Download presentation

Presentation is loading. Please wait.

Published byChrystal Rice Modified over 5 years ago

1
News on ZEUS Leading Baryon analyses Roberto Sacchi Università di Torino and INFN DIS2004 Workshop Slovakia, April 14-18, 2004 Introduction Study of the pion trajectory in p interactions with LN Study of DIS events containing a LP Conclusions Legenda: LP = Leading Proton LN = Leading Neutron LB = Leading Baryon OPE = One Pion Exchange

2
p,n Introduction Events with LB are a large fraction of the HERA cross-section Production mechanism is still unclear Models: p,n , IR, IP Standard fragmentation LB from hadronization of p remenant MC models Virtual particle exchange LP : neutral iso-scalar iso-vector ( , IR, IP) LN : charged iso-vector ( +, +,...) Vertex factorization LP, LN : also from p fragmentation in diffractive processes Lepton variables: Q 2, W, x, y LB variables: x L = E’ LB /E p t = (p-p’) 2

3
p beam window of acceptance n <0.8 mrad =0 o ZEUS forward detectors FNC: 10 I Pb-sci. sandwich /E = 65%/ E e-scale accuracy 2% FNT: scintillator hodoscope at 1 I installed in 1998 X,Y = 0.23 cm = 22 rad LPS: 6 stations with strip detectors only stations S4-S6 analyzed sofar hit position resolution 30 m X L < 1% P T ~ few MeV momentum accuracy <1% For both, p T resolution is dominated by p T spread of p-beam (50-100 MeV) Z = 106m

4
ZEUS forward detectors: acceptance Limited by apertures and detector size (LPS) Integrating over the azimuth: LPS (s4-s6): p T range varies with x L ; for x L >0.6, p T 2 <0.5 GeV 2 acceptance 15 % FNC: restricted to n <0.8 mrad p T range increases with x L ; for x L >0.6, n < 0.8 mrad acceptance 25 % FNC coverage n <0.8 mrad 10 -3 10 -2 10 -1

5
In the following: Study of the pion trajectory in p interactions with LN (DESY-04-037, submitted to Phys. Lett. B, hep-ex/0404002) Study of DIS events containing a LP in 1997 data (EPS03 #544) Main Issues in LB analyses Measure x L, Pt spectra of LB; Compare to hadronization and particle exchange models Test validity of vertex factorization hypotesis with different reactions In LN production, test the validity of OPE , F 2

6
2000 data, L = 9 pb -1 special LUMI + FNC trigger Kinematic range: Q 2 < 0.02 GeV 2 = 220 GeV 0.6 < x L < 0.925 0.05<|t|<0.425 GeV 2 (1-x L ) distributions are consistent with a power-law dependence dN/dxL (1- x L ) a(t) x L distribution vs t in p nX reaction Aim: test the consistency of the OPE model Lumi FNC

7
Interpretation: the reggeized OPE model Pion flux: Total p cross section: where 0.1 (IP) and 0.5 (IR) dominant term even at largest x L (s’ min 60 GeV) Neglecting the (s’) - term, the OPE model predicts the power law dependence dN/dx L (1-X L ) a(t) where: Pomeron intercept Pion slope ignored

8
Powers a(t) as a function of t Powers a(t) nicely fit to a line. Assuming a(t)= IP (0) - 2 ’ ·t yields Consistent with: soft pomeron intercept IP (0) 1.1 pion trajectory (t) = t-m 2 Note: contribution of a trajectory (t) = 0.5 + t would lead to a(t) = 2.08 - 2·t Data further support OPE as the dominant process in p nX reaction

9
DIS events containing a leading proton 1997 data, L = 12.8 pb -1 4 X larger statistics ! Standard DIS selection + LPS track pipe >0.4 mm pot >0.2 mm E+P Z >1655 GeV DA reconstruction used Kinematic range: Q 2 > 3 GeV 2 45 < W < 225 GeV x L > 0.56 p T 2 < 0.5 GeV 2 CAL LPS track containment (rejects beam halo)

10
DIS events containing a leading proton MC used: Ariadne+SCI (diff. and nondiff.DIS) (K + and + contamination) Pythia (PHP) Reweight Ariadne to reproduce LP data distributions flat x L (nondiff. part) exponential p T 2 with b=7.0 GeV -2 diff/total in bins of x L good description Remaining background: PHP and low Q 2 (11%) residual beam halo (7% at x L >0.98) K + and + (max 8% at x L =0.56) Note: K + and + contamination cross-checked with LPS+FNC coincidences

11
Cross section vs x L diffractive peak Constant bin widths chosen according to resolution ( x L =0.03) Syst. uncertainties added. vary Vz, Ee’, E-p Z cuts vary pipe and pot cuts vary MC p T 2 slope vary K + and + fraction Effect normally within statistical error data precise ! Flat distribution up to the diffractive peak (expected from pp interactions) Note: p-dissociative diffraction included in low x L spectrum

12
Cross section vs p T 2 Variable bin widths chosen according to p T 2 resolution Line shown is just to guide the eye Decrease by an order of magnitude in the p T 2 range considered; data are not well described by exponential function with single slope steepness decreases at high p T 2

13
Cross section vs p T 2 and x L p T 2 range in each xL bin determined by LPS acceptance range; few bins with low or unstable acceptance excluded; fit to exponential function with single slope performed in each bin;

14
b-slopes vs x L Result consistent with 95 measurement; smaller slopes observed around x L =0.75 and x L =0.95; partially explained as the effect of the different p T 2 range in different x L bins. No clear evidence of x L dependence of the exponential fall-off with p T 2

15
Summary Lot of leading baryon pre-upgrade data are available; analyses still alive and making progresses LN (1-x L ) distributions in p interactions measured at fixed t satisfy power law dN/dx L (1-x L ) a(t) a(t) consistent with pion trajectory being exchanged supports OPE model LP DIS cross section measured with high statistics vs x L and p T 2 flat xL distribution below diffractive peak exponential fit with single slope inadequate falling p T 2 distribution almost independent of x L

16
Outlook Increase knowledge on xL, pT spectra, vertex factorisation by completing the analyses of the available data Extend the x L range (LPS) by adding the S1-S3 stations Theoretical input needed....

Similar presentations

© 2021 SlidePlayer.com Inc.

All rights reserved.

To make this website work, we log user data and share it with processors. To use this website, you must agree to our Privacy Policy, including cookie policy.

Ads by Google