Strangeness Measurements in Strangeness Measurements in BRAHMSBRAHMS

J.H. LeePhysics Department

Brookhaven National Laboratory

For the BRAHMS CollaborationSQM2003

Mar. 13 2003

Results from Au+Au at sNN =200 GeV ,K,p at selected rapidities Ratios, yields, slopes for Central Collisions As a function of centrality at y=0 Plan and summary

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J.H. Lee (BNL) 2

BRAHMS measures over a broad rapidity range

SNN=200GeV

AndMore…

Summary of BRAHMS data from RHIC2001 (Run2) running

Data• Au+Au and p+p at full energy: sNN =200 GeV• All detectors were installed and working at all centralities• Higher level triggers (Vertex/Centrality/Spectrometer)

implemented• ~25M physics events taken• Initial scan of “soft” physics • Selected high-pt and HBT runs

Measurements• Charged particle multiplicity (dN/d): published in PRL • Particle ratios: Will be published in PRL• Identified hadron spectra and yields at selected rapidities - Net-proton - dN/dy, slope vs y for ,K,p• High-pT hadrons/ (up to pT ~ 6 GeV/c at y ~ 0, pT~4 at y~2)• Limited HBT

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The BRAHMS experimentSetup used for Au+Au data in 2001

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BRAHMS Acceptance

90o

4o

MRS FS

A wide range of y and pt is covered by rotating two spectrometers with various magnetic fields.

25 GeV/c

2.3 degree

10 degree

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Anti-particle/particle ratios vs rapidity at SNN=200 GeV

• At y=0 (20% central) pbar/p = 0.75 ±0.04 K-/K+ = 0.95 ±0.05 = 1.01 ±0.04• Highest pbar/p ratio but still

incomplete transparency (~17% increase from 130 GeV)

• Ratios ~identical over +-1 unit around mid-rapidity.

• Weak centrality and pT dependence

• No Hyperon feed down correction applied: less then 5% correction assuming

• Lambda/p ~ 0.5 and pbar/p ~ Lambda-Bar/Lambda

To be published in PRL : nucl-ex/0207006

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Ratios: Data and AMPT 0-20% at SNN=200 GeV

•K-/K+ Ratio decreases with y : Inconsistent with models: AMPT, HIJING (AMPT describe other rapidity dependent measurements best so far)•Where is the rest of strangeness at forward? Lambda?

AMPT 20%Central (all pt)

K/K+

Pbar/p

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• By simple quark counting in quark recombination K-/K+

= exp(2s/T)exp(-2q/T)

= exp(2s/T)(pbar/p)1/3

= (pbar/p)1/3

by assuming local (y) strangeness conservation

• K-/K+=(pbar/p) = 0.24±0.02 for BRAHMS = 0.20±0.01 for SPS• Good agreement with the statistical-

thermal model prediction by Beccatini et al. (PRC64 2001): Based on SPS results and assuming T=170 MeV

“Universal” Correlation in K-/K+ vs pbar/p?

To be published in PRL

At y=0

From y=0 to 3

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,K,p Spectra at 0-10% Central at y=0 and y = 3

• Spectra gets softer at higher rapidity• pbar yield drops rapidly with rapidity• protons and pions

converge/cross: - y~0: pT 2 GeV/c

- y~3: pT 1.2 GeV/c • Protons over K+

- y~0: at high pT (>1GeV/c)

- y~3: at all pT

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dN/dy at sNN =200 GeV 0-10% central

• y width: ,K+ > K- • K broader than SPS• ,K spectra can

be fitted by a single Gaussian

• Integrated yields are consistent with dNcharged/d distributions

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Strangeness : ratio K/

ratio increases as pT increases at y=0 and y=3

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Inverse mT Slope vs. Mass for 0-10% central

• All fits are in mT:

over same range for all particles, at all rapidities

• Show only positive but Negative Positive

• Inverse slope decreases as y increases

• Inverse slope increase with mass: transverse flow at all covered rapidities

y~3

y~0, 0.9

BRAHMS Preliminary

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Strangeness : K/ systematics

Y=0

Y=3

• K/ ratio flattens at RHIC energy at y~0

• K/ at y~3: similar to SPS (Pb+Pb Central at 17 GeV)

- Inverse mT slope also similar

- K: T~230

: T~200

BRAHMS Preliminary

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dN/dy of Net-proton and Models for 0-10% central

• “Plateau” at |y| < 1 the yields by 18, 20% at

y=0,2.9• Net-baryon at y =0: ~16 (if N(proton)/N(neutron) 1 ) • More data to be analyzed (at

y~2,3.3)• Hyperon feed down will

reduce

• A range of models is still allowed with these data.

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• Estimating y = (ybeam-y) dN/dy / dN/dy , as has been done for lower energy data.

• Baryon conservation tells us net(p) ~ 68 for Npart~340 (0-10%) or ~85 in the case of full proton/neutron equilibration, N(p) = N(n).

• The net(p) measured is ~36. Distributing the remaining 32(53) protons in rapidity interval 3 - 5.4 with a variety of assumptions leads to an estimated range of

y of 1.8 - 2.4. I.e. 2.1 ±0.3. Either extremes would require unusual

rapidity distributions.• Even though we do not have

measurements in 3-5.4, we may extend another .4 units in future how can we estimate rapidity loss.

• We plan to refine this value once all data have been analyzed.

Estimate of amount of stopping

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• Mean pt: -increase at low pt -decrease at high pt as <Npart> increase • Collective flow at low pt + Suppression at high pt

Charged Hadron Spectra as a function of rapidity at y=0

BRAHMS Preliminary

BRAHMS Preliminary

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High-pT Physics:Central/Semi-peripheral collisions at y = 0

Yield/<Ncoll>0-10%/Yield/<Ncoll>40-60%

• Charged hadron spectra scaled by the number of binary collisions.

• high pT suppression

in central collisions (0-10%) compared to

semi-peripheral (40-60%)

• Identified particles at y=0,2:analysis in progress .

BRAHMS Preliminary

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Spectra vs Centrality at y=0 sNN =200 GeV

BRAHMS Preliminary

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K/ ratios at y = 0 sNN =200 GeV

• K/ ratios increase with pT and centrality

BRAHMS Preliminary

BRAHMS Preliminary

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dN/dy per participant at y=0 sNN =200 GeVdN/dy per participant at y=0 sNN =200 GeV

• For all the particle species, the yield per participant increase with Npart.

• K±, p, pbar yields per participant rise faster than

± yield.• Errors statistical only on

plot. • Systematic error ~10-20%• Dominant syst. error from

Npart determination, and extrapolation of yields.

BRAHMS Preliminary

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<pt> vs Npart at y=0<pt> vs Npart at y=0

• <pT>-pTmin

• 0.4-2.4 for pion• 0.6-2.2 for kaon• 0.5-3.4 for p/pbar

• <pt> increase with <Npart> and mass: p and pbar increase

fast with <Npart>:

consistent with radial expansion picture

BRAHMS Preliminary

p

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Extended PID for High pt measurements at y=0 – 1

New Cherenkov detector C4 + TOFW2 at Mid-Rapidity Spectrometer

Currently taking data (d+Au)

/K identification up to p = 8 GeV/c (Forward Spectrometer PID up to p = 25 GeV/c)

“high-pt” pion measurement up to 5 GeV at y ~ 0 (luminosity limited)

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What to expect in the near future

Analysis in Progress• Centrality dependent yield/specta at y ~ 0,1,2,3• Net-proton y ~ 2, 3.3: Better understanding of rapidity loss• Blast-Wave Fit in all rapidities

• Identified High-pT (< 4GeV/c) spectra at y=0 and y=2

Run3 (d+Au,p+p), Run4 (Au+Au)• d+Au run in progrsss

• Identified high-pt physics: up to pT = 8 GeV at y=0

• Identified yields as a function of reaction plane for y=0-3 with re-configured Si-detector (in discussion)• HBT as a function of rapidity and reaction plane at y=1,3

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Summary: Strangeness Measurements in BRAHMS at sNN = 200 GeVAt y = 0 – 3:

• K-/K+: approximately constant over ±1 unit of rapidity and fall off with y

• ”Universal” correlation: K-/K+~(pbar/p)1/4

• K±/±increase with pT for all rapidities

• Kaon production at y=3 at sNN = 200 GeV similar as y=0 at SPS

• Kaon inverse slope decreases with rapidity • Low to high chemical potential from y=0 to t=3At y=0:

• For K±, the yield per participant increase with Npart.• K± yields per participant rise faster than ± yield.

BRAHMS Publications

“Rapidity dependence of anti-proton to proton ratios in Au+Au collisions at snn =130 GeV”

Phys. Rev. Lett. 87 (2001) 112305 “Charged particle densities from Au+Au Collisions at

snn =130 GeV”

Phys. Lett. B 523 (2001) 227 “Pseudorapidity distributions of charged particles from

Au+Au collisions at the maximum RHIC energy” Phys. Rev. Lett. 88 (2002) 202301 “Rapidity dependence of anti-particle-to-particle ratios

in Au+Au collisions at snn =200 GeV”

Will be published in Phys. Rev. Lett. : nucl-ex/0207006

More information in http://www.rhic.bnl.gov/brahms

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I.G. Bearden7, D. Beavis1, C. Besliu10, Y. Blyakhman6,J. Bondorf7, J.Brzychczyk4, B. Budick6, H. Bøggild7, C. Chasman1, C. H.Christensen7, P. Christiansen7, J.Cibor4, R.Debbe1, J. J. Gaardhøje7, K. Grotowski4, K. Hagel8, O. Hansen7, H. Heiselberg7, A. Holm7, A.K. Holme12, H. Ito11, E.Jacobsen7,Jipa10, J. I. Jordre10, F. Jundt2, C. E. Jørgensen7, T.Keutgen9, E. J. Kim5, T. Kozik3, T.M.Larsen12, J. H.

Lee1, Y. K.Lee5, G. Løvhøjden2, Z. Majka3, A. Makeev8, B. McBreen1, M. Murray8, J.Natowitz8, B.S.Nielsen7, K. Olchanski1, D. Ouerdane7, R.Planeta4, F.Rami2, C.Ristea10, D.Roehrich9,

B. H. Samset12, S. J. Sanders11, R.A.Sheetz1, Z.Sosin3, P. Staszel7,T.S. Tveter12, F.Videbæk1, R.Wada8 and A.Wieloch3, S.Zgura10.

1Brookhaven National Laboratory, USA 2IReS and Université Louis Pasteur, Strasbourg, France

3Jagiellonian University, Cracow, Poland 4Institute of Nuclear Physics, Cracow, Poland

5Johns Hopkins University, Baltimore, USA 6New York University, USA

7Niels Bohr Institute, Blegdamsvej 17, University of Copenhagen, Denmark

8Texas A&M University, College Station, USA 9University of Bergen, Norway 10University of

Bucharest, Romania 11University of Kansas, Lawrence,USA 12

University of Oslo Norway

The BRAHMS Collaboration

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Backup Slides

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• The ratio for central events (0-10%) are almost flat over 0.5<pt<3.5GeV/c.

• R(central)~R(peripheral)

R=0.78+-0.01 (0-10%)

R=0.81+-0.03 (40-60%)

pT and centrality dependent pbar/p ratios at y=0

BRAHMS Preliminary

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MRS particle identification : TOFW

125 slats: time of flight resolution ~ 75psec

/K separation ~ up to 2.5 GeV/c

K/p separation ~ up to 4 GeV/c

Cherenkov counter will be installed for identifying higher pT particles

(/K separation: up to 8 GeV)

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PID in Back Forward Spectrometer : RICH

PID up to p=25 GeV/c (can go higher changing pressure)

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Hardware additions for Run3

95°

30°

30°

15°

2.3°

C4

Trigger (for track and d(p)A and pp)

More Si and reconfiguration

Second TOF

Event Characterization: Collision Centrality Determination

Measured by the Centrality Detector (SiMA+TMA)

Corrected for Vertex position dependence

Minimum-biased multiplicity: Data + MC (HIJING+GEANT)

BB Multiplicity is used for the centrality determination for BB analysis (consistent with SiMA+TMA selections)

Npart is calculated using HIJING

SiMA

TMA

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R (proton/neutron) in Models

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Multiplicity: dNch/dat SNN=200 GeV

Centrality bins shown are for 0-5%,5-10%, 10-20%,…, 40-50%. (Statistical errors only) Systematic errors ~ 8-10% SiMA: -3 < < 3 Beam-Beam Counter: 2 < || < 4.7 Consistent with measurements using reconstructed tracks in TPC at y = 0

Published in PRL 88 (2002)

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PID in Front Forward Spectrometer : ToF + C1

ToF H1 pion vetoed by C1

C1 π threshold

H1 & C1

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Comparison to models

UrQMD

Hijing

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Inverse pT Slope vs. mass

• All fits are in pT:

over same range for all particles, at all rapidities

• Negative Positive

• Inverse slope decreases as y increases

• Flow at all covered rapidities

BRAHMS Preliminary: 200 GeV 10% Central

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HBT:Rapidity-Dependent Transverse Source Size Measurements

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Particle Ratios:centrality and pt dependence

• No centrality dependence in range 0-20%• No transverse momentum dependence

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y = 0 y = 3

BRAHMS Preliminary: 200 GeV 10% Central

Spectra

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p and pbar yields B

RA

HM

S P

relim

inary

S

NN

=2

00

GeV

: 1

0%

Cen

tral

Y = 0

• pbar

Yield =10.5 0.8

(Inverse pt slope =325.517.29) • proton

Yield = 33.7 1.8

(Inverse pt slope = 341.8 13.8

Y = 0

Y = 0.8

Y = 2.9

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Models, models…

• HIJING: emphasis on purturbative QCD processes leading to multiple mini-jet production from parton scattering (X.Wang and M.Gyulassy Phys. Rev. D (1991) 3501)

• AMPT: (A Multiphase Transport Model) HIJING to generate the initial phase space of parton, then extends to quark-gluon to hadronic-matter transition and the final hadron interaction (B. Zhang, C.M. Ko, B. Li, Z.Lin Phys. Rev. C 61 (2001) 067901)

• UrQMD: hadronic + string including all known resonances (S.A.Bass et al. Prog. Part. Nucl. Phys. 41 (1998)

• FRITIOF: string dynamics + LUND. Hadron behaves like relativistic strings with confined color field (H.Pi, Comp. Phys. Comm. 71 (1992) )

• …