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Experimental background at the presence of pressure rise in RHIC
Angelika Drees, Ubaldo Iriso-Ariz
RHIC
How to measure collision rates
Vacuum and collision data
Summary
Angelika Drees eCloud 04, Apr 22, 2004
RHIC
eCloud 04, Apr 2004
The STARExperiment
*=1m4m Be2x4m Al
maximumprojection
minimumprojection
physics target
Best 7 days: delivered 179 (b)-1 to Phenix
New records reached
The cross section to measure luminosity
eCloud 04, Apr 2004
The ZDC detector
eCloud 04, Apr 2004
Located behindDX magnets
•ZDCs are common to all IRs •Shielded by the DX magnets (small backgrounds)•Small acceptance (small backgrounds)•Sensitive to neutrons only (small backgrounds)
Expected collision rates
eCloud 04, Apr 2004
RZDC (Hz) = ZDC * LCross section has been calculated and measured to better than +/- 10%
Fill pattern in 04
eCloud 04, Apr 2004
STAR and PHENIX had both *=1m
For most of the run the abort gap was aligned such that it crossed in PHENIX and BRAHMS
Needs to be corrected for to compare experiments
=> ~7% less expected collision rates in STAR
Blue gap
Yellow gap
Automated Luminosity Steering
LISA commissioning version used for Vernier Scans in Run 3. Used for automated collision steering, using feedback from ZDC at the beginning of every store.
Vacuum history at STAR during 04
eCloud 04, Apr 2004
“bad” vacuum periods
difference between “good” and “bad” < x5
Background conditions in STAR
eCloud 04, Apr 2004
Backgrounds during period of high vacuum
ZDC coincidence
ZDC coincidence
Blue bkgdYellow bkgd
Background during period of “good” vacuum
Background and pressure after rebucketing
Different vacuum conditions
eCloud 04, Apr 2004
“good”
“bad”
Pressure evolution during a store in STAR and PHOBOS
Evolution in store is very different (?). Causes unacceptable backgrounds in PHOBOS and high trigger rates in STAR
Fill 4471 ZDC coincidence, pressure and backgrounds
eCloud 04, Apr 2004
No excess rate at STAR
Decent background
Small pressure rise
Fill 4420 ZDC coincidence and vacuum
eCloud 04, Apr 2004
ZDC coinc.
Pressure @ STAR
Excess rate STAR should show 7% less coincidence rates than PHENIX
Use STAR-PHENIX as a measure for accidental collisons due to beam-gas.
eCloud 04, Apr 2004
Beam-gas cross section
Calculating Accidental Collision rates
eCloud 04, Apr 2004
=> Racc.coin ~ p2
Accidental Collisions vs. Pressure (I)
eCloud 04, Apr 2004
Accidental Collisions vs. Pressure (II)
eCloud 04, Apr 2004
Predicted vacuum distribution
eCloud 04, Apr 2004
Without beam (VACCALC)*Instantaneous pressuredistribution as created by EC
* Ping He, BNL
Summary
eCloud 04, Apr 2004
The ZDCs are a detector with very small background contributionsDue to automatic luminosity optimization expected coincidence are very well knownPressure rise due to EC is a problem not only at PHOBOSPressure evolution is quite different at PHOBOS and STARAccidental collision rate is consistent with beam-gas and can be calculated to benchmark different models for EC simulations