2011 QCD and High Energy Interactions - Rencontres de Moriond ...

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AA,Pythia I 2.5 2.0 1.5 1.0 0.5 0.0 Near side 8 GeV/c destal Line: v2 subtracted ALICE preliminary p de 8 GeV/c destal Line: v2 subtracted Figure 4: IAA,Pythia: the data points are calculated with a flat pedestal; the line is based on v2 subtracted yields. that the away side is described well without applying an additional scaling. The scaling factor interpolated to the Pb-Pb energy of 2.76 TeV is then found to be 0.93 ± 13%. Yields extracted from Pythia 6.4 Perugia-0 with the mentioned scaling factor are used to measure IAA,Pythia, shown in Fig. 4. As before the data points use the flat pedestal subtraction and the lines use the v2 subtraction. The difference is rather small and only in the smallest pT,assoc bins. IAA,Pythia in peripheral events is consistent with unity, but the near side is slightly higher than the away side. This could indicate a slightly different description of the near and away side in the MC. The qualitative behavior of IAA,Pythia in central events is consistent with ICP. The away side is suppressed and the near side significantly enhanced. Such an enhancement has not been reported at lower energies. E.g. STAR measured a near-side IAA consistent with unity 3 . Near-Side Enhancement A near-side enhancement at LHC was predicted albeit for larger pT,trig: an enhancement of 10 − 20% is reported and attributed to the enhanced relative abundance of quarks w.r.t. gluons escaping the medium. 8 Gluons couple stronger to the medium due to their different color charge and their abundance is reduced. The quarks fragment harder and thus produce an enhanced associated yield. Furthermore, a near-side enhancement can be understood if one assumes that the near-side parton is also quenched. Then trigger particles with similar pT stem from partons with higher pT in Pb-Pb collisions than in pp collisions. Consequently, more energy is available for particle production on near and away side. It should be stressed that a MC was used as a reference for IAA,Pythia and it will be interesting to study if IAA using pp collisions shows the same behavior. Such a study is ongoing using newly taken data of pp collisions provided by the LHC in the week after this conference. References 1. K. Aamodt et al. [ ALICE Collaboration ], Phys. Lett. B696 (2011) 30-39. 2. A. Adare et al. [ PHENIX Collaboration ], Phys. Rev. Lett. 104 (2010) 252301. 3. J. Adams et al. [ STAR Collaboration ], Phys. Rev. Lett. 97 (2006) 162301. 4. K. Aamodt et al. [ ALICE Collaboration ], JINST 3 (2008) S08002. 5. K. Aamodt et al. [ ALICE Collaboration ], Phys. Rev. Lett. 105, 252302 (2010). 6. T. Sjöstrand, Comput. Phys. Commun. 82, 74 (1994) 7. P.Z. Skands, arXiv:0905.3418[hep-ph] (2009). 8. T. Renk and K. J. Eskola, Phys. Rev. C 77 (2008) 044905.
Jet Reconstruction and Jet Quenching in Heavy Ion Collisions at ATLAS Martin Spousta ∗ on behalf of the ATLAS Collaboration ∗ Charles University in Prague, Institute of Particle and Nuclear Physics, V Holesovickach 2, 180 00 Prague 8, Czech republic We present a measurement of dijet asymmetry and dijet azimuthal correlations in Pb+Pb collisions at √ sNN = 2.76 TeV using the ATLAS detector. This measurement provides the first evidence of a strong jet quenching in relativistic heavy ion collisions at TeV energies. The jet reconstruction procedure is discussed as well as studies which have been performed to check that the observed asymmetry is not produced by detector effects and underlying event backgrounds. 1 Introduction Ultra-relativistic heavy ion collisions are expected to produce hot and dense QCD matter. One of the main tools to study the production of such matter and its properties is a measurement of jets. Fast quarks or gluons produced in hard processes are expected to lose energy and/or have their parton shower modified in the medium of high color-charge density 1 . This may lead to a modification of jet yields and/or the structure of jets. Such an effect is called “jet quenching”. The first indirect evidence for jet quenching has been observed by experiments at the Relativistic Heavy Ion Collider (RHIC) by measuring the spectra of fast hadrons or di-hadron azimuthal correlation 2,3 . Even if there are many phenomenological models aiming to describe the effect of the jet quenching, there is no unique understanding of mechanisms responsible for the inmedium jet modifications. LHC energies provide an opportunity to study fully reconstructed jets and their properties. In these proceedings we present a first observation of a possible jet modification measured using the ATLAS detector 4 . For this study, jets are defined using the anti-kT clustering algorithm with the distance parameter R = 0.4. The inputs to this algorithm are “towers” of calorimeter cells of size ∆η × ∆φ = 0.1 × 0.1 with the cell energies weighted using energy-density-dependent factors to correct for calorimeter non-compensation and other energy losses. Jet four-momenta are constructed by the vectorial addition of cell four-vectors which are assumed to be massless. The average contribution from the underlying event (UE) to the jet energy is subtracted from each jet candidate. The estimate of UE contribution is calculated independently for each event as a function of longitudinal calorimeter layer in bins of width ∆η = 0.1 by averaging the transverse energy over the azimuth outside of jet regions of interest. Jet regions of interest are selected using a ratio of maximum tower energy to mean tower energy inside a jet which is required to be greater than 5. The value of this discriminant cut is based on simulation studies, and the results have been tested to be stable against variations in this parameter. The efficiency of the jet reconstruction algorithm, and other event properties, have been studied using PYTHIA 5 jet
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2011 QCD and High Energy Interactio
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Proceedings of the XLVIth RENCONTRE
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2011 RENCONTRES DE MORIOND The XLVI
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Foreword Contents 1. Higgs Searches
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1. Higgs
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95% CL Limit/SM 10 1 Tevatron Run I
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Events/5 GeV 6 10 5 10 4 10 3 10 2
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Events / 0.5 CDF Run II Preliminary
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For the most sensitive sub-channel
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Table 1: Table listing the various
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various SM Higgs mass hypotheses. T
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constraints on parameters are given
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Figure 2: Invariant mass of the ele
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Figure 4: CDF Exclusion limits for
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Table 1: Main phases of 2010 commis
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Table 4: Parameter list for early (
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luminosity of 1.2×10 33 cm −2 s
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2 QCD Analysis settings HERA PDFs a
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min 2 - 2 20 15 10 5 0 H1 and ZEUS
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SM σ / σ 95% CL Limit on 3 10 2 1
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NNLO σ/ σSM 95% CL Upper Bound on
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the report of this working group. I
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2.3 The impact of different PDF par
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SUSY Searches at the Tevatron Ph. G
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on the quality (loose or tight) and
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SUSY searches at ATLAS N. Barlow, o
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channel. These results are combined
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Figure 2: The top left plot shows t
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2010 data. Analysis techniques for
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as main discriminator between event
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sign leptons is particularly intere
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N of events 5 10 DATA 10 4 3 10 10
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) [pb] ν e → B(W’ × σ 10 1 -
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2 Searches in the dijet final state
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ing that the neutrinos were the onl
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The Quasi-Classical Model in SU(N)
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g (γ µ kµ) γ µ Aa µ g (pk)
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3. Top
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of their vertex with respect to the
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of about 9%. 3.1 Differential Cross
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Figure 5: Summary of most recent CD
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the minimum number of jets identifi
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where f’s are probability functio
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hood technique, with a simultaneous
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momentum direction of the b quark f
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Events 200 150 100 50 -1 DØ L=5.4
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after all corrections in the M t¯t
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for prompt J/ψ under the fully tra
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2 Events / 20 MeV/c 50 40 30 20 10
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ATLAS - consists of four parts (mon
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5 D mesons High cross-sections of D
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μ +X') [nb/GeV] → b+X → (pp T
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GeV) μ |
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HEAVY FLAVOUR IN A NUTSHELL Robert
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Figure 1: Overlapping constraints o
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Figure 3: Constraints on new physic
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RECENT B PHYSICS RESULTS FROM THE T
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(IP) distributions are fitted separ
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decays CDF extracts Using a 5.94 fb
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Search for B 0 s → µ+ µ − and
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Ref. 10,11 . The expected GL distri
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IN PURSUIT OF NEW PHYSICS WITH B DE
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τK + K −/τBs 1.01 1.00 0.99 0.9
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CHARMLESS HADRONIC B-DECAYS AT BABA
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surements (fL ∼ 0.5). Several att
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Estimating the Higher Order Hadroni
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the resulting exponent suggests to
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The counterpart of the ground-state
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(a) Tree level signal decay b ¯Bs
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the B0 d system LHCb profits from i
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This result is based on averaging o
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y non-perturbative effects. Using t
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e M(Dπ) distributions obtained D +
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CHARM PHYSICS RESULTS AND PROSPECTS
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LHCb is working towards its first m
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Two body hadronic D decays Yu Fushe
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where the effective coefficients aA
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6. J. J. Sakurai, Phys. Rev. 156, 1
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states: 6π, 2K4π, 4K2π, KSK3π 1
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egion of X(3872), which corresponds
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Figure 1: The π 0 recoil mass spec
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η → π + π − π 0 η ′ →
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conservation. This second principle
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many of them come from gluon nonper
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Latest Jets Results from the Tevatr
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in for the inclusive trijet event s
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RECENT RESULTS ON JETS FROM CMS F.
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dy (pb/GeV) /dp 2 d 10 10 10 9 10
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RECENT RESULTS ON JETS WITH ATLAS G
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| y| < 0.3 ATLAS Preliminary 2.1 <
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EPOS 2 and LHC Results TanguyPierog
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positions are randomly distributed
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ABOUT THE HELIX STRUCTURE OF THE LU
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Figure 2: Left: Correlations betwee
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Improving NLO-parton shower matched
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due to the inclusion of higher orde
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New Results in Soft Gluon Physics C
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Figure 2: Spacetime depiction of Dr
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Central Exclusive Meson Pair Produc
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in the CEP cross section. However i
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AN AVERAGE b-QUARK FRAGMENTATION FU
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1/N dN/dx 3.5 3 2.5 2 1.5 1 0.5 ALE
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W + W + jj at NLO in QCD: an exotic
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Σ fb Σ fb 3.5 3.0 2.5 2.0 0.65 0.
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W/Z+Jets and W/Z+HF Production at t
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Figure 2: Measured inclusive jet di
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W and Z physics with the ATLAS dete
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SHERPA 9 MC generators but not by P
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W/Z + Jets results from CMS V. CIUL
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Events / 0.1 600 500 400 300 200 10
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TEVATRON RESULTS ON MULTI-PARTON IN
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iterative midpoint cone algorithm w
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INVESTIGATIONS OF DOUBLE PARTON SCA
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¦ § ¦ ¨ ¥ ¦ ¨ § ¦ © ¦ §
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Figure 4: Two-dimensional distribut
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SOFT QCD RESULTS FROM ATLAS AND CMS
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as a function of multiplicity for t
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Determination of αS using hadronic
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α S (m Z 0) 0.15 0.14 0.13 0.12 0.
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Reaching beyond NLO in processes wi
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dσ/dp t,max [fb/GeV] 10 5 10 4 10
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Nonlocal Condensate Model for QCD S
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The lower bound for the integration
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AN ALTERNATIVE SUBTRACTION SCHEME F
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where MBorn,g is the underlying Bor
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THE NNPDF2.1 PARTON SET F. CERUTTI
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ottom masses mb of 4.25, 4.5, 5.0 a
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HOLOGRAPHIC DESCRIPTION OF HADRONS
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∫ SYM = κ d 4 ( 1 xdzTr 2 h(z)F
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Nuclear matter and chiral phase tra
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fact that for Nc ≫ 3 a gas of fre
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Recent Results on Light Hadron Spec
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Figure 3: Mass spectrum fitting wit
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Page 297: The singular term, on the other han
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Page 311: 7. Heavy Ions
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Page 342 and 343: Here D is the diffusion coefficient
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Figure 10: Top pair mass spectrum m
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Figure 13: Particle densities (left
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4 Low energy precision Spectroscopy
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asymmetries associated to Bd and Bs
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XLVIth Rencontres de Moriond QCD an
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