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QCD PAC recommendations

Emilio Chiavassa

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• Charmonium spectroscopy

• QCD exotics

• Hypernuclear Physics

• Charm in Nuclei

PANDA main goals

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PANDA

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PANDA - Recommendations of QCD PAC

The PANDA collaboration presently consists of 340 physicists from 46 institutions in 14 countries. The PANDA physics programme addresses very important questions forQCD in the transition from the non-perturbative to perturbative regimes.

The experiment offers a unique opportunity to study a large range of initial spin-paritystates in a gluon-rich environment. It can be realistically expected that PANDA will deliver important new results on the charmonium spectrum, QCD exotics, hypernuclearphysics, charm production and other processes in nuclei. There are also exciting possi-bilities of studying exclusive two-body processes (such as gamma-gamma, pi-pi), electromagnetic form factors in the time-like region and single spin asymmetries, ifpolarized antiprotons become available. The physics issues addressed will go beyondthe CEBAF programme and a possible Charm Factory, which will study e+ e- collisionsin the 3-5 GeV c.m. region. The committee agrees that the requested antiproton beamtime of 6 months per year would be adequate.

The PAC welcomes the TDR, which is a comprehensive and clear report that addressesall relevant questions. Since the LoI, very good progress towards the final detector design has been made. For example, the light yield of PWO crystals at -25 deg hasshown to be sufficiently high for achieving an excellent resolution in the electromagneticcalorimeter.

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The PAC believes the experiment to be feasible with present technology and the humanresources in the collaboration appear to be adequate. The analysis of 10 benchmark channels based on the TDR detector specifications shows that the goals of the experi-ment are in reach of the detector.

The PAC encourages focussing on adequate and cost effective solutions, and to choosebetween alternatives as soon as possible. For example, the PWO option now seems tobe favored over the BGO option for the calorimeter. R+D should be pursued vigorouslyto clarify the remaining questions: the pellet target performance to reach the envisagedluminosity of 2·1032 cm-2 s-1, thinner pixel detectors to minimize conversions and allowtrigger-less operations, DIRC readout with APDs instead of PMTs to save costs, thedesign of the magnet of the forward spectrometer, and the relative merits of a high-rateTPC over the Straw Tube Tracker.

The cost of the PANDA detector (49.5 M€, including 4.5 M€ contingency) has considera-bly increased over the estimate in the CDR. The cost now seems to be adequate. Thecontingency is needed for technical risks. The scarcity of suppliers for PWO crystalsimplies an additional risk. Since final state separation, 4π coverage, high rate capabilityand energy resolution are crucial for most of the physics program, there is little room forstaging of the detector. Overall, the PAC considers the risk associated with the PANDAdetector as low for a project at this stage.

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In-medium modifications of hadrons onset of chiral symmetry restoration at high B

measure: , , e+e- open charm (D mesons) Strangeness in matter (strange matter?) enhanced strangeness production ?

measure: K, , , ,

Indications for deconfinement at high B anomalous charmonium suppression ?

measure: J/, D

Critical point event-by-event fluctuations

CBM main goals.

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CBM

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PAC report on CBM

CBM is a core experiment at FAIR. The physics case as already been discussed in theCDR and reiterated in the present Technical Status Report is excellent. CBM addressesfundamental issues of high density QCD: in-medium modification of hadronic properties,chiral symmetry restoration through the measurement of low-mass dileptons, deconfine-ment through the measurement of J/psi production and the search for a possible criticalpoint in the phase diagram of strongly interacting matter (temperature vs chemical poten-tial) via the measurements of event-by-event fluctuations of for example strange particleyields. CBM fills the gap left unexplored between SPS and AGS energies. Measureme-nts of the p-p and p-A reactions provide important reference data as well as interestingphysics in their own right.

The Committee recognizes the progress achieved since the presentation of the LoI inJune 2004. The Collaboration has obtained encouraging results in the studies of the ratecapabilities of RPC with the use of suitable electrode materials, semiconducting glasses and doped polymers. The development of a global simulation framework, CBMroot, is a major milestone for the study of the detector performance. Another major milestone is the development of the concept of a free streaming architecture of the DAQ and event processing systems.

The Committee feels, however, that the two major measurements, low mass dileptons andopen and hidden charm, are imposing not necessarily compatible requirements on the experiment and possibly cannot be done with a common single setup. For example, the

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7 layers of Si complicate the pattern recognition of low-mass pairs, and the present setupappears to lack sufficient rejection of conversion and Dalitz decay. For this reason theCommittee recommends that the collaboration optimize the charm and the dilepton experiments separately by rearranging dedicated and common detector elements.

The feasibility of each of the combinations should be supported by detailed and realistic detector simulations. In a staged approach an upgraded HADES detector could measurelow-mass pairs in stage 2 whereas CBM will be commissioned for measurements at fullenergy in stage 3.

At this time it is too early to comment on the detailed cost of the experiment but theCommittee believes that the physics goals of the CBM experiment can be reached witha detector having a price tag of about 50 M Euros. We, however, urge the collaborationto critically scrutinize all individual components of the detector concerning the technologychoices as well as the required coverage to optimize the costs.

The committee remains concerned about adequate human resources available to thecollaboration. The collaboration stated goal is to submit a full TDR by the end of 2006.While this is a challenge, the collaboration must work with the FAIR management topresent a viable project definition in a time scale compatible with the overall FAIRdecision schedule.

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As a preamble to the PAX and ASSIA reports, the PAC would like to stress again theuniqueness of the program with polarized anti-protons and polarized protons that could become available at GSI. The primary physics goals are the measurement of the transversity distribution h1 in the valence quark region with the polarized Drell-Yanprocess, exclusive polarized anti-proton-proton scattering and the separation of the time-like form factors of the proton including the determination of their phase difference.The PAC also reiterates that there should be only one dedicated polarized antiprotonexperiment in the initial stages of the FAIR project.

Preamble to PAX and ASSIA

PAX main goals.

Transversity distribution on the nucleon using proton and antiprotons polarized- directly accessible uniquely via the double transverse spin asymmetry ATT in the Drell-Yan production of lepton pairs. - time-like form factors of the proton including the determination of their phase difference.

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Antiproton Polarizer Ring (APR)Antiproton Polarizer Ring (APR)

e-coolere-coolerAPR

CSR

ABS

Polarizer Target

InternalExperiment

||EM||EM Q2

Siberian Snake

B

Injection

Extraction

150 m

Polarization Buildup in APR parallel to measurement in HESR

F. Rathmann et al., PRL 94, 014801 (2005)β=0.2 m

q=1.5·1017 s-1

T=100 KLongitudinal Q (300 mT)

db=ψacc·β·2dt=dt(ψacc)

lb=40 cm (=2·β)

df=1 cm, lf=15 cm

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Antiproton spin polarization proposed scheme

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The PAX collaboration has made significant progress from the last PAC meeting in deve-loping the concept for polarizing antiprotons at low energy in an antiproton polarizationring (APR) via polarization transfer from polarized electrons, accelerating them to .5 GeV/c in a 2nd ring (CSR) and then injecting them into the HESR for acceleration to 15 GeV/c. Polarized protons could also be stored in the CSR where asymmetric collisionscould take place. The PAX collaboration also proposed a staged experimental approachstarting with polarized antiprotons on a polarized gas target in the CSR, which could likelyrun simultaneously with PANDA.

In our opinion the critical h1 measurement requires a minimum s of 200 GeV2 and a mini-mum average luminosity of 1031 cm-2s-1 to be compelling. At present the projected lumi-nosity at high energy does not reach the 1031 goal. Therefore we believe it is premature to approve the present proposal.

However the PAC considers it is essential for the FAIR project to commit to polarized anti-proton capability at this time and include polarized transport and acceleration capability inthe HESR, space for installation of the APR and CSR and associated hardware, and theAPR in the core project.

The PAC report on PAX

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We request the PAX collaboration to:

1- Commit to the construction and testing of the APR (IKP Jülich appears to be the optimal location)2- Explore all options to increase the luminosity to the target value specified above3- Prepare a more detailed physics proposal and detector design for each of the proposed stages. These stages may include:

a- 3.5 GeV/c polarized antiprotons on a polarized proton target b- 15 GeV/c polarized antiprotons with the PANDA detector (for single spin asymmetries) c- 15 GeV/c polarized antiprotons on a polarized proton target in a dedicated detector

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Collisions of 15 GeV/c antiprotons with 3.5 GeV/c polarized protons.The opportunities and physics case are certainly advanced if the HESR is able to run at momenta higher than 15 GeV/c, as well as improved antiproton production rate and cooling capabilities in CR and RESR, and we encourage initiatives to reach that goal.

The PAC understands this approach places a significant additional burden on the FAIR accelerator team to face the additional constraints and developments associated with this project. The PAX proposed acceleration scheme has been presented to the TAC and a separate report will be provided. It is anticipated that the expertise and facilities of the COSY team could make major contributions.

The PAX collaboration is already strong with about 200 people (in typically 30 labs from 8 countries), who stress their strong commitment in this project. Also there is a strong connection (MoU is signed) between the GSI and FZJ laboratories.

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The document provided by the ASSIA collaboration is not at the level of a proposal.

They still consider that studies of optimum luminosity and energy requirements should bepursued, in particular to perform measurements of the transversity observables in the so-called safe region (above the J/y resonance region).

At this stage, the detector is not defined due to the unspecified aspects of the accelera-tion scheme proposed by this collaboration. The PAC reiterates its opinion that there should be only one detector dedicated to spin physics.

The ASSIA collaboration is about 100 people, with 2-3 leading laboratories. Severalgroups are however heavily involved in other experiments over the next 5 years, and there were concerns for their commitments to the FAIR project.

The ASSIA people are willing to join working groups on acceleration issues. This could initiate a possible future collaboration between PAX and ASSIA, which is strongly encouraged by the PAC.

PAC report on ASSIA