Strangeness Production Measurements and H0 Di-baryon Search by AGS Experiment E896

1. An update on the strangeness production measurements and H0 di-baryon search as performed by AGS experiment E896 AGS/RHIC USERS MEETING BNL AUGUST 7/8 2000

2. Space Science Laboratory M.Bennett, H.Crawford, J.Engelage, I.Flores, L.Greiner, E.Judd, A.Tratner Brookhaven National Laboratory W.Christie, R.Debbe,T.Hallman,T.Ljubicic, R.Longacre, D.Lynn, J.Mitchell, E.Mogavero, A.Saulys University of California, Los Angeles Huan Huang, G.Igo, S.Kelly, S.Trentalange Carnegie Mellon University M.Kaplan, Z.Milosevich, D.Russ, J.Witfield University of Catania S.Albergo, D.Boemi, Z.Caccia, S.Costa, A.Insolia, C.Nocifero, R.Potenza, G.Russo, A.Tricoma, C.Tuve Johns Hopkins University L.Madansky Lawrence Berkeley Laboratory P.Lindstrom, C.Tull NASA - Goddard Space Flight Center J.Mitchell Ohio State University H.Caines, T.Humanic, I.Kotov, G.Lo Curto, E.Sugarbaker Rice University B.Bonner, K.Kainz, W.Llope, E.Platner University of Texas G.Hoffman, P.Jensen, S.Paganis, P.Riley, J.Schambach, J.Tang Wayne State University R.Bellwied, S.Nehmeh, S.Pandey, J.Sheen, J.Takahashi, K.Wilson

3. Outline • Experiment • DDC • SDDA • L Spectra Analysis • L Polarization Analysis • H0 Search • Conclusions

4. The E896 Experiment

5. The Distributed Drift Chamber The DDC has 144 planes with ~8000 output channels. There are 12 modules each containing planes of 3 different wire orientations 0,+15,-15, with eight 0 degree planes, and 2 each of the +15,-15 in each module Charge collected on these wires along with the plane coordinate allow an unambiguous 3D space point to be determined Active volume of 120 x 67.5 x 20 cm Located 1.3m downstream of the target in a 1.7T analyzer magnet

6. The Silicon Drift Detector Array Ionizing particle 15 planes of SDD with a spacing of 1.5cm Located ~10cm from the target Proto-type wafers and electronics for the STAR SVT Y-position from readout anode number SDD X-position from drift time X Electron cloud SDD gives unique position in X-Y * 6.3 cm x 6.3 cm area * 280 mm thick n-type Si wafer * 20 mmposition resolution

7. The Design of E896 E896 was optimized to search for the H0 di-baryon (a 6 quark state of uuddss) via the decay channels H0 S-p p np- andH0  L pp- and assuming a lower limit ofct = 4cm (ct H0 = ctL/2).

8. The Design of E896 (2) • SDDA identifies: • p,p and heavier particles using dE/dx • L, K0sat mid-rapidity • L polarization as function of pt and xf • DDC identifies: • L, K0sat high rapidity, low pt • L polarizationas a function of pt • The phase space coverage of the SDDA and DDC • is complementary —

9. An Event in SDDA and DDC SDDA DDC X 35 X [cm] -5 480 Z 380 Note: These are different events there is no DAQ connection between the two tracking detectors Z [cm]

10. The SDDA PID d Preliminary } t RQMD p He k 0 1.6 GeV Only identify ~1% of produced protons with dE/dx Preliminary

11. The 896 L Acceptance SDDA DDC Our large acceptance for Ls will allow E896 to measure the L production from mid-rapidity to near-beam rapidity. The symmetry of the collision means we should be able to report on virtually the whole rapidity region

12. DDC L coverage Although there are many secondary vertices outside of the DDC volume we do not use them as the strongly varying B-Field makes their mass/mtm reconstruction bad

13. The Armenteros Plots SDDA DDC K0s K0s L L

14. Invariant Mass Distributions from the DDC 26 Million Events, z>381.5cm 71,788 L, s=4 MeV/c 3720 K0s , s=10 MeV/c Preliminary

15. DDC L Mt Distributions Comparison to E891 –Consistent except at low mt where E891 sees a plateau Fit to data – Good Fits Our coverage too small to allow extraction of inverse slopes Preliminary Preliminary

16. DDC L Mt Distributions Comparison to RQMD 2.4 – Very good in range covered Preliminary

17. Invariant Mass Distribution of L from the SDDA 5700 L, s=5 MeV/c Counts From ~340000 events mass(GeV/c)

18. Ldistributions from the SDDA Preliminary Preliminary T vs y mt distributions – Varying y slices

19. L Polarization Parity conservation in strong interactions meansL spin is aligned normal to the production plane n = PB x PL Transverse polarization of the L is determined from the angular distribution of the decay proton dN/d cos(q ) = A(1 + a P cos (q)) P- Polarization, a = 0.642 the proton asymmetry, q - angle between the decay p and the normal in center of mass of the L

20. Trends in L Polarization Acceptance Transverse polarization is negative with respect to the normal to the production plane Polarization is linear in pt up to pt~1GeV/c Saturation value of polarization is a linear function of xf and is 0 at xf=0 P-Be various energies

21. E896 L Polarization Acceptance Xf – Fraction of the incident p momentum carried by the longitudinal momentum of theL Pt (GeV/c) SDDA Coverage DDCCoverage: Xf > 0.7 pt < 0.6 GeV/c Xf

22. SDDA L Polarization SDDA Data xf < 0.25 <pt> 0.8 GeV/c 0.25<Xf <0.4 <pt> 1.2 GeV/c xf > 0.4 <pt> 1.7 GeV/c Preliminary • Average p-Be data • at same pt and xf

23. DDC L Polarization Preliminary xf >0.7

24. What is the H0 di-baryon (uuddss) u d s u d s H0 s u s d d u di-L The standard model states that all quarks are confined within colour singlets. Currently we have only detected mesons (qq) and baryons (qqq) however the existence of (qqqq) and (qqqqqq) etc are not precluded. Calculations show that the uuuddd state is heavier than the deuteron by ~350MeV and so would not be stable. However work by Jaffe over 20 years ago predicted that the uuddss was deeper bound than the colour singlet sub-system alternative the di-L The H0 is the lowest lying 6-quark state. It is NOT a bound di-L. It differs in that all 6 quarks are contained in a single bag. In the di-L you have two 3-quark colour singlets. In the case of the H0 only the 6-quark system has to be in a colour singlet.

25. Present Status – Limits established • To date there have been over 20 experiments designed to look for • evidence of the H0.. All have been null, inconclusive or controversial. • However they have produced upper limits on production cross-sections and limits on the H0 mass. • Limits Established: • For the H0 to be stable (against strong decay) it must have a • H0mass<2L • If a di-L hypernuclei weak decay can be observed • H0mass >2L-BLL(A,Z) • Akio et al. (Prog. Theor. Phys. 85 1991) set an upper limit on the B.E. of double-L to be 30MeV via energy reconstruction from its observed decay (only 1 event) •  2200 < MH0 < 2230 MeV

26. E896 and the H0 di-baryon • E896 extends the search into the short lifetime (ct=4cm) • Heavy-ion collisions via their copious L production produce a favourable environment for the H0 and di-L production. (Previous experiments tend to use Kaon or proton beams where the probability for 2 Ls to be produced is greatly reduced) • Offers a new, more probable, production channel through the coalescence of two Ls into either a bound di-L moleculeor the spontaneous decay into the H0. • If a QGP is formed the H0 production probability is greatly enhanced. • Sensitive to low binding energy

27. The H0 Search H0 S-p  p n p- First search for a stiff positive particle (highlighted here in green) Look for a negative track which forms a secondary vertex in the DDC. Identify the kink in the negative track H0 embedded into a real event p H0 S-

28. The H0 Kink angle The majority of S- from an H0 decay in the DDC decay with a small kink angle. The H0 search to date had an efficiency that was strongly dependant on the decay angle. Work is now in progress to improve the efficiency for small angle kink decays

29. The H0 Sensitivity H0 -> S- p From calculations of the acceptance and efficiency for H0’s we can estimate our sensitivity for reconstructing the H0 The sensitivity is dependent on the lifetime of the H0 Min. # Min # H0’s produced in collision #H0’s detected =2, #Events=108, eff=5%, BR = 1/3, acc determined from simulation

30. Conclusions • L Spectra • Pt spectrum agree with RQMD at high rapidity • Inverse slopes appear to follow protons • First measurements at mid-rapidity • L Polarization Indications of polarization at high pt and xf in Au+Au collisions. Polarization is in agreement with the p-p data These measurements have not been made previously • H0 search • The search continues..