Production asymmetries of b and c hadrons at LHCb

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1 Journal of Phyic: Conference Serie PAPER OPEN ACCESS Production aymmetrie of b and c hadron at o cite thi article: F Ferrari and Collaboration 26 J. Phy.: Conf. Ser Related content - Hadron Beam For Hadron Phyic Winton Robert - hree Lecture on Hadron Phyic Craig D. Robert - On dynamic of hard elatic cattering of hadron O V Kancheli View the article online for update and enhancement. hi content wa downloaded from IP addre on 24/2/28 at 9:8

2 BEACH 26 Journal of Phyic: Conference Serie 77 (26 25 doi:.88/ /77//25 Production aymmetrie of b and c hadron at F Ferrari on behalf of the Collaboration Univerità di Bologna, Dipartimento di Fiica ed Atronomia, via Irnerio 46, (426 Bologna, Italy 2 INFN - Sezione di Bologna, viale B. Pichat 6/2, (426 Bologna, Italy fabio.ferrari@cern.ch Abtract. Uing a data ample correponding to an integrated luminoity of. fb, collected by in pp colliion at a centre-of-ma energy of 7 ev, the D +, D +, B and B production aymmetrie are determined. hee quantitie are meaured by mean of D + φ(k + K π +, D + KS(π + π π +, B J/ψ(µ + µ K (K + π, B D (K + π π π + and B D (K + K π π + decay. Moreover, uing the full Run integrated luminoity, correponding to. fb at 7 ev and 2. fb at 8 ev, the production and decay aymmetry of the Λ b baryon, +D(Λ b, i determined by mean of Λ b J/ψ(µ + µ pk decay. All aymmetrie are meaured a a function of p and y (or η in the D +, B and B cae of the involved hadron, in order to check if there i a dependence on kinematic.. Introduction he production rate of b(c- and b( c-hadron in pp colliion at the LHC are not expected to be identical. hi phenomenon, commonly referred to a production aymmetry, i related to the fact that the b( c quark produced in the hard cattering of the two colliding proton could coalece with a u or d pectator quark in the proton remnant, wherea the oppoite i not poible for a b(c quark. Some theoretical model alo predict an enhancement of thi effect in the forward region, where the produced b b(c c pair i cloer to the remnant of the colliding proton; finally, there are alo prediction of other effect coming into play at high tranvere momentum [],[2],[3]. he determination of production aymmetrie i very important, ince in CP violation meaurement one need to dientagle the phyical aymmetry from other puriou effect, that could reemble the effect of CP violation. he production aymmetrie of D +, D +, B and B meon are defined a (B ( = σ(b ( σ(b ( σ(b ( + σ(b (, (D + ( = σ(d + ( σ(d ( σ(d + ( + ( σ(d (, where σ tand for the production cro ection. he production and decay aymmetry for the Λ b J/ψpK mode can be written a +D (Λ b = σ(λ b σ(λ b σ(λ b + σ(λ b + A CP (Λ b J/ψpK (2 Content from thi work may be ued under the term of the Creative Common Attribution 3. licence. Any further ditribution of thi work mut maintain attribution to the author( and the title of the work, journal citation and DOI. Publihed under licence by Ltd

3 BEACH 26 Journal of Phyic: Conference Serie 77 (26 25 doi:.88/ /77//25 (% (a = 7 ev (% (b = 7 ev - Magnet up Magnet down Average - Magnet up Magnet down Average y p (GeV Figure. Production aymmetry of D + meon a a function of (a rapidity and (b tranvere momentum for (red circle magnet up and (blue quare magnet down data. he reult obtained for both magnet polaritie are compatible. No ignificant trend i oberved within the current experimental preciion. where the firt term on the right hand ide i the analogue of the term in Equation ( and the econd term i the CP aymmetry in the decay. If one aume that CP violation in the Λ b J/ψpK decay i zero, then +D (Λ b = (Λ b. 2. D + production aymmetry he D + production aymmetry [4] can be written a the um of it variou contribution (D + = A RAW (D + φπ + A CP (D + φπ + A D (π + + A D (K + K, (3 where A RAW (D + φπ + i defined a the difference between D + and D ignal yield divided by their um. he CP aymmetry in the decay i neglected, a thi mode i Cabibbo favoured and no ignificant CP violation i expected [5],[6]. A the final tate i ymmetric with repect to charge of the kaon, the detection aymmetry of the kaon pair, A D (K + K, i zero. Hence the only correction that need to be applied i due to the π ± detection aymmetry. hi latter quantity can be derived by taking the ratio of the pion detection efficiencie ε(π + /ε(π. In order to meaure the pion efficiencie, the decay equence D + π + D (K π + π + π i employed. Auming that the D + come from the primary vertex, there are enough contraint to allow for the detection of thi decay even if one pion from the D decay i mied. One can alo fully recontruct thi decay, if no charged track i mied. he ratio of fully to partially recontructed D decay give a meaurement of the pion detection efficiency. he ignal yield i obtained performing binned maximum likelihood fit to the invariant ma pectrum. he ignal model employed i compoed of triple Gauian where all parameter are free to vary, except that two of the three Gauian that are required to have a common mean. he background i parameteried by mean of a econd order polynomial. he overall production aymmetry in the range 2. < y < 4.5 and p > 2 GeV i (D + = (.33 ±.22 ±.% where the firt error i tatitical and the econd ytematic. he production aymmetry a a function of y and p of the D + meon i hown in Figure. No ignificant dependence on thee variable i oberved within the current experimental uncertaintie. 2

4 BEACH 26 Journal of Phyic: Conference Serie 77 (26 25 doi:.88/ /77//25 Production aymmetry.5 (a Production aymmetry (b p [GeV/c] η Figure 2. Production aymmetry of D + meon a a function of (a tranvere momentum and (b peudorapidity. Although non-zero lope are found a central value, the uncertaintie are till too large to draw any concluion on the preence of a kinematic dependence. 3. D + production aymmetry he D + production aymmetry [7] can be obtained by (D + = A RAW (D + K Sπ + A CP (D + K Sπ + + A D (π + + A ɛ, (4 where the raw aymmetry i defined taking the difference of D + and D ignal yield divided by their um. he number of ignal candidate i obtained by mean of binned maximum likelihood fit to the KS π+ invariant ma ditribution. he ignal component i parameteried uing Crujiff function [8], while the background i decribed by a linear function plu a Gauian function accounting for D + KS π+ π decay, where the neutral pion i not recontructed. CP violation in the decay, A CP (D + KS π+, i etimated to be at mot 4 [9] and thu neglected. he pion detection aymmetry, A D (π +, i corrected for uing the reult obtained in the D + production aymmetry meaurement. he aymmetry due to CP violation in the neutral kaon ytem, A ɛ, depend on the decay time acceptance for KS meon. hi quantity i obtained by fitting the K S decay time ditribution with an empirical function. he value obtained for the aymmetry i A ɛ = ( , where the quoted uncertainty i tatitical only. he D + production aymmetry i obtained in the kinematic range 2. < p < 8. GeV and 2.2 < η < 4.75, excluding the region with 2. < p < 3.2 GeV and 2.2 < η < 2.8, and i found to be (D + = (.96 ±.26 ±.8%. he production aymmetry a a function of D + meon p and η i hown in Figure 2. dependence i oberved within the current experimental uncertaintie. No 4. B and B production aymmetrie he B and B production aymmetrie [] are obtained by mean of two dimenional maximum likelihood invariant ma and decay time fit to the relevant ditribution. he ignal ma component i parameteried by two Gauian with the ame mean and different width. he partially recontructed contribution are decribed by hape obtained from a kernel etimation technique [] baed on invariant ma ditribution obtained from fully imulated event. he combinatorial component i fitted uing an exponential function. A for the decay time, the ignal i parameterized by a theoretical function decribing the time dependent decay rate of a B ( (B ( to a flavour pecific final tate f(f convolved with a 3

5 BEACH 26 Journal of Phyic: Conference Serie 77 (26 25 doi:.88/ /77//25 (B (B p (B [GeV/c] (B (B η (B p (B [GeV/c] η(b Figure 3. Production aymmetry of (top B and (bottom B meon a a function of (left tranvere momentum and (right peudorapidity. No ignificant trend i oberved within the current experimental preciion, although the firt bin in η hint at a poible feature. reolution function and multiplied by an acceptance function. Concerning the combinatorial and partially recontructed background, the hape are obtained from empirical parameterization of the decay time pectra in high and low invariant ma ideband in data. he production aymmetrie a a function of the b-meon p and η are hown in Figure 3. he B and B production aymmetrie, integrated in the range 4 < p < 3 GeV/c and 2.5 < η < 4.5, are found to be (B = (.35 ±.76 ±.28% and (B = (.9 ± 2.6 ±.66%, where the firt uncertaintie are tatitical, and the econd uncertaintie are ytematic. No evidence of production aymmetry i found within the current preciion. 5. Λ b production aymmetry he Λ b production and decay aymmetry [2] can be obtained a the um of variou term +D (Λ b = A RAW(Λ b J/ψpK + ID (Λ b J/ψpK + A D (p + A D (K, (5 where A RAW (Λ b J/ψpK i the raw aymmetry defined a the difference between Λ b and Λ b ignal yield divided by their um, ID (Λ b J/ψpK i the aymmetry between the particle identification aymmetrie of Λ b and Λ b, and A D (p(a D (K i the proton (kaon detection aymmetry. he ignal yield are obtained from unbinned extended maximum likelihood fit to the invariant ma ditribution of Λ b and Λ b. he ignal component i parameteried uing an 4

6 BEACH 26 Journal of Phyic: Conference Serie 77 (26 25 doi:.88/ /77//25 a p+d.2 a p+d ev fit 7 ev data. 7 ev fit 7 ev data.2 8 ev fit 8 ev data p [GeV/c].2 8 ev fit 8 ev data y Figure 4. Production and decay aymmetry a a function of (left tranvere momentum and (right rapidity of the b-hadron. double ided Crytal Ball function, that i compoed by a Gauian hape with power-law tail. he combinatorial background i modelled uing an exponential function, while the contribution from Λ b J/ψK+ p decay i taken into account uing the ame hape a for the ignal. he particle identification correction i calculated uing ample of data with track from the decay J/ψ µ + µ, D + D (K π + π + and Λ + c pk π +, which can be identified without requiring any particle identification cut on the daughter. he kaon detection aymmetry i obtained from a previou publication [3], while the proton detection aymmetry i etimated from imulated event. he quantity +D a a function of p and y i hown in Figure 4. he p reult i conitent with a null lope, wherea the combined reult for +D (y give +D (y = (. ±.7 + (.58 ±.4(y y, where y = 3. i the average rapidity of the Λ b in the ample. he quoted error i the combination of the tatitical and ytematic contribution to the uncertainty. 6. Concluion hank to the unprecented amount of b- and c-hadron produced in the LHC pp colliion, i in an excellent poition to perform high-preciion CP violation meaurement. One key ingredient to perform uch meaurement i the determination of the b- and c-hadron production aymmetrie. hee proceeding ummarie the preent tatu at for D +, D +, B, B and Λ b hadron. will continue to produce reult in thi ector a more data are being collected. Reference [] Chaichian M and Fridman A, On a poibility for meauring effect of CP violation at pp collider, PLB, 298,, 993. [2] Norrbin E and Vogt R, Bottom Production Aymmetrie at the LHC, arxiv:hep-ph/356. [3] Norrbin E and Sjötrand, Production and Hadronization of Heavy Quark, European Phyic Journal C, 7,, 2. [4] Aaij R et al. ( Collaboration, Meaurement of the D + D production aymmetry in 7 ev pp colliion, Phyic Letter B 73 (22, pp [5] Groman Y, Kagan A L, and Nir Y, New phyic and CP violation in ingly Cabibbo uppreed D decay, Phy. Rev. D 75 (27 368, arxiv:hep-ph/6978. [6] Bergmann S and Nir Y, New phyic effect in doubly Cabibbo uppreed D decay, JHEP 9 (999 3, arxiv:hep-ph/

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