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STARSTAR
Slide 1 of 40Brovko, Haag, CebraJanuary 06, 2011
LF Spectra Phone Conference
STAR as a Fixed Target Experiment?
Sam Brovko, Brooke Haag, Daniel CebraAbstract for APS meeting: Analysis of fixed target collisions between gold ions in the beam and aluminum nuclei in the beam pipe using the STAR detector at RHIC will be presented. These fixed target collisions allow us to study a region of collision energy below the lowest energy scheduled for the RHIC beam energy scan. This might extend the region baryon chemical potential available for discovery of the critical point in the hadronic gas to quark-gluon plasma boundary in the nuclear matter phase diagram. In this talk, we will show preliminary results of pion, proton and light nuclei spectra as well as dN/dy distributions for pions and protons. Comparisons will be made to results from the AGS heavy ion program and to UrQMD simulations.
STARSTAR
Slide 2 of 40
Low Energy Reach of Fixed Target Collision Energy(GeV)
Single Beam Energy
Single Beam Pz (GeV/c)
Fixed TargetRoot S
Single Beam Rapidity
Center of Mass Rapidity
200 100 99.996 13.7 5.41 2.70
64 32 31.98 7.72 4.23 2.11
39 19.5 19.48 6.17 3.93 1.97
27 13.5 13.47 5.19 3.37 1.68
18 9.0 8.95 4.30 2.96 1.48
11.5 5.75 5.67 3.53 2.48 1.24
7.7 3.85 3.73 2.98 2.07 1.04
6.1 3.05 2.90 2.73 1.84 0.92
Bea
m E
nerg
y S
can
STARSTAR
Slide 3 of 40
Beam Energy Scan
64 GeV
Fixed Target points
What if the critical point is here?
Or here?
STARSTAR
Slide 5 of 40
Required Steps:1) Demonstrate that we can select Al target events2) Demonstrate that we can demonstrate that we have
am Au projectile3) Demonstrate that we know that collision energy
3 AGeV 197Au + 27Al
STARSTAR
Slide 6 of 40
Selecting Aluminum Target
“7.7 GeV” Data set:Select Events with 100 < |Vz| < 200 and 2 < Vr < 5 cm
Vz Vx
VyCou
nts
Al AlBe
FTPC SVT Support Au+AuBeam pipe
STARSTAR
Slide 7 of 40
Determining the Collision Energy
Challenge – We have “oriented” the target parallel to the beam axis The target is infinitely “thick”.
The initial projectile energy is 2.94 AGeV. How much energy is lost prior to the Au+Al nuclear collision?
Range of 3 AGeV Au in Al is 64.8 cm due to dE/dxThe Au+Al nuclear interaction length is 3.63 cm.The Au ion travels only 5% of its range before
experiencing a nuclear collision, therefore it will lose only 5% of its energy.
Collision Energy is 2.8 +/- 0.2 AGeV
STARSTAR
Slide 8 of 40
Data to Support Collision Energy
Note, protons show a narrow distribution around mid-rapidity.
p+ contamination
STARSTAR
Slide 9 of 40Daniel CebraOctober 6, 2009
STAR Collaboration MeetingLBNL
Determining that the projection is Au
7.7 GeV Au+AuProjectile + 27Al
From E895 Au+AuMmax at 2 AGeV is ~200Mmax at 4 AGeV is ~300
Npart ~380
Mmax ~50
For Au+Al:Npart ~70
Expect Mmax ~45 fromextrapolation of E895
STARSTAR
Slide 10 of 40
Determining that the projection is Au
Glauber Prediction for 3 AGeV Au+Al
STAR3 AGeV Au+Aldata
STARSTAR
Slide 14 of 40
Conclusions
• We can select fixed target Au+Al events • The collision energy is fairly well defined
• Fixed target geometry is adequate to RHIC sub-injection energy beams.
• We will focus on charged particle spectra.
STARSTAR
Slide 25 of 40
STAR Beam Pipe LocationA description of the STAR beam pipe can be found at arXiv:nucl-ex/0205008v1
Features:• Diameter of the central region of the beam pipe is 7.62 cm• There is/was a support disk for the SVT at 54.8 cm with OD
128 mm and ID 89 mm• From 0 to 76 cm => pipe is made of 1.0 mm thick beryllium• At 76 cm there is a weld to an 1.24 mm thick aluminum pipe• At 130 cm there is an Al to Al weld, no change in pipe
diameter or thickness.• From 76 to 402 cm => the pipe is 1.24 mm thick aluminum• There is a flange and bellows at 4 meters, the pipe diameter
goes to 12.7 cm• There is another flange and bellows at 7.12 meters.
STARSTAR
Slide 27 of 40Daniel CebraApril 26, 2010
19.6 GeV Au+Au 2001 9.2 GeV Au+Au 2008
Vxy Vxy
Vz(r>2)
Vz
(r>2)
Al AlAlAl
Be Be
6733 Au+Au4150 Beam pipe
100863 Au+Au2882 Beam pipe
~3000 Au+Al~1000 Au+Be
2241 Au+Al641 Au+Be
Au+Al |Vz|>75Au+Be |Vz|<75
Au+Au r<2Au+pipe r>2
Beam Pipe Locations
STARSTAR
Slide 28 of 40
22.4 GeV Cu+Cu 2005 7.7 GeV Au+Au 2010
Vxy
Vz
(r>2)AlAl Be
Au+Au Beam pipe
Au+Al |Vz|>75Au+Be |Vz|<75
Au+Au r<2Au+pipe r>2
Vxy
Vz(r>2)
Al Al
Be
Cu+Cu Beam pipe
Beam pipe supports