Archivi tag: quarks

15th International Conference on Strangeness in Quak Matter

This Topical conference is devoted to Strangeness and Heavy Flavour production in Heavy Ion Collisions. The conference will focus on new experimental and theoretical developments on the role of strange and heavy-flavour quarks in proton-proton and in heavy-ion collisions, and in astrophysical phenomena. New results are expected, from the LHC, from RHIC and from other experimental programmes. Continua a leggere 15th International Conference on Strangeness in Quak Matter

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Flavor and top physics @ 100 TeV

A 100 TeV collider will have the ability to probe directly our microscopic nature at distances well beyond that of the LHC or any other known experiment. It would thus become the most powerful microscope ever built. Furthermore, such a machine would be potentially capable of producing more than 1011 tops and an order of magnitude more bottom and charm quarks than the LHC. Thus, it would allow for an exploration of the complementary weakly coupled regime with unprecedented accuracy. Continua a leggere Flavor and top physics @ 100 TeV

Quarks and Nuclear Physics

QNP2015 is the Seventh International Conference devoted to Quarks and Nuclear Physics. It is anticipated that QCD practitioners, both experimentalists and theorists, will gather at the Universidad Técnica Federico Santa María, in Valparaíso, Chile during the week of March 2, 2015 to present and discuss the latest advances in the field. Continua a leggere Quarks and Nuclear Physics

LHCb, l’anomalia di un decadimento particellare

I fisici che lavorano all’esperimento LHCb hanno registrato inaspettatamente una anomalia relativa al decadimento di alcune particelle subatomiche. Oggi, un gruppo di fisici guidati da Benjamin Grinstein, un professore di fisica all’University of California, San Diego, hanno riconsiderato la matematica che descrive le previsioni del modello standard. I loro risultati sono pubblicati su Physical Review Letters.

Continua a leggere LHCb, l’anomalia di un decadimento particellare

La scoperta di un nuovo mesone fornisce preziosi indizi per lo studio dell’interazione forte

Un gruppo di fisici guidati dai colleghi dell’Università di Warwick hanno scoperto una particella che contribuirà a fornire una maggiore comprensione dell’interazione forte, una delle quattro forze fondamentali della natura che tiene uniti i protoni del nucleo atomico. Denominata con la sigla Ds3 * (2860) ˉ, si tratta di un nuovo tipo di mesone, cioè un tipo di particella subatomica composte da un quark e un antiquark legati dalla forza forte, che è stato individuato dopo una serie di analisi dei dati raccolti con il rivelatore LHCb al CERN di Ginevra. L’esperimento LHCb, gestito da una grande collaborazione internazionale, è stato progettato per studiare le proprietà delle particelle elementari contenenti i cosiddetti quark-bottom e quark-charm e rappresenta a tutt’oggi l’unico esperimento in grado di realizzare questo tipo di scoperte. Date le similitudini con il modo in cui si trovano confinati i protoni negli atomi, i ricercatori sperano ora di essere in grado di studiare la particella per comprendere meglio l’interazione forte.

University of Warwick: Discovery of new subatomic particle sheds light on fundamental force of nature

arXiv: Observation of overlapping spin-1 and spin-3 D0K– resonances at mass 2.86 GeV/c2

arXiv: Dalitz plot analysis of Bs0→D0Kπ+ decays

Confermata l’esistenza di una particella esotica composta da 6 quarks

For a long time, physicists were only able to reliably verify two different classes of hadrons: baryons and mesons. Experiments performed at Jülich’s accelerator COSY have now shown that, in fact, another class of exotic particles made up of six quarks exists. Source: Forschungszentrum Jülich/SeitenPlan

Per decenni, i fisici hanno tentato in vano di identificare un particolare legame che comprende più di tre quark. Oggi, una serie di esperimenti che sono stati realizzati presso l’acceleratore COSY hanno ora mostrato che, di fatto, questo stato quantico esiste davvero in natura. Le misure hanno confermato i risultati del 2011 quando allora più di 120 scienziati di 8 nazioni scoprirono per la prima volta una forte evidenza dell’esistenza di una particella esotica, chiamata dibarione, formata da sei quark.

Jülich: Exotic Particle Confirmed

arXiv: Evidence for a New Resonance from Polarized Neutron-Proton Scattering

 

LHCb observes an exotic particle outside the quark model

The black points at the left image above show the ψ’π- invariant mass squared distribution of the data. The blue histogram shows the Z(4430) contribution. Credit. LHCb
I fisici che lavorano all’esperimento LHCb hanno pubblicato un articolo in merito ad una serie di misure di una particella esotica denominata Z(4430). Secondo il modello standard che descrive i quark, le particelle che sono soggette all’interazione forte, cioè gli adroni, sono formate sia da coppie quark-antiquark (mesoni) o da tre quark (barioni). Da quasi 50 anni, gli scienziati stanno cercando di identificare queste particelle, chiamate adroni esotici, che potrebbero non essere classificate secondo gli schemi tradizionali. Sono stati proposti numerosi candidati ma fino ad oggi non c’è stata alcuna evidenza sperimentale che confermasse con certezza la loro esistenza.

The first evidence for the Z(4430) particle has been presented in 2008 by the Belle Collaboration as narrow peak in the ψπ mass distribution in the B → ψ decays. In the latest Belle publication the observation of the Z(4430) particle is confirmed with a significance of 5.2σ and a 3.4σ evidence is presented that the quantum numbers JP = 1+ are favored over the other spin assignments. There are many so called charmonium cc* neutral states in this mass region. The fact that the Z(4430) is a charged particle does not allow to classify it as a charmonium state making this particle an excellent exotic candidate. The BaBar collaboration could explain the Z(4430) enhancement in their data by a possible feature of experimental analysis (so called reflections, for experts), not contradicting in the same time the Belle evidence. The LHCb Collaboration has reported today an analysis of about 25 200 B0 → ψ, ψ → μ+μ decays observed in 3 fb−1 of pp-collision data collected at √s = 7 and 8 TeV. The LHCb data sample exceeds by an order of magnitude that of Belle and BaBar together.

The significance of the Z(4430) signal is overwhelming, at least 13.9σ, confirming the existence of this state.

The Z(4430) quantum numbers are determined to be JP = 1+ by ruling out 0, 1, 2+ and 2 assignments at more than 9.7σ, confirming the evidence from Belle. The LHCb analysis establishes the, so called, resonant nature of the observed structure in the data, and in this way proving unambiguously that the Z(4430) is really a particle. The minimal quark content of the Z(4430) state is cc*du*. It is therefore a four quark state or a two-quark plus two-antiquark state.

LHCb: Unambiguous observation of an exotic particle which cannot be classified within the traditional quark model
The Conversation: Quirky quark combination creates exotic new particle

Quantum Diaries: Major harvest of four-leaf clover
arXiv:  Observation of the resonant character of the Z(4430)^- state

Evidence for single top quark production through the weak nuclear force

Dopo una serie di tentativi che durano ormai da circa 20 anni, finalmente gli scienziati che lavorano agli esperimenti CDF e DZero presso il Fermi National Accelerator Laboratory hanno annunciato di aver trovato il modo di produrre un quark top. I due gruppi hanno affermato di aver osservato uno dei tanti metodi decisamente rari di produrre questa particella attraverso la forza nucleare debole, nel cosiddetto “canale-s”. Per arrivare a questo risultato, i ricercatori hanno dovuto analizzare più di 500 trilioni di collisioni protoni-antiprotoni che sono state realizzate con l’acceleratore Tevatron tra il 2001 e il 2011. I risultati indicano che in circa 40 collisioni, dove è stata prodotta la forza nucleare debole, sono stati identificati singolarmente quark top assieme a quark bottom.

Top quarks are the heaviest and among the most puzzling elementary particles. They weigh even more than the Higgs boson, as much as an atom of gold, and only two machines have ever produced them: Fermilab’s Tevatron and the Large Hadron Collider at CERN. There are several ways to produce them, as predicted by the theoretical framework known as the Standard Model, and the most common one was the first one discovered: a collision in which the strong nuclear force creates a pair consisting of a top quark and its antimatter cousin, the anti-top quark. Collisions that produce a single top quark through the weak nuclear force are rarer, and the process scientists on the Tevatron experiments have just announced is the most challenging of these to detect.

This method of producing single top quarks is among the rarest interactions allowed by the laws of physics.

The detection of this process was one of the ultimate goals of the Tevatron, which for 25 years was the most powerful particle collider in the world. “This is an important discovery that provides a valuable addition to the picture of the Standard Model Universe”, said James Siegrist, DOE associate director of science for high energy physics. “It completes a portrait of one of the fundamental particles of our universe by showing us one of the rarest ways to create them”. Searching for single top quarks is like looking for a needle in billions of haystacks. Only one in every 50 billion Tevatron collisions produced a single s-channel top quark, and the CDF and DZero collaborations only selected a small fraction of those to separate them from background, which is why the number of observed occurrences of this particular channel is so small. However, the statistical significance of the CDF and DZero data exceeds that required to claim a discovery. “Kudos to the CDF and DZero collaborations for their work in discovering this process”, said Saul Gonzalez, program director for the National Science Foundation. “Researchers from around the world, including dozens of universities in the United States, contributed to this important find”. The CDF and DZero experiments first observed particle collisions that created single top quarks through a different process of the weak nuclear force in 2009. This observation was later confirmed by scientists using the Large Hadron Collider. Scientists from 27 countries collaborated on the Tevatron CDF and DZero experiments and continue to study the reams of data produced during the collider’s run, using ever more sophisticated techniques and computing methods. “I’m pleased that the CDF and DZero collaborations have brought their study of the top quark full circle”, said Fermilab Director Nigel Lockyer. “The legacy of the Tevatron is indelible, and this discovery makes the breadth of that research even more remarkable”.

Fermilab: Scientists complete the top quark puzzle

Fermilab: Observation of s-channel production of single top quarks at the Tevatron
arXiv: Evidence for s-channel Single-Top-Quark Production in Events with one Charged Lepton and two Jets at CDF

arXiv: Search for s-channel Single Top Quark Production in the Missing Energy Plus Jets Sample using the Full CDF II Data Set

arXiv: Evidence for s-channel single top quark production in pp¯ collisions at s√ = 1.96 TeV

Heavy quarks as ideal probes for quark-gluon plasma studies

Subito dopo il Big Bang, lo spazio era caratterizzato da una sorta di “zuppa primordiale” composta di quark e gluoni, ossia particelle di materia e di interazioni fondamentali. Questo plasma super denso si raffreddò quasi istantaneamente e la sua, seppure breve, esistenza contribuì sostanzialmente a creare le condizioni iniziali da cui si è successivamente evoluto il nostro Universo. Ma per capire meglio queste fasi iniziali della storia cosmica, gli scienziati devono ricreare nei grandi acceleratori di particelle quel plasma primordiale: è il caso del Relativistic Heavy Ion Collider (RHIC) presso il Brookhaven National Laboratory (BNL) dove si stanno analizzando i dati degli ultimi anni grazie ad un esperimento noto come STAR (Solenoidal Tracker at RHIC). A tale complesso è stato aggiunto di recente un nuovo rivelatore, denominato Heavy Flavor Tracker, il più avanzato nel suo genere e che servirà per studiare i processi di decadimento degli adroni costituiti da quark charm e bottom.

Scientists and engineers at the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab), have played a major role in the development of the STAR Heavy Flavor Tracker. The STAR HFT is actually the collective name for three separate silicon-based detector systems that make it possible for the first time to directly track the decay products of hadrons comprised of flavors (types) of quarks, “charm” and “bottom,” with heavy mass. Heavy quarks are considered ideal probes for quark-gluon plasma studies; however, their low production yield and short life-span (a fraction of a microsecond) make them difficult to study in heavy ion collisions that also produce huge quantities of light flavor particles. The HFT was first conceived nearly 15 years ago by Berkeley Lab’s Howard Wieman, a physicist with the Lab’s Nuclear Sciences Division who also played a prominent role in the creation of STAR. The HFT construction project, which began a few years later, was initially led at Berkeley Lab by Hans Georg Ritter, a physicist who served as head of the Nuclear Science Division’s Relativistic Nuclear Collisions program (RNC) for many years. “The HFT enables precision tracking measurements of heavy quarks at low momentum where the particle production is most sensitive to the bulk medium created in heavy ion collisions”, says Nu Xu, a physicist also with Berkeley Lab’s Nuclear Science Division who is the current spokesperson for the STAR experiment. “This allows us to distinguish the decay vertices of heavy flavor particles from primary vertices and significantly reduces combinational background, which yields cleaner measurements with a higher level of significance”. The importance of the HFT’s precision measurements at low momentum to quark-gluon plasma studies is explained by Peter Jacobs, a Berkeley Lab physicist who now heads the Nuclear Science Division’s RNC program. “Theorists claim they can calculate the dynamical behavior of heavy quarks in matter more accurately than that of light quarks or gluons. Some even think they can calculate the dynamical behavior of heavy quarks in the quark-gluon plasma using models inspired by string theory”, Jacobs says. “One of the things we will be testing with the HFT is the different predictions of the behavior of heavy flavors in the quark-gluon plasma made by string-inspired models versus more conventional physics”.

Berkeley Lab scientists and engineers are now developing a new, larger version of the HFT which they propose to be fabricated for the ALICE detector at CERN’s Large Hadron Collider. “If approved, this will be an upgrade to the Inner Tracking System of the ALICE experiment at the LHC that is a direct follow-on to the STAR HFT, utilizing a number of HFT developments”, says Jacobs. “It is proposed to be installed during the next long LHC shutdown in 2018 and will essentially be a 25 giga-pixel camera made up of 11 square meters of silicon, about 30 times larger than the HFT at STAR”.

LBL: Heavy Flavor Tracker for STAR

arXiv: Heavy Flavor Tracker (HFT) : A new inner tracking device at STAR

Looking for ‘new physics’ in the Universe

Con il termine “nuova fisica” si intende un nuovo campo di ricerca che tenta di spiegare quei fenomeni della natura che i fisici non sono ancora in grado di descrivere. Oggi, sta prendendo piede sempre più l’idea in base alla quale l’Universo può essere caratterizzato da una struttura diversa rispetto a quanto previsto dagli attuali modelli o teorie. In tal senso, un gruppo di fisici hanno avviato uno studio che avrà lo scopo di aiutare gli scienziati a rendere più facile, almeno in parte, la comprensione di alcuni fenomeni della fisica fondamentale.

New physics is about searching for unknown physical phenomena not known from the current perception of the Universe. Such phenomena are inherently very difficult to detect“, explains Matin Mojaza from CP3-Origins. Together with colleagues Stanley J. Brodsky from Stanford University in the U.S. and Xing-Gang Wu from Chongqing University in China, Mojaza has now succeeding in creating a new method that can make it easier to search for new physics in the Universe (post).

The method is a so called scalesetting procedure, and it fills out some empty, but very important, holes in the theories, models and simulations, which form the basis for all particle physics today.

With this method we can eliminate much of the uncertainty in theories and models of today“, says Matin Mojaza. Many theories and models in particle physics today has the problem that they, together with their predictions, provide some parameters that scientists do not know how to set. “Physicists do not know what values they should give these parameters. For example, when we study the Standard Model and see these unknown parameters, we cannot know whether they should be interpreted as conditions that support or oppose to the Standard Model, this makes it quite difficult to study the Standard Model accurately enough to investigate its value”, explains Matin Mojaza. With the new approach researchers can now completely clean their models for the unknown parameters and thus become better at assessing whether a theory or a model holds water.

The Standard Model has for the last 50 years been the prevailing theory of how the Universe is constructed. According to this theory, 16 (17 if we include the Higgs particle) subatomic particles form the basis for everything in the Universe.

But the Standard Model is starting to fall short, so it is now necessary to look for new physics in the Universe. One of the Standard Model’s major problems is that it cannot explain gravity, and another is that it cannot explain the existence of dark matter, believed to make up 25 percent of all matter in the Universe. In addition, the properties of the newly discovered Higgs particle, as described in the Standard Model, is incompatible with a stable Universe. “A part of the Standard Model is the theory of quantum chromodynamics, and this is one of the first things, we want to review with our new method, so that we can clean it from the uncertainties“, explains Matin Mojaza. The theory of quantum chromodynamics predicts how quarks (such as protons and neutrons) and gluons (particles that keeps quarks in place inside the protons and neutrons) interact. Matin and his Chinese and American colleagues now estimate that there may be a basis for reviewing many scientific calculations to clean the results from uncertainties and thus obtain a more reliable picture of whether the results support or contradict current models and theories. “Maybe we find new indications of new physics, which we would not have exposed if we had not had this new method”, says Matin Mojaza.

He believes that the Standard Model needs to be extended so that it can explain the Higgs particle, dark matter and gravity.

One possibility in this regard is to examine the so-called technicolor theory, and another is the theory of supersymmetry. According to the supersymmetry theory, each particle has a partner somewhere in the Universe (these have not yet been found though). According to the technicolor theory there is a special techni-force that binds so-called techni-quarks, which can form other particles, perhaps this is how the Higgs particle is formed. This could explain the problems with the current model of the Higgs particle. Also Rolf-Dieter Heuer, director of CERN in Switzerland, where the famous 27 km long particle accelerator, the LHC, is situated, believes that the search for new physics is important. According to him, the Standard Model cannot be the ultimate theory, and it is only capable of describing about 35 percent of the Universe. Like CP3-Origins, also CERN has put focus on weeding out old theories and search for new physics, this happening in 2015, when the accelerator starts up again (post).

University of Southern Denmark: New groundbreaking research may expose new aspects of the Universe

arXiv: A Systematic All-Orders Method to Eliminate Renormalization-Scale and Scheme Ambiguities in PQCD