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Figure 1: Average nuclear modification factor < RAA > for direct photons in Au+Au and Cu+Cu collisions at 200 GeV, plotted versus Npart. expansion of the azimuthal distribution. The elliptic flow of thermal direct photons is sensitive to the thermalization time τ0 of the QGP, small τ0 would lead to small v2. 4 Direct photonscanbemeasuredusingdifferentsubsystemsofthecentral armofthePHENIX detector, withdifferentmethodsofmeasurement. ThePHENIXdetectorisdescribedelsewhere. 5 Photons can be measured directly using the Electromagnetic Calorimeters, the decay photons fromπ 0 andothermesonsaresubtractedstatistically fromthemeasuredinclusivephotonsample, charged hadrons and electrons are rejected with the help of the central arm tracking detectors. This method is described in more detail in earlier publications 6 . It is most feasible at high pT, at low pT the signal to background ratio gets too small to make a significant measurement. Therefore, two other methods have been developed, using the electron ID capabilities of the PHENIX detector and measuring direct photons indirectly through conversions. The so-called internal conversion method uses the idea that virtual direct photons are produced in conjunction with real direct photons, and convert into low mass e + e − pairs, in aprocess similar to the π 0 Dalitz decay. The method benefits from the limited phase space of such pairs from the π 0 Dalitz decay, hence the signal to background ratio is improved compared to the direct calorimeter measurement at low pT. The method is based on the measurement of e + e − pairs, the background is removed using like-sign pairs, the resulting distribution is compared to a cocktail of dilepton pairs that includes all expected hadronic sources. An excess over that cocktail at low invariant mass is then interpreted as a virtual direct photon signal. A more detailed description of this method is given in 7 . A new method has been developed to measure direct photons through external conversions in the detector material. The back plane of the PHENIX Hadron-Blind Detector (HBD), which was installed during the 2007 RHIC run for commissioning, offers a well-defined conversion point for photons, about 60 cm away from the interaction point, with a radiation length of about 4%X0. To account for the wrongly reconstructed opening angle of such conversion pairs, that leads to an apparent invariant mass, an alternate track model was developed that assumes the origin of the pairs at the HBD back plane. Using this model moves the peak of the invariant mass from about 12 MeV/c 2 to 0, it also helps separating the conversion pair from pairs from Dalitz decays. Using this method, the misidentification rate of conversion photons is found to be less than 3%. This method is described in more detail in 8 . The nuclear modification factor RAA has been measured in 200 GeV Au+Au collisions and was found to be consistent with unity for most pT. 9 This result is a confirmation that 〈TAA〉 scaling works, since at a first approximation, photons are not affected by the QGP. However, there appears to be a possible suppression of photons at pT > 15 GeV/c, which is not fully understood. Such a suppression could be an initial state effect, for example an effect of the different isospin composition of the proton and of the gold nuclei, and would thus be visible in
Figure 2: Fraction of direct photons over inclusive photons, for different collision systems, at center-of-mass energy of 200 GeV: p+p, d+Au. Cu+Cu, Au+Au (from left to right). ξ dN/d trig 1/N 1 -1 10 -2 10 -3 10 -4 PHENIX Au+Au 0-20% 5
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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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MEASUREMENT OF THE J/ψ INCLUSIVE P
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2 Counts per 40 MeV/c 120 100 80 60
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STUDY OF Ke4 DECAYS IN THE NA48/2 E
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photons were accepted while particl
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6. Structure Functions Diffraction
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2 Hadronic Final States and Diffrac
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3 Summary A brief overview of recen
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Using HERA Data to Determine the In
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k f n 0.4 0.2 0 -0.2 0.4 0.2 0 -0.2
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The singular term, on the other han
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Pomeron Kernel: The leading order B
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DIFFRACTION, SATURATION AND pp CROS
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In Ref. 6 , the saturated Froissart
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Transverse Energy Flow with Forward
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