find a (non-ideal perhaps) point which we can prove that works • We then will try and move (adiabatically?) towards our goal of beta*=1mm, L*=4m This is work in progress. Please stay tuned for news

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