P-P PHYSICS AT LHC. Minimum Bias events. W/Z Produc1on. Lecture 3

Transcription

1 P-P PHYSICS A LHC Minimum Bias events. W/Z Producon Lecture

2 MINIMUM BIAS EVENS rigger requirements bias the type of events towards interesting hard scattering processes single high pt lepton high pt leptons high pt jet(s) large missing energy jets + missing energy Majority of events produced in collisions are due to QCD and not represented by the events triggering and written to tape Minimum bias: minimize as much as possible requirements on tracks and energy deposits in order to have an unbias sample of all type of events very low pt requirements use beam scintillators to trigger presence of beams and collisions require presence of at least one primary vertex 44

3 RACK MULIPLICIY - P n Preliminary.9 ev UA5 ALICE η <. (x) η <.4 (x) P n P n Preliminary.6 ev η <.4 (x) η <. (x) Preliminary 7 ev ALICE η <.4 (x) P n η <.5 (x) η <. (x) η <.5 (x) Preliminary.6 7 ev ev η <.4 (x) η <. (x) η <. (x) η <.5 (x) η <.5 (x) η <. (x) η <. (x) η <.5 (x) η <.5 (x) ALICE 9 n n - - η <.5 (x) η <. (x) η <.5 (x) η <.5 (x) η <. (x) η <. (x) η <.5 (x) n Count number of charged tracks (pt > MeV)for different center of mass energies and different pseudo-rapidity intervals n Figure : he fully corrected multiplicity spectrum in.6, and 7. ev, compared with other measurements centre-of-mass energy [4, 5,, ]. Results in differe with a multiplicative factor for clarity. 45

4 MONECARLO UNING WIH 7 EV DAA Charged rack Multiplicity pt spectrum P n - 7 ev (x).6 ev (x).9 ev (x) Preliminary PYHIA D6 PYHIA 8 PHOJE > [GeV/c] a + <p.5.5 η <.4 PYHIA D6 PYHIA 8 PHOJE Preliminary 7 ev (a=).6 ev (a=.5) - -6 η <.4 p >.5 GeV/c n n Existing MC models describe well LEP and evatron data BU fail to describe current LHC tributions data in <.4 for p Figure > 5: (left) A comparison and of erent PYHIA Early LHC models data (even andjust the few PHOJE days) to improve model MC predictions before more sophisticated measurements reasons of clarity. ent center-of-mass energies are scaled with a.5.9 ev (a=) p versus n for <.4 with two different P the PHOJE model at s =.9,.6, and 7. ev. Results for different ene 46

5 reasons of clarity. RACK MULIPLICIY SCALING <n> η <.4 NA Preliminary 5 UA UA5 5 Faster rise at higher energy 5 Likhoded et al. Levin et al ln(s) +.5 ln (s) s [GeV] Figure 6: he evolution of the mean charge multiplicity with the centre-of-mass energy for <.4. Data from lower energy experiments for <.5, NA [5], UA [7] and UA5 [4, 4], are also shown. All data points are parametrized with a quadratic polynomial in ln s and compared with predictions from the analytical Regge-inspired model by Likhoded et al. [8] 47

6 UNDERLYING EVEN Leading track jet Jet reconstruction with only charged tracks Use leading jet (jet with highest pt in the event) to define forward direction Study activity in 4 different regions 48

7 Η SPECRUM dn ch /dη leading track-jet p > GeV/c (p >.5 GeV/c) Data 7 ev PYHIA-6 D6 PYHIA-6 DW PYHIA-6 P PYHIA-6 CW PYHIA η η MC predictions agree in shape but fail (specially at low momentum) the normalization discrepancy up to 5% possible causes: description of parton fragmentation and radiation and of underlying event dn ch /dη leading track-jet p > GeV/c (p >.5 GeV/c) Data 7 ev PYHIA-6 D6 PYHIA-6 DW PYHIA-6 P PYHIA-6 CW PYHIA-8 49

8 . RANSVERSE ACIVIY Δφ [degrees] /dη d(δφ) [GeV/c] Σp d leading track p / dη d(δφ) [GeV/c] Σp d > GeV/c charged 5 particles Data (p 7 ev PYHIA-6 D6 PYHIA-6 DW 4 preliminary PYHIA-6 P PYHIA-6 CW PYHIA-8 >.5 GeV/c, η <.) Data 7 ev PYHIA-6 D6 PYHIA-6 DW PYHIA-6 P PYHIA-6 CW PYHIA-8 (p >.5 GeV/c, η < ) fragmentation Δφ and [degrees] Δφ [degrees] radiation of st parton in hard process leading track-jet p > GeV/c / dη d(δφ) [GeV/c] Σp d Δφ [degrees] required to have (left) p > GeV/c, or (right) p > GeV/c (note the differ Data 7 ev PYHIA-6 D6 PYHIA-6 DW PYHIA-6 P PYHIA-6 CW PYHIA-8 fragmentation of nd parton in hard process (p >.5 GeV/c, η < ) leading track-jet p > GeV/c Average scalar sum of transverse momenta, p, of w and <, per Largest unit discrepancy of pseudorapidity in transverse region and at low per momentum: radian, plotted as a functi angle difference multiple parton relative interaction to the (MPI) leading description object with < : (upper row) is required to have (left) p > GeV/c, or (right) p > GeV/c (in these on of the leading track at = is not included in p ); (lower row) th

9 P AND MULIPLICIY / dn ch ev ) dn ev (/N / / dn ch ev ev ) ) dn ev ev (/N Data 7 ev PYHIA-6 D6 PYHIA-6 DW PYHIA-6 P PYHIA-6 CW PYHIA-8 (p >.5 GeV/c, η <, 6 < Δφ < ) leading track-jet p > GeV/c 4 Data Data 7 ev PYHIA-6 ev PYHIA-6 D6 D6 PYHIA-6 PYHIA-6 DW PYHIA-6 DW PYHIA-6 P PYHIA-6 P PYHIA-6 CW PYHIA-8 CW PYHIA-8 leading track-jet p leading track-jet N ch ch charged p particles >.5.5 GeV/c, GeV/c, η η < (6 (6 < Δφ Δφ < ) ) > GeV/c GeV/c 4 4 N ch ch Shahram Rahatlou, Roma Sapienza preliminary preliminary & INFN ] [(GeV/c) / dσp ev ev ) dn ev ev (/N ] ] [(GeV/c) / / dσp Data 7 ev PYHIA-6 D6 PYHIA-6 DW PYHIA-6 P P PYHIA-6 CW PYHIA (p (p >.5.5 GeV/c, η η <,, 6 6 < Δφ Δφ < ) ) leading track-jet p > GeV/c ev ev ) ) dn ev ev (/N ] ] - - Σp Σp Σp [GeV/c] - Data - Data 7 ev PYHIA-6 ev PYHIA-6 D6 D6 PYHIA-6 PYHIA-6 DW PYHIA-6 DW PYHIA-6 P PYHIA-6 P PYHIA-6 CW CW PYHIA-8 PYHIA-8 (p >.5 GeV/c, η <, 6 < Δφ < ) (p.5 GeV/c, η, 6 < Δφ < ) leading track-jet p > GeV/c leading track-jet p > GeV/c [GeV/c] [GeV/c] preliminary preliminary ] [(GeV/c) / dp dn ch ch ] ] [(GeV/c) / / dp dp dn dn ch ch Data 77 ev ev PYHIA-6 D6 D6 PYHIA-6 DW DW PYHIA-6 P P PYHIA-6 CW CW PYHIA-8 (p (p > >.5.5 GeV/c, GeV/c, η η < <,, 6 6 < < Δφ Δφ < < ) ) leading leading track-jet track-jet pp > > GeV/c GeV/c p [GeV/c] Data Data 7 7 ev PYHIA-6 ev PYHIA-6 D6 D6 PYHIA-6 PYHIA-6 DW DW - PYHIA-6 - PYHIA-6 P P PYHIA-6 PYHIA-6 CW PYHIA-8 CW PYHIA-8 (p >.5 GeV/c, η <, 6 < Δφ < ) (p >.5 GeV/c, η <, 6 < Δφ < ) leading track-jet p > GeV/c leading track-jet p > GeV/c pp [GeV/c] [GeV/c] preliminary preliminary 5

10 RANSVERSE ACIVIY WIH S / dη d(δφ) N ch d / dη d(δφ) N ch 7 ev /.9 ev d Data 7 ev Data.9 ev PYHIA-6 D6, 7 ev PYHIA-6 D6,.9 ev PYHIA-6 DW, 7 ev PYHIA-6 DW,.9 ev (p >.5 GeV/c, η <, 6 < Δφ < ) Leading track-jet p Data PYHIA-6 D6 PYHIA-6 DW PYHIA-6 P PYHIA-6 CW [GeV/c] (p >.5 GeV/c, η <, 6 < Δφ < ) Leading track-jet p [GeV/c] / dη d(δφ) [GeV/c] Σp d / dη d(δφ) Σp 7 ev /.9 ev d Data 7 ev Data.9 ev PYHIA-6 D6, 7 ev PYHIA-6 D6,.9 ev PYHIA-6 DW, 7 ev PYHIA-6 DW,.9 ev (p >.5 GeV/c, η <, 6 < Δφ < ) Leading track-jet p Data PYHIA-6 D6 PYHIA-6 DW PYHIA-6 P PYHIA-6 CW Leading track-jet p [GeV/c] (p >.5 GeV/c, η <, 6 < Δφ < ) [GeV/c] 5

11 WHA DID WE LEARN? Strong underlying activity both in number of tracks and total transverse momentum Different models agree at different levels but large discrepancies remain Discrepancies much larger at lower momentum scale ransverse activity grows with center-of-mass energy beyond prediction compare.9 ev and 7 ev data Differences in models include parton fragmentation parton radiation Multiple parton interaction description and dependence on s LHC runs at ev and 4 ev will improve our understanding 5

12 ENERGY INCREASE O EV 54

13 FIRS EV DAA ] otal Integrated Luminosity [pb ALAS Online Luminosity LHC Delivered ALAS Recorded otal Delivered: 4 pb otal Recorded: 95 pb s = ev 7/5 6/6 6/7 6/8 Day in 5 /.5] Delivered Luminosity [pb 6 ALAS Online Luminosity 5, s= ev 5 5ns: <µ> = 5ns: <µ> = Mean Number of Interactions per Crossing 55

14 INELASIC SCAERING A EV 56

15 INCLUSIVE JE CROSS SECION,O!"#$%&' 9 5 5B5. - / / / / D/ D / D / D? / D / D@ / <I)#"Z>#.='CF="A#>.F#I.BD;.F#''$H S]N'^ S]N'H 7SW, =;F" Z"A/" <"D O>#>'=;AA"=#"B'#;'_>BA;F'?"`"? XOY'HCF'EE'GA"?.Z.F>AI S7[\P\[S] U7 'L7S+'^: ' P;+QQ94#&=G+,9E6=G+9!I6=69%9-R#+;H' > /> O>#>'=;AA"=#"B'#;'#_"'D>A#;F'?"`"? / KLM'DaXO'%b<'X&%a'RS7''$ 'G *9,.BD;.F#''$H S]N'^ S]N'H 7SW, =;F" Z"A/" <"D U7 S7[\P\[S]'''''''''' 'L7S+'^: ' GOY'CF="A#>.F#I';F'DaXO H<&'9+'*'X&%a'RS7 O>#>'*'KLM'DaXO <I)#"Z>#.='CF="A#>.F#I <I)#"Z>#.='CF="A#>.F#I'.F=?CB.F/ & DN / / DA KLM'DaXO'%b<'X&%a'RS7''$ 'G N M#=. -!"#$%&' Very nice agreement between data and theory predictions at evatron Experimental challenge Jet detector response: determine true energy of the jet from measured energy jet algorithms Jet Energy Scale: calorimeter response and containment Determine corrections from jet to parton level in order to compare to theory e.g. evaluate contamination from underlying event for a given radius in jet & *9, XOY'HCF'EE'GA"?.Z.F>AI > N M#=. -!"#$%&' 57

16 INCLUSIVE JE CROSS LHC Analysis does not require enormous data systematically limited Almost /5 of total accumulated luminosity at end of run 5 fb 7 ev 6 fb 8 ev 58