# Presentation: 682269

- Agnes Richard
- for NA49

- Hot Quarks 2004

- Energy dependence of hyperon production in Pb+Pb collisions at the CERN-SPS

## Introduction    - motivation

- 				- overview of strangeness carriers
**Analysis:****	**- datasets, decay topologies
-                               - invariant mass spectra
**Results:**	          - mt  and rapidity spectra
**Discussion:**	- energy dependence
- 				- comparison to models
**Summary**

## Introduction

- Pb+Pb (Au+Au)

- observation in the energy dependence of strangeness production: maximum in K+ / π+ ratio around 30 AGeV

- how do the     hyperons behave?

- p+p

**Introduction**

##                       s                   =                    s 

-                       s                   =                    s
-       K+   (u s)      K0  (d s)              K-    (s u)    K0   (s d)
**               **

**KAONS:**
**sensitive to total strangeness**

****

- high baryon density

- strangeness conservation

**ANTIKAONS AND  (ANTI)-HYPERONS:**
** ****sensitive to total strangeness AND baryon density**

**strangeness carriers**

**Indtroduction**

**<**

**<**

**<**

**<**

- <<

- isospin
- symmetry

**                        **** **     (u d s)     <<                         (u d s)
-                          Ξ-     (d s s)                             Ξ-    (d s s)
-                          Ω     (s s s)                             Ω     (s s s)**                             **

## published     :  Phys. Rev. Lett. 93, 022302 (2004)

- published     :  Phys. Rev. Lett. 93, 022302 (2004)
-                     :  hep-ex/0202037, Phys.Lett.B538 (2002) 275
- preliminary  :  J.Phys. G30 (2004) S175 – S180
- 	      :  J.Phys. G30 (2004) S357 – S362
- to be expected soon

## π -

- p

- π -

**Λ**  p π -   : BR 63.9 %
- m = 1.11568 GeV/c2
- cτ = 7.89 cm

**d****ecay topologies**

## 

-        20 AGeV          30 AGeV              40 AGeV             40 AGeV

- 

- 

- 

- 

## the raw data are corrected for: 

**the raw data are corrected for:**** **
-  reconstruction efficiency
-  geometrical acceptance
-  branching ratio
**based on**:
-  Monte Carlo simulations
-  embedding of the simulated signals in raw data events
**feeddown** **for the ******** from********  decays:**
- the correction is calculated for 20 & 30 AGeV, for 40, 80 &158 AGeV estimated as 6% for  and 12% for  ):

## 158 AGeV

- 40 AGeV

-  x0.2
-  x0.2
-  x0.1

-  x 2
-  x0.3
-  +  x0.3

-  +

##     exponential fit:

- mt – m0(GeV)

- 158 AGeV
-  80 AGeV
-  40 AGeV
-  30 AGeV
-  20 AGeV

-     exponential fit:
-                                  in the mt – m0 range 0.4 – 1.4 GeV/c2

- mt – m0(GeV)

****** **

****

## (extracted from mt-spectra in the range 0.4 – 1.4 GeV/c2)

- (extracted from mt-spectra in the range 0.4 – 1.4 GeV/c2)

##  

-          40 AGeV                           158 AGeV

****** **
**Ξ  **(x 5)**    **
****** **+** ******
- (x 15)

##      20 AGeV        30 AGeV        40 AGeV        80 AGeV       158 AGeV

-      20 AGeV        30 AGeV        40 AGeV        80 AGeV       158 AGeV

**< ******** > :** 28 ± 1.5      41.9 ± 3.2      45.6 ± 1.9       47.4 ± 2.8     44.1 ± 3.2
**    ******** ****:** 0.76 ± 0.02    0.99 ± 0.04   1.16 ± 0.06              -                    -
- (statistical errors only)

##     30 AGeV            40 AGeV            80 AGeV            158 AGeV

-     30 AGeV            40 AGeV            80 AGeV            158 AGeV

**< ******** > :** 0.32 ± 0.07         0.74 ± 0.04         2.26 ± 0.25         3.87 ± 0.18
-       ****** ****:** 0.69 ± 0.08 	    0.71 ± 0.05         0.85 ± 0.13          0.95 ± 0.05
- (statistical error only)

## preliminary

- < >  = 1.5 ( <+> + <-> )

- AGS      SPS            RHIC

## location of the anomalies in the ratio of strange to non-strange particles ()

**location of the anomalies in the ratio of strange to non-strange particles (********)**
- maximum in  <  > / <  >  at around 30 AGeV      (              7.62 )
- and
- < K+ > / < + >   around  30 AGeV
- kink in
- < K- > / < - >    around  30 AGeV
- not reproduced by hadron gas model!
- ref.: Cleymans & Redlich, Phys.Rev.C60:054908, 1999 nucl-th/9903063

##  

****** **
**Ξ  **(x 7)**    **
****** **+** ******
- (x 20)

**Energy dependence**** of ****hyperon to pion ratio**

- < >  = 1.5 ( <+> + <-> )

- AGS      SPS

## hadron gas (1)

- hadron gas (1)
- Braun-Munzinger et al.,
- Nucl.Phys. A697:902-912
- hadron gas (free)
- Becattini et al.,
- Phys.Rev.C69:024905, 2004
- UrQMD 1.3.:
- Bleicher private communication

##  rich data on hyperons (in central Pb+Pb collisions available in NA49

-  rich data on hyperons (in central Pb+Pb collisions available in NA49
-  at 20 and 30 AGeV presented for the first time
-  maximum in the  / ratio is observed
-  around 30 GeV
- appears at the same point as the anomalies in K+/ and K-/  ratios

## EXTRA SLIDES

## Slide 21

## Slide 22

## ?

**Ξ  **

****

## 

- 

- p

- x

- y

- z

- 

- Target position

-   impact parameter in     the target plane
-  z vertex of the  decay

## ln (p)