H1 Collaboration, C. Adloff et al., Nucl. Phys. B538, 3 (1998); H1 Collaboration, S. Aid et al., Phys. Lett. B356, 118 (1995); ZEUS Collaboration, J. Breitweg et al., Eur. Phys. J. C6, 239 (1998).  Home/Search   Document Not in Database   Summary   Related Articles   Check

....momentum transfer squared Q 2 , which can range from zero to 10 5 GeV 2 at HERA. Thus there should be a wide region in which the value and running of ff s (Q 2 ) can be observed with good precision. One possible method for ff s determination is the measurement of jet fractions [1], defined according to one of the several available infrared safe jet al..gorithms [2,3] By definition, jet rates defined by an infrared safe algorithm can be computed in perturbation theory, and next to leading order calculations are now available [4,5] The ff s values obtained by comparing jet ....

H1 Collaboration, T. Ahmed et. al., Phys. Lett. 346B (1995) 415; ZEUS Collaboration, M. Derrick et al., Phys. Lett. 363B (1995) 201.

....model is undershooting data. On the other hand, there is nice agreement with data for the jj jet j distribution when using SaS 2D. 3. 2 Forward Jet Cross Sections Jet cross sections as a function of Bjorken x, x Bj , for forward jet production (in the proton direction) have been measured at HERA [20]. The objective is to probe the dynamics of the QCD cascade at small x Bj . The forward jet is restricted in polar angle w.r.t. the proton and the transverse momenta p jet should be of the same order as the virtuality of the photon, suppressing an evolution in transverse momenta. If the jet ....

....ansatz made for the photon flux is expected to be valid in this kinematical range; interference terms are suppressed by Q 2 1 Q 2 2 =W 2 fl fl . However, differences in the application of the cone jet al..gorithm may affect the results. The forward jet cross section presented by H1 [20] is well described by an ordinary parton shower prescription including the possibility of having resolved photons. The criteria that the p jet should be of the same order as Q 2 , makes the scale choice crucial and 2 2 = p 2 Q 2 is favoured by data, as concluded in [21] With this ....

H1 Collaboration, C. Adloff et al., Nucl. Phys. B538 (1998) 3; H1 Collaboration, S. Aid et al., Phys. Lett. B356 (1995) 118; ZEUS Collaboration, J. Breitweg et al., Eur. Phys. J. C6 (1998) 239.

.... Gamma2:5 j Gamma0:5 and 0:3 y 0:6. Only resolved events are used to show the sensitivity to the photon parton distribution. 3.2. 4 Forward Jets in ep Jet cross sections as a function of Bjorken x, x Bj , for forward jet production (in the proton direction) have been measured at HERA [36]. The objective is to probe the dynamics of the QCD cascade at small x Bj . The forward jet is restricted in polar angle w.r.t. the proton and the transverse momenta p jet should be of the same order as the virtuality of the photon, suppressing an evolution in transverse momenta. If the jet ....

....as a function of x. p jet 5 GeV, x jet 0:035, 0:5 (p jet ) 2 =Q 2 2 and 3 ffi jet 20 ffi . by Q 2 1 Q 2 2 =W 2 fl fl . However, differences in the application of the cone jet al..gorithm may affect the results. The forward jet cross section presented by H1 [36] is well described by an ordinary parton shower prescription including the possibility of having resolved photons. The criteria that the p jet should be of the same order as Q 2 , makes the scale choice crucial and 2 5 = p 2 Q 2 is favoured by data, as concluded in [24] With this ....

H1 Collaboration, C. Adloff et al., Nucl. Phys. B538 (1998) 3; H1 Collaboration, S. Aid et al., Phys. Lett. B356 (1995) 118; ZEUS Collaboration, J. Breitweg et al., Eur. Phys. J. C6 (1998) 239. 36

....data sets. This implies a much larger SM uncertainty than commonly assumed. In addition, the modified parton distributions provide another possible mechanism to account for the CDF high p t jet excess which occurs at similar x and Q 2 values. Recently the H1 and ZEUS experiments at HERA [1] have reported an excess of large x; Q 2 deep inelastic scattering (DIS) events compared to next toleading order QCD expectations (NLO QCD) In order to determine whether this enhancement constitutes a signal for new physics, it is crucial to investigate all possible explanations within the ....

H1 Collaboration (C. Adloff et al.), DESY-97-024, February 1997. ZEUS Collaboration (J. Breitweg et al.), DESY-97-025, February 1997.

....affected very much. In conclusion, one may say that the higher order corrections affect the structure of the cross section more than its overall size. It will be very useful to study a more exclusive observable namely the di jet cross section. Quite interesting phenomenology is coming out of HERA [61]: it allows to separate on an 33 Figure 21: Jet pt distributions. Left: The NLO cross section using the full structure functions (solid line) compared to the case when only the perturbative part is kept (dashed line) Right: the same as above (solid line) in the LO approximation and the cross ....

T. Ahmed, H1 collaboration, Nucl. Phys. B445 (1995) 195; M. Derrick, ZEUS collaboration, Phys. Lett. B348 (1995) 665.

....parton density QCD, since the HERA experimental data show that the gluon density is high [6, 7] However, the same experimental data can be used as the experimental confirmation of the BFKL Pomeron; 3. The new HERA data shows that the BFKL Pomeron is needed to describe the forward jet production [8]. These data change the entire attitude to the BFKL Pomeron, which from a theoretical toy, becomes a tool for the description of the experimental data and, therefore, a part of DIS phenomenology which should be included in the MC codes. The question still remains could the experimental data of ....

....These data change the entire attitude to the BFKL Pomeron, which from a theoretical toy, becomes a tool for the description of the experimental data and, therefore, a part of DIS phenomenology which should be included in the MC codes. The question still remains could the experimental data of Ref. [8] be described without the BFKL Pomeron You will answer this question better than me. The map of disaster: It is well known that in the leading order the BFKL Pomeron leads to Regge like asymptotics: oe tot ( BFKL LO ) e LO L (y Gammay 0 ) Gamma (r Gammar 0 ) 2 4D LO (y Gammay 0 ) 1) ....

H1 Collaboration,S. Aid et. al.,Phys. Lett. B 356, 118 (1995); ZEUS Collaboration, J. Breitweg et al., DESY-98-050.

....Structure, Krakow, January 5 6,1996; presented by E. Mirkes I. INTRODUCTION Deep inelastic scattering (DIS) at HERA is a copious source of multi jet events. Typical two jet cross sections 1 are in the 100 pb to few nb range and thus provide sufficiently high statistics for precision QCD tests [1]. Clearly, next to leading order (NLO) QCD corrections are mandatory on the theoretical side for such tests. Full NLO corrections for one and two jet production cross sections and distributions are now available and implemented in the ep n jets event generator MEPJET, which allows to analyze ....

....with the smallest invariant mass squared is below y cut W 2 , the pair is clustered according to a recombination scheme. This process is repeated until all invariant masses are above y cut W 2 . The resolution parameter y cut is fixed to 0:02. 2) JADE scheme: The experimental analyses in [1] are based on a variant of the W scheme, the JADE algorithm [14] It is obtained from the W scheme by replacing the invariant definition s ij = p i p j ) 2 by M 2 ij = 2E i E j (1 Gamma cos ij ) where all quantities are defined in the laboratory frame. Neglecting the explicit mass ....

H1 Collaboration, T. Ahmed et. al., Phys. Lett. B346 (1995) 415; ZEUS Collaboration, M. Derrick et al., Phys. Lett. B363 (1995) 201.

No context found.

I. Abt et al. [H1 Collaboration], Nucl. Phys. B 407 (1993) 515. M. Derrick et al. [ZEUS Collaboration], Phys. Lett. B 316 (1993) 412.

No context found.

H1 Collaboration, S. Aid et al., Nucl. Phys. B 449 (1995) 3; ZEUS Collaboration, M. Derrick et al., Phys. Lett. B 363 (1995) 201; H1 Collaboration, C. Adloff et al., Eur. Phys. J. C5 (1998) 625; H1 Collaboration, C. Adloff et al., Eur. Phys. J. C6 (1999) 575.

No context found.

H1 Collaboration, I. Abt et al., Z. Phys. C61 (1994) 59; ZEUS Collaboration, M. Derrick et al., Z. Phys. C67 (1995) 81.

No context found.

H1 Collaboration, I. Abt et al., Nucl. Phys. B396 (1993) 3; ZEUS Collaboration, M. Derrick et al., Z. Phys. C65 (1994) 627

....[7] These events are generally understood to be of a diffractive nature and to result from the exchange of a colorless object (usually called the pomeron) with the quantum numbers of the vacuum. Evidence for a partonic structure of the pomeron in DIS has also been observed by the HERA experiments [8]. In CC processes, the coupling of the exchanged W is sensitive to the flavor of the pomeron constituents, which could provide additional information on the pomeron structure. The search also is sensitive to high Q 2 diffractive production of exclusive hadronic states such as vector or ....

ZEUS Collaboration, M.Derrick et al., Phys. Lett. B346(1995)399; H1 Collaboration, T.Ahmed et al., Phys. Lett. B348(1995)681; ZEUS Collaboration, M.Derrick et al., Phys. Lett. B356(1995)129.

.... resolved photoproduction events of light and heavy quarks were considered for background studies using the generator [18] The parton densities in the proton used throughout are taken from the MRS D Gamma [21] parametrization which is close to recent F 2 structure function measurements at HERA [22]. The parton densities in the photon are taken from the GRV G LO parametrization [23] The difference in the results obtained using other existing parametrizations will be discussed later. To compare data and the SM expectation an absolute normalization based on the predicted cross section and ....

H1 Collaboration, I. Abt et al., Nucl. Phys. B407 (1993) 515, ZEUS Collaboration, M. Derrick et al., Phys. Lett. B316 (1993) 412.

.... at HERA [6 8] At HERA, diffractive scattering is studied both in photoproduction and at large Q 2 using events of the type ep eXY , where the hadronic systems X and Y are separated by a large region of pseudorapidity that is devoid of hadronic activity [9, 10] and Y is predominantly a proton [11]. The contribution from such processes to the total photoproduction cross section at flp centre of mass energies W 200 GeV exceeds 20 [12, 13] The leading twist large rapidity gap component represents approximately 10 of the total deep inelastic scattering (DIS) cross section [14 16] 3 The ....

....GeV Gamma2 . This x IP dependence matches that extracted by H1 in a fit to F D(3) 2 (fit B of [16] the normalisation and t dependences being the same as those assumed in that fit. 3 The t dependence is consistent with that recently measured in diffractive DIS by the ZEUS collaboration [11]. 2 This relationship is derived from equations ( 3 5) assuming that the photon interacts directly (u = q) and that the parton v entering the hard scattering is massless. 3 The normalisations of the pomeron flux factor [equation ( 11) and the eIP cross section are separately ambiguous, ....

[Article contains additional citation context not shown here]

ZEUS Collaboration, J. Breitweg et al., Eur. Phys. J. C1 (1998) 81. ZEUS Collaboration, J. Breitweg et al., Eur. Phys. J. C2 (1998) 237.

....starting scale underestimate the photoproduction and DIS differential cross sections by factors varying between 3 and 6. The models in which the diffractive parton distributions are dominated by hard gluons are much closer to the data, confirming the conclusions of other HERA diffractive analyses [7, 8, 14, 16, 26 28, 55] that a large gluon component is required in the pomeron parton distributions. The successful description of the dijet cross sections by the hard gluon models lends support to the concept of factorisable pomeron parton distributions, appropriate for the modelling of diffractive interactions with ....

ZEUS Collaboration, M. Derrick et al., Phys. Lett. B346 (1995) 399. ZEUS Collaboration, M. Derrick et al., Phys. Lett. B356 (1995) 129.

....have been observed clearly [1] and quantitative tests of QCD and the determination of the strong coupling constant ff s are made possible. Previous jet analyses and determinations of ff s at HERA were based on the measurement of R 2 1 (Q 2 ) the (2 1) jet event rate as a function of Q 2 [2]. The jets were found by applying the modified JADE jet al..gorithm [3] in the laboratory frame for a fixed value of the jet resolution parameter. In particular, the measurement of R 2 1 (Q 2 ) allows the dependence of ff s on the scale Q 2 to be studied in a single experiment. In this analysis ....

....are calculated with MEPJET, version 1.4 [8] MEPJet al..lows arbitrary jet definitions and the application of cuts in terms of parton four momenta. Other programs [22] were limited to a specific jet al..gorithm and made approximations in regions of phase space relevant for previous ff s analyses [2] that turned out to be imprecise [23] MEPJET uses a phase space slicing method [24] to deal with final state infrared and collinear divergences associated with real emissions of partons. If the invariant mass squared s of a pair of partons in a multi parton state is smaller than a technical ....

H1 Collaboration, T. Ahmed et al., Phys. Lett. B346 (1995) 415; ZEUS Collaboration, M. Derrick et al., Phys. Lett. B363 (1995) 201. 16

....elastic J= cross section than the Donnachie Landshoff approach. The energy dependence in the Ryskin model is coupled to the low x behaviour of the gluon density in the proton. Using a gluon density increasing towards low x which describes recent measurements of the structure function F 2 at HERA[8], results in a fast increase of the cross section for elastic photoproduction of J= 7] In elastic J= production at small momentum transfer the J= meson retains approximately the full photon energy (z 1 with z = E =E fl in the proton rest system) J= production with proton dissociation ....

T. Ahmed et al., H1 Collaboration, Nucl. Phys. B439 (1995) 471 M. Derrick et al., ZEUS Collaboration, Z. Phys. C65 (1995) 379

No context found.

H1 Collaboration, C. Adloff et al., Nucl. Phys. B538, 3 (1998); H1 Collaboration, S. Aid et al., Phys. Lett. B356, 118 (1995); ZEUS Collaboration, J. Breitweg et al., Eur. Phys. J. C6, 239 (1998).

No context found.

T. Ahmed, H1 collaboration, Nucl. Phys. B445 (1995) 195; M. Derrick, ZEUS collaboration, Phys. Lett. B348 (1995) 665.

No context found.

H1 Collaboration, C. Adloff et al., Nucl. Phys. B538 (1998) 3; H1 Collaboration, S. Aid et al., Phys. Lett. B356 (1995) 118; ZEUS Collaboration, J. Breitweg et al., Eur. Phys. J. C6 (1998) 239. 36

No context found.

UA1 Collaboration, Phys. Lett. 132B (1983) 214; D0 Collaboration, S. Abachi et al., Phys. Lett. B357 (1995) 500; ZEUS Collaboration, J. Breitweg et al., Eur. Phys. J. C1 (1998) 109

No context found.

T. Ahmed and al. (ZEUS Collaboration), Nuc. Phys. B429,477(1994).

No context found.

T. Ahmed and al. (ZEUS Collaboration), Nuc. Phys. B429,477(1994).

No context found.

H1 Collaboration, I. Abt et al. : Nucl. Phys. B407 (1993) 515; ZEUS Collaboration, M. Derrick et al. : Phys. Lett. 316B (1993) 412.

No context found.

H1 Collaboration, Phys. Lett. B346 (1995) 415; ZEUS Collaboration, Phys. Lett. B363 (1995) 201.

First 50 documents  Next 50

Online articles have much greater impact   More about CiteSeer.IST   Add search form to your site   Submit documents   Feedback  

CiteSeer.IST - Copyright Penn State and NEC