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Pentaquark Searches at the Relativistic Heavy Ion Collider
Sonia KabanaUniversity of Nantes and SUBATECH, Nantes,
France
EINN 2005Milos, Greece, 20 Sept. 2005
OutlineOutline
• Introduction• Pentaquark Searches in STAR
theta++Xi0/N0theta+Xi--
• Pentaquark Searches in PHENIXanti-theta-
• Conclusions and outlook
IntroductionIntroduction
Relativistic Heavy Ion Collider at Brookhaven Lab:RHIC energy <= sqrt(s)=200 GeV per NN collisionsCollisions studied: AuAu, pp, dAu, CuCuFour experiments: Phenix, Star, Phobos, BrahmsPhysics goals:
-QCD phase transition at Tc 200 MeV new signature seen: jet quenching-Spin of the nucleon
PR
L 92
(20
04
) 05
23
02
; PR
L 91
(20
03
) 18
23
01
What is special about RHIC for exotic particle searches ?What is special about RHIC for exotic particle searches ?
STAR, PHENIX: Elliptic flow of hadrons scales with the nr of quarks -->Data suggest hadron formation through quark coalescence --> quark coalescence as new production mechanism opens up for multi-q/g states
Measurements from Heavy Ion Collisions at SPS and RHIC suggest strongly that a new state of matter is formed in these collisions made by (100eds) of deconfined quarks and gluons
RHIC may be a unique source of multiquark and gluon states made by coalescence possibly out of a hadronizing QGP
STAR
PHENIX
STAR identification capabilities used in this study:
TPC inside a magnet, dE/dx id, topological id for decays in the TPC STAR is able to detect many strange particles in large acceptance (full phi, =-1,1): , , 0s, , , (1530), (1520), K+- etc.
Dedx plot
One event p+p with a Xi or L embedded to illustrate the topological cuts
STARSTAR
STAR theta++/+, Xi-- SearchesSTAR theta++/+, Xi-- SearchesXi-- -> pi- Xi-+ p + KS
++ p + K+
Data Set:Au + Au 200 GeV run 2 (~1.7 M, 30-80%) p + p data 200 GeV run 2 (~6.5 M, Z<75cm)d + Au 200 GeV run 3 (18.6 M)Au + Au 63 GeV run 4 (5.6 M)Cu + Cu 63 GeV run 5 (16.5 M)Au + Au 200 GeV Run 4 (10.7 M, 20-80%)
H. Huang, Y. Ma, S. Salur, C. Markert
Results shown in : J Ma, APS april 2005, H Huang Beijing june 2005, H Huang, DNP Hawai 19-25 Sept 2005
dAu results
The invariant mass distribution is fitted to a Gaussian plus a linear function. A 3.5-5.0 sigma signal is seen Measured mass is about 1.53 GeV/c2. Full width is about 15 MeV
AuAu 62.4 GeV Results
AuAu 62 GeV data20-80% centrality bin5.6 M eventsWeak Signal (3sigma) if any
Kaon p&pt (0.2, 0.6)Proton p&pt (0.3, 1.5)
Year 4 AuAu 200 GeV data20-80% centrality bin10.7 M eventsNo Significant Signal (2)Kaon p&pt (0.2, 0.6)
Proton p&pt (0.3, 1.5)
AuAu 200 GeV Run 4 Results
Cu+Cu 62.4 GeV Run 5 Data
Year 5 CuCu 62 GeV data0-70% centrality bin16.5 M eventsNo signal at all !!
Kaon p&pt (0.2, 0.6)Proton p&pt (0.3, 1.5)
Is There an Obvious Contradiction ?
The signal is not significant in Au+Au systems
d+Au a favored system ?: signal strength and low combinatorial background --> RHIC should have another long d+Au run
A Stringent Limit from HERA-BA Stringent Limit from HERA-B
HERA-B hep-ex/0408048sqrt(s) 42 GeVpA (C,Ti,W) 200 M inelastic events+/ <0.92%; 95%CL+/(1520) <2.7%; 95% CL
Our Estimate in STARd+Au sqrt(s) 200 GeV/ ~ 0.35%
Does this imply (1520)/ ~ 34%?
STAR(1520)/ ~ 10% (corrected for branching ratio) !
Spectrum?
Spectrum includes ++ and -- Mt-exponential fit yields:dN/dy = 0.0012 +- 0.0006T = 315 +- 30 MeV
Yields for some particles in dAuKs: 0.321 +- 0.006 +- 0.03L+Lbar: 0.339 +- 0.007Xi+Xibar: 0.0251 +- 0.0006Phi: 0.0642
After acceptance and efficiency correction
Assuming 100% branching ratio
++/ ~ 2%
−−→ )1530(
+−→ )1530(
+−++ →
−−−− →
Data: dAu MinBias, 15M events. Black lines are from event mixing. Clear signals were seen for the (1530) particle. No signal for the -- has yet been seen.
From 14,000 -
From 11,600 +
STAR Preliminary
Invariant Mass (GeV/c2)
Invariant Mass (GeV/c2) Invariant Mass (GeV/c2)
Invariant Mass (GeV/c2)
Jingguo Ma, UCLA APS Meeting
05/01/2004
Xi-- STAR searchesXi-- STAR searches
Minv [GeV/c2] Minv [GeV/c2]
Star Preliminary d+Au
Star Preliminary p+p
Cou
nts
?
Star Preliminary p+p
Signal
Mixed Event
Background
?
2 MeV bin size
Sevil Salur, Yale Univ. APS Meeting 05/01/2004STAR theta+ --> pK0s searchesSTAR theta+ --> pK0s searches
dAu data, Ks0 was identified by topological method
There is some excess at invariant mass around 1540 MeV/c2, but it is not too significant statistically.
STAR Preliminary
0)( spKsuudd →+
J Ma, APS april 2005
STAR Xi0/N0 --> L K0s searchSTAR Xi0/N0 --> L K0s searchS. Kabana, R. Witt, M. Heinz
S. Kabana, 20th Winter Workshop on Nuclear Dynamics
Jamaica, 15-20 March 2004
Identification of and K0s in the present study
Topological cuts:
- Search for p - and K0s + - decay pattern (V0, requiring sec. decay vertex)
- Distance of Closest Approach (DCA) between daughters < 0.8 cm
- DCA of V0 to primary vertex < 0.4 cm, V0 Decay Length > 6 cm
- DCA of V0 daughters to primary vertex > 1.3 cm (K0s), 1.0 cm p(), 2.5 cm ()
- Accept only unambiguous K0s and , namely satisfying only one hypothesis
- Quality cuts: Nr. of hits(track) > 15 (out of max 45), Avoid same tracks used in both V0s
STAR Au+Au coll. 200 GeV preliminary
De/dx cuts:
- De/dx(tracks) < 3 from expected De/dx
- Momentum(proton) < 0.7 GeV, Momentum(pion) < 0.5 GeV
…..Identification of and K0s in the present study
Data sample:
Au + Au collisions at s(NN)=200 GeV Trigger: minimum bias, 1.45 Million events
-Require a defined primary vertex, with |Z| <25 cm
-Mass range used around the mean to select K0s and : K0s: +-35 MeV, : +-10 MeV
STAR Au+Au coll. 200 GeV preliminary
Preliminary results of STAR pentaquark searches in the K0s channel
Observation of a possible narrow peak at 1734 MeV in K0s inv.mass
Au+Au min. bias (s)NN=200 GeV Cut out upper ~10% of (tot) to suppress background
Region +- 3 MeV (~1.5 ) around maximum: S/(B)=30.6/ ( 35.4)= 5.15, S/(S+B)=3.77, Mass = 1733.6 +-0.5 MeV +-5 MeV (syst), < 4.6 +-2.4 MeV (Gauss,1 MeV bin)
Bin size 3 MeV
Blue line: mixed event
background
STAR Au+Au coll. 200 GeV preliminary
Best Significance obtained in semiperipheral ev.: S/(B)=19.36/ (10.64)=5.93
(1232) p() pi-(K0s) + K0s(pi+ pi-) = 1232+497.67 = 1729.7 MeV
Could fake possibly a peak near 1734 MeV ? Note STAR syst. error ~ 5 MeV
- Difficult to result to a narrow peak ( width ~120 MeV)
--Test 1: Cut more on DCA(p,pi) to primary vertex does not destroy the peak
Test 2: Cut Inv.Mass( p() pi-(K0s) ) out of mass +- 30 MeV does not destroy the peak
STAR Au+Au coll. 200 GeV preliminary
Phenix is the only experiment which could search up to now for the
anti-theta- --> anti-n K-
Decay channel, thanks to its ability to identify antineutrons in the electromagnetic calorimeter
Antiparticle/particle ratios at RHIC are high: >=0.7
PHENIX pentaquark searchesPHENIX pentaquark searches
K-
`n
Simulated- K- +n
Dch+PC1
PC2
EMC+PC3
Anti Pentaquarks in PHENIXAnti Pentaquarks in PHENIX
Looks fairly straightforward: Search for a big cluster in the electromagnetic calorimeter caused by ann annihilationand combine it with a K
-
0+p Fairly hopeless due to small acceptance(three particles in small aperture)
But how about the Anti Particle?
- K- +n
+ K++nNeutron difficult to identify in PHENIX
K identification up to p=1.5 GeV using TOF (EMCAL), momentum from central tracker
EMCal response for p and anti-p. The annihilation energy of anti-p leads to larger clusters, which is a signature also for anti-n identification.
C. Pinkenburg, QM2004
QuickTime™ and aTIFF (Uncompressed) decompressor
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QuickTime™ and aTIFF (Uncompressed) decompressor
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PHENIX anti-theta- --> K- anti-n identification capabilities PHENIX anti-theta- --> K- anti-n identification capabilities
Reliability of Anti-n CandidateReliability of Anti-n Candidate
pT [GeV/c]
mas
s pe
ak [G
eV/c
]
Marker : Data
Dash line : MC
-
+
mas
s fr
om P
DG
– Invariant mass peak of
-(1189.4) n + - : R.R. 99.85%, c-= 2.396cm
+(1197.4) n + + : B.R. 48.31%, c+= 4.434cm
• Mass shift due to no TOF calibration for n in EMCal is <~5%
• Quick check by Monte-Carlo shows agreement with data
- +
1.1 1.2 1.3 1.4 1.5 1.6 1.1 1.2 1.3 1.4 1.5 1.6
Cou
nts
/ bin
n + - n + +
No pT cut No pT cut
200 GeV p+p 200 GeV p+p
Same event
Mixed eventMinBias trigger
Invariant mass [GeV/c2]
No signal seen in the channel K+ anti-n, in which no signal is expected.
K+ anti-n inv. mass
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C. Pinkenburg, QM2004
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K- anti-n inv. mass
While a signal was visible near 1.53 GeV without a needed timing correction for the anti-n in EMCAL, after this correction was done the signal dissapeared.
--> Anti-sigma- signal is 2 times larger without timing correction
C. Pinkenburg, QM2004
No signal seen for anti-theta- --> K- anti-n with timing correction Remaining Mystery: why no signal in K+ anti-n without timing correction?
C Pinkenburg RHIC AGS meeting may 2004
Data SetsData Sets
• dAu @ s=200GeV ~500*106 Events
• pp @ s=200GeV ~50*106 Events
• AuAu @ s=200GeV ~36*106 Events
• From rough simulations we estimate a 0.2% reconstruction efficiency for the-
• dAu @ s=200GeV ~500*106 Events
• pp @ s=200GeV ~50*106 Events
• AuAu @ s=200GeV ~36*106 Events
• From rough simulations we estimate a 0.2% reconstruction efficiency for the-
- K- +n (pp) - K- +n (pp)
Statistically challenged analysis,So far no signal (we hope for the manypp events we are going to take in Run5)
Courtesy of Hisayuki Tori
- K- +n (AuAu)- K- +n (AuAu)Top 30% central 30-50% 50-92%
work-in-progress
work-in-progress
work-in-progress
Small plots but trust me there is currently no signal either
Courtesy of Masashi Kaneta
We now have 50 times more AuAu events from Run4!
Masashi’s thermal model predicts -/+~0.1 for central events (assuming J=1/2 for the -). Testing this should be within reach.
Future plansFuture plans• We probably can reduce the background in our K- n
invariant mass distribution• Improve the EMCal Hadron timing, that will hopefully
bring the masses closer to pdg• We can recover nearly a factor of 2 of Anti Neutrons
by recovering broken up clusters• The look very promising, we can do upper limits on
ratios since the and K efficiencies are known and the difficult Anti Neutron efficiency drops out
• 1.5*109 fresh AuAu Events @ s=200 are waiting for us
• We probably can reduce the background in our K- n invariant mass distribution
• Improve the EMCal Hadron timing, that will hopefully bring the masses closer to pdg
• We can recover nearly a factor of 2 of Anti Neutrons by recovering broken up clusters
• The look very promising, we can do upper limits on ratios since the and K efficiencies are known and the difficult Anti Neutron efficiency drops out
• 1.5*109 fresh AuAu Events @ s=200 are waiting for us
Comment: Present limit of momentum of K- to enable TOF id and related pi contamination, allows for AntiSigma- detection, but is this good enough for a much rarer pentaquark signals ?
--> Small searched signal implies need to reduce the background more than needed for detection usual hadrons (Lambdas, Sigmas..)
--> Would be clearly of interest to select K- in the momentum region with the smallest possible contamination and look for pentaquarks with this sample !
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Heavy Ion collisions at RHIC may offer a unique opportunity to produce multi-q/g states through coalescence out of a QGP
- PHENIX: searches for anti-theta- --> K- anti-n
--> no signal found in dAu, pp anf AuAu collisions at sqrt(s)=200 GeV
--> studies with lower pi contamination important, higher stat AuAu to be analysed
-STAR: - Peak seen in theta++ and theta-- channel in d+Au collisions at sqrt(s)=200 GeV consistent with detector resolution, and below UL of HERA for theta+
- Low significance in Au+Au at 62 and 200 geV
- No peak seen in Cu+Cu 62 GeV
Conclusions and outlookConclusions and outlook
Conclusions contConclusions cont
theta+ --> p K0s : No significant peak seen in pp, dAu and AuAu collisions --> Ongoing work
N0/X0 --> LK0s : peak seen at m=1734 MeV, width consistent with the det. Resolution and S/sqrt(B)=5-6 in Au+Au collisions at 200 GeV
Future plans for both Phenix and STAR include analysis of more data : 2004 AuAu 200 GeV 2005 Cu+Cu 62 and 200 GeV, pp at 200 GeV
To search and confirm or reject the seen candidates: Theta++(1530) and N0/Xi0(1734) and search for anti-theta- , theta+ and Xi--
Possible Sources of BackgroundPossible Sources of Background
Double Conversion of 0 photons
0 e+e- e+e-
Same-sign e’s within the K and p bands
mostly in the low mass region opening angle cut very effective
Associated production K+ p
These background sources contribute to the residuals in the event-mixing. But they do not produce a narrow peak !
in p+p, d+Au and Au+Au collisions at 200 GeV
Sevil Salur
Yale University
Talk given in the APS meeting, Denver, 05/01/2004
and
Poster presented in this meeting
STAR theta_ --> K0s p searchesSTAR theta_ --> K0s p searches
Reconstruction OUTPUT
STAR Preliminary
Signal
Mixed Event Background
Signal after Background Subtraction
One MC (Tinv slope =250 MeV ) is embedded in each real p+p event.
Only 3% of these ’s were reconstructed after cuts.
The width and the mass remain consistent with the MC input after the reconstruction.
Monte Carlo INPUT
Simulation Studies II
(10 MeV ) (1.54 GeV/c2 )
Sevil Salur, Yale Univ. APS Meeting
05/01/2004
Proton K0s
Momentum Distributions from Monte Carlo +
Identified from real events.
Simulation Studies
Cuts to optimize signal over background
can be reconstructed in
this PT and y range
PT [GeV/c]
NE
ntri
es
NE
ntri
es
PT [GeV/c]
Sevil Salur, Yale Univ. APS Meeting
05/01/2004
Feasibility Studies with current Au+Au dataFeasibility Studies with current Au+Au dataW. Liu, C.M. Ko Phys.Rev.C68:045203,2003 J.Letessier, G.Torrieri, S.Steinke and J.Rafelski hep-ph/0310188 Jorgen Randrup nucl-th/0307042
~0.5-1.5 per event for AuAu
Sevil Salur, Yale Univ. APS Meeting 05/01/2004
•0.5-1.5 X 1.5 Million 0.8-2.3 Million
•Efficiency 3% 25-70 K
•Branching Ratio 50% 10-35 K
•BR 50% from K0 s 5-17K
Background pairs per event in the mass range of is 2.
•2 X 1.5 Million 3 Million
Significance = Signal/√(2 X Background+Signal)
2-7
−+ + KppK +−+ KppK
++ and (1520) Using the Same Analysis Procedure
(1520)
Same charge Sign (SS) and Opposite Sign (OS) background different
Background Shape Depends on Cuts
M (GeV/c2)M (GeV/c2)
K [0.2-0.6] GeV/cP [0.3-1.5] GeV/c
K [0.2-0.6] GeV/cP [0.3-1.0] GeV/c
Monte Carlo 1733 K0s
Momentum of K0s is lower than of
Suggests cut : mom(K0s) < ~1 GeV
1733 K0s generated (inv. Slope(mt)= 500 MeV)
1730 K0s in detector acceptance.
Generated with: y=-1.5 to 1.5, inv. Slope(mt) = 250 MeV, width=1 MeV
K0s
STAR preliminary
Bin size= 1.5 MeV, Fit: Breit Wigner + polyn. Mom(proton)< 0.9 GeV mom(pi) < 0.7 GeV
Detector resolution (1730 K0s ) ~ width = 6.3 ± 1.7 MeV --> measured width of 4.6 +-2.4 MeV is consistent with the exp. resolution within errors
Mass= 1729 ± 0.7 MeV
Monte Carlo 1730 K0s
Mass=1730 MeV, Breit Wigner Width=1 MeV, inv. Slope(mt)=250 MeV, y=(-1.5,1.5)
Geant + embedding in real data from p+p collisions at 200 GeV
Investigations of systematic errors:
-Split track investigation: Cut on nr of hits(tracks) > 25 (maximal possible 45)
STAR Au+Au coll. 200 GeV preliminary
Split track investigation II :
| MomentumZ(pos. track(Lambda) – MomentumZ(pos. track(K0s) | > 30 MeV
| MomentumZ(neg. track(Lambda) – MomentumZ(neg. track(K0s) | > 30 MeV
Split track investigation II :
| MomentumZ(pos. track(Lambda) – MomentumZ(pos. track(K0s) | < 30 MeV
| MomentumZ(neg. track(Lambda) – MomentumZ(neg. track(K0s) | < 30 MeV
Split track investigation II :
| MomentumZ(pos. track(Lambda) – MomentumZ(pos. track(K0s) | < 100 MeV
| MomentumZ(neg. track(Lambda) – MomentumZ(neg. track(K0s) | < 100 MeV
Same result when this cut is performed additionally in pT
Testing self-correlations arising from same tracks used in both V0’s:
-- Plot inv. Mass if positive tracks have the same id -> no entries
-- Plot inv. Mass if negative tracks have the same id : 8 entries all around 1.663 GeV
Cos(theta*) of in the ( K0s) parent rest frame
Inv. Mass( K0s) = 1733 +- 3 MeV Inv. Mass ( K0s) < 2 GeV
STAR Au+Au coll. 200 GeV preliminary
pT( K0s) parent
(uncorrected)
What could the Lambda K0s peak at 1734 MeV be ?
- PDG states nearby : N(1710) N(1730) has large width ~100 MeV
- Partial wave analysis suggests two new narrow N states at :
1680 and/or 1730 MeV width < 30 MeV (nucl-th/0312126, R Arndt et al)
-Cannot be the 0 I=3/2 pentaquark because K0s decay violates isospin
-It is a candidate for two pentaquark states:
^0 I=1/2 K0 (1st octet, expected m~1700 or ~1860 MeV)
N^0 anti-K0 (2d octet, expected m~1730MeV, or anti-10)
The K0s channel allows to separate the I=1/2 (octet) from I=3/2 (anti-10)
No peak near 1860 MeV disfavours picture of degenerate 8 and anti-10
Is there a way to resolve the ambiguity (ussdd*) or N(uddss*) ?
Yes
Through the measurement of their isospin partners:
N+ K+ and - I=1/2 K-
Correlated diquark model (B Jaffe, F Wilzcek): octet and anti-10 are degenerate
(Diakonov et al) : two octets (1/2+) below 2 GeV mass, PDG or new:N0(1440) N+(1440)
+(1660)-(1660)
0(1690)-(1690)
Seen
(1535)
Seen(1860)
N+(1710)N0(1710)
-(1950?)
-(1880) +(1880)
0(1950?)
0(1660)
0(1600)
0(1880)
01810)
N(1650-90)
(1750-1800)
Theoretical models: Soliton model, Correl. Quark model, Uncor. Quark model etc
STAR candidate
Inv. Mass of anti- K0s in min. bias Au+Au collisions at 200 GeV
-No peak is observed at 1734 MeV above the background -> ongoing analysis
- This non observation could be understood as a low anti-pent./pent. ratio arising from dominant (a)pentaquark production through quark coalescence:
Anti-N0/N0 ~ (u*d*s*d*s/udsds*) ~ (q*/q)^3 ~ p*/p ~ 0.73 (p*/p value taken from STAR coll., PLB 567 (2003) 167)
Anti-Xi0/Xi0 ~ (u*d*s*s*d/udssd*) ~ (q*/q) (s*/s)^2 ~ (q*/q) ~ 0.90
Favours the N0 hypothesis
STAR preliminary
The detectorThe detector
• Maximal Set of Observables– Photons, Electrons, Muons, ID-hadrons
• Highly Selective Triggering– High Rate Capability.– Rare Processes.
Charged Hadron PID AnalysisCharged Hadron PID Analysis Detectors for hadron PID
DCH+PC1+TOF+BBC = /8, -0.35 < < 0.35
Momentum Resolution
TOF resolution TOF ~ 130 ps.
Hadron PID in m2 vs. p space with asymmetric PID cuts.
• 0.2< < 3.0 GeV/c , • 0.4< K < 2.0 GeV/c, • 0.6< p < 3.7 GeV/c.
€
δp / p ≈ 0.7%⊕1.0% × p (GeV/c)
]1)[( 222 −×
=Lct
pm
- Suppression of charged particle hit background, by vetoing charged particles with a layer of pad chambers (PC3) positioned infront of the EMCal.
- Use of p and anti-p momentum and TOF info to determine features of annihilation signal of anti-p in EMC
- Clusters produced by photons were removed by a timing cut (> 3 nsec) and requiring a poor fit to the shower shape expected for a photon
- Important validation of anti-n identification and method for anti-theta- searches :
* through measurement of the
anti-Sigma- --> pi+ anti-n
* through study of the channel K+ anti-n which should not show a signal
Reliability of Anti-n CandidateReliability of Anti-n Candidate• Anti-n momentum resolution
checked– Applying the reconstruction method
to anti-proton
• Comparison of momentum from TOF and tracking
– Resolution<4%,10%,15% in pT<1.0,
1.5, 2.0 GeV/c, respectively
– Momentum shift <~5%
• Anti-n momentum resolution checked
– Applying the reconstruction method to anti-proton
• Comparison of momentum from TOF and tracking
– Resolution<4%,10%,15% in pT<1.0,
1.5, 2.0 GeV/c, respectively
– Momentum shift <~5%
pT [GeV/c]
mas
s pe
ak [G
eV/c
]
Marker : Data
Dash line : MC
-
+
mas
s fr
om P
DG
– Invariant mass peak of
-(1189.4) n + - : R.R. 99.85%, c-= 2.396cm
+(1197.4) n + + : B.R. 48.31%, c+= 4.434cm
• Mass shift due to no TOF calibration for n in EMCal is <~5%• Quick check by Monte-Carlo shows agreement with data
- +
1.1 1.2 1.3 1.4 1.5 1.6 1.1 1.2 1.3 1.4 1.5 1.6
Cou
nts
/ bin
n + - n + +
No pT cut No pT cut
200 GeV p+p 200 GeV p+p
Same eventhigh pT photon trigger
Mixed eventMinBias trigger
Invariant mass [GeV/c2]
work in progress
•Run3 ÖsNN = 200 GeV d+Au• Minimum bias trigger• 91 M events• 5 MeV/c2 per bin
Same event
Mixed event
Cou
nts
/ bin
K + +n in p +p, d+Au, Au+AuK + +n in p +p, d+Au, Au+Au
Top 30% central 30-50% 50-92%
work in progress
work in progress
work in progress
Same event
Mixed event
•Run2 sNN = 200GeV Au+Au– Minimum bias trigger
– 36M events– 4 MeV/c2 per bin
Cou
nts
/ bin
No significant signal seen
•Run3 Ös = 200 GeV p+p• Minimum bias trigger• 35 M events• 5 MeV/c2 per bin
work-in progressSame event
Mixed event
Cou
nts
/ bin
More Strangeness at PHENIXMore Strangeness at PHENIX• From combinations of ±, K±,
p,p, andn• From combinations of ±, K±,
p,p, andn
Invariant mass [GeV/c2]
0
K0s pT =1-2 GeV/c
Invariant mass [GeV/c2]
pT =1-2 GeV/c
Invariant mass [GeV/c2]
K*0
pT =1-2 GeV/c
Invariant mass [GeV/c2]
Not enoughstatistics..
pT =1-2 GeV/c
Invariant mass [GeV/c2]
pT =1-2 GeV/c
Invariant mass [GeV/c2]
pT =1-2 GeV/c
Invariant mass [GeV/c2]
pT =1-2 GeV/c
• Demonstration from– Run3 sNN =200 GeV p+p
– ~24M events of Min Bias trigger
• Blue histograms– Pair from save event
• Red histograms– Combinatorial back ground
from event mixing from Min. Bias trigger
– Normalization range» solid filled area
Anti-Sigma- --> pi+ anti-n is measured, giving a mass close to nominal mass of 1.197 GeV
Pi+ anti-n inv. mass
Pi+ anti-n inv. mass
After mixed event background subtraction
C. Pinkenburg, QM2004
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Summary and conclusions
- +(s), - -(1860), 0(1860), -(1850), (c) candidates observed
- STAR preliminary results show a possible narrow peak in the K0s inv.mass at m=1734 +- 0.5+-5(syst) MeV, width < 4.6 +-2.4 MeV, S/sqrt(B)= 30.6/ ( 35.4)= 5.15, S/(S+B)=3.77. Best S/sqrt(B)=5.93 obtained in semiperipheral events. If this peak reflects a real state, it is a candidate for the pentaquark states:
0 I=1/2 (1st octet) and N0 (2d octet or anti-10) K0s
- This peak is not observed in the anti- K0s channel (work in progress)
-The mass agrees well with the PWA result suggesting two new narrow states at 1680, 1730 MeV (Arndt et al)
- We observe a peak at m=1693+-0.5 MeV with S/sqrt(B)=2.92, candidate for PDG Xi(1690) state. STAR can improve the previous limit of <30 MeV (2002 PDG). Xi(1690) maybe a candidate for the Xi0 I=1/2 pentaquark (1st octet)
- We don’t observe a peak in K0s near 1850,1860 from an octet
Suggests that NA49 observed three anti-10 ’s, disfavouring a degenerate 8 and anti-10 (Jaffe et al), however Br. Ratios may differ in and K0s
Outlook:
- Pentaquark searches in other decay modes e.g. + p K0s (S Salur QM04) are on the way and K+- to find the isospin partners
- New data taken in 2004 will enhance significantly the STAR statistics
STAR – Exciting Physics Program A full TOF and Heavy Flavor Tracker upgrade will greatly enhance STAR’s capability !!
RHIC – Exotic Particle Factory
Heavy Flavor TrackerUsing Active Pixel Sensor
two layers of thin silicon detector 1.5 cm and 4 cm radius Charmed Exotics?!Full Barrel TOF Using MRPC
The machine The machine • Relativistic Heavy Ion Collider• Brookhaven National Lab• 2 counter-circulating rings• 3.834 km circumference• Superconducting magnets(3.5T)• 192 dipoles per ring• 246 quadrupoles per ring• Time between collisions: 0.213 microseconds• Crossing angle: 0• Bunch length: 20 cm• Bunches per ring: 56• Luminosity lifetime: 3-10 hours• Particles per bunch (units 1010):
– Au+Au: 0.1– p+p : 10
• Top energies (each beam):– 100 GeV/nucleon Au+Au.– 100 GeV/nucleon d+Au– 100 GeV polarized p+p
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