We show that the most popular method to simulate Bose-Einstein (BE)
interference effects predicts negligible correlations between identical pions
originating from the hadronic decay of different W's produced in e+e- -> W+W-
-> 4 jets at typical linear collider energies.Comment: 5 pages, 2 eps figures, Proccedings of the Workshop "Physics Studies
  for a Future Linear Collider", QCD Working Group, 2000, DESY 123

Chekanov, S. V.

De Roeck, A.

De Wolf, E. A.

English

arXiv

We show that the most popular method to simulate Bose-Einstein (BE) interference effects predicts negligible correlations between identical pions originating from the hadronic decay of different W's produced in $e^+ e^- \to W^+ W^- \to 4$ jets at typical linear collider energies

De wolf, E. A.

DESY

Bose-Einstein correlations in $e^+ e^- \to W^+ W^-$ at a linear collider

We show that the most popular method to simulate Bose-Einstein (BE) interference effects predicts negligible correlations between identical pions originating from the hadronic decay of different W's produced in e+e- -> W+W- -> 4 jets at typical linear collider energies.We show that the most popular method to simulate Bose-Einstein (BE) interference effects predicts negligible correlations between identical pions originating from the hadronic decay of different W's produced in e+e- -> W+W- -> 4 jets at typical linear collider energies

Chekanov, S.V.

De wolf, E.A.

CERN Document Server

arXiv:hep-ph/0001081v1  11 Jan 2000ANL-HEP-CP-00-03January 10, 2000Bose-Einstein Correlations in e+e− →W +W−at a Linear ColliderS. V. Chekanova, A. De Roeckb and E.A. De Wolfca Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439 USAb Deutsches Electron-Synchrotron DESY, Notkestrasse 85, D-22603, Hamburg, FRGand CERN, 1211 Geneva 23, Switzerlandc Department of Physics, Universitaire Instelling Antwerp, B-2610 Wilrijk, BelgiumProceedings of the Workshop ”Physics Studies for a Future Linear Collider”,QCD Working Group, 2000, DESY 123FAbstractWe show that the most popular method to simulate Bose-Einstein (BE) inter-ference effects predicts negligible correlations between identical pions originatingfrom the hadronic decay of different W ’s produced in e+e− → W+W− → 4 jetsat typical linear collider energies.It is known that the Bose-Einstein (BE) effect can produce a systematic uncertaintyon the W mass measurement in the process e+e− → W+W− → 4 jets. For the LEP2experiments, this uncertainty can be serious [1] if it is as large as expected from thestandard BE simulation included in the PYTHIA/JETSET Monte Carlo model [2].Considering that the TESLA linear collider (LC) will make it possible to study e+e−annihilation with much larger statistics and at much higher centre-of-mass-energy, itis important to understand how strongly the W -mass measurement at a LC could beaffected by the BE effect.In this study we use the most popular and simplest BE simulation technique basedon the LUBOEI algorithm, as included in PYTHIA/JETSET model. It is known thatthis algorithm has a strong effect on the W -mass reconstruction and the systematicuncertainties on the W mass can be as large as 50 MeV at LEP2 energies [3]. Othermethods of BE simulation usually show much smaller uncertainties at LEP2 energies(see [4] for recent reviews).In this paper we investigate the BE correlations at TESLA energies using the toolsproposed in [5] and [6], without attempts to calculate shifts of the W mass for aparticular reconstruction method. By comparing the behaviour of the correlationswith those observed at LEP2 energies, quantitative information can be obtained onpossible effects on W mass measurements.To analyse the BE correlations, we use the following two methods:1) Division method [5]. Here the correlations are measured using the ratio:R∗ =ρww(±,±)− 2 ρw(±,±)ρww(+,−)− 2 ρw(+,−) , (1)where ρww and ρw are the two-particle densities for 4 and 2-jet hadronic W decays,respectively, and (±,±) and (+,−) denote like-charge and unlike-charge particle com-binations. With this definition, R∗ is unity if there is no cross-talk between two W ’s.Thus R∗ can be used as an indicator of BE interference between hadrons from differentW bosons. We note that this quantity resembles the standard BE correlation functionwhen unlike-charged particles are used as a reference, but has, in fact, little to do withit [6].2) Subtraction method [6]:δρ = ρww(±,±)− 2 ρw(±,±)− ρww(+,−) + 2 ρw(+,−). (2)In the absence of cross-talk between W ’s, one has δρ = 0. In the following we use1 + δρ, rather than (2) in analogy with R∗.The two methods differ mainly in the fact that, for δρ the so-called mixing terms(terms determined by the product of single-particle densities) cancel, whereas suchmixing terms are still present in the method 1, and largely determine the behaviour ofR∗ in the case of cross-talk between W bosons [6].Results for both methods, using the LUBOEI algorithm, have been presented forLEP2 energies in [6]. About 20K WW events were generated at√s = 190 GeV. Aclear enhancement of R∗ and δρ was observed when the squared 4-momentum differenceQ12 ≡√−(p1 − p2)2 between two like-sign particles decreases (see Fig. 8 and 9 of [6]).Here we present results of a similar study at√s = 180 GeV and√s = 500 GeV,for a LC. The LC is expected to operate at√s = 500 GeV most of the time, collectingan integrated luminosity of 200 fb−1 per year. The TESLA proposal for the LC willinclude an option to run at smaller beam energies, down to√s = 90 GeV, but withreduced luminosity. If the physics motivation is sufficiently strong, TESLA can alsorun at energies slightly above the WW threshold, e.g. at√s = 180 or 200 GeV. Eventsamples which can reasonably expected to be collected at this energy, amount to 10-20fb−1, i.e. about 20 times larger than the data samples collected at LEP2.The results for R∗ and 1+ δρ are shown in Fig. 1 and Fig. 2. The solid lines in thefigures correspond to the case of no BE correlations. At each energy 200K WW events2were generated, corresponding to a luminosity of 15 fb−1 and 30 fb−1 at√s = 180 GeVand√s = 500 GeV, respectively.The figures show no increase of R∗ and 1 + δρ for small Q12 at√s = 500 GeV,whereas BE correlations are clearly seen at 180 GeV. At an intermediate energy,√s =300 GeV, both correlation quantities have also been studied (not shown). The BEeffect was found to be much smaller than that at√s = 180 GeV. Therefore, in orderto detect this effect at√s = 300 GeV much higher statistics than at LEP is needed.The statistics used for the present paper are ten times larger than that used forLEP2 studies [6]. The figures illustrate that, with the much higher statistics expectedat LC more details in the behaviour of BE correlations can be observed, especially for1 + δρ. This correlation function is slightly below unity for Q12 ∼ 0.3− 1.2 GeV andhas a rather complex structure. This is much less evident for R∗, where the details ofthe genuine correlations are hidden due to the presence of large mixing terms in thedefinition (1).Our results demonstrate that BE correlations between hadrons from different W ’scan be studied at energies close to the WW threshold. At much higher energies theeffect is negligible. This is related to the large phase space available for secondaryparticles from hadronic W decays at high energy, and the small probability for twoidentical secondary particles from different W ’s to be emitted close in Q12 -phasespace1.In conclusion, studies at√s = 500 GeV do not indicate the presence of Bose-Einstein correlations between identical hadrons from decays of different W bosons forrealistic statistics attainable at a LC. The systematic uncertainty on a measurementof the W mass caused by these correlations is therefore expected to be negligible. Thisresult is based on the most popular method to simulate BE correlations (LUBOEI inPYTHIA/JETSET) and two different experimental techniques. The LUBOEI algo-rithm is known to produce the largest effect on the W mass reconstruction at LEP2energies. It is therefore reasonable to expect that the use of other available models,known to lead to smaller uncertainties on the reconstruction of W mass, can onlystrengthen the above conclusion. However when the LC will be operated at an energyclose to but above the WW threshold, collecting event samples of the order of 10-20fb−1, BE effects between different W ’s can be studied with uncanny precision.1A similar observation was made in [7]3References[1] L. Lo¨nnblad and T. Sjo¨strand, Phys. Lett. B 351, 293 (1995)[2] T. Sjo¨strand, Comp. Phys. Comm. 82, 74 (1994)[3] Sˇ. Todorova-Nova´, Workshop on WW Physics at LEP200, Kolymbari-Chania(Greece), October 1999.[4] L. Lo¨nnblad, Proc. of the Workshop ”Correlations and Fluctuations”, Ed.T. Cso¨rgo´ et al. Matrahaza, Hungary 1998 (World Scientific, 1999) p.1;W. Kittel, Interconnection Effects and W+W− Decays (a critical (p)(re)view),hep-ph/9905394, to be published in Proc. Recontres de Moriond 1998.[5] DELPHI Coll., P. Abreu et al., Phys. Lett. B 401 (1997) 181[6] S. V. Chekanov, E. A. De Wolf, W. Kittel, Eur. J. Phys. C 6 (1999) 403[7] J. Schieck, to appear in “Physics Studies for a Future Linear Collider”, R. Heuer,F. Richard and P. Zerwas Eds., DESY123F (2000).412R* /0.1GeVPYTHIA 6.1: 180 GeV0.511.522.50 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2Q12, GeVPYTHIA 6.1: 500 GeVFigure 1: R∗ for PYTHIA Monte Carlo model without and with BE correlations at√s = 180, 500 GeV. The solid line corresponds to the model without BE effect.0.511.52(1+δρ) / 0.1GeVPYTHIA 6.1: 180 GeV0.511.50 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2Q12, GeVPYTHIA 6.1: 500 GeVFigure 2: 1 + δρ for PYTHIA Monte Carlo model without and with BE correlationsat√s = 180, 500 GeV. The solid line corresponds to the model without BE effect.5

Bose-Einstein Correlations in $e^{+}e^{-} \to W^{+}W^{-}$ at a Linear Collider

http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.343.2306

Bose-Einstein Correlations in e+e- -> W+W- at a Linear Collider

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