STAR as a Fixed Target Experiment?

1. STAR as a Fixed Target Experiment? Sam Brovko, Brooke Haag, Daniel Cebra Abstract 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. LF Spectra Phone Conference

2. Low Energy Reach of Fixed Target Beam Energy Scan

3. Beam Energy Scan 64 GeV What if the critical point is here? Fixed Target points Or here?

4. h=1.0 h=1.5 h=1.0 h=1.5 h=2.0 h=2.0 Al Beam Pipe Be Beam Pipe Al Beam Pipe

5. 3 AGeV 197Au + 27Al • Required Steps: • Demonstrate that we can select Al target events • Demonstrate that we can demonstrate that we have am Au projectile • Demonstrate that we know that collision energy

6. Selecting Aluminum Target “7.7 GeV” Data set: Select Events with 100 < |Vz| < 200 and 2 < Vr < 5 cm FTPC SVT Support Beam pipe Au+Au Counts Vy Al Be Al Vz Vx

7. 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/dx • The 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

8. Data to Support Collision Energy Note, protons show a narrow distribution around mid-rapidity. p+ contamination

9. Determining that the projection is Au Projectile + 27Al 7.7 GeV Au+Au Mmax ~50 For Au+Al: Npart ~70 Expect Mmax ~45 from extrapolation of E895 From E895 Au+Au Mmax at 2 AGeV is ~200 Mmax at 4 AGeV is ~300 Npart ~380 STAR Collaboration Meeting LBNL

10. Determining that the projection is Au STAR 3 AGeV Au+Al data Glauber Prediction for 3 AGeV Au+Al

11. STAR Collaboration Meeting LBNL

12. Pion Spectra from 3.85 AGeV Au+Al

13. Acceptance for Fixed Target h = 1.8

14. 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.

15. Backup Slides

16. STAR Collaboration Meeting LBNL

17. STAR Collaboration Meeting LBNL

18. STAR Collaboration Meeting LBNL

19. STAR Collaboration Meeting LBNL

20. STAR Collaboration Meeting LBNL

21. STAR Collaboration Meeting LBNL

22. STAR Collaboration Meeting LBNL

23. STAR Collaboration Meeting LBNL

24. STAR Collaboration Meeting LBNL

25. STAR Beam Pipe Location A 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.

26. Schematic Diagram of the beam pipe profile

27. Beam Pipe Locations 19.6 GeV Au+Au 2001 9.2 GeV Au+Au 2008 Vxy Vxy 6733 Au+Au 4150 Beam pipe Au+Au r<2 Au+pipe r>2 100863 Au+Au 2882 Beam pipe Vz (r>2) Be Be Vz (r>2) Au+Al |Vz|>75 Au+Be |Vz|<75 Al Al Al Al 2241 Au+Al 641 Au+Be ~3000 Au+Al ~1000 Au+Be

28. 22.4 GeV Cu+Cu 2005 7.7 GeV Au+Au 2010 Vxy Vxy Au+Au Beam pipe Au+Au r<2 Au+pipe r>2 Cu+Cu Beam pipe Be Vz (r>2) Au+Al |Vz|>75 Au+Be |Vz|<75 Vz (r>2) Al Al Be Al Al Beam pipe supports

29. Beam-on-Pipe Collisions