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M. Svec

Publications and source records attributed to M. Svec.

12 recordsLinked to original sources
arXiv2009

Pattern recognition and PID for COMPASS RICH-1

A package for pattern recognition and PID by COMPASS RICH-1 has been developed and used for the analysis of COMPASS data collected in the years 2002 to 2004, and 2006-2007 with the upgraded RICH-1 photon detectors. It has allowed the full characterization of the detector in the starting version and in the upgraded one, as well as the PID for physics results. We report about the package structure and algorithms, and the detector characterization and PID results.

physics.ins-det↗
arXiv2002

Sigma(770) Resonance and the Breaking of Scale and Chiral Symmetry in Effective QCD

CERN measurements of pi(-)p->pi(-)pi(+)n on polarized target at 17.2 GeV/c enable experimental determination of partial wave production amplitudes below 1080 MeV. The measured S-wave transversity amplitudes provide evidence for a narrow scalar resonance sigma(770). The assumption of analyticity of production amplitudes in dipion mass allows to determine S-wave helicity amplitudes S_0 and S_1. The amplitude S_1 is related to pi(-)pi(+)->pi(-)pi(+) scattering. There are four "down" solutions (1, 1bar), (2, 1bar), (1, 2bar) and (2, 2bar) selected by unitarity in pipi scattering. Ellis-Lanik relation between the mass m_sigma and partial width Gamma(sigma->pi(-)pi(+)) derived from an effective QCD theory with broken scale and chiral symmetry selects solutions (1, 1bar) and (1, 2bar) and imparts the sigma(770) resonance with a dilaton-gluonium interpretation. Weinberg's mended symmetry selects solutions (1, 1bar) and (2, 1bar). The combin ed solution (1, 1bar) has m_sigma=769 +/- 13 MeV and Gamma_sigma=154 +/- 22 MeV. The observed sigma-rho^0 degeneracy leads to two new relations between gluon condensate and pion decay constant and SU(2) chiral condensate. Both relations are well satisfied. Ellis-Lanik relation relates the existence of sigma(770) to breaking of scale symmetry in QCD. Interaction of chirally invariant and narrow sigma(770) with a chirally noninvariant QCD vacuum in pi(-)pi(+)->pi(-)pi(+) scattering is proposed as a possible mechanism for the metamorphosis of sigma(770) into a broad resonant S-wave structure in pi(-)pi(+)->pi(-)pi(+) related to spontaneous breaking of chiral symmetry in QCD.

hep-ph↗
arXiv2002

Evidence for a narrow sigma(770) resonance and its suppression in pipi scattering from measurements of pi(-)p->pi(-)pi(+)n on polarized target at 17.2 GeV/c

We present a new model independent amplitude analysis of reaction pi(-)p->pi(-) pi(+)n measured at CERN at 17.2 GeV/c on polarized target using a Monte Carlo method for dipion mass 580-1080 MeV. The two solutions for measured moduli |Sbar|^2 and |S|^2 of the two S-wave transversity amplitudes Sbar and S show res onant behaviour below 800 MeV corresponding to a scalar resonance sigma(770). Simultaneous fits to |Sbar|^2 and |S|^2 include f_0(980). The CERN data on polar ized target supplemented by the assumption of analyticity of production amplitud es in dipion mass allow to determine the helicity amplitudes S_0 (a_1 exchange) and S_1 (pi exchange) from fitted transversity amplitudes. The sign ambiguity in sigma(770) contribution leads to 2 solutions. In the "down" solution sigma(770) is suppressed in the helicity flip amplitude S_1 and thus also in pi(-)pi(+)-> pi(-)pi(+) scattering. Most contribution of sigma(770) to pion production is in the nonflip amplitude S_0, or in pi(-)a_1(+)->pi(-)pi(+) scattering. In the "up" solution the situation is reversed. The "up" solution is excluded by unitarity in pipi scattering. The "down" solution, and thus the evidence for sigma(770), is in agreement with unitarity in both pi(-)pi(+)->pi(-)pi(+) and pi(-)a_1(+)-> pi(-)pi(+) scattering. There are 4 "down" solutions (1, 1bar), (2, 1bar), (1, 2bar) and (2, 2bar). The sigma(770) resonance manifests itself as a broad resonant structure at ~ 720 MeV in the flip amplitude |S_1|^2 in solutions (1, 1bar) and (2, 1bar). The contribution of sigma(770) to |S_1|^2 is small in solutions (1, 2bar) and (2, 2bar). The metamorphosis of a narrow sigma(770) in the nonflip amplitude S_0 into a broad resonant structure in the flip amplitude S_1 is a new phenomenon related to breaking of scale and chiral symmetry in QCD.

hep-ph↗
arXiv2001

Unitarity and Interfering Resonances in pipi Scattering and in Pion Production piN->pipiN

Additivity of Breit-Wigner phases has been proposed to describe interfering resonances in partial waves in $ππ$ scattering. This assumption leads to an expression for partial wave amplitudes that involves products of Breit-Wigner amplitudes. We show that this expression is equivalent to a coherent sum of Breit-Wigner amplitudes with specific complex coefficients which depend on the resonance parameters of all contributing resonances. We use analyticity of $ππ$ partial wave amplitudes to show that they must have the form of a coherent sum of Breit-Wigner amplitudes with complex coefficients and a complex coherent background. The assumption of additivity of Breit-Wigner phases restricts the partial waves to analytical functions with very specific form of residues of Breit-Wigner poles. We argue that the general form provided by the analyticity is more appropriate in fits to data to determine resonance parameters. The partial wave unitarity can be imposed using the modern methods of constrained optimization. We discuss unitarity and the production amplitudes in $πN\toππN$ and use analyticity in the dipion mass variable to justify the common practice of writing the production amplitudes as a coherent sum of Breit-Wigner amplitudes with free complex coefficients and a complex coherent background in fits to mass spectra with interfering resonances.

hep-ph↗
arXiv1997

Mass and width of sigma(750) scalar meson from measurements of pi(-)p->pi(-)pi(+)n on polarized target

Model independent amplitude analyses of $π^- p_\uparrow \to π^- π^+ n$ on polarized target at 17.2 GeV/c reveal resonant structure of S-wave transversity amplitudes $|\bar S|^2Σ$ and $|S|^2Σ$ near 750 MeV. Simultaneous fit to $|\bar S|^2Σ$ and $|S|^2Σ$ with a single $σ$ pole yields $m_σ= 775 \pm 17$ MeV and $Γ_σ= 147 \pm 33$ MeV. Simultaneous fit with two common $σ$ poles yields a lower $χ^2/dpt$. Their resonance parameters are $m_σ= 786 \pm 24$ MeV, $Γ_σ= 130 \pm 47$ MeV and $m_{σ^\prime} = 670 \pm 30$ MeV, $Γ_{σ^\prime} = 59 \pm 58$ MeV.

hep-ph↗
arXiv1997

Study of resonant structure of S-wave amplitudes in pi(-)p->pi(-)pi(+)n measured on polarized target at 17.2 GeV/c in the mass range of 580-1080 MeV

We have performed a new model independent amplitude analysis of reaction $π^- p \to π^- π^+ n$ measured at CERN at 17.2 GeV/c on polarized target. The analysis extends the range of dipion mass from 600--880 MeV used in the previous study to 580--1080 MeV. Our purpose is to study the role of $f_0(980)$ interference and to better determine the resonance parameters of $σ(750)$ resonance from fits to both S-wave amplitudes $|\bar S|^2Σ$ and $|S|^2Σ$ with recoil nucleon transversities ``up'' and ``down'', respectively. This work is the first attempt to determine resonance parameters of a resonance from Breit-Wigner fits to production amplitudes of opposite transversity. We used several fitting procedures to understand the resonant structure of the S-wave amplitudes in this mass range. The simultaneous fit to $|\bar S|^2Σ$ and $|S|^2Σ$ with two common $σ$ poles yields an excellent fit with a lower $χ^2/dpt$ than the separate fits. All amplitudes are dominated by a $σ$ state with $m_σ= 786 \pm 24$ MeV and $Γ_σ= 130\pm 47$ MeV. All amplitudes receive a weaker contribution from a narrower $σ'$ state with $m_{σ'} = 670 \pm 30$ MeV and $Γ_{σ'} = 59 \pm 58$ MeV. We propose to identify $σ'(670)$ and $σ(786)$ with colour-electric and colour-magnetic modes of lowest mass scalar gluonium $0^{++} (gg)$.

hep-ph↗
arXiv1996

Amplitude analysis of reactions pi(-)p->etapi(-)p and pi(-)p->etapi(0)n on polarized target and the exotic 1-+ meson

Recently several experimental groups analysed data on $π^- p \to ηπ^- p$ and $π^- p \to ηπ^0 n$ reactions with exotic $1^{-+}$ $P$-wave and found a conflicting evidence for an exotic meson $I=1 1^{-+} (1405)$. High statistics data on these reactions are presently analysed by BNL E852 Collaboration. All these analyses are based on the crucial assumption that the production amplitudes do not depend on nucleon spin. This assumption is in sharp conflict with the results of measurements of $π^- p \to π^- π^+ n$, $π^+ n \to π^+ π^- p$ and $K^+ n \to K^+ π^- p$ on polarized targets at CERN which find a strong dependence of production amplitudes on nucleon spin. To ascertain the existence of exotic meson $1^{-+} (1405)$, it is necessary to perform a model-independent amplitude analysis of reactions $π^- p \to ηπ^- p$ and $π^- p \to ηπ^0 n$. We demonstrate that measurements of these reactions on transversely polarized targets enable the required model independent amplitude analysis without the assumption that production amplitudes are independent on nucleon spin. We suggest that high statistics measurements of reactions $π^- p \to ηπ^- p$ and $π^- p \toηπ^0 n$ be made on polarized targets at BNL and at Protvino IHEP, and that model-independent amplitude analyses of this polarized data be performed to advance hadron spectroscopy on the level of spin dependent production amplitudes.

hep-ph↗
arXiv1996

Relevance of nucleon spin in amplitude analysis of reactions pi(-)p->pi(0)pi(0)n and pi(-)p->eta eta n

The measurements of reactions $π^- p \to π^- π^+ n$ and $π^+ n \to π^+ π^- p$ on polarized targets at CERN found a strong dependence of pion production amplitudes on nucleon spin. Analyses of recent measurements of $π^- p \to π^0π^0 n$ reaction on unpolarized targets by GAMS Collaboration at 38 GeV/c and BNL E852 Collaboration at 18 GeV/c use the assumption that pion production amplitudes do not depend on nucleon spin, in conflict with the CERN results on polarized targets. We show that measurements of $π^- p \to π^0π^0 n$ and $π^- p \to ηηn$ on unpolarized targets can be analysed in a model independent way in terms of 4 partial-wave intensities and 3 independent interference phases in the mass region where $S$- and $D$-wave dominate. We also describe model-independent amplitude analysis of $π^- p \to π^0π^0 n$ reaction measured on polarized target, both in the absence and in the presence of $G$-wave amplitudes. We suggest that high statistics measurements of reactions $π^- p \to π^0 π^0 n$ and $π^- p \to ηηn$ be made on polarized targets at Protvino IHEP and at BNL, and that model-independent amplitude analyses of this polarized data be performed to advance hadron spectroscopy on the level of spin dependent production amplitudes.

hep-ph↗
arXiv1996

Mass and width of sigma(750) scalar meson from measurements of piN->pi(-)pi(+)N on polarized targets

The measurements of reactions $π^- p_\uparrow \to π^- π^+ n$ at 17.2 GeV/c and $π^+ n_\uparrow \to π^+ π^- p$ at 5.98 and 11.85 GeV/c made at CERN with polarized targets provide a model-independent and solution-independent evidence for a narrow scalar state sigma(750). The original chi^2 minimization method and the recent Monte Carlo method for amplitude analysis of data at 17.2 GeV/c are in excellent agreement. Both methods find that the mass distribution of the measured amplitude $|\overline S |^2Σ$ with recoil transversity ``up'' resonates near 750 MeV while the amplitude $|S|^2Σ$ with recoil transversity ``down'' is large and nonresonating. The amplitude $|S|^2Σ$ contributes as a strong background to S-wave intensity I_S = (|S|^2 + |\overline S |^2)Σ$ and distorts the determinations of $σ$ resonance parameters from $I_S$. To avoid this problem we perform a series of Breit-Wigner fits directly to the measured distribution $|\overline S |^2Σ$. The inclusion of various backgrounds causes the width of sigma(750) to become very narrow. Our best fit with $t$-averaged coherent background yields $m_σ= 753 \pm 19$ MeV and $Γ_σ= 108 \pm 53$ MeV. These values are in excellent agreement with Ellis-Lanik theorem for the width of scalar gluonium. The gluonium interpretation of $σ(750)$ is also supported by the absence of $σ(750)$ in reactions $γγ\to ππ$. We also show how data on polarized target invalidate essential assumptions of past determinations of $ππ$ phase shifts .

hep-ph↗
arXiv1995

Study of sigma(750) and rho0(770) production in measurements of piN(polarized) -> pi(+)pi(-)n on a polarized target at 5.98,11.85 and 17.2 GeV/c

We present a new and improved model independent amplitude analysis of reactions $π^+ n_\uparrow \to π^+ π^- p$ at 5.98 and 11.85 GeV/c and $π^- p_\uparrow \to π^- π^+ n$ at 17.2 GeV/c measured with transversely polarized targets at the CERN Proton Synchrotron. A clear signal for $σ(750)$ resonance emerges in all four solutions for $S$-wave intensity $I_S$ at 5.98 and 11.85 GeV/c and in both solutions for $S$-wave amplitude $|\overline S|^2Σ$ at 17.2 GeV/c. Its $π^+π^-$ decay width is estimated to be in the range 200--300 MeV. We find significant suppression of $ρ^0$ production in the amplitudes $|U|^2Σ$, $|\overline N |^2Σ$ and, at 17.2 GeV/c, in $|L|^2Σ$. The mass dependence of amplitudes $|\overline L |^2Σ$ and $|L|^2Σ$ shows unexpected structures within the $ρ^0$ mass region which correlate the mass spectra corresponding to opposite nucleon spins. These features of $P$-wave moduli reveal the essential role of nucleon spin in pion production process and contradict the factorization hypothesis. Our results emphasize the need for a systematic study of pion production on the level of amplitudes in a new generation of dedicated experiments with spin at the recently proposed high-intensity hadron facilities.

hep-ph↗