Latest CMS results on low x physics and di raction

Transcription

1 Latet CMS reult on low x hyic and di raction Benoit Roland (DESY) On behalf of the CMS Collaboration eracale Workho 04-3 December 04 DESY, Hamburg Benoit Roland (DESY) Latet CMS reult low x and di raction eracale Workho 04 / 3

2 Outline Study QCD in the larget oible hae-ace oward the lowet oible oward the larget oible o be able to robe he di erent comonent of the hadron roduction he tranition from the erturbative to the non-erturbative region he imortance of the higher-order emiion he aymtotic behaviour of QCD at mall-x Uing incluive and excluive obervable Peudoraidity ditribution of charged article Incluive di ractive cro ection Integrated leading jet cro ection Underlying event decrition Multijet roduction Benoit Roland (DESY) Latet CMS reult low x and di raction eracale Workho 04 / 3

3 Peudoraidity ditribution of charged article at 8 ev dn ch /dη Incluive Incluive CMS-OEM, - = 8 ev, L = 45 µb dn ch /dη NSD-enhanced NSD-enhanced CMS-OEM, - = 8 ev, L = 45 µb dn ch /dη Eur. Phy. J. C 74 (04) 0, 3053 SD-enhanced 4 3 SD-enhanced CMS-OEM, Pythia6 Z*-LEP - = 8 ev, L = 45 µb Pythia8 4C Herwig++ EE3-CEQ6L EPOS LHC QGSJetII Pythia6 Z* Pythia8 4C Herwig++ EE3-CEQ6L EPOS LHC QGSJetII Pythia6 Z* Pythia8 4C Herwig++ EE3-CEQ6L EPOS LHC QGSJetII-04 N ch in 5.3<η<6.5 or -6.5<η<-5.3 N ch in 5.3<η<6.5 and -6.5<η<-5.3 N ch in only 5.3<η<6.5 or only -6.5<η<-5.3 MC / MC / MC / η η η Bulk of article roduced in colliion from emi-hard (multi)arton interaction! Phenomenological model! uning baed on exerimental data CMS + OEM! et of model rediction from central to forward region Minimum-bia trigger from OEM telecoe (5.3 < < 6.4 and > 40 MeV) Charged article in <. and5.3 < < 6.4 -Extraolationdownto =0 None of the model conidered rovide a conitent decrition of the ditribution U to 0 % (30 %) dicreancy in the central (forward) region! valuable inut for tuning Benoit Roland (DESY) Latet CMS reult low x and di raction eracale Workho 04 3 / 3

4 Incluive di ractive cro ection (mb) ξ dσ/dlog 0.4. SD and DD cro ection a a function of - CMS Piminary, = 7 ev, L = 6. µb SD ( X) (mb) ξ dσ/dlog X 0.4 CMS PYHIA verion: DD ( XY). P8-MBR =0.08 P8-MBR (default) =0.04 = M X ξ X P8-4C P6 0.5<log (M /GeV)<. 0 Y - CMS Piminary, = 7 ev, L = 6. µb FSQ-PAS log ξ log ξ 0 X MBR model reented for value of the Pomeron intercet IP (0) =.08 &.04 Both decribe well the SD cro ection - DD better decribed with maller IP (0) value Schuler & Sjotrand model imlemented in PYHIA8-4C and PYHIA6 Can decribe the DD cro ection - But not the SD falling behavior Benoit Roland (DESY) Latet CMS reult low x and di raction eracale Workho 04 4 / 3

5 Integrated leading jet cro ection at low- Z Z otal! artoniccroection: ( min )= d min i divergent toward low min and eventually become larger than At LHC energie: ( min ) > inel already for min 5GeV! Cro ection need to be tamed in the low region In PYHIA: the rie of the! artoniccroectionicontroledby: a regularization factor 0 tuned to data: ( min ) / min + 0 multile artonic interaction (MPI): Phy. Rev. D 86 (0) 750 dy d d dy / min inel < n MPI >= ( min )/ inel Obervable enitive to the aturation in the low region! Normalized integrated leading jet cro ection: X dn jet leading N event d leading > leading min Benoit Roland (DESY) Latet CMS reult low x and di raction eracale Workho 04 5 / 3

6 Integrated leading jet cro ection at low- FSQ-PAS--03 Minimum-bia trigger from OEM telecoe (5.3 < < 6.4 and > 40 MeV) Leading jet with <.9 and > GeV-fromtrackwith <.4 and > GeV Stable article level defined a above, but without or cut on the charged article > min )/σ vi 0 CMS Piminary Incluive = 8 ev N ch ( > 40 MeV) > 0 in 5.3 < η < 6.5 or -6.5 < η < -5.3 Charged-Particle Jet, η <.9 Anti-Kt, R = 0.5 > min )/σ vi 0 CMS Piminary Incluive = 8 ev N ch ( > 40 MeV) > 0 in 5.3 < η < 6.5 or -6.5 < η < -5.3 Charged-Particle Jet, η <.9 Anti-Kt, R = 0.5 σ(, leading ch. jet CMS Pythia6 Z* Pythia6 CUE Pythia6 (default, MPI on) Pythia6 (default, MPI off) Pythia6 (default, MPI off, no at) MC caled to data at, min = 4.3 GeV σ(, leading ch. jet CMS Pythia8 4C Pythia8 CUE Pythia8 MONASH QGSJetII-04 EPOS LHC Herwig++ UE-EE-3C MC caled to data at, min = 4.3 GeV MC/.5 MC/ [GeV] min 0 [GeV] min Event cro ection! reduced enitivity to jet multilicitie! reduced enitivity to MPI Normalized cro ection! converge to one at low by contruction PYHIA and HERWIG do not decribe the data Comic Ray MC: data decribed by EPOS, not by QGSJE Benoit Roland (DESY) Latet CMS reult low x and di raction eracale Workho 04 6 / 3

7 Underlying Event Underlying Event: activity not attributed to the hard cattering between arton Initial-State Radiation and Final-State Radiation Beam Remnant Multile Partonic Interaction (with it own ISR and FSR) he Underlying Event i characterized by a maller cale than the hard cattering Semi-hard (multi)arton interaction! Phenomenological model! uning baed on exerimental data Meaurement at 0.9 and 7 ev were available!.76 ev wa miing Some MPI can be harder! Double Parton Scattering Benoit Roland (DESY) Latet CMS reult low x and di raction eracale Workho 04 7 / 3

8 Underlying Event at 0.9,.76 and 7 ev FSQ-PAS--05 /[ η ( φ)] ch N. 0. CMS Piminary = 7 ev =.76 ev = 0.9 ev ranvere denity Leading η <, > GeV Charged article: η <, > 0.5 GeV PYHIA 8 CUEP8S PYHIA 8 Monah PYHIA 8 CUEP8M jet [GeV] 00 Reference: direction of the leading track jet /[ η ( φ)] [GeV] Σ CMS Piminary.5 = 7 ev =.76 ev ranvere denity Leading η <, > GeV Charged article: 0.5 η <, > 0.5 GeV = 0.9 ev PYHIA 8 CUEP8S PYHIA 8 Monah PYHIA 8 CUEP8M jet [GeV] 00 ranvere region (60 < < 0 )motenitivetotheueactivity Fat rie at low due to the increae of MPI activity Plateau region: MPI aturated, increae of activity due to ISR and FSR Strong growth of the UE activity with New tune redict energy deendence very well Benoit Roland (DESY) Latet CMS reult low x and di raction eracale Workho 04 8 / 3

9 DPS in four-jet event Phy. Rev. D 89 (04) 0900 Afour-jetfinaltatemayariefromoneortwochain he two additional jet may be roduced via a hard radiation or a econd hard cattering SPS background DPS ignal Selection of exactly four jet in < 4.7: jetwith > 50 GeV jetwith > 0 GeV Jet aociated in air: hard-jet air: the two leading jet with > 50 GeV oft-jet air: the two other jet with > 0 GeV Dicriminating obervable! toology of the jet in the tranvere lane: oft = oft oft = oft oft + oft + oft oft hard S =arcco oft!dps eak at - SPS flat oft hard! DPS eak at 0 - SPS eak at! DPS flat - SPS eak at Benoit Roland (DESY) Latet CMS reult low x and di raction eracale Workho 04 9 / 3

10 Coration obervable: normalized cro ection CMS, - = 7 ev, L = 36 b, 4j+X - CMS, = 7 ev, L = 36 b, 4j+X CMS, - = 7 ev, L = 36 b, 4j+X (/σ) (/σ) dσ/ φ dσ/d S (/rad) oft oft η < 4.7 t nd, 0 > 50 GeV 0 rd th 3, 4 > 0 GeV SHERPA PYHIA8 4C otal Uncertainty oft oft (/σ) dσ/d η < 4.7 t nd, > 50 GeV 0 rd th 3, 4 > 0 GeV oft SHERPA PYHIA8 4C otal Uncertainty (/σ) (/σ) dσ/d S (/rad) oft η < 4.7 t nd, 0 > 50 GeV 0 rd th 3, 4 > 0 GeV SHERPA PYHIA8 4C otal Uncertainty S MC/ SHERPA.8 PYHIA8 4C.6.4 otal Uncertainty φ S (rad) oft oft MC/ 0 0. SHERPA.8 PYHIA8 4C.6.4 otal Uncertainty oft oft and oft :noignificantdi erenceamonggenerator S: better decribed by SHERPA and PYHIA8 POWHEG without MPI underetimate the data for oft and MC/ oft and S enitive to MPI contribution! DPS extraction SHERPA.8 PYHIA8 4C.6.4 otal Uncertainty S (rad) oft S Benoit Roland (DESY) Latet CMS reult low x and di raction eracale Workho 04 0 / 3

11 Coration obervable: normalized cro ection CMS, - = 7 ev, L = 36 b, 4j+X - CMS, = 7 ev, L = 36 b, 4j+X CMS, - = 7 ev, L = 36 b, 4j+X (/σ) (/σ) dσ/ φ dσ/d S (/rad) oft oft η < 4.7 t nd, 0 > 50 GeV 0 rd th 3, 4 > 0 GeV SHERPA PYHIA8 4C otal Uncertainty oft oft (/σ) dσ/d η < 4.7 t nd, > 50 GeV 0 rd th 3, 4 > 0 GeV oft SHERPA PYHIA8 4C otal Uncertainty (/σ) (/σ) dσ/d S (/rad) oft η < 4.7 t nd, 0 > 50 GeV 0 rd th 3, 4 > 0 GeV SHERPA PYHIA8 4C otal Uncertainty S MC/ SHERPA.8 PYHIA8 4C.6.4 otal Uncertainty φ S (rad) oft oft MC/ 0 0. SHERPA.8 PYHIA8 4C.6.4 otal Uncertainty oft MC/ SHERPA.8 PYHIA8 4C.6.4 otal Uncertainty S (rad) oft Uual way: temlate method! ambiguou definition of background and ignal Here: tuning method! UE arameter from the bet fit define the value of PYHIA8 DPS tune CDPSP8S-4j: e = mb Value conitent with reviou meaurement e Benoit Roland (DESY) Latet CMS reult low x and di raction eracale Workho 04 0 / 3

12 Dl-Yan + jet Dl-Yan ectrum ued a a tool to tudy higher-order QCD rocee FSQ-PAS a.u. - 0 PYHIA imulation DY DY+jet DY+jet without PS At large :Dl-Yan ectrum decribed by fixed-order QCD matrix element At low :fixed-ordercalculationdivergeand higher-order contribution need to be taken into account! low region dominated by the reummation of higher-order emiion DY (GeV) Incluive Dl-Yan roduction: ectrum i maximum around 5GeV Small hae-ace for extra QCD emiion Dl-Yan roduction in aociation with jet: maximum hifted to higher value Larger hae-ace for extra QCD emiion PYHIA: Higher-order emiion treated by the initial-tate arton hower Without arton hower! higher-order emiion miing! har cuto below the eak Benoit Roland (DESY) Latet CMS reult low x and di raction eracale Workho 04 / 3

13 Dl-Yan + jet ) - (GeV (/σ Z ) dσ/d CMS Piminary,, 4.9 fb, µµ 60 < m < 0GeV =7 ev yt. unc. MADGRAPH+PYHIA6 PYHIA6 Z* (Z/γ*) POWHEG+P6 Z* Incluive Dl-Yan ) - (GeV (/σ Z ) dσ/d CMS Piminary,, 4.9 fb, DY+jet µµ 60 < m < 0GeV Dl-Yan + jet =7 ev yt. unc. MADGRAPH+PYHIA6 PYHIA6 Z* (Z/γ*) PYHIA6 Z* (O(α S )) POWHEG+P6 Z* MC/ µµ dimuon Incluive Dl-Yan roduction: (GeV) MC/ µµ dimuon (GeV) 0 µµ dimuon (GeV) Lowet-order and higher-order calculation decribe the data equally well Maximum of the ditribution at 5GeV Dl-Yan roduction in aociation with at leat Maximum hifted to higher value - Larger hae-ace for extra emiion High- tail decribed equally well by all Monte Carlo Low region not decribed by lowet-order rediction, higher-order needed Benoit Roland (DESY) Latet CMS reult low x and di raction eracale Workho 04 / 3

14 Concluion Preented everal obervable which enable to contrain QCD at di erent cale Ditribution of charged article - Underlying Event - Di ractive cro ection Semi-hard (multi)arton interaction uning of henomenological model Integrated leading jet cro ection ranition from the erturbative to the non-erturbative region Saturation of the! artoniccroection Four-jet event - Dl-Yan + jet Higher-order QCD emiion Benoit Roland (DESY) Latet CMS reult low x and di raction eracale Workho 04 3 / 3