Inclusive Photon Research Articles

On ηc line shape in charmonium transitions

The line shapes to observe ηc in charmonium transitions, i.e., Ψ (2S), J/Ψ → γηc, are investigated. The ηc line shapes in exclusive decays or by observing the inclusive photon spectrum are given. The sensitivities to measure the ηc resonance parameters are also evaluated. With more than two thousand ηc events observed, the precision of the ηc decay width measurement will be improved by better than 3%. However, the uncertainties associated with the ηc modified line shapes will dominate the systematic errors and this will prohibit precision mass and width measurements.

J/ϕ Inclusive Photon Spectrum at BESIII

With a 15M J/ϕ inclusive Monte Carlo sample, the absolute branching fraction of J/ϕ → γη′ from the J/ϕ inclusive photon spectrum is measured to be Br(J/ϕ → γ η′) = (4.68 ± 0.08 ± 0.27) × 10−3, which is in good agreement with the input value. The J/ϕ→ γfJ(2220) is also searched for using the same sample. Under our assumptions, the statistical significances of J/ϕ → γfJ(2220) are larger than 7σ.

Production of Direct Photons and Jets at the Tevatron

Recent differential cross section measurements of isolated photon and jet production from the CDF and DO collaborations are presented. NLO pQCD calculations agree, within uncertainties, with the inclusive photon measurements but disagree with the photon+jet cross sections. NLO pQCD agrees very well with both the inclusive jet and dijet data. Limits on several exotic models are set based on the dijet mass distribution.

Inclusive photon production and photon-jet correlations in hadronic collisions

We compare results of $k_t$-factorization approach and next-to-leading order collinear-factorization approach for photon-jet correlations in $pp$ and $p \bar p$ collisions at RHIC, Tevatron and LHC energies. We discuss correlations in azimuthal angle between photon and jet as well as correlations in two-dimensional space of photon and jet transverse momenta. Different unintegrated gluon/parton distributions are used in the $k_t$-factorization approach. The results depend on UGDF/UPDF used. The collinear NLO $2 \to 3$ contributions dominate over $k_t$-factorization cross section at small relative azimuthal angles as well as for asymmetric transverse momentum configurations.

Elliptic flow of inclusive photons in Au–Au and Cu–Cu collisions at GeV

The first results on centrality, rapidity and system size dependence of elliptic flow of inclusive photons in Au–Au and Cu–Cu collisions at GeV at forward rapidities are presented. The elliptic flow of photons has been studied with respect to the event plane determined by charged particles measured at mid-rapidity in the STAR experiment. v2 scaled with two-particle eccentricity (v2/ϵ) shows scaling for different system sizes for the same values of Npart.

Deep inelastic scattering and prompt photon production within the framework of the quark Reggeization hypothesis

We study $ep$ deep inelastic scattering and the inclusive production of prompt photon within the framework of the quasi-multi-Regge-kinematic approach, applying the quark Reggeization hypothesis. We describe structure functions ${F}_{2}$ and ${F}_{L}$ supposing that a virtual photon scatters on a Reggeized quark from a proton, via the effective gamma-Reggeon-quark vertex. It is shown that the main mechanism of the inclusive prompt photon production in $p\overline{p}$ collisions is the fusion of a Reggeized quark and a Reggeized antiquark into a photon, via the effective Regeon-Reggeon-gamma vertex. We describe the inclusive photon transverse momentum spectra measured by the CDF and D0 Collaborations within errors and without free parameters, using the Kimber-Martin-Ryskin unintegrated quark and gluon distribution functions in a proton.

Measurement of the moments of the photon energy spectrum inB→Xsγdecays and determination of|Vcb|andmbat Belle

Using the previous Belle measurement of the inclusive photon energy in B→Xsγ decays, we determine the first and second moments of this spectrum for minimum photon energies in the B meson rest frame ranging from 1.8 to 2.3 GeV. Combining these measurements with recent Belle data on the lepton energy and hadronic mass moments in B→Xclν decays, we perform fits to theoretical expressions derived in the 1S and kinetic mass schemes and extract the magnitude of the Cabibbo-Kobayashi-Maskawa matrix element Vcb, the b-quark mass, and other nonperturbative parameters. In the 1S scheme analysis we find |Vcb|=(41.56±0.68(fit)±0.08(τB))×10-3 and mb1S=(4.723±0.055)GeV. In the kinetic scheme, we obtain |Vcb|=(41.58±0.69(fit)±0.08(τB)±0.58(th))×10-3 and mbkin=(4.543±0.075)GeV. © 2008 The American Physical Society.

Measurement of upper limits forΥ→γ+Rdecays

Motivated by concerns regarding possible two-body contributions to the recently-measured inclusive Upsilon(nS)->gamma+X (n=1, 2, 3) direct photon spectra, we report on a new study of exclusive radiative decays of these narrow Upsilon(nS) resonances into two-body final states R+gamma, with R a narrow resonant hadronic state decaying into four or more charged particles. Such two-body processes are not explicitly addressed in the extant theoretical frameworks used to calculate the inclusive direct photon spectra, and must also be explicitly inserted into Monte Carlo simulations. Using data collected from the CLEO III detector at the Cornell Electron Storage Ring, we present upper limits of order 0.01 per cent for such bottomonium two-body decays as a function of the R recoil mass.

Extraction of|Vub|with reduced dependence on shape functions

Using BABAR measurements of the inclusive electron spectrum in B {yields} X{sub u}e{nu} decays and the inclusive photon spectrum in B {yields} X{sub s}{gamma} decays, we extract the magnitude of the CKM matrix element V{sub ub}. The extraction is based on theoretical calculations designed to reduce the theoretical uncertainties by exploiting the assumption that the leading shape functions are the same for all b {yields} q transitions (q is a light quark). The results agree well with the previous analysis, have indeed smaller theoretical errors, but are presently limited by the knowledge of the photon spectrum and the experimental errors on the lepton spectrum.

Direct photons and dileptons via color dipoles

Drell–Yan dilepton pair production and inclusive direct photon production can be described within a unified framework in the color dipole approach. The inclusion of non-perturbative primordial transverse momenta and DGLAP evolution is studied. We successfully describe data for dilepton spectra from 800-GeV pp collisions, inclusive direct photon spectra for pp collisions at RHIC energies s = 200 GeV , and for p p ¯ collisions at tevatron energies s = 1.8 TeV , in a formalism that is free from any extra parameters.

AZIMUTHAL ANISOTROPY MEASUREMENT OF DIRECT PHOTON IN $\sqrt{^SNN} = 200\ {\rm GeV}$Au + Au COLLISIONS AT RHIC-PHENIX

Azimuthal anisotropy of direct photons is measured in [Formula: see text] Au + Au collisions by the PHENIX experiment at RHIC. Direct photons are one of the most effective probes to study properties of hot dense medium at initial state (also QGP state) of heavy ion collisions because photons do not interact strongly with medium once produced. They keep their conditions when they are created. Within statistical and systematic errors, the elliptic flow parameter (v2) of direct photons is consistent with zero. Direct photons v2 is measured by the hadron decay photon background v2 from inclusive photon v2 in intermediate to high transverse momentum (pT) region (0 to 10 GeV/c) for 3 centrality selections (20% steps) and minimum bias.

INCLUSIVE PHOTON v2 AND THE APPROACH TO DIRECT PHOTON v2 IN $\sqrt{^SNN} = 200\ {\rm GEV}$AU+AU COLLISIONS

We present the STAR preliminary results of inclusive photon v2 as a function of pT in [Formula: see text] AU + AU collisions. Photons are identified in the STAR Barrel Electromagnetic Calorimeter (BEMC). Non-flow effects are suppressed by obtaining the event plane in different pseudo-rapidity regions. The v2 of π0 decay products is calculated from the known v2 and spectra of hadrons and is compared to the inclusive photon v2. The comparison indicates that direct photon v2 is small.

AZIMUTHAL CORRELATIONS BETWEEN PHOTONS AND CHARGED HADRONS IN p+p AND d+Au COLLISIONS AT $\sqrt{^SNN} = 200\ {\rm GeV}$

We present a systematic analysis of azimuthal correlations between inclusive photons detected in the STAR Barrel Electromagnetic Calorimeter and tracks measured in the Time Projection Chamber in p + p and d + Au collisions. These measurements provide insight in basic properties of jet fragmentation in p + p and d + Au collisions at RHIC energies and also serve as a reference for medium-modified fragmentation in nuclear collisions. The on-line trigger on high-pT photons in the Barrel Calorimeter provides a substantial sample of triggered events with photons at high-pT. Even at this pT, the photon sample is dominated by π0 decays, allowing to explore jet fragmentation with a leading π0 in detail.

First Results from Photon Multiplicity Detector at RHIC

We present the first measurement of multiplicity and pseudorapidity distributions of photons in the pseudorapidity region 2.3 ⩽ η ⩽ 3.7 for different centralities in Au + Au collisions at √sNN = 62.4 GeV. The pseudorapidity distribution of photons, dominated by neutral pion decays, has been compared to those of identified charged pions, photons, and inclusive charged particles from heavy ion and nucleon-nucleon collisions at various energies. Scaling of photon yield with number of participating nucleons and limiting fragmentation scenario for inclusive photon production has been studied.

Measurement of the direct photon momentum spectrum inΥ(1S),Υ(2S), andΥ(3S)decays

Using data taken with the CLEO III detector at the Cornell Electron Storage Ring, we have investigated the direct photon spectrum in the decays Upsilon(1S) -> gggamma, Upsilon(2S) -> gggamma, Upsilon}(3S) -> gggamma. The latter two of these are first measurements. Our analysis procedures differ from previous ones in the following ways: a) background estimates (primarily from pi^0 decays are based on isospin symmetry rather than a determination of the pi^0 spectrum, which permits measurement of the Upsilon(2S) and Upsilon(3S) direct photon spectra without explicit corrections for pi^0 backgrounds from, e.g., chi_bJ states, b) we estimate the branching fractions with a parametrized functional form (exponential) used for the background, c) we use the high-statistics sample of Upsilon(2S) -> pi+ pi- Upsilon(1S) to obtain a tagged-sample of Upsilon(1S) -> gamma + X events, for which there are no QED backgrounds. We determine values for the ratio of the inclusive direct photon decay rate to that of the dominant three-gluon decay Upsilon -> ggg (R_gamma=B(gggamma)/B(ggg)) to be: R_gamma(1S)=(2.70+/-0.01+/-0.13+/-0.24)%, R_gamma(2S)=(3.18+/-0.04+/-0.22+/-0.41)%, and R_gamma(3S)=(2.72+/-0.06+/-0.32+/-0.37)%, where the errors shown are statistical, systematic, and theoretical model-dependent, respectively. Given a value of Q^2, one can estimate a value for the strong coupling constant alpha_s(Q^2) from R_gamma.

Measurement of Identifiedπ0and Inclusive Photon Second-Harmonic Parameterv2and Implications for Direct Photon Production insNN=200 GeVAu+Au

The azimuthal distribution of identified pi0 and inclusive photons has been measured in [FORMULA: SEE TEXT] Au+Au collisions with the PHENIX experiment at the Relativistic Heavy-Ion Collider (RHIC). The second-harmonic parameter (nu2) was measured to describe the observed anisotropy of the azimuthal distribution. The measured inclusive photon is consistent with the value expected for the photons from hadron decay and is also consistent with the lack of direct photon signal over the measured pT range 1-6 GeV/c. An attempt is made to extract nu2 of direct photons.

Measurement of the inclusive electron spectrum in charmless semileptonicBdecays near the kinematic end point and determination of|Vub|

We present a measurement of the inclusive electron spectrum in charmless semileptonic B decays near the kinematic limit for B->X_c e\nu transitions, using a sample of 88 million Upsilon(4S) decays recorded by the BABAR detector. Partial branching fraction measurements are performed in five overlapping intervals of the electron momentum. For the interval of 2.0-2.6 GeV/c we obtain \Delta Br(B->X_u e\nu) = (0.572+-0.041(stat)+-0.065(syst))x10^{-3}. Combining this result with shape function parameters extracted from BABAR measurements of moments of the inclusive photon spectrum in B->X_s+gamma decays and moments of the hadron mass and lepton energy spectra in B->X_c l\nu decays we determine |V_{ub}|=((4.44+-0.25(exp) ^{+0.42}_{-0.38}(SF)+-0.22(theory))x10^{-3}. Here the first error represents the combined statistical and systematic experimental uncertainties of the partial branching fraction measurement, the second error refers to the uncertainty of the determination of the shape function parameters, and the third error is due to theoretical uncertainties in the QCD calculations.

Centrality and transverse momentum dependence of collective flow in 158 A GeV Pb + Pb collisions measured via inclusive photons

Directed and elliptic flow of inclusive photons near mid-rapidity in 158 A GeV Pb + Pb collisions has been studied. The data have been obtained with the photon spectrometer LEDA of the WA98 experiment at the CERN SPS. The flow strength has been measured for various centralities as a function of p T and rapidity over 0.18 < p T < 1.5 GeV / c and 2.3 < y < 2.9 . The angular anisotropy has been studied relative to an event plane obtained in the target fragmentation region that shows the elliptic flow to be in-plane. The elliptic flow has also been studied using two-particle correlations and shown to give similar results. A small directed flow component is observed. Both the directed and elliptic flow strengths increase with p T . The photon flow results are used to estimate the corresponding neutral pion flow.

Precise measurement of spin-averagedχcJ(1P)mass using photon conversions inψ(2S)→γχcJ

Using photon conversions to e{sup +}e{sup -} pairs, the energy spectrum of inclusive photons from {psi}(2S) radiative decays is measured with photon energy resolution ({sigma}{sub E{sub {gamma}}}) in the range from 2.3 to 3.8 MeV by BESII at the Beijing Electron-Positron Collider. The {chi}{sub cJ}(1P) states (J=0,1,2) are clearly observed, and their masses and the spin-averaged {chi}{sub cJ} mass are determined to be M{sub {chi}{sub c}{sub 0}}=3414.21{+-}0.39{+-}0.27, M{sub {chi}{sub c}{sub 1}}=3510.30{+-}0.14{+-}0.16, M{sub {chi}{sub c}{sub 2}}=3555.70{+-}0.59{+-}0.39, and M({sup 3}P{sub cog})=3524.85{+-}0.32{+-}0.30 MeV/c{sup 2}, respectively.

Photon Transitions inΥ(2S)andΥ(3S)Decays

We have studied the inclusive photon spectra in Upsilon(2S) and \Upsilon(3S) decays using a large statistics data sample obtained with the CLEO III detector. We present the most precise measurements of electric dipole (E1) photon transition rates and photon energies for Upsilon(2S)->gamma chi_bJ(1P) and Upsilon(3S)->gamma chi_bJ(2P) J=0,1,2. We measure the rate for a rare E1 transition Upsilon(3S)->gamma chi_b0(1P) for the first time. We also set upper limits on the rates for the hindered magnetic dipole (M1) transitions to the eta_b(1S) and eta_b(2S) states.