PANDA - p Annihilation at Darmstadt

B. Dulach, P. Gianotti (Resp. Naz.), M. Giardoni, C. Guaraldo, M. Iliescu (Art. 23),V. Lucherini, D. Orecchini (Tecn.), E. Pace, L. Passamonti (Tecn.), D. Pierluigi, (Tecn.),

D. Pietreanu (Ass. Ric.), A. Russo (Tecn.), D. Sirghi (Art. 2222)

1 Introduction

PANDA is one of the biggest future experiments in hadron and nuclear physics that will be carried

out at the new Facility for Antiproton and Ion Research (FAIR) at Darmstadt, Germany. It is

dedicated to study annihilations of antiprotons on nucleons and nuclei up to a maximum center-

of-mass energy in pp of 5.5 GeV. Presently, the PANDA collaboration consists of 400 physicists

from 17 countries spread all over the world. The Italian groups involved are: Torino, University,

Politecnico and INFN, Trieste, University and INFN, Genova INFN, Pavia, University and INFN,

Ferrara, University and INFN, Frascati INFN laboratory, Catania, University and INFN. The LNF

group is involved in the design and construction of the central tracker of the PANDA detector.

2 PANDA experiment

A new facility for hadronic physics is under construction in Germany. It consists of a major upgrade

of the presently running GSI accelerator complex of Darmstadt 1). An intense, high momentum

Figure 1: A schematic view of the PANDA detector.

resolution antiproton beam, with momenta between 1.5 and 15 GeV/c, will be available at the High

Energy Storage Ring (HESR), and the experimental activity will be carried out using a general

purpose detector PANDA that will be build surrounding an internal target station installed in

one of the two straight sections of the storage ring. Fig. 1 shows a schematic drawing of the

PANDA detector. It is designed as a large acceptance multi-purpose detector consisting of two

MATERIAL

S.P.A.S

DRAWINGPART.N DIMENSIONS DENOMINATION Q.TY

SIZE

APPROVED

REPLACE DRAW

CHECKED

DRAWNNATIONAL INSTITUTE FOR NUCLEAR PHISYCS

NATIONAL LAB OF FRASCATI

DRAWING N.SCALE

PROJECTION

General tolerances ISO 2768−mk−E

DATE

SHEET N.

Geometrical tolerances ISO 8015−ERoughness ISO 1302

Figure 2: The layout of the STT. Details are in the text.

distinct parts: a solenoidal spectrometer, surrounding the interaction target region, and a forward

spectrometer to cover the solid angle between 5 and 22 degrees.

3 The PANDA Central Tracker

The PANDA Central Tracker has to satisfy the following requirements:

• almost full solid angle coverage;

• momentum resolution δp/p ∼ 1.5%;

• low material budget X/X0 ∼ few %;

• good spatial resolution σr,φ = 150 µm, σz = few mm.

This detector will be placed around the Micro Vertex Detector (MVD) at a radial distance from

the interaction point between 15 and 42 cm. Along the beam axis the allowed space is 150 cm.

Presently, for this detector, two options are under discussion: a Straw Tube Tracker (STT) and a

Time Projection Chamber (TPC). The LNF PANDA group, having experience in straw tubes, is

involved in the realization of the STT.

3.1 Straw tube detector layout

The overall PANDA tracking volume will be divided in two half by the target pipe, therefore the

detector will consist of two identical semi-chambers. In the hypothesis of a straw tube tracker, each

one will be made of aluminized mylar straw tubes, diameter 10 mm, length 1500 mm, thickness

30 µm, arranged in planar double layers. Inside a double layer the tubes are glued together and

Figure 3: Layout of the STT mechanical structure. The arrowsindicated removable elements (seetext for more details)

operated with an Ar+CO2 (90+10) gas mixture with an over-pressure of 1 bar. This solution will

help to avoid strong support structures and will keep the detector design modular and simple.

To measure also particle z coordinate, some layers will be mounted with a skew angle ± 3◦ with

respect to the beam axis.

Figure 2 shows the layout for the STT. There are 4 internal double-layers parallel to the

beam axis, then 4 double-layers mounted with an opposite skew angle, and finally 2 other layers

parallel to the beam axis. To fill up the cylindrical volume, the remaining region houses smaller

tube layers.

One basic advantage of the proposed solution is that each double-layer is an independent

object that can be treated separately from the others.

In order to support the straw tube double-layers, and to precisely position them, an external

mechanical structure is necessary.

4 Activity of the LNF PANDA group

The activity of the LNF PANDA group during 2008 has been devoted to the design of this me-

chanical structure. The structure of this support is very light, and, in the hypothesis of using

Aluminum for the realization, we will have the following numbers:

• density 2.7 g/cm3 ;

• Youngs modulus: 70 GPa;

• radiation Length (Xo): 9 cm;

• thermal expansion: 24 ppm/◦C;

with a total weight of 8.2 kg. The two internal rods (signed with the arrows in fig.3 ) are needed

only during the straw double-layers mounting phase, and then could be removed. To check the

Figure 4: Prototype of the Straw Tube Tracker.

mounting procedure of straw tube double-layers a first prototype of the mechanical structure flanges

has been build at the LNF mechanical workshop, and mounted on dummy supports. On these

flanges 4 axial double-layers and 2 skewed ones can be mounted. Fig. 4 is a picture taken during

the mounting phase.

For 2009 tests with cosmic rays and beams are foreseen for the STT prototype. The group

will also continue the design activity approaching the problems related with the integration of the

STT with the other components of the PANDA detector. Furthermore a Technical Design Report

for the STT will be prepared.

5 Conference presentations

1. P. Gianotti, “Physics with antiprotons at FAIR”, invited talk at the XLVI International

Winter Meeting on Nuclear Physics, Bormio (Italy) 26-30 January, 2008.

2. P. Gianotti, “Baryon Form Factors at FAIR”, invited talk at the International Workshop on

e+e− collisions from φ to ψ (PHIPSI08), Frascati (Italy) 7-10 April, 2008.

References

1. http://www.gsi.de/fair/

2. http://www-panda.gsi.de/auto/ home.htm