First analysis of Long-Range (Forward-Backward) pt and multiplicity correlations in ALICE in pp collisions at 900 GeV G.Feofilov, A.Ivanov, V.Vechernin (for the ALICE Collaboration) V. Fock Institute for Physics Saint-Petersburg State University The 5th International Nordic "LHC and Beyond" Workshop "The First LHC Physics and Major Spin-Offs", 8-11 June

Goal: We continue studies of Long-range correlations proposed for ALICE[1] “ Forward-Backward ” correlations (“FB”) here refer to the limited rapidity coverage of the ALICE central barrel Measurement of the correlation coefficients by scanning in separated pseudorapidity intervals is a model independent method to reveal the presence of the collective effects, relevant to the early stages of hadronic matter formation both in pp and AA collisions [1] ALICE collaboration “ALICE: Physics Performance Report, Volume II”, J. Phys. G: Nucl. Part. Phys. 32 (2006) (Section: Long- range correlations, p.1749) 2

Outline “ Forward-Backward ” correlations (FB) Comparison of simulated and reconstructed PYTHIA data in the framework of ALICE experimental setup in terms of FB correlations FB correlations analysis Conclusions and outlook 3

For each event: 1)the event mean multiplicity in BACKWARD or FORWARD rapidity windows: 2) the event mean transverse momentum for BACKWARD and FORWARD rapidity windows: Event-by-event: We define the mean value of the observable in one rapidity window at the given value of another observable in the second window(regression), for example: “BACWARD” “FORWARD” Forward-Backward /Long-Range CORRELATIONS: 2 rapidity intervals separated by gap 4

“BACWARD” “FORWARD” Types of correlations: 1) -n - the correlation between the event mean charged particle multiplicity in one rapidity interval and the charged particle multiplicity in another interval 2) -n - the correlation between the event mean transverse momentum in one rapidity interval and the charged particle multiplicity in another interval. 3) -pt - the correlation between the event mean transverse momentum obtained in the backward (B) rapidity window and the event mean transverse momentum in the forward (F) rapidity window 5 Forward-Backward /Long-Range CORRELATIONS: 2 rapidity intervals separated by gap

Usually: Correlation coefficients are defined – in the region where some linearity exists - for the absolute values of observables as: Correlation coefficients (for the normalized observables): Here the strength of the multiplicity correlation is measured by the coefficient

Long-Range correlations dependence on η gap and on η window size windows Analysis General: study of -n, -n and -pt correlation coefficient dependences on η windows size and positions. Now: only ITS+TPC data Plans: to include FMD as multiplicity detector for -n and -n correlations.

Comparison of simulated and reconstructed PYTHIA data in the framework of ALICE experimental setup in terms of FB correlations 8 Comparison of Kinematics and ESD in Pythia LHC10a8 production in terms of FB correlations: -n and -n correlation functions in relative observables. Forward η window (-0.8 – 0.0) Backward η window (0.0 – 0.8) Pt cut (0.3 < Pt < 1.5 ), Kinematics events are triggered together with ESDs. N-N correlationPt-N correlation

The 1 st analysis of BF -n and -n correlations in “B”{-0.8, 0.0}, “F”{0.0, 0.8}. 9 pp 900GeV run pass 5 ESDs : Global tracking, TPC clusters > 80, Sigma < 3.5. No kink daughters. normalized values of observables p_t cut: (0.3 < P_t < 1.5 ) A.U.

-n “FB” correlation in narrow (0.2) windows, ƞ gap dependence 10 A.U.

-n FB correlation in narrow (0.2) windows, ƞ gap dependence 11 A.U.

-n and -n FB correlations in ƞ gap dependence 12 Correlation coefficient dependence on ƞ gap between window centers and windows size (δ ƞ ) A.U.

-n and -n FB correlations in ƞ gap dependence 13 Correlation coefficient dependence on ƞ gap between window centers. Windows in ƞ : of 0.2 units. Data in comparison with results of Pythia D6T LHC10a8 N-N correlations Pt-N correlations A.U.

Conclusions 14  First LRC analysis is completed on pp 900GeV ALICE ITS+TPC data  The good agreement of simulated and reconstructed PYTHIA data in the framework of ALICE experimental setup shows that the use of the relative observables for selected pt region (0.3 GeV/c < pt < 1.5 GeV/c) allows one to obtain the unbiased correlation functions without the additional systematic corrections.  Noticeable FB/Long-Range -n, -n and -pt correlations are observed in pp collisions at 900 GeV with the rapidity gap extented up to 1.4 units of pseudorapidity  We see also a difference between Pythia D6T and the data

Thanks for attention 15

Backup

Long-Range correlations dependence on ETA gap and window size ETA windows Azimuthal windows 1.Jet dependence analysis 2.Event asymmetry study 3.May be sensible to flow Main analysis: Study of -n and -n and -p_t correlation coefficient dependences on windows size and positions. Now only in TPC acceptance, plans for FMD as multiplicity detector for -n and -n.

LONG RANGE CORRELATIONS: Absolute and relative observables 18 “BACWARD” “FORWARD” EVERYTHING IS UNCORRECTED Absolute observablesRelative observables