Minutes of HERA Meeting      07.08.2002

Aim of the Meeting

HERA 

• Using a constraint of Ie*Ip = 600mA**2, the present maximum currents were H1  is able to turn on the central drift chamber, the optimum luminosity is obtained for Ie=17mA and Ip=33mA with 60 colliding bunches. The luminosity is expected to be 1.7*10**31 cm-2 s-1. The bunch parameters and luminosity are similar to the values in 2000.
• About 60 machine shifts are required from August to October, about 2 machine development days per week. Polarization studies are not included, which would require at least one week of study time with the experimental solenoids turned off. This could be done in November or December.
• A very rough time estimate of dedicated background studies is 40 shifts.
• Significant improvement of the vacuum is expected after an integrated positron beam current of 30 A*h. Doing parasitic bake-out, assuming <Ie>=15mA/2 and an efficiency of 30% duration of 3 days/week, would take about 18 weeks.  

ZEUS 

• B.Loehr pointed out that understanding and solving the background problems must have the highest priority.
• F.Willeke said that the proton beam background is most likely due to beam gas interaction just upstream of the interaction region. Coasting proton beam is still present. HERA B observes somewhat less coasting beam than in 2000. Dedicate experiments should be performed to study the contribution and effect of coasting beam.

H1 

• The CJC2 chamber scales linearly with the positron beam current. The estimate of the maximum current (positron beam only) is 50mA. The observed number of random hits is roughly in agreement with the calculations. For proton beam only, the drift chamber can probably be turned on up to currents of 100mA (There is a large  uncertainty on the maximum current. The extrapolation is based on 3 points.) For luminosity operation, the maximum beam currents are given by the product: Ie*Ip=600mA**2.
• The dynamic vacuum still needs to improve by a factor of 3. During collisions 3/4 of the events have a z-vertex at the C5b collimator. A reduction of the collimator thickness is being studied.
• A tilt and position scan of both beams should be done. A test run at reduced proton beam energy was proposed in order to study the proton background.

HERMES

• So far HERMES has only had 4 days of useful data taking this year.
• The detector is ready for data taking. At positron currents of 15mA, corresponding to a factor of 3 less luminosity than in 2000, big parts of the physics program (like DVCS) are not possible as there is no beam polarization and a continuous running to take data for transversity needs an increase in HERA-e currents from 15mA to 30 mA until October.
• Polarization studies are considered to be essential.

• Commissioning of the detector has been very inefficient. HERA B got only 4 hours of beam time during the last 10 days. In total, about 42 shifts are required for detector commissioning until September. Half of this has been done so far. 60 proton bunches are fine for commissioning (interaction rates of 1 - 2 MHz). The full bunch structure is needed for data taking.
• HERA-B pointed out, that in case a long shut down to modify the interaction regions of H1 and ZEUS will happen, HERA-B will make very strong request to get enough dedicated beam time BEFORE this shut down to complete his physics program, since there is a high probability that HERA-B will not be in a position to switch on the experiment again after such a shut down.

Until the next HERA coordination meeting the weekly schedule is:

• Monday to Wednesday: machine shifts and dedicated background studies.
• Thursday to Sunday: luminosity operation using the beam and bunch parameters proposed by F.Willeke. After some runs for re-establishing luminosity at low currents, the positron current will be slowly increased starting at 20mA in 60 bunches.  HERA will then go to 120 bunches.

                           Uwe Schneekloth