Minutes of the HERA Meeting 21.3.2006

HERA (F.Willeke):

Lumi production with 58% duty cycle over the last 7 days.
Electron current was gradually increased to 36 mA.
L_int = 6.9 pb^-1 measured at ZEUS, 5.9 at H1.
Peak Lumi was 4.4 10^31/cm^2/s at ZEUS.
There is a significant discrepancy in measured lumi between H1 and ZEUS.
Lspec as measured by ZEUS follows more closely the expectations from
machine parameters at the start of collisions, H1 is low.

Optics corrections to reduce the beta-beat from 15-20% to 10% will be
loaded today.

Main problem: background conditions at ZEUS.
Suspicion of coasting beam not confirmed.
Orbit, collimator, and tune adjustment often help, but not consistently.
So far, no suspicious proton power supply causing spikes was identified.

Polarisation starts at 25%, rising towards 40% during a fill.
e tunes were not aggressively lowered towards resonances for better
polarisation.

Proton intensity limited by pre-accelerators (dipole corrections during
ramp in DESY 3). Current in HERA dropped from 89 to 79 mA during the week.


ZEUS (T.Schoerner):

Collected data with 66% average efficiency. 2 good fills had 91%, others
were limited by background spikes, mostly from the p beam.
Source of background not known.

HERA proposed to measure p beam diffusion rate in each fill:
scrape halo by deep insertion of a collimator (all exp. off), measure
repopulation of tails. Require some time to prepare diagnostic tools.

Optics corrections might also reduce backgrounds.


H1 (P. Laycock):

Took data in good conditions, HV efficiency up to 98% (for the fill on
Sunday).
VFPS roman pots suffer from p spikes, frequently retracted.


Hermes:

Low backgrounds at injection and during lumi.
Changed from H to D target gas, at low density.
Recoil magnet is off: problem with He valve regulation, caused a quench
last Wed. Reprogramming in progress, ready by Thu or Fri.
High density running will be resumed then.


Plan:

Continue lumi operation, increase electron current towards and beyond
40 mA.

The proton multibunch feedback system will be active, for shorter bunches
and less energy spread. For the same effect, the 4th 208 MHz cavity will
be phase shifted at the end of the proton ramp to assist the other 3.

End of fill: dump or 1 hour high density run at 14 mA.

H1 is coordinating experiment.

Daniel Pitzl