ROBERTO PETRONZIO (April 21, 1949 - July 28, 2016)

Luciano Maiani, July 28, 2016

A student of Nicola Cabibbo, Roberto Petronzio started his career in theoretical physics in Roma in 1972. He was a bright, communicative, hard working student, who immediately started to interact and work with us, in different configurations: with Nicola, of course, with myself and Guido Altarelli, then Keith Ellis, then Giorgio Parisi. These were very exciting times, with the discovery of the Standard Theory, asymptotic free- dom, neutral currents and, in 1974, the J/Psi. Discoveries were coming almost every week from laboratories all over the world and the Roma group was very active in confronting the data with the predictions of the Standard Theory. Roberto started with a work on neutrino interactions in a specific parton model that our group, including him, had developed at the time [1] and he became soon a world recognized expert in electroweak deep inelastic interactions and QCD. A selection of Petronzio’s most quoted papers during his stay in Roma is given in [2]. Roberto went to CERN in 1977, first with a TH group fellowship and then, in 1979 until 1986, with a CERN staff position. A selection of the most quoted papers done at CERN on deep inelastic and electroweak interactions is given in [3] [4]. After CERN, as visiting professor, he was in Ecole` Normale Superi´eure,Paris, Max Planck Institute, Munich, and Boston University. In Munich, he made the interesting proposal to test the formation of a deconfined quark gluon plasma by the suppression of J/Psi production [5], which received much experimental attention. In 1987, Roberto became full professor in Theoretical Physics at Universit´adi Roma Tor Ver- gata, a position he held until his early retirement, forced by his illness, in 2015. When at CERN, Roberto got interested in the numerical, non-perturbative simulation of QCD with Montecarlo methods. With Nicola Cabibbo and Guido Martinelli, in 1984, he made a pio- neering work on the calculation of the QCD renormalisation of four-fermion operators, a case of interest for non-leptonic Weak Interactions [6]. The paper opened up a new road to compute the non-perturbative renormalisation of weak interaction matrix elements (the so-called B-factors), which was to have an important impact on the determination of the Cabibbo-Kobayashi-Maskawa matrix, providing a crucial test of the Standard Theory. With Cabibbo and Parisi, he was a leading figure of the APE project (Array Processor Experi- ment) aiming at design and construction of a highly performant, highly parallel processor optimized for QCD calculations [7].

1 FIG. 1: Roberto Petronzio at ICTP.

Back in Roma, Roberto dedicated himself to teaching and to grow up a school of young people, working in numerical lattice QCD and in electroweak interactions [8] and participating in the proposals to extend APE into higher performance arrays [9]. In Roma, Roberto grew an interest in science administration, first as Member of the Adminis- tration Council of Tor Vergata University, 1992-2002, then as a Member of the Executive Board of INFN, 2002-2003. In 2004 he was appointed as President of INFN, a charge he took until 2011. He was the Italian scientific delegate to the CERN Council, 2006-2011, and representative of the Italian Government and President of the Steering Committee of ICTP, Trieste, 2006-2014, Fig. 1. A much appreciated science manager, Roberto went through a difficult period of reformation of the Italian Research Institutions. While increasing transparency and accountability of the organ- isation, he succeeded to maintain the independence, autonomy and form of governance of INFN, that have been at the basis of the indisputable success of this Institution. At ICTP, he guaranteed an efficient connection between ICTP and the Italian Government. He brought ICTP and INFN closer together and strengthened the existing links between the two institutions, promoting a very successful collaborative agreement between ICTP and INFN. Roberto has been a first class scientist who was able to work on all fronts of modern theoretical

2 physics. He was creative, hard worker and he liked to share with others his enthusiasm for research and to work in team. A fine mathematical mind, Roberto never lost sight of the relationship that goes between theory and experiment and was able to suggest meaningful experiments himself, to test delicate aspects of the theory. For this, he was widely appreciated and respected. Towards the end of his INFN mandate, Roberto launched the ambitious program to build in Italy, with an international venture, an advanced accelerator to study the decay of B-mesons and the physics of flavour. For lack of resources, the original project of a very high luminosity B-factory had to be scaled down to a charm-tau factory. It was this project that Roberto was working at when, in 2014, he was caught by a stroke that left him confined in bed, in very severe conditions, until his untimely end. Unfortunately, even the reduced project has been abandoned and it is now to the Italian par- ticle physics community to take the challenge of a tradition which started with Enrico Fermi and continued with Bruno Touschek, Nicola Cabibbo and so many others, Roberto Petronzio included.

3 [1] G. Altarelli, N. Cabibbo, L. Maiani and R. Petronzio, The Nucleon as a bound state of three quarks and deep inelastic phenomena, Nucl. Phys. B 69 (1974) 531. [2] G. Altarelli, N. Cabibbo, L. Maiani and R. Petronzio, Neutrino processes in a compound model for the nucleon, Phys. Lett. B 48 (1974) 435. G. Altarelli, R. K. Ellis, L. Maiani and R. Petronzio, The Structure of Parity Violating Strangeness Conserving Weak Nonleptonic Amplitudes in an Asymptotically Free Theory, Nucl. Phys. B 88 (1975) 215. G. Altarelli, G. Parisi and R. Petronzio, Charmed Quarks and Asymptotic Freedom in Neutrino Scatter- ing, Phys. Lett. B 63 (1976) 183. G. Parisi and R. Petronzio, On the Breaking of Bjorken Scaling, Phys. Lett. B 62 (1976) 331. G. Altarelli, N. Cabibbo, L. Maiani and R. Petronzio, Must the New Heavy Lepton Have Its Own Neutrino?, Phys. Lett. B 67 (1977) 463. G. Altarelli, L. Baulieu, N. Cabib[6]bo, L. Maiani and R. Petronzio, Muon Number Nonconserving Processes in Gauge Theories of Weak Interactions, Nucl. Phys. B 125 (1977) 285 Erratum: [Nucl. Phys. B 130 (1977) 516]. G. Altarelli, G. Parisi and R. Petronzio, Transverse Momentum in Drell-Yan Processes, Phys. Lett. B 76 (1978) 351. L. Maiani, G. Parisi and R. Petronzio, Bounds on the Number and Masses of Quarks and Leptons Nucl. Phys. B 136 (1978) 115. [3] G. Altarelli, G. Parisi and R. Petronzio, Transverse Momentum of Muon Pairs Produced in Hadronic Collisions, Phys. Lett. B 76 (1978) 356. D. Amati, R. Petronzio and G. Veneziano, Relating Hard QCD Processes Through Universality of Mass Singularities, Nucl. Phys. B 140 (1978) 54; D. Amati, R. Petronzio and G. Veneziano, ıRelating Hard QCD Processes Through Universality of Mass Singularities. 2., Nucl. Phys. B 146 (1978) 29. A. De Rujula, R. Petronzio and A. Savoy-Navarro, Radiative Corrections to High-Energy Neutrino Scattering, Nucl. Phys. B 154 (1979) 394. W. Furmanski, R. Petronzio and S. Pokorski, Heavy Flavor Multiplicities at Very High-Energies Nucl. Phys. B 155 (1979) 253. G. Parisi and R. Petronzio, Small Transverse Momentum Distributions in Hard Processes, Nucl. Phys. B 154 (1979) 427. N. Cabibbo, L. Maiani, G. Parisi and R. Petronzio, Bounds on the Fermions and Higgs Boson Masses in Grand Unified Theories, Nucl. Phys. B 158 (1979) 295. G. Curci, W. Furmanski and R. Petronzio, Evolution of Parton Densities Beyond Leading Order: The Nonsinglet Case, Nucl. Phys. B 175 (1980) 27. W. Furmanski and R. Petronzio, Singlet Parton Densities Beyond Leading Order, Phys. Lett. B 97

4 (1980) 437. R. K. Ellis, W. Furmanski and R. Petronzio, Unraveling Higher Twists, Nucl. Phys. B 212 (1983) 29. [4] L. Maiani, R. Petronzio and E. Zavattini, Effects of Nearly Massless, Spin Zero Particles on Light Propagation in a Magnetic Field, Phys. Lett. B 175 (1986) 359. [5] F. Karsch and R. Petronzio, Momentum Distribution of J/psi in the Presence of a Quark - Gluon Plasma, Phys. Lett. B 193 (1987) 105.and Boston University; χ and J/ψ Suppression in Heavy Ion Collisions and a Model for Its Momentum Dependence, Z. Phys. C 37 (1988) 627. [6] N. Cabibbo, G. Martinelli and R. Petronzio, Weak Interactions on the Lattice, Nucl. Phys. B 244 (1984) 381. [7] P. Bacilieri et al., The Ape Project: A Gigaflop Parallel Processor For Lattice Calculations, CERN-TH- 4283/85, ROM2F/85/28. [8] S. Cortese and R. Petronzio, The Single top production channel at Tevatron energies, Phys. Lett. B 253 (1991) 494. G. de Divitiis et al. [Alpha Collaboration], Universality and the approach to the continuum limit in lattice gauge theory, Nucl. Phys. B 437 (1995) 447 G. M. de Divitiis, R. Petronzio and L. Silvestrini, Flavor changing top decays in supersymmetric exten- sions of the standard model, Nucl. Phys. B 504 (1997) 45 G. M. de Divitiis, R. Petronzio and N. Tantalo, On the discretization of physical momenta in lattice QCD, Phys. Lett. B 595 (2004) 408 A. Masiero, P. Paradisi and R. Petronzio, Probing new physics through mu - e universality in K —¿ l nu, Phys. Rev. D 74 (2006) 011701 L. Del Debbio, L. Giusti, M. Luscher, R. Petronzio and N. Tantalo, Stability of lattice QCD simulations and the thermodynamic limit, JHEP 0602 (2006) 011 L. Del Debbio, L. Giusti, M. Luscher, R. Petronzio and N. Tantalo, QCD with light Wilson quarks on fine lattices (I): First experiences and physics results, JHEP 0702 (2007) 056. [9] F. Bodin et al., The apeNEXT project, Nucl. Phys. Proc. Suppl. 106 (2002) 173 R. Ammendola et al., APEnet+: a 3D toroidal network enabling Petaflops scale Lattice QCD simulations on commodity clusters PoS LATTICE 2010 (2010) 022.

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