p and transverse momentum p BF

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1 Strangene roduction at high Q with the H detector Julia E. Ruiz abaco Centro de Invetigacione y Etio Avanzado del Intituto Politécnico Nacional Antigua carretera a Progreo Km. 6 97, Mérida, Yucatán, México jruiz@mda.cinvetav.mx he roduction of KS meon i tied uing dee-inelatic cattering event (DIS) recorded with the H detector at the HERA e collider. he meaurement i erformed in the hae ace defined by the four-momentum tranfer quared of the hoton, 45 GeV < Q < GeV. he differential roduction cro ection are reented a function of the tranvere momentum of the article in the laboratory frame, and a function of the caled momentum fraction x BF and tranvere momentum BF in the Breit frame. he KS roduction rate i alo comared to the roduction of charged article and to the roduction of DIS event in the ame region of hae ace. he data are comared to theoretical rediction, baed on leading order Monte Carlo rogram with matched arton hower. he Monte Carlo model are ued to ty the flavour contribution to the K S roduction. PoS(DIS ) XVIII International Workho on Dee-Inelatic Scattering and Related Subject Aril 9 -, Convitto della Calza, Firenze, Italy hank to Karin Daum for reenting the talk at the conference while I wa marooned in Mexico by the volcano Eyjafjallajökull On behalf of the H Collaboration. c Coyright owned by the author() under the term of the Creative Common Attribution-NonCommercial-ShareAlike Licence. htt://o.ia.it/

2 Strangene roduction at high Q with the H detector. Introduction he roduction of trange hadron in high energy article colliion allow the invetigation of trong interaction in the erturbative and non-erturbative regime. Strange quark are created in the non-erturbative roce of colour tring fragmentation, which contitute the dominant roduction mechanim of trange hadron. In dee-inelatic cattering (DIS), trange quark alo originate from the trange ea in the nucleon, boon-gluon fuion and heavy quark decay. Meaurement of trangene roduction have been ued to invetigate the ureion of trangene relative to lighter flavour in fragmentation. Previou tie of trangene roduction have been done by the H collaboration, a the mot recent ublihed reult at low value of the four-momentum quared of the hoton GeV < Q < GeV []. he analyi reented here, correond to the firt meaurement of trangene roduction in the range, 45 GeV < Q < GeV, in dee-inelatic cattering event (DIS) recorded with the H detector at the HERA e collider. he KS meon i tied through it decay channel KS π+ π. he differential cro ection a function of the tranvere momentum of the trange article i determined in the laboratory frame. he analyi i alo carried out in the Breit frame [] a function of the caled momentum fraction x BF and the tranvere momentum BF in both, current () and target (BF) hemihere. he ratio of the differential cro ection of the KS over the charged article (K S /h ) and the KS over the DIS event (KS /DIS) are alo determined. wo model are ued for the comarion to data, the CDM and MEPS model baed on ARI- ADNE [] and LEPO [4], reectively. Both are interfaced to the LUND tring fragmentation [5] for the modeling of the hadronization roce, where the trangene ureion factor λ i the mot imortant arameter for thi ty and rereent the relative robability of roducing a air with reect to the creation of a light flavour qq air. he contribution of different quark flavour to the KS roduction i tied uing the MEPS model. From the meaurement, the theoretical model of the hadronization and fragmentation rocee are teted allowing to otimize their arameter. In articular, for the LUND model, a tet of λ univerality i carried out. PoS(DIS ). Selection of DIS event, charged article and K S candidate he analyed data eriod correond to the year from 4 to 7 where the HERA machine oerated with a center of ma energy of = 9 GeV. he total accumulated luminoity collected by the H detector i L = 4 b. DIS event are identified by the detection of the cattered electron and elected in the high range of the four-momentum quared of the hoton 45 GeV < Q < GeV and inelaticity in the range of. < y <.6. he KS meon i recontructed through the track of it daughter π+ and π, which mut be in the central region of the H detector (-.5 < η <.5) and hare a common econdary vertex with the direction of flight of the mother contrained to the rimary event vertex. he tranvere momentum of the KS i choen to be higher than. GeV. he DIS event ued for the meaurement of the ratio of the KS roduction cro ection to the incluive DIS cro ection mut atify

3 Strangene roduction at high Q with the H detector Entrie / MeV 5 4 H Preliminary K π + - π N(K ) = M (π + π ) [GeV] Figure : Invariant ma ditribution of the K S candidate identified in the decay channel K S π+ π. he fit function to decribe the ignal and the background are hown in dahed line. the ame Q and y range a the KS. he charged article h conidered for the ratio KS /h mut originate from the rimary vertex and have to fulfill the ame hae ace election criteria than the KS. he invariant ma ditribution of the KS candidate i reented in Figure. he total number of KS candidate i extracted from the fit to a t-tent ditribution to decribe the ignal and the function (x.44) Ex( x + x + 4 x ) for the background. In total, candidate are oberved with a fitted ma value in concordance with the value reorted in PDG [6].. Reult e e K X e e K 4 X (Breit Frame) a) b) c) [b/gev] dσ/d CDM (λ =.) MEPS (λ =.) CDM (λ =.86) MEPS (λ =.86) [GeV] CDM (λ =.) MEPS (λ =.) CDM (λ =.86) MEPS (λ =.86) - x BF e e K X (Breit Frame) CDM (λ =.) MEPS (λ =.) CDM (λ =.86) MEPS (λ =.86) - xbf PoS(DIS ) Figure : he KS differential cro ection a function of a) the tranvere momentum of the article in the laboratory frame, and the caled momentum fraction in b) current x and c) target x BF hemihere in the Breit frame. he meaured incluive cro ection of K S roduction in the viible kinematic range i: σ vi = 5 7(tat.) +7 9 (yt.) b,

4 Strangene roduction at high Q with the H detector which i conitent with the rediction from the CDM and MEPS model with λ =.86. Figure how the differential cro ection of KS roduction a a function of in the laboratory frame and of the caled momenta x and x BF in the current and target hemihere of the Breit frame, reectively. he meaurement are comared to CDM and MEPS model with two different value of trangene factor, λ =. and λ =.86. Both model with λ =.86 give imilar decrition and agree better with data in hae and normalization than the model with λ =.. he i mainly enitive to the dynamic of the hard ub-roce while in the BF the influence from hadronization i exected to be ignificant. herefore more enitivity to λ in x BF comared to x i exected. However, the data of the current meaurement are not recie enough to ee ignificant difference in the enitivity to hadronization of the two hemihere. e e K X e e K X (Breit Frame) a) b) c) [b/gev] dσ/d [GeV] x BF e e K X (Breit Frame) - - xbf Figure : Differential cro ection of the KS earated in flavour contribution a function of a) the tranvere momentum in laboratory frame and the caled momentum fraction b) in current x and c) target region in the Breit frame. x BF Figure how the flavour decomoition of KS roduction a a function of, x and x BF a obtained by the MEPS Monte Carlo rogram. hi figure how that KS meon are mainly originating from u and d quark in thi analyi. he econd larget contribution i obtained from the decay of heavy flavoured hadron. Strange quark contribute only very little to the KS roduction cro ection in general. he contribution increae at large a well a at large x. In thee hae ace region the KS roduction from heavy flavour are ureed becaue charm and beauty mainly originate from boon-gluon fuion. he meaured differential ratio of the KS cro ection over the charged article roduction in the ame hae ace, refered a K /h, are hown in Figure 4 a) and b) a function of Q and in laboratory frame. hi ratio i almot contant in Q while it rie ignificantly with, which i exected due to the heavier ma of the KS with reect to the mot common charged article. All ditribution agree bet with the rediction for a trangene ureion factor λ =.86. he denity (K /DIS), or roduction rate of the KS comared to the DIS event elected in the ame kinematic hae ace, give a flat ditribution around.4 indeendently of Q a hown in Figure 4 c). Again, both model with λ =.86 decribe the data but in x a mall decreae i redicted, which i not oberved from the meaurement. PoS(DIS ) 4

5 Strangene roduction at high Q with the H detector e e K X / e e h e e K X / e e h a). b). c) X) X)/dσ(e eh dσ(e ek CDM (λ =.) MEPS (λ =.) CDM (λ =.86) MEPS (λ =.86) X Q [GeV ] X) X)/dσ(e eh dσ(e ek CDM (λ =.) MEPS (λ =.) CDM (λ =.86) MEPS (λ =.86) X [GeV] X)/σ(e e X) σ(e e K e e K X / e e X CDM (λ =.) MEPS (λ =.) CDM (λ =.86) MEPS (λ =.86) Q [GeV ] Figure 4: he meaured ratio of the K S over charged article (h ) a function of a) four-momentum of the tranfer hoton Q and b) the tranvere momentum of the K S. c) he denity ditribution K S /DIS a function of Q. 4. Concluion Reult on KS roduction at high Q from the H Collaboration have been reented. Differential cro ection a a function of, x and x BF have been hown. he ratio of KS to charged hadron roduction ha been determined. It ha been hown that KS roduction at HERA i dominated by fragmentation in the kinematic range of thi analyi. All meaurement are found to be decribed bet by a trangene ureion factor λ =.86 indeendently of the model under conideration. Reference [] F. D. Aaron, et. al., H Collaboration, Strangene roduction at low Q in dee-inelatic e cattering at HERA, Eur. Phy. J. C6 (9) 85 [he-ex/8.46]. [] R. P. Feynman, Photon-Hadron Interaction, Benjamín, N.Y. (97). [] L. Lönnblad, Ariadne Verion 4: A rogram for imulation of QCD cacade imlementing the colour diole model, Comut. Phy. Commun. 7 (99) 5. [4] G. Ingelmanm A. Edin and J. Rathman, LEPO A Monte Carlo generator for dee inelatic leton-nucleon cattering, Comut. Phy. Commun. (997) 8. [5] B. Anderon, G.Gutafon, G. Ingelman and. Sjötrand, Parton fragmentation and tring dynamic, Phy. Ret. 97 (98). [6] htt://dg.lbl.gov/ PoS(DIS ) 5