# Presentation: 371873

## Energy dependence of 

**K****0**** and hyperon production**
**at CERN SPS**** **
- Domenico Elia
*INFN - *Bari (Italy)
- on behalf of the ***NA57 Collaboration***

**s**

- QM2004, Oakland - January 11-17, 2004

- D. Elia, INFN Bari (Italy)

## Contents

- QM2004, Oakland - January 11-17, 2004

- D. Elia, INFN Bari (Italy)

## Physics motivation

-   NA57 physics goals:

-     study of the dependence of hyperon enhancements on
** ****interaction volume** (centrality down to Nwound  50)
** ****collision energy** (data at both 40 and 160 A GeV)

| System | Beam energy | Sample size |
| --- | --- | --- |
| Pb-Pb | 160 A GeV | (230+230) x 106  evts |
| Pb-Pb | 40 A GeV | 240 x 106 evts |
| p-Be | 40 A GeV | (60+110) x 106 evts |

*WA97 p-Be sample used as reference data at 160 A GeV*

-   Data samples:

- QM2004, Oakland - January 11-17, 2004

- D. Elia, INFN Bari (Italy)

## Experimental apparatus

**placed inside the 1.4 T field of the GOLIATH magnet**** **

**Target:**** **1% Pb, 8% Be
**Scintillator petals: **centrality trigger (Pb-Pb)
**MSD 1 & 2:**** **
- multiplicity detector (Pb-Pb)
**Tracking device:**
- silicon pixel planes
- (5 x 5 cm2 cross section,
-  50 x 500 m2 cell size,
-  total of   **1 M channels**)
**Lever arm: **
- pixels + double side
- strips

- QM2004, Oakland - January 11-17, 2004

- D. Elia, INFN Bari (Italy)

## Strange particle detection

**Silicon telescope**

- target

-  1 M channels

- QM2004, Oakland - January 11-17, 2004

- D. Elia, INFN Bari (Italy)

## Yields and enhancements

-   Double differential cross sections
-    for each particle fitted to:
-    assuming flat rapidity distribution in the selected acceptance regions
-    Inverse slope of *m*T distribution *( T = T**app **)* free parameter of the fit.

- QM2004, Oakland - January 11-17, 2004

- D. Elia, INFN Bari (Italy)

## Collision centrality

-   Centrality determination from measured charged particle multiplicity
-   Nwound from trigger cross section (Glauber Model calculations)

- QM2004, Oakland - January 11-17, 2004

- D. Elia, INFN Bari (Italy)

## Collision centrality

-   Centrality determination from measured charged particle multiplicity
-   Nwound from trigger cross section (Glauber Model calculations)

| Class |  / tot |    < Nwound >
160 GeV         40 GeV |  |
| --- | --- | --- | --- |
| 0 | 42 – 56% | 62 | 57 |
| 1 | 25 – 42% | 121 | 119 |
| 2 | 12 – 25% | 209 | 208 |
| 3 | 5 – 12% | 290 | 292 |
| 4 | 0 – 5% | 349 | 346 |

-   Same class definition
-     at 40 and 160 GeV

- QM2004, Oakland - January 11-17, 2004

- D. Elia, INFN Bari (Italy)

## Comparison NA57-NA49

- Particle yields per participant

|  | NA57 | NA49* |
| --- | --- | --- |
| 40 GeV | 5% | 7% |
| 160 GeV (K) | 5% | 7% |
| 160 GeV 
(, ) | 12% | 10% |

- *Refs: Physical Review C 66, 054902 (2002), nucl-ex/0311024,
-             Phys. Lett. B 538 (2002), 275.

**Centrality regions:**

- QM2004, Oakland - January 11-17, 2004

- D. Elia, INFN Bari (Italy)

## Comparison NA57-NA49

- Particle yields per participant

|  | NA57 | NA49* |
| --- | --- | --- |
| 40 GeV | 5% | 7% |
| 160 GeV (K) | 5% | 7% |
| 160 GeV 
(, ) | 12% | 10% |

- *Refs: Physical Review C 66, 054902 (2002), nucl-ex/0311024,
-             Phys. Lett. B 538 (2002), 275.

-  about 30% systematics on the absolute value of the
-     yields (under investigation) but ...

**Centrality regions:**

- QM2004, Oakland - January 11-17, 2004

- D. Elia, INFN Bari (Italy)

## Comparison NA57-NA49

- Particle ratios

- *Refs: Physical Review C 66, 054902 (2002), nucl-ex/0311024,
-             nucl-ex/0305021, nucl-ex/0311029

-  ... particle ratios compatible within errors
-             		(i.e. no impact on relative yields)

- QM2004, Oakland - January 11-17, 2004

- D. Elia, INFN Bari (Italy)

## Energy dependence

- of hyperon ratios from SPS to RHIC

- *Ref: Physics Letters B 567 (2003), 167.

**         ****Centrality regions:****	****NA57:****	****0 - 12%**
**	****	****     ****	****STAR*:****	****0 - 11%**

- QM2004, Oakland - January 11-17, 2004

- D. Elia, INFN Bari (Italy)

## Energy dependence

- of particle yields from SPS to RHIC

- *Refs: Physical Review Letters 89 (2002), 092301
-             nucl-ex/0206008, nucl-ex/0307024

**               ****Centrality regions: ****	****NA57:****   ****0-5% (********K), 0-12% (********)**
**	****	****      ****	****STAR*:**** ****0-5% (********), 0-6% (K), 0-10% (********)**

- QM2004, Oakland - January 11-17, 2004

- D. Elia, INFN Bari (Italy)

## Centrality dependence

- of strange particle yields

- QM2004, Oakland - January 11-17, 2004

- D. Elia, INFN Bari (Italy)

## Centrality dependence

- of strange particle yields

- QM2004, Oakland - January 11-17, 2004

- D. Elia, INFN Bari (Italy)

## Centrality dependence

- of strange particle yields

- Yields fitted to:

- Y  <Nwound>****

- QM2004, Oakland - January 11-17, 2004

- D. Elia, INFN Bari (Italy)

## Centrality dependence

- of strange particle yields

- Yields fitted to:

-   steeper centrality
-      dependence of
-      the 40 A GeV
-      yields

|  | 160 A GeV |  | 40 A GeV |  |
| --- | --- | --- | --- | --- |
|  |  | 2 / ndf |  | 2 / ndf |
|  | 1.20 ± 0.04 | 3.2 / 3 | 1.49 ± 0.04 | 1.6 / 3 |
|  | 1.21 ± 0.05 | 0.9 / 3 | 1.52 ± 0.04 | 6.6 / 3 |
|  | 1.00 ± 0.07 | 8.6 / 3 | 1.18 ± 0.08 | 4.3 / 3 |
|  | 1.40 ± 0.04 | 6.3 / 3 | 1.85 ± 0.13 | 6.3 / 3 |
|  | 1.30 ± 0.11 | 5.8 / 3 | 0.84 ± 0.60 | 1.1 / 3 |
|  | 1.45 ± 0.28 | 0.6 / 3 | 1.45 ± 0.86 | 0.1 / 2 |
|  | 1.49 ± 0.36 | 0.2 / 3 |  |  |

- Y  <Nwound>****

- QM2004, Oakland - January 11-17, 2004

- D. Elia, INFN Bari (Italy)

## Hyperon enhancements

-   same hierarchy at 160 and 40 GeV:  E() < E()

- QM2004, Oakland - January 11-17, 2004

- D. Elia, INFN Bari (Italy)

## Summary

-   Comparison with NA49:
-   ratios compatible,   30% systematics in the yields
-   Energy dependence of yields and ratios:
-   stronger dependence for anti-particles than for particles
-      (larger baryon density at 40 A GeV)
-   Centrality dependence of the yields:
-   steeper centrality dependence of the 40 A GeV yields
-   Enhancements at 40 A GeV:
-   hyperon yields enhanced at 40 A GeV too, E()<E()
-   steeper centrality dependence at lower energy

- QM2004, Oakland - January 11-17, 2004

- D. Elia, INFN Bari (Italy)

## The NA57 Collaboration

- 	*Physics Department, University of ****Athens****, Greece**; **Dipartimento IA di Fisica dell'Università e del Politecnico di Bari and INFN, ****Bari****, Italy**; **Fysisk Institutt , Universitetet i Bergen, ****Bergen****, Norway **; **Høgskolen i Bergen, Bergen, Norway**; **University of Birmingham, ****Birmingham****, UK**; **Comenius University, ****Bratislava****, Slovakia**; **University of Catania and INFN, ****Catania****, Italy**; ****CERN****, European Laboratory for Particle Physics, Geneva, Switzerland**; **Institute of Experimental Physics Slovak Academy of Science, ****Kosice****, Slovakia**; **P.J. Safárik University, Kosice, Slovakia**; **Fysisk institutt, Universitetet i Oslo, ****Oslo****, Norway**; **University of Padua and INFN, ****Padua****, Italy**; **Collège de France, ****Paris****, France**; **Institute of Physics, ****Prague****, Czech Republic**; **University “La Sapienza'' and INFN, ****Rome****, Italy**; **Dipartimento di Scienze Fisiche “E.R. Caianiello'' dell'Università and INFN, ****Salerno****, Italy;** **State University of St. Petersburg, ****St. Petersburg****, Russia**; **IReS/ULP, ****Strasbourg****, France**; **Utrecht University and NIKHEF, ****Utrecht****, The Netherlands.*

- QM2004, Oakland - January 11-17, 2004

- D. Elia, INFN Bari (Italy)