# Presentation: 663168

## Slide 1

- HQ2004, Taos Valley - July 18-24, 2004

- D. Elia, INFN Bari (Italy)

## Contents

-   Measuring strangeness with NA57
-   **Particle yields and ratios: **
-  energy and centrality dependence in Pb-Pb
-  enhancements with respect to p-Be
-   Conclusions

- Also @HQ2004: ***Study of the m******T  ******spectra of strange particles ***
***                           ******in Pb-Pb collisions at the SPS***  (talk by G.E. Bruno)

- HQ2004, Taos Valley - July 18-24, 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)

- HQ2004, Taos Valley - July 18-24, 2004

- D. Elia, INFN Bari (Italy)

## Physics motivation

-   NA57 physics goals:

-      study of the dependence of **hyperon enhancements** on

| 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:

**  ****interaction volume** (centrality down to Nwound  50)
-   **collision energy** (data at both 40 and 160 A GeV)

- HQ2004, Taos Valley - July 18-24, 2004

- D. Elia, INFN Bari (Italy)

## Strange particle detection

**Acceptance:** y  1 around mid-rapidity

- HQ2004, Taos Valley - July 18-24, 2004

- D. Elia, INFN Bari (Italy)

## Collision centrality

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

| Class |  / tot |    < Nwound >
160 GeV         40 GeV |  |
| --- | --- | --- | --- |
| 0 | 42 – 53% | 62 | 57 |
| 1 | 25 – 40% | 121 | 119 |
| 2 | 11 – 23% | 209 | 208 |
| 3 | 5 – 11% | 290 | 292 |
| 4 | 0 – 5% | 349 | 346 |

-   Same class definition
-     at 40 and 160 GeV

- HQ2004, Taos Valley - July 18-24, 2004

- D. Elia, INFN Bari (Italy)

## Yields and enhancements

- HQ2004, Taos Valley - July 18-24, 2004

- D. Elia, INFN Bari (Italy)

## Energy dependence

**of hyperon ratios from SPS to RHIC**

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

**Centrality region****: ****0 - 11%****  **(both for NA57 and STAR*)

- HQ2004, Taos Valley - July 18-24, 2004

- D. Elia, INFN Bari (Italy)

## Energy dependence

**of mid-rapidity yields from SPS to RHIC**

- *Refs: Physical Review Letters 89 (2002), 092301
-             Nucl. Phys. A 715 (2003) 470c, nucl-ex/0307024

**               ****Centrality regions:**** ****	****NA57:****   0-5% (********K), 0-11% (********)**
**	****	****      ****	****STAR*:**** 0-5% (********), 0-6% (K), 0-10% (********)**

-   stronger energy dependence for
****- and all anti-hyperons

- HQ2004, Taos Valley - July 18-24, 2004

- D. Elia, INFN Bari (Italy)

## Centrality dependence

**of mid-rapidity yields**

- HQ2004, Taos Valley - July 18-24, 2004

- D. Elia, INFN Bari (Italy)

## Centrality dependence

**Centrality dependence**
**of mid-rapidity yields**

- Yield  <Nwound>

- HQ2004, Taos Valley - July 18-24, 2004

- D. Elia, INFN Bari (Italy)

## Centrality dependence

**of mid-rapidity yields**

- Yields fitted to:

- Y  <Nwound>****

- HQ2004, Taos Valley - July 18-24, 2004

- D. Elia, INFN Bari (Italy)

## Centrality dependence

**Centrality dependence**
**of mid-rapidity 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 |  |  |

- Yields fitted to:

- Y  <Nwound>****

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

- HQ2004, Taos Valley - July 18-24, 2004

- D. Elia, INFN Bari (Italy)

## Centrality dependence

**of hyperon enhancements at 160 A GeV/c**

**      ****systematic **
**      ****errors:**
-       10%  for , 
-        15%  for 
**Most peripheral **
**class:**
-    <Nwound> = 62  4

- [  ]

- HQ2004, Taos Valley - July 18-24, 2004

- D. Elia, INFN Bari (Italy)

## Centrality dependence

**of hyperon enhancements at 40 A GeV/c**

**      ****systematic **
**      ****errors:**
-       10%  for , 
-        15%  for 
**Most peripheral **
**class:**
-    <Nwound> = 57  4

**(95 % confidence level)**

-   Enhancements still there at 40 A GeV
-    	with the same hierarchy as for higher energy data: E() < E()

- [  ]

- HQ2004, Taos Valley - July 18-24, 2004

- D. Elia, INFN Bari (Italy)

## Energy dependence

**of hyperon enhancements**

-   enhancements in the most central collisions (classes 3-4) are
-      larger at 40 GeV than at 160 GeV
- 	**(qualitative agreement with canonical suppression, ***Redlich et al, QM2002***)**

-   steeper increase with centrality at lower energy

- HQ2004, Taos Valley - July 18-24, 2004

- D. Elia, INFN Bari (Italy)

## Conclusions

-   Energy dependence of yields and ratios:
-   stronger dependence for anti-particles than for particles
-      (larger baryon density at 40 A GeV)
-   and - yields stay roughly constant with energy increase
-   Centrality dependence of the yields:
-   steeper centrality dependence of the 40 A GeV yields

-   Enhancements at 40 and 160 A GeV:
-   enhancements at 40 GeV similar to those at higher energy
-   same hierarchy at both energies: E() < E()
-   steeper centrality dependence at lower energy

- HQ2004, Taos Valley - July 18-24, 2004

- D. Elia, INFN Bari (Italy)