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..