CFT Occupancy dependence on Beam Luminosity

David Lam

Nov 2003

CFT Occupancy vs. Luminosity

Choose 3 classes of events for the study: Zero-biased triggered Minimum-biased triggered Jet triggered

Events with delivered luminosity range from 6E30 to ~40E30 (cm-2 s-1)

Two set of events: Set 1: 10 events between Feb and Mar 2003 Set 2: 11 events in August (just before the shutdown)

Method Use a modified version of cft_offline_mon Use D0TriggerFilter to pick out the desired events. Once the desired trigger is found, no further restrictions

are applied to other triggers. For example, some of the min-biased events may also have zero-biased and jet triggers.

However, due to the large prescales applied to min-biased and zero-biased events (in order of 105 – 106), we don’t see any overlapping of triggers in our data sample.

That is, all the min-biased events found in the data contain min-biased trigger only. This applies to zero-biased events as well.

Occupancy distributions (180790)

Blue: JT_45TT

Red: JT_95TT

Green: JT_125TT

Results

Fitting results show occupancies increased with luminosity as expected Green: Zero-biased triggered Red: Min-biased triggered Blue: JT_45TT triggered Grey: JT_95TT triggered Yellow: JT_125TT triggered (for set 2 only)

MC min-biased and zero-biased events are also included.

When extrapolated, at 200E30, jet triggered occupancy is approximately: 0.40 - 0.44 (CFTX1)

Events between Feb. and Mar.

Events in Aug (before shutdown)

Zero-biased and min-biased results

Zero-biased events triggered on beam crossing: Contain mostly electronic background “noise” Occupancy variation due to p/anti-p halo

Min-based events triggered on collision: Signal in luminosity monitors above threshold on both ends Number of collision increases with luminosity – Poisson

distribution. Supposedly, occupancies increase faster with luminosity

compared to zero-biased event. But, slopes for the fits of min-biased events are lower

than zero-biased and jet triggered – so dig deeper….

Jet triggers results

The different jet trigger fits (JT_45TT, JT_95TT and JT_125TT) look similar, and the slopes are close to the slopes of zero-biased events.

As the delivered luminosity reaches 200E30, the average CFT occupancies for Axial layer 1 is close to 0.40-0.44.

Trigger luminosity

Look into the recorded luminosity for each event Recorded luminosity are stored by luminosity

block (LBN), which usually corresponds to time interval of 1 minute.

Multiply the recorded luminosity by appropriate L1 prescales to obtain trigger luminosity.

Plot occupancy vs. trigger luminosity for each trigger. Luminosities are in unit of (1030 cm-2), which corresponds to luminosity in a LBN

Occupancy vs. triggered luminosity (Set 1)

Occupancy vs. triggered luminosity (Set 2)

Result (cont.)

The fits look similar to the occupancy vs. beam (delivered) luminosity plots.

Again, the min-biased events have the smaller slopes compared to zero-based and jet triggered events. This suggest zero-biased events not only contain detector noise but also include min-biased events as well.

JT_95TT trigger is not prescaled for Runs in set 1. This trigger is used to compare with prescaled JT_45TT trigger, and the fit for the two triggers agree well.

JT_45TT trigger for set 2

It turns out JT_95TT is also not prescaled for Runs in set 2 as well, by comparing with JT_125TT trigger (which is never prescaled).

However, the triggered luminosity for JT_45TT for set 2 are about 10 times larger than expected (after prescale correction) – suggest something wrong with the prescales?

JT_45TT Events (Set 2)

Conclusion

This confirms that CFT occupancies increase with delivered luminosities.

The dependencies are linear in the range of beam luminosities investigated (6E30 ~ 40E30), for events of different triggers.

If such dependencies still hold in luminosity range up to 200E30, the expected occupancy for Axial layer 1 will be around 0.40 – 0.44.