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

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lower x, or forward rapidity one expects a suppression of the two-particle correlation function. To quantify the effect, we define first the correlated yield CY = (Npair/ɛassoc)/Ntrig corrected for efficiency. We can then make a comparison between the correlated yields in d+Au collisions and p+p collisions by defining IdAu = CY |dAu/CY |pp. Fig. 2b shows IdAu as a function of Ncoll, i.e. the centrality. In this case the forward π 0 is required to have a pT of between 0.45 and 1.6 GeV/c, and the particle in the central arm can either be a π 0 with pT =2-5 GeV/c or a charged hadron with pT =1-2 GeV/c. b As expected, one sees a increasing suppression as one goes to more central collisions. We can require both hadrons (π 0 s) to be in the MPC, where we reach the lowest value of x. In the CGC picture, the scattering occurs coherently off of many gluons and the correlation should completely disappear. 8c Fig. 2 c,d,e shows the acceptance corrected correlation function CF = 1 dN(∆φ) acc d(∆φ) for p+p, peripheral d+Au, and central Au+Au events. In p+p the CF shows the away side peak at ∆φ = π from the scattered gluon. As one goes from p+p to peripheral d+Au to central Au+Au, the away side peak disappears, presumably since the momentum is being absorbed by a “condensate” of gluons. 4 Conclusions Both the J/ψ and the pion correlation results from PHENIX are consistent with a CGC picture, however, other pictures may explain all or some of the data. Further work will be forthcoming, making more complete comparisons with models, in particular for the pion correlation data 3 . There are also many other channels in which the various models can be tested, for example heavy quark production, direct photon production, and the correlations of fully reconstructed jets. It is important that we find a unified, single picture of the cold nucleus at low-x which can explain the variety of phenomena, both in hadron-nucleus and nucleus-nucleus collisions. The sQGP is a low pT phenomena, whose initial state is from low-x gluons. To a large extent pQCD inspired techniques will probably not work in the relevant region. We will need non-perturbative models such as the CGC, and and other methods not mentioned here (e.g. AdS/CFT based calculations) to make a major headway in our understanding. References 1. K. Adcox et al. [PHENIX Collaboration], Nucl. Instrum. Meth. A 499, 469 (2003). 2. A. Adare et al., arXiv:1010.1246. 3. PHENIX collaboration, in preparation. 4. K. J. Eskola, H. Paukkunen and C. A. Salgado, JHEP 0904, 065 (2009) 5. L. McLerran, Nucl. Phys. A 752, 355 (2005). 6. R. Vogt, Phys. Rev. C 71, 054902 (2005). 7. D. Kharzeev and K. Tuchin, Nucl. Phys. A 770, 40 (2006). 8. J. L. Albacete and C. Marquet, Phys. Rev. Lett. 105, 162301 (2010). 9. L. Frankfurt, V. Guzey and M. Strikman, Phys. Rev. D 71, 054001 (2005). 10. J. W. Qiu, J. P. Vary and X. F. Zhang, Phys. Rev. Lett. 88, 232301 (2002). 11. B. Z. Kopeliovich, et al, Phys. Rev. C 83, 014912 (2011). b We show the case where the trigger particle is in the central arm and the associated particle is in the MPC which is strictly speaking different than the case where the trigger particle is in the MPC. However in practice they are equivalent since the suppression factor for hadrons in the central arm is essentially unity in d+Au collisions. c This is reminiscent of the Mössbauer effect in crystals. (3)
Measurement of jet quenching with ICP and IAA,Pythia in Pb-Pb collisions at √ sNN = 2.76TeV with ALICE Jan Fiete Grosse-Oetringhaus for the ALICE collaboration CERN, 1211 Geneva 23 This paper discusses the measurement of ICP and IAA,Pythia with ALICE (A Large Ion Collider Experiment). An away-side suppression is found expected from in-medium energy loss. Further, and unexpected, a near-side enhancement is seen which has not been reported by previous experiments at lower energies. The objective of the study of ultra-relativistic heavy ion-collisions is the characterization of the quark–gluon plasma, the deconfined state of quarks and gluons. Recent measurements by ALICE indicate that in central Pb-Pb collisions at the LHC unprecedented color charge densities are reached. For example, the suppression of charged hadrons in central Pb-Pb collisions at √ sNN = 2.76TeV expressed as the nuclear modification factor RAA as a function of transverse momentum (pT) reaches a value as low as 0.14. 1 Di-hadron correlations allow for the further study of in-medium energy because for most pairs of partons scattered in opposite directions, one will have a longer path through the medium than the other. Thus, two-particle correlations can be used to study medium effects without the need of jet reconstruction. In such studies the near-side (particles found close to each other in azimuthal angle) and the away-side (particles found at azimuthal angles different by about π) yields are compared between central and peripheral events (ICP) or studied with respect to a pp reference (IAA). Previous measurements at RHIC have shown a significant suppression of the away-side yield consistent with a strongly interacting medium. 2,3 On the near-side no significant modifications have been observed at high pT. Such analysis usually require the subtraction of non-jet correlations, e.g. flow, which are present in A+A collisions but not in pp collisions and therefore have influence on the extracted yields. This analysis chooses a pT-region where the jet peak is the dominant correlated signal and thus the influence of non-jet correlations is small. 1 Detector and Data Sample The ALICE detector is described in detail elsewhere. 4 For the present analysis the Inner Tracking System (ITS) and the Time Projection Chamber (TPC) are used for vertex finding and tracking. The TPC has a uniform acceptance in azimuthal angle and a pseudorapidity coverage of |η| < 0.9. The uniform acceptance results in only small required acceptance corrections. Forward scintillators (V0) are used to determine the centrality of the collisions. About 12 million minimum-bias events recorded in fall 2010 have been used in the analysis. Good-quality tracks are selected by requiring at least 70 (out of 159) associated clusters in the TPC, and a χ 2 per space point of the momentum fit smaller than 4. In addition, tracks are required to originate from within 2 − 3cm of the primary vertex.
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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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ut also for valence quarks involved
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The sensitivity to Standard Model H
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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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