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

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

Outline

Experiment

DDC

SDDA

Spectra Analysis

Polarization Analysis

HSearch

Conclusions

The E896 Experiment

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

The Silicon Drift Detector Array

SDD gives unique position in X-Y

* 6.3 cm x 6.3 cm area

* 280 m thick n-type Si wafer

* 20 m position resolution

Ionizing particle

X-position from drift time

Electron cloud

X

SDD

Y-position from readout anode number

15 planes of SDD with a spacing of 1.5cm

Located ~10cm from the target

Proto-type wafers and electronics for the STAR SVT

E896 was optimized to search for the H0 di-baryon (a 6 quark state of uuddss) via the decay channels

H0 -p p n -

and H0 p -

and assuming a lower limit of c4cm (cc/2).

The Design of E896

The Design of E896 (2)

SDDA identifies:

p,p and heavier particles using dE/dx

K0s at mid-rapidity

polarization as function of pt and xf

DDC identifies:

, K0s at high rapidity, low pt

polarization as a function of pt

The phase space coverage of the SDDA and DDC

is complementary

—

An Event in SDDA and DDC

Z [cm]

X [cm

]

Z

X

380

480-5

35

Note: These are different events there is no DAQ connection between the two tracking detectors

SDDA DDC

The SDDA PID

Only identify ~1% of produced protons with dE/dxPreliminary

d

p

k

RQMD}t

He

0 1.6 GeV

Preliminary

Our large acceptance for s will allow E896 to measure the 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

The 896 Acceptance

SDDA

DDC

DDC 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

The Armenteros Plots

SDDA DDC

K0s

K0s

Invariant Mass Distributions from the DDC

3720 K0s ,

=10 MeV/c

26 Million Events, z>381.5cm

Preliminary

=4 MeV/c

DDC Mt Distributions

Fit to data – Good Fits Our coverage too small to allow extraction of inverse slopes

Comparison to E891 –Consistent except at low mt where E891

sees a plateau

Preliminary Preliminary

DDC Mt Distributions

Comparison to RQMD 2.4 – Very good in range covered

Preliminary

Invariant Mass Distribution of from the SDDA

mass(GeV/c)

Cou

nts

From ~340000 events

5700

=5 MeV/c

distributions from the SDDA

Preliminary

Preliminary

T vs ymt distributions – Varying y slices

Polarization

Parity conservation in strong interactions means spin is aligned normal to the production plane

n = PB x P

Transverse polarization of the is determined from the angular distribution of the decay proton

dN/d cos() = A(1 +P cos ())

P- Polarization, = 0.642 the proton asymmetry,

- angle between the decay p and the normal in center of mass of the

Trends in 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

E896 Polarization Acceptance

Pt (

GeV

/c)

Xf

Xf – Fraction of the incident p momentum carried by the longitudinal momentum of the

SDDA Coverage

DDC Coverage:

Xf > 0.7

pt < 0.6 GeV/c

SDDA 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

DDC Polarization

xf >0.7

Preliminary

What is the H0 di-baryon (uuddss)

u

su d

sd

di-

u

dsd

su

H0

The H0 is the lowest lying 6-quark state. It is NOT a bound di-. It differs in that all 6 quarks are

contained in a single bag.In the di- 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.

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-

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<2

• If a di- hypernuclei weak decay can be observed

H0mass >2-B(A,Z)

Akio et al. (Prog. Theor. Phys. 85 1991) set an upper limit on the B.E. of double- to be 30MeV via energy reconstruction from its observed decay (only 1 event)

2200 < MH0 < 2230 MeV

Present Status – Limits established

E896 and the H0 di-baryon

•E896 extends the search into the short lifetime (c=4cm)

• Heavy-ion collisions via their copious production produce a favourable environment for the H0 and di- production. (Previous experiments tend to use Kaon or proton beams where the probability for 2 s to be produced is greatly reduced)

•Offers a new, more probable, production channel through the coalescence of two s into either a bound di-moleculeor the spontaneous decay into the H0.

•If a QGP is formed the H0 production probability is greatly enhanced.

•Sensitive to low binding energy

The H0 Search

H0 -p p n -

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

H0 -

p

The H0 Kink angle

The majority of - 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

The H0 Sensitivity

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

BReffaccEvents

ectedsHo

***#

det_'#

#H0’s detected =2, #Events=108, eff=5%, BR = 1/3,

acc determined from simulation

H0 -> - p

Min # H0’s produced in collision

Min

. #

Conclusions

Spectra

Pt spectrum agree with RQMD at high rapidity

Inverse slopes appear to follow protons

First measurements at mid-rapidity

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..